ScalarEvolution.cpp

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//===- ScalarEvolution.cpp - Scalar Evolution Analysis --------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file contains the implementation of the scalar evolution analysis
// engine, which is used primarily to analyze expressions involving induction
// variables in loops.
//
// There are several aspects to this library.  First is the representation of
// scalar expressions, which are represented as subclasses of the SCEV class.
// These classes are used to represent certain types of subexpressions that we
// can handle. We only create one SCEV of a particular shape, so
// pointer-comparisons for equality are legal.
//
// One important aspect of the SCEV objects is that they are never cyclic, even
// if there is a cycle in the dataflow for an expression (ie, a PHI node).  If
// the PHI node is one of the idioms that we can represent (e.g., a polynomial
// recurrence) then we represent it directly as a recurrence node, otherwise we
// represent it as a SCEVUnknown node.
//
// In addition to being able to represent expressions of various types, we also
// have folders that are used to build the *canonical* representation for a
// particular expression.  These folders are capable of using a variety of
// rewrite rules to simplify the expressions.
//
// Once the folders are defined, we can implement the more interesting
// higher-level code, such as the code that recognizes PHI nodes of various
// types, computes the execution count of a loop, etc.
//
// TODO: We should use these routines and value representations to implement
// dependence analysis!
//
//===----------------------------------------------------------------------===//
//
// There are several good references for the techniques used in this analysis.
//
//  Chains of recurrences -- a method to expedite the evaluation
//  of closed-form functions
//  Olaf Bachmann, Paul S. Wang, Eugene V. Zima
//
//  On computational properties of chains of recurrences
//  Eugene V. Zima
//
//  Symbolic Evaluation of Chains of Recurrences for Loop Optimization
//  Robert A. van Engelen
//
//  Efficient Symbolic Analysis for Optimizing Compilers
//  Robert A. van Engelen
//
//  Using the chains of recurrences algebra for data dependence testing and
//  induction variable substitution
//  MS Thesis, Johnie Birch
//
//===----------------------------------------------------------------------===//
 
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/FoldingSet.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/ScopeExit.h"
#include "llvm/ADT/Sequence.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/Analysis/ScalarEvolutionPatternMatch.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/IR/Argument.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/ConstantRange.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GlobalAlias.h"
#include "llvm/IR/GlobalValue.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Operator.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/Use.h"
#include "llvm/IR/User.h"
#include "llvm/IR/Value.h"
#include "llvm/IR/Verifier.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/InterleavedRange.h"
#include "llvm/Support/KnownBits.h"
#include "llvm/Support/SaveAndRestore.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cassert>
#include <climits>
#include <cstdint>
#include <cstdlib>
#include <map>
#include <memory>
#include <numeric>
#include <optional>
#include <tuple>
#include <utility>
#include <vector>
 
using namespace llvm;
using namespace PatternMatch;
using namespace SCEVPatternMatch;
 
#define DEBUG_TYPE "scalar-evolution"
 
STATISTIC(NumExitCountsComputed,
          "Number of loop exits with predictable exit counts");
STATISTIC(NumExitCountsNotComputed,
          "Number of loop exits without predictable exit counts");
STATISTIC(NumBruteForceTripCountsComputed,
          "Number of loops with trip counts computed by force");
 
#ifdef EXPENSIVE_CHECKS
bool llvm::VerifySCEV = true;
#else
bool llvm::VerifySCEV = false;
#endif
 
static cl::opt<unsigned>
    MaxBruteForceIterations("scalar-evolution-max-iterations", cl::ReallyHidden,
                            cl::desc("Maximum number of iterations SCEV will "
                                     "symbolically execute a constant "
                                     "derived loop"),
                            cl::init(100));
 
static cl::opt<bool, true> VerifySCEVOpt(
    "verify-scev", cl::Hidden, cl::location(VerifySCEV),
    cl::desc("Verify ScalarEvolution's backedge taken counts (slow)"));
static cl::opt<bool> VerifySCEVStrict(
    "verify-scev-strict", cl::Hidden,
    cl::desc("Enable stricter verification with -verify-scev is passed"));
 
static cl::opt<bool> VerifyIR(
    "scev-verify-ir", cl::Hidden,
    cl::desc("Verify IR correctness when making sensitive SCEV queries (slow)"),
    cl::init(false));
 
static cl::opt<unsigned> MulOpsInlineThreshold(
    "scev-mulops-inline-threshold", cl::Hidden,
    cl::desc("Threshold for inlining multiplication operands into a SCEV"),
    cl::init(32));
 
static cl::opt<unsigned> AddOpsInlineThreshold(
    "scev-addops-inline-threshold", cl::Hidden,
    cl::desc("Threshold for inlining addition operands into a SCEV"),
    cl::init(500));
 
static cl::opt<unsigned> MaxSCEVOperationsImplicationDepth(
    "scalar-evolution-max-scev-operations-implication-depth", cl::Hidden,
    cl::desc("Maximum depth of recursive SCEV operations implication analysis"),
    cl::init(2));
 
static cl::opt<unsigned> MaxValueCompareDepth(
    "scalar-evolution-max-value-compare-depth", cl::Hidden,
    cl::desc("Maximum depth of recursive value complexity comparisons"),
    cl::init(2));
 
static cl::opt<unsigned>
    MaxArithDepth("scalar-evolution-max-arith-depth", cl::Hidden,
                  cl::desc("Maximum depth of recursive arithmetics"),
                  cl::init(32));
 
static cl::opt<unsigned> MaxConstantEvolvingDepth(
    "scalar-evolution-max-constant-evolving-depth", cl::Hidden,
    cl::desc("Maximum depth of recursive constant evolving"), cl::init(32));
 
static cl::opt<unsigned>
    MaxCastDepth("scalar-evolution-max-cast-depth", cl::Hidden,
                 cl::desc("Maximum depth of recursive SExt/ZExt/Trunc"),
                 cl::init(8));
 
static cl::opt<unsigned>
    MaxAddRecSize("scalar-evolution-max-add-rec-size", cl::Hidden,
                  cl::desc("Max coefficients in AddRec during evolving"),
                  cl::init(8));
 
static cl::opt<unsigned>
    HugeExprThreshold("scalar-evolution-huge-expr-threshold", cl::Hidden,
                  cl::desc("Size of the expression which is considered huge"),
                  cl::init(4096));
 
static cl::opt<unsigned> RangeIterThreshold(
    "scev-range-iter-threshold", cl::Hidden,
    cl::desc("Threshold for switching to iteratively computing SCEV ranges"),
    cl::init(32));
 
static cl::opt<unsigned> MaxLoopGuardCollectionDepth(
    "scalar-evolution-max-loop-guard-collection-depth", cl::Hidden,
    cl::desc("Maximum depth for recursive loop guard collection"), cl::init(1));
 
static cl::opt<unsigned> MaxGuardDomTreeSteps(
    "scalar-evolution-max-guard-dom-tree-steps", cl::Hidden,
    cl::desc("Maximum number of immediate dominator steps taken when "
             "collecting loop guards"),
    cl::init(8));
 
static cl::opt<bool>
ClassifyExpressions("scalar-evolution-classify-expressions",
    cl::Hidden, cl::init(true),
    cl::desc("When printing analysis, include information on every instruction"));
 
static cl::opt<bool> UseExpensiveRangeSharpening(
    "scalar-evolution-use-expensive-range-sharpening", cl::Hidden,
    cl::init(false),
    cl::desc("Use more powerful methods of sharpening expression ranges. May "
             "be costly in terms of compile time"));
 
static cl::opt<bool>
    EnableFiniteLoopControl("scalar-evolution-finite-loop", cl::Hidden,
                            cl::desc("Handle <= and >= in finite loops"),
                            cl::init(true));
 
static cl::opt<bool> UseContextForNoWrapFlagInference(
    "scalar-evolution-use-context-for-no-wrap-flag-strenghening", cl::Hidden,
    cl::desc("Infer nuw/nsw flags using context where suitable"),
    cl::init(true));
 
//===----------------------------------------------------------------------===//
//                           SCEV class definitions
//===----------------------------------------------------------------------===//
 
void SCEV::computeAndSetCanonical(ScalarEvolution &SE) {
  // Leaf nodes are always their own canonical.
  switch (getSCEVType()) {
  case scConstant:
  case scVScale:
  case scUnknown:
    CanonicalSCEV = this;
    return;
  default:
    break;
  }
 
  // For all other expressions, check whether any immediate operand has a
  // different canonical. Since operands are always created before their parent,
  // their canonical pointers are already set — no recursion needed.
  if (all_of(operands(), [](SCEVUse Op) { return Op.isCanonical(); })) {
    CanonicalSCEV = this;
    return;
  }
 
  SmallVector<SCEVUse, 4> CanonOps(
      map_range(operands(), [](SCEVUse Op) { return Op.getCanonical(); }));
  // Rebuild the expression from the canonical operands, stripping use flags.
  CanonicalSCEV = SE.getWithOperands(this, CanonOps);
}
 
//===----------------------------------------------------------------------===//
// Implementation of the SCEV class.
//
 
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_DUMP_METHOD void SCEV::dump() const {
  print(dbgs());
  dbgs() << '\n';
}
#endif
 
void SCEV::print(raw_ostream &OS) const {
  switch (getSCEVType()) {
  case scConstant:
    cast<SCEVConstant>(this)->getValue()->printAsOperand(OS, false);
    return;
  case scVScale:
    OS << "vscale";
    return;
  case scPtrToAddr: {
    const SCEVCastExpr *PtrCast = cast<SCEVCastExpr>(this);
    SCEVUse Op = PtrCast->getOperand();
    OS << "(ptrtoaddr " << *Op->getType() << " " << Op << " to "
       << *PtrCast->getType() << ")";
    return;
  }
  case scTruncate: {
    const SCEVTruncateExpr *Trunc = cast<SCEVTruncateExpr>(this);
    SCEVUse Op = Trunc->getOperand();
    OS << "(trunc " << *Op->getType() << " " << Op << " to "
       << *Trunc->getType() << ")";
    return;
  }
  case scZeroExtend: {
    const SCEVZeroExtendExpr *ZExt = cast<SCEVZeroExtendExpr>(this);
    SCEVUse Op = ZExt->getOperand();
    OS << "(zext " << *Op->getType() << " " << Op << " to " << *ZExt->getType()
       << ")";
    return;
  }
  case scSignExtend: {
    const SCEVSignExtendExpr *SExt = cast<SCEVSignExtendExpr>(this);
    SCEVUse Op = SExt->getOperand();
    OS << "(sext " << *Op->getType() << " " << Op << " to " << *SExt->getType()
       << ")";
    return;
  }
  case scAddRecExpr: {
    const SCEVAddRecExpr *AR = cast<SCEVAddRecExpr>(this);
    OS << "{" << AR->getOperand(0);
    for (unsigned i = 1, e = AR->getNumOperands(); i != e; ++i)
      OS << ",+," << AR->getOperand(i);
    OS << "}<";
    if (AR->hasNoUnsignedWrap())
      OS << "nuw><";
    if (AR->hasNoSignedWrap())
      OS << "nsw><";
    if (AR->hasNoSelfWrap() && !AR->hasNoUnsignedWrap() &&
        !AR->hasNoSignedWrap())
      OS << "nw><";
    AR->getLoop()->getHeader()->printAsOperand(OS, /*PrintType=*/false);
    OS << ">";
    return;
  }
  case scAddExpr:
  case scMulExpr:
  case scUMaxExpr:
  case scSMaxExpr:
  case scUMinExpr:
  case scSMinExpr:
  case scSequentialUMinExpr: {
    const SCEVNAryExpr *NAry = cast<SCEVNAryExpr>(this);
    const char *OpStr = nullptr;
    switch (NAry->getSCEVType()) {
    case scAddExpr: OpStr = " + "; break;
    case scMulExpr: OpStr = " * "; break;
    case scUMaxExpr: OpStr = " umax "; break;
    case scSMaxExpr: OpStr = " smax "; break;
    case scUMinExpr:
      OpStr = " umin ";
      break;
    case scSMinExpr:
      OpStr = " smin ";
      break;
    case scSequentialUMinExpr:
      OpStr = " umin_seq ";
      break;
    default:
      llvm_unreachable("There are no other nary expression types.");
    }
    OS << "(" << llvm::interleaved(NAry->operands(), OpStr) << ")";
    switch (NAry->getSCEVType()) {
    case scAddExpr:
    case scMulExpr:
      if (NAry->hasNoUnsignedWrap())
        OS << "<nuw>";
      if (NAry->hasNoSignedWrap())
        OS << "<nsw>";
      break;
    default:
      // Nothing to print for other nary expressions.
      break;
    }
    return;
  }
  case scUDivExpr: {
    const SCEVUDivExpr *UDiv = cast<SCEVUDivExpr>(this);
    OS << "(" << UDiv->getLHS() << " /u " << UDiv->getRHS() << ")";
    return;
  }
  case scUnknown:
    cast<SCEVUnknown>(this)->getValue()->printAsOperand(OS, false);
    return;
  case scCouldNotCompute:
    OS << "***COULDNOTCOMPUTE***";
    return;
  }
  llvm_unreachable("Unknown SCEV kind!");
}
 
ArrayRef<SCEVUse> SCEV::operands() const {
  switch (getSCEVType()) {
  case scConstant:
  case scVScale:
  case scUnknown:
    return {};
  case scPtrToAddr:
  case scTruncate:
  case scZeroExtend:
  case scSignExtend:
    return cast<SCEVCastExpr>(this)->operands();
  case scAddRecExpr:
  case scAddExpr:
  case scMulExpr:
  case scUMaxExpr:
  case scSMaxExpr:
  case scUMinExpr:
  case scSMinExpr:
  case scSequentialUMinExpr:
    return cast<SCEVNAryExpr>(this)->operands();
  case scUDivExpr:
    return cast<SCEVUDivExpr>(this)->operands();
  case scCouldNotCompute:
    llvm_unreachable("Attempt to use a SCEVCouldNotCompute object!");
  }
  llvm_unreachable("Unknown SCEV kind!");
}
 
bool SCEV::isZero() const { return match(this, m_scev_Zero()); }
 
bool SCEV::isOne() const { return match(this, m_scev_One()); }
 
bool SCEV::isAllOnesValue() const { return match(this, m_scev_AllOnes()); }
 
bool SCEV::isNonConstantNegative() const {
  const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(this);
  if (!Mul) return false;
 
  // If there is a constant factor, it will be first.
  const SCEVConstant *SC = dyn_cast<SCEVConstant>(Mul->getOperand(0));
  if (!SC) return false;
 
  // Return true if the value is negative, this matches things like (-42 * V).
  return SC->getAPInt().isNegative();
}
 
SCEVCouldNotCompute::SCEVCouldNotCompute()
    : SCEV(FoldingSetNodeIDRef(), scCouldNotCompute, 0, nullptr) {}
 
bool SCEVCouldNotCompute::classof(const SCEV *S) {
  return S->getSCEVType() == scCouldNotCompute;
}
 
const SCEV *ScalarEvolution::getConstant(ConstantInt *V) {
  auto &Entry = ConstantSCEVs[V];
  if (Entry)
    return Entry;
 
  FoldingSetNodeID ID;
  ID.AddInteger(scConstant);
  ID.AddPointer(V);
  FoldingSetInsertToken Token;
  if (SCEVConstant *S =
          static_cast<SCEVConstant *>(UniqueSCEVs.lookup(ID, Token)))
    return Entry = S;
  SCEVConstant *S =
      new (SCEVAllocator) SCEVConstant(ID.Intern(SCEVAllocator), V);
  UniqueSCEVs.insert(S, Token);
  S->computeAndSetCanonical(*this);
  return Entry = S;
}
 
const SCEV *ScalarEvolution::getConstant(const APInt &Val) {
  return getConstant(ConstantInt::get(getContext(), Val));
}
 
const SCEV *
ScalarEvolution::getConstant(Type *Ty, uint64_t V, bool isSigned) {
  IntegerType *ITy = cast<IntegerType>(getEffectiveSCEVType(Ty));
  // TODO: Avoid implicit trunc?
  // See https://github.com/llvm/llvm-project/issues/112510.
  return getConstant(
      ConstantInt::get(ITy, V, isSigned, /*ImplicitTrunc=*/true));
}
 
const SCEV *ScalarEvolution::getVScale(Type *Ty) {
  FoldingSetNodeID ID;
  ID.AddInteger(scVScale);
  ID.AddPointer(Ty);
  FoldingSetInsertToken Token;
  if (const SCEV *S = UniqueSCEVs.lookup(ID, Token))
    return S;
  SCEV *S = new (SCEVAllocator) SCEVVScale(ID.Intern(SCEVAllocator), Ty);
  UniqueSCEVs.insert(S, Token);
  S->computeAndSetCanonical(*this);
  return S;
}
 
const SCEV *ScalarEvolution::getElementCount(Type *Ty, ElementCount EC,
                                             SCEVFlags Flags) {
  const SCEV *Res = getConstant(Ty, EC.getKnownMinValue());
  if (EC.isScalable())
    Res = getMulExpr(Res, getVScale(Ty), Flags);
  return Res;
}
 
SCEVCastExpr::SCEVCastExpr(const FoldingSetNodeIDRef ID, SCEVTypes SCEVTy,
                           SCEVUse op, Type *ty)
    : SCEV(ID, SCEVTy, computeExpressionSize(op), ty), Op(op) {}
 
SCEVPtrToAddrExpr::SCEVPtrToAddrExpr(const FoldingSetNodeIDRef ID,
                                     const SCEV *Op, Type *ITy)
    : SCEVCastExpr(ID, scPtrToAddr, Op, ITy) {
  assert(getOperand()->getType()->isPointerTy() && getType()->isIntegerTy() &&
         "Must be a non-bit-width-changing pointer-to-integer cast!");
}
 
SCEVIntegralCastExpr::SCEVIntegralCastExpr(const FoldingSetNodeIDRef ID,
                                           SCEVTypes SCEVTy, SCEVUse op,
                                           Type *ty)
    : SCEVCastExpr(ID, SCEVTy, op, ty) {}
 
SCEVTruncateExpr::SCEVTruncateExpr(const FoldingSetNodeIDRef ID, SCEVUse op,
                                   Type *ty)
    : SCEVIntegralCastExpr(ID, scTruncate, op, ty) {
  assert(getOperand()->getType()->isIntOrPtrTy() && getType()->isIntOrPtrTy() &&
         "Cannot truncate non-integer value!");
}
 
SCEVZeroExtendExpr::SCEVZeroExtendExpr(const FoldingSetNodeIDRef ID, SCEVUse op,
                                       Type *ty)
    : SCEVIntegralCastExpr(ID, scZeroExtend, op, ty) {
  assert(getOperand()->getType()->isIntOrPtrTy() && getType()->isIntOrPtrTy() &&
         "Cannot zero extend non-integer value!");
}
 
SCEVSignExtendExpr::SCEVSignExtendExpr(const FoldingSetNodeIDRef ID, SCEVUse op,
                                       Type *ty)
    : SCEVIntegralCastExpr(ID, scSignExtend, op, ty) {
  assert(getOperand()->getType()->isIntOrPtrTy() && getType()->isIntOrPtrTy() &&
         "Cannot sign extend non-integer value!");
}
 
void SCEVUnknown::deleted() {
  // Clear this SCEVUnknown from various maps.
  SE->forgetMemoizedResults({this});
 
  // Remove this SCEVUnknown from the uniquing map.
  SE->UniqueSCEVs.erase(this);
 
  // Release the value.
  setValPtr(nullptr);
}
 
void SCEVUnknown::allUsesReplacedWith(Value *New) {
  // Clear this SCEVUnknown from various maps.
  SE->forgetMemoizedResults({this});
 
  // Remove this SCEVUnknown from the uniquing map.
  SE->UniqueSCEVs.erase(this);
 
  // Replace the value pointer in case someone is still using this SCEVUnknown.
  setValPtr(New);
}
 
//===----------------------------------------------------------------------===//
//                               SCEV Utilities
//===----------------------------------------------------------------------===//
 
/// Compare the two values \p LV and \p RV in terms of their "complexity" where
/// "complexity" is a partial (and somewhat ad-hoc) relation used to order
/// operands in SCEV expressions.
static int CompareValueComplexity(const LoopInfo *const LI, Value *LV,
                                  Value *RV, unsigned Depth) {
  if (Depth > MaxValueCompareDepth)
    return 0;
 
  // Order pointer values after integer values. This helps SCEVExpander form
  // GEPs.
  bool LIsPointer = LV->getType()->isPointerTy(),
       RIsPointer = RV->getType()->isPointerTy();
  if (LIsPointer != RIsPointer)
    return (int)LIsPointer - (int)RIsPointer;
 
  // Compare getValueID values.
  unsigned LID = LV->getValueID(), RID = RV->getValueID();
  if (LID != RID)
    return (int)LID - (int)RID;
 
  // Sort arguments by their position.
  if (const auto *LA = dyn_cast<Argument>(LV)) {
    const auto *RA = cast<Argument>(RV);
    unsigned LArgNo = LA->getArgNo(), RArgNo = RA->getArgNo();
    return (int)LArgNo - (int)RArgNo;
  }
 
  if (const auto *LGV = dyn_cast<GlobalValue>(LV)) {
    const auto *RGV = cast<GlobalValue>(RV);
 
    if (auto L = LGV->getLinkage() - RGV->getLinkage())
      return L;
 
    const auto IsGVNameSemantic = [&](const GlobalValue *GV) {
      auto LT = GV->getLinkage();
      return !(GlobalValue::isPrivateLinkage(LT) ||
               GlobalValue::isInternalLinkage(LT));
    };
 
    // Use the names to distinguish the two values, but only if the
    // names are semantically important.
    if (IsGVNameSemantic(LGV) && IsGVNameSemantic(RGV))
      return LGV->getName().compare(RGV->getName());
  }
 
  // For instructions, compare their loop depth, and their operand count.  This
  // is pretty loose.
  if (const auto *LInst = dyn_cast<Instruction>(LV)) {
    const auto *RInst = cast<Instruction>(RV);
 
    // Compare loop depths.
    const BasicBlock *LParent = LInst->getParent(),
                     *RParent = RInst->getParent();
    if (LParent != RParent) {
      unsigned LDepth = LI->getLoopDepth(LParent),
               RDepth = LI->getLoopDepth(RParent);
      if (LDepth != RDepth)
        return (int)LDepth - (int)RDepth;
    }
 
    // Compare the number of operands.
    unsigned LNumOps = LInst->getNumOperands(),
             RNumOps = RInst->getNumOperands();
    if (LNumOps != RNumOps)
      return (int)LNumOps - (int)RNumOps;
 
    for (unsigned Idx : seq(LNumOps)) {
      int Result = CompareValueComplexity(LI, LInst->getOperand(Idx),
                                          RInst->getOperand(Idx), Depth + 1);
      if (Result != 0)
        return Result;
    }
  }
 
  return 0;
}
 
// Return negative, zero, or positive, if LHS is less than, equal to, or greater
// than RHS, respectively. A three-way result allows recursive comparisons to be
// more efficient. The result is a total order.
static int CompareSCEVComplexity(const LoopInfo *const LI, SCEVUse LHS,
                                 SCEVUse RHS, DominatorTree &DT) {
  // Fast-path: SCEVs are uniqued so we can do a quick equality check.
  if (LHS == RHS)
    return 0;
 
  if (LHS.getPointer() == RHS.getPointer())
    return (int)LHS.getUseNoWrapFlags() - (int)RHS.getUseNoWrapFlags();
 
  // Primarily, sort the SCEVs by their getSCEVType().
  SCEVTypes LType = LHS->getSCEVType(), RType = RHS->getSCEVType();
  if (LType != RType)
    return (int)LType - (int)RType;
 
  // Aside from the getSCEVType() ordering, the particular ordering
  // isn't very important except that it's beneficial to be consistent,
  // so that (a + b) and (b + a) don't end up as different expressions.
  switch (LType) {
  case scUnknown: {
    const SCEVUnknown *LU = cast<SCEVUnknown>(LHS);
    const SCEVUnknown *RU = cast<SCEVUnknown>(RHS);
 
    if (int X = CompareValueComplexity(LI, LU->getValue(), RU->getValue(),
                                       /*Depth=*/0))
      return X;
    return LU->getOrderID() < RU->getOrderID() ? -1 : 1;
  }
 
  case scConstant: {
    const SCEVConstant *LC = cast<SCEVConstant>(LHS);
    const SCEVConstant *RC = cast<SCEVConstant>(RHS);
 
    // Compare constant values.
    const APInt &LA = LC->getAPInt();
    const APInt &RA = RC->getAPInt();
    unsigned LBitWidth = LA.getBitWidth(), RBitWidth = RA.getBitWidth();
    if (LBitWidth != RBitWidth)
      return (int)LBitWidth - (int)RBitWidth;
    return LA.ult(RA) ? -1 : 1;
  }
 
  case scVScale: {
    const auto *LTy = cast<IntegerType>(cast<SCEVVScale>(LHS)->getType());
    const auto *RTy = cast<IntegerType>(cast<SCEVVScale>(RHS)->getType());
    return LTy->getBitWidth() - RTy->getBitWidth();
  }
 
  case scAddRecExpr: {
    const SCEVAddRecExpr *LA = cast<SCEVAddRecExpr>(LHS);
    const SCEVAddRecExpr *RA = cast<SCEVAddRecExpr>(RHS);
 
    // There is always a dominance between two recs that are used by one SCEV,
    // so we can safely sort recs by loop header dominance. We require such
    // order in getAddExpr.
    const Loop *LLoop = LA->getLoop(), *RLoop = RA->getLoop();
    if (LLoop != RLoop) {
      const BasicBlock *LHead = LLoop->getHeader(), *RHead = RLoop->getHeader();
      assert(LHead != RHead && "Two loops share the same header?");
      if (DT.dominates(LHead, RHead))
        return 1;
      assert(DT.dominates(RHead, LHead) &&
             "No dominance between recurrences used by one SCEV?");
      return -1;
    }
 
    [[fallthrough]];
  }
 
  case scTruncate:
  case scZeroExtend:
  case scSignExtend:
  case scPtrToAddr:
  case scAddExpr:
  case scMulExpr:
  case scUDivExpr:
  case scSMaxExpr:
  case scUMaxExpr:
  case scSMinExpr:
  case scUMinExpr:
  case scSequentialUMinExpr: {
    ArrayRef<SCEVUse> LOps = LHS->operands();
    ArrayRef<SCEVUse> ROps = RHS->operands();
 
    // Lexicographically compare n-ary-like expressions.
    unsigned LNumOps = LOps.size(), RNumOps = ROps.size();
    if (LNumOps != RNumOps)
      return (int)LNumOps - (int)RNumOps;
 
    for (unsigned i = 0; i != LNumOps; ++i) {
      auto X = CompareSCEVComplexity(LI, LOps[i], ROps[i], DT);
      if (X != 0)
        return X;
    }
 
    assert(isa<SCEVCastExpr>(LHS) && "distinct SCEVs compare equal");
    unsigned LBitWidth = cast<IntegerType>(LHS->getType())->getBitWidth();
    unsigned RBitWidth = cast<IntegerType>(RHS->getType())->getBitWidth();
    assert(LBitWidth != RBitWidth && "distinct SCEVs compare equal");
    return (int)LBitWidth - (int)RBitWidth;
  }
 
  case scCouldNotCompute:
    llvm_unreachable("Attempt to use a SCEVCouldNotCompute object!");
  }
  llvm_unreachable("Unknown SCEV kind!");
}
 
/// Given a list of SCEV objects, order them by their complexity, and group
/// objects of the same complexity together by value.  When this routine is
/// finished, we know that any duplicates in the vector are consecutive and that
/// complexity is monotonically increasing.
///
/// Note that we go take special precautions to ensure that we get deterministic
/// results from this routine.  In other words, we don't want the results of
/// this to depend on where the addresses of various SCEV objects happened to
/// land in memory.
static void GroupByComplexity(SmallVectorImpl<SCEVUse> &Ops, LoopInfo *LI,
                              DominatorTree &DT) {
  if (Ops.size() < 2) return;  // Noop
 
  // Whether LHS has provably less complexity than RHS.
  auto IsLessComplex = [&](SCEVUse LHS, SCEVUse RHS) {
    return CompareSCEVComplexity(LI, LHS, RHS, DT) < 0;
  };
  if (Ops.size() == 2) {
    // This is the common case, which also happens to be trivially simple.
    // Special case it.
    SCEVUse &LHS = Ops[0], &RHS = Ops[1];
    if (IsLessComplex(RHS, LHS))
      std::swap(LHS, RHS);
    return;
  }
 
  llvm::sort(Ops, IsLessComplex);
}
 
/// Returns true if \p Ops contains a huge SCEV (the subtree of S contains at
/// least HugeExprThreshold nodes).
static bool hasHugeExpression(ArrayRef<SCEVUse> Ops) {
  return any_of(Ops, [](const SCEV *S) {
    return S->getExpressionSize() >= HugeExprThreshold;
  });
}
 
/// Performs a number of common optimizations on the passed \p Ops. If the
/// whole expression reduces down to a single operand, it will be returned.
///
/// The following optimizations are performed:
///  * Fold constants using the \p Fold function.
///  * Remove identity constants satisfying \p IsIdentity.
///  * If a constant satisfies \p IsAbsorber, return it.
///  * Sort operands by complexity.
template <typename FoldT, typename IsIdentityT, typename IsAbsorberT>
static const SCEV *
constantFoldAndGroupOps(ScalarEvolution &SE, LoopInfo &LI, DominatorTree &DT,
                        SmallVectorImpl<SCEVUse> &Ops, FoldT Fold,
                        IsIdentityT IsIdentity, IsAbsorberT IsAbsorber) {
  const SCEVConstant *Folded = nullptr;
  for (unsigned Idx = 0; Idx < Ops.size();) {
    const SCEV *Op = Ops[Idx];
    if (const auto *C = dyn_cast<SCEVConstant>(Op)) {
      if (!Folded)
        Folded = C;
      else
        Folded = cast<SCEVConstant>(
            SE.getConstant(Fold(Folded->getAPInt(), C->getAPInt())));
      Ops.erase(Ops.begin() + Idx);
      continue;
    }
    ++Idx;
  }
 
  if (Ops.empty()) {
    assert(Folded && "Must have folded value");
    return Folded;
  }
 
  if (Folded && IsAbsorber(Folded->getAPInt()))
    return Folded;
 
  GroupByComplexity(Ops, &LI, DT);
  if (Folded && !IsIdentity(Folded->getAPInt()))
    Ops.insert(Ops.begin(), Folded);
 
  return Ops.size() == 1 ? Ops[0] : nullptr;
}
 
//===----------------------------------------------------------------------===//
//                      Simple SCEV method implementations
//===----------------------------------------------------------------------===//
 
/// Compute BC(It, K).  The result has width W.  Assume, K > 0.
static const SCEV *BinomialCoefficient(const SCEV *It, unsigned K,
                                       ScalarEvolution &SE,
                                       Type *ResultTy) {
  // Handle the simplest case efficiently.
  if (K == 1)
    return SE.getTruncateOrZeroExtend(It, ResultTy);
 
  // We are using the following formula for BC(It, K):
  //
  //   BC(It, K) = (It * (It - 1) * ... * (It - K + 1)) / K!
  //
  // Suppose, W is the bitwidth of the return value.  We must be prepared for
  // overflow.  Hence, we must assure that the result of our computation is
  // equal to the accurate one modulo 2^W.  Unfortunately, division isn't
  // safe in modular arithmetic.
  //
  // However, this code doesn't use exactly that formula; the formula it uses
  // is something like the following, where T is the number of factors of 2 in
  // K! (i.e. trailing zeros in the binary representation of K!), and ^ is
  // exponentiation:
  //
  //   BC(It, K) = (It * (It - 1) * ... * (It - K + 1)) / 2^T / (K! / 2^T)
  //
  // This formula is trivially equivalent to the previous formula.  However,
  // this formula can be implemented much more efficiently.  The trick is that
  // K! / 2^T is odd, and exact division by an odd number *is* safe in modular
  // arithmetic.  To do exact division in modular arithmetic, all we have
  // to do is multiply by the inverse.  Therefore, this step can be done at
  // width W.
  //
  // The next issue is how to safely do the division by 2^T.  The way this
  // is done is by doing the multiplication step at a width of at least W + T
  // bits.  This way, the bottom W+T bits of the product are accurate. Then,
  // when we perform the division by 2^T (which is equivalent to a right shift
  // by T), the bottom W bits are accurate.  Extra bits are okay; they'll get
  // truncated out after the division by 2^T.
  //
  // In comparison to just directly using the first formula, this technique
  // is much more efficient; using the first formula requires W * K bits,
  // but this formula less than W + K bits. Also, the first formula requires
  // a division step, whereas this formula only requires multiplies and shifts.
  //
  // It doesn't matter whether the subtraction step is done in the calculation
  // width or the input iteration count's width; if the subtraction overflows,
  // the result must be zero anyway.  We prefer here to do it in the width of
  // the induction variable because it helps a lot for certain cases; CodeGen
  // isn't smart enough to ignore the overflow, which leads to much less
  // efficient code if the width of the subtraction is wider than the native
  // register width.
  //
  // (It's possible to not widen at all by pulling out factors of 2 before
  // the multiplication; for example, K=2 can be calculated as
  // It/2*(It+(It*INT_MIN/INT_MIN)+-1). However, it requires
  // extra arithmetic, so it's not an obvious win, and it gets
  // much more complicated for K > 3.)
 
  // Protection from insane SCEVs; this bound is conservative,
  // but it probably doesn't matter.
  if (K > 1000)
    return SE.getCouldNotCompute();
 
  unsigned W = SE.getTypeSizeInBits(ResultTy);
 
  // Calculate K! / 2^T and T; we divide out the factors of two before
  // multiplying for calculating K! / 2^T to avoid overflow.
  // Other overflow doesn't matter because we only care about the bottom
  // W bits of the result.
  APInt OddFactorial(W, 1);
  unsigned T = 1;
  for (unsigned i = 3; i <= K; ++i) {
    unsigned TwoFactors = countr_zero(i);
    T += TwoFactors;
    OddFactorial *= (i >> TwoFactors);
  }
 
  // We need at least W + T bits for the multiplication step
  unsigned CalculationBits = W + T;
 
  // Calculate 2^T, at width T+W.
  APInt DivFactor = APInt::getOneBitSet(CalculationBits, T);
 
  // Calculate the multiplicative inverse of K! / 2^T;
  // this multiplication factor will perform the exact division by
  // K! / 2^T.
  APInt MultiplyFactor = OddFactorial.multiplicativeInverse();
 
  // Calculate the product, at width T+W
  IntegerType *CalculationTy = IntegerType::get(SE.getContext(),
                                                      CalculationBits);
  const SCEV *Dividend = SE.getTruncateOrZeroExtend(It, CalculationTy);
  for (unsigned i = 1; i != K; ++i) {
    const SCEV *S = SE.getMinusSCEV(It, SE.getConstant(It->getType(), i));
    Dividend = SE.getMulExpr(Dividend,
                             SE.getTruncateOrZeroExtend(S, CalculationTy));
  }
 
  // Divide by 2^T
  const SCEV *DivResult = SE.getUDivExpr(Dividend, SE.getConstant(DivFactor));
 
  // Truncate the result, and divide by K! / 2^T.
 
  return SE.getMulExpr(SE.getConstant(MultiplyFactor),
                       SE.getTruncateOrZeroExtend(DivResult, ResultTy));
}
 
/// Return the value of this chain of recurrences at the specified iteration
/// number.  We can evaluate this recurrence by multiplying each element in the
/// chain by the binomial coefficient corresponding to it.  In other words, we
/// can evaluate {A,+,B,+,C,+,D} as:
///
///   A*BC(It, 0) + B*BC(It, 1) + C*BC(It, 2) + D*BC(It, 3)
///
/// where BC(It, k) stands for binomial coefficient.
const SCEV *SCEVAddRecExpr::evaluateAtIteration(const SCEV *It,
                                                ScalarEvolution &SE) const {
  return evaluateAtIteration(operands(), It, SE);
}
 
SCEVUse SCEVAddRecExpr::evaluateAtIteration(ArrayRef<SCEVUse> Operands,
                                            const SCEV *It, ScalarEvolution &SE,
                                            SCEVFlags UseFlags) {
  assert(Operands.size() > 0);
  assert((Operands.size() == 2 || UseFlags == SCEV::FlagNone) &&
         "use-specific flags only supported for affine AddRecs");
  SCEVUse Result = Operands[0].getPointer();
  for (unsigned i = 1, e = Operands.size(); i != e; ++i) {
    // The computation is correct in the face of overflow provided that the
    // multiplication is performed _after_ the evaluation of the binomial
    // coefficient.
    const SCEV *Coeff = BinomialCoefficient(It, i, SE, Result->getType());
    if (isa<SCEVCouldNotCompute>(Coeff))
      return Coeff;
 
    SCEVUse Mul = SE.getMulExpr(Operands[i].getPointer(), Coeff,
                                {SCEV::FlagNone, UseFlags});
    Result = SE.getAddExpr(Result, Mul, {SCEV::FlagNone, UseFlags});
  }
  return Result;
}
 
SCEVUse SCEVAddRecExpr::getExitValue(ScalarEvolution &SE) const {
  const SCEV *BTC = SE.getBackedgeTakenCount(getLoop());
  if (isa<SCEVCouldNotCompute>(BTC))
    return BTC;
  // The loop reaches iteration BTC, so the value this recurrence computes there
  // is the value it had, and that did not wrap.
  return evaluateAtIteration(operands(), BTC, SE,
                             isAffine() ? getNoWrapFlags(SCEV::FlagNUW)
                                        : SCEV::FlagNone);
}
 
//===----------------------------------------------------------------------===//
//                    SCEV Expression folder implementations
//===----------------------------------------------------------------------===//
 
/// The SCEVCastSinkingRewriter takes a scalar evolution expression,
/// which computes a pointer-typed value, and rewrites the whole expression
/// tree so that *all* the computations are done on integers, and the only
/// pointer-typed operands in the expression are SCEVUnknown.
/// The CreatePtrCast callback is invoked to create the actual conversion
/// (ptrtoint or ptrtoaddr) at the SCEVUnknown leaves.
class SCEVCastSinkingRewriter
    : public SCEVRewriteVisitor<SCEVCastSinkingRewriter> {
  using Base = SCEVRewriteVisitor<SCEVCastSinkingRewriter>;
  using ConversionFn = function_ref<const SCEV *(const SCEVUnknown *)>;
  Type *TargetTy;
  ConversionFn CreatePtrCast;
 
public:
  SCEVCastSinkingRewriter(ScalarEvolution &SE, Type *TargetTy,
                          ConversionFn CreatePtrCast)
      : Base(SE), TargetTy(TargetTy), CreatePtrCast(std::move(CreatePtrCast)) {}
 
  static const SCEV *rewrite(const SCEV *Scev, ScalarEvolution &SE,
                             Type *TargetTy, ConversionFn CreatePtrCast) {
    SCEVCastSinkingRewriter Rewriter(SE, TargetTy, std::move(CreatePtrCast));
    return Rewriter.visit(Scev);
  }
 
  const SCEV *visit(const SCEV *S) {
    Type *STy = S->getType();
    // If the expression is not pointer-typed, just keep it as-is.
    if (!STy->isPointerTy())
      return S;
    // Else, recursively sink the cast down into it.
    return Base::visit(S);
  }
 
  const SCEV *visitAddExpr(const SCEVAddExpr *Expr) {
    // Preserve wrap flags on rewritten SCEVAddExpr, which the default
    // implementation drops.
    SmallVector<SCEVUse, 2> Operands;
    bool Changed = false;
    for (SCEVUse Op : Expr->operands()) {
      Operands.push_back(visit(Op.getPointer()));
      Changed |= Op.getPointer() != Operands.back();
    }
    return !Changed ? Expr : SE.getAddExpr(Operands, Expr->getNoWrapFlags());
  }
 
  const SCEV *visitUnknown(const SCEVUnknown *Expr) {
    assert(Expr->getType()->isPointerTy() &&
           "Should only reach pointer-typed SCEVUnknown's.");
    // Perform some basic constant folding. If the operand of the cast is a
    // null pointer, don't create a cast SCEV expression (that will be left
    // as-is), but produce a zero constant.
    if (isa<ConstantPointerNull>(Expr->getValue()))
      return SE.getZero(TargetTy);
    return CreatePtrCast(Expr);
  }
};
 
const SCEV *ScalarEvolution::getPtrToAddrExpr(const SCEV *Op) {
  assert(Op->getType()->isPointerTy() && "Op must be a pointer");
 
  // Treat pointers with unstable representation conservatively, since the
  // address bits may change.
  if (DL.hasUnstableRepresentation(Op->getType()))
    return getCouldNotCompute();
 
  Type *Ty = DL.getAddressType(Op->getType());
 
  // Use the rewriter to sink the cast down to SCEVUnknown leaves.
  // The rewriter handles null pointer constant folding.
  const SCEV *IntOp = SCEVCastSinkingRewriter::rewrite(
      Op, *this, Ty, [this, Ty](const SCEVUnknown *U) {
        FoldingSetNodeID ID;
        ID.AddInteger(scPtrToAddr);
        ID.AddPointer(U);
        ID.AddPointer(Ty);
        FoldingSetInsertToken Token;
        if (const SCEV *S = UniqueSCEVs.lookup(ID, Token))
          return S;
        SCEV *S = new (SCEVAllocator)
            SCEVPtrToAddrExpr(ID.Intern(SCEVAllocator), U, Ty);
        UniqueSCEVs.insert(S, Token);
        S->computeAndSetCanonical(*this);
        registerUser(S, {U});
        return static_cast<const SCEV *>(S);
      });
  assert(IntOp->getType()->isIntegerTy() &&
         "We must have succeeded in sinking the cast, "
         "and ending up with an integer-typed expression!");
  return IntOp;
}
 
const SCEV *ScalarEvolution::getTruncateExpr(SCEVUse Op, Type *Ty,
                                             unsigned Depth) {
  assert(getTypeSizeInBits(Op->getType()) > getTypeSizeInBits(Ty) &&
         "This is not a truncating conversion!");
  assert(isSCEVable(Ty) &&
         "This is not a conversion to a SCEVable type!");
  assert(!Op->getType()->isPointerTy() && "Can't truncate pointer!");
  Ty = getEffectiveSCEVType(Ty);
 
  FoldingSetNodeID ID;
  ID.AddInteger(scTruncate);
  ID.AddPointer(Op.getOpaqueValue());
  ID.AddPointer(Ty);
  FoldingSetInsertToken Token;
  if (const SCEV *S = UniqueSCEVs.lookup(ID, Token))
    return S;
 
  // Fold if the operand is constant.
  if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(Op))
    return getConstant(
      cast<ConstantInt>(ConstantExpr::getTrunc(SC->getValue(), Ty)));
 
  // trunc(trunc(x)) --> trunc(x)
  if (const SCEVTruncateExpr *ST = dyn_cast<SCEVTruncateExpr>(Op))
    return getTruncateExpr(ST->getOperand(), Ty, Depth + 1);
 
  // trunc(sext(x)) --> sext(x) if widening or trunc(x) if narrowing
  if (const SCEVSignExtendExpr *SS = dyn_cast<SCEVSignExtendExpr>(Op))
    return getTruncateOrSignExtend(SS->getOperand(), Ty, Depth + 1);
 
  // trunc(zext(x)) --> zext(x) if widening or trunc(x) if narrowing
  if (const SCEVZeroExtendExpr *SZ = dyn_cast<SCEVZeroExtendExpr>(Op))
    return getTruncateOrZeroExtend(SZ->getOperand(), Ty, Depth + 1);
 
  if (Depth > MaxCastDepth) {
    SCEV *S =
        new (SCEVAllocator) SCEVTruncateExpr(ID.Intern(SCEVAllocator), Op, Ty);
    UniqueSCEVs.insert(S, Token);
    S->computeAndSetCanonical(*this);
    registerUser(S, Op);
    return S;
  }
 
  // trunc(x1 + ... + xN) --> trunc(x1) + ... + trunc(xN) and
  // trunc(x1 * ... * xN) --> trunc(x1) * ... * trunc(xN),
  // if after transforming we have at most one truncate, not counting truncates
  // that replace other casts.
  if (isa<SCEVAddExpr>(Op) || isa<SCEVMulExpr>(Op)) {
    auto *CommOp = cast<SCEVCommutativeExpr>(Op);
    SmallVector<SCEVUse, 4> Operands;
    unsigned numTruncs = 0;
    for (unsigned i = 0, e = CommOp->getNumOperands(); i != e && numTruncs < 2;
         ++i) {
      const SCEV *S = getTruncateExpr(CommOp->getOperand(i), Ty, Depth + 1);
      if (!isa<SCEVIntegralCastExpr>(CommOp->getOperand(i)) &&
          isa<SCEVTruncateExpr>(S))
        numTruncs++;
      Operands.push_back(S);
    }
    if (numTruncs < 2) {
      if (isa<SCEVAddExpr>(Op))
        return getAddExpr(Operands);
      if (isa<SCEVMulExpr>(Op))
        return getMulExpr(Operands);
      llvm_unreachable("Unexpected SCEV type for Op.");
    }
    // Although we checked in the beginning that ID is not in the cache, it is
    // possible that during recursion and different modification ID was inserted
    // into the cache. So if we find it, just return it.
    if (const SCEV *S = UniqueSCEVs.lookup(ID, Token))
      return S;
  }
 
  // If the input value is a chrec scev, truncate the chrec's operands.
  if (const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(Op)) {
    SmallVector<SCEVUse, 4> Operands;
    for (const SCEV *Op : AddRec->operands())
      Operands.push_back(getTruncateExpr(Op, Ty, Depth + 1));
    return getAddRecExpr(Operands, AddRec->getLoop(), SCEV::FlagNone);
  }
 
  // Return zero if truncating to known zeros.
  uint32_t MinTrailingZeros = getMinTrailingZeros(Op);
  if (MinTrailingZeros >= getTypeSizeInBits(Ty))
    return getZero(Ty);
 
  // The cast wasn't folded; create an explicit cast node. We can reuse
  // the existing insert position since if we get here, we won't have
  // made any changes which would invalidate it.
  SCEV *S = new (SCEVAllocator) SCEVTruncateExpr(ID.Intern(SCEVAllocator),
                                                 Op, Ty);
  UniqueSCEVs.insert(S, Token);
  S->computeAndSetCanonical(*this);
  registerUser(S, Op);
  return S;
}
 
// Get the limit of a recurrence such that incrementing by Step cannot cause
// signed overflow as long as the value of the recurrence within the
// loop does not exceed this limit before incrementing.
static const SCEV *getSignedOverflowLimitForStep(const SCEV *Step,
                                                 ICmpInst::Predicate *Pred,
                                                 ScalarEvolution *SE) {
  unsigned BitWidth = SE->getTypeSizeInBits(Step->getType());
  if (SE->isKnownPositive(Step)) {
    *Pred = ICmpInst::ICMP_SLT;
    return SE->getConstant(APInt::getSignedMinValue(BitWidth) -
                           SE->getSignedRangeMax(Step));
  }
  if (SE->isKnownNegative(Step)) {
    *Pred = ICmpInst::ICMP_SGT;
    return SE->getConstant(APInt::getSignedMaxValue(BitWidth) -
                           SE->getSignedRangeMin(Step));
  }
  return nullptr;
}
 
// Get the limit of a recurrence such that incrementing by Step cannot cause
// unsigned overflow as long as the value of the recurrence within the loop does
// not exceed this limit before incrementing.
static const SCEV *getUnsignedOverflowLimitForStep(const SCEV *Step,
                                                   ICmpInst::Predicate *Pred,
                                                   ScalarEvolution *SE) {
  unsigned BitWidth = SE->getTypeSizeInBits(Step->getType());
  *Pred = ICmpInst::ICMP_ULT;
 
  return SE->getConstant(APInt::getMinValue(BitWidth) -
                         SE->getUnsignedRangeMax(Step));
}
 
namespace {
 
struct ExtendOpTraitsBase {
  typedef const SCEV *(ScalarEvolution::*GetExtendExprTy)(SCEVUse, Type *,
                                                          unsigned);
};
 
// Used to make code generic over signed and unsigned overflow.
template <typename ExtendOp> struct ExtendOpTraits {
  // Members present:
  //
  // static const SCEVFlags WrapType;
  //
  // static const ExtendOpTraitsBase::GetExtendExprTy GetExtendExpr;
  //
  // static const SCEV *getOverflowLimitForStep(const SCEV *Step,
  //                                           ICmpInst::Predicate *Pred,
  //                                           ScalarEvolution *SE);
};
 
template <>
struct ExtendOpTraits<SCEVSignExtendExpr> : public ExtendOpTraitsBase {
  static const SCEVFlags WrapType = SCEV::FlagNSW;
 
  static const GetExtendExprTy GetExtendExpr;
 
  static const SCEV *getOverflowLimitForStep(const SCEV *Step,
                                             ICmpInst::Predicate *Pred,
                                             ScalarEvolution *SE) {
    return getSignedOverflowLimitForStep(Step, Pred, SE);
  }
};
 
const ExtendOpTraitsBase::GetExtendExprTy ExtendOpTraits<
    SCEVSignExtendExpr>::GetExtendExpr = &ScalarEvolution::getSignExtendExpr;
 
template <>
struct ExtendOpTraits<SCEVZeroExtendExpr> : public ExtendOpTraitsBase {
  static const SCEVFlags WrapType = SCEV::FlagNUW;
 
  static const GetExtendExprTy GetExtendExpr;
 
  static const SCEV *getOverflowLimitForStep(const SCEV *Step,
                                             ICmpInst::Predicate *Pred,
                                             ScalarEvolution *SE) {
    return getUnsignedOverflowLimitForStep(Step, Pred, SE);
  }
};
 
const ExtendOpTraitsBase::GetExtendExprTy ExtendOpTraits<
    SCEVZeroExtendExpr>::GetExtendExpr = &ScalarEvolution::getZeroExtendExpr;
 
} // end anonymous namespace
 
// The recurrence AR has been shown to have no signed/unsigned wrap or something
// close to it. Typically, if we can prove NSW/NUW for AR, then we can just as
// easily prove NSW/NUW for its preincrement or postincrement sibling. This
// allows normalizing a sign/zero extended AddRec as such: {sext/zext(Step +
// Start),+,Step} => {(Step + sext/zext(Start),+,Step} As a result, the
// expression "Step + sext/zext(PreIncAR)" is congruent with
// "sext/zext(PostIncAR)"
template <typename ExtendOpTy>
static const SCEV *getPreStartForExtend(const SCEVAddRecExpr *AR,
                                        ScalarEvolution *SE, unsigned Depth) {
  auto WrapType = ExtendOpTraits<ExtendOpTy>::WrapType;
  auto GetExtendExpr = ExtendOpTraits<ExtendOpTy>::GetExtendExpr;
 
  const Loop *L = AR->getLoop();
  const SCEV *Start = AR->getStart();
  const SCEV *Step = AR->getStepRecurrence(*SE);
 
  // Check for a simple looking step prior to loop entry.
  const SCEVAddExpr *SA = dyn_cast<SCEVAddExpr>(Start);
  if (!SA)
    return nullptr;
 
  // Create an AddExpr for "PreStart" after subtracting Step. Full SCEV
  // subtraction is expensive. For this purpose, perform a quick and dirty
  // difference, by checking for Step in the operand list. Note, that
  // SA might have repeated ops, like %a + %a + ..., so only remove one.
  SmallVector<SCEVUse, 4> DiffOps(SA->operands());
  for (auto It = DiffOps.begin(); It != DiffOps.end(); ++It)
    if (*It == Step) {
      DiffOps.erase(It);
      break;
    }
 
  if (DiffOps.size() == SA->getNumOperands())
    return nullptr;
 
  // Try to prove `WrapType` (SCEV::FlagNSW or SCEV::FlagNUW) on `PreStart` +
  // `Step`:
 
  // 1. NSW/NUW flags on the step increment.
  auto PreStartFlags =
    ScalarEvolution::maskFlags(SA->getNoWrapFlags(), SCEV::FlagNUW);
  const SCEV *PreStart = SE->getAddExpr(DiffOps, PreStartFlags);
  const SCEVAddRecExpr *PreAR = dyn_cast<SCEVAddRecExpr>(
      SE->getAddRecExpr(PreStart, Step, L, SCEV::FlagNone));
 
  // "{S,+,X} is <nsw>/<nuw>" and "the backedge is taken at least once" implies
  // "S+X does not sign/unsign-overflow".
  //
 
  const SCEV *BECount = SE->getBackedgeTakenCount(L);
  if (PreAR && any(PreAR->getNoWrapFlags(WrapType)) &&
      !isa<SCEVCouldNotCompute>(BECount) && SE->isKnownPositive(BECount))
    return PreStart;
 
  // 2. Direct overflow check on the step operation's expression.
  unsigned BitWidth = SE->getTypeSizeInBits(AR->getType());
  Type *WideTy = IntegerType::get(SE->getContext(), BitWidth * 2);
  const SCEV *OperandExtendedStart =
      SE->getAddExpr((SE->*GetExtendExpr)(PreStart, WideTy, Depth),
                     (SE->*GetExtendExpr)(Step, WideTy, Depth));
  if ((SE->*GetExtendExpr)(Start, WideTy, Depth) == OperandExtendedStart) {
    if (PreAR && any(AR->getNoWrapFlags(WrapType))) {
      // If we know `AR` == {`PreStart`+`Step`,+,`Step`} is `WrapType` (FlagNSW
      // or FlagNUW) and that `PreStart` + `Step` is `WrapType` too, then
      // `PreAR` == {`PreStart`,+,`Step`} is also `WrapType`.  Cache this fact.
      SE->setNoWrapFlags(const_cast<SCEVAddRecExpr *>(PreAR), WrapType);
    }
    return PreStart;
  }
 
  // 3. Loop precondition.
  ICmpInst::Predicate Pred;
  const SCEV *OverflowLimit =
      ExtendOpTraits<ExtendOpTy>::getOverflowLimitForStep(Step, &Pred, SE);
 
  if (OverflowLimit &&
      SE->isLoopEntryGuardedByCond(L, Pred, PreStart, OverflowLimit))
    return PreStart;
 
  return nullptr;
}
 
// Get the normalized zero or sign extended expression for this AddRec's Start.
template <typename ExtendOpTy>
static const SCEV *getExtendAddRecStart(const SCEVAddRecExpr *AR, Type *Ty,
                                        ScalarEvolution *SE,
                                        unsigned Depth) {
  auto GetExtendExpr = ExtendOpTraits<ExtendOpTy>::GetExtendExpr;
 
  const SCEV *PreStart = getPreStartForExtend<ExtendOpTy>(AR, SE, Depth);
  if (!PreStart)
    return (SE->*GetExtendExpr)(AR->getStart(), Ty, Depth);
 
  return SE->getAddExpr((SE->*GetExtendExpr)(AR->getStepRecurrence(*SE), Ty,
                                             Depth),
                        (SE->*GetExtendExpr)(PreStart, Ty, Depth));
}
 
// Try to prove away overflow by looking at "nearby" add recurrences.  A
// motivating example for this rule: if we know `{0,+,4}` is `ult` `-1` and it
// does not itself wrap then we can conclude that `{1,+,4}` is `nuw`.
//
// Formally:
//
//     {S,+,X} == {S-T,+,X} + T
//  => Ext({S,+,X}) == Ext({S-T,+,X} + T)
//
// If ({S-T,+,X} + T) does not overflow  ... (1)
//
//  RHS == Ext({S-T,+,X} + T) == Ext({S-T,+,X}) + Ext(T)
//
// If {S-T,+,X} does not overflow  ... (2)
//
//  RHS == Ext({S-T,+,X}) + Ext(T) == {Ext(S-T),+,Ext(X)} + Ext(T)
//      == {Ext(S-T)+Ext(T),+,Ext(X)}
//
// If (S-T)+T does not overflow  ... (3)
//
//  RHS == {Ext(S-T)+Ext(T),+,Ext(X)} == {Ext(S-T+T),+,Ext(X)}
//      == {Ext(S),+,Ext(X)} == LHS
//
// Thus, if (1), (2) and (3) are true for some T, then
//   Ext({S,+,X}) == {Ext(S),+,Ext(X)}
//
// (3) is implied by (1) -- "(S-T)+T does not overflow" is simply "({S-T,+,X}+T)
// does not overflow" restricted to the 0th iteration.  Therefore we only need
// to check for (1) and (2).
//
// In the current context, S is `Start`, X is `Step`, Ext is `ExtendOpTy` and T
// is `Delta` (defined below).
template <typename ExtendOpTy>
bool ScalarEvolution::proveNoWrapByVaryingStart(const SCEV *Start,
                                                const SCEV *Step,
                                                const Loop *L) {
  auto WrapType = ExtendOpTraits<ExtendOpTy>::WrapType;
 
  // We restrict `Start` to a constant to prevent SCEV from spending too much
  // time here.  It is correct (but more expensive) to continue with a
  // non-constant `Start` and do a general SCEV subtraction to compute
  // `PreStart` below.
  const SCEVConstant *StartC = dyn_cast<SCEVConstant>(Start);
  if (!StartC)
    return false;
 
  APInt StartAI = StartC->getAPInt();
 
  for (unsigned Delta : {-2, -1, 1, 2}) {
    const SCEV *PreStart = getConstant(StartAI - Delta);
    const auto *PreAR = static_cast<SCEVAddRecExpr *>(
        findExistingSCEVInCache(scAddRecExpr, {PreStart, Step}, L));
 
    // Give up if we don't already have the add recurrence we need because
    // actually constructing an add recurrence is relatively expensive.
    if (PreAR && any(PreAR->getNoWrapFlags(WrapType))) { // proves (2)
      const SCEV *DeltaS = getConstant(StartC->getType(), Delta);
      ICmpInst::Predicate Pred = ICmpInst::BAD_ICMP_PREDICATE;
      const SCEV *Limit = ExtendOpTraits<ExtendOpTy>::getOverflowLimitForStep(
          DeltaS, &Pred, this);
      if (Limit && isKnownPredicate(Pred, PreAR, Limit))  // proves (1)
        return true;
    }
  }
 
  return false;
}
 
// Finds an integer D for an expression (C + x + y + ...) such that the top
// level addition in (D + (C - D + x + y + ...)) would not wrap (signed or
// unsigned) and the number of trailing zeros of (C - D + x + y + ...) is
// maximized, where C is the \p ConstantTerm, x, y, ... are arbitrary SCEVs, and
// the (C + x + y + ...) expression is \p WholeAddExpr.
static APInt extractConstantWithoutWrapping(ScalarEvolution &SE,
                                            const SCEVConstant *ConstantTerm,
                                            const SCEVAddExpr *WholeAddExpr) {
  const APInt &C = ConstantTerm->getAPInt();
  const unsigned BitWidth = C.getBitWidth();
  // Find number of trailing zeros of (x + y + ...) w/o the C first:
  uint32_t TZ = BitWidth;
  for (unsigned I = 1, E = WholeAddExpr->getNumOperands(); I < E && TZ; ++I)
    TZ = std::min(TZ, SE.getMinTrailingZeros(WholeAddExpr->getOperand(I)));
  if (TZ) {
    // Set D to be as many least significant bits of C as possible while still
    // guaranteeing that adding D to (C - D + x + y + ...) won't cause a wrap:
    return TZ < BitWidth ? C.trunc(TZ).zext(BitWidth) : C;
  }
  return APInt(BitWidth, 0);
}
 
// Finds an integer D for an affine AddRec expression {C,+,x} such that the top
// level addition in (D + {C-D,+,x}) would not wrap (signed or unsigned) and the
// number of trailing zeros of (C - D + x * n) is maximized, where C is the \p
// ConstantStart, x is an arbitrary \p Step, and n is the loop trip count.
static APInt extractConstantWithoutWrapping(ScalarEvolution &SE,
                                            const APInt &ConstantStart,
                                            const SCEV *Step) {
  const unsigned BitWidth = ConstantStart.getBitWidth();
  const uint32_t TZ = SE.getMinTrailingZeros(Step);
  if (TZ)
    return TZ < BitWidth ? ConstantStart.trunc(TZ).zext(BitWidth)
                         : ConstantStart;
  return APInt(BitWidth, 0);
}
 
static void insertFoldCacheEntry(
    const ScalarEvolution::FoldID &ID, const SCEV *S,
    DenseMap<ScalarEvolution::FoldID, const SCEV *> &FoldCache,
    DenseMap<const SCEV *, SmallVector<ScalarEvolution::FoldID, 2>>
        &FoldCacheUser) {
  auto I = FoldCache.insert({ID, S});
  if (!I.second) {
    // Remove FoldCacheUser entry for ID when replacing an existing FoldCache
    // entry.
    auto &UserIDs = FoldCacheUser[I.first->second];
    assert(count(UserIDs, ID) == 1 && "unexpected duplicates in UserIDs");
    for (unsigned I = 0; I != UserIDs.size(); ++I)
      if (UserIDs[I] == ID) {
        std::swap(UserIDs[I], UserIDs.back());
        break;
      }
    UserIDs.pop_back();
    I.first->second = S;
  }
  FoldCacheUser[S].push_back(ID);
}
 
const SCEV *ScalarEvolution::getZeroExtendExpr(SCEVUse Op, Type *Ty,
                                               unsigned Depth) {
  assert(getTypeSizeInBits(Op->getType()) < getTypeSizeInBits(Ty) &&
         "This is not an extending conversion!");
  assert(isSCEVable(Ty) &&
         "This is not a conversion to a SCEVable type!");
  assert(!Op->getType()->isPointerTy() && "Can't extend pointer!");
  Ty = getEffectiveSCEVType(Ty);
 
  FoldID ID(scZeroExtend, Op, Ty);
  if (const SCEV *S = FoldCache.lookup(ID))
    return S;
 
  const SCEV *S = getZeroExtendExprImpl(Op, Ty, Depth);
  if (!isa<SCEVZeroExtendExpr>(S))
    insertFoldCacheEntry(ID, S, FoldCache, FoldCacheUser);
  return S;
}
 
const SCEV *ScalarEvolution::getZeroExtendExprImpl(SCEVUse Op, Type *Ty,
                                                   unsigned Depth) {
  assert(getTypeSizeInBits(Op->getType()) < getTypeSizeInBits(Ty) &&
         "This is not an extending conversion!");
  assert(isSCEVable(Ty) && "This is not a conversion to a SCEVable type!");
  assert(!Op->getType()->isPointerTy() && "Can't extend pointer!");
 
  // Fold if the operand is constant.
  if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(Op))
    return getConstant(SC->getAPInt().zext(getTypeSizeInBits(Ty)));
 
  // zext(zext(x)) --> zext(x)
  if (const SCEVZeroExtendExpr *SZ = dyn_cast<SCEVZeroExtendExpr>(Op))
    return getZeroExtendExpr(SZ->getOperand(), Ty, Depth + 1);
 
  // If the operand is an affine AddRec with the no-unsigned-wrap flag, the
  // zero-extension distributes over the recurrence.
  const SCEV *Start, *Step;
  const Loop *L;
  if (Depth <= MaxCastDepth &&
      match(Op, m_scev_AffineAddRec(m_SCEV(Start), m_SCEV(Step), m_Loop(L)))) {
    const auto *AR = cast<SCEVAddRecExpr>(Op);
    if (AR->hasNoUnsignedWrap()) {
      Start = getExtendAddRecStart<SCEVZeroExtendExpr>(AR, Ty, this, Depth + 1);
      Step = getZeroExtendExpr(Step, Ty, Depth + 1);
      return getAddRecExpr(Start, Step, L, AR->getNoWrapFlags());
    }
  }
 
  // Before doing any expensive analysis, check to see if we've already
  // computed a SCEV for this Op and Ty.
  FoldingSetNodeID ID;
  ID.AddInteger(scZeroExtend);
  ID.AddPointer(Op.getOpaqueValue());
  ID.AddPointer(Ty);
  FoldingSetInsertToken Token;
  if (const SCEV *S = UniqueSCEVs.lookup(ID, Token))
    return S;
  if (Depth > MaxCastDepth) {
    SCEV *S = new (SCEVAllocator) SCEVZeroExtendExpr(ID.Intern(SCEVAllocator),
                                                     Op, Ty);
    UniqueSCEVs.insert(S, Token);
    S->computeAndSetCanonical(*this);
    registerUser(S, Op);
    return S;
  }
 
  // zext(trunc(x)) --> zext(x) or x or trunc(x)
  if (const SCEVTruncateExpr *ST = dyn_cast<SCEVTruncateExpr>(Op)) {
    // It's possible the bits taken off by the truncate were all zero bits. If
    // so, we should be able to simplify this further.
    const SCEV *X = ST->getOperand();
    ConstantRange CR = getUnsignedRange(X);
    unsigned TruncBits = getTypeSizeInBits(ST->getType());
    unsigned NewBits = getTypeSizeInBits(Ty);
    if (CR.truncate(TruncBits).zeroExtend(NewBits).contains(
            CR.zextOrTrunc(NewBits)))
      return getTruncateOrZeroExtend(X, Ty, Depth);
  }
 
  // If the input value is a chrec scev, and we can prove that the value
  // did not overflow the old, smaller, value, we can zero extend all of the
  // operands (often constants).  This allows analysis of something like
  // this:  for (unsigned char X = 0; X < 100; ++X) { int Y = X; }
  if (match(Op, m_scev_AffineAddRec(m_SCEV(Start), m_SCEV(Step), m_Loop(L)))) {
    const auto *AR = cast<SCEVAddRecExpr>(Op);
    unsigned BitWidth = getTypeSizeInBits(AR->getType());
 
    // The no-unsigned-wrap case is handled before the uniquing lookup above.
 
    // Check whether the backedge-taken count is SCEVCouldNotCompute.
    // Note that this serves two purposes: It filters out loops that are
    // simply not analyzable, and it covers the case where this code is
    // being called from within backedge-taken count analysis, such that
    // attempting to ask for the backedge-taken count would likely result
    // in infinite recursion. In the later case, the analysis code will
    // cope with a conservative value, and it will take care to purge
    // that value once it has finished.
    const SCEV *MaxBECount = getConstantMaxBackedgeTakenCount(L);
    if (!isa<SCEVCouldNotCompute>(MaxBECount)) {
      // Manually compute the final value for AR, checking for overflow.
 
      // Check whether the backedge-taken count can be losslessly casted to
      // the addrec's type. The count is always unsigned.
      const SCEV *CastedMaxBECount =
          getTruncateOrZeroExtend(MaxBECount, Start->getType(), Depth);
      const SCEV *RecastedMaxBECount = getTruncateOrZeroExtend(
          CastedMaxBECount, MaxBECount->getType(), Depth);
      if (MaxBECount == RecastedMaxBECount) {
        Type *WideTy = IntegerType::get(getContext(), BitWidth * 2);
        // Check whether Start+Step*MaxBECount has no unsigned overflow.
        const SCEV *ZMul =
            getMulExpr(CastedMaxBECount, Step, SCEV::FlagNone, Depth + 1);
        const SCEV *ZAdd = getZeroExtendExpr(
            getAddExpr(Start, ZMul, SCEV::FlagNone, Depth + 1), WideTy,
            Depth + 1);
        const SCEV *WideStart = getZeroExtendExpr(Start, WideTy, Depth + 1);
        const SCEV *WideMaxBECount =
            getZeroExtendExpr(CastedMaxBECount, WideTy, Depth + 1);
        const SCEV *OperandExtendedAdd =
            getAddExpr(WideStart,
                       getMulExpr(WideMaxBECount,
                                  getZeroExtendExpr(Step, WideTy, Depth + 1),
                                  SCEV::FlagNone, Depth + 1),
                       SCEV::FlagNone, Depth + 1);
        if (ZAdd == OperandExtendedAdd) {
          // Cache knowledge of AR NUW, which is propagated to this AddRec.
          setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR), SCEV::FlagNUW);
          // Return the expression with the addrec on the outside.
          Start =
              getExtendAddRecStart<SCEVZeroExtendExpr>(AR, Ty, this, Depth + 1);
          Step = getZeroExtendExpr(Step, Ty, Depth + 1);
          return getAddRecExpr(Start, Step, L, AR->getNoWrapFlags());
        }
        // Similar to above, only this time treat the step value as signed.
        // This covers loops that count down.
        OperandExtendedAdd =
            getAddExpr(WideStart,
                       getMulExpr(WideMaxBECount,
                                  getSignExtendExpr(Step, WideTy, Depth + 1),
                                  SCEV::FlagNone, Depth + 1),
                       SCEV::FlagNone, Depth + 1);
        if (ZAdd == OperandExtendedAdd) {
          // Cache knowledge of AR NW, which is propagated to this AddRec.
          // Negative step causes unsigned wrap, but it still can't self-wrap.
          setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR), SCEV::FlagNW);
          // Return the expression with the addrec on the outside.
          Start =
              getExtendAddRecStart<SCEVZeroExtendExpr>(AR, Ty, this, Depth + 1);
          Step = getSignExtendExpr(Step, Ty, Depth + 1);
          return getAddRecExpr(Start, Step, L, AR->getNoWrapFlags());
        }
      }
    }
 
    // Normally, in the cases we can prove no-overflow via a
    // backedge guarding condition, we can also compute a backedge
    // taken count for the loop.  The exceptions are assumptions and
    // guards present in the loop -- SCEV is not great at exploiting
    // these to compute max backedge taken counts, but can still use
    // these to prove lack of overflow.  Use this fact to avoid
    // doing extra work that may not pay off.
    if (!isa<SCEVCouldNotCompute>(MaxBECount) || HasGuards ||
        !AC.assumptions().empty()) {
 
      auto NewFlags = proveNoUnsignedWrapViaInduction(AR);
      setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR), NewFlags);
      if (AR->hasNoUnsignedWrap()) {
        // Same as nuw case above - duplicated here to avoid a compile time
        // issue.  It's not clear that the order of checks does matter, but
        // it's one of two issue possible causes for a change which was
        // reverted.  Be conservative for the moment.
        Start =
            getExtendAddRecStart<SCEVZeroExtendExpr>(AR, Ty, this, Depth + 1);
        Step = getZeroExtendExpr(Step, Ty, Depth + 1);
        return getAddRecExpr(Start, Step, L, AR->getNoWrapFlags());
      }
 
      // For a negative step, we can extend the operands iff doing so only
      // traverses values in the range zext([0,UINT_MAX]).
      if (isKnownNegative(Step)) {
        const SCEV *N =
            getConstant(APInt::getMaxValue(BitWidth) - getSignedRangeMin(Step));
        if (isLoopBackedgeGuardedByCond(L, ICmpInst::ICMP_UGT, AR, N) ||
            isKnownOnEveryIteration(ICmpInst::ICMP_UGT, AR, N)) {
          // Cache knowledge of AR NW, which is propagated to this
          // AddRec.  Negative step causes unsigned wrap, but it
          // still can't self-wrap.
          setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR), SCEV::FlagNW);
          // Return the expression with the addrec on the outside.
          Start =
              getExtendAddRecStart<SCEVZeroExtendExpr>(AR, Ty, this, Depth + 1);
          Step = getSignExtendExpr(Step, Ty, Depth + 1);
          return getAddRecExpr(Start, Step, L, AR->getNoWrapFlags());
        }
      }
    }
 
    // zext({C,+,Step}) --> (zext(D) + zext({C-D,+,Step}))<nuw><nsw>
    // if D + (C - D + Step * n) could be proven to not unsigned wrap
    // where D maximizes the number of trailing zeros of (C - D + Step * n)
    if (const auto *SC = dyn_cast<SCEVConstant>(Start)) {
      const APInt &C = SC->getAPInt();
      const APInt &D = extractConstantWithoutWrapping(*this, C, Step);
      if (D != 0) {
        const SCEV *SZExtD = getZeroExtendExpr(getConstant(D), Ty, Depth);
        const SCEV *SResidual =
            getAddRecExpr(getConstant(C - D), Step, L, AR->getNoWrapFlags());
        const SCEV *SZExtR = getZeroExtendExpr(SResidual, Ty, Depth + 1);
        return getAddExpr(SZExtD, SZExtR, SCEV::FlagNSW | SCEV::FlagNUW,
                          Depth + 1);
      }
    }
 
    if (proveNoWrapByVaryingStart<SCEVZeroExtendExpr>(Start, Step, L)) {
      setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR), SCEV::FlagNUW);
      Start = getExtendAddRecStart<SCEVZeroExtendExpr>(AR, Ty, this, Depth + 1);
      Step = getZeroExtendExpr(Step, Ty, Depth + 1);
      return getAddRecExpr(Start, Step, L, AR->getNoWrapFlags());
    }
  }
 
  // zext(A % B) --> zext(A) % zext(B)
  {
    const SCEV *LHS;
    const SCEV *RHS;
    if (match(Op, m_scev_URem(m_SCEV(LHS), m_SCEV(RHS), *this)))
      return getURemExpr(getZeroExtendExpr(LHS, Ty, Depth + 1),
                         getZeroExtendExpr(RHS, Ty, Depth + 1));
  }
 
  // zext(A / B) --> zext(A) / zext(B).
  if (auto *Div = dyn_cast<SCEVUDivExpr>(Op))
    return getUDivExpr(getZeroExtendExpr(Div->getLHS(), Ty, Depth + 1),
                       getZeroExtendExpr(Div->getRHS(), Ty, Depth + 1));
 
  if (auto *SA = dyn_cast<SCEVAddExpr>(Op)) {
    // zext((A + B + ...)<nuw>) --> (zext(A) + zext(B) + ...)<nuw>
    if (SA->hasNoUnsignedWrap()) {
      // If the addition does not unsign overflow then we can, by definition,
      // commute the zero extension with the addition operation.
      SmallVector<SCEVUse, 4> Ops;
      for (SCEVUse Op : SA->operands())
        Ops.push_back(getZeroExtendExpr(Op, Ty, Depth + 1));
      return getAddExpr(Ops, SCEV::FlagNUW, Depth + 1);
    }
 
    const APInt *C, *C2;
    // zext (C + A)<nsw> -> (sext(C) + sext(A))<nsw> if zext (C + A)<nsw> >=s 0.
    // Currently the non-negative check is done manually, as isKnownNonNegative
    // is too expensive.
    if (SA->hasNoSignedWrap() &&
        match(SA, m_scev_Add(m_scev_APInt(C),
                             m_scev_SMax(m_scev_APInt(C2), m_SCEV()))) &&
        C->isNegative() && !C->isMinSignedValue() && C2->sge(C->abs())) {
      assert(isKnownNonNegative(SA) && "incorrectly determined non-negative");
      return getAddExpr(getSignExtendExpr(SA->getOperand(0), Ty, Depth + 1),
                        getSignExtendExpr(SA->getOperand(1), Ty, Depth + 1),
                        SCEV::FlagNSW, Depth + 1);
    }
 
    // zext(C + x + y + ...) --> (zext(D) + zext((C - D) + x + y + ...))
    // if D + (C - D + x + y + ...) could be proven to not unsigned wrap
    // where D maximizes the number of trailing zeros of (C - D + x + y + ...)
    //
    // Often address arithmetics contain expressions like
    // (zext (add (shl X, C1), C2)), for instance, (zext (5 + (4 * X))).
    // This transformation is useful while proving that such expressions are
    // equal or differ by a small constant amount, see LoadStoreVectorizer pass.
    if (const auto *SC = dyn_cast<SCEVConstant>(SA->getOperand(0))) {
      const APInt &D = extractConstantWithoutWrapping(*this, SC, SA);
      if (D != 0) {
        const SCEV *SZExtD = getZeroExtendExpr(getConstant(D), Ty, Depth);
        const SCEV *SResidual =
            getAddExpr(getConstant(-D), SA, SCEV::FlagNone, Depth);
        const SCEV *SZExtR = getZeroExtendExpr(SResidual, Ty, Depth + 1);
        return getAddExpr(SZExtD, SZExtR, (SCEV::FlagNSW | SCEV::FlagNUW),
                          Depth + 1);
      }
    }
  }
 
  if (auto *SM = dyn_cast<SCEVMulExpr>(Op)) {
    // zext((A * B * ...)<nuw>) --> (zext(A) * zext(B) * ...)<nuw>
    if (SM->hasNoUnsignedWrap()) {
      // If the multiply does not unsign overflow then we can, by definition,
      // commute the zero extension with the multiply operation.
      SmallVector<SCEVUse, 4> Ops;
      for (SCEVUse Op : SM->operands())
        Ops.push_back(getZeroExtendExpr(Op, Ty, Depth + 1));
      return getMulExpr(Ops, SCEV::FlagNUW, Depth + 1);
    }
 
    // zext(2^K * (trunc X to iN)) to iM ->
    // 2^K * (zext(trunc X to i{N-K}) to iM)<nuw>
    //
    // Proof:
    //
    //     zext(2^K * (trunc X to iN)) to iM
    //   = zext((trunc X to iN) << K) to iM
    //   = zext((trunc X to i{N-K}) << K)<nuw> to iM
    //     (because shl removes the top K bits)
    //   = zext((2^K * (trunc X to i{N-K}))<nuw>) to iM
    //   = (2^K * (zext(trunc X to i{N-K}) to iM))<nuw>.
    //
    const APInt *C;
    const SCEV *TruncRHS;
    if (match(SM,
              m_scev_Mul(m_scev_APInt(C), m_scev_Trunc(m_SCEV(TruncRHS)))) &&
        C->isPowerOf2()) {
      int NewTruncBits =
          getTypeSizeInBits(SM->getOperand(1)->getType()) - C->logBase2();
      Type *NewTruncTy = IntegerType::get(getContext(), NewTruncBits);
      return getMulExpr(
          getZeroExtendExpr(SM->getOperand(0), Ty),
          getZeroExtendExpr(getTruncateExpr(TruncRHS, NewTruncTy), Ty),
          SCEV::FlagNUW, Depth + 1);
    }
  }
 
  // zext(umin(x, y)) -> umin(zext(x), zext(y))
  // zext(umax(x, y)) -> umax(zext(x), zext(y))
  if (isa<SCEVUMinExpr>(Op) || isa<SCEVUMaxExpr>(Op)) {
    auto *MinMax = cast<SCEVMinMaxExpr>(Op);
    SmallVector<SCEVUse, 4> Operands;
    for (SCEVUse Operand : MinMax->operands())
      Operands.push_back(getZeroExtendExpr(Operand, Ty));
    if (isa<SCEVUMinExpr>(MinMax))
      return getUMinExpr(Operands);
    return getUMaxExpr(Operands);
  }
 
  // zext(umin_seq(x, y)) -> umin_seq(zext(x), zext(y))
  if (auto *MinMax = dyn_cast<SCEVSequentialMinMaxExpr>(Op)) {
    assert(isa<SCEVSequentialUMinExpr>(MinMax) && "Not supported!");
    SmallVector<SCEVUse, 4> Operands;
    for (SCEVUse Operand : MinMax->operands())
      Operands.push_back(getZeroExtendExpr(Operand, Ty));
    return getUMinExpr(Operands, /*Sequential*/ true);
  }
 
  // The cast wasn't folded; create an explicit cast node.
  // Recompute the insert position, as it may have been invalidated.
  if (const SCEV *S = UniqueSCEVs.lookup(ID, Token))
    return S;
  SCEV *S = new (SCEVAllocator) SCEVZeroExtendExpr(ID.Intern(SCEVAllocator),
                                                   Op, Ty);
  UniqueSCEVs.insert(S, Token);
  S->computeAndSetCanonical(*this);
  registerUser(S, Op);
  return S;
}
 
const SCEV *ScalarEvolution::getSignExtendExpr(SCEVUse Op, Type *Ty,
                                               unsigned Depth) {
  assert(getTypeSizeInBits(Op->getType()) < getTypeSizeInBits(Ty) &&
         "This is not an extending conversion!");
  assert(isSCEVable(Ty) &&
         "This is not a conversion to a SCEVable type!");
  assert(!Op->getType()->isPointerTy() && "Can't extend pointer!");
  Ty = getEffectiveSCEVType(Ty);
 
  FoldID ID(scSignExtend, Op, Ty);
  if (const SCEV *S = FoldCache.lookup(ID))
    return S;
 
  const SCEV *S = getSignExtendExprImpl(Op, Ty, Depth);
  if (!isa<SCEVSignExtendExpr>(S))
    insertFoldCacheEntry(ID, S, FoldCache, FoldCacheUser);
  return S;
}
 
const SCEV *ScalarEvolution::getSignExtendExprImpl(SCEVUse Op, Type *Ty,
                                                   unsigned Depth) {
  assert(getTypeSizeInBits(Op->getType()) < getTypeSizeInBits(Ty) &&
         "This is not an extending conversion!");
  assert(isSCEVable(Ty) && "This is not a conversion to a SCEVable type!");
  assert(!Op->getType()->isPointerTy() && "Can't extend pointer!");
  Ty = getEffectiveSCEVType(Ty);
 
  // Fold if the operand is constant.
  if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(Op))
    return getConstant(SC->getAPInt().sext(getTypeSizeInBits(Ty)));
 
  // sext(sext(x)) --> sext(x)
  if (const SCEVSignExtendExpr *SS = dyn_cast<SCEVSignExtendExpr>(Op))
    return getSignExtendExpr(SS->getOperand(), Ty, Depth + 1);
 
  // sext(zext(x)) --> zext(x)
  if (const SCEVZeroExtendExpr *SZ = dyn_cast<SCEVZeroExtendExpr>(Op))
    return getZeroExtendExpr(SZ->getOperand(), Ty, Depth + 1);
 
  // If the operand is an affine AddRec with the no-signed-wrap flag, the
  // sign-extension distributes over the recurrence.
  const SCEV *Start, *Step;
  const Loop *L;
  if (Depth <= MaxCastDepth &&
      match(Op, m_scev_AffineAddRec(m_SCEV(Start), m_SCEV(Step), m_Loop(L)))) {
    const auto *AR = cast<SCEVAddRecExpr>(Op);
    if (AR->hasNoSignedWrap()) {
      Start = getExtendAddRecStart<SCEVSignExtendExpr>(AR, Ty, this, Depth + 1);
      Step = getSignExtendExpr(Step, Ty, Depth + 1);
      return getAddRecExpr(Start, Step, L, AR->getNoWrapFlags());
    }
  }
 
  // Before doing any expensive analysis, check to see if we've already
  // computed a SCEV for this Op and Ty.
  FoldingSetNodeID ID;
  ID.AddInteger(scSignExtend);
  ID.AddPointer(Op.getOpaqueValue());
  ID.AddPointer(Ty);
  FoldingSetInsertToken Token;
  if (const SCEV *S = UniqueSCEVs.lookup(ID, Token))
    return S;
  // Limit recursion depth.
  if (Depth > MaxCastDepth) {
    SCEV *S = new (SCEVAllocator) SCEVSignExtendExpr(ID.Intern(SCEVAllocator),
                                                     Op, Ty);
    UniqueSCEVs.insert(S, Token);
    S->computeAndSetCanonical(*this);
    registerUser(S, Op);
    return S;
  }
 
  // sext(trunc(x)) --> sext(x) or x or trunc(x)
  if (const SCEVTruncateExpr *ST = dyn_cast<SCEVTruncateExpr>(Op)) {
    // It's possible the bits taken off by the truncate were all sign bits. If
    // so, we should be able to simplify this further.
    const SCEV *X = ST->getOperand();
    ConstantRange CR = getSignedRange(X);
    unsigned TruncBits = getTypeSizeInBits(ST->getType());
    unsigned NewBits = getTypeSizeInBits(Ty);
    if (CR.truncate(TruncBits).signExtend(NewBits).contains(
            CR.sextOrTrunc(NewBits)))
      return getTruncateOrSignExtend(X, Ty, Depth);
  }
 
  if (auto *SA = dyn_cast<SCEVAddExpr>(Op)) {
    // sext((A + B + ...)<nsw>) --> (sext(A) + sext(B) + ...)<nsw>
    if (SA->hasNoSignedWrap()) {
      // If the addition does not sign overflow then we can, by definition,
      // commute the sign extension with the addition operation.
      SmallVector<SCEVUse, 4> Ops;
      for (SCEVUse Op : SA->operands())
        Ops.push_back(getSignExtendExpr(Op, Ty, Depth + 1));
      return getAddExpr(Ops, SCEV::FlagNSW, Depth + 1);
    }
 
    // sext(C + x + y + ...) --> (sext(D) + sext((C - D) + x + y + ...))
    // if D + (C - D + x + y + ...) could be proven to not signed wrap
    // where D maximizes the number of trailing zeros of (C - D + x + y + ...)
    //
    // For instance, this will bring two seemingly different expressions:
    //     1 + sext(5 + 20 * %x + 24 * %y)  and
    //         sext(6 + 20 * %x + 24 * %y)
    // to the same form:
    //     2 + sext(4 + 20 * %x + 24 * %y)
    if (const auto *SC = dyn_cast<SCEVConstant>(SA->getOperand(0))) {
      const APInt &D = extractConstantWithoutWrapping(*this, SC, SA);
      if (D != 0) {
        const SCEV *SSExtD = getSignExtendExpr(getConstant(D), Ty, Depth);
        const SCEV *SResidual =
            getAddExpr(getConstant(-D), SA, SCEV::FlagNone, Depth);
        const SCEV *SSExtR = getSignExtendExpr(SResidual, Ty, Depth + 1);
        return getAddExpr(SSExtD, SSExtR, (SCEV::FlagNSW | SCEV::FlagNUW),
                          Depth + 1);
      }
    }
  }
  // If the input value is a chrec scev, and we can prove that the value
  // did not overflow the old, smaller, value, we can sign extend all of the
  // operands (often constants).  This allows analysis of something like
  // this:  for (signed char X = 0; X < 100; ++X) { int Y = X; }
  if (match(Op, m_scev_AffineAddRec(m_SCEV(Start), m_SCEV(Step), m_Loop(L)))) {
    const auto *AR = cast<SCEVAddRecExpr>(Op);
    unsigned BitWidth = getTypeSizeInBits(AR->getType());
 
    // The no-signed-wrap case is handled before the uniquing lookup above.
 
    // Check whether the backedge-taken count is SCEVCouldNotCompute.
    // Note that this serves two purposes: It filters out loops that are
    // simply not analyzable, and it covers the case where this code is
    // being called from within backedge-taken count analysis, such that
    // attempting to ask for the backedge-taken count would likely result
    // in infinite recursion. In the later case, the analysis code will
    // cope with a conservative value, and it will take care to purge
    // that value once it has finished.
    const SCEV *MaxBECount = getConstantMaxBackedgeTakenCount(L);
    if (!isa<SCEVCouldNotCompute>(MaxBECount)) {
      // Manually compute the final value for AR, checking for
      // overflow.
 
      // Check whether the backedge-taken count can be losslessly casted to
      // the addrec's type. The count is always unsigned.
      const SCEV *CastedMaxBECount =
          getTruncateOrZeroExtend(MaxBECount, Start->getType(), Depth);
      const SCEV *RecastedMaxBECount = getTruncateOrZeroExtend(
          CastedMaxBECount, MaxBECount->getType(), Depth);
      if (MaxBECount == RecastedMaxBECount) {
        Type *WideTy = IntegerType::get(getContext(), BitWidth * 2);
        // Check whether Start+Step*MaxBECount has no signed overflow.
        const SCEV *SMul =
            getMulExpr(CastedMaxBECount, Step, SCEV::FlagNone, Depth + 1);
        const SCEV *SAdd = getSignExtendExpr(
            getAddExpr(Start, SMul, SCEV::FlagNone, Depth + 1), WideTy,
            Depth + 1);
        const SCEV *WideStart = getSignExtendExpr(Start, WideTy, Depth + 1);
        const SCEV *WideMaxBECount =
            getZeroExtendExpr(CastedMaxBECount, WideTy, Depth + 1);
        const SCEV *OperandExtendedAdd =
            getAddExpr(WideStart,
                       getMulExpr(WideMaxBECount,
                                  getSignExtendExpr(Step, WideTy, Depth + 1),
                                  SCEV::FlagNone, Depth + 1),
                       SCEV::FlagNone, Depth + 1);
        if (SAdd == OperandExtendedAdd) {
          // Cache knowledge of AR NSW, which is propagated to this AddRec.
          setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR), SCEV::FlagNSW);
          // Return the expression with the addrec on the outside.
          Start =
              getExtendAddRecStart<SCEVSignExtendExpr>(AR, Ty, this, Depth + 1);
          Step = getSignExtendExpr(Step, Ty, Depth + 1);
          return getAddRecExpr(Start, Step, L, AR->getNoWrapFlags());
        }
        // Similar to above, only this time treat the step value as unsigned.
        // This covers loops that count up with an unsigned step.
        OperandExtendedAdd =
            getAddExpr(WideStart,
                       getMulExpr(WideMaxBECount,
                                  getZeroExtendExpr(Step, WideTy, Depth + 1),
                                  SCEV::FlagNone, Depth + 1),
                       SCEV::FlagNone, Depth + 1);
        if (SAdd == OperandExtendedAdd) {
          // If AR wraps around then
          //
          //    abs(Step) * MaxBECount > unsigned-max(AR->getType())
          // => SAdd != OperandExtendedAdd
          //
          // Thus (AR is not NW => SAdd != OperandExtendedAdd) <=>
          // (SAdd == OperandExtendedAdd => AR is NW)
 
          setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR), SCEV::FlagNW);
 
          // Return the expression with the addrec on the outside.
          Start =
              getExtendAddRecStart<SCEVSignExtendExpr>(AR, Ty, this, Depth + 1);
          Step = getZeroExtendExpr(Step, Ty, Depth + 1);
          return getAddRecExpr(Start, Step, L, AR->getNoWrapFlags());
        }
      }
    }
 
    auto NewFlags = proveNoSignedWrapViaInduction(AR);
    setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR), NewFlags);
    if (AR->hasNoSignedWrap()) {
      // Same as nsw case above - duplicated here to avoid a compile time
      // issue.  It's not clear that the order of checks does matter, but
      // it's one of two issue possible causes for a change which was
      // reverted.  Be conservative for the moment.
      Start = getExtendAddRecStart<SCEVSignExtendExpr>(AR, Ty, this, Depth + 1);
      Step = getSignExtendExpr(Step, Ty, Depth + 1);
      return getAddRecExpr(Start, Step, L, AR->getNoWrapFlags());
    }
 
    // sext({C,+,Step}) --> (sext(D) + sext({C-D,+,Step}))<nuw><nsw>
    // if D + (C - D + Step * n) could be proven to not signed wrap
    // where D maximizes the number of trailing zeros of (C - D + Step * n)
    if (const auto *SC = dyn_cast<SCEVConstant>(Start)) {
      const APInt &C = SC->getAPInt();
      const APInt &D = extractConstantWithoutWrapping(*this, C, Step);
      if (D != 0) {
        const SCEV *SSExtD = getSignExtendExpr(getConstant(D), Ty, Depth);
        const SCEV *SResidual =
            getAddRecExpr(getConstant(C - D), Step, L, AR->getNoWrapFlags());
        const SCEV *SSExtR = getSignExtendExpr(SResidual, Ty, Depth + 1);
        return getAddExpr(SSExtD, SSExtR, (SCEV::FlagNSW | SCEV::FlagNUW),
                          Depth + 1);
      }
    }
 
    if (proveNoWrapByVaryingStart<SCEVSignExtendExpr>(Start, Step, L)) {
      setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR), SCEV::FlagNSW);
      Start = getExtendAddRecStart<SCEVSignExtendExpr>(AR, Ty, this, Depth + 1);
      Step = getSignExtendExpr(Step, Ty, Depth + 1);
      return getAddRecExpr(Start, Step, L, AR->getNoWrapFlags());
    }
  }
 
  // If the input value is provably positive and we could not simplify
  // away the sext build a zext instead.
  if (isKnownNonNegative(Op))
    return getZeroExtendExpr(Op, Ty, Depth + 1);
 
  // sext(smin(x, y)) -> smin(sext(x), sext(y))
  // sext(smax(x, y)) -> smax(sext(x), sext(y))
  if (isa<SCEVSMinExpr>(Op) || isa<SCEVSMaxExpr>(Op)) {
    auto *MinMax = cast<SCEVMinMaxExpr>(Op);
    SmallVector<SCEVUse, 4> Operands;
    for (SCEVUse Operand : MinMax->operands())
      Operands.push_back(getSignExtendExpr(Operand, Ty));
    if (isa<SCEVSMinExpr>(MinMax))
      return getSMinExpr(Operands);
    return getSMaxExpr(Operands);
  }
 
  // The cast wasn't folded; create an explicit cast node.
  // Recompute the insert position, as it may have been invalidated.
  if (const SCEV *S = UniqueSCEVs.lookup(ID, Token))
    return S;
  SCEV *S = new (SCEVAllocator) SCEVSignExtendExpr(ID.Intern(SCEVAllocator),
                                                   Op, Ty);
  UniqueSCEVs.insert(S, Token);
  S->computeAndSetCanonical(*this);
  registerUser(S, Op);
  return S;
}
 
const SCEV *ScalarEvolution::getCastExpr(SCEVTypes Kind, SCEVUse Op, Type *Ty) {
  switch (Kind) {
  case scTruncate:
    return getTruncateExpr(Op, Ty);
  case scZeroExtend:
    return getZeroExtendExpr(Op, Ty);
  case scSignExtend:
    return getSignExtendExpr(Op, Ty);
  case scPtrToAddr: {
    const SCEV *Expr = getPtrToAddrExpr(Op);
    assert(Expr->getType() == Ty && "requested type must match");
    return Expr;
  }
  default:
    llvm_unreachable("Not a SCEV cast expression!");
  }
}
 
/// getAnyExtendExpr - Return a SCEV for the given operand extended with
/// unspecified bits out to the given type.
const SCEV *ScalarEvolution::getAnyExtendExpr(SCEVUse Op, Type *Ty) {
  assert(getTypeSizeInBits(Op->getType()) < getTypeSizeInBits(Ty) &&
         "This is not an extending conversion!");
  assert(isSCEVable(Ty) &&
         "This is not a conversion to a SCEVable type!");
  Ty = getEffectiveSCEVType(Ty);
 
  // Sign-extend negative constants.
  if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(Op))
    if (SC->getAPInt().isNegative())
      return getSignExtendExpr(Op, Ty);
 
  // Peel off a truncate cast.
  if (const SCEVTruncateExpr *T = dyn_cast<SCEVTruncateExpr>(Op)) {
    const SCEV *NewOp = T->getOperand();
    if (getTypeSizeInBits(NewOp->getType()) < getTypeSizeInBits(Ty))
      return getAnyExtendExpr(NewOp, Ty);
    return getTruncateOrNoop(NewOp, Ty);
  }
 
  // Next try a zext cast. If the cast is folded, use it.
  const SCEV *ZExt = getZeroExtendExpr(Op, Ty);
  if (!isa<SCEVZeroExtendExpr>(ZExt))
    return ZExt;
 
  // Next try a sext cast. If the cast is folded, use it.
  const SCEV *SExt = getSignExtendExpr(Op, Ty);
  if (!isa<SCEVSignExtendExpr>(SExt))
    return SExt;
 
  // Force the cast to be folded into the operands of an addrec.
  if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(Op)) {
    SmallVector<SCEVUse, 4> Ops;
    for (const SCEV *Op : AR->operands())
      Ops.push_back(getAnyExtendExpr(Op, Ty));
    return getAddRecExpr(Ops, AR->getLoop(), SCEV::FlagNW);
  }
 
  // If the expression is obviously signed, use the sext cast value.
  if (isa<SCEVSMaxExpr>(Op))
    return SExt;
 
  // Absent any other information, use the zext cast value.
  return ZExt;
}
 
/// Process the given Ops list, which is a list of operands to be added under
/// the given scale, update the given map. This is a helper function for
/// getAddRecExpr. As an example of what it does, given a sequence of operands
/// that would form an add expression like this:
///
///    m + n + 13 + (A * (o + p + (B * (q + m + 29)))) + r + (-1 * r)
///
/// where A and B are constants, update the map with these values:
///
///    (m, 1+A*B), (n, 1), (o, A), (p, A), (q, A*B), (r, 0)
///
/// and add 13 + A*B*29 to AccumulatedConstant.
/// This will allow getAddRecExpr to produce this:
///
///    13+A*B*29 + n + (m * (1+A*B)) + ((o + p) * A) + (q * A*B)
///
/// This form often exposes folding opportunities that are hidden in
/// the original operand list.
///
/// Return true iff it appears that any interesting folding opportunities
/// may be exposed. This helps getAddRecExpr short-circuit extra work in
/// the common case where no interesting opportunities are present, and
/// is also used as a check to avoid infinite recursion.
static bool
CollectAddOperandsWithScales(SmallDenseMap<const SCEV *, APInt, 16> &M,
                             SmallVectorImpl<SCEVUse> &NewOps,
                             APInt &AccumulatedConstant, ArrayRef<SCEVUse> Ops,
                             const APInt &Scale, ScalarEvolution &SE) {
  bool Interesting = false;
 
  // Iterate over the add operands. They are sorted, with constants first.
  unsigned i = 0;
  while (const SCEVConstant *C = dyn_cast<SCEVConstant>(Ops[i])) {
    ++i;
    // Pull a buried constant out to the outside.
    if (Scale != 1 || AccumulatedConstant != 0 || C->getValue()->isZero())
      Interesting = true;
    AccumulatedConstant += Scale * C->getAPInt();
  }
 
  // Next comes everything else. We're especially interested in multiplies
  // here, but they're in the middle, so just visit the rest with one loop.
  for (; i != Ops.size(); ++i) {
    const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(Ops[i]);
    if (Mul && isa<SCEVConstant>(Mul->getOperand(0))) {
      APInt NewScale =
          Scale * cast<SCEVConstant>(Mul->getOperand(0))->getAPInt();
      if (Mul->getNumOperands() == 2 && isa<SCEVAddExpr>(Mul->getOperand(1))) {
        // A multiplication of a constant with another add; recurse.
        const SCEVAddExpr *Add = cast<SCEVAddExpr>(Mul->getOperand(1));
        Interesting |= CollectAddOperandsWithScales(
            M, NewOps, AccumulatedConstant, Add->operands(), NewScale, SE);
      } else {
        // A multiplication of a constant with some other value. Update
        // the map.
        SmallVector<SCEVUse, 4> MulOps(drop_begin(Mul->operands()));
        const SCEV *Key = SE.getMulExpr(MulOps)->getCanonical();
        auto Pair = M.insert({Key, NewScale});
        if (Pair.second) {
          NewOps.push_back(Pair.first->first);
        } else {
          Pair.first->second += NewScale;
          // The map already had an entry for this value, which may indicate
          // a folding opportunity.
          Interesting = true;
        }
      }
    } else {
      // An ordinary operand. Update the map.
      auto Pair = M.insert({Ops[i]->getCanonical(), Scale});
      if (Pair.second) {
        NewOps.push_back(Pair.first->first);
      } else {
        Pair.first->second += Scale;
        // The map already had an entry for this value, which may indicate
        // a folding opportunity.
        Interesting = true;
      }
    }
  }
 
  return Interesting;
}
 
bool ScalarEvolution::willNotOverflow(Instruction::BinaryOps BinOp, bool Signed,
                                      const SCEV *LHS, const SCEV *RHS,
                                      const Instruction *CtxI) {
  auto Operation = [this, BinOp](SCEVUse L, SCEVUse R) -> const SCEV * {
    switch (BinOp) {
    default:
      llvm_unreachable("Unsupported binary op");
    case Instruction::Add:
      return getAddExpr(L, R);
    case Instruction::Sub:
      return getMinusSCEV(L, R);
    case Instruction::Mul:
      return getMulExpr(L, R);
    }
  };
 
  const SCEV *(ScalarEvolution::*Extension)(SCEVUse, Type *, unsigned) =
      Signed ? &ScalarEvolution::getSignExtendExpr
             : &ScalarEvolution::getZeroExtendExpr;
 
  // Check ext(LHS op RHS) == ext(LHS) op ext(RHS)
  auto *NarrowTy = cast<IntegerType>(LHS->getType());
  auto *WideTy =
      IntegerType::get(NarrowTy->getContext(), NarrowTy->getBitWidth() * 2);
 
  const SCEV *A = (this->*Extension)(Operation(LHS, RHS), WideTy, 0);
  const SCEV *LHSB = (this->*Extension)(LHS, WideTy, 0);
  const SCEV *RHSB = (this->*Extension)(RHS, WideTy, 0);
  const SCEV *B = Operation(LHSB, RHSB);
  if (A == B)
    return true;
  // Can we use context to prove the fact we need?
  if (!CtxI)
    return false;
  // TODO: Support mul.
  if (BinOp == Instruction::Mul)
    return false;
  auto *RHSC = dyn_cast<SCEVConstant>(RHS);
  // TODO: Lift this limitation.
  if (!RHSC)
    return false;
  APInt C = RHSC->getAPInt();
  unsigned NumBits = C.getBitWidth();
  bool IsSub = (BinOp == Instruction::Sub);
  bool IsNegativeConst = (Signed && C.isNegative());
  // Compute the direction and magnitude by which we need to check overflow.
  bool OverflowDown = IsSub ^ IsNegativeConst;
  APInt Magnitude = C;
  if (IsNegativeConst) {
    if (C == APInt::getSignedMinValue(NumBits))
      // TODO: SINT_MIN on inversion gives the same negative value, we don't
      // want to deal with that.
      return false;
    Magnitude = -C;
  }
 
  ICmpInst::Predicate Pred = Signed ? ICmpInst::ICMP_SLE : ICmpInst::ICMP_ULE;
  if (OverflowDown) {
    // To avoid overflow down, we need to make sure that MIN + Magnitude <= LHS.
    APInt Min = Signed ? APInt::getSignedMinValue(NumBits)
                       : APInt::getMinValue(NumBits);
    APInt Limit = Min + Magnitude;
    return isKnownPredicateAt(Pred, getConstant(Limit), LHS, CtxI);
  } else {
    // To avoid overflow up, we need to make sure that LHS <= MAX - Magnitude.
    APInt Max = Signed ? APInt::getSignedMaxValue(NumBits)
                       : APInt::getMaxValue(NumBits);
    APInt Limit = Max - Magnitude;
    return isKnownPredicateAt(Pred, LHS, getConstant(Limit), CtxI);
  }
}
 
std::optional<SCEVFlags> ScalarEvolution::getStrengthenedNoWrapFlagsFromBinOp(
    const OverflowingBinaryOperator *OBO) {
  // It cannot be done any better.
  if (OBO->hasNoUnsignedWrap() && OBO->hasNoSignedWrap())
    return std::nullopt;
 
  SCEVFlags Flags = SCEVFlags::FlagNone;
 
  if (OBO->hasNoUnsignedWrap())
    Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNUW);
  if (OBO->hasNoSignedWrap())
    Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNSW);
 
  bool Deduced = false;
 
  Instruction::BinaryOps Opcode = (Instruction::BinaryOps)OBO->getOpcode();
  const SCEV *LHS = getSCEV(OBO->getOperand(0));
  const SCEV *RHS = getSCEV(OBO->getOperand(1));
 
  bool CanUseNSW = true;
  const APInt *ShiftAmt;
  // Treat `shl %a, C` as `mul %a, 1 << C`.
  if (match(OBO, m_Shl(m_Value(), m_APInt(ShiftAmt)))) {
    unsigned BitWidth = ShiftAmt->getBitWidth();
    if (ShiftAmt->uge(BitWidth))
      return std::nullopt;
    // NSW only transfers if the shift amount is < BitWidth - 1, as INT_MIN * -1
    // overflows.
    CanUseNSW = ShiftAmt->ult(BitWidth - 1);
    Opcode = Instruction::Mul;
    RHS = getConstant(APInt::getOneBitSet(BitWidth, ShiftAmt->getZExtValue()));
  } else if (Opcode != Instruction::Add && Opcode != Instruction::Sub &&
             Opcode != Instruction::Mul) {
    return std::nullopt;
  }
 
  const Instruction *CtxI =
      UseContextForNoWrapFlagInference ? dyn_cast<Instruction>(OBO) : nullptr;
  if (!OBO->hasNoUnsignedWrap() &&
      willNotOverflow(Opcode, /* Signed */ false, LHS, RHS, CtxI)) {
    Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNUW);
    Deduced = true;
  }
 
  if (CanUseNSW && !OBO->hasNoSignedWrap() &&
      willNotOverflow(Opcode, /* Signed */ true, LHS, RHS, CtxI)) {
    Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNSW);
    Deduced = true;
  }
 
  if (Deduced)
    return Flags;
  return std::nullopt;
}
 
// We're trying to construct a SCEV of type `Type' with `Ops' as operands and
// `OldFlags' as can't-wrap behavior.  Infer a more aggressive set of
// can't-overflow flags for the operation if possible.
static SCEVFlags StrengthenNoWrapFlags(ScalarEvolution *SE, SCEVTypes Type,
                                       ArrayRef<SCEVUse> Ops, SCEVFlags Flags) {
  using namespace std::placeholders;
 
  using OBO = OverflowingBinaryOperator;
 
  bool CanAnalyze =
      Type == scAddExpr || Type == scAddRecExpr || Type == scMulExpr;
  (void)CanAnalyze;
  assert(CanAnalyze && "don't call from other places!");
 
  SCEVFlags SignOrUnsignMask = SCEV::FlagNUW | SCEV::FlagNSW;
  SCEVFlags SignOrUnsignWrap =
      ScalarEvolution::maskFlags(Flags, SignOrUnsignMask);
 
  // If FlagNSW is true and all the operands are non-negative, infer FlagNUW.
  auto IsKnownNonNegative = [&](SCEVUse U) {
    return SE->isKnownNonNegative(U);
  };
 
  if (SignOrUnsignWrap == SCEV::FlagNSW && all_of(Ops, IsKnownNonNegative))
    Flags = ScalarEvolution::setFlags(Flags, SignOrUnsignMask);
 
  SignOrUnsignWrap = ScalarEvolution::maskFlags(Flags, SignOrUnsignMask);
 
  if (SignOrUnsignWrap != SignOrUnsignMask &&
      (Type == scAddExpr || Type == scMulExpr) && Ops.size() == 2 &&
      isa<SCEVConstant>(Ops[0])) {
 
    auto Opcode = [&] {
      switch (Type) {
      case scAddExpr:
        return Instruction::Add;
      case scMulExpr:
        return Instruction::Mul;
      default:
        llvm_unreachable("Unexpected SCEV op.");
      }
    }();
 
    const APInt &C = cast<SCEVConstant>(Ops[0])->getAPInt();
 
    // (A <opcode> C) --> (A <opcode> C)<nsw> if the op doesn't sign overflow.
    if (!(SignOrUnsignWrap & SCEV::FlagNSW)) {
      auto NSWRegion =
          ConstantRange::makeExactNoWrapRegion(Opcode, C, OBO::NoSignedWrap);
      if (NSWRegion.contains(SE->getSignedRange(Ops[1])))
        Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNSW);
    }
 
    // (A <opcode> C) --> (A <opcode> C)<nuw> if the op doesn't unsign overflow.
    if (!(SignOrUnsignWrap & SCEV::FlagNUW)) {
      auto NUWRegion =
          ConstantRange::makeExactNoWrapRegion(Opcode, C, OBO::NoUnsignedWrap);
      if (NUWRegion.contains(SE->getUnsignedRange(Ops[1])))
        Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNUW);
    }
  }
 
  // <0,+,nonnegative><nw> is also nuw
  // TODO: Add corresponding nsw case
  if (Type == scAddRecExpr && ScalarEvolution::hasFlags(Flags, SCEV::FlagNW) &&
      !ScalarEvolution::hasFlags(Flags, SCEV::FlagNUW) && Ops.size() == 2 &&
      Ops[0]->isZero() && IsKnownNonNegative(Ops[1]))
    Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNUW);
 
  // both (udiv X, Y) * Y and Y * (udiv X, Y) are always NUW
  if (Type == scMulExpr && !ScalarEvolution::hasFlags(Flags, SCEV::FlagNUW) &&
      Ops.size() == 2) {
    if (auto *UDiv = dyn_cast<SCEVUDivExpr>(Ops[0]))
      if (UDiv->getOperand(1) == Ops[1])
        Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNUW);
    if (auto *UDiv = dyn_cast<SCEVUDivExpr>(Ops[1]))
      if (UDiv->getOperand(1) == Ops[0])
        Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNUW);
  }
 
  return Flags;
}
 
bool ScalarEvolution::isAvailableAtLoopEntry(const SCEV *S, const Loop *L) {
  return isLoopInvariant(S, L) && properlyDominates(S, L->getHeader());
}
 
/// Get a canonical add expression, or something simpler if possible.
SCEVUse ScalarEvolution::getAddExpr(SmallVectorImpl<SCEVUse> &Ops,
                                    SCEVFlagsPair Flags, unsigned Depth) {
  SCEVFlags ExprFlags = Flags.ExprFlags;
  SCEVFlags UseFlags = Flags.UseFlags;
  assert(!(ExprFlags & ~(SCEV::FlagNUW | SCEV::FlagNSW)) &&
         "only nuw or nsw allowed");
  assert(!(UseFlags & ~(SCEV::FlagNUW | SCEV::FlagNSW)) &&
         "only nuw or nsw allowed");
  assert(!Ops.empty() && "Cannot get empty add!");
  if (Ops.size() == 1) return Ops[0];
#ifndef NDEBUG
  Type *ETy = getEffectiveSCEVType(Ops[0]->getType());
  for (unsigned i = 1, e = Ops.size(); i != e; ++i)
    assert(getEffectiveSCEVType(Ops[i]->getType()) == ETy &&
           "SCEVAddExpr operand types don't match!");
  unsigned NumPtrs = count_if(
      Ops, [](const SCEV *Op) { return Op->getType()->isPointerTy(); });
  assert(NumPtrs <= 1 && "add has at most one pointer operand");
#endif
 
  const SCEV *Folded = constantFoldAndGroupOps(
      *this, LI, DT, Ops,
      [](const APInt &C1, const APInt &C2) { return C1 + C2; },
      [](const APInt &C) { return C.isZero(); }, // identity
      [](const APInt &C) { return false; });     // absorber
  if (Folded)
    return Folded;
 
#ifndef NDEBUG
  // Keep track of operands after constant folding, for verification when adding
  // use-specific flags.
  const SmallVector<SCEVUse, 8> OrigOps(Ops.begin(), Ops.end());
#endif
 
  unsigned Idx = isa<SCEVConstant>(Ops[0]) ? 1 : 0;
 
  // Delay expensive flag strengthening until necessary.
  auto ComputeFlags = [this, ExprFlags](ArrayRef<SCEVUse> Ops) {
    return StrengthenNoWrapFlags(this, scAddExpr, Ops, ExprFlags);
  };
 
  // Limit recursion calls depth.
  if (Depth > MaxArithDepth || hasHugeExpression(Ops))
    return {getOrCreateAddExpr(Ops, ComputeFlags(Ops)), UseFlags};
 
  if (SCEV *S = findExistingSCEVInCache(scAddExpr, Ops)) {
    // Don't strengthen flags if we have no new information.
    SCEVAddExpr *Add = static_cast<SCEVAddExpr *>(S);
    if (Add->getNoWrapFlags(ExprFlags) != ExprFlags)
      Add->setNoWrapFlags(ComputeFlags(Ops));
    return {S, UseFlags};
  }
 
  // Okay, check to see if the same value occurs in the operand list more than
  // once.  If so, merge them together into an multiply expression.  Since we
  // sorted the list, these values are required to be adjacent.
  Type *Ty = Ops[0]->getType();
  bool FoundMatch = false;
  for (unsigned i = 0, e = Ops.size(); i != e-1; ++i)
    if (SCEVUse Op = SCEVUse::getCommon(Ops[i], Ops[i + 1])) {
      //  X + Y + Y  -->  X + Y*2
      // Scan ahead to count how many equal operands there are.
      unsigned Count = 2;
      for (; i + Count != e; ++Count) {
        SCEVUse Common = SCEVUse::getCommon(Op, Ops[i + Count]);
        if (!Common)
          break;
        Op = Common;
      }
      // Merge the values into a multiply.
      SCEVUse Scale = getConstant(Ty, Count);
      SCEVUse Mul = getMulExpr(Scale, Op, SCEV::FlagNone, Depth + 1);
      if (Ops.size() == Count)
        return Mul;
      Ops[i] = Mul;
      Ops.erase(Ops.begin()+i+1, Ops.begin()+i+Count);
      --i; e -= Count - 1;
      FoundMatch = true;
    }
  if (FoundMatch)
    return getAddExpr(Ops, ExprFlags, Depth + 1);
 
  // Check for truncates. If all the operands are truncated from the same
  // type, see if factoring out the truncate would permit the result to be
  // folded. eg., n*trunc(x) + m*trunc(y) --> trunc(trunc(m)*x + trunc(n)*y)
  // if the contents of the resulting outer trunc fold to something simple.
  auto FindTruncSrcType = [&]() -> Type * {
    // We're ultimately looking to fold an addrec of truncs and muls of only
    // constants and truncs, so if we find any other types of SCEV
    // as operands of the addrec then we bail and return nullptr here.
    // Otherwise, we return the type of the operand of a trunc that we find.
    if (auto *T = dyn_cast<SCEVTruncateExpr>(Ops[Idx]))
      return T->getOperand()->getType();
    if (const auto *Mul = dyn_cast<SCEVMulExpr>(Ops[Idx])) {
      SCEVUse LastOp = Mul->getOperand(Mul->getNumOperands() - 1);
      if (const auto *T = dyn_cast<SCEVTruncateExpr>(LastOp))
        return T->getOperand()->getType();
    }
    return nullptr;
  };
  if (auto *SrcType = FindTruncSrcType()) {
    SmallVector<SCEVUse, 8> LargeOps;
    bool Ok = true;
    // Check all the operands to see if they can be represented in the
    // source type of the truncate.
    for (const SCEV *Op : Ops) {
      if (const SCEVTruncateExpr *T = dyn_cast<SCEVTruncateExpr>(Op)) {
        if (T->getOperand()->getType() != SrcType) {
          Ok = false;
          break;
        }
        LargeOps.push_back(T->getOperand());
      } else if (const SCEVConstant *C = dyn_cast<SCEVConstant>(Op)) {
        LargeOps.push_back(getAnyExtendExpr(C, SrcType));
      } else if (const SCEVMulExpr *M = dyn_cast<SCEVMulExpr>(Op)) {
        SmallVector<SCEVUse, 8> LargeMulOps;
        for (unsigned j = 0, f = M->getNumOperands(); j != f && Ok; ++j) {
          if (const SCEVTruncateExpr *T =
                dyn_cast<SCEVTruncateExpr>(M->getOperand(j))) {
            if (T->getOperand()->getType() != SrcType) {
              Ok = false;
              break;
            }
            LargeMulOps.push_back(T->getOperand());
          } else if (const auto *C = dyn_cast<SCEVConstant>(M->getOperand(j))) {
            LargeMulOps.push_back(getAnyExtendExpr(C, SrcType));
          } else {
            Ok = false;
            break;
          }
        }
        if (Ok)
          LargeOps.push_back(
              getMulExpr(LargeMulOps, SCEV::FlagNone, Depth + 1));
      } else {
        Ok = false;
        break;
      }
    }
    if (Ok) {
      // Evaluate the expression in the larger type.
      const SCEV *Fold = getAddExpr(LargeOps, SCEV::FlagNone, Depth + 1);
      // If it folds to something simple, use it. Otherwise, don't.
      if (isa<SCEVConstant>(Fold) || isa<SCEVUnknown>(Fold))
        return getTruncateExpr(Fold, Ty);
    }
  }
 
  if (Ops.size() == 2) {
    // Check if we have an expression of the form ((X + C1) - C2), where C1 and
    // C2 can be folded in a way that allows retaining wrapping flags of (X +
    // C1).
    const SCEV *A = Ops[0];
    const SCEV *B = Ops[1];
    auto *AddExpr = dyn_cast<SCEVAddExpr>(B);
    auto *C = dyn_cast<SCEVConstant>(A);
    if (AddExpr && C && isa<SCEVConstant>(AddExpr->getOperand(0))) {
      auto C1 = cast<SCEVConstant>(AddExpr->getOperand(0))->getAPInt();
      auto C2 = C->getAPInt();
      SCEVFlags PreservedFlags = SCEV::FlagNone;
 
      APInt ConstAdd = C1 + C2;
      auto AddFlags = AddExpr->getNoWrapFlags();
      // Adding a smaller constant is NUW if the original AddExpr was NUW.
      if (ScalarEvolution::hasFlags(AddFlags, SCEV::FlagNUW) &&
          ConstAdd.ule(C1)) {
        PreservedFlags =
            ScalarEvolution::setFlags(PreservedFlags, SCEV::FlagNUW);
      }
 
      // Adding a constant with the same sign and small magnitude is NSW, if the
      // original AddExpr was NSW.
      if (ScalarEvolution::hasFlags(AddFlags, SCEV::FlagNSW) &&
          C1.isSignBitSet() == ConstAdd.isSignBitSet() &&
          ConstAdd.abs().ule(C1.abs())) {
        PreservedFlags =
            ScalarEvolution::setFlags(PreservedFlags, SCEV::FlagNSW);
      }
 
      if (PreservedFlags != SCEV::FlagNone) {
        SmallVector<SCEVUse, 4> NewOps(AddExpr->operands());
        NewOps[0] = getConstant(ConstAdd);
        return getAddExpr(NewOps, PreservedFlags);
      }
    }
 
    // Try to push the constant operand into a ZExt: A + zext (-A + B) -> zext
    // (B), if trunc (A) + -A + B  does not unsigned-wrap.
    const SCEVAddExpr *InnerAdd;
    if (match(B, m_scev_ZExt(m_scev_Add(InnerAdd)))) {
      const SCEV *NarrowA = getTruncateExpr(A, InnerAdd->getType());
      if (NarrowA == getNegativeSCEV(InnerAdd->getOperand(0)) &&
          getZeroExtendExpr(NarrowA, B->getType()) == A &&
          hasFlags(StrengthenNoWrapFlags(this, scAddExpr, {NarrowA, InnerAdd},
                                         SCEV::FlagNone),
                   SCEV::FlagNUW)) {
        return getZeroExtendExpr(getAddExpr(NarrowA, InnerAdd), B->getType());
      }
    }
  }
 
  // Canonicalize (-1 * urem X, Y) + X --> (Y * X/Y)
  const SCEV *Y;
  if (Ops.size() == 2 &&
      match(Ops[0],
            m_scev_Mul(m_scev_AllOnes(),
                       m_scev_URem(m_scev_Specific(Ops[1]), m_SCEV(Y), *this))))
    return getMulExpr(Y, getUDivExpr(Ops[1], Y));
 
  // Skip past any other cast SCEVs.
  while (Idx < Ops.size() && Ops[Idx]->getSCEVType() < scAddExpr)
    ++Idx;
 
  // If there are add operands they would be next.
  if (Idx < Ops.size()) {
    bool DeletedAdd = false;
    // If the original flags and all inlined SCEVAddExprs are NUW, use the
    // common NUW flag for expression after inlining. Other flags cannot be
    // preserved, because they may depend on the original order of operations.
    SCEVFlags CommonFlags = maskFlags(ExprFlags, SCEV::FlagNUW);
    while (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(Ops[Idx])) {
      if (Ops.size() > AddOpsInlineThreshold ||
          Add->getNumOperands() > AddOpsInlineThreshold)
        break;
      // If we have an add, expand the add operands onto the end of the operands
      // list.
      Ops.erase(Ops.begin()+Idx);
      append_range(Ops, Add->operands());
      DeletedAdd = true;
      CommonFlags = maskFlags(CommonFlags, Add->getNoWrapFlags());
    }
 
    // If we deleted at least one add, we added operands to the end of the list,
    // and they are not necessarily sorted.  Recurse to resort and resimplify
    // any operands we just acquired.
    if (DeletedAdd)
      return getAddExpr(Ops, CommonFlags, Depth + 1);
  }
 
  // Skip over the add expression until we get to a multiply.
  while (Idx < Ops.size() && Ops[Idx]->getSCEVType() < scMulExpr)
    ++Idx;
 
  // Check to see if there are any folding opportunities present with
  // operands multiplied by constant values.
  if (Idx < Ops.size() && isa<SCEVMulExpr>(Ops[Idx])) {
    uint64_t BitWidth = getTypeSizeInBits(Ty);
    SmallDenseMap<const SCEV *, APInt, 16> M;
    SmallVector<SCEVUse, 8> NewOps;
    APInt AccumulatedConstant(BitWidth, 0);
    if (CollectAddOperandsWithScales(M, NewOps, AccumulatedConstant,
                                     Ops, APInt(BitWidth, 1), *this)) {
      struct APIntCompare {
        bool operator()(const APInt &LHS, const APInt &RHS) const {
          return LHS.ult(RHS);
        }
      };
 
      // Some interesting folding opportunity is present, so its worthwhile to
      // re-generate the operands list. Group the operands by constant scale,
      // to avoid multiplying by the same constant scale multiple times.
      std::map<APInt, SmallVector<SCEVUse, 4>, APIntCompare> MulOpLists;
      for (SCEVUse NewOp : NewOps)
        MulOpLists[M.find(NewOp)->second].push_back(NewOp);
      // Re-generate the operands list.
      Ops.clear();
      if (AccumulatedConstant != 0)
        Ops.push_back(getConstant(AccumulatedConstant));
      for (auto &MulOp : MulOpLists) {
        if (MulOp.first == 1) {
          Ops.push_back(getAddExpr(MulOp.second, SCEV::FlagNone, Depth + 1));
        } else if (MulOp.first != 0) {
          Ops.push_back(
              getMulExpr(getConstant(MulOp.first),
                         getAddExpr(MulOp.second, SCEV::FlagNone, Depth + 1),
                         SCEV::FlagNone, Depth + 1));
        }
      }
      if (Ops.empty())
        return getZero(Ty);
      if (Ops.size() == 1)
        return Ops[0];
      return getAddExpr(Ops, SCEV::FlagNone, Depth + 1);
    }
  }
 
  // Given a SCEVMulExpr and an operand index, return the product of all
  // operands except the one at OpIdx.
  auto StripFactor = [&](const SCEVMulExpr *M, unsigned OpIdx) -> SCEVUse {
    if (M->getNumOperands() == 2)
      return M->getOperand(OpIdx == 0);
    SmallVector<SCEVUse, 4> Remaining(M->operands().take_front(OpIdx));
    append_range(Remaining, M->operands().drop_front(OpIdx + 1));
    return getMulExpr(Remaining, SCEV::FlagNone, Depth + 1);
  };
 
  // If we are adding something to a multiply expression, make sure the
  // something is not already an operand of the multiply.  If so, merge it into
  // the multiply.
  for (; Idx < Ops.size() && isa<SCEVMulExpr>(Ops[Idx]); ++Idx) {
    const SCEVMulExpr *Mul = cast<SCEVMulExpr>(Ops[Idx]);
    for (unsigned MulOp = 0, e = Mul->getNumOperands(); MulOp != e; ++MulOp) {
      // Scan all terms to find every occurrence of common factor MulOpSCEV
      // and fold them in one shot:
      //   A1*X + A2*X + ... + An*X  -->  X * (A1 + A2 + ... + An)
      SCEVUse MulOpSCEV = Mul->getOperand(MulOp);
      if (isa<SCEVConstant>(MulOpSCEV))
        continue;
 
      // Cofactors: 1 for bare addends matching MulOpSCEV, or the
      // remaining product for multiply terms containing MulOpSCEV.
      SmallVector<SCEVUse, 4> Cofactors;
      SmallVector<unsigned, 4> DeadIndices;
      for (unsigned AddOp = 0, e = Ops.size(); AddOp != e; ++AddOp) {
        if (SCEVUse Common = SCEVUse::getCommon(MulOpSCEV, Ops[AddOp])) {
          // W + X + (X * Y * Z)  -->  W + (X * ((Y*Z)+1))
          MulOpSCEV = Common;
          Cofactors.push_back(getOne(Ty));
          DeadIndices.push_back(AddOp);
          continue;
        }
 
        if (AddOp <= Idx || !isa<SCEVMulExpr>(Ops[AddOp]))
          continue;
 
        const SCEVMulExpr *OtherMul = cast<SCEVMulExpr>(Ops[AddOp]);
        for (unsigned OMulOp = 0, OE = OtherMul->getNumOperands(); OMulOp != OE;
             ++OMulOp) {
          if (SCEVUse Common =
                  SCEVUse::getCommon(MulOpSCEV, OtherMul->getOperand(OMulOp))) {
            // (A*B*C) + (A*D*E)  -->  A * (B*C + D*E)
            MulOpSCEV = Common;
            Cofactors.push_back(StripFactor(OtherMul, OMulOp));
            DeadIndices.push_back(AddOp);
            break;
          }
        }
      }
 
      // Fold all collected cofactors with the anchor multiply's cofactor:
      //   MulOpSCEV * (Cofactor_1 + ... + Cofactor_n + AnchorCofactor)
      if (!Cofactors.empty()) {
        Cofactors.push_back(StripFactor(Mul, MulOp));
 
        SCEVUse InnerSum = getAddExpr(Cofactors, SCEV::FlagNone, Depth + 1);
        SCEVUse OuterMul =
            getMulExpr(MulOpSCEV, InnerSum, SCEV::FlagNone, Depth + 1);
 
        // DeadIndices does not include Idx (the anchor), hence +1.
        if (Ops.size() == DeadIndices.size() + 1)
          return OuterMul;
 
        // Erase Ops[Idx] first, then erase DeadIndices in reverse order.
        // The -1 adjustment accounts for the shift from removing Idx;
        // reverse order means each erasure only shifts later positions,
        // which have already been processed.
        Ops.erase(Ops.begin() + Idx);
        for (unsigned Dead : reverse(DeadIndices))
          Ops.erase(Ops.begin() + (Dead > Idx ? Dead - 1 : Dead));
 
        Ops.push_back(OuterMul);
        return getAddExpr(Ops, SCEV::FlagNone, Depth + 1);
      }
    }
  }
 
  // If there are any add recurrences in the operands list, see if any other
  // added values are loop invariant.  If so, we can fold them into the
  // recurrence.
  while (Idx < Ops.size() && Ops[Idx]->getSCEVType() < scAddRecExpr)
    ++Idx;
 
  // Scan over all recurrences, trying to fold loop invariants into them.
  for (; Idx < Ops.size() && isa<SCEVAddRecExpr>(Ops[Idx]); ++Idx) {
    // Scan all of the other operands to this add and add them to the vector if
    // they are loop invariant w.r.t. the recurrence.
    SmallVector<SCEVUse, 8> LIOps;
    const SCEVAddRecExpr *AddRec = cast<SCEVAddRecExpr>(Ops[Idx]);
    const Loop *AddRecLoop = AddRec->getLoop();
    for (unsigned i = 0, e = Ops.size(); i != e; ++i)
      if (isAvailableAtLoopEntry(Ops[i], AddRecLoop)) {
        LIOps.push_back(Ops[i]);
        Ops.erase(Ops.begin()+i);
        --i; --e;
      }
 
    // If we found some loop invariants, fold them into the recurrence.
    if (!LIOps.empty()) {
      // Compute nowrap flags for the addition of the loop-invariant ops and
      // the addrec. Temporarily push it as an operand for that purpose. These
      // flags are valid in the scope of the addrec only.
      LIOps.push_back(AddRec);
      SCEVFlags Flags = ComputeFlags(LIOps);
      LIOps.pop_back();
 
      //  NLI + LI + {Start,+,Step}  -->  NLI + {LI+Start,+,Step}
      LIOps.push_back(AddRec->getStart());
 
      SmallVector<SCEVUse, 4> AddRecOps(AddRec->operands());
 
      // It is not in general safe to propagate flags valid on an add within
      // the addrec scope to one outside it.  We must prove that the inner
      // scope is guaranteed to execute if the outer one does to be able to
      // safely propagate.  We know the program is undefined if poison is
      // produced on the inner scoped addrec.  We also know that *for this use*
      // the outer scoped add can't overflow (because of the flags we just
      // computed for the inner scoped add) without the program being undefined.
      // Proving that entry to the outer scope neccesitates entry to the inner
      // scope, thus proves the program undefined if the flags would be violated
      // in the outer scope.
      SCEVFlags AddFlags = Flags;
      if (AddFlags != SCEV::FlagNone) {
        auto *DefI = getDefiningScopeBound(LIOps);
        auto *ReachI = &*AddRecLoop->getHeader()->begin();
        if (!isGuaranteedToTransferExecutionTo(DefI, ReachI))
          AddFlags = SCEV::FlagNone;
      }
      AddRecOps[0] = getAddExpr(LIOps, AddFlags, Depth + 1);
 
      // Build the new addrec. Propagate the NUW and NSW flags if both the
      // outer add and the inner addrec are guaranteed to have no overflow.
      // Always propagate NW.
      Flags = AddRec->getNoWrapFlags(setFlags(Flags, SCEV::FlagNW));
      const SCEV *NewRec = getAddRecExpr(AddRecOps, AddRecLoop, Flags);
 
      // If all of the other operands were loop invariant, we are done.
      if (Ops.size() == 1) return NewRec;
 
      // Otherwise, add the folded AddRec by the non-invariant parts.
      for (unsigned i = 0;; ++i)
        if (Ops[i] == AddRec) {
          Ops[i] = NewRec;
          break;
        }
      return getAddExpr(Ops, SCEV::FlagNone, Depth + 1);
    }
 
    // Okay, if there weren't any loop invariants to be folded, check to see if
    // there are multiple AddRec's with the same loop induction variable being
    // added together.  If so, we can fold them.
    for (unsigned OtherIdx = Idx+1;
         OtherIdx < Ops.size() && isa<SCEVAddRecExpr>(Ops[OtherIdx]);
         ++OtherIdx) {
      // We expect the AddRecExpr's to be sorted in reverse dominance order,
      // so that the 1st found AddRecExpr is dominated by all others.
      assert(DT.dominates(
           cast<SCEVAddRecExpr>(Ops[OtherIdx])->getLoop()->getHeader(),
           AddRec->getLoop()->getHeader()) &&
        "AddRecExprs are not sorted in reverse dominance order?");
      if (AddRecLoop == cast<SCEVAddRecExpr>(Ops[OtherIdx])->getLoop()) {
        // Other + {A,+,B}<L> + {C,+,D}<L>  -->  Other + {A+C,+,B+D}<L>
        SmallVector<SCEVUse, 4> AddRecOps(AddRec->operands());
        for (; OtherIdx != Ops.size() && isa<SCEVAddRecExpr>(Ops[OtherIdx]);
             ++OtherIdx) {
          const auto *OtherAddRec = cast<SCEVAddRecExpr>(Ops[OtherIdx]);
          if (OtherAddRec->getLoop() == AddRecLoop) {
            for (unsigned i = 0, e = OtherAddRec->getNumOperands();
                 i != e; ++i) {
              if (i >= AddRecOps.size()) {
                append_range(AddRecOps, OtherAddRec->operands().drop_front(i));
                break;
              }
              AddRecOps[i] =
                  getAddExpr(AddRecOps[i], OtherAddRec->getOperand(i),
                             SCEV::FlagNone, Depth + 1);
            }
            Ops.erase(Ops.begin() + OtherIdx); --OtherIdx;
          }
        }
        // Step size has changed, so we cannot guarantee no self-wraparound.
        Ops[Idx] = getAddRecExpr(AddRecOps, AddRecLoop, SCEV::FlagNone);
        return getAddExpr(Ops, SCEV::FlagNone, Depth + 1);
      }
    }
 
    // Otherwise couldn't fold anything into this recurrence.  Move onto the
    // next one.
  }
 
  // Okay, it looks like we really DO need an add expr.  Check to see if we
  // already have one, otherwise create a new one.
  assert((UseFlags == SCEV::FlagNone || equal(OrigOps, Ops)) &&
         "Tried to add SCEVUse flags after operands changed");
  return {getOrCreateAddExpr(Ops, ComputeFlags(Ops)), UseFlags};
}
 
const SCEV *ScalarEvolution::getOrCreateAddExpr(ArrayRef<SCEVUse> Ops,
                                                SCEVFlags Flags) {
  FoldingSetNodeID ID;
  ID.AddInteger(scAddExpr);
  for (SCEVUse Op : Ops)
    ID.AddPointer(Op.getOpaqueValue());
  FoldingSetInsertToken Token;
  SCEVAddExpr *S = static_cast<SCEVAddExpr *>(UniqueSCEVs.lookup(ID, Token));
  if (!S) {
    SCEVUse *O = SCEVAllocator.Allocate<SCEVUse>(Ops.size());
    llvm::uninitialized_copy(Ops, O);
    S = new (SCEVAllocator)
        SCEVAddExpr(ID.Intern(SCEVAllocator), O, Ops.size());
    UniqueSCEVs.insert(S, Token);
    S->computeAndSetCanonical(*this);
    registerUser(S, Ops);
  }
  S->setNoWrapFlags(Flags);
  return S;
}
 
const SCEV *ScalarEvolution::getOrCreateAddRecExpr(ArrayRef<SCEVUse> Ops,
                                                   const Loop *L,
                                                   SCEVFlags Flags) {
  FoldingSetNodeID ID;
  ID.AddInteger(scAddRecExpr);
  for (SCEVUse Op : Ops)
    ID.AddPointer(Op.getOpaqueValue());
  ID.AddPointer(L);
  FoldingSetInsertToken Token;
  SCEVAddRecExpr *S =
      static_cast<SCEVAddRecExpr *>(UniqueSCEVs.lookup(ID, Token));
  if (!S) {
    SCEVUse *O = SCEVAllocator.Allocate<SCEVUse>(Ops.size());
    llvm::uninitialized_copy(Ops, O);
    S = new (SCEVAllocator)
        SCEVAddRecExpr(ID.Intern(SCEVAllocator), O, Ops.size(), L);
    UniqueSCEVs.insert(S, Token);
    S->computeAndSetCanonical(*this);
    LoopUsers[L].push_back(S);
    registerUser(S, Ops);
  }
  setNoWrapFlags(S, Flags);
  return S;
}
 
const SCEV *ScalarEvolution::getOrCreateMulExpr(ArrayRef<SCEVUse> Ops,
                                                SCEVFlags Flags) {
  FoldingSetNodeID ID;
  ID.AddInteger(scMulExpr);
  for (SCEVUse Op : Ops)
    ID.AddPointer(Op.getOpaqueValue());
  FoldingSetInsertToken Token;
  SCEVMulExpr *S = static_cast<SCEVMulExpr *>(UniqueSCEVs.lookup(ID, Token));
  if (!S) {
    SCEVUse *O = SCEVAllocator.Allocate<SCEVUse>(Ops.size());
    llvm::uninitialized_copy(Ops, O);
    S = new (SCEVAllocator) SCEVMulExpr(ID.Intern(SCEVAllocator),
                                        O, Ops.size());
    UniqueSCEVs.insert(S, Token);
    S->computeAndSetCanonical(*this);
    registerUser(S, Ops);
  }
  S->setNoWrapFlags(Flags);
  return S;
}
 
const SCEV *ScalarEvolution::getOrCreateUDivExpr(SCEVUse LHS, SCEVUse RHS) {
  FoldingSetNodeID ID;
  ID.AddInteger(scUDivExpr);
  ID.AddPointer(LHS.getOpaqueValue());
  ID.AddPointer(RHS.getOpaqueValue());
  FoldingSetInsertToken Token;
  SCEV *S = UniqueSCEVs.lookup(ID, Token);
  if (!S) {
    S = new (SCEVAllocator) SCEVUDivExpr(ID.Intern(SCEVAllocator), LHS, RHS);
    UniqueSCEVs.insert(S, Token);
    S->computeAndSetCanonical(*this);
    registerUser(S, {LHS, RHS});
  }
  return S;
}
 
static uint64_t umul_ov(uint64_t i, uint64_t j, bool &Overflow) {
  uint64_t k = i*j;
  if (j > 1 && k / j != i) Overflow = true;
  return k;
}
 
/// Compute the result of "n choose k", the binomial coefficient.  If an
/// intermediate computation overflows, Overflow will be set and the return will
/// be garbage. Overflow is not cleared on absence of overflow.
static uint64_t Choose(uint64_t n, uint64_t k, bool &Overflow) {
  // We use the multiplicative formula:
  //     n(n-1)(n-2)...(n-(k-1)) / k(k-1)(k-2)...1 .
  // At each iteration, we take the n-th term of the numeral and divide by the
  // (k-n)th term of the denominator.  This division will always produce an
  // integral result, and helps reduce the chance of overflow in the
  // intermediate computations. However, we can still overflow even when the
  // final result would fit.
 
  if (n == 0 || n == k) return 1;
  if (k > n) return 0;
 
  if (k > n/2)
    k = n-k;
 
  uint64_t r = 1;
  for (uint64_t i = 1; i <= k; ++i) {
    r = umul_ov(r, n-(i-1), Overflow);
    r /= i;
  }
  return r;
}
 
/// Determine if any of the operands in this SCEV are a constant or if
/// any of the add or multiply expressions in this SCEV contain a constant.
static bool containsConstantInAddMulChain(const SCEV *StartExpr) {
  struct FindConstantInAddMulChain {
    bool FoundConstant = false;
 
    bool follow(const SCEV *S) {
      FoundConstant |= isa<SCEVConstant>(S);
      return isa<SCEVAddExpr>(S) || isa<SCEVMulExpr>(S);
    }
 
    bool isDone() const {
      return FoundConstant;
    }
  };
 
  FindConstantInAddMulChain F;
  SCEVTraversal<FindConstantInAddMulChain> ST(F);
  ST.visitAll(StartExpr);
  return F.FoundConstant;
}
 
/// Get a canonical multiply expression, or something simpler if possible.
SCEVUse ScalarEvolution::getMulExpr(SmallVectorImpl<SCEVUse> &Ops,
                                    SCEVFlagsPair Flags, unsigned Depth) {
  SCEVFlags ExprFlags = Flags.ExprFlags;
  SCEVFlags UseFlags = Flags.UseFlags;
  assert(ExprFlags == maskFlags(ExprFlags, SCEV::FlagNUW | SCEV::FlagNSW) &&
         "only nuw or nsw allowed");
  assert(UseFlags == maskFlags(UseFlags, SCEV::FlagNUW | SCEV::FlagNSW) &&
         "only nuw or nsw allowed");
  assert(!Ops.empty() && "Cannot get empty mul!");
  if (Ops.size() == 1) return Ops[0];
#ifndef NDEBUG
  Type *ETy = Ops[0]->getType();
  assert(!ETy->isPointerTy());
  for (unsigned i = 1, e = Ops.size(); i != e; ++i)
    assert(Ops[i]->getType() == ETy &&
           "SCEVMulExpr operand types don't match!");
#endif
 
  const SCEV *Folded = constantFoldAndGroupOps(
      *this, LI, DT, Ops,
      [](const APInt &C1, const APInt &C2) { return C1 * C2; },
      [](const APInt &C) { return C.isOne(); },   // identity
      [](const APInt &C) { return C.isZero(); }); // absorber
  if (Folded)
    return Folded;
 
#ifndef NDEBUG
  // Keep track of operands after constant folding, for verification when adding
  // use-specific flags.
  const SmallVector<SCEVUse, 8> OrigOps(Ops.begin(), Ops.end());
#endif
 
  // Delay expensive flag strengthening until necessary.
  auto ComputeFlags = [this, ExprFlags](const ArrayRef<SCEVUse> Ops) {
    return StrengthenNoWrapFlags(this, scMulExpr, Ops, ExprFlags);
  };
 
  // Limit recursion calls depth.
  if (Depth > MaxArithDepth || hasHugeExpression(Ops))
    return {getOrCreateMulExpr(Ops, ComputeFlags(Ops)), UseFlags};
 
  if (SCEV *S = findExistingSCEVInCache(scMulExpr, Ops)) {
    // Don't strengthen flags if we have no new information.
    SCEVMulExpr *Mul = static_cast<SCEVMulExpr *>(S);
    if (Mul->getNoWrapFlags(ExprFlags) != ExprFlags)
      Mul->setNoWrapFlags(ComputeFlags(Ops));
    return {S, UseFlags};
  }
 
  if (const SCEVConstant *LHSC = dyn_cast<SCEVConstant>(Ops[0])) {
    if (Ops.size() == 2) {
      // C1*(C2+V) -> C1*C2 + C1*V
      // If any of Add's ops are Adds or Muls with a constant, apply this
      // transformation as well.
      //
      // TODO: There are some cases where this transformation is not
      // profitable; for example, Add = (C0 + X) * Y + Z.  Maybe the scope of
      // this transformation should be narrowed down.
      const SCEV *Op0, *Op1;
      if (match(Ops[1], m_scev_Add(m_SCEV(Op0), m_SCEV(Op1))) &&
          containsConstantInAddMulChain(Ops[1])) {
        const SCEV *LHS = getMulExpr(LHSC, Op0, SCEV::FlagNone, Depth + 1);
        const SCEV *RHS = getMulExpr(LHSC, Op1, SCEV::FlagNone, Depth + 1);
        return getAddExpr(LHS, RHS, SCEV::FlagNone, Depth + 1);
      }
 
      if (Ops[0]->isAllOnesValue()) {
        // If we have a mul by -1 of an add, try distributing the -1 among the
        // add operands.
        if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(Ops[1])) {
          SmallVector<SCEVUse, 4> NewOps;
          bool AnyFolded = false;
          for (const SCEV *AddOp : Add->operands()) {
            const SCEV *Mul =
                getMulExpr(Ops[0], SCEVUse(AddOp), SCEV::FlagNone, Depth + 1);
            if (!isa<SCEVMulExpr>(Mul)) AnyFolded = true;
            NewOps.push_back(Mul);
          }
          if (AnyFolded)
            return getAddExpr(NewOps, SCEV::FlagNone, Depth + 1);
        } else if (const auto *AddRec = dyn_cast<SCEVAddRecExpr>(Ops[1])) {
          // Negation preserves a recurrence's no self-wrap property.
          SmallVector<SCEVUse, 4> Operands;
          for (const SCEV *AddRecOp : AddRec->operands())
            Operands.push_back(getMulExpr(Ops[0], SCEVUse(AddRecOp),
                                          SCEV::FlagNone, Depth + 1));
          // Let M be the minimum representable signed value. AddRec with nsw
          // multiplied by -1 can have signed overflow if and only if it takes a
          // value of M: M * (-1) would stay M and (M + 1) * (-1) would be the
          // maximum signed value. In all other cases signed overflow is
          // impossible.
          auto FlagsMask = SCEV::FlagNW;
          if (AddRec->hasNoSignedWrap()) {
            auto MinInt =
                APInt::getSignedMinValue(getTypeSizeInBits(AddRec->getType()));
            if (getSignedRangeMin(AddRec) != MinInt)
              FlagsMask = setFlags(FlagsMask, SCEV::FlagNSW);
          }
          return getAddRecExpr(Operands, AddRec->getLoop(),
                               AddRec->getNoWrapFlags(FlagsMask));
        }
      }
 
      // Try to push the constant operand into a ZExt: C * zext (A + B) ->
      // zext (C*A + C*B) if trunc (C) * (A + B)  does not unsigned-wrap.
      const SCEVAddExpr *InnerAdd;
      if (match(Ops[1], m_scev_ZExt(m_scev_Add(InnerAdd)))) {
        const SCEV *NarrowC = getTruncateExpr(LHSC, InnerAdd->getType());
        if (isa<SCEVConstant>(InnerAdd->getOperand(0)) &&
            getZeroExtendExpr(NarrowC, Ops[1]->getType()) == LHSC &&
            hasFlags(StrengthenNoWrapFlags(this, scMulExpr, {NarrowC, InnerAdd},
                                           SCEV::FlagNone),
                     SCEV::FlagNUW)) {
          const SCEV *Res =
              getMulExpr(NarrowC, InnerAdd, SCEV::FlagNUW, Depth + 1);
          return getZeroExtendExpr(Res, Ops[1]->getType(), Depth + 1);
        };
      }
 
      // Try to fold (C1 * D /u C2) -> C1/C2 * D, if C1 and C2 are powers-of-2,
      // D is a multiple of C2, and C1 is a multiple of C2. If C2 is a multiple
      // of C1, fold to (D /u (C2 /u C1)).
      const SCEV *D;
      APInt C1V = LHSC->getAPInt();
      // (C1 * D /u C2) == -1 * -C1 * D /u C2 when C1 != INT_MIN. Don't treat -1
      // as -1 * 1, as it won't enable additional folds.
      if (C1V.isNegative() && !C1V.isMinSignedValue() && !C1V.isAllOnes())
        C1V = C1V.abs();
      const SCEVConstant *C2;
      if (C1V.isPowerOf2() &&
          match(Ops[1], m_scev_UDiv(m_SCEV(D), m_SCEVConstant(C2))) &&
          C2->getAPInt().isPowerOf2() &&
          C1V.logBase2() <= getMinTrailingZeros(D)) {
        const SCEV *NewMul = nullptr;
        if (C1V.uge(C2->getAPInt())) {
          NewMul = getMulExpr(getUDivExpr(getConstant(C1V), C2), D);
        } else if (C2->getAPInt().logBase2() <= getMinTrailingZeros(D)) {
          assert(C1V.ugt(1) && "C1 <= 1 should have been folded earlier");
          NewMul = getUDivExpr(D, getUDivExpr(C2, getConstant(C1V)));
        }
        if (NewMul)
          return C1V == LHSC->getAPInt() ? NewMul : getNegativeSCEV(NewMul);
      }
    }
  }
 
  // Skip over the add expression until we get to a multiply.
  unsigned Idx = 0;
  while (Idx < Ops.size() && Ops[Idx]->getSCEVType() < scMulExpr)
    ++Idx;
 
  // If there are mul operands inline them all into this expression.
  if (Idx < Ops.size()) {
    bool DeletedMul = false;
    while (const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(Ops[Idx])) {
      if (Ops.size() > MulOpsInlineThreshold)
        break;
      // If we have an mul, expand the mul operands onto the end of the
      // operands list.
      Ops.erase(Ops.begin()+Idx);
      append_range(Ops, Mul->operands());
      DeletedMul = true;
    }
 
    // If we deleted at least one mul, we added operands to the end of the
    // list, and they are not necessarily sorted.  Recurse to resort and
    // resimplify any operands we just acquired.
    if (DeletedMul)
      return getMulExpr(Ops, SCEV::FlagNone, Depth + 1);
  }
 
  // If there are any add recurrences in the operands list, see if any other
  // added values are loop invariant.  If so, we can fold them into the
  // recurrence.
  while (Idx < Ops.size() && Ops[Idx]->getSCEVType() < scAddRecExpr)
    ++Idx;
 
  // Scan over all recurrences, trying to fold loop invariants into them.
  for (; Idx < Ops.size() && isa<SCEVAddRecExpr>(Ops[Idx]); ++Idx) {
    // Scan all of the other operands to this mul and add them to the vector
    // if they are loop invariant w.r.t. the recurrence.
    SmallVector<SCEVUse, 8> LIOps;
    const SCEVAddRecExpr *AddRec = cast<SCEVAddRecExpr>(Ops[Idx]);
    for (unsigned i = 0, e = Ops.size(); i != e; ++i)
      if (isAvailableAtLoopEntry(Ops[i], AddRec->getLoop())) {
        LIOps.push_back(Ops[i]);
        Ops.erase(Ops.begin()+i);
        --i; --e;
      }
 
    // If we found some loop invariants, fold them into the recurrence.
    if (!LIOps.empty()) {
      //  NLI * LI * {Start,+,Step}  -->  NLI * {LI*Start,+,LI*Step}
      SmallVector<SCEVUse, 4> NewOps;
      NewOps.reserve(AddRec->getNumOperands());
      const SCEV *Scale = getMulExpr(LIOps, SCEV::FlagNone, Depth + 1);
 
      // If both the mul and addrec are nuw, we can preserve nuw.
      // If both the mul and addrec are nsw, we can only preserve nsw if either
      // a) they are also nuw, or
      // b) all multiplications of addrec operands with scale are nsw.
      SCEVFlags Flags = AddRec->getNoWrapFlags(ComputeFlags({Scale, AddRec}));
 
      for (unsigned i = 0, e = AddRec->getNumOperands(); i != e; ++i) {
        NewOps.push_back(getMulExpr(Scale, AddRec->getOperand(i),
                                    SCEV::FlagNone, Depth + 1));
 
        if (hasFlags(Flags, SCEV::FlagNSW) && !hasFlags(Flags, SCEV::FlagNUW)) {
          ConstantRange NSWRegion = ConstantRange::makeGuaranteedNoWrapRegion(
              Instruction::Mul, getSignedRange(Scale),
              OverflowingBinaryOperator::NoSignedWrap);
          if (!NSWRegion.contains(getSignedRange(AddRec->getOperand(i))))
            Flags = clearFlags(Flags, SCEV::FlagNSW);
        }
      }
 
      const SCEV *NewRec = getAddRecExpr(NewOps, AddRec->getLoop(), Flags);
 
      // If all of the other operands were loop invariant, we are done.
      if (Ops.size() == 1) return NewRec;
 
      // Otherwise, multiply the folded AddRec by the non-invariant parts.
      for (unsigned i = 0;; ++i)
        if (Ops[i] == AddRec) {
          Ops[i] = NewRec;
          break;
        }
      return getMulExpr(Ops, SCEV::FlagNone, Depth + 1);
    }
 
    // Okay, if there weren't any loop invariants to be folded, check to see
    // if there are multiple AddRec's with the same loop induction variable
    // being multiplied together.  If so, we can fold them.
 
    // {A1,+,A2,+,...,+,An}<L> * {B1,+,B2,+,...,+,Bn}<L>
    // = {x=1 in [ sum y=x..2x [ sum z=max(y-x, y-n)..min(x,n) [
    //       choose(x, 2x)*choose(2x-y, x-z)*A_{y-z}*B_z
    //   ]]],+,...up to x=2n}.
    // Note that the arguments to choose() are always integers with values
    // known at compile time, never SCEV objects.
    //
    // The implementation avoids pointless extra computations when the two
    // addrec's are of different length (mathematically, it's equivalent to
    // an infinite stream of zeros on the right).
    bool OpsModified = false;
    for (unsigned OtherIdx = Idx+1;
         OtherIdx != Ops.size() && isa<SCEVAddRecExpr>(Ops[OtherIdx]);
         ++OtherIdx) {
      const SCEVAddRecExpr *OtherAddRec =
        dyn_cast<SCEVAddRecExpr>(Ops[OtherIdx]);
      if (!OtherAddRec || OtherAddRec->getLoop() != AddRec->getLoop())
        continue;
 
      // Limit max number of arguments to avoid creation of unreasonably big
      // SCEVAddRecs with very complex operands.
      if (AddRec->getNumOperands() + OtherAddRec->getNumOperands() - 1 >
          MaxAddRecSize || hasHugeExpression({AddRec, OtherAddRec}))
        continue;
 
      bool Overflow = false;
      Type *Ty = AddRec->getType();
      bool LargerThan64Bits = getTypeSizeInBits(Ty) > 64;
      SmallVector<SCEVUse, 7> AddRecOps;
      for (int x = 0, xe = AddRec->getNumOperands() +
             OtherAddRec->getNumOperands() - 1; x != xe && !Overflow; ++x) {
        SmallVector<SCEVUse, 7> SumOps;
        for (int y = x, ye = 2*x+1; y != ye && !Overflow; ++y) {
          uint64_t Coeff1 = Choose(x, 2*x - y, Overflow);
          for (int z = std::max(y-x, y-(int)AddRec->getNumOperands()+1),
                 ze = std::min(x+1, (int)OtherAddRec->getNumOperands());
               z < ze && !Overflow; ++z) {
            uint64_t Coeff2 = Choose(2*x - y, x-z, Overflow);
            uint64_t Coeff;
            if (LargerThan64Bits)
              Coeff = umul_ov(Coeff1, Coeff2, Overflow);
            else
              Coeff = Coeff1*Coeff2;
            const SCEV *CoeffTerm = getConstant(Ty, Coeff);
            const SCEV *Term1 = AddRec->getOperand(y-z);
            const SCEV *Term2 = OtherAddRec->getOperand(z);
            SumOps.push_back(
                getMulExpr(CoeffTerm, Term1, Term2, SCEV::FlagNone, Depth + 1));
          }
        }
        if (SumOps.empty())
          SumOps.push_back(getZero(Ty));
        AddRecOps.push_back(getAddExpr(SumOps, SCEV::FlagNone, Depth + 1));
      }
      if (!Overflow) {
        const SCEV *NewAddRec =
            getAddRecExpr(AddRecOps, AddRec->getLoop(), SCEV::FlagNone);
        if (Ops.size() == 2) return NewAddRec;
        Ops[Idx] = NewAddRec;
        Ops.erase(Ops.begin() + OtherIdx); --OtherIdx;
        OpsModified = true;
        AddRec = dyn_cast<SCEVAddRecExpr>(NewAddRec);
        if (!AddRec)
          break;
      }
    }
    if (OpsModified)
      return getMulExpr(Ops, SCEV::FlagNone, Depth + 1);
 
    // Otherwise couldn't fold anything into this recurrence.  Move onto the
    // next one.
  }
 
  // Okay, it looks like we really DO need an mul expr.  Check to see if we
  // already have one, otherwise create a new one.
  assert((UseFlags == SCEV::FlagNone || equal(OrigOps, Ops)) &&
         "Tried to add SCEVUse flags after operands changed");
  return {getOrCreateMulExpr(Ops, ComputeFlags(Ops)), UseFlags};
}
 
/// Represents an unsigned remainder expression based on unsigned division.
const SCEV *ScalarEvolution::getURemExpr(SCEVUse LHS, SCEVUse RHS) {
  assert(getEffectiveSCEVType(LHS->getType()) ==
         getEffectiveSCEVType(RHS->getType()) &&
         "SCEVURemExpr operand types don't match!");
 
  // Short-circuit easy cases
  if (const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(RHS)) {
    // If constant is one, the result is trivial
    if (RHSC->getValue()->isOne())
      return getZero(LHS->getType()); // X urem 1 --> 0
 
    // If constant is a power of two, fold into a zext(trunc(LHS)).
    if (RHSC->getAPInt().isPowerOf2()) {
      Type *FullTy = LHS->getType();
      Type *TruncTy =
          IntegerType::get(getContext(), RHSC->getAPInt().logBase2());
      return getZeroExtendExpr(getTruncateExpr(LHS, TruncTy), FullTy);
    }
  }
 
  // Fallback to %a == %x urem %y == %x -<nuw> ((%x udiv %y) *<nuw> %y)
  const SCEV *UDiv = getUDivExpr(LHS, RHS);
  const SCEV *Mult = getMulExpr(UDiv, RHS, SCEV::FlagNUW);
  return getMinusSCEV(LHS, Mult, SCEV::FlagNUW);
}
 
/// Get a canonical unsigned division expression, or something simpler if
/// possible.
const SCEV *ScalarEvolution::getUDivExpr(SCEVUse LHS, SCEVUse RHS) {
  assert(!LHS->getType()->isPointerTy() &&
         "SCEVUDivExpr operand can't be pointer!");
  assert(LHS->getType() == RHS->getType() &&
         "SCEVUDivExpr operand types don't match!");
 
  if (SCEV *S = findExistingSCEVInCache(scUDivExpr, {LHS, RHS}))
    return S;
 
  // 0 udiv Y == 0
  if (match(LHS, m_scev_Zero()))
    return LHS;
 
  if (const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(RHS)) {
    if (RHSC->getValue()->isOne())
      return LHS;                               // X udiv 1 --> x
    // If the denominator is zero, the result of the udiv is undefined. Don't
    // try to analyze it, because the resolution chosen here may differ from
    // the resolution chosen in other parts of the compiler.
    if (!RHSC->getValue()->isZero()) {
      // Determine if the division can be folded into the operands of
      // its operands.
      // TODO: Generalize this to non-constants by using known-bits information.
      Type *Ty = LHS->getType();
      unsigned LZ = RHSC->getAPInt().countl_zero();
      unsigned MaxShiftAmt = getTypeSizeInBits(Ty) - LZ - 1;
      // For non-power-of-two values, effectively round the value up to the
      // nearest power of two.
      if (!RHSC->getAPInt().isPowerOf2())
        ++MaxShiftAmt;
      IntegerType *ExtTy =
        IntegerType::get(getContext(), getTypeSizeInBits(Ty) + MaxShiftAmt);
      if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(LHS))
        if (const SCEVConstant *Step =
            dyn_cast<SCEVConstant>(AR->getStepRecurrence(*this))) {
          // {X,+,N}/C --> {X/C,+,N/C} if safe and N/C can be folded.
          const APInt &StepInt = Step->getAPInt();
          const APInt &DivInt = RHSC->getAPInt();
          if (!StepInt.urem(DivInt) &&
              getZeroExtendExpr(AR, ExtTy) ==
                  getAddRecExpr(getZeroExtendExpr(AR->getStart(), ExtTy),
                                getZeroExtendExpr(Step, ExtTy), AR->getLoop(),
                                SCEV::FlagNone)) {
            SmallVector<SCEVUse, 4> Operands;
            for (const SCEV *Op : AR->operands())
              Operands.push_back(getUDivExpr(Op, RHS));
            return getAddRecExpr(Operands, AR->getLoop(), SCEV::FlagNW);
          }
          /// Get a canonical UDivExpr for a recurrence.
          /// {X,+,N}/C => {Y,+,N}/C where Y=X-(X%N). Safe when C%N=0.
          const APInt *StartRem;
          if (!DivInt.urem(StepInt) && match(getURemExpr(AR->getStart(), Step),
                                             m_scev_APInt(StartRem))) {
            bool NoWrap =
                getZeroExtendExpr(AR, ExtTy) ==
                getAddRecExpr(getZeroExtendExpr(AR->getStart(), ExtTy),
                              getZeroExtendExpr(Step, ExtTy), AR->getLoop(),
                              SCEV::FlagNone);
 
            // With N <= C and both N, C as powers-of-2, the transformation
            // {X,+,N}/C => {(X - X%N),+,N}/C preserves division results even
            // if wrapping occurs, as the division results remain equivalent for
            // all offsets in [[(X - X%N), X).
            bool CanFoldWithWrap = StepInt.ule(DivInt) && // N <= C
                                   StepInt.isPowerOf2() && DivInt.isPowerOf2();
            // Only fold if the subtraction can be folded in the start
            // expression.
            const SCEV *NewStart =
                getMinusSCEV(AR->getStart(), getConstant(*StartRem));
            if (*StartRem != 0 && (NoWrap || CanFoldWithWrap) &&
                !isa<SCEVAddExpr>(NewStart)) {
              const SCEV *NewLHS =
                  getAddRecExpr(NewStart, Step, AR->getLoop(),
                                NoWrap ? SCEV::FlagNW : SCEV::FlagNone);
              if (LHS != NewLHS)
                return getUDivExpr(NewLHS, RHS);
            }
          }
        }
      // (A*B)/C --> A*(B/C) if safe and B/C can be folded.
      if (const SCEVMulExpr *M = dyn_cast<SCEVMulExpr>(LHS)) {
        if (M->hasNoUnsignedWrap()) {
          // Find an operand that's safely divisible.
          for (unsigned i = 0, e = M->getNumOperands(); i != e; ++i) {
            const SCEV *Op = M->getOperand(i);
            const SCEV *Div = getUDivExpr(Op, RHSC);
            if (!isa<SCEVUDivExpr>(Div) && getMulExpr(Div, RHSC) == Op) {
              SmallVector<SCEVUse, 4> Operands(M->operands());
              Operands[i] = Div;
              return getMulExpr(Operands);
            }
          }
 
          // Even if it's not divisible, try to remove a common factor.
          if (const auto *LHSC = dyn_cast<SCEVConstant>(M->getOperand(0))) {
            APInt Factor = APIntOps::GreatestCommonDivisor(LHSC->getAPInt(),
                                                           RHSC->getAPInt());
            if (!Factor.isIntN(1)) {
              SmallVector<SCEVUse, 2> NewOperands;
              NewOperands.push_back(getConstant(LHSC->getAPInt().udiv(Factor)));
              append_range(NewOperands, M->operands().drop_front());
              const SCEV *NewMul = getMulExpr(NewOperands);
              return getUDivExpr(NewMul,
                                 getConstant(RHSC->getAPInt().udiv(Factor)));
            }
          }
        }
      }
 
      // (A/B)/C --> A/(B*C) if safe and B*C can be folded.
      if (const SCEVUDivExpr *OtherDiv = dyn_cast<SCEVUDivExpr>(LHS)) {
        if (auto *DivisorConstant =
                dyn_cast<SCEVConstant>(OtherDiv->getRHS())) {
          bool Overflow = false;
          APInt NewRHS =
              DivisorConstant->getAPInt().umul_ov(RHSC->getAPInt(), Overflow);
          if (Overflow) {
            return getConstant(RHSC->getType(), 0, false);
          }
          return getUDivExpr(OtherDiv->getLHS(), getConstant(NewRHS));
        }
      }
 
      // (A+B)/C --> (A/C + B/C) if the add does not unsigned wrap and A/C and
      // B/C can be folded.
      if (const SCEVAddExpr *A = dyn_cast<SCEVAddExpr>(LHS)) {
        if (A->hasNoUnsignedWrap()) {
          SmallVector<SCEVUse, 4> Operands;
          for (unsigned i = 0, e = A->getNumOperands(); i != e; ++i) {
            const SCEV *Op = getUDivExpr(A->getOperand(i), RHS);
            if (isa<SCEVUDivExpr>(Op) ||
                getMulExpr(Op, RHS) != A->getOperand(i))
              break;
            Operands.push_back(Op);
          }
          if (Operands.size() == A->getNumOperands())
            return getAddExpr(Operands);
        }
      }
 
      // ((N - M) + (M * A)) / N --> ((N - 1) + (M * A)) / N
      // This is an idiom for rounding A up to the next multiple of N, where A
      // is aready known to be a multiple of M. In this case, instcombine can
      // see that some low bits of the added constant are unused, so can clear
      // them, but we want to canonicalise to set the low bits. This makes the
      // pattern easier to match, without needing to check for known bits in
      // A*M.
      const APInt &N = RHSC->getAPInt();
      const APInt *NMinusM, *M;
      const SCEV *A;
      if (match(LHS, m_scev_Add(m_scev_APInt(NMinusM),
                                m_scev_Mul(m_scev_APInt(M), m_SCEV(A))))) {
        if (N.isPowerOf2() && M->isPowerOf2() && M->ult(N) &&
            *NMinusM == N - *M) {
          return getUDivExpr(
              getAddExpr(getConstant(N - 1), getMulExpr(getConstant(*M), A)),
              RHS);
        }
      }
 
      // Fold if both operands are constant.
      if (const SCEVConstant *LHSC = dyn_cast<SCEVConstant>(LHS))
        return getConstant(LHSC->getAPInt().udiv(RHSC->getAPInt()));
    }
  }
 
  // ((-C + (C smax %x)) /u %x) evaluates to zero, for any positive constant C.
  const APInt *NegC, *C;
  if (match(LHS,
            m_scev_Add(m_scev_APInt(NegC),
                       m_scev_SMax(m_scev_APInt(C), m_scev_Specific(RHS)))) &&
      NegC->isNegative() && !NegC->isMinSignedValue() && *C == -*NegC)
    return getZero(LHS->getType());
 
  // (%a * %b)<nuw> / %b -> %a
  const auto *Mul = dyn_cast<SCEVMulExpr>(LHS);
  if (Mul && Mul->hasNoUnsignedWrap()) {
    for (int i = 0, e = Mul->getNumOperands(); i != e; ++i) {
      if (Mul->getOperand(i) == RHS) {
        SmallVector<SCEVUse, 2> Operands;
        append_range(Operands, Mul->operands().take_front(i));
        append_range(Operands, Mul->operands().drop_front(i + 1));
        return getMulExpr(Operands);
      }
    }
  }
 
  // TODO: Generalize to handle any common factors.
  // udiv (mul nuw a, vscale), (mul nuw b, vscale) --> udiv a, b
  const SCEV *NewLHS, *NewRHS;
  if (match(LHS, m_scev_c_NUWMul(m_SCEV(NewLHS), m_SCEVVScale())) &&
      match(RHS, m_scev_c_NUWMul(m_SCEV(NewRHS), m_SCEVVScale())))
    return getUDivExpr(NewLHS, NewRHS);
 
  return getOrCreateUDivExpr(LHS, RHS);
}
 
/// Get a canonical unsigned division expression, or something simpler if
/// possible. There is no representation for an exact udiv in SCEV IR, but we
/// can attempt to optimize it prior to construction.
const SCEV *ScalarEvolution::getUDivExactExpr(SCEVUse LHS, SCEVUse RHS) {
  // Currently there is no exact specific logic.
 
  return getUDivExpr(LHS, RHS);
}
 
/// Get an add recurrence expression for the specified loop.  Simplify the
/// expression as much as possible.
SCEVUse ScalarEvolution::getAddRecExpr(SCEVUse Start, SCEVUse Step,
                                       const Loop *L, SCEVFlagsPair Flags) {
  SmallVector<SCEVUse, 4> Operands;
  Operands.push_back(Start);
  if (const SCEVAddRecExpr *StepChrec = dyn_cast<SCEVAddRecExpr>(Step))
    if (StepChrec->getLoop() == L) {
      append_range(Operands, StepChrec->operands());
      // The use flags describe the two-operand recurrence, not the flattened
      // one built here, so drop them just like the expression's NUW/NSW.
      return getAddRecExpr(Operands, L,
                           maskFlags(Flags.ExprFlags, SCEV::FlagNW));
    }
 
  Operands.push_back(Step);
  return getAddRecExpr(Operands, L, Flags);
}
 
/// Get an add recurrence expression for the specified loop.  Simplify the
/// expression as much as possible.
SCEVUse ScalarEvolution::getAddRecExpr(SmallVectorImpl<SCEVUse> &Operands,
                                       const Loop *L, SCEVFlagsPair NWFlags) {
  SCEVFlags ExprFlags = NWFlags.ExprFlags;
  SCEVFlags UseFlags = NWFlags.UseFlags;
  assert(!(UseFlags & ~(SCEV::FlagNUW | SCEV::FlagNSW)) &&
         "only nuw or nsw allowed");
  if (Operands.size() == 1) return Operands[0];
#ifndef NDEBUG
  Type *ETy = getEffectiveSCEVType(Operands[0]->getType());
  for (const SCEV *Op : llvm::drop_begin(Operands)) {
    assert(getEffectiveSCEVType(Op->getType()) == ETy &&
           "SCEVAddRecExpr operand types don't match!");
    assert(!Op->getType()->isPointerTy() && "Step must be integer");
  }
  for (const SCEV *Op : Operands)
    assert(isAvailableAtLoopEntry(Op, L) &&
           "SCEVAddRecExpr operand is not available at loop entry!");
 
  // Keep track of the original operands, for verification when adding
  // use-specific flags.
  const SmallVector<SCEVUse, 4> OrigOperands(Operands.begin(), Operands.end());
#endif
 
  if (Operands.back()->isZero()) {
    Operands.pop_back();
    return getAddRecExpr(Operands, L, SCEV::FlagNone); // {X,+,0}  -->  X
  }
 
  // It's tempting to want to call getConstantMaxBackedgeTakenCount count here and
  // use that information to infer NUW and NSW flags. However, computing a
  // BE count requires calling getAddRecExpr, so we may not yet have a
  // meaningful BE count at this point (and if we don't, we'd be stuck
  // with a SCEVCouldNotCompute as the cached BE count).
 
  ExprFlags = StrengthenNoWrapFlags(this, scAddRecExpr, Operands, ExprFlags);
 
  // Canonicalize nested AddRecs in by nesting them in order of loop depth.
  if (const SCEVAddRecExpr *NestedAR = dyn_cast<SCEVAddRecExpr>(Operands[0])) {
    const Loop *NestedLoop = NestedAR->getLoop();
    if (L->contains(NestedLoop)
            ? (L->getLoopDepth() < NestedLoop->getLoopDepth())
            : (!NestedLoop->contains(L) &&
               DT.dominates(L->getHeader(), NestedLoop->getHeader()))) {
      SmallVector<SCEVUse, 4> NestedOperands(NestedAR->operands());
      Operands[0] = NestedAR->getStart();
      // AddRecs require their operands be loop-invariant with respect to their
      // loops. Don't perform this transformation if it would break this
      // requirement.
      bool AllInvariant = all_of(
          Operands, [&](const SCEV *Op) { return isLoopInvariant(Op, L); });
 
      if (AllInvariant) {
        // Create a recurrence for the outer loop with the same step size.
        //
        // The outer recurrence keeps its NW flag but only keeps NUW/NSW if the
        // inner recurrence has the same property.
        SCEVFlags OuterFlags =
            maskFlags(ExprFlags, SCEV::FlagNW | NestedAR->getNoWrapFlags());
 
        NestedOperands[0] = getAddRecExpr(Operands, L, OuterFlags);
        AllInvariant = all_of(NestedOperands, [&](const SCEV *Op) {
          return isLoopInvariant(Op, NestedLoop);
        });
 
        if (AllInvariant) {
          // Ok, both add recurrences are valid after the transformation.
          //
          // The inner recurrence keeps its NW flag but only keeps NUW/NSW if
          // the outer recurrence has the same property.
          SCEVFlags InnerFlags =
              maskFlags(NestedAR->getNoWrapFlags(), SCEV::FlagNW | ExprFlags);
          return getAddRecExpr(NestedOperands, NestedLoop, InnerFlags);
        }
      }
      // Reset Operands to its original state.
      Operands[0] = NestedAR;
    }
  }
 
  // Okay, it looks like we really DO need an addrec expr.  Check to see if we
  // already have one, otherwise create a new one.
  assert((UseFlags == SCEV::FlagNone || equal(OrigOperands, Operands)) &&
         "Tried to add SCEVUse flags after operands changed");
  return {getOrCreateAddRecExpr(Operands, L, ExprFlags), UseFlags};
}
 
const SCEV *ScalarEvolution::getGEPExpr(GEPOperator *GEP,
                                        ArrayRef<SCEVUse> IndexExprs) {
  const SCEV *BaseExpr = getSCEV(GEP->getPointerOperand());
  // getSCEV(Base)->getType() has the same address space as Base->getType()
  // because SCEV::getType() preserves the address space.
  GEPNoWrapFlags NW = GEP->getNoWrapFlags();
  if (NW != GEPNoWrapFlags::none()) {
    // We'd like to propagate flags from the IR to the corresponding SCEV nodes,
    // but to do that, we have to ensure that said flag is valid in the entire
    // defined scope of the SCEV.
    // TODO: non-instructions have global scope.  We might be able to prove
    // some global scope cases
    auto *GEPI = dyn_cast<Instruction>(GEP);
    if (!GEPI || !isSCEVExprNeverPoison(GEPI))
      NW = GEPNoWrapFlags::none();
  }
 
  return getGEPExpr(BaseExpr, IndexExprs, GEP->getSourceElementType(), NW);
}
 
const SCEV *ScalarEvolution::getGEPExpr(SCEVUse BaseExpr,
                                        ArrayRef<SCEVUse> IndexExprs,
                                        Type *SrcElementTy, GEPNoWrapFlags NW) {
  SCEVFlags OffsetWrap = SCEV::FlagNone;
  if (NW.hasNoUnsignedSignedWrap())
    OffsetWrap = setFlags(OffsetWrap, SCEV::FlagNSW);
  if (NW.hasNoUnsignedWrap())
    OffsetWrap = setFlags(OffsetWrap, SCEV::FlagNUW);
 
  Type *CurTy = BaseExpr->getType();
  Type *IntIdxTy = getEffectiveSCEVType(BaseExpr->getType());
  bool FirstIter = true;
  SmallVector<SCEVUse, 4> Offsets;
  for (SCEVUse IndexExpr : IndexExprs) {
    // Compute the (potentially symbolic) offset in bytes for this index.
    if (StructType *STy = dyn_cast<StructType>(CurTy)) {
      // For a struct, add the member offset.
      ConstantInt *Index = cast<SCEVConstant>(IndexExpr)->getValue();
      unsigned FieldNo = Index->getZExtValue();
      const SCEV *FieldOffset = getOffsetOfExpr(IntIdxTy, STy, FieldNo);
      Offsets.push_back(FieldOffset);
 
      // Update CurTy to the type of the field at Index.
      CurTy = STy->getTypeAtIndex(Index);
    } else {
      // Update CurTy to its element type.
      if (FirstIter) {
        assert(isa<PointerType>(CurTy) &&
               "The first index of a GEP indexes a pointer");
        CurTy = SrcElementTy;
        FirstIter = false;
      } else {
        CurTy = GetElementPtrInst::getTypeAtIndex(CurTy, (uint64_t)0);
      }
      // For an array, add the element offset, explicitly scaled.
      const SCEV *ElementSize = getSizeOfExpr(IntIdxTy, CurTy);
      // Getelementptr indices are signed.
      IndexExpr = getTruncateOrSignExtend(IndexExpr, IntIdxTy);
 
      // Multiply the index by the element size to compute the element offset.
      const SCEV *LocalOffset = getMulExpr(IndexExpr, ElementSize, OffsetWrap);
      Offsets.push_back(LocalOffset);
    }
  }
 
  // Handle degenerate case of GEP without offsets.
  if (Offsets.empty())
    return BaseExpr;
 
  // Add the offsets together, assuming nsw if inbounds.
  const SCEV *Offset = getAddExpr(Offsets, OffsetWrap);
  // Add the base address and the offset. We cannot use the nsw flag, as the
  // base address is unsigned. However, if we know that the offset is
  // non-negative, we can use nuw.
  bool NUW = NW.hasNoUnsignedWrap() ||
             (NW.hasNoUnsignedSignedWrap() && isKnownNonNegative(Offset));
  SCEVFlags BaseWrap = NUW ? SCEV::FlagNUW : SCEV::FlagNone;
  const SCEV *GEPExpr = getAddExpr(BaseExpr, Offset, BaseWrap);
  assert(BaseExpr->getType() == GEPExpr->getType() &&
         "GEP should not change type mid-flight.");
  return GEPExpr;
}
 
SCEV *ScalarEvolution::findExistingSCEVInCache(SCEVTypes SCEVType,
                                               ArrayRef<SCEVUse> Ops,
                                               const Loop *L) {
  assert((SCEVType != scAddRecExpr || L) &&
         "L must be passed to find existing AddRecs");
  FoldingSetNodeID ID;
  ID.AddInteger(SCEVType);
  for (SCEVUse Op : Ops)
    ID.AddPointer(Op.getOpaqueValue());
  if (L)
    ID.AddPointer(L);
  FoldingSetInsertToken Token;
  return UniqueSCEVs.lookup(ID, Token);
}
 
const SCEV *ScalarEvolution::getAbsExpr(const SCEV *Op, bool IsNSW) {
  SCEVFlags Flags = IsNSW ? SCEV::FlagNSW : SCEV::FlagNone;
  return getSMaxExpr(Op, getNegativeSCEV(Op, Flags));
}
 
const SCEV *ScalarEvolution::getMinMaxExpr(SCEVTypes Kind,
                                           SmallVectorImpl<SCEVUse> &Ops) {
  assert(SCEVMinMaxExpr::isMinMaxType(Kind) && "Not a SCEVMinMaxExpr!");
  assert(!Ops.empty() && "Cannot get empty (u|s)(min|max)!");
  if (Ops.size() == 1) return Ops[0];
#ifndef NDEBUG
  Type *ETy = getEffectiveSCEVType(Ops[0]->getType());
  for (unsigned i = 1, e = Ops.size(); i != e; ++i) {
    assert(getEffectiveSCEVType(Ops[i]->getType()) == ETy &&
           "Operand types don't match!");
    assert(Ops[0]->getType()->isPointerTy() ==
               Ops[i]->getType()->isPointerTy() &&
           "min/max should be consistently pointerish");
  }
#endif
 
  bool IsSigned = Kind == scSMaxExpr || Kind == scSMinExpr;
  bool IsMax = Kind == scSMaxExpr || Kind == scUMaxExpr;
 
  const SCEV *Folded = constantFoldAndGroupOps(
      *this, LI, DT, Ops,
      [&](const APInt &C1, const APInt &C2) {
        switch (Kind) {
        case scSMaxExpr:
          return APIntOps::smax(C1, C2);
        case scSMinExpr:
          return APIntOps::smin(C1, C2);
        case scUMaxExpr:
          return APIntOps::umax(C1, C2);
        case scUMinExpr:
          return APIntOps::umin(C1, C2);
        default:
          llvm_unreachable("Unknown SCEV min/max opcode");
        }
      },
      [&](const APInt &C) {
        // identity
        if (IsMax)
          return IsSigned ? C.isMinSignedValue() : C.isMinValue();
        else
          return IsSigned ? C.isMaxSignedValue() : C.isMaxValue();
      },
      [&](const APInt &C) {
        // absorber
        if (IsMax)
          return IsSigned ? C.isMaxSignedValue() : C.isMaxValue();
        else
          return IsSigned ? C.isMinSignedValue() : C.isMinValue();
      });
  if (Folded)
    return Folded;
 
  // Check if we have created the same expression before.
  if (const SCEV *S = findExistingSCEVInCache(Kind, Ops)) {
    return S;
  }
 
  // Find the first operation of the same kind
  unsigned Idx = 0;
  while (Idx < Ops.size() && Ops[Idx]->getSCEVType() < Kind)
    ++Idx;
 
  // Check to see if one of the operands is of the same kind. If so, expand its
  // operands onto our operand list, and recurse to simplify.
  if (Idx < Ops.size()) {
    bool DeletedAny = false;
    while (Ops[Idx]->getSCEVType() == Kind) {
      const SCEVMinMaxExpr *SMME = cast<SCEVMinMaxExpr>(Ops[Idx]);
      Ops.erase(Ops.begin()+Idx);
      append_range(Ops, SMME->operands());
      DeletedAny = true;
    }
 
    if (DeletedAny)
      return getMinMaxExpr(Kind, Ops);
  }
 
  // Okay, check to see if the same value occurs in the operand list twice.  If
  // so, delete one.  Since we sorted the list, these values are required to
  // be adjacent.
  llvm::CmpInst::Predicate GEPred =
      IsSigned ? ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE;
  llvm::CmpInst::Predicate LEPred =
      IsSigned ? ICmpInst::ICMP_SLE : ICmpInst::ICMP_ULE;
  llvm::CmpInst::Predicate FirstPred = IsMax ? GEPred : LEPred;
  llvm::CmpInst::Predicate SecondPred = IsMax ? LEPred : GEPred;
  for (unsigned i = 0, e = Ops.size() - 1; i != e; ++i) {
    if (SCEVUse Common = SCEVUse::getCommon(Ops[i], Ops[i + 1]))
      Ops[i] = Ops[i + 1] = Common;
    if (Ops[i] == Ops[i + 1] ||
        isKnownViaNonRecursiveReasoning(FirstPred, Ops[i], Ops[i + 1])) {
      //  X op Y op Y  -->  X op Y
      //  X op Y       -->  X, if we know X, Y are ordered appropriately
      Ops.erase(Ops.begin() + i + 1, Ops.begin() + i + 2);
      --i;
      --e;
    } else if (isKnownViaNonRecursiveReasoning(SecondPred, Ops[i],
                                               Ops[i + 1])) {
      //  X op Y       -->  Y, if we know X, Y are ordered appropriately
      Ops.erase(Ops.begin() + i, Ops.begin() + i + 1);
      --i;
      --e;
    }
  }
 
  if (Ops.size() == 1) return Ops[0];
 
  assert(!Ops.empty() && "Reduced smax down to nothing!");
 
  // Okay, it looks like we really DO need an expr.  Check to see if we
  // already have one, otherwise create a new one.
  FoldingSetNodeID ID;
  ID.AddInteger(Kind);
  for (SCEVUse Op : Ops)
    ID.AddPointer(Op.getOpaqueValue());
  FoldingSetInsertToken Token;
  const SCEV *ExistingSCEV = UniqueSCEVs.lookup(ID, Token);
  if (ExistingSCEV)
    return ExistingSCEV;
  SCEVUse *O = SCEVAllocator.Allocate<SCEVUse>(Ops.size());
  llvm::uninitialized_copy(Ops, O);
  SCEV *S = new (SCEVAllocator)
      SCEVMinMaxExpr(ID.Intern(SCEVAllocator), Kind, O, Ops.size());
 
  UniqueSCEVs.insert(S, Token);
  S->computeAndSetCanonical(*this);
  registerUser(S, Ops);
  return S;
}
 
namespace {
 
class SCEVSequentialMinMaxDeduplicatingVisitor final
    : public SCEVVisitor<SCEVSequentialMinMaxDeduplicatingVisitor,
                         std::optional<const SCEV *>> {
  using RetVal = std::optional<const SCEV *>;
 
  ScalarEvolution &SE;
  const SCEVTypes RootKind; // Must be a sequential min/max expression.
  const SCEVTypes NonSequentialRootKind; // Non-sequential variant of RootKind.
  SmallPtrSet<const SCEV *, 16> SeenOps;
 
  bool canRecurseInto(SCEVTypes Kind) const {
    // We can only recurse into the SCEV expression of the same effective type
    // as the type of our root SCEV expression.
    return RootKind == Kind || NonSequentialRootKind == Kind;
  };
 
  RetVal visit(const SCEV *S) {
    // Has the whole operand been seen already?
    if (!SeenOps.insert(S).second)
      return std::nullopt;
    if (isa<SCEVMinMaxExpr, SCEVSequentialMinMaxExpr>(S)) {
      SCEVTypes Kind = S->getSCEVType();
 
      if (!canRecurseInto(Kind))
        return S;
 
      auto *NAry = cast<SCEVNAryExpr>(S);
      SmallVector<SCEVUse> NewOps;
      bool Changed = visit(Kind, NAry->operands(), NewOps);
 
      if (!Changed)
        return S;
      if (NewOps.empty())
        return std::nullopt;
 
      return isa<SCEVSequentialMinMaxExpr>(S)
                 ? SE.getSequentialMinMaxExpr(Kind, NewOps)
                 : SE.getMinMaxExpr(Kind, NewOps);
    }
    return S;
  }
 
public:
  SCEVSequentialMinMaxDeduplicatingVisitor(ScalarEvolution &SE,
                                           SCEVTypes RootKind)
      : SE(SE), RootKind(RootKind),
        NonSequentialRootKind(
            SCEVSequentialMinMaxExpr::getEquivalentNonSequentialSCEVType(
                RootKind)) {}
 
  bool /*Changed*/ visit(SCEVTypes Kind, ArrayRef<SCEVUse> OrigOps,
                         SmallVectorImpl<SCEVUse> &NewOps) {
    bool Changed = false;
    SmallVector<SCEVUse> Ops;
    Ops.reserve(OrigOps.size());
 
    for (const SCEV *Op : OrigOps) {
      RetVal NewOp = visit(Op);
      if (NewOp != Op)
        Changed = true;
      if (NewOp)
        Ops.emplace_back(*NewOp);
    }
 
    if (Changed)
      NewOps = std::move(Ops);
    return Changed;
  }
};
 
} // namespace
 
static bool scevUnconditionallyPropagatesPoisonFromOperands(SCEVTypes Kind) {
  switch (Kind) {
  case scConstant:
  case scVScale:
  case scTruncate:
  case scZeroExtend:
  case scSignExtend:
  case scPtrToAddr:
  case scAddExpr:
  case scMulExpr:
  case scUDivExpr:
  case scAddRecExpr:
  case scUMaxExpr:
  case scSMaxExpr:
  case scUMinExpr:
  case scSMinExpr:
  case scUnknown:
    // If any operand is poison, the whole expression is poison.
    return true;
  case scSequentialUMinExpr:
    // FIXME: if the *first* operand is poison, the whole expression is poison.
    return false; // Pessimistically, say that it does not propagate poison.
  case scCouldNotCompute:
    llvm_unreachable("Attempt to use a SCEVCouldNotCompute object!");
  }
  llvm_unreachable("Unknown SCEV kind!");
}
 
namespace {
// The only way poison may be introduced in a SCEV expression is from a
// poison SCEVUnknown (ConstantExprs are also represented as SCEVUnknown,
// not SCEVConstant). Notably, SCEVFlags on SCEV nodes can *not*
// introduce poison -- they encode guaranteed, non-speculated knowledge.
//
// Additionally, all SCEV nodes propagate poison from inputs to outputs,
// with the notable exception of umin_seq, where only poison from the first
// operand is (unconditionally) propagated.
struct SCEVPoisonCollector {
  bool LookThroughMaybePoisonBlocking;
  SmallPtrSet<const SCEVUnknown *, 4> MaybePoison;
  SCEVPoisonCollector(bool LookThroughMaybePoisonBlocking)
      : LookThroughMaybePoisonBlocking(LookThroughMaybePoisonBlocking) {}
 
  bool follow(const SCEV *S) {
    if (!LookThroughMaybePoisonBlocking &&
        !scevUnconditionallyPropagatesPoisonFromOperands(S->getSCEVType()))
      return false;
 
    if (auto *SU = dyn_cast<SCEVUnknown>(S)) {
      if (!isGuaranteedNotToBePoison(SU->getValue()))
        MaybePoison.insert(SU);
    }
    return true;
  }
  bool isDone() const { return false; }
};
} // namespace
 
/// Return true if V is poison given that AssumedPoison is already poison.
static bool impliesPoison(const SCEV *AssumedPoison, const SCEV *S) {
  // First collect all SCEVs that might result in AssumedPoison to be poison.
  // We need to look through potentially poison-blocking operations here,
  // because we want to find all SCEVs that *might* result in poison, not only
  // those that are *required* to.
  SCEVPoisonCollector PC1(/* LookThroughMaybePoisonBlocking */ true);
  visitAll(AssumedPoison, PC1);
 
  // AssumedPoison is never poison. As the assumption is false, the implication
  // is true. Don't bother walking the other SCEV in this case.
  if (PC1.MaybePoison.empty())
    return true;
 
  // Collect all SCEVs in S that, if poison, *will* result in S being poison
  // as well. We cannot look through potentially poison-blocking operations
  // here, as their arguments only *may* make the result poison.
  SCEVPoisonCollector PC2(/* LookThroughMaybePoisonBlocking */ false);
  visitAll(S, PC2);
 
  // Make sure that no matter which SCEV in PC1.MaybePoison is actually poison,
  // it will also make S poison by being part of PC2.MaybePoison.
  return llvm::set_is_subset(PC1.MaybePoison, PC2.MaybePoison);
}
 
void ScalarEvolution::getPoisonGeneratingValues(
    SmallPtrSetImpl<const Value *> &Result, const SCEV *S) {
  SCEVPoisonCollector PC(/* LookThroughMaybePoisonBlocking */ false);
  visitAll(S, PC);
  for (const SCEVUnknown *SU : PC.MaybePoison)
    Result.insert(SU->getValue());
}
 
bool ScalarEvolution::canReuseInstruction(
    const SCEV *S, Instruction *I,
    SmallVectorImpl<Instruction *> &DropPoisonGeneratingInsts) {
  // If the instruction cannot be poison, it's always safe to reuse.
  if (programUndefinedIfPoison(I))
    return true;
 
  // Otherwise, it is possible that I is more poisonous that S. Collect the
  // poison-contributors of S, and then check whether I has any additional
  // poison-contributors. Poison that is contributed through poison-generating
  // flags is handled by dropping those flags instead.
  SmallPtrSet<const Value *, 8> PoisonVals;
  getPoisonGeneratingValues(PoisonVals, S);
 
  SmallVector<Value *> Worklist;
  SmallPtrSet<Value *, 8> Visited;
  Worklist.push_back(I);
  unsigned NumVisitedInsts = 0;
  const unsigned InstLimit = std::max<unsigned>(16, S->getExpressionSize());
  while (!Worklist.empty()) {
    Value *V = Worklist.pop_back_val();
    if (!Visited.insert(V).second)
      continue;
 
    // Either the value can't be poison, or the S would also be poison if it
    // is.
    if (PoisonVals.contains(V) || ::isGuaranteedNotToBePoison(V))
      continue;
 
    // Avoid walking large instruction graphs.
    if (++NumVisitedInsts > InstLimit)
      return false;
 
    auto *I = dyn_cast<Instruction>(V);
    if (!I)
      return false;
 
    // Disjoint or instructions are interpreted as adds by SCEV. However, we
    // can't replace an arbitrary add with disjoint or, even if we drop the
    // flag. We would need to convert the or into an add.
    if (auto *PDI = dyn_cast<PossiblyDisjointInst>(I))
      if (PDI->isDisjoint())
        return false;
 
    // FIXME: Ignore vscale, even though it technically could be poison. Do this
    // because SCEV currently assumes it can't be poison. Remove this special
    // case once we proper model when vscale can be poison.
    if (auto *II = dyn_cast<IntrinsicInst>(I);
        II && II->getIntrinsicID() == Intrinsic::vscale)
      continue;
 
    if (canCreatePoison(cast<Operator>(I), /*ConsiderFlagsAndMetadata*/ false))
      return false;
 
    // If the instruction can't create poison, we can recurse to its operands.
    if (I->hasPoisonGeneratingAnnotations())
      DropPoisonGeneratingInsts.push_back(I);
 
    llvm::append_range(Worklist, I->operands());
  }
  return true;
}
 
const SCEV *
ScalarEvolution::getSequentialMinMaxExpr(SCEVTypes Kind,
                                         SmallVectorImpl<SCEVUse> &Ops) {
  assert(SCEVSequentialMinMaxExpr::isSequentialMinMaxType(Kind) &&
         "Not a SCEVSequentialMinMaxExpr!");
  assert(!Ops.empty() && "Cannot get empty (u|s)(min|max)!");
  if (Ops.size() == 1)
    return Ops[0];
#ifndef NDEBUG
  Type *ETy = getEffectiveSCEVType(Ops[0]->getType());
  for (unsigned i = 1, e = Ops.size(); i != e; ++i) {
    assert(getEffectiveSCEVType(Ops[i]->getType()) == ETy &&
           "Operand types don't match!");
    assert(Ops[0]->getType()->isPointerTy() ==
               Ops[i]->getType()->isPointerTy() &&
           "min/max should be consistently pointerish");
  }
#endif
 
  // Note that SCEVSequentialMinMaxExpr is *NOT* commutative,
  // so we can *NOT* do any kind of sorting of the expressions!
 
  // Check if we have created the same expression before.
  if (const SCEV *S = findExistingSCEVInCache(Kind, Ops))
    return S;
 
  // FIXME: there are *some* simplifications that we can do here.
 
  // Keep only the first instance of an operand.
  {
    SCEVSequentialMinMaxDeduplicatingVisitor Deduplicator(*this, Kind);
    bool Changed = Deduplicator.visit(Kind, Ops, Ops);
    if (Changed)
      return getSequentialMinMaxExpr(Kind, Ops);
  }
 
  // Check to see if one of the operands is of the same kind. If so, expand its
  // operands onto our operand list, and recurse to simplify.
  {
    unsigned Idx = 0;
    bool DeletedAny = false;
    while (Idx < Ops.size()) {
      if (Ops[Idx]->getSCEVType() != Kind) {
        ++Idx;
        continue;
      }
      const auto *SMME = cast<SCEVSequentialMinMaxExpr>(Ops[Idx]);
      Ops.erase(Ops.begin() + Idx);
      Ops.insert(Ops.begin() + Idx, SMME->operands().begin(),
                 SMME->operands().end());
      DeletedAny = true;
    }
 
    if (DeletedAny)
      return getSequentialMinMaxExpr(Kind, Ops);
  }
 
  const SCEV *SaturationPoint;
  ICmpInst::Predicate Pred;
  switch (Kind) {
  case scSequentialUMinExpr:
    SaturationPoint = getZero(Ops[0]->getType());
    Pred = ICmpInst::ICMP_ULE;
    break;
  default:
    llvm_unreachable("Not a sequential min/max type.");
  }
 
  for (unsigned i = 1, e = Ops.size(); i != e; ++i) {
    if (!isGuaranteedNotToCauseUB(Ops[i]))
      continue;
    // We can replace %x umin_seq %y with %x umin %y if either:
    //  * %y being poison implies %x is also poison.
    //  * %x cannot be the saturating value (e.g. zero for umin).
    if (::impliesPoison(Ops[i], Ops[i - 1]) ||
        isKnownViaNonRecursiveReasoning(ICmpInst::ICMP_NE, Ops[i - 1],
                                        SaturationPoint)) {
      SmallVector<SCEVUse, 2> SeqOps = {Ops[i - 1], Ops[i]};
      Ops[i - 1] = getMinMaxExpr(
          SCEVSequentialMinMaxExpr::getEquivalentNonSequentialSCEVType(Kind),
          SeqOps);
      Ops.erase(Ops.begin() + i);
      return getSequentialMinMaxExpr(Kind, Ops);
    }
    // Fold %x umin_seq %y to %x if %x ule %y.
    // TODO: We might be able to prove the predicate for a later operand.
    if (isKnownViaNonRecursiveReasoning(Pred, Ops[i - 1], Ops[i])) {
      Ops.erase(Ops.begin() + i);
      return getSequentialMinMaxExpr(Kind, Ops);
    }
  }
 
  // Okay, it looks like we really DO need an expr.  Check to see if we
  // already have one, otherwise create a new one.
  FoldingSetNodeID ID;
  ID.AddInteger(Kind);
  for (SCEVUse Op : Ops)
    ID.AddPointer(Op.getOpaqueValue());
  FoldingSetInsertToken Token;
  const SCEV *ExistingSCEV = UniqueSCEVs.lookup(ID, Token);
  if (ExistingSCEV)
    return ExistingSCEV;
 
  SCEVUse *O = SCEVAllocator.Allocate<SCEVUse>(Ops.size());
  llvm::uninitialized_copy(Ops, O);
  SCEV *S = new (SCEVAllocator)
      SCEVSequentialMinMaxExpr(ID.Intern(SCEVAllocator), Kind, O, Ops.size());
 
  UniqueSCEVs.insert(S, Token);
  S->computeAndSetCanonical(*this);
  registerUser(S, Ops);
  return S;
}
 
const SCEV *ScalarEvolution::getSMaxExpr(SCEVUse LHS, SCEVUse RHS) {
  SmallVector<SCEVUse, 2> Ops = {LHS, RHS};
  return getMinMaxExpr(scSMaxExpr, Ops);
}
 
const SCEV *ScalarEvolution::getSMaxExpr(SmallVectorImpl<SCEVUse> &Ops) {
  return getMinMaxExpr(scSMaxExpr, Ops);
}
 
const SCEV *ScalarEvolution::getUMaxExpr(SCEVUse LHS, SCEVUse RHS) {
  SmallVector<SCEVUse, 2> Ops = {LHS, RHS};
  return getMinMaxExpr(scUMaxExpr, Ops);
}
 
const SCEV *ScalarEvolution::getUMaxExpr(SmallVectorImpl<SCEVUse> &Ops) {
  return getMinMaxExpr(scUMaxExpr, Ops);
}
 
const SCEV *ScalarEvolution::getSMinExpr(SCEVUse LHS, SCEVUse RHS) {
  SmallVector<SCEVUse, 2> Ops = {LHS, RHS};
  return getMinMaxExpr(scSMinExpr, Ops);
}
 
const SCEV *ScalarEvolution::getSMinExpr(SmallVectorImpl<SCEVUse> &Ops) {
  return getMinMaxExpr(scSMinExpr, Ops);
}
 
const SCEV *ScalarEvolution::getUMinExpr(SCEVUse LHS, SCEVUse RHS,
                                         bool Sequential) {
  SmallVector<SCEVUse, 2> Ops = {LHS, RHS};
  return getUMinExpr(Ops, Sequential);
}
 
const SCEV *ScalarEvolution::getUMinExpr(SmallVectorImpl<SCEVUse> &Ops,
                                         bool Sequential) {
  return Sequential ? getSequentialMinMaxExpr(scSequentialUMinExpr, Ops)
                    : getMinMaxExpr(scUMinExpr, Ops);
}
 
const SCEV *
ScalarEvolution::getSizeOfExpr(Type *IntTy, TypeSize Size) {
  const SCEV *Res = getConstant(IntTy, Size.getKnownMinValue());
  if (Size.isScalable())
    Res = getMulExpr(Res, getVScale(IntTy));
  return Res;
}
 
const SCEV *ScalarEvolution::getSizeOfExpr(Type *IntTy, Type *AllocTy) {
  return getSizeOfExpr(IntTy, getDataLayout().getTypeAllocSize(AllocTy));
}
 
const SCEV *ScalarEvolution::getStoreSizeOfExpr(Type *IntTy, Type *StoreTy) {
  return getSizeOfExpr(IntTy, getDataLayout().getTypeStoreSize(StoreTy));
}
 
const SCEV *ScalarEvolution::getOffsetOfExpr(Type *IntTy,
                                             StructType *STy,
                                             unsigned FieldNo) {
  // We can bypass creating a target-independent constant expression and then
  // folding it back into a ConstantInt. This is just a compile-time
  // optimization.
  const StructLayout *SL = getDataLayout().getStructLayout(STy);
  assert(!SL->getSizeInBits().isScalable() &&
         "Cannot get offset for structure containing scalable vector types");
  return getConstant(IntTy, SL->getElementOffset(FieldNo));
}
 
const SCEV *ScalarEvolution::getUnknown(Value *V) {
  // Don't attempt to do anything other than create a SCEVUnknown object
  // here.  createSCEV only calls getUnknown after checking for all other
  // interesting possibilities, and any other code that calls getUnknown
  // is doing so in order to hide a value from SCEV canonicalization.
 
  FoldingSetNodeID ID;
  ID.AddInteger(scUnknown);
  ID.AddPointer(V);
  FoldingSetInsertToken Token;
  if (SCEV *S = UniqueSCEVs.lookup(ID, Token)) {
    assert(cast<SCEVUnknown>(S)->getValue() == V &&
           "Stale SCEVUnknown in uniquing map!");
    return S;
  }
  SCEV *S = new (SCEVAllocator) SCEVUnknown(ID.Intern(SCEVAllocator), V, this,
                                            FirstUnknown, NextUnknownOrderID++);
  FirstUnknown = cast<SCEVUnknown>(S);
  UniqueSCEVs.insert(S, Token);
  S->computeAndSetCanonical(*this);
  return S;
}
 
//===----------------------------------------------------------------------===//
//            Basic SCEV Analysis and PHI Idiom Recognition Code
//
 
/// Test if values of the given type are analyzable within the SCEV
/// framework. This primarily includes integer types, and it can optionally
/// include pointer types if the ScalarEvolution class has access to
/// target-specific information.
bool ScalarEvolution::isSCEVable(Type *Ty) const {
  // Integers and pointers are always SCEVable.
  return Ty->isIntOrPtrTy();
}
 
/// Return the size in bits of the specified type, for which isSCEVable must
/// return true.
uint64_t ScalarEvolution::getTypeSizeInBits(Type *Ty) const {
  assert(isSCEVable(Ty) && "Type is not SCEVable!");
  if (Ty->isPointerTy())
    return getDataLayout().getIndexTypeSizeInBits(Ty);
  return getDataLayout().getTypeSizeInBits(Ty);
}
 
/// Return a type with the same bitwidth as the given type and which represents
/// how SCEV will treat the given type, for which isSCEVable must return
/// true. For pointer types, this is the pointer index sized integer type.
Type *ScalarEvolution::getEffectiveSCEVType(Type *Ty) const {
  assert(isSCEVable(Ty) && "Type is not SCEVable!");
 
  if (Ty->isIntegerTy())
    return Ty;
 
  // The only other support type is pointer.
  assert(Ty->isPointerTy() && "Unexpected non-pointer non-integer type!");
  return getDataLayout().getIndexType(Ty);
}
 
Type *ScalarEvolution::getWiderType(Type *T1, Type *T2) const {
  return  getTypeSizeInBits(T1) >= getTypeSizeInBits(T2) ? T1 : T2;
}
 
bool ScalarEvolution::instructionCouldExistWithOperands(const SCEV *A,
                                                        const SCEV *B) {
  /// For a valid use point to exist, the defining scope of one operand
  /// must dominate the other.
  bool PreciseA, PreciseB;
  auto *ScopeA = getDefiningScopeBound({A}, PreciseA);
  auto *ScopeB = getDefiningScopeBound({B}, PreciseB);
  if (!PreciseA || !PreciseB)
    // Can't tell.
    return false;
  return (ScopeA == ScopeB) || DT.dominates(ScopeA, ScopeB) ||
    DT.dominates(ScopeB, ScopeA);
}
 
const SCEV *ScalarEvolution::getCouldNotCompute() {
  return CouldNotCompute.get();
}
 
bool ScalarEvolution::checkValidity(const SCEV *S) const {
  bool ContainsNulls = SCEVExprContains(S, [](const SCEV *S) {
    auto *SU = dyn_cast<SCEVUnknown>(S);
    return SU && SU->getValue() == nullptr;
  });
 
  return !ContainsNulls;
}
 
bool ScalarEvolution::containsAddRecurrence(const SCEV *S) {
  HasRecMapType::iterator I = HasRecMap.find(S);
  if (I != HasRecMap.end())
    return I->second;
 
  bool FoundAddRec =
      SCEVExprContains(S, [](const SCEV *S) { return isa<SCEVAddRecExpr>(S); });
  HasRecMap.insert({S, FoundAddRec});
  return FoundAddRec;
}
 
/// Return the ValueOffsetPair set for \p S. \p S can be represented
/// by the value and offset from any ValueOffsetPair in the set.
ArrayRef<Value *> ScalarEvolution::getSCEVValues(const SCEV *S) {
  ExprValueMapType::iterator SI = ExprValueMap.find_as(S);
  if (SI == ExprValueMap.end())
    return {};
  return SI->second;
}
 
/// Erase Value from ValueExprMap and ExprValueMap. ValueExprMap.erase(V)
/// cannot be used separately. eraseValueFromMap should be used to remove
/// V from ValueExprMap and ExprValueMap at the same time.
void ScalarEvolution::eraseValueFromMap(Value *V) {
  ValueExprMapType::iterator I = ValueExprMap.find_as(V);
  if (I != ValueExprMap.end()) {
    auto EVIt = ExprValueMap.find(I->second);
    assert(is_contained(EVIt->second, V) && "Value not in ExprValueMap?");
    llvm::erase(EVIt->second, V);
    ValueExprMap.erase(I);
  }
}
 
void ScalarEvolution::insertValueToMap(Value *V, const SCEV *S) {
  // A recursive query may have already computed the SCEV. It should be
  // equivalent, but may not necessarily be exactly the same, e.g. due to lazily
  // inferred nowrap flags.
  if (ValueExprMap.insert({SCEVCallbackVH(V, this), S}).second)
    ExprValueMap[S].push_back(V);
}
 
/// Return an existing SCEV if it exists, otherwise analyze the expression and
/// create a new one.
const SCEV *ScalarEvolution::getSCEV(Value *V) {
  assert(isSCEVable(V->getType()) && "Value is not SCEVable!");
 
  if (const SCEV *S = getExistingSCEV(V))
    return S;
  return createSCEVIter(V);
}
 
const SCEV *ScalarEvolution::getExistingSCEV(Value *V) {
  assert(isSCEVable(V->getType()) && "Value is not SCEVable!");
 
  ValueExprMapType::iterator I = ValueExprMap.find_as(V);
  if (I != ValueExprMap.end()) {
    const SCEV *S = I->second;
    assert(checkValidity(S) &&
           "existing SCEV has not been properly invalidated");
    return S;
  }
  return nullptr;
}
 
/// Return a SCEV corresponding to -V = -1*V
const SCEV *ScalarEvolution::getNegativeSCEV(const SCEV *V, SCEVFlags Flags) {
  if (const SCEVConstant *VC = dyn_cast<SCEVConstant>(V))
    return getConstant(
               cast<ConstantInt>(ConstantExpr::getNeg(VC->getValue())));
 
  Type *Ty = V->getType();
  Ty = getEffectiveSCEVType(Ty);
  return getMulExpr(V, getMinusOne(Ty), Flags);
}
 
/// If Expr computes ~A, return A else return nullptr
static const SCEV *MatchNotExpr(const SCEV *Expr) {
  const SCEV *MulOp;
  if (match(Expr, m_scev_Add(m_scev_AllOnes(),
                             m_scev_Mul(m_scev_AllOnes(), m_SCEV(MulOp)))))
    return MulOp;
  return nullptr;
}
 
/// Return a SCEV corresponding to ~V = -1-V
const SCEV *ScalarEvolution::getNotSCEV(const SCEV *V) {
  assert(!V->getType()->isPointerTy() && "Can't negate pointer");
 
  if (const SCEVConstant *VC = dyn_cast<SCEVConstant>(V))
    return getConstant(
                cast<ConstantInt>(ConstantExpr::getNot(VC->getValue())));
 
  // Fold ~(u|s)(min|max)(~x, ~y) to (u|s)(max|min)(x, y)
  if (const SCEVMinMaxExpr *MME = dyn_cast<SCEVMinMaxExpr>(V)) {
    auto MatchMinMaxNegation = [&](const SCEVMinMaxExpr *MME) {
      SmallVector<SCEVUse, 2> MatchedOperands;
      for (const SCEV *Operand : MME->operands()) {
        const SCEV *Matched = MatchNotExpr(Operand);
        if (!Matched)
          return (const SCEV *)nullptr;
        MatchedOperands.push_back(Matched);
      }
      return getMinMaxExpr(SCEVMinMaxExpr::negate(MME->getSCEVType()),
                           MatchedOperands);
    };
    if (const SCEV *Replaced = MatchMinMaxNegation(MME))
      return Replaced;
  }
 
  Type *Ty = V->getType();
  Ty = getEffectiveSCEVType(Ty);
  return getMinusSCEV(getMinusOne(Ty), V);
}
 
const SCEV *ScalarEvolution::removePointerBase(const SCEV *P) {
  assert(P->getType()->isPointerTy());
 
  if (auto *AddRec = dyn_cast<SCEVAddRecExpr>(P)) {
    // The base of an AddRec is the first operand.
    SmallVector<SCEVUse> Ops{AddRec->operands()};
    Ops[0] = removePointerBase(Ops[0]);
    // Don't try to transfer nowrap flags for now. We could in some cases
    // (for example, if pointer operand of the AddRec is a SCEVUnknown).
    return getAddRecExpr(Ops, AddRec->getLoop(), SCEV::FlagNone);
  }
  if (auto *Add = dyn_cast<SCEVAddExpr>(P)) {
    // The base of an Add is the pointer operand.
    SmallVector<SCEVUse> Ops{Add->operands()};
    SCEVUse *PtrOp = nullptr;
    for (SCEVUse &AddOp : Ops) {
      if (AddOp->getType()->isPointerTy()) {
        assert(!PtrOp && "Cannot have multiple pointer ops");
        PtrOp = &AddOp;
      }
    }
    *PtrOp = removePointerBase(*PtrOp);
    // Don't try to transfer nowrap flags for now. We could in some cases
    // (for example, if the pointer operand of the Add is a SCEVUnknown).
    return getAddExpr(Ops);
  }
  // Any other expression must be a pointer base.
  return getZero(P->getType());
}
 
const SCEV *ScalarEvolution::getMinusSCEV(SCEVUse LHS, SCEVUse RHS,
                                          SCEVFlags Flags, unsigned Depth) {
  // Fast path: X - X --> 0.
  if (SCEVUse::getCommon(LHS, RHS))
    return getZero(LHS->getType());
 
  // If we subtract two pointers with different pointer bases, bail.
  // Eventually, we're going to add an assertion to getMulExpr that we
  // can't multiply by a pointer.
  if (RHS->getType()->isPointerTy()) {
    if (!LHS->getType()->isPointerTy() ||
        getPointerBase(LHS) != getPointerBase(RHS))
      return getCouldNotCompute();
    LHS = removePointerBase(LHS);
    RHS = removePointerBase(RHS);
  }
 
  // We represent LHS - RHS as LHS + (-1)*RHS. This transformation
  // makes it so that we cannot make much use of NUW.
  auto AddFlags = SCEV::FlagNone;
  const bool RHSIsNotMinSigned =
      !getSignedRangeMin(RHS).isMinSignedValue();
  if (hasFlags(Flags, SCEV::FlagNSW)) {
    // Let M be the minimum representable signed value. Then (-1)*RHS
    // signed-wraps if and only if RHS is M. That can happen even for
    // a NSW subtraction because e.g. (-1)*M signed-wraps even though
    // -1 - M does not. So to transfer NSW from LHS - RHS to LHS +
    // (-1)*RHS, we need to prove that RHS != M.
    //
    // If LHS is non-negative and we know that LHS - RHS does not
    // signed-wrap, then RHS cannot be M. So we can rule out signed-wrap
    // either by proving that RHS > M or that LHS >= 0.
    if (RHSIsNotMinSigned || isKnownNonNegative(LHS)) {
      AddFlags = SCEV::FlagNSW;
    }
  }
 
  // FIXME: Find a correct way to transfer NSW to (-1)*M when LHS -
  // RHS is NSW and LHS >= 0.
  //
  // The difficulty here is that the NSW flag may have been proven
  // relative to a loop that is to be found in a recurrence in LHS and
  // not in RHS. Applying NSW to (-1)*M may then let the NSW have a
  // larger scope than intended.
  auto NegFlags = RHSIsNotMinSigned ? SCEV::FlagNSW : SCEV::FlagNone;
 
  return getAddExpr(LHS, getNegativeSCEV(RHS, NegFlags), AddFlags, Depth);
}
 
const SCEV *ScalarEvolution::getTruncateOrZeroExtend(const SCEV *V, Type *Ty,
                                                     unsigned Depth) {
  Type *SrcTy = V->getType();
  assert(SrcTy->isIntOrPtrTy() && Ty->isIntOrPtrTy() &&
         "Cannot truncate or zero extend with non-integer arguments!");
  if (getTypeSizeInBits(SrcTy) == getTypeSizeInBits(Ty))
    return V;  // No conversion
  if (getTypeSizeInBits(SrcTy) > getTypeSizeInBits(Ty))
    return getTruncateExpr(V, Ty, Depth);
  return getZeroExtendExpr(V, Ty, Depth);
}
 
const SCEV *ScalarEvolution::getTruncateOrSignExtend(const SCEV *V, Type *Ty,
                                                     unsigned Depth) {
  Type *SrcTy = V->getType();
  assert(SrcTy->isIntOrPtrTy() && Ty->isIntOrPtrTy() &&
         "Cannot truncate or zero extend with non-integer arguments!");
  if (getTypeSizeInBits(SrcTy) == getTypeSizeInBits(Ty))
    return V;  // No conversion
  if (getTypeSizeInBits(SrcTy) > getTypeSizeInBits(Ty))
    return getTruncateExpr(V, Ty, Depth);
  return getSignExtendExpr(V, Ty, Depth);
}
 
const SCEV *ScalarEvolution::getNoopOrZeroExtend(const SCEV *V, Type *Ty) {
  Type *SrcTy = V->getType();
  assert(SrcTy->isIntOrPtrTy() && Ty->isIntOrPtrTy() &&
         "Cannot noop or zero extend with non-integer arguments!");
  assert(getTypeSizeInBits(SrcTy) <= getTypeSizeInBits(Ty) &&
         "getNoopOrZeroExtend cannot truncate!");
  if (getTypeSizeInBits(SrcTy) == getTypeSizeInBits(Ty))
    return V;  // No conversion
  return getZeroExtendExpr(V, Ty);
}
 
const SCEV *ScalarEvolution::getNoopOrSignExtend(const SCEV *V, Type *Ty) {
  Type *SrcTy = V->getType();
  assert(SrcTy->isIntOrPtrTy() && Ty->isIntOrPtrTy() &&
         "Cannot noop or sign extend with non-integer arguments!");
  assert(getTypeSizeInBits(SrcTy) <= getTypeSizeInBits(Ty) &&
         "getNoopOrSignExtend cannot truncate!");
  if (getTypeSizeInBits(SrcTy) == getTypeSizeInBits(Ty))
    return V;  // No conversion
  return getSignExtendExpr(V, Ty);
}
 
const SCEV *ScalarEvolution::getNoopOrAnyExtend(const SCEV *V, Type *Ty) {
  Type *SrcTy = V->getType();
  assert(SrcTy->isIntOrPtrTy() && Ty->isIntOrPtrTy() &&
         "Cannot noop or any extend with non-integer arguments!");
  assert(getTypeSizeInBits(SrcTy) <= getTypeSizeInBits(Ty) &&
         "getNoopOrAnyExtend cannot truncate!");
  if (getTypeSizeInBits(SrcTy) == getTypeSizeInBits(Ty))
    return V;  // No conversion
  return getAnyExtendExpr(V, Ty);
}
 
const SCEV *ScalarEvolution::getTruncateOrNoop(const SCEV *V, Type *Ty) {
  Type *SrcTy = V->getType();
  assert(SrcTy->isIntOrPtrTy() && Ty->isIntOrPtrTy() &&
         "Cannot truncate or noop with non-integer arguments!");
  assert(getTypeSizeInBits(SrcTy) >= getTypeSizeInBits(Ty) &&
         "getTruncateOrNoop cannot extend!");
  if (getTypeSizeInBits(SrcTy) == getTypeSizeInBits(Ty))
    return V;  // No conversion
  return getTruncateExpr(V, Ty);
}
 
const SCEV *ScalarEvolution::getUMaxFromMismatchedTypes(const SCEV *LHS,
                                                        const SCEV *RHS) {
  const SCEV *PromotedLHS = LHS;
  const SCEV *PromotedRHS = RHS;
 
  if (getTypeSizeInBits(LHS->getType()) > getTypeSizeInBits(RHS->getType()))
    PromotedRHS = getZeroExtendExpr(RHS, LHS->getType());
  else
    PromotedLHS = getNoopOrZeroExtend(LHS, RHS->getType());
 
  return getUMaxExpr(PromotedLHS, PromotedRHS);
}
 
const SCEV *ScalarEvolution::getUMinFromMismatchedTypes(const SCEV *LHS,
                                                        const SCEV *RHS,
                                                        bool Sequential) {
  SmallVector<SCEVUse, 2> Ops = {LHS, RHS};
  return getUMinFromMismatchedTypes(Ops, Sequential);
}
 
const SCEV *
ScalarEvolution::getUMinFromMismatchedTypes(SmallVectorImpl<SCEVUse> &Ops,
                                            bool Sequential) {
  assert(!Ops.empty() && "At least one operand must be!");
  // Trivial case.
  if (Ops.size() == 1)
    return Ops[0];
 
  // Find the max type first.
  Type *MaxType = nullptr;
  for (SCEVUse S : Ops)
    if (MaxType)
      MaxType = getWiderType(MaxType, S->getType());
    else
      MaxType = S->getType();
  assert(MaxType && "Failed to find maximum type!");
 
  // Extend all ops to max type.
  SmallVector<SCEVUse, 2> PromotedOps;
  for (SCEVUse S : Ops)
    PromotedOps.push_back(getNoopOrZeroExtend(S, MaxType));
 
  // Generate umin.
  return getUMinExpr(PromotedOps, Sequential);
}
 
const SCEV *ScalarEvolution::getPointerBase(const SCEV *V) {
  // A pointer operand may evaluate to a nonpointer expression, such as null.
  if (!V->getType()->isPointerTy())
    return V;
 
  while (true) {
    if (auto *AddRec = dyn_cast<SCEVAddRecExpr>(V)) {
      V = AddRec->getStart();
    } else if (auto *Add = dyn_cast<SCEVAddExpr>(V)) {
      const SCEV *PtrOp = nullptr;
      for (const SCEV *AddOp : Add->operands()) {
        if (AddOp->getType()->isPointerTy()) {
          assert(!PtrOp && "Cannot have multiple pointer ops");
          PtrOp = AddOp;
        }
      }
      assert(PtrOp && "Must have pointer op");
      V = PtrOp;
    } else // Not something we can look further into.
      return V;
  }
}
 
/// Push users of the given Instruction onto the given Worklist.
static void PushDefUseChildren(Instruction *I,
                               SmallVectorImpl<Instruction *> &Worklist,
                               SmallPtrSetImpl<Instruction *> &Visited) {
  // Push the def-use children onto the Worklist stack.
  for (User *U : I->users()) {
    auto *UserInsn = cast<Instruction>(U);
    if (Visited.insert(UserInsn).second)
      Worklist.push_back(UserInsn);
  }
}
 
namespace {
 
/// Takes SCEV S and Loop L. For each AddRec sub-expression, use its start
/// expression in case its Loop is L. If it is not L then
/// if IgnoreOtherLoops is true then use AddRec itself
/// otherwise rewrite cannot be done.
/// If SCEV contains non-invariant unknown SCEV rewrite cannot be done.
class SCEVInitRewriter : public SCEVRewriteVisitor<SCEVInitRewriter> {
public:
  static const SCEV *rewrite(const SCEV *S, const Loop *L, ScalarEvolution &SE,
                             bool IgnoreOtherLoops = true) {
    SCEVInitRewriter Rewriter(L, SE);
    const SCEV *Result = Rewriter.visit(S);
    if (Rewriter.hasSeenLoopVariantSCEVUnknown())
      return SE.getCouldNotCompute();
    return Rewriter.hasSeenOtherLoops() && !IgnoreOtherLoops
               ? SE.getCouldNotCompute()
               : Result;
  }
 
  const SCEV *visitUnknown(const SCEVUnknown *Expr) {
    if (!SE.isLoopInvariant(Expr, L))
      SeenLoopVariantSCEVUnknown = true;
    return Expr;
  }
 
  const SCEV *visitAddRecExpr(const SCEVAddRecExpr *Expr) {
    // Only re-write AddRecExprs for this loop.
    if (Expr->getLoop() == L)
      return Expr->getStart();
    SeenOtherLoops = true;
    return Expr;
  }
 
  bool hasSeenLoopVariantSCEVUnknown() { return SeenLoopVariantSCEVUnknown; }
 
  bool hasSeenOtherLoops() { return SeenOtherLoops; }
 
private:
  explicit SCEVInitRewriter(const Loop *L, ScalarEvolution &SE)
      : SCEVRewriteVisitor(SE), L(L) {}
 
  const Loop *L;
  bool SeenLoopVariantSCEVUnknown = false;
  bool SeenOtherLoops = false;
};
 
/// Takes SCEV S and Loop L. For each AddRec sub-expression, use its post
/// increment expression in case its Loop is L. If it is not L then
/// use AddRec itself.
/// If SCEV contains non-invariant unknown SCEV rewrite cannot be done.
class SCEVPostIncRewriter : public SCEVRewriteVisitor<SCEVPostIncRewriter> {
public:
  static const SCEV *rewrite(const SCEV *S, const Loop *L, ScalarEvolution &SE) {
    SCEVPostIncRewriter Rewriter(L, SE);
    const SCEV *Result = Rewriter.visit(S);
    return Rewriter.hasSeenLoopVariantSCEVUnknown()
        ? SE.getCouldNotCompute()
        : Result;
  }
 
  const SCEV *visitUnknown(const SCEVUnknown *Expr) {
    if (!SE.isLoopInvariant(Expr, L))
      SeenLoopVariantSCEVUnknown = true;
    return Expr;
  }
 
  const SCEV *visitAddRecExpr(const SCEVAddRecExpr *Expr) {
    // Only re-write AddRecExprs for this loop.
    if (Expr->getLoop() == L)
      return Expr->getPostIncExpr(SE);
    SeenOtherLoops = true;
    return Expr;
  }
 
  bool hasSeenLoopVariantSCEVUnknown() { return SeenLoopVariantSCEVUnknown; }
 
  bool hasSeenOtherLoops() { return SeenOtherLoops; }
 
private:
  explicit SCEVPostIncRewriter(const Loop *L, ScalarEvolution &SE)
      : SCEVRewriteVisitor(SE), L(L) {}
 
  const Loop *L;
  bool SeenLoopVariantSCEVUnknown = false;
  bool SeenOtherLoops = false;
};
 
/// This class evaluates the compare condition by matching it against the
/// condition of loop latch. If there is a match we assume a true value
/// for the condition while building SCEV nodes.
class SCEVBackedgeConditionFolder
    : public SCEVRewriteVisitor<SCEVBackedgeConditionFolder> {
public:
  static const SCEV *rewrite(const SCEV *S, const Loop *L,
                             ScalarEvolution &SE) {
    bool IsPosBECond = false;
    Value *BECond = nullptr;
    if (BasicBlock *Latch = L->getLoopLatch()) {
      if (CondBrInst *BI = dyn_cast<CondBrInst>(Latch->getTerminator())) {
        assert(BI->getSuccessor(0) != BI->getSuccessor(1) &&
               "Both outgoing branches should not target same header!");
        BECond = BI->getCondition();
        IsPosBECond = BI->getSuccessor(0) == L->getHeader();
      } else {
        return S;
      }
    }
    SCEVBackedgeConditionFolder Rewriter(L, BECond, IsPosBECond, SE);
    return Rewriter.visit(S);
  }
 
  const SCEV *visitUnknown(const SCEVUnknown *Expr) {
    const SCEV *Result = Expr;
    bool InvariantF = SE.isLoopInvariant(Expr, L);
 
    if (!InvariantF) {
      Instruction *I = cast<Instruction>(Expr->getValue());
      switch (I->getOpcode()) {
      case Instruction::Select: {
        SelectInst *SI = cast<SelectInst>(I);
        std::optional<const SCEV *> Res =
            compareWithBackedgeCondition(SI->getCondition());
        if (Res) {
          bool IsOne = cast<SCEVConstant>(*Res)->getValue()->isOne();
          Result = SE.getSCEV(IsOne ? SI->getTrueValue() : SI->getFalseValue());
        }
        break;
      }
      default: {
        std::optional<const SCEV *> Res = compareWithBackedgeCondition(I);
        if (Res)
          Result = *Res;
        break;
      }
      }
    }
    return Result;
  }
 
private:
  explicit SCEVBackedgeConditionFolder(const Loop *L, Value *BECond,
                                       bool IsPosBECond, ScalarEvolution &SE)
      : SCEVRewriteVisitor(SE), L(L), BackedgeCond(BECond),
        IsPositiveBECond(IsPosBECond) {}
 
  std::optional<const SCEV *> compareWithBackedgeCondition(Value *IC);
 
  const Loop *L;
  /// Loop back condition.
  Value *BackedgeCond = nullptr;
  /// Set to true if loop back is on positive branch condition.
  bool IsPositiveBECond;
};
 
std::optional<const SCEV *>
SCEVBackedgeConditionFolder::compareWithBackedgeCondition(Value *IC) {
 
  // If value matches the backedge condition for loop latch,
  // then return a constant evolution node based on loopback
  // branch taken.
  if (BackedgeCond == IC)
    return IsPositiveBECond ? SE.getOne(Type::getInt1Ty(SE.getContext()))
                            : SE.getZero(Type::getInt1Ty(SE.getContext()));
  return std::nullopt;
}
 
class SCEVShiftRewriter : public SCEVRewriteVisitor<SCEVShiftRewriter> {
public:
  static const SCEV *rewrite(const SCEV *S, const Loop *L,
                             ScalarEvolution &SE) {
    SCEVShiftRewriter Rewriter(L, SE);
    const SCEV *Result = Rewriter.visit(S);
    return Rewriter.isValid() ? Result : SE.getCouldNotCompute();
  }
 
  const SCEV *visitUnknown(const SCEVUnknown *Expr) {
    // Only allow AddRecExprs for this loop.
    if (!SE.isLoopInvariant(Expr, L))
      Valid = false;
    return Expr;
  }
 
  const SCEV *visitAddRecExpr(const SCEVAddRecExpr *Expr) {
    if (Expr->getLoop() == L && Expr->isAffine())
      return SE.getMinusSCEV(Expr, Expr->getStepRecurrence(SE));
    Valid = false;
    return Expr;
  }
 
  bool isValid() { return Valid; }
 
private:
  explicit SCEVShiftRewriter(const Loop *L, ScalarEvolution &SE)
      : SCEVRewriteVisitor(SE), L(L) {}
 
  const Loop *L;
  bool Valid = true;
};
 
} // end anonymous namespace
 
void ScalarEvolution::inferNoWrapViaConstantRanges(const SCEVAddRecExpr *AR) {
  if (!AR->isAffine())
    return;
 
  // Force computation of ranges, which will also perform range-based flag
  // inference.
  if (!AR->hasNoSignedWrap())
    (void)getSignedRange(AR);
 
  if (!AR->hasNoUnsignedWrap())
    (void)getUnsignedRange(AR);
 
  if (!AR->hasNoSelfWrap()) {
    const SCEV *BECount = getConstantMaxBackedgeTakenCount(AR->getLoop());
    if (const SCEVConstant *BECountMax = dyn_cast<SCEVConstant>(BECount)) {
      ConstantRange StepCR = getSignedRange(AR->getStepRecurrence(*this));
      const APInt &BECountAP = BECountMax->getAPInt();
      unsigned NoOverflowBitWidth =
        BECountAP.getActiveBits() + StepCR.getMinSignedBits();
      if (NoOverflowBitWidth <= getTypeSizeInBits(AR->getType()))
        const_cast<SCEVAddRecExpr *>(AR)->setNoWrapFlags(SCEV::FlagNW);
    }
  }
}
 
SCEVFlags
ScalarEvolution::proveNoSignedWrapViaInduction(const SCEVAddRecExpr *AR) {
  SCEVFlags Result = AR->getNoWrapFlags();
 
  if (AR->hasNoSignedWrap())
    return Result;
 
  if (!AR->isAffine())
    return Result;
 
  // This function can be expensive, only try to prove NSW once per AddRec.
  if (!SignedWrapViaInductionTried.insert(AR).second)
    return Result;
 
  const SCEV *Step = AR->getStepRecurrence(*this);
  const Loop *L = AR->getLoop();
 
  // Check whether the backedge-taken count is SCEVCouldNotCompute.
  // Note that this serves two purposes: It filters out loops that are
  // simply not analyzable, and it covers the case where this code is
  // being called from within backedge-taken count analysis, such that
  // attempting to ask for the backedge-taken count would likely result
  // in infinite recursion. In the later case, the analysis code will
  // cope with a conservative value, and it will take care to purge
  // that value once it has finished.
  const SCEV *MaxBECount = getConstantMaxBackedgeTakenCount(L);
 
  // Normally, in the cases we can prove no-overflow via a
  // backedge guarding condition, we can also compute a backedge
  // taken count for the loop.  The exceptions are assumptions and
  // guards present in the loop -- SCEV is not great at exploiting
  // these to compute max backedge taken counts, but can still use
  // these to prove lack of overflow.  Use this fact to avoid
  // doing extra work that may not pay off.
 
  if (isa<SCEVCouldNotCompute>(MaxBECount) && !HasGuards &&
      AC.assumptions().empty())
    return Result;
 
  // If the backedge is guarded by a comparison with the pre-inc  value the
  // addrec is safe. Also, if the entry is guarded by a comparison with the
  // start value and the backedge is guarded by a comparison with the post-inc
  // value, the addrec is safe.
  ICmpInst::Predicate Pred;
  const SCEV *OverflowLimit =
    getSignedOverflowLimitForStep(Step, &Pred, this);
  if (OverflowLimit &&
      (isLoopBackedgeGuardedByCond(L, Pred, AR, OverflowLimit) ||
       isKnownOnEveryIteration(Pred, AR, OverflowLimit))) {
    Result = setFlags(Result, SCEV::FlagNSW);
  }
  return Result;
}
SCEVFlags
ScalarEvolution::proveNoUnsignedWrapViaInduction(const SCEVAddRecExpr *AR) {
  SCEVFlags Result = AR->getNoWrapFlags();
 
  if (AR->hasNoUnsignedWrap())
    return Result;
 
  if (!AR->isAffine())
    return Result;
 
  // This function can be expensive, only try to prove NUW once per AddRec.
  if (!UnsignedWrapViaInductionTried.insert(AR).second)
    return Result;
 
  const SCEV *Step = AR->getStepRecurrence(*this);
  const Loop *L = AR->getLoop();
 
  // Check whether the backedge-taken count is SCEVCouldNotCompute.
  // Note that this serves two purposes: It filters out loops that are
  // simply not analyzable, and it covers the case where this code is
  // being called from within backedge-taken count analysis, such that
  // attempting to ask for the backedge-taken count would likely result
  // in infinite recursion. In the later case, the analysis code will
  // cope with a conservative value, and it will take care to purge
  // that value once it has finished.
  const SCEV *MaxBECount = getConstantMaxBackedgeTakenCount(L);
 
  // Normally, in the cases we can prove no-overflow via a
  // backedge guarding condition, we can also compute a backedge
  // taken count for the loop.  The exceptions are assumptions and
  // guards present in the loop -- SCEV is not great at exploiting
  // these to compute max backedge taken counts, but can still use
  // these to prove lack of overflow.  Use this fact to avoid
  // doing extra work that may not pay off.
 
  if (isa<SCEVCouldNotCompute>(MaxBECount) && !HasGuards &&
      AC.assumptions().empty())
    return Result;
 
  // If the backedge is guarded by a comparison with the pre-inc  value the
  // addrec is safe. Also, if the entry is guarded by a comparison with the
  // start value and the backedge is guarded by a comparison with the post-inc
  // value, the addrec is safe.
  if (isKnownPositive(Step)) {
    ICmpInst::Predicate Pred;
    const SCEV *OverflowLimit =
        getUnsignedOverflowLimitForStep(Step, &Pred, this);
    if (isLoopBackedgeGuardedByCond(L, Pred, AR, OverflowLimit) ||
        isKnownOnEveryIteration(Pred, AR, OverflowLimit))
      Result = setFlags(Result, SCEV::FlagNUW);
  }
  return Result;
}
 
namespace {
 
/// Represents an abstract binary operation.  This may exist as a
/// normal instruction or constant expression, or may have been
/// derived from an expression tree.
struct BinaryOp {
  unsigned Opcode;
  Value *LHS;
  Value *RHS;
  bool IsNSW = false;
  bool IsNUW = false;
 
  /// Op is set if this BinaryOp corresponds to a concrete LLVM instruction or
  /// constant expression.
  Operator *Op = nullptr;
 
  explicit BinaryOp(Operator *Op)
      : Opcode(Op->getOpcode()), LHS(Op->getOperand(0)), RHS(Op->getOperand(1)),
        Op(Op) {
    if (auto *OBO = dyn_cast<OverflowingBinaryOperator>(Op)) {
      IsNSW = OBO->hasNoSignedWrap();
      IsNUW = OBO->hasNoUnsignedWrap();
    }
  }
 
  explicit BinaryOp(unsigned Opcode, Value *LHS, Value *RHS, bool IsNSW = false,
                    bool IsNUW = false)
      : Opcode(Opcode), LHS(LHS), RHS(RHS), IsNSW(IsNSW), IsNUW(IsNUW) {}
};
 
} // end anonymous namespace
 
/// Try to map \p V into a BinaryOp, and return \c std::nullopt on failure.
static std::optional<BinaryOp> MatchBinaryOp(Value *V, const DataLayout &DL,
                                             AssumptionCache &AC,
                                             const DominatorTree &DT,
                                             const Instruction *CtxI) {
  auto *Op = dyn_cast<Operator>(V);
  if (!Op)
    return std::nullopt;
 
  // Implementation detail: all the cleverness here should happen without
  // creating new SCEV expressions -- our caller knowns tricks to avoid creating
  // SCEV expressions when possible, and we should not break that.
 
  switch (Op->getOpcode()) {
  case Instruction::Add:
  case Instruction::Sub:
  case Instruction::Mul:
  case Instruction::UDiv:
  case Instruction::URem:
  case Instruction::And:
  case Instruction::AShr:
  case Instruction::Shl:
    return BinaryOp(Op);
 
  case Instruction::Or: {
    // Convert or disjoint into add nuw nsw.
    if (cast<PossiblyDisjointInst>(Op)->isDisjoint()) {
      BinaryOp BinOp(Instruction::Add, Op->getOperand(0), Op->getOperand(1),
                     /*IsNSW=*/true, /*IsNUW=*/true);
      // Keep the reference to the original instruction so that we can later
      // check whether it can produce poison value or not.
      BinOp.Op = Op;
      return BinOp;
    }
    return BinaryOp(Op);
  }
 
  case Instruction::Xor:
    if (auto *RHSC = dyn_cast<ConstantInt>(Op->getOperand(1)))
      // If the RHS of the xor is a signmask, then this is just an add.
      // Instcombine turns add of signmask into xor as a strength reduction step.
      if (RHSC->getValue().isSignMask())
        return BinaryOp(Instruction::Add, Op->getOperand(0), Op->getOperand(1));
    // Binary `xor` is a bit-wise `add`.
    if (V->getType()->isIntegerTy(1))
      return BinaryOp(Instruction::Add, Op->getOperand(0), Op->getOperand(1));
    return BinaryOp(Op);
 
  case Instruction::LShr:
    // Turn logical shift right of a constant into a unsigned divide.
    if (ConstantInt *SA = dyn_cast<ConstantInt>(Op->getOperand(1))) {
      uint32_t BitWidth = cast<IntegerType>(Op->getType())->getBitWidth();
 
      // If the shift count is not less than the bitwidth, the result of
      // the shift is undefined. Don't try to analyze it, because the
      // resolution chosen here may differ from the resolution chosen in
      // other parts of the compiler.
      if (SA->getValue().ult(BitWidth)) {
        Constant *X =
            ConstantInt::get(SA->getContext(),
                             APInt::getOneBitSet(BitWidth, SA->getZExtValue()));
        return BinaryOp(Instruction::UDiv, Op->getOperand(0), X);
      }
    }
    return BinaryOp(Op);
 
  case Instruction::ExtractValue: {
    auto *EVI = cast<ExtractValueInst>(Op);
    if (EVI->getNumIndices() != 1 || EVI->getIndices()[0] != 0)
      break;
 
    auto *WO = dyn_cast<WithOverflowInst>(EVI->getAggregateOperand());
    if (!WO)
      break;
 
    Instruction::BinaryOps BinOp = WO->getBinaryOp();
    bool Signed = WO->isSigned();
    // TODO: Should add nuw/nsw flags for mul as well.
    if (BinOp == Instruction::Mul || !isOverflowIntrinsicNoWrap(WO, DT))
      return BinaryOp(BinOp, WO->getLHS(), WO->getRHS());
 
    // Now that we know that all uses of the arithmetic-result component of
    // CI are guarded by the overflow check, we can go ahead and pretend
    // that the arithmetic is non-overflowing.
    return BinaryOp(BinOp, WO->getLHS(), WO->getRHS(),
                    /* IsNSW = */ Signed, /* IsNUW = */ !Signed);
  }
 
  default:
    break;
  }
 
  // Recognise intrinsic loop.decrement.reg, and as this has exactly the same
  // semantics as a Sub, return a binary sub expression.
  if (auto *II = dyn_cast<IntrinsicInst>(V))
    if (II->getIntrinsicID() == Intrinsic::loop_decrement_reg)
      return BinaryOp(Instruction::Sub, II->getOperand(0), II->getOperand(1));
 
  return std::nullopt;
}
 
/// Helper function to createAddRecFromPHIWithCasts. We have a phi
/// node whose symbolic (unknown) SCEV is \p SymbolicPHI, which is updated via
/// the loop backedge by a SCEVAddExpr, possibly also with a few casts on the
/// way. This function checks if \p Op, an operand of this SCEVAddExpr,
/// follows one of the following patterns:
/// Op == (SExt ix (Trunc iy (%SymbolicPHI) to ix) to iy)
/// Op == (ZExt ix (Trunc iy (%SymbolicPHI) to ix) to iy)
/// If the SCEV expression of \p Op conforms with one of the expected patterns
/// we return the type of the truncation operation, and indicate whether the
/// truncated type should be treated as signed/unsigned by setting
/// \p Signed to true/false, respectively.
static Type *isSimpleCastedPHI(const SCEV *Op, const SCEVUnknown *SymbolicPHI,
                               bool &Signed, ScalarEvolution &SE) {
  // The case where Op == SymbolicPHI (that is, with no type conversions on
  // the way) is handled by the regular add recurrence creating logic and
  // would have already been triggered in createAddRecForPHI. Reaching it here
  // means that createAddRecFromPHI had failed for this PHI before (e.g.,
  // because one of the other operands of the SCEVAddExpr updating this PHI is
  // not invariant).
  //
  // Here we look for the case where Op = (ext(trunc(SymbolicPHI))), and in
  // this case predicates that allow us to prove that Op == SymbolicPHI will
  // be added.
  if (Op == SymbolicPHI)
    return nullptr;
 
  unsigned SourceBits = SE.getTypeSizeInBits(SymbolicPHI->getType());
  unsigned NewBits = SE.getTypeSizeInBits(Op->getType());
  if (SourceBits != NewBits)
    return nullptr;
 
  if (match(Op, m_scev_SExt(m_scev_Trunc(m_scev_Specific(SymbolicPHI))))) {
    Signed = true;
    return cast<SCEVCastExpr>(Op)->getOperand()->getType();
  }
  if (match(Op, m_scev_ZExt(m_scev_Trunc(m_scev_Specific(SymbolicPHI))))) {
    Signed = false;
    return cast<SCEVCastExpr>(Op)->getOperand()->getType();
  }
  return nullptr;
}
 
static const Loop *isIntegerLoopHeaderPHI(const PHINode *PN, LoopInfo &LI) {
  if (!PN->getType()->isIntegerTy())
    return nullptr;
  const Loop *L = LI.getLoopFor(PN->getParent());
  if (!L || L->getHeader() != PN->getParent())
    return nullptr;
  return L;
}
 
// Analyze \p SymbolicPHI, a SCEV expression of a phi node, and check if the
// computation that updates the phi follows the following pattern:
//   (SExt/ZExt ix (Trunc iy (%SymbolicPHI) to ix) to iy) + InvariantAccum
// which correspond to a phi->trunc->sext/zext->add->phi update chain.
// If so, try to see if it can be rewritten as an AddRecExpr under some
// Predicates. If successful, return them as a pair. Also cache the results
// of the analysis.
//
// Example usage scenario:
//    Say the Rewriter is called for the following SCEV:
//         8 * ((sext i32 (trunc i64 %X to i32) to i64) + %Step)
//    where:
//         %X = phi i64 (%Start, %BEValue)
//    It will visitMul->visitAdd->visitSExt->visitTrunc->visitUnknown(%X),
//    and call this function with %SymbolicPHI = %X.
//
//    The analysis will find that the value coming around the backedge has
//    the following SCEV:
//         BEValue = ((sext i32 (trunc i64 %X to i32) to i64) + %Step)
//    Upon concluding that this matches the desired pattern, the function
//    will return the pair {NewAddRec, SmallPredsVec} where:
//         NewAddRec = {%Start,+,%Step}
//         SmallPredsVec = {P1, P2, P3} as follows:
//           P1(WrapPred): AR: {trunc(%Start),+,(trunc %Step)}<nsw> Flags: <nssw>
//           P2(EqualPred): %Start == (sext i32 (trunc i64 %Start to i32) to i64)
//           P3(EqualPred): %Step == (sext i32 (trunc i64 %Step to i32) to i64)
//    The returned pair means that SymbolicPHI can be rewritten into NewAddRec
//    under the predicates {P1,P2,P3}.
//    This predicated rewrite will be cached in PredicatedSCEVRewrites:
//         PredicatedSCEVRewrites[{%X,L}] = {NewAddRec, {P1,P2,P3)}
//
// TODO's:
//
// 1) Extend the Induction descriptor to also support inductions that involve
//    casts: When needed (namely, when we are called in the context of the
//    vectorizer induction analysis), a Set of cast instructions will be
//    populated by this method, and provided back to isInductionPHI. This is
//    needed to allow the vectorizer to properly record them to be ignored by
//    the cost model and to avoid vectorizing them (otherwise these casts,
//    which are redundant under the runtime overflow checks, will be
//    vectorized, which can be costly).
//
// 2) Support additional induction/PHISCEV patterns: We also want to support
//    inductions where the sext-trunc / zext-trunc operations (partly) occur
//    after the induction update operation (the induction increment):
//
//      (Trunc iy (SExt/ZExt ix (%SymbolicPHI + InvariantAccum) to iy) to ix)
//    which correspond to a phi->add->trunc->sext/zext->phi update chain.
//
//      (Trunc iy ((SExt/ZExt ix (%SymbolicPhi) to iy) + InvariantAccum) to ix)
//    which correspond to a phi->trunc->add->sext/zext->phi update chain.
//
// 3) Outline common code with createAddRecFromPHI to avoid duplication.
std::optional<std::pair<const SCEV *, SmallVector<const SCEVPredicate *, 3>>>
ScalarEvolution::createAddRecFromPHIWithCastsImpl(const SCEVUnknown *SymbolicPHI) {
  SmallVector<const SCEVPredicate *, 3> Predicates;
 
  // *** Part1: Analyze if we have a phi-with-cast pattern for which we can
  // return an AddRec expression under some predicate.
 
  auto *PN = cast<PHINode>(SymbolicPHI->getValue());
  const Loop *L = isIntegerLoopHeaderPHI(PN, LI);
  assert(L && "Expecting an integer loop header phi");
 
  // The loop may have multiple entrances or multiple exits; we can analyze
  // this phi as an addrec if it has a unique entry value and a unique
  // backedge value.
  Value *BEValueV = nullptr, *StartValueV = nullptr;
  for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
    Value *V = PN->getIncomingValue(i);
    if (L->contains(PN->getIncomingBlock(i))) {
      if (!BEValueV) {
        BEValueV = V;
      } else if (BEValueV != V) {
        BEValueV = nullptr;
        break;
      }
    } else if (!StartValueV) {
      StartValueV = V;
    } else if (StartValueV != V) {
      StartValueV = nullptr;
      break;
    }
  }
  if (!BEValueV || !StartValueV)
    return std::nullopt;
 
  const SCEV *BEValue = getSCEV(BEValueV);
 
  // If the value coming around the backedge is an add with the symbolic
  // value we just inserted, possibly with casts that we can ignore under
  // an appropriate runtime guard, then we found a simple induction variable!
  const auto *Add = dyn_cast<SCEVAddExpr>(BEValue);
  if (!Add)
    return std::nullopt;
 
  // If there is a single occurrence of the symbolic value, possibly
  // casted, replace it with a recurrence.
  unsigned FoundIndex = Add->getNumOperands();
  Type *TruncTy = nullptr;
  bool Signed;
  for (unsigned i = 0, e = Add->getNumOperands(); i != e; ++i)
    if ((TruncTy =
             isSimpleCastedPHI(Add->getOperand(i), SymbolicPHI, Signed, *this)))
      if (FoundIndex == e) {
        FoundIndex = i;
        break;
      }
 
  if (FoundIndex == Add->getNumOperands())
    return std::nullopt;
 
  // Create an add with everything but the specified operand.
  SmallVector<SCEVUse, 8> Ops;
  for (unsigned i = 0, e = Add->getNumOperands(); i != e; ++i)
    if (i != FoundIndex)
      Ops.push_back(Add->getOperand(i));
  const SCEV *Accum = getAddExpr(Ops);
 
  // The runtime checks will not be valid if the step amount is
  // varying inside the loop.
  if (!isLoopInvariant(Accum, L))
    return std::nullopt;
 
  // *** Part2: Create the predicates
 
  // Analysis was successful: we have a phi-with-cast pattern for which we
  // can return an AddRec expression under the following predicates:
  //
  // P1: A Wrap predicate that guarantees that Trunc(Start) + i*Trunc(Accum)
  //     fits within the truncated type (does not overflow) for i = 0 to n-1.
  // P2: An Equal predicate that guarantees that
  //     Start = (Ext ix (Trunc iy (Start) to ix) to iy)
  // P3: An Equal predicate that guarantees that
  //     Accum = (Ext ix (Trunc iy (Accum) to ix) to iy)
  //
  // As we next prove, the above predicates guarantee that:
  //     Start + i*Accum = (Ext ix (Trunc iy ( Start + i*Accum ) to ix) to iy)
  //
  //
  // More formally, we want to prove that:
  //     Expr(i+1) = Start + (i+1) * Accum
  //               = (Ext ix (Trunc iy (Expr(i)) to ix) to iy) + Accum
  //
  // Given that:
  // 1) Expr(0) = Start
  // 2) Expr(1) = Start + Accum
  //            = (Ext ix (Trunc iy (Start) to ix) to iy) + Accum :: from P2
  // 3) Induction hypothesis (step i):
  //    Expr(i) = (Ext ix (Trunc iy (Expr(i-1)) to ix) to iy) + Accum
  //
  // Proof:
  //  Expr(i+1) =
  //   = Start + (i+1)*Accum
  //   = (Start + i*Accum) + Accum
  //   = Expr(i) + Accum
  //   = (Ext ix (Trunc iy (Expr(i-1)) to ix) to iy) + Accum + Accum
  //                                                             :: from step i
  //
  //   = (Ext ix (Trunc iy (Start + (i-1)*Accum) to ix) to iy) + Accum + Accum
  //
  //   = (Ext ix (Trunc iy (Start + (i-1)*Accum) to ix) to iy)
  //     + (Ext ix (Trunc iy (Accum) to ix) to iy)
  //     + Accum                                                     :: from P3
  //
  //   = (Ext ix (Trunc iy ((Start + (i-1)*Accum) + Accum) to ix) to iy)
  //     + Accum                            :: from P1: Ext(x)+Ext(y)=>Ext(x+y)
  //
  //   = (Ext ix (Trunc iy (Start + i*Accum) to ix) to iy) + Accum
  //   = (Ext ix (Trunc iy (Expr(i)) to ix) to iy) + Accum
  //
  // By induction, the same applies to all iterations 1<=i<n:
  //
 
  // Create a truncated addrec for which we will add a no overflow check (P1).
  const SCEV *StartVal = getSCEV(StartValueV);
  const SCEV *PHISCEV =
      getAddRecExpr(getTruncateExpr(StartVal, TruncTy),
                    getTruncateExpr(Accum, TruncTy), L, SCEV::FlagNone);
 
  // PHISCEV can be either a SCEVConstant or a SCEVAddRecExpr.
  // ex: If truncated Accum is 0 and StartVal is a constant, then PHISCEV
  // will be constant.
  //
  //  If PHISCEV is a constant, then P1 degenerates into P2 or P3, so we don't
  // add P1.
  if (const auto *AR = dyn_cast<SCEVAddRecExpr>(PHISCEV)) {
    SCEVWrapPredicate::IncrementWrapFlags AddedFlags =
        Signed ? SCEVWrapPredicate::IncrementNSSW
               : SCEVWrapPredicate::IncrementNUSW;
    const SCEVPredicate *AddRecPred = getWrapPredicate(AR, AddedFlags);
    Predicates.push_back(AddRecPred);
  }
 
  // Create the Equal Predicates P2,P3:
 
  // It is possible that the predicates P2 and/or P3 are computable at
  // compile time due to StartVal and/or Accum being constants.
  // If either one is, then we can check that now and escape if either P2
  // or P3 is false.
 
  // Construct the extended SCEV: (Ext ix (Trunc iy (Expr) to ix) to iy)
  // for each of StartVal and Accum
  auto getExtendedExpr = [&](const SCEV *Expr,
                             bool CreateSignExtend) -> const SCEV * {
    assert(isLoopInvariant(Expr, L) && "Expr is expected to be invariant");
    const SCEV *TruncatedExpr = getTruncateExpr(Expr, TruncTy);
    const SCEV *ExtendedExpr =
        CreateSignExtend ? getSignExtendExpr(TruncatedExpr, Expr->getType())
                         : getZeroExtendExpr(TruncatedExpr, Expr->getType());
    return ExtendedExpr;
  };
 
  // Given:
  //  ExtendedExpr = (Ext ix (Trunc iy (Expr) to ix) to iy
  //               = getExtendedExpr(Expr)
  // Determine whether the predicate P: Expr == ExtendedExpr
  // is known to be false at compile time
  auto PredIsKnownFalse = [&](const SCEV *Expr,
                              const SCEV *ExtendedExpr) -> bool {
    return Expr != ExtendedExpr &&
           isKnownPredicate(ICmpInst::ICMP_NE, Expr, ExtendedExpr);
  };
 
  const SCEV *StartExtended = getExtendedExpr(StartVal, Signed);
  if (PredIsKnownFalse(StartVal, StartExtended)) {
    LLVM_DEBUG(dbgs() << "P2 is compile-time false\n";);
    return std::nullopt;
  }
 
  // The Step is always Signed (because the overflow checks are either
  // NSSW or NUSW)
  const SCEV *AccumExtended = getExtendedExpr(Accum, /*CreateSignExtend=*/true);
  if (PredIsKnownFalse(Accum, AccumExtended)) {
    LLVM_DEBUG(dbgs() << "P3 is compile-time false\n";);
    return std::nullopt;
  }
 
  auto AppendPredicate = [&](const SCEV *Expr,
                             const SCEV *ExtendedExpr) -> void {
    if (Expr != ExtendedExpr &&
        !isKnownPredicate(ICmpInst::ICMP_EQ, Expr, ExtendedExpr)) {
      const SCEVPredicate *Pred = getEqualPredicate(Expr, ExtendedExpr);
      LLVM_DEBUG(dbgs() << "Added Predicate: " << *Pred);
      Predicates.push_back(Pred);
    }
  };
 
  AppendPredicate(StartVal, StartExtended);
  AppendPredicate(Accum, AccumExtended);
 
  // *** Part3: Predicates are ready. Now go ahead and create the new addrec in
  // which the casts had been folded away. The caller can rewrite SymbolicPHI
  // into NewAR if it will also add the runtime overflow checks specified in
  // Predicates.
  const SCEV *NewAR = getAddRecExpr(StartVal, Accum, L, SCEV::FlagNone);
 
  std::pair<const SCEV *, SmallVector<const SCEVPredicate *, 3>> PredRewrite =
      std::make_pair(NewAR, Predicates);
  // Remember the result of the analysis for this SCEV at this locayyytion.
  PredicatedSCEVRewrites[{SymbolicPHI, L}] = PredRewrite;
  return PredRewrite;
}
 
std::optional<std::pair<const SCEV *, SmallVector<const SCEVPredicate *, 3>>>
ScalarEvolution::createAddRecFromPHIWithCasts(const SCEVUnknown *SymbolicPHI) {
  auto *PN = cast<PHINode>(SymbolicPHI->getValue());
  const Loop *L = isIntegerLoopHeaderPHI(PN, LI);
  if (!L)
    return std::nullopt;
 
  // Check to see if we already analyzed this PHI.
  auto I = PredicatedSCEVRewrites.find({SymbolicPHI, L});
  if (I != PredicatedSCEVRewrites.end()) {
    std::pair<const SCEV *, SmallVector<const SCEVPredicate *, 3>> Rewrite =
        I->second;
    // Analysis was done before and failed to create an AddRec:
    if (Rewrite.first == SymbolicPHI)
      return std::nullopt;
    // Analysis was done before and succeeded to create an AddRec under
    // a predicate:
    assert(isa<SCEVAddRecExpr>(Rewrite.first) && "Expected an AddRec");
    assert(!(Rewrite.second).empty() && "Expected to find Predicates");
    return Rewrite;
  }
 
  std::optional<std::pair<const SCEV *, SmallVector<const SCEVPredicate *, 3>>>
    Rewrite = createAddRecFromPHIWithCastsImpl(SymbolicPHI);
 
  // Record in the cache that the analysis failed
  if (!Rewrite) {
    SmallVector<const SCEVPredicate *, 3> Predicates;
    PredicatedSCEVRewrites[{SymbolicPHI, L}] = {SymbolicPHI, Predicates};
    return std::nullopt;
  }
 
  return Rewrite;
}
 
// FIXME: This utility is currently required because the Rewriter currently
// does not rewrite this expression:
// {0, +, (sext ix (trunc iy to ix) to iy)}
// into {0, +, %step},
// even when the following Equal predicate exists:
// "%step == (sext ix (trunc iy to ix) to iy)".
bool PredicatedScalarEvolution::areAddRecsEqualWithPreds(
    const SCEVAddRecExpr *AR1, const SCEVAddRecExpr *AR2,
    ArrayRef<const SCEVPredicate *> NoWrapPreds) const {
  if (AR1 == AR2)
    return true;
 
  SCEVUnionPredicate NoWrapUnionPred(NoWrapPreds, SE);
  SCEVUnionPredicate AllPreds = Preds->getUnionWith(&NoWrapUnionPred, SE);
  auto areExprsEqual = [&](const SCEV *Expr1, const SCEV *Expr2) -> bool {
    if (Expr1 != Expr2 &&
        !AllPreds.implies(SE.getEqualPredicate(Expr1, Expr2), SE) &&
        !AllPreds.implies(SE.getEqualPredicate(Expr2, Expr1), SE))
      return false;
    return true;
  };
 
  if (!areExprsEqual(AR1->getStart(), AR2->getStart()) ||
      !areExprsEqual(AR1->getStepRecurrence(SE), AR2->getStepRecurrence(SE)))
    return false;
  return true;
}
 
static SCEVFlags getNoWrapFlagsForGEP(GEPOperator *GEP, const SCEV *Accum,
                                      ScalarEvolution &SE) {
  SCEVFlags Flags = SCEV::FlagNone;
  GEPNoWrapFlags NW = GEP->getNoWrapFlags();
  // If the increment has any nowrap flags, then we know the address
  // space cannot be wrapped around.
  if (NW != GEPNoWrapFlags::none())
    Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNW);
  // If the GEP is nuw or nusw with non-negative offset, we know that
  // no unsigned wrap occurs. We cannot set the nsw flag as only the
  // offset is treated as signed, while the base is unsigned.
  if (NW.hasNoUnsignedWrap() ||
      (NW.hasNoUnsignedSignedWrap() && SE.isKnownNonNegative(Accum)))
    Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNUW);
 
  return Flags;
}
 
/// A helper function for createAddRecFromPHI to handle simple cases.
///
/// This function tries to find an AddRec expression for the simplest (yet most
/// common) cases: PN = PHI(Start, OP(Self, LoopInvariant)).
/// If it fails, createAddRecFromPHI will use a more general, but slow,
/// technique for finding the AddRec expression.
const SCEV *ScalarEvolution::createSimpleAffineAddRec(PHINode *PN,
                                                      Value *BEValueV,
                                                      Value *StartValueV) {
  const Loop *L = LI.getLoopFor(PN->getParent());
  assert(L && L->getHeader() == PN->getParent());
  assert(BEValueV && StartValueV);
 
  const SCEV *Accum = nullptr;
  SCEVFlags Flags = SCEV::FlagNone;
  if (auto BO = MatchBinaryOp(BEValueV, getDataLayout(), AC, DT, PN)) {
    if (BO->Opcode != Instruction::Add)
      return nullptr;
 
    if (BO->LHS == PN && L->isLoopInvariant(BO->RHS))
      Accum = getSCEV(BO->RHS);
    else if (BO->RHS == PN && L->isLoopInvariant(BO->LHS))
      Accum = getSCEV(BO->LHS);
 
    if (!Accum)
      return nullptr;
 
    if (BO->IsNUW)
      Flags = setFlags(Flags, SCEV::FlagNUW);
    if (BO->IsNSW)
      Flags = setFlags(Flags, SCEV::FlagNSW);
  } else {
    // Handle pointer induction variable: PN = PHI(Start, gep PN,
    // LoopInvariant).
    auto *GEP = dyn_cast<GEPOperator>(BEValueV);
    if (!GEP || GEP->getPointerOperand() != PN || GEP->getNumIndices() != 1)
      return nullptr;
    Value *Idx = *GEP->idx_begin();
    if (!L->isLoopInvariant(Idx))
      return nullptr;
 
    Type *IntIdxTy = getEffectiveSCEVType(GEP->getType());
    Accum = getMulExpr(getTruncateOrSignExtend(getSCEV(Idx), IntIdxTy),
                       getSizeOfExpr(IntIdxTy, GEP->getSourceElementType()));
    Flags = getNoWrapFlagsForGEP(GEP, Accum, *this);
  }
 
  const SCEV *StartVal = getSCEV(StartValueV);
  const SCEV *PHISCEV = getAddRecExpr(StartVal, Accum, L, Flags);
  insertValueToMap(PN, PHISCEV);
 
  if (auto *AR = dyn_cast<SCEVAddRecExpr>(PHISCEV))
    inferNoWrapViaConstantRanges(AR);
 
  // We can add Flags to the post-inc expression only if we
  // know that it is *undefined behavior* for BEValueV to
  // overflow.
  if (auto *BEInst = dyn_cast<Instruction>(BEValueV)) {
    assert(isLoopInvariant(Accum, L) &&
           "Accum is defined outside L, but is not invariant?");
    if (isAddRecNeverPoison(BEInst, L))
      (void)getAddRecExpr(getAddExpr(StartVal, Accum), Accum, L, Flags);
  }
 
  return PHISCEV;
}
 
const SCEV *ScalarEvolution::createAddRecFromPHI(PHINode *PN) {
  const Loop *L = LI.getLoopFor(PN->getParent());
  if (!L || L->getHeader() != PN->getParent())
    return nullptr;
 
  // The loop may have multiple entrances or multiple exits; we can analyze
  // this phi as an addrec if it has a unique entry value and a unique
  // backedge value.
  Value *BEValueV = nullptr, *StartValueV = nullptr;
  for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
    Value *V = PN->getIncomingValue(i);
    if (L->contains(PN->getIncomingBlock(i))) {
      if (!BEValueV) {
        BEValueV = V;
      } else if (BEValueV != V) {
        BEValueV = nullptr;
        break;
      }
    } else if (!StartValueV) {
      StartValueV = V;
    } else if (StartValueV != V) {
      StartValueV = nullptr;
      break;
    }
  }
  if (!BEValueV || !StartValueV)
    return nullptr;
 
  assert(ValueExprMap.find_as(PN) == ValueExprMap.end() &&
         "PHI node already processed?");
 
  // First, try to find AddRec expression without creating a fictituos symbolic
  // value for PN.
  if (auto *S = createSimpleAffineAddRec(PN, BEValueV, StartValueV))
    return S;
 
  // Handle PHI node value symbolically.
  const SCEV *SymbolicName = getUnknown(PN);
  insertValueToMap(PN, SymbolicName);
 
  // Using this symbolic name for the PHI, analyze the value coming around
  // the back-edge.
  const SCEV *BEValue = getSCEV(BEValueV);
 
  // NOTE: If BEValue is loop invariant, we know that the PHI node just
  // has a special value for the first iteration of the loop.
 
  // If the value coming around the backedge is an add with the symbolic
  // value we just inserted, then we found a simple induction variable!
  if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(BEValue)) {
    // If there is a single occurrence of the symbolic value, replace it
    // with a recurrence.
    unsigned FoundIndex = Add->getNumOperands();
    for (unsigned i = 0, e = Add->getNumOperands(); i != e; ++i)
      if (Add->getOperand(i) == SymbolicName)
        if (FoundIndex == e) {
          FoundIndex = i;
          break;
        }
 
    if (FoundIndex != Add->getNumOperands()) {
      // Create an add with everything but the specified operand.
      SmallVector<SCEVUse, 8> Ops;
      for (unsigned i = 0, e = Add->getNumOperands(); i != e; ++i)
        if (i != FoundIndex)
          Ops.push_back(SCEVBackedgeConditionFolder::rewrite(Add->getOperand(i),
                                                             L, *this));
      const SCEV *Accum = getAddExpr(Ops);
 
      // This is not a valid addrec if the step amount is varying each
      // loop iteration, but is not itself an addrec in this loop.
      if (isLoopInvariant(Accum, L) ||
          (isa<SCEVAddRecExpr>(Accum) &&
           cast<SCEVAddRecExpr>(Accum)->getLoop() == L)) {
        SCEVFlags Flags = SCEV::FlagNone;
 
        if (auto BO = MatchBinaryOp(BEValueV, getDataLayout(), AC, DT, PN)) {
          if (BO->Opcode == Instruction::Add && BO->LHS == PN) {
            if (BO->IsNUW)
              Flags = setFlags(Flags, SCEV::FlagNUW);
            if (BO->IsNSW)
              Flags = setFlags(Flags, SCEV::FlagNSW);
          }
        } else if (GEPOperator *GEP = dyn_cast<GEPOperator>(BEValueV)) {
          if (GEP->getOperand(0) == PN)
            Flags = getNoWrapFlagsForGEP(GEP, Accum, *this);
 
          // We cannot transfer nuw and nsw flags from subtraction
          // operations -- sub nuw X, Y is not the same as add nuw X, -Y
          // for instance.
        }
 
        const SCEV *StartVal = getSCEV(StartValueV);
        const SCEV *PHISCEV = getAddRecExpr(StartVal, Accum, L, Flags);
 
        // Okay, for the entire analysis of this edge we assumed the PHI
        // to be symbolic.  We now need to go back and purge all of the
        // entries for the scalars that use the symbolic expression.
        forgetMemoizedResults({SymbolicName});
        insertValueToMap(PN, PHISCEV);
 
        if (auto *AR = dyn_cast<SCEVAddRecExpr>(PHISCEV))
          inferNoWrapViaConstantRanges(AR);
 
        // We can add Flags to the post-inc expression only if we
        // know that it is *undefined behavior* for BEValueV to
        // overflow.
        if (auto *BEInst = dyn_cast<Instruction>(BEValueV))
          if (isLoopInvariant(Accum, L) && isAddRecNeverPoison(BEInst, L))
            (void)getAddRecExpr(getAddExpr(StartVal, Accum), Accum, L, Flags);
 
        return PHISCEV;
      }
    }
  } else {
    // Otherwise, this could be a loop like this:
    //     i = 0;  for (j = 1; ..; ++j) { ....  i = j; }
    // In this case, j = {1,+,1}  and BEValue is j.
    // Because the other in-value of i (0) fits the evolution of BEValue
    // i really is an addrec evolution.
    //
    // We can generalize this saying that i is the shifted value of BEValue
    // by one iteration:
    //   PHI(f(0), f({1,+,1})) --> f({0,+,1})
 
    // Do not allow refinement in rewriting of BEValue.
    const SCEV *Shifted = SCEVShiftRewriter::rewrite(BEValue, L, *this);
    const SCEV *Start = SCEVInitRewriter::rewrite(Shifted, L, *this, false);
    if (Shifted != getCouldNotCompute() && Start != getCouldNotCompute() &&
        isGuaranteedNotToCauseUB(Shifted) && ::impliesPoison(Shifted, Start)) {
      const SCEV *StartVal = getSCEV(StartValueV);
      if (Start == StartVal) {
        // Okay, for the entire analysis of this edge we assumed the PHI
        // to be symbolic.  We now need to go back and purge all of the
        // entries for the scalars that use the symbolic expression.
        forgetMemoizedResults({SymbolicName});
        insertValueToMap(PN, Shifted);
        return Shifted;
      }
    }
  }
 
  // Remove the temporary PHI node SCEV that has been inserted while intending
  // to create an AddRecExpr for this PHI node. We can not keep this temporary
  // as it will prevent later (possibly simpler) SCEV expressions to be added
  // to the ValueExprMap.
  eraseValueFromMap(PN);
 
  return nullptr;
}
 
// Try to match a control flow sequence that branches out at BI and merges back
// at Merge into a "C ? LHS : RHS" select pattern.  Return true on a successful
// match.
static bool BrPHIToSelect(DominatorTree &DT, CondBrInst *BI, PHINode *Merge,
                          Value *&C, Value *&LHS, Value *&RHS) {
  C = BI->getCondition();
 
  BasicBlockEdge LeftEdge(BI->getParent(), BI->getSuccessor(0));
  BasicBlockEdge RightEdge(BI->getParent(), BI->getSuccessor(1));
 
  Use &LeftUse = Merge->getOperandUse(0);
  Use &RightUse = Merge->getOperandUse(1);
 
  if (DT.dominates(LeftEdge, LeftUse) && DT.dominates(RightEdge, RightUse)) {
    LHS = LeftUse;
    RHS = RightUse;
    return true;
  }
 
  if (DT.dominates(LeftEdge, RightUse) && DT.dominates(RightEdge, LeftUse)) {
    LHS = RightUse;
    RHS = LeftUse;
    return true;
  }
 
  return false;
}
 
static bool getOperandsForSelectLikePHI(DominatorTree &DT, PHINode *PN,
                                        Value *&Cond, Value *&LHS,
                                        Value *&RHS) {
  auto IsReachable =
      [&](BasicBlock *BB) { return DT.isReachableFromEntry(BB); };
  if (PN->getNumIncomingValues() == 2 && all_of(PN->blocks(), IsReachable)) {
    // Try to match
    //
    //  br %cond, label %left, label %right
    // left:
    //  br label %merge
    // right:
    //  br label %merge
    // merge:
    //  V = phi [ %x, %left ], [ %y, %right ]
    //
    // as "select %cond, %x, %y"
 
    BasicBlock *IDom = DT[PN->getParent()]->getIDom()->getBlock();
    assert(IDom && "At least the entry block should dominate PN");
 
    auto *BI = dyn_cast<CondBrInst>(IDom->getTerminator());
    return BI && BrPHIToSelect(DT, BI, PN, Cond, LHS, RHS);
  }
  return false;
}
 
const SCEV *ScalarEvolution::createNodeFromSelectLikePHI(PHINode *PN) {
  Value *Cond = nullptr, *LHS = nullptr, *RHS = nullptr;
  if (getOperandsForSelectLikePHI(DT, PN, Cond, LHS, RHS) &&
      properlyDominates(getSCEV(LHS), PN->getParent()) &&
      properlyDominates(getSCEV(RHS), PN->getParent()))
    return createNodeForSelectOrPHI(PN, Cond, LHS, RHS);
 
  return nullptr;
}
 
static BinaryOperator *getCommonInstForPHI(PHINode *PN) {
  BinaryOperator *CommonInst = nullptr;
  // Check if instructions are identical.
  for (Value *Incoming : PN->incoming_values()) {
    auto *IncomingInst = dyn_cast<BinaryOperator>(Incoming);
    if (!IncomingInst)
      return nullptr;
    if (CommonInst) {
      if (!CommonInst->isIdenticalToWhenDefined(IncomingInst))
        return nullptr; // Not identical, give up
    } else {
      // Remember binary operator
      CommonInst = IncomingInst;
    }
  }
  return CommonInst;
}
 
/// Returns SCEV for the first operand of a phi if all phi operands have
/// identical opcodes and operands
/// eg.
/// a: %add = %a + %b
///    br %c
/// b: %add1 = %a + %b
///    br %c
/// c: %phi = phi [%add, a], [%add1, b]
/// scev(%phi) => scev(%add)
const SCEV *
ScalarEvolution::createNodeForPHIWithIdenticalOperands(PHINode *PN) {
  BinaryOperator *CommonInst = getCommonInstForPHI(PN);
  if (!CommonInst)
    return nullptr;
 
  // Check if SCEV exprs for instructions are identical.
  const SCEV *CommonSCEV = getSCEV(CommonInst);
  bool SCEVExprsIdentical =
      all_of(drop_begin(PN->incoming_values()),
             [this, CommonSCEV](Value *V) { return CommonSCEV == getSCEV(V); });
  return SCEVExprsIdentical ? CommonSCEV : nullptr;
}
 
const SCEV *ScalarEvolution::createNodeForPHI(PHINode *PN) {
  if (const SCEV *S = createAddRecFromPHI(PN))
    return S;
 
  // We do not allow simplifying phi (undef, X) to X here, to avoid reusing the
  // phi node for X.
  if (Value *V = simplifyInstruction(
          PN, {getDataLayout(), &TLI, &DT, &AC, /*CtxI=*/nullptr,
               /*UseInstrInfo=*/true, /*CanUseUndef=*/false}))
    return getSCEV(V);
 
  if (const SCEV *S = createNodeForPHIWithIdenticalOperands(PN))
    return S;
 
  if (const SCEV *S = createNodeFromSelectLikePHI(PN))
    return S;
 
  // If it's not a loop phi, we can't handle it yet.
  return getUnknown(PN);
}
 
bool SCEVMinMaxExprContains(const SCEV *Root, const SCEV *OperandToFind,
                            SCEVTypes RootKind) {
  struct FindClosure {
    const SCEV *OperandToFind;
    const SCEVTypes RootKind; // Must be a sequential min/max expression.
    const SCEVTypes NonSequentialRootKind; // Non-seq variant of RootKind.
 
    bool Found = false;
 
    bool canRecurseInto(SCEVTypes Kind) const {
      // We can only recurse into the SCEV expression of the same effective type
      // as the type of our root SCEV expression, and into zero-extensions.
      return RootKind == Kind || NonSequentialRootKind == Kind ||
             scZeroExtend == Kind;
    };
 
    FindClosure(const SCEV *OperandToFind, SCEVTypes RootKind)
        : OperandToFind(OperandToFind), RootKind(RootKind),
          NonSequentialRootKind(
              SCEVSequentialMinMaxExpr::getEquivalentNonSequentialSCEVType(
                  RootKind)) {}
 
    bool follow(const SCEV *S) {
      Found = S == OperandToFind;
 
      return !isDone() && canRecurseInto(S->getSCEVType());
    }
 
    bool isDone() const { return Found; }
  };
 
  FindClosure FC(OperandToFind, RootKind);
  visitAll(Root, FC);
  return FC.Found;
}
 
std::optional<const SCEV *>
ScalarEvolution::createNodeForSelectOrPHIInstWithICmpInstCond(Type *Ty,
                                                              ICmpInst *Cond,
                                                              Value *TrueVal,
                                                              Value *FalseVal) {
  // Try to match some simple smax or umax patterns.
  auto *ICI = Cond;
 
  Value *LHS = ICI->getOperand(0);
  Value *RHS = ICI->getOperand(1);
 
  switch (ICI->getPredicate()) {
  case ICmpInst::ICMP_SLT:
  case ICmpInst::ICMP_SLE:
  case ICmpInst::ICMP_ULT:
  case ICmpInst::ICMP_ULE:
    std::swap(LHS, RHS);
    [[fallthrough]];
  case ICmpInst::ICMP_SGT:
  case ICmpInst::ICMP_SGE:
  case ICmpInst::ICMP_UGT:
  case ICmpInst::ICMP_UGE:
    // a > b ? a+x : b+x  ->  max(a, b)+x
    // a > b ? b+x : a+x  ->  min(a, b)+x
    if (getTypeSizeInBits(LHS->getType()) <= getTypeSizeInBits(Ty)) {
      bool Signed = ICI->isSigned();
      const SCEV *LA = getSCEV(TrueVal);
      const SCEV *RA = getSCEV(FalseVal);
      const SCEV *LS = getSCEV(LHS);
      const SCEV *RS = getSCEV(RHS);
      if (LA->getType()->isPointerTy()) {
        // FIXME: Handle cases where LS/RS are pointers not equal to LA/RA.
        // Need to make sure we can't produce weird expressions involving
        // negated pointers.
        if (LA == LS && RA == RS)
          return Signed ? getSMaxExpr(LS, RS) : getUMaxExpr(LS, RS);
        if (LA == RS && RA == LS)
          return Signed ? getSMinExpr(LS, RS) : getUMinExpr(LS, RS);
      }
      auto CoerceOperand = [&](const SCEV *Op) -> const SCEV * {
        if (Op->getType()->isPointerTy()) {
          Op = getPtrToAddrExpr(Op);
          if (isa<SCEVCouldNotCompute>(Op))
            return Op;
        }
        if (Signed)
          Op = getNoopOrSignExtend(Op, Ty);
        else
          Op = getNoopOrZeroExtend(Op, Ty);
        return Op;
      };
      LS = CoerceOperand(LS);
      RS = CoerceOperand(RS);
      if (isa<SCEVCouldNotCompute>(LS) || isa<SCEVCouldNotCompute>(RS))
        break;
      const SCEV *LDiff = getMinusSCEV(LA, LS);
      const SCEV *RDiff = getMinusSCEV(RA, RS);
      if (LDiff == RDiff)
        return getAddExpr(Signed ? getSMaxExpr(LS, RS) : getUMaxExpr(LS, RS),
                          LDiff);
      LDiff = getMinusSCEV(LA, RS);
      RDiff = getMinusSCEV(RA, LS);
      if (LDiff == RDiff)
        return getAddExpr(Signed ? getSMinExpr(LS, RS) : getUMinExpr(LS, RS),
                          LDiff);
    }
    break;
  case ICmpInst::ICMP_NE:
    // x != 0 ? x+y : C+y  ->  x == 0 ? C+y : x+y
    std::swap(TrueVal, FalseVal);
    [[fallthrough]];
  case ICmpInst::ICMP_EQ:
    // x == 0 ? C+y : x+y  ->  umax(x, C)+y   iff C u<= 1
    if (getTypeSizeInBits(LHS->getType()) <= getTypeSizeInBits(Ty) &&
        isa<ConstantInt>(RHS) && cast<ConstantInt>(RHS)->isZero()) {
      const SCEV *X = getNoopOrZeroExtend(getSCEV(LHS), Ty);
      const SCEV *TrueValExpr = getSCEV(TrueVal);    // C+y
      const SCEV *FalseValExpr = getSCEV(FalseVal);  // x+y
      const SCEV *Y = getMinusSCEV(FalseValExpr, X); // y = (x+y)-x
      const SCEV *C = getMinusSCEV(TrueValExpr, Y);  // C = (C+y)-y
      if (isa<SCEVConstant>(C) && cast<SCEVConstant>(C)->getAPInt().ule(1))
        return getAddExpr(getUMaxExpr(X, C), Y);
    }
    // x == 0 ? 0 : umin    (..., x, ...)  ->  umin_seq(x, umin    (...))
    // x == 0 ? 0 : umin_seq(..., x, ...)  ->  umin_seq(x, umin_seq(...))
    // x == 0 ? 0 : umin    (..., umin_seq(..., x, ...), ...)
    //                    ->  umin_seq(x, umin (..., umin_seq(...), ...))
    if (isa<ConstantInt>(RHS) && cast<ConstantInt>(RHS)->isZero() &&
        isa<ConstantInt>(TrueVal) && cast<ConstantInt>(TrueVal)->isZero()) {
      const SCEV *X = getSCEV(LHS);
      while (auto *ZExt = dyn_cast<SCEVZeroExtendExpr>(X))
        X = ZExt->getOperand();
      if (getTypeSizeInBits(X->getType()) <= getTypeSizeInBits(Ty)) {
        const SCEV *FalseValExpr = getSCEV(FalseVal);
        if (SCEVMinMaxExprContains(FalseValExpr, X, scSequentialUMinExpr))
          return getUMinExpr(getNoopOrZeroExtend(X, Ty), FalseValExpr,
                             /*Sequential=*/true);
      }
    }
    break;
  default:
    break;
  }
 
  return std::nullopt;
}
 
static std::optional<const SCEV *>
createNodeForSelectViaUMinSeq(ScalarEvolution *SE, const SCEV *CondExpr,
                              const SCEV *TrueExpr, const SCEV *FalseExpr) {
  assert(CondExpr->getType()->isIntegerTy(1) &&
         TrueExpr->getType() == FalseExpr->getType() &&
         TrueExpr->getType()->isIntegerTy(1) &&
         "Unexpected operands of a select.");
 
  // i1 cond ? i1 x : i1 C  -->  C + (i1  cond ? (i1 x - i1 C) : i1 0)
  //                        -->  C + (umin_seq  cond, x - C)
  //
  // i1 cond ? i1 C : i1 x  -->  C + (i1  cond ? i1 0 : (i1 x - i1 C))
  //                        -->  C + (i1 ~cond ? (i1 x - i1 C) : i1 0)
  //                        -->  C + (umin_seq ~cond, x - C)
 
  // FIXME: while we can't legally model the case where both of the hands
  // are fully variable, we only require that the *difference* is constant.
  if (!isa<SCEVConstant>(TrueExpr) && !isa<SCEVConstant>(FalseExpr))
    return std::nullopt;
 
  const SCEV *X, *C;
  if (isa<SCEVConstant>(TrueExpr)) {
    CondExpr = SE->getNotSCEV(CondExpr);
    X = FalseExpr;
    C = TrueExpr;
  } else {
    X = TrueExpr;
    C = FalseExpr;
  }
  return SE->getAddExpr(C, SE->getUMinExpr(CondExpr, SE->getMinusSCEV(X, C),
                                           /*Sequential=*/true));
}
 
static std::optional<const SCEV *>
createNodeForSelectViaUMinSeq(ScalarEvolution *SE, Value *Cond, Value *TrueVal,
                              Value *FalseVal) {
  if (!isa<ConstantInt>(TrueVal) && !isa<ConstantInt>(FalseVal))
    return std::nullopt;
 
  const auto *SECond = SE->getSCEV(Cond);
  const auto *SETrue = SE->getSCEV(TrueVal);
  const auto *SEFalse = SE->getSCEV(FalseVal);
  return createNodeForSelectViaUMinSeq(SE, SECond, SETrue, SEFalse);
}
 
const SCEV *ScalarEvolution::createNodeForSelectOrPHIViaUMinSeq(
    Value *V, Value *Cond, Value *TrueVal, Value *FalseVal) {
  assert(Cond->getType()->isIntegerTy(1) && "Select condition is not an i1?");
  assert(TrueVal->getType() == FalseVal->getType() &&
         V->getType() == TrueVal->getType() &&
         "Types of select hands and of the result must match.");
 
  // For now, only deal with i1-typed `select`s.
  if (!V->getType()->isIntegerTy(1))
    return getUnknown(V);
 
  if (std::optional<const SCEV *> S =
          createNodeForSelectViaUMinSeq(this, Cond, TrueVal, FalseVal))
    return *S;
 
  return getUnknown(V);
}
 
const SCEV *ScalarEvolution::createNodeForSelectOrPHI(Value *V, Value *Cond,
                                                      Value *TrueVal,
                                                      Value *FalseVal) {
  // Handle "constant" branch or select. This can occur for instance when a
  // loop pass transforms an inner loop and moves on to process the outer loop.
  if (auto *CI = dyn_cast<ConstantInt>(Cond))
    return getSCEV(CI->isOne() ? TrueVal : FalseVal);
 
  if (auto *I = dyn_cast<Instruction>(V)) {
    if (auto *ICI = dyn_cast<ICmpInst>(Cond)) {
      if (std::optional<const SCEV *> S =
              createNodeForSelectOrPHIInstWithICmpInstCond(I->getType(), ICI,
                                                           TrueVal, FalseVal))
        return *S;
    }
  }
 
  return createNodeForSelectOrPHIViaUMinSeq(V, Cond, TrueVal, FalseVal);
}
 
/// Expand GEP instructions into add and multiply operations. This allows them
/// to be analyzed by regular SCEV code.
const SCEV *ScalarEvolution::createNodeForGEP(GEPOperator *GEP) {
  assert(GEP->getSourceElementType()->isSized() &&
         "GEP source element type must be sized");
 
  SmallVector<SCEVUse, 4> IndexExprs;
  for (Value *Index : GEP->indices())
    IndexExprs.push_back(getSCEV(Index));
  return getGEPExpr(GEP, IndexExprs);
}
 
APInt ScalarEvolution::getConstantMultipleImpl(const SCEV *S,
                                               const Instruction *CtxI) {
  uint64_t BitWidth = getTypeSizeInBits(S->getType());
  auto GetShiftedByZeros = [BitWidth](uint32_t TrailingZeros) {
    return TrailingZeros >= BitWidth
               ? APInt::getZero(BitWidth)
               : APInt::getOneBitSet(BitWidth, TrailingZeros);
  };
  auto GetGCDMultiple = [this, CtxI](const SCEVNAryExpr *N) {
    // The result is GCD of all operands results.
    APInt Res = getConstantMultiple(N->getOperand(0), CtxI);
    for (unsigned I = 1, E = N->getNumOperands(); I < E && Res != 1; ++I)
      Res = APIntOps::GreatestCommonDivisor(
          Res, getConstantMultiple(N->getOperand(I), CtxI));
    return Res;
  };
 
  switch (S->getSCEVType()) {
  case scConstant:
    return cast<SCEVConstant>(S)->getAPInt();
  case scPtrToAddr:
    return getConstantMultiple(cast<SCEVCastExpr>(S)->getOperand());
  case scUDivExpr:
  case scVScale:
    return APInt(BitWidth, 1);
  case scTruncate: {
    // Only multiples that are a power of 2 will hold after truncation.
    const SCEVTruncateExpr *T = cast<SCEVTruncateExpr>(S);
    uint32_t TZ = getMinTrailingZeros(T->getOperand(), CtxI);
    return GetShiftedByZeros(TZ);
  }
  case scZeroExtend: {
    const SCEVZeroExtendExpr *Z = cast<SCEVZeroExtendExpr>(S);
    return getConstantMultiple(Z->getOperand(), CtxI).zext(BitWidth);
  }
  case scSignExtend: {
    // Only multiples that are a power of 2 will hold after sext.
    const SCEVSignExtendExpr *E = cast<SCEVSignExtendExpr>(S);
    uint32_t TZ = getMinTrailingZeros(E->getOperand(), CtxI);
    return GetShiftedByZeros(TZ);
  }
  case scMulExpr: {
    const SCEVMulExpr *M = cast<SCEVMulExpr>(S);
    if (M->hasNoUnsignedWrap()) {
      // The result is the product of all operand results.
      APInt Res = getConstantMultiple(M->getOperand(0), CtxI);
      for (const SCEV *Operand : M->operands().drop_front())
        Res = Res * getConstantMultiple(Operand, CtxI);
      return Res;
    }
 
    // If there are no wrap guarentees, find the trailing zeros, which is the
    // sum of trailing zeros for all its operands.
    uint32_t TZ = 0;
    for (const SCEV *Operand : M->operands())
      TZ += getMinTrailingZeros(Operand, CtxI);
    return GetShiftedByZeros(TZ);
  }
  case scAddExpr:
  case scAddRecExpr: {
    const SCEVNAryExpr *N = cast<SCEVNAryExpr>(S);
    if (N->hasNoUnsignedWrap())
        return GetGCDMultiple(N);
    // Find the trailing bits, which is the minimum of its operands.
    uint32_t TZ = getMinTrailingZeros(N->getOperand(0), CtxI);
    for (const SCEV *Operand : N->operands().drop_front())
      TZ = std::min(TZ, getMinTrailingZeros(Operand, CtxI));
    return GetShiftedByZeros(TZ);
  }
  case scUMaxExpr:
  case scSMaxExpr:
  case scUMinExpr:
  case scSMinExpr:
  case scSequentialUMinExpr:
    return GetGCDMultiple(cast<SCEVNAryExpr>(S));
  case scUnknown: {
    // Ask ValueTracking for known bits. SCEVUnknown only become available at
    // the point their underlying IR instruction has been defined. If CtxI was
    // not provided, use:
    // * the first instruction in the entry block if it is an argument
    // * the instruction itself otherwise.
    const SCEVUnknown *U = cast<SCEVUnknown>(S);
    if (!CtxI) {
      if (isa<Argument>(U->getValue()))
        CtxI = &*F.getEntryBlock().begin();
      else if (auto *I = dyn_cast<Instruction>(U->getValue()))
        CtxI = I;
    }
    unsigned Known =
        computeKnownBits(U->getValue(),
                         SimplifyQuery(getDataLayout(), &DT, &AC, CtxI)
                             .allowEphemerals(true))
            .countMinTrailingZeros();
    return GetShiftedByZeros(Known);
  }
  case scCouldNotCompute:
    llvm_unreachable("Attempt to use a SCEVCouldNotCompute object!");
  }
  llvm_unreachable("Unknown SCEV kind!");
}
 
APInt ScalarEvolution::getConstantMultiple(const SCEV *S,
                                           const Instruction *CtxI) {
  // Skip looking up and updating the cache if there is a context instruction,
  // as the result will only be valid in the specified context.
  if (CtxI)
    return getConstantMultipleImpl(S, CtxI);
 
  auto I = ConstantMultipleCache.find(S);
  if (I != ConstantMultipleCache.end())
    return I->second;
 
  APInt Result = getConstantMultipleImpl(S, CtxI);
  auto InsertPair = ConstantMultipleCache.insert({S, Result});
  assert(InsertPair.second && "Should insert a new key");
  return InsertPair.first->second;
}
 
APInt ScalarEvolution::getNonZeroConstantMultiple(const SCEV *S) {
  APInt Multiple = getConstantMultiple(S);
  return Multiple == 0 ? APInt(Multiple.getBitWidth(), 1) : Multiple;
}
 
uint32_t ScalarEvolution::getMinTrailingZeros(const SCEV *S,
                                              const Instruction *CtxI) {
  return std::min(getConstantMultiple(S, CtxI).countTrailingZeros(),
                  (unsigned)getTypeSizeInBits(S->getType()));
}
 
/// Helper method to assign a range to V from metadata present in the IR.
static std::optional<ConstantRange> GetRangeFromMetadata(Value *V) {
  if (Instruction *I = dyn_cast<Instruction>(V)) {
    if (MDNode *MD = I->getMetadata(LLVMContext::MD_range))
      return getConstantRangeFromMetadata(*MD);
    if (const auto *CB = dyn_cast<CallBase>(V))
      if (std::optional<ConstantRange> Range = CB->getRange())
        return Range;
  }
  if (auto *A = dyn_cast<Argument>(V))
    if (std::optional<ConstantRange> Range = A->getRange())
      return Range;
 
  return std::nullopt;
}
 
void ScalarEvolution::setNoWrapFlags(SCEVAddRecExpr *AddRec, SCEVFlags Flags) {
  SCEVFlags NWFlags = Flags & SCEV::FlagsNoWrapMask;
  if (AddRec->getNoWrapFlags(NWFlags) != NWFlags) {
    AddRec->setNoWrapFlags(NWFlags);
    UnsignedRanges.erase(AddRec);
    SignedRanges.erase(AddRec);
    ConstantMultipleCache.erase(AddRec);
  }
}
 
ConstantRange ScalarEvolution::
getRangeForUnknownRecurrence(const SCEVUnknown *U) {
  const DataLayout &DL = getDataLayout();
 
  unsigned BitWidth = getTypeSizeInBits(U->getType());
  const ConstantRange FullSet(BitWidth, /*isFullSet=*/true);
 
  // Match a simple recurrence of the form: <start, ShiftOp, Step>, and then
  // use information about the trip count to improve our available range.  Note
  // that the trip count independent cases are already handled by known bits.
  // WARNING: The definition of recurrence used here is subtly different than
  // the one used by AddRec (and thus most of this file).  Step is allowed to
  // be arbitrarily loop varying here, where AddRec allows only loop invariant
  // and other addrecs in the same loop (for non-affine addrecs).  The code
  // below intentionally handles the case where step is not loop invariant.
  auto *P = dyn_cast<PHINode>(U->getValue());
  if (!P)
    return FullSet;
 
  // Make sure that no Phi input comes from an unreachable block. Otherwise,
  // even the values that are not available in these blocks may come from them,
  // and this leads to false-positive recurrence test.
  for (auto *Pred : predecessors(P->getParent()))
    if (!DT.isReachableFromEntry(Pred))
      return FullSet;
 
  BinaryOperator *BO;
  Value *Start, *Step;
  if (!matchSimpleRecurrence(P, BO, Start, Step))
    return FullSet;
 
  // If we found a recurrence in reachable code, we must be in a loop. Note
  // that BO might be in some subloop of L, and that's completely okay.
  auto *L = LI.getLoopFor(P->getParent());
  assert(L && L->getHeader() == P->getParent());
  if (!L->contains(BO->getParent()))
    // NOTE: This bailout should be an assert instead.  However, asserting
    // the condition here exposes a case where LoopFusion is querying SCEV
    // with malformed loop information during the midst of the transform.
    // There doesn't appear to be an obvious fix, so for the moment bailout
    // until the caller issue can be fixed.  PR49566 tracks the bug.
    return FullSet;
 
  // TODO: Extend to other opcodes such as mul, and div
  switch (BO->getOpcode()) {
  default:
    return FullSet;
  case Instruction::AShr:
  case Instruction::LShr:
  case Instruction::Shl:
    break;
  };
 
  if (BO->getOperand(0) != P)
    // TODO: Handle the power function forms some day.
    return FullSet;
 
  unsigned TC = getSmallConstantMaxTripCount(L);
  if (!TC || TC >= BitWidth)
    return FullSet;
 
  auto KnownStart = computeKnownBits(Start, DL, &AC, nullptr, &DT);
  auto KnownStep = computeKnownBits(Step, DL, &AC, nullptr, &DT);
  assert(KnownStart.getBitWidth() == BitWidth &&
         KnownStep.getBitWidth() == BitWidth);
 
  // Compute total shift amount, being careful of overflow and bitwidths.
  auto MaxShiftAmt = KnownStep.getMaxValue();
  APInt TCAP(BitWidth, TC-1);
  bool Overflow = false;
  auto TotalShift = MaxShiftAmt.umul_ov(TCAP, Overflow);
  if (Overflow)
    return FullSet;
 
  switch (BO->getOpcode()) {
  default:
    llvm_unreachable("filtered out above");
  case Instruction::AShr: {
    // For each ashr, three cases:
    //   shift = 0 => unchanged value
    //   saturation => 0 or -1
    //   other => a value closer to zero (of the same sign)
    // Thus, the end value is closer to zero than the start.
    auto KnownEnd = KnownBits::ashr(KnownStart,
                                    KnownBits::makeConstant(TotalShift));
    if (KnownStart.isNonNegative())
      // Analogous to lshr (simply not yet canonicalized)
      return ConstantRange::getNonEmpty(KnownEnd.getMinValue(),
                                        KnownStart.getMaxValue() + 1);
    if (KnownStart.isNegative())
      // End >=u Start && End <=s Start
      return ConstantRange::getNonEmpty(KnownStart.getMinValue(),
                                        KnownEnd.getMaxValue() + 1);
    break;
  }
  case Instruction::LShr: {
    // For each lshr, three cases:
    //   shift = 0 => unchanged value
    //   saturation => 0
    //   other => a smaller positive number
    // Thus, the low end of the unsigned range is the last value produced.
    auto KnownEnd = KnownBits::lshr(KnownStart,
                                    KnownBits::makeConstant(TotalShift));
    return ConstantRange::getNonEmpty(KnownEnd.getMinValue(),
                                      KnownStart.getMaxValue() + 1);
  }
  case Instruction::Shl: {
    // Iff no bits are shifted out, value increases on every shift.
    auto KnownEnd = KnownBits::shl(KnownStart,
                                   KnownBits::makeConstant(TotalShift));
    if (TotalShift.ult(KnownStart.countMinLeadingZeros()))
      return ConstantRange(KnownStart.getMinValue(),
                           KnownEnd.getMaxValue() + 1);
    break;
  }
  };
  return FullSet;
}
 
// The goal of this function is to check if recursively visiting the operands
// of this PHI might lead to an infinite loop. If we do see such a loop,
// there's no good way to break it, so we avoid analyzing such cases.
//
// getRangeRef previously used a visited set to avoid infinite loops, but this
// caused other issues: the result was dependent on the order of getRangeRef
// calls, and the interaction with createSCEVIter could cause a stack overflow
// in some cases (see issue #148253).
//
// FIXME: The way this is implemented is overly conservative; this checks
// for a few obviously safe patterns, but anything that doesn't lead to
// recursion is fine.
static bool RangeRefPHIAllowedOperands(DominatorTree &DT, PHINode *PHI) {
  Value *Cond = nullptr, *LHS = nullptr, *RHS = nullptr;
  if (getOperandsForSelectLikePHI(DT, PHI, Cond, LHS, RHS))
    return true;
 
  if (all_of(PHI->operands(),
             [&](Value *Operand) { return DT.dominates(Operand, PHI); }))
    return true;
 
  return false;
}
 
const ConstantRange &
ScalarEvolution::getRangeRefIter(const SCEV *S,
                                 ScalarEvolution::RangeSignHint SignHint) {
  DenseMap<const SCEV *, ConstantRange> &Cache =
      SignHint == ScalarEvolution::HINT_RANGE_UNSIGNED ? UnsignedRanges
                                                       : SignedRanges;
  SmallVector<SCEVUse> WorkList;
  SmallPtrSet<const SCEV *, 8> Seen;
 
  // Add Expr to the worklist, if Expr is either an N-ary expression or a
  // SCEVUnknown PHI node.
  auto AddToWorklist = [&WorkList, &Seen, &Cache](const SCEV *Expr) {
    if (!Seen.insert(Expr).second)
      return;
    if (Cache.contains(Expr))
      return;
    switch (Expr->getSCEVType()) {
    case scUnknown:
      if (!isa<PHINode>(cast<SCEVUnknown>(Expr)->getValue()))
        break;
      [[fallthrough]];
    case scConstant:
    case scVScale:
    case scTruncate:
    case scZeroExtend:
    case scSignExtend:
    case scPtrToAddr:
    case scAddExpr:
    case scMulExpr:
    case scUDivExpr:
    case scAddRecExpr:
    case scUMaxExpr:
    case scSMaxExpr:
    case scUMinExpr:
    case scSMinExpr:
    case scSequentialUMinExpr:
      WorkList.push_back(Expr);
      break;
    case scCouldNotCompute:
      llvm_unreachable("Attempt to use a SCEVCouldNotCompute object!");
    }
  };
  AddToWorklist(S);
 
  // Build worklist by queuing operands of N-ary expressions and phi nodes.
  for (unsigned I = 0; I != WorkList.size(); ++I) {
    const SCEV *P = WorkList[I];
    auto *UnknownS = dyn_cast<SCEVUnknown>(P);
    // If it is not a `SCEVUnknown`, just recurse into operands.
    if (!UnknownS) {
      for (const SCEV *Op : P->operands())
        AddToWorklist(Op);
      continue;
    }
    // `SCEVUnknown`'s require special treatment.
    if (PHINode *P = dyn_cast<PHINode>(UnknownS->getValue())) {
      if (!RangeRefPHIAllowedOperands(DT, P))
        continue;
      for (auto &Op : reverse(P->operands()))
        AddToWorklist(getSCEV(Op));
    }
  }
 
  if (!WorkList.empty()) {
    // Use getRangeRef to compute ranges for items in the worklist in reverse
    // order. This will force ranges for earlier operands to be computed before
    // their users in most cases.
    for (const SCEV *P : reverse(drop_begin(WorkList))) {
      getRangeRef(P, SignHint);
    }
  }
 
  return getRangeRef(S, SignHint, 0);
}
 
const APInt *ScalarEvolution::getConstantAPIntOrNull(const SCEV *S) {
  if (const auto *C = dyn_cast<SCEVConstant>(S))
    return &C->getAPInt();
  return nullptr;
}
 
/// Determine the range for a particular SCEV.  If SignHint is
/// HINT_RANGE_UNSIGNED (resp. HINT_RANGE_SIGNED) then getRange prefers ranges
/// with a "cleaner" unsigned (resp. signed) representation.
const ConstantRange &ScalarEvolution::getRangeRef(
    const SCEV *S, ScalarEvolution::RangeSignHint SignHint, unsigned Depth) {
  DenseMap<const SCEV *, ConstantRange> &Cache =
      SignHint == ScalarEvolution::HINT_RANGE_UNSIGNED ? UnsignedRanges
                                                       : SignedRanges;
  ConstantRange::PreferredRangeType RangeType =
      SignHint == ScalarEvolution::HINT_RANGE_UNSIGNED ? ConstantRange::Unsigned
                                                       : ConstantRange::Signed;
 
  // See if we've computed this range already.
  auto I = Cache.find(S);
  if (I != Cache.end())
    return I->second;
 
  if (const SCEVConstant *C = dyn_cast<SCEVConstant>(S))
    return setRange(C, SignHint, ConstantRange(C->getAPInt()));
 
  // Switch to iteratively computing the range for S, if it is part of a deeply
  // nested expression.
  if (Depth > RangeIterThreshold)
    return getRangeRefIter(S, SignHint);
 
  unsigned BitWidth = getTypeSizeInBits(S->getType());
  ConstantRange ConservativeResult(BitWidth, /*isFullSet=*/true);
  using OBO = OverflowingBinaryOperator;
 
  // If the value has known zeros, the maximum value will have those known zeros
  // as well.
  if (SignHint == ScalarEvolution::HINT_RANGE_UNSIGNED) {
    APInt Multiple = getNonZeroConstantMultiple(S);
    APInt Remainder = APInt::getMaxValue(BitWidth).urem(Multiple);
    if (!Remainder.isZero())
      ConservativeResult =
          ConstantRange(APInt::getMinValue(BitWidth),
                        APInt::getMaxValue(BitWidth) - Remainder + 1);
  }
  else {
    uint32_t TZ = getMinTrailingZeros(S);
    if (TZ != 0) {
      ConservativeResult = ConstantRange(
          APInt::getSignedMinValue(BitWidth),
          APInt::getSignedMaxValue(BitWidth).ashr(TZ).shl(TZ) + 1);
    }
  }
 
  switch (S->getSCEVType()) {
  case scConstant:
    llvm_unreachable("Already handled above.");
  case scVScale:
    return setRange(S, SignHint, getVScaleRange(&F, BitWidth));
  case scTruncate: {
    const SCEVTruncateExpr *Trunc = cast<SCEVTruncateExpr>(S);
    ConstantRange X = getRangeRef(Trunc->getOperand(), SignHint, Depth + 1);
    return setRange(
        Trunc, SignHint,
        ConservativeResult.intersectWith(X.truncate(BitWidth), RangeType));
  }
  case scZeroExtend: {
    const SCEVZeroExtendExpr *ZExt = cast<SCEVZeroExtendExpr>(S);
    ConstantRange X = getRangeRef(ZExt->getOperand(), SignHint, Depth + 1);
    return setRange(
        ZExt, SignHint,
        ConservativeResult.intersectWith(X.zeroExtend(BitWidth), RangeType));
  }
  case scSignExtend: {
    const SCEVSignExtendExpr *SExt = cast<SCEVSignExtendExpr>(S);
    ConstantRange X = getRangeRef(SExt->getOperand(), SignHint, Depth + 1);
    return setRange(
        SExt, SignHint,
        ConservativeResult.intersectWith(X.signExtend(BitWidth), RangeType));
  }
  case scPtrToAddr: {
    const SCEVCastExpr *Cast = cast<SCEVCastExpr>(S);
    ConstantRange X = getRangeRef(Cast->getOperand(), SignHint, Depth + 1);
    return setRange(Cast, SignHint, X);
  }
  case scAddExpr: {
    const SCEVAddExpr *Add = cast<SCEVAddExpr>(S);
    // Check if this is a URem pattern: A - (A / B) * B, which is always < B.
    const SCEV *URemLHS = nullptr, *URemRHS = nullptr;
    if (SignHint == ScalarEvolution::HINT_RANGE_UNSIGNED &&
        match(S, m_scev_URem(m_SCEV(URemLHS), m_SCEV(URemRHS), *this))) {
      ConstantRange LHSRange = getRangeRef(URemLHS, SignHint, Depth + 1);
      ConstantRange RHSRange = getRangeRef(URemRHS, SignHint, Depth + 1);
      ConservativeResult =
          ConservativeResult.intersectWith(LHSRange.urem(RHSRange), RangeType);
    }
    ConstantRange X = getRangeRef(Add->getOperand(0), SignHint, Depth + 1);
    unsigned WrapType = OBO::AnyWrap;
    if (Add->hasNoSignedWrap())
      WrapType |= OBO::NoSignedWrap;
    if (Add->hasNoUnsignedWrap())
      WrapType |= OBO::NoUnsignedWrap;
    for (const SCEV *Op : drop_begin(Add->operands()))
      X = X.addWithNoWrap(getRangeRef(Op, SignHint, Depth + 1), WrapType,
                          RangeType);
    return setRange(Add, SignHint,
                    ConservativeResult.intersectWith(X, RangeType));
  }
  case scMulExpr: {
    const SCEVMulExpr *Mul = cast<SCEVMulExpr>(S);
    ConstantRange X = getRangeRef(Mul->getOperand(0), SignHint, Depth + 1);
    for (const SCEV *Op : drop_begin(Mul->operands()))
      X = X.multiply(getRangeRef(Op, SignHint, Depth + 1));
    return setRange(Mul, SignHint,
                    ConservativeResult.intersectWith(X, RangeType));
  }
  case scUDivExpr: {
    const SCEVUDivExpr *UDiv = cast<SCEVUDivExpr>(S);
    ConstantRange X = getRangeRef(UDiv->getLHS(), SignHint, Depth + 1);
    ConstantRange Y = getRangeRef(UDiv->getRHS(), SignHint, Depth + 1);
    return setRange(UDiv, SignHint,
                    ConservativeResult.intersectWith(X.udiv(Y), RangeType));
  }
  case scAddRecExpr: {
    const SCEVAddRecExpr *AddRec = cast<SCEVAddRecExpr>(S);
    // If there's no unsigned wrap, the value will never be less than its
    // initial value.
    if (AddRec->hasNoUnsignedWrap()) {
      APInt UnsignedMinValue = getUnsignedRangeMin(AddRec->getStart());
      if (!UnsignedMinValue.isZero())
        ConservativeResult = ConservativeResult.intersectWith(
            ConstantRange(UnsignedMinValue, APInt(BitWidth, 0)), RangeType);
    }
 
    // If there's no signed wrap, and all the operands except initial value have
    // the same sign or zero, the value won't ever be:
    // 1: smaller than initial value if operands are non negative,
    // 2: bigger than initial value if operands are non positive.
    // For both cases, value can not cross signed min/max boundary.
    if (AddRec->hasNoSignedWrap()) {
      bool AllNonNeg = true;
      bool AllNonPos = true;
      for (unsigned i = 1, e = AddRec->getNumOperands(); i != e; ++i) {
        if (!isKnownNonNegative(AddRec->getOperand(i)))
          AllNonNeg = false;
        if (!isKnownNonPositive(AddRec->getOperand(i)))
          AllNonPos = false;
      }
      if (AllNonNeg)
        ConservativeResult = ConservativeResult.intersectWith(
            ConstantRange::getNonEmpty(getSignedRangeMin(AddRec->getStart()),
                                       APInt::getSignedMinValue(BitWidth)),
            RangeType);
      else if (AllNonPos)
        ConservativeResult = ConservativeResult.intersectWith(
            ConstantRange::getNonEmpty(APInt::getSignedMinValue(BitWidth),
                                       getSignedRangeMax(AddRec->getStart()) +
                                           1),
            RangeType);
    }
 
    // TODO: non-affine addrec
    if (AddRec->isAffine()) {
      const SCEV *MaxBEScev =
          getConstantMaxBackedgeTakenCount(AddRec->getLoop());
      if (!isa<SCEVCouldNotCompute>(MaxBEScev)) {
        APInt MaxBECount = cast<SCEVConstant>(MaxBEScev)->getAPInt();
 
        // Adjust MaxBECount to the same bitwidth as AddRec. We can truncate if
        // MaxBECount's active bits are all <= AddRec's bit width.
        if (MaxBECount.getBitWidth() > BitWidth &&
            MaxBECount.getActiveBits() <= BitWidth)
          MaxBECount = MaxBECount.trunc(BitWidth);
        else if (MaxBECount.getBitWidth() < BitWidth)
          MaxBECount = MaxBECount.zext(BitWidth);
 
        if (MaxBECount.getBitWidth() == BitWidth) {
          auto [RangeFromAffine, Flags] = getRangeForAffineAR(
              AddRec->getStart(), AddRec->getStepRecurrence(*this), MaxBECount);
          ConservativeResult =
              ConservativeResult.intersectWith(RangeFromAffine, RangeType);
          const_cast<SCEVAddRecExpr *>(AddRec)->setNoWrapFlags(Flags);
 
          auto RangeFromFactoring = getRangeViaFactoring(
              AddRec->getStart(), AddRec->getStepRecurrence(*this), MaxBECount);
          ConservativeResult =
              ConservativeResult.intersectWith(RangeFromFactoring, RangeType);
        }
      }
 
      // Now try symbolic BE count and more powerful methods.
      if (UseExpensiveRangeSharpening) {
        const SCEV *SymbolicMaxBECount =
            getSymbolicMaxBackedgeTakenCount(AddRec->getLoop());
        if (!isa<SCEVCouldNotCompute>(SymbolicMaxBECount) &&
            getTypeSizeInBits(MaxBEScev->getType()) <= BitWidth &&
            AddRec->hasNoSelfWrap()) {
          auto RangeFromAffineNew = getRangeForAffineNoSelfWrappingAR(
              AddRec, SymbolicMaxBECount, BitWidth, SignHint);
          ConservativeResult =
              ConservativeResult.intersectWith(RangeFromAffineNew, RangeType);
        }
      }
    }
 
    return setRange(AddRec, SignHint, std::move(ConservativeResult));
  }
  case scUMaxExpr:
  case scSMaxExpr:
  case scUMinExpr:
  case scSMinExpr:
  case scSequentialUMinExpr: {
    Intrinsic::ID ID;
    switch (S->getSCEVType()) {
    case scUMaxExpr:
      ID = Intrinsic::umax;
      break;
    case scSMaxExpr:
      ID = Intrinsic::smax;
      break;
    case scUMinExpr:
    case scSequentialUMinExpr:
      ID = Intrinsic::umin;
      break;
    case scSMinExpr:
      ID = Intrinsic::smin;
      break;
    default:
      llvm_unreachable("Unknown SCEVMinMaxExpr/SCEVSequentialMinMaxExpr.");
    }
 
    const auto *NAry = cast<SCEVNAryExpr>(S);
    ConstantRange X = getRangeRef(NAry->getOperand(0), SignHint, Depth + 1);
    for (unsigned i = 1, e = NAry->getNumOperands(); i != e; ++i)
      X = X.intrinsic(
          ID, {X, getRangeRef(NAry->getOperand(i), SignHint, Depth + 1)});
    return setRange(S, SignHint,
                    ConservativeResult.intersectWith(X, RangeType));
  }
  case scUnknown: {
    const SCEVUnknown *U = cast<SCEVUnknown>(S);
    Value *V = U->getValue();
 
    // Check if the IR explicitly contains !range metadata.
    std::optional<ConstantRange> MDRange = GetRangeFromMetadata(V);
    if (MDRange)
      ConservativeResult =
          ConservativeResult.intersectWith(*MDRange, RangeType);
 
    // Use facts about recurrences in the underlying IR.  Note that add
    // recurrences are AddRecExprs and thus don't hit this path.  This
    // primarily handles shift recurrences.
    auto CR = getRangeForUnknownRecurrence(U);
    ConservativeResult = ConservativeResult.intersectWith(CR);
 
    // See if ValueTracking can give us a useful range.
    const DataLayout &DL = getDataLayout();
    KnownBits Known = computeKnownBits(V, DL, &AC, nullptr, &DT);
    if (Known.getBitWidth() != BitWidth)
      Known = Known.zextOrTrunc(BitWidth);
 
    // ValueTracking may be able to compute a tighter result for the number of
    // sign bits than for the value of those sign bits.
    unsigned NS = ComputeNumSignBits(V, DL, &AC, nullptr, &DT);
    if (U->getType()->isPointerTy()) {
      // NS counts the sign bits of the whole pointer; drop those above the
      // index bits.
      unsigned PtrIdxDiff =
          DL.getPointerTypeSizeInBits(U->getType()) - BitWidth;
      NS = NS > PtrIdxDiff ? NS - PtrIdxDiff : 1;
    }
 
    if (NS > 1) {
      // If we know any of the sign bits, we know all of the sign bits.
      if (!Known.Zero.getHiBits(NS).isZero())
        Known.Zero.setHighBits(NS);
      if (!Known.One.getHiBits(NS).isZero())
        Known.One.setHighBits(NS);
    }
 
    if (Known.getMinValue() != Known.getMaxValue() + 1)
      ConservativeResult = ConservativeResult.intersectWith(
          ConstantRange(Known.getMinValue(), Known.getMaxValue() + 1),
          RangeType);
    if (NS > 1)
      ConservativeResult = ConservativeResult.intersectWith(
          ConstantRange(APInt::getSignedMinValue(BitWidth).ashr(NS - 1),
                        APInt::getSignedMaxValue(BitWidth).ashr(NS - 1) + 1),
          RangeType);
 
    if (U->getType()->isPointerTy() && SignHint == HINT_RANGE_UNSIGNED) {
      // Strengthen the range if the underlying IR value is a
      // global/alloca/heap allocation using the size of the object.
      bool CanBeNull;
      uint64_t DerefBytes = V->getPointerDereferenceableBytes(
          DL, CanBeNull, /*CanBeFreed=*/nullptr);
      if (DerefBytes > 1 && isUIntN(BitWidth, DerefBytes)) {
        // The highest address the object can start is DerefBytes bytes before
        // the end (unsigned max value). If this value is not a multiple of the
        // alignment, the last possible start value is the next lowest multiple
        // of the alignment. Note: The computations below cannot overflow,
        // because if they would there's no possible start address for the
        // object.
        APInt MaxVal =
            APInt::getMaxValue(BitWidth) - APInt(BitWidth, DerefBytes);
        uint64_t Align = U->getValue()->getPointerAlignment(DL).value();
        uint64_t Rem = MaxVal.urem(Align);
        MaxVal -= APInt(BitWidth, Rem);
        APInt MinVal = APInt::getZero(BitWidth);
        if (llvm::isKnownNonZero(V, DL))
          MinVal = Align;
        ConservativeResult = ConservativeResult.intersectWith(
            ConstantRange::getNonEmpty(MinVal, MaxVal + 1), RangeType);
      }
    }
 
    // A range of Phi is a subset of union of all ranges of its input.
    if (PHINode *Phi = dyn_cast<PHINode>(V)) {
      // SCEVExpander sometimes creates SCEVUnknowns that are secretly
      // AddRecs; return the range for the corresponding AddRec.
      if (auto *AR = dyn_cast<SCEVAddRecExpr>(getSCEV(V)))
        return getRangeRef(AR, SignHint, Depth + 1);
 
      // Make sure that we do not run over cycled Phis.
      if (RangeRefPHIAllowedOperands(DT, Phi)) {
        ConstantRange RangeFromOps(BitWidth, /*isFullSet=*/false);
 
        for (const auto &Op : Phi->operands()) {
          auto OpRange = getRangeRef(getSCEV(Op), SignHint, Depth + 1);
          RangeFromOps = RangeFromOps.unionWith(OpRange);
          // No point to continue if we already have a full set.
          if (RangeFromOps.isFullSet())
            break;
        }
        ConservativeResult =
            ConservativeResult.intersectWith(RangeFromOps, RangeType);
      }
    }
 
    // vscale can't be equal to zero
    if (const auto *II = dyn_cast<IntrinsicInst>(V))
      if (II->getIntrinsicID() == Intrinsic::vscale) {
        ConstantRange Disallowed = APInt::getZero(BitWidth);
        ConservativeResult = ConservativeResult.difference(Disallowed);
      }
 
    return setRange(U, SignHint, std::move(ConservativeResult));
  }
  case scCouldNotCompute:
    llvm_unreachable("Attempt to use a SCEVCouldNotCompute object!");
  }
 
  return setRange(S, SignHint, std::move(ConservativeResult));
}
 
// Given a StartRange, Step and MaxBECount for an expression compute a range of
// values that the expression can take. Initially, the expression has a value
// from StartRange and then is changed by Step up to MaxBECount times. Signed
// argument defines if we treat Step as signed or unsigned. The second return
// value indicates that no wrapping occurred.
static std::pair<ConstantRange, bool>
getRangeForAffineARHelper(APInt Step, const ConstantRange &StartRange,
                          const APInt &MaxBECount, bool Signed) {
  unsigned BitWidth = Step.getBitWidth();
  assert(BitWidth == StartRange.getBitWidth() &&
         BitWidth == MaxBECount.getBitWidth() && "mismatched bit widths");
  // If either Step or MaxBECount is 0, then the expression won't change, and we
  // just need to return the initial range.
  if (Step == 0 || MaxBECount == 0)
    return {StartRange, true};
 
  // If we don't know anything about the initial value (i.e. StartRange is
  // FullRange), then we don't know anything about the final range either.
  // Return FullRange.
  if (StartRange.isFullSet())
    return {ConstantRange::getFull(BitWidth), false};
 
  // If Step is signed and negative, then we use its absolute value, but we also
  // note that we're moving in the opposite direction.
  bool Descending = Signed && Step.isNegative();
 
  if (Signed)
    // This is correct even for INT_SMIN. Let's look at i8 to illustrate this:
    // abs(INT_SMIN) = abs(-128) = abs(0x80) = -0x80 = 0x80 = 128.
    // This equations hold true due to the well-defined wrap-around behavior of
    // APInt.
    Step = Step.abs();
 
  // Check if Offset is more than full span of BitWidth. If it is, the
  // expression is guaranteed to overflow.
  if (APInt::getMaxValue(StartRange.getBitWidth()).udiv(Step).ult(MaxBECount))
    return {ConstantRange::getFull(BitWidth), false};
 
  // Offset is by how much the expression can change. Checks above guarantee no
  // overflow here.
  APInt Offset = Step * MaxBECount;
 
  // Minimum value of the final range will match the minimal value of StartRange
  // if the expression is increasing and will be decreased by Offset otherwise.
  // Maximum value of the final range will match the maximal value of StartRange
  // if the expression is decreasing and will be increased by Offset otherwise.
  APInt StartLower = StartRange.getLower();
  APInt StartUpper = StartRange.getUpper() - 1;
  bool Overflow;
  APInt MovedBoundary;
  if (Signed) {
    // This does not use sadd_ov, as we want to check overflow for a signed
    // start with an unsigned offset.
    if (Descending) {
      MovedBoundary = StartLower - std::move(Offset);
      Overflow = MovedBoundary.sgt(StartLower) || StartRange.isSignWrappedSet();
    } else {
      MovedBoundary = StartUpper + std::move(Offset);
      Overflow = MovedBoundary.slt(StartUpper) || StartRange.isSignWrappedSet();
    }
  } else {
    MovedBoundary = StartUpper.uadd_ov(std::move(Offset), Overflow);
    Overflow |= StartRange.isWrappedSet();
  }
 
  // It's possible that the new minimum/maximum value will fall into the initial
  // range (due to wrap around). This means that the expression can take any
  // value in this bitwidth, and we have to return full range.
  if (StartRange.contains(MovedBoundary))
    return {ConstantRange::getFull(BitWidth), false};
 
  APInt NewLower =
      Descending ? std::move(MovedBoundary) : std::move(StartLower);
  APInt NewUpper =
      Descending ? std::move(StartUpper) : std::move(MovedBoundary);
  NewUpper += 1;
 
  // No overflow detected, return [StartLower, StartUpper + Offset + 1) range.
  return {ConstantRange::getNonEmpty(std::move(NewLower), std::move(NewUpper)),
          !Overflow};
}
 
std::pair<ConstantRange, SCEVFlags>
ScalarEvolution::getRangeForAffineAR(const SCEV *Start, const SCEV *Step,
                                     const APInt &MaxBECount) {
  assert(getTypeSizeInBits(Start->getType()) ==
             getTypeSizeInBits(Step->getType()) &&
         getTypeSizeInBits(Start->getType()) == MaxBECount.getBitWidth() &&
         "mismatched bit widths");
 
  // First, consider step signed.
  ConstantRange StartSRange = getSignedRange(Start);
  ConstantRange StepSRange = getSignedRange(Step);
 
  // If Step can be both positive and negative, we need to find ranges for the
  // maximum absolute step values in both directions and union them.
  auto [SR, NSW] = getRangeForAffineARHelper(
      StepSRange.getSignedMin(), StartSRange, MaxBECount, /*Signed=*/true);
  // A singleton step has identical signed bounds, so the second computation
  // would produce the same range and no-wrap result.
  if (!StepSRange.isSingleElement()) {
    auto [SRMax, NSWMax] = getRangeForAffineARHelper(
        StepSRange.getSignedMax(), StartSRange, MaxBECount, /*Signed=*/true);
    SR = SR.unionWith(SRMax);
    NSW &= NSWMax;
  }
 
  // Next, consider step unsigned.
  auto [UR, NUW] = getRangeForAffineARHelper(
      getUnsignedRangeMax(Step), getUnsignedRange(Start), MaxBECount,
      /*Signed=*/false);
 
  SCEVFlags Flags = SCEV::FlagNone;
  if (NUW)
    Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNUW);
  if (NSW)
    Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNSW);
 
  // Finally, intersect signed and unsigned ranges.
  return {SR.intersectWith(UR, ConstantRange::Smallest), Flags};
}
 
ConstantRange ScalarEvolution::getRangeForAffineNoSelfWrappingAR(
    const SCEVAddRecExpr *AddRec, const SCEV *MaxBECount, unsigned BitWidth,
    ScalarEvolution::RangeSignHint SignHint) {
  assert(AddRec->isAffine() && "Non-affine AddRecs are not suppored!\n");
  assert(AddRec->hasNoSelfWrap() &&
         "This only works for non-self-wrapping AddRecs!");
  const bool IsSigned = SignHint == HINT_RANGE_SIGNED;
  const SCEV *Step = AddRec->getStepRecurrence(*this);
  // Only deal with constant step to save compile time.
  if (!isa<SCEVConstant>(Step))
    return ConstantRange::getFull(BitWidth);
  // Let's make sure that we can prove that we do not self-wrap during
  // MaxBECount iterations. We need this because MaxBECount is a maximum
  // iteration count estimate, and we might infer nw from some exit for which we
  // do not know max exit count (or any other side reasoning).
  // TODO: Turn into assert at some point.
  if (getTypeSizeInBits(MaxBECount->getType()) >
      getTypeSizeInBits(AddRec->getType()))
    return ConstantRange::getFull(BitWidth);
  MaxBECount = getNoopOrZeroExtend(MaxBECount, AddRec->getType());
  const SCEV *RangeWidth = getMinusOne(AddRec->getType());
  const SCEV *StepAbs = getUMinExpr(Step, getNegativeSCEV(Step));
  const SCEV *MaxItersWithoutWrap = getUDivExpr(RangeWidth, StepAbs);
  if (!isKnownPredicateViaConstantRanges(ICmpInst::ICMP_ULE, MaxBECount,
                                         MaxItersWithoutWrap))
    return ConstantRange::getFull(BitWidth);
 
  ICmpInst::Predicate LEPred =
      IsSigned ? ICmpInst::ICMP_SLE : ICmpInst::ICMP_ULE;
  ICmpInst::Predicate GEPred =
      IsSigned ? ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE;
  const SCEV *End = AddRec->evaluateAtIteration(MaxBECount, *this);
 
  // We know that there is no self-wrap. Let's take Start and End values and
  // look at all intermediate values V1, V2, ..., Vn that IndVar takes during
  // the iteration. They either lie inside the range [Min(Start, End),
  // Max(Start, End)] or outside it:
  //
  // Case 1:   RangeMin    ...    Start V1 ... VN End ...           RangeMax;
  // Case 2:   RangeMin Vk ... V1 Start    ...    End Vn ... Vk + 1 RangeMax;
  //
  // No self wrap flag guarantees that the intermediate values cannot be BOTH
  // outside and inside the range [Min(Start, End), Max(Start, End)]. Using that
  // knowledge, let's try to prove that we are dealing with Case 1. It is so if
  // Start <= End and step is positive, or Start >= End and step is negative.
  const SCEV *Start = applyLoopGuards(AddRec->getStart(), AddRec->getLoop());
  ConstantRange StartRange = getRangeRef(Start, SignHint);
  ConstantRange EndRange = getRangeRef(End, SignHint);
  ConstantRange RangeBetween = StartRange.unionWith(EndRange);
  // If they already cover full iteration space, we will know nothing useful
  // even if we prove what we want to prove.
  if (RangeBetween.isFullSet())
    return RangeBetween;
  // Only deal with ranges that do not wrap (i.e. RangeMin < RangeMax).
  bool IsWrappedSet = IsSigned ? RangeBetween.isSignWrappedSet()
                               : RangeBetween.isWrappedSet();
  if (IsWrappedSet)
    return ConstantRange::getFull(BitWidth);
 
  if (isKnownPositive(Step) &&
      isKnownPredicateViaConstantRanges(LEPred, Start, End))
    return RangeBetween;
  if (isKnownNegative(Step) &&
           isKnownPredicateViaConstantRanges(GEPred, Start, End))
    return RangeBetween;
  return ConstantRange::getFull(BitWidth);
}
 
ConstantRange ScalarEvolution::getRangeViaFactoring(const SCEV *Start,
                                                    const SCEV *Step,
                                                    const APInt &MaxBECount) {
  //    RangeOf({C?A:B,+,C?P:Q}) == RangeOf(C?{A,+,P}:{B,+,Q})
  // == RangeOf({A,+,P}) union RangeOf({B,+,Q})
 
  unsigned BitWidth = MaxBECount.getBitWidth();
  assert(getTypeSizeInBits(Start->getType()) == BitWidth &&
         getTypeSizeInBits(Step->getType()) == BitWidth &&
         "mismatched bit widths");
 
  struct SelectPattern {
    Value *Condition = nullptr;
    APInt TrueValue;
    APInt FalseValue;
 
    explicit SelectPattern(ScalarEvolution &SE, unsigned BitWidth,
                           const SCEV *S) {
      std::optional<unsigned> CastOp;
      APInt Offset(BitWidth, 0);
 
      assert(SE.getTypeSizeInBits(S->getType()) == BitWidth &&
             "Should be!");
 
      // Peel off a constant offset. In the future we could consider being
      // smarter here and handle {Start+Step,+,Step} too.
      const APInt *Off;
      if (match(S, m_scev_Add(m_scev_APInt(Off), m_SCEV(S))))
        Offset = *Off;
 
      // Peel off a cast operation
      if (auto *SCast = dyn_cast<SCEVIntegralCastExpr>(S)) {
        CastOp = SCast->getSCEVType();
        S = SCast->getOperand();
      }
 
      using namespace llvm::PatternMatch;
 
      auto *SU = dyn_cast<SCEVUnknown>(S);
      const APInt *TrueVal, *FalseVal;
      if (!SU ||
          !match(SU->getValue(), m_Select(m_Value(Condition), m_APInt(TrueVal),
                                          m_APInt(FalseVal)))) {
        Condition = nullptr;
        return;
      }
 
      TrueValue = *TrueVal;
      FalseValue = *FalseVal;
 
      // Re-apply the cast we peeled off earlier
      if (CastOp)
        switch (*CastOp) {
        default:
          llvm_unreachable("Unknown SCEV cast type!");
 
        case scTruncate:
          TrueValue = TrueValue.trunc(BitWidth);
          FalseValue = FalseValue.trunc(BitWidth);
          break;
        case scZeroExtend:
          TrueValue = TrueValue.zext(BitWidth);
          FalseValue = FalseValue.zext(BitWidth);
          break;
        case scSignExtend:
          TrueValue = TrueValue.sext(BitWidth);
          FalseValue = FalseValue.sext(BitWidth);
          break;
        }
 
      // Re-apply the constant offset we peeled off earlier
      TrueValue += Offset;
      FalseValue += Offset;
    }
 
    bool isRecognized() { return Condition != nullptr; }
  };
 
  SelectPattern StartPattern(*this, BitWidth, Start);
  if (!StartPattern.isRecognized())
    return ConstantRange::getFull(BitWidth);
 
  SelectPattern StepPattern(*this, BitWidth, Step);
  if (!StepPattern.isRecognized())
    return ConstantRange::getFull(BitWidth);
 
  if (StartPattern.Condition != StepPattern.Condition) {
    // We don't handle this case today; but we could, by considering four
    // possibilities below instead of two. I'm not sure if there are cases where
    // that will help over what getRange already does, though.
    return ConstantRange::getFull(BitWidth);
  }
 
  // NB! Calling ScalarEvolution::getConstant is fine, but we should not try to
  // construct arbitrary general SCEV expressions here.  This function is called
  // from deep in the call stack, and calling getSCEV (on a sext instruction,
  // say) can end up caching a suboptimal value.
 
  // FIXME: without the explicit `this` receiver below, MSVC errors out with
  // C2352 and C2512 (otherwise it isn't needed).
 
  const SCEV *TrueStart = this->getConstant(StartPattern.TrueValue);
  const SCEV *TrueStep = this->getConstant(StepPattern.TrueValue);
  const SCEV *FalseStart = this->getConstant(StartPattern.FalseValue);
  const SCEV *FalseStep = this->getConstant(StepPattern.FalseValue);
 
  ConstantRange TrueRange =
      this->getRangeForAffineAR(TrueStart, TrueStep, MaxBECount).first;
  ConstantRange FalseRange =
      this->getRangeForAffineAR(FalseStart, FalseStep, MaxBECount).first;
 
  return TrueRange.unionWith(FalseRange);
}
 
SCEVFlags ScalarEvolution::getNoWrapFlagsFromUB(const Value *V) {
  if (isa<ConstantExpr>(V))
    return SCEV::FlagNone;
  const BinaryOperator *BinOp = cast<BinaryOperator>(V);
 
  // Return early if there are no flags to propagate to the SCEV.
  SCEVFlags Flags = SCEV::FlagNone;
  if (auto *PDI = dyn_cast<PossiblyDisjointInst>(BinOp);
      PDI && PDI->isDisjoint()) {
    Flags = ScalarEvolution::setFlags(SCEV::FlagNUW, SCEV::FlagNSW);
  } else {
    if (BinOp->hasNoUnsignedWrap())
      Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNUW);
    if (BinOp->hasNoSignedWrap())
      Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNSW);
  }
  if (Flags == SCEV::FlagNone)
    return SCEV::FlagNone;
 
  return isSCEVExprNeverPoison(BinOp) ? Flags : SCEV::FlagNone;
}
 
const Instruction *
ScalarEvolution::getNonTrivialDefiningScopeBound(const SCEV *S) {
  if (auto *AddRec = dyn_cast<SCEVAddRecExpr>(S))
    return &*AddRec->getLoop()->getHeader()->begin();
  if (auto *U = dyn_cast<SCEVUnknown>(S))
    if (auto *I = dyn_cast<Instruction>(U->getValue()))
      return I;
  return nullptr;
}
 
const Instruction *ScalarEvolution::getDefiningScopeBound(ArrayRef<SCEVUse> Ops,
                                                          bool &Precise) {
  Precise = true;
  // Do a bounded search of the def relation of the requested SCEVs.
  SmallPtrSet<const SCEV *, 16> Visited;
  SmallVector<SCEVUse> Worklist;
  auto pushOp = [&](const SCEV *S) {
    if (!Visited.insert(S).second)
      return;
    // Threshold of 30 here is arbitrary.
    if (Visited.size() > 30) {
      Precise = false;
      return;
    }
    Worklist.push_back(S);
  };
 
  for (SCEVUse S : Ops)
    pushOp(S);
 
  const Instruction *Bound = nullptr;
  while (!Worklist.empty()) {
    SCEVUse S = Worklist.pop_back_val();
    if (auto *DefI = getNonTrivialDefiningScopeBound(S)) {
      if (!Bound || DT.dominates(Bound, DefI))
        Bound = DefI;
    } else {
      for (SCEVUse Op : S->operands())
        pushOp(Op);
    }
  }
  return Bound ? Bound : &*F.getEntryBlock().begin();
}
 
const Instruction *
ScalarEvolution::getDefiningScopeBound(ArrayRef<SCEVUse> Ops) {
  bool Discard;
  return getDefiningScopeBound(Ops, Discard);
}
 
bool ScalarEvolution::isGuaranteedToTransferExecutionTo(const Instruction *A,
                                                        const Instruction *B) {
  if (A->getParent() == B->getParent() &&
      isGuaranteedToTransferExecutionToSuccessor(A->getIterator(),
                                                 B->getIterator()))
    return true;
 
  auto *BLoop = LI.getLoopFor(B->getParent());
  if (BLoop && BLoop->getHeader() == B->getParent() &&
      BLoop->getLoopPreheader() == A->getParent() &&
      isGuaranteedToTransferExecutionToSuccessor(A->getIterator(),
                                                 A->getParent()->end()) &&
      isGuaranteedToTransferExecutionToSuccessor(B->getParent()->begin(),
                                                 B->getIterator()))
    return true;
  return false;
}
 
bool ScalarEvolution::isGuaranteedNotToBePoison(const SCEV *Op) {
  SCEVPoisonCollector PC(/* LookThroughMaybePoisonBlocking */ true);
  visitAll(Op, PC);
  return PC.MaybePoison.empty();
}
 
bool ScalarEvolution::isGuaranteedNotToCauseUB(const SCEV *Op) {
  return !SCEVExprContains(Op, [this](const SCEV *S) {
    const SCEV *Op1;
    bool M = match(S, m_scev_UDiv(m_SCEV(), m_SCEV(Op1)));
    // The UDiv may be UB if the divisor is poison or zero. Unless the divisor
    // is a non-zero constant, we have to assume the UDiv may be UB.
    return M && (!isKnownNonZero(Op1) || !isGuaranteedNotToBePoison(Op1));
  });
}
 
bool ScalarEvolution::isSCEVExprNeverPoison(const Instruction *I) {
  // Only proceed if we can prove that I does not yield poison.
  if (!programUndefinedIfPoison(I))
    return false;
 
  // At this point we know that if I is executed, then it does not wrap
  // according to at least one of NSW or NUW. If I is not executed, then we do
  // not know if the calculation that I represents would wrap. Multiple
  // instructions can map to the same SCEV. If we apply NSW or NUW from I to
  // the SCEV, we must guarantee no wrapping for that SCEV also when it is
  // derived from other instructions that map to the same SCEV. We cannot make
  // that guarantee for cases where I is not executed. So we need to find a
  // upper bound on the defining scope for the SCEV, and prove that I is
  // executed every time we enter that scope.  When the bounding scope is a
  // loop (the common case), this is equivalent to proving I executes on every
  // iteration of that loop.
  SmallVector<SCEVUse> SCEVOps;
  for (const Use &Op : I->operands()) {
    // I could be an extractvalue from a call to an overflow intrinsic.
    // TODO: We can do better here in some cases.
    if (isSCEVable(Op->getType()))
      SCEVOps.push_back(getSCEV(Op));
  }
  auto *DefI = getDefiningScopeBound(SCEVOps);
  return isGuaranteedToTransferExecutionTo(DefI, I);
}
 
bool ScalarEvolution::isAddRecNeverPoison(const Instruction *I, const Loop *L) {
  // If we know that \c I can never be poison period, then that's enough.
  if (isSCEVExprNeverPoison(I))
    return true;
 
  // If the loop only has one exit, then we know that, if the loop is entered,
  // any instruction dominating that exit will be executed. If any such
  // instruction would result in UB, the addrec cannot be poison.
  //
  // This is basically the same reasoning as in isSCEVExprNeverPoison(), but
  // also handles uses outside the loop header (they just need to dominate the
  // single exit).
 
  auto *ExitingBB = L->getExitingBlock();
  if (!ExitingBB || !loopHasNoAbnormalExits(L))
    return false;
 
  SmallPtrSet<const Value *, 16> KnownPoison;
  SmallVector<const Instruction *, 8> Worklist;
 
  // We start by assuming \c I, the post-inc add recurrence, is poison.  Only
  // things that are known to be poison under that assumption go on the
  // Worklist.
  KnownPoison.insert(I);
  Worklist.push_back(I);
 
  while (!Worklist.empty()) {
    const Instruction *Poison = Worklist.pop_back_val();
 
    for (const Use &U : Poison->uses()) {
      const Instruction *PoisonUser = cast<Instruction>(U.getUser());
      if (mustTriggerUB(PoisonUser, KnownPoison) &&
          DT.dominates(PoisonUser->getParent(), ExitingBB))
        return true;
 
      if (propagatesPoison(U) && L->contains(PoisonUser))
        if (KnownPoison.insert(PoisonUser).second)
          Worklist.push_back(PoisonUser);
    }
  }
 
  return false;
}
 
ScalarEvolution::LoopProperties
ScalarEvolution::getLoopProperties(const Loop *L) {
  using LoopProperties = ScalarEvolution::LoopProperties;
 
  auto Itr = LoopPropertiesCache.find(L);
  if (Itr == LoopPropertiesCache.end()) {
    auto HasSideEffects = [](Instruction *I) {
      if (auto *SI = dyn_cast<StoreInst>(I))
        return !SI->isSimple();
 
      if (I->mayThrow())
        return true;
 
      // Non-volatile memset / memcpy do not count as side-effect for forward
      // progress.
      if (isa<MemIntrinsic>(I) && !I->isVolatile())
        return false;
 
      // Droppable intrinsics only model a memory write; they are not progress.
      if (I->isDroppable())
        return false;
 
      return I->mayWriteToMemory();
    };
 
    LoopProperties LP = {/* HasNoAbnormalExits */ true,
                         /*HasNoSideEffects*/ true};
 
    for (auto *BB : L->getBlocks())
      for (auto &I : *BB) {
        if (!isGuaranteedToTransferExecutionToSuccessor(&I))
          LP.HasNoAbnormalExits = false;
        if (HasSideEffects(&I))
          LP.HasNoSideEffects = false;
        if (!LP.HasNoAbnormalExits && !LP.HasNoSideEffects)
          break; // We're already as pessimistic as we can get.
      }
 
    auto InsertPair = LoopPropertiesCache.insert({L, LP});
    assert(InsertPair.second && "We just checked!");
    Itr = InsertPair.first;
  }
 
  return Itr->second;
}
 
bool ScalarEvolution::loopIsFiniteByAssumption(const Loop *L) {
  // A mustprogress loop without side effects must be finite.
  // TODO: The check used here is very conservative.  It's only *specific*
  // side effects which are well defined in infinite loops.
  return isFinite(L) || (isMustProgress(L) && loopHasNoSideEffects(L));
}
 
const SCEV *ScalarEvolution::createSCEVIter(Value *V) {
  // Worklist item with a Value and a bool indicating whether all operands have
  // been visited already.
  using PointerTy = PointerIntPair<Value *, 1, bool>;
  SmallVector<PointerTy> Stack;
 
  Stack.emplace_back(V, false);
  while (!Stack.empty()) {
    auto E = Stack.back();
    Value *CurV = E.getPointer();
 
    if (getExistingSCEV(CurV)) {
      Stack.pop_back();
      continue;
    }
 
    SmallVector<Value *> Ops;
    const SCEV *CreatedSCEV = nullptr;
    // If all operands have been visited already, create the SCEV.
    if (E.getInt()) {
      CreatedSCEV = createSCEV(CurV);
    } else {
      // Otherwise get the operands we need to create SCEV's for before creating
      // the SCEV for CurV. If the SCEV for CurV can be constructed trivially,
      // just use it.
      CreatedSCEV = getOperandsToCreate(CurV, Ops);
    }
 
    if (CreatedSCEV) {
      insertValueToMap(CurV, CreatedSCEV);
      Stack.pop_back();
    } else {
      Stack.back().setInt(true);
      // Queue its operands which need to be constructed.
      for (Value *Op : Ops)
        Stack.emplace_back(Op, false);
    }
  }
 
  return getExistingSCEV(V);
}
 
const SCEV *
ScalarEvolution::getOperandsToCreate(Value *V, SmallVectorImpl<Value *> &Ops) {
  if (!isSCEVable(V->getType()))
    return getUnknown(V);
 
  if (Instruction *I = dyn_cast<Instruction>(V)) {
    // Don't attempt to analyze instructions in blocks that aren't
    // reachable. Such instructions don't matter, and they aren't required
    // to obey basic rules for definitions dominating uses which this
    // analysis depends on.
    if (!DT.isReachableFromEntry(I->getParent()))
      return getUnknown(PoisonValue::get(V->getType()));
  } else if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
    return getConstant(CI);
  else if (isa<GlobalAlias>(V))
    return getUnknown(V);
  else if (!isa<ConstantExpr>(V))
    return getUnknown(V);
 
  Operator *U = cast<Operator>(V);
  if (auto BO =
          MatchBinaryOp(U, getDataLayout(), AC, DT, dyn_cast<Instruction>(V))) {
    bool IsConstArg = isa<ConstantInt>(BO->RHS);
    switch (BO->Opcode) {
    case Instruction::Add:
    case Instruction::Mul: {
      // For additions and multiplications, traverse add/mul chains for which we
      // can potentially create a single SCEV, to reduce the number of
      // get{Add,Mul}Expr calls.
      do {
        if (BO->Op) {
          if (BO->Op != V && getExistingSCEV(BO->Op)) {
            Ops.push_back(BO->Op);
            break;
          }
        }
        Ops.push_back(BO->RHS);
        auto NewBO = MatchBinaryOp(BO->LHS, getDataLayout(), AC, DT,
                                   dyn_cast<Instruction>(V));
        if (!NewBO ||
            (BO->Opcode == Instruction::Add &&
             (NewBO->Opcode != Instruction::Add &&
              NewBO->Opcode != Instruction::Sub)) ||
            (BO->Opcode == Instruction::Mul &&
             NewBO->Opcode != Instruction::Mul)) {
          Ops.push_back(BO->LHS);
          break;
        }
        // CreateSCEV calls getNoWrapFlagsFromUB, which under certain conditions
        // requires a SCEV for the LHS.
        if (BO->Op && (BO->IsNSW || BO->IsNUW)) {
          auto *I = dyn_cast<Instruction>(BO->Op);
          if (I && programUndefinedIfPoison(I)) {
            Ops.push_back(BO->LHS);
            break;
          }
        }
        BO = NewBO;
      } while (true);
      return nullptr;
    }
    case Instruction::Sub:
    case Instruction::UDiv:
    case Instruction::URem:
      break;
    case Instruction::AShr:
    case Instruction::Shl:
    case Instruction::Xor:
      if (!IsConstArg)
        return nullptr;
      break;
    case Instruction::And:
    case Instruction::Or:
      if (!IsConstArg && !BO->LHS->getType()->isIntegerTy(1))
        return nullptr;
      break;
    case Instruction::LShr:
      return getUnknown(V);
    default:
      llvm_unreachable("Unhandled binop");
      break;
    }
 
    Ops.push_back(BO->LHS);
    Ops.push_back(BO->RHS);
    return nullptr;
  }
 
  switch (U->getOpcode()) {
  case Instruction::Trunc:
  case Instruction::ZExt:
  case Instruction::SExt:
  case Instruction::PtrToAddr:
  case Instruction::PtrToInt:
    Ops.push_back(U->getOperand(0));
    return nullptr;
 
  case Instruction::BitCast:
    if (isSCEVable(U->getType()) && isSCEVable(U->getOperand(0)->getType())) {
      Ops.push_back(U->getOperand(0));
      return nullptr;
    }
    return getUnknown(V);
 
  case Instruction::SDiv:
  case Instruction::SRem:
    Ops.push_back(U->getOperand(0));
    Ops.push_back(U->getOperand(1));
    return nullptr;
 
  case Instruction::GetElementPtr:
    assert(cast<GEPOperator>(U)->getSourceElementType()->isSized() &&
           "GEP source element type must be sized");
    llvm::append_range(Ops, U->operands());
    return nullptr;
 
  case Instruction::IntToPtr:
    return getUnknown(V);
 
  case Instruction::PHI:
    // getNodeForPHI has four ways to turn a PHI into a SCEV; retrieve the
    // relevant nodes for each of them.
    //
    // The first is just to call simplifyInstruction, and get something back
    // that isn't a PHI.
    if (Value *V = simplifyInstruction(
            cast<PHINode>(U),
            {getDataLayout(), &TLI, &DT, &AC, /*CtxI=*/nullptr,
             /*UseInstrInfo=*/true, /*CanUseUndef=*/false})) {
      assert(V);
      Ops.push_back(V);
      return nullptr;
    }
    // The second is createNodeForPHIWithIdenticalOperands: this looks for
    // operands which all perform the same operation, but haven't been
    // CSE'ed for whatever reason.
    if (BinaryOperator *BO = getCommonInstForPHI(cast<PHINode>(U))) {
      assert(BO);
      Ops.push_back(BO);
      return nullptr;
    }
    // The third is createNodeFromSelectLikePHI; this takes a PHI which
    // is equivalent to a select, and analyzes it like a select.
    {
      Value *Cond = nullptr, *LHS = nullptr, *RHS = nullptr;
      if (getOperandsForSelectLikePHI(DT, cast<PHINode>(U), Cond, LHS, RHS)) {
        assert(Cond);
        assert(LHS);
        assert(RHS);
        if (auto *CondICmp = dyn_cast<ICmpInst>(Cond)) {
          Ops.push_back(CondICmp->getOperand(0));
          Ops.push_back(CondICmp->getOperand(1));
        }
        Ops.push_back(Cond);
        Ops.push_back(LHS);
        Ops.push_back(RHS);
        return nullptr;
      }
    }
    // The fourth way is createAddRecFromPHI. It's complicated to handle here,
    // so just construct it recursively.
    //
    // In addition to getNodeForPHI, also construct nodes which might be needed
    // by getRangeRef.
    if (RangeRefPHIAllowedOperands(DT, cast<PHINode>(U))) {
      for (Value *V : cast<PHINode>(U)->operands())
        Ops.push_back(V);
      return nullptr;
    }
    return nullptr;
 
  case Instruction::Select: {
    // Check if U is a select that can be simplified to a SCEVUnknown.
    auto CanSimplifyToUnknown = [this, U]() {
      if (U->getType()->isIntegerTy(1) || isa<ConstantInt>(U->getOperand(0)))
        return false;
 
      auto *ICI = dyn_cast<ICmpInst>(U->getOperand(0));
      if (!ICI)
        return false;
      Value *LHS = ICI->getOperand(0);
      Value *RHS = ICI->getOperand(1);
      if (ICI->getPredicate() == CmpInst::ICMP_EQ ||
          ICI->getPredicate() == CmpInst::ICMP_NE) {
        if (!(isa<ConstantInt>(RHS) && cast<ConstantInt>(RHS)->isZero()))
          return true;
      } else if (getTypeSizeInBits(LHS->getType()) >
                 getTypeSizeInBits(U->getType()))
        return true;
      return false;
    };
    if (CanSimplifyToUnknown())
      return getUnknown(U);
 
    llvm::append_range(Ops, U->operands());
    return nullptr;
    break;
  }
  case Instruction::Call:
  case Instruction::Invoke:
    if (Value *RV = cast<CallBase>(U)->getReturnedArgOperand()) {
      Ops.push_back(RV);
      return nullptr;
    }
 
    if (auto *II = dyn_cast<IntrinsicInst>(U)) {
      switch (II->getIntrinsicID()) {
      case Intrinsic::abs:
        Ops.push_back(II->getArgOperand(0));
        return nullptr;
      case Intrinsic::umax:
      case Intrinsic::umin:
      case Intrinsic::smax:
      case Intrinsic::smin:
      case Intrinsic::usub_sat:
      case Intrinsic::uadd_sat:
        Ops.push_back(II->getArgOperand(0));
        Ops.push_back(II->getArgOperand(1));
        return nullptr;
      case Intrinsic::start_loop_iterations:
      case Intrinsic::annotation:
      case Intrinsic::ptr_annotation:
        Ops.push_back(II->getArgOperand(0));
        return nullptr;
      default:
        break;
      }
    }
    break;
  }
 
  return nullptr;
}
 
const SCEV *ScalarEvolution::createSCEV(Value *V) {
  if (!isSCEVable(V->getType()))
    return getUnknown(V);
 
  if (Instruction *I = dyn_cast<Instruction>(V)) {
    // Don't attempt to analyze instructions in blocks that aren't
    // reachable. Such instructions don't matter, and they aren't required
    // to obey basic rules for definitions dominating uses which this
    // analysis depends on.
    if (!DT.isReachableFromEntry(I->getParent()))
      return getUnknown(PoisonValue::get(V->getType()));
  } else if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
    return getConstant(CI);
  else if (isa<GlobalAlias>(V))
    return getUnknown(V);
  else if (!isa<ConstantExpr>(V))
    return getUnknown(V);
 
  const SCEV *LHS;
  const SCEV *RHS;
 
  Operator *U = cast<Operator>(V);
  if (auto BO =
          MatchBinaryOp(U, getDataLayout(), AC, DT, dyn_cast<Instruction>(V))) {
    switch (BO->Opcode) {
    case Instruction::Add: {
      // The simple thing to do would be to just call getSCEV on both operands
      // and call getAddExpr with the result. However if we're looking at a
      // bunch of things all added together, this can be quite inefficient,
      // because it leads to N-1 getAddExpr calls for N ultimate operands.
      // Instead, gather up all the operands and make a single getAddExpr call.
      // LLVM IR canonical form means we need only traverse the left operands.
      SmallVector<SCEVUse, 4> AddOps;
      do {
        if (BO->Op) {
          if (auto *OpSCEV = getExistingSCEV(BO->Op)) {
            AddOps.push_back(OpSCEV);
            break;
          }
 
          // If a NUW or NSW flag can be applied to the SCEV for this
          // addition, then compute the SCEV for this addition by itself
          // with a separate call to getAddExpr. We need to do that
          // instead of pushing the operands of the addition onto AddOps,
          // since the flags are only known to apply to this particular
          // addition - they may not apply to other additions that can be
          // formed with operands from AddOps.
          const SCEV *RHS = getSCEV(BO->RHS);
          SCEVFlags Flags = getNoWrapFlagsFromUB(BO->Op);
          if (Flags != SCEV::FlagNone) {
            const SCEV *LHS = getSCEV(BO->LHS);
            if (BO->Opcode == Instruction::Sub)
              AddOps.push_back(getMinusSCEV(LHS, RHS, Flags));
            else
              AddOps.push_back(getAddExpr(LHS, RHS, Flags));
            break;
          }
        }
 
        if (BO->Opcode == Instruction::Sub)
          AddOps.push_back(getNegativeSCEV(getSCEV(BO->RHS)));
        else
          AddOps.push_back(getSCEV(BO->RHS));
 
        auto NewBO = MatchBinaryOp(BO->LHS, getDataLayout(), AC, DT,
                                   dyn_cast<Instruction>(V));
        if (!NewBO || (NewBO->Opcode != Instruction::Add &&
                       NewBO->Opcode != Instruction::Sub)) {
          AddOps.push_back(getSCEV(BO->LHS));
          break;
        }
        BO = NewBO;
      } while (true);
 
      return getAddExpr(AddOps);
    }
 
    case Instruction::Mul: {
      SmallVector<SCEVUse, 4> MulOps;
      do {
        if (BO->Op) {
          if (auto *OpSCEV = getExistingSCEV(BO->Op)) {
            MulOps.push_back(OpSCEV);
            break;
          }
 
          SCEVFlags Flags = getNoWrapFlagsFromUB(BO->Op);
          if (Flags != SCEV::FlagNone) {
            LHS = getSCEV(BO->LHS);
            RHS = getSCEV(BO->RHS);
            MulOps.push_back(getMulExpr(LHS, RHS, Flags));
            break;
          }
        }
 
        MulOps.push_back(getSCEV(BO->RHS));
        auto NewBO = MatchBinaryOp(BO->LHS, getDataLayout(), AC, DT,
                                   dyn_cast<Instruction>(V));
        if (!NewBO || NewBO->Opcode != Instruction::Mul) {
          MulOps.push_back(getSCEV(BO->LHS));
          break;
        }
        BO = NewBO;
      } while (true);
 
      return getMulExpr(MulOps);
    }
    case Instruction::UDiv:
      LHS = getSCEV(BO->LHS);
      RHS = getSCEV(BO->RHS);
      return getUDivExpr(LHS, RHS);
    case Instruction::URem:
      LHS = getSCEV(BO->LHS);
      RHS = getSCEV(BO->RHS);
      return getURemExpr(LHS, RHS);
    case Instruction::Sub: {
      SCEVFlags Flags = SCEV::FlagNone;
      if (BO->Op)
        Flags = getNoWrapFlagsFromUB(BO->Op);
 
      // Try to use ptrtoaddr for subtracts with at least one ptrtoint
      // operand. While we don't model ptrtoint directly in SCEV, the
      // difference between two pointer addresses is well-defined.
      Value *PtrLHS = nullptr, *PtrRHS = nullptr;
      bool HasPtrLHS = match(BO->LHS, m_PtrToInt(m_Value(PtrLHS)));
      bool HasPtrRHS = match(BO->RHS, m_PtrToInt(m_Value(PtrRHS)));
      if (HasPtrLHS || HasPtrRHS) {
        // Convert a ptrtoint operand (OrigOp) to ptrtoaddr of its pointer
        // PtrOp. When only one side is ptrtoint (BothPtr is false), skip
        // SCEVUnknown pointers since wrapping them in ptrtoaddr adds no
        // useful structure.
        auto GetOp = [&](bool HasPtr, Value *PtrOp, Value *OrigOp,
                         bool BothPtr) -> const SCEV * {
          if (!HasPtr)
            return getSCEV(OrigOp);
          const SCEV *PtrSCEV = getSCEV(PtrOp);
          if (BothPtr || !isa<SCEVUnknown>(PtrSCEV)) {
            const SCEV *Addr = getPtrToAddrExpr(PtrSCEV);
            if (!isa<SCEVCouldNotCompute>(Addr) &&
                getTypeSizeInBits(OrigOp->getType()) <=
                    getTypeSizeInBits(Addr->getType()))
              return getTruncateOrNoop(Addr, OrigOp->getType());
          }
          return getSCEV(OrigOp);
        };
        const SCEV *L = GetOp(HasPtrLHS, PtrLHS, BO->LHS, HasPtrRHS);
        const SCEV *R = GetOp(HasPtrRHS, PtrRHS, BO->RHS, HasPtrLHS);
        return getMinusSCEV(L, R, Flags);
      }
 
      LHS = getSCEV(BO->LHS);
      RHS = getSCEV(BO->RHS);
      return getMinusSCEV(LHS, RHS, Flags);
    }
    case Instruction::And:
      // For an expression like x&255 that merely masks off the high bits,
      // use zext(trunc(x)) as the SCEV expression.
      if (ConstantInt *CI = dyn_cast<ConstantInt>(BO->RHS)) {
        if (CI->isZero())
          return getSCEV(BO->RHS);
        if (CI->isMinusOne())
          return getSCEV(BO->LHS);
        const APInt &A = CI->getValue();
 
        // Instcombine's ShrinkDemandedConstant may strip bits out of
        // constants, obscuring what would otherwise be a low-bits mask.
        // Use computeKnownBits to compute what ShrinkDemandedConstant
        // knew about to reconstruct a low-bits mask value.
        unsigned LZ = A.countl_zero();
        unsigned TZ = A.countr_zero();
        unsigned BitWidth = A.getBitWidth();
        KnownBits Known(BitWidth);
        computeKnownBits(BO->LHS, Known, getDataLayout(), &AC, nullptr, &DT);
 
        APInt EffectiveMask =
            APInt::getLowBitsSet(BitWidth, BitWidth - LZ - TZ).shl(TZ);
        if ((LZ != 0 || TZ != 0) && !((~A & ~Known.Zero) & EffectiveMask)) {
          const SCEV *MulCount = getConstant(APInt::getOneBitSet(BitWidth, TZ));
          const SCEV *LHS = getSCEV(BO->LHS);
          const SCEV *ShiftedLHS = nullptr;
          if (auto *LHSMul = dyn_cast<SCEVMulExpr>(LHS)) {
            if (auto *OpC = dyn_cast<SCEVConstant>(LHSMul->getOperand(0))) {
              // For an expression like (x * 8) & 8, simplify the multiply.
              unsigned MulZeros = OpC->getAPInt().countr_zero();
              unsigned GCD = std::min(MulZeros, TZ);
              APInt DivAmt = APInt::getOneBitSet(BitWidth, TZ - GCD);
              SmallVector<SCEVUse, 4> MulOps;
              MulOps.push_back(getConstant(OpC->getAPInt().ashr(GCD)));
              append_range(MulOps, LHSMul->operands().drop_front());
              const SCEV *NewMul = getMulExpr(MulOps, LHSMul->getNoWrapFlags());
              ShiftedLHS = getUDivExpr(NewMul, getConstant(DivAmt));
            }
          }
          if (!ShiftedLHS)
            ShiftedLHS = getUDivExpr(LHS, MulCount);
          return getMulExpr(
              getZeroExtendExpr(
                  getTruncateExpr(ShiftedLHS,
                      IntegerType::get(getContext(), BitWidth - LZ - TZ)),
                  BO->LHS->getType()),
              MulCount);
        }
      }
      // Binary `and` is a bit-wise `umin`.
      if (BO->LHS->getType()->isIntegerTy(1)) {
        LHS = getSCEV(BO->LHS);
        RHS = getSCEV(BO->RHS);
        return getUMinExpr(LHS, RHS);
      }
      break;
 
    case Instruction::Or:
      // Binary `or` is a bit-wise `umax`.
      if (BO->LHS->getType()->isIntegerTy(1)) {
        LHS = getSCEV(BO->LHS);
        RHS = getSCEV(BO->RHS);
        return getUMaxExpr(LHS, RHS);
      }
      break;
 
    case Instruction::Xor:
      if (ConstantInt *CI = dyn_cast<ConstantInt>(BO->RHS)) {
        // If the RHS of xor is -1, then this is a not operation.
        if (CI->isMinusOne())
          return getNotSCEV(getSCEV(BO->LHS));
 
        // Model xor(and(x, C), C) as and(~x, C), if C is a low-bits mask.
        // This is a variant of the check for xor with -1, and it handles
        // the case where instcombine has trimmed non-demanded bits out
        // of an xor with -1.
        if (auto *LBO = dyn_cast<BinaryOperator>(BO->LHS))
          if (ConstantInt *LCI = dyn_cast<ConstantInt>(LBO->getOperand(1)))
            if (LBO->getOpcode() == Instruction::And &&
                LCI->getValue() == CI->getValue())
              if (const SCEVZeroExtendExpr *Z =
                      dyn_cast<SCEVZeroExtendExpr>(getSCEV(BO->LHS))) {
                Type *UTy = BO->LHS->getType();
                const SCEV *Z0 = Z->getOperand();
                Type *Z0Ty = Z0->getType();
                unsigned Z0TySize = getTypeSizeInBits(Z0Ty);
 
                // If C is a low-bits mask, the zero extend is serving to
                // mask off the high bits. Complement the operand and
                // re-apply the zext.
                if (CI->getValue().isMask(Z0TySize))
                  return getZeroExtendExpr(getNotSCEV(Z0), UTy);
 
                // If C is a single bit, it may be in the sign-bit position
                // before the zero-extend. In this case, represent the xor
                // using an add, which is equivalent, and re-apply the zext.
                APInt Trunc = CI->getValue().trunc(Z0TySize);
                if (Trunc.zext(getTypeSizeInBits(UTy)) == CI->getValue() &&
                    Trunc.isSignMask())
                  return getZeroExtendExpr(getAddExpr(Z0, getConstant(Trunc)),
                                           UTy);
              }
      }
      break;
 
    case Instruction::Shl:
      // Turn shift left of a constant amount into a multiply.
      if (ConstantInt *SA = dyn_cast<ConstantInt>(BO->RHS)) {
        uint32_t BitWidth = cast<IntegerType>(SA->getType())->getBitWidth();
 
        // If the shift count is not less than the bitwidth, the result of
        // the shift is undefined. Don't try to analyze it, because the
        // resolution chosen here may differ from the resolution chosen in
        // other parts of the compiler.
        if (SA->getValue().uge(BitWidth))
          break;
 
        // We can safely preserve the nuw flag in all cases. It's also safe to
        // turn a nuw nsw shl into a nuw nsw mul. However, nsw in isolation
        // requires special handling. It can be preserved as long as we're not
        // left shifting by bitwidth - 1.
        auto Flags = SCEV::FlagNone;
        if (BO->Op) {
          auto MulFlags = getNoWrapFlagsFromUB(BO->Op);
          if (any(MulFlags & SCEV::FlagNSW) &&
              (any(MulFlags & SCEV::FlagNUW) ||
               SA->getValue().ult(BitWidth - 1)))
            Flags = Flags | SCEV::FlagNSW;
          if (any(MulFlags & SCEV::FlagNUW))
            Flags = Flags | SCEV::FlagNUW;
        }
 
        ConstantInt *X = ConstantInt::get(
            getContext(), APInt::getOneBitSet(BitWidth, SA->getZExtValue()));
        return getMulExpr(getSCEV(BO->LHS), getConstant(X), Flags);
      }
      break;
 
    case Instruction::AShr:
      // AShr X, C, where C is a constant.
      ConstantInt *CI = dyn_cast<ConstantInt>(BO->RHS);
      if (!CI)
        break;
 
      Type *OuterTy = BO->LHS->getType();
      uint64_t BitWidth = getTypeSizeInBits(OuterTy);
      // If the shift count is not less than the bitwidth, the result of
      // the shift is undefined. Don't try to analyze it, because the
      // resolution chosen here may differ from the resolution chosen in
      // other parts of the compiler.
      if (CI->getValue().uge(BitWidth))
        break;
 
      if (CI->isZero())
        return getSCEV(BO->LHS); // shift by zero --> noop
 
      uint64_t AShrAmt = CI->getZExtValue();
      Type *TruncTy = IntegerType::get(getContext(), BitWidth - AShrAmt);
 
      Operator *L = dyn_cast<Operator>(BO->LHS);
      const SCEV *AddTruncateExpr = nullptr;
      ConstantInt *ShlAmtCI = nullptr;
      const SCEV *AddConstant = nullptr;
 
      if (L && L->getOpcode() == Instruction::Add) {
        // X = Shl A, n
        // Y = Add X, c
        // Z = AShr Y, m
        // n, c and m are constants.
 
        Operator *LShift = dyn_cast<Operator>(L->getOperand(0));
        ConstantInt *AddOperandCI = dyn_cast<ConstantInt>(L->getOperand(1));
        if (LShift && LShift->getOpcode() == Instruction::Shl) {
          if (AddOperandCI) {
            const SCEV *ShlOp0SCEV = getSCEV(LShift->getOperand(0));
            ShlAmtCI = dyn_cast<ConstantInt>(LShift->getOperand(1));
            // since we truncate to TruncTy, the AddConstant should be of the
            // same type, so create a new Constant with type same as TruncTy.
            // Also, the Add constant should be shifted right by AShr amount.
            APInt AddOperand = AddOperandCI->getValue().ashr(AShrAmt);
            AddConstant = getConstant(AddOperand.trunc(BitWidth - AShrAmt));
            // we model the expression as sext(add(trunc(A), c << n)), since the
            // sext(trunc) part is already handled below, we create a
            // AddExpr(TruncExp) which will be used later.
            AddTruncateExpr = getTruncateExpr(ShlOp0SCEV, TruncTy);
          }
        }
      } else if (L && L->getOpcode() == Instruction::Shl) {
        // X = Shl A, n
        // Y = AShr X, m
        // Both n and m are constant.
 
        const SCEV *ShlOp0SCEV = getSCEV(L->getOperand(0));
        ShlAmtCI = dyn_cast<ConstantInt>(L->getOperand(1));
        AddTruncateExpr = getTruncateExpr(ShlOp0SCEV, TruncTy);
      }
 
      if (AddTruncateExpr && ShlAmtCI) {
        // We can merge the two given cases into a single SCEV statement,
        // incase n = m, the mul expression will be 2^0, so it gets resolved to
        // a simpler case. The following code handles the two cases:
        //
        // 1) For a two-shift sext-inreg, i.e. n = m,
        //    use sext(trunc(x)) as the SCEV expression.
        //
        // 2) When n > m, use sext(mul(trunc(x), 2^(n-m)))) as the SCEV
        //    expression. We already checked that ShlAmt < BitWidth, so
        //    the multiplier, 1 << (ShlAmt - AShrAmt), fits into TruncTy as
        //    ShlAmt - AShrAmt < Amt.
        const APInt &ShlAmt = ShlAmtCI->getValue();
        if (ShlAmt.ult(BitWidth) && ShlAmt.uge(AShrAmt)) {
          APInt Mul = APInt::getOneBitSet(BitWidth - AShrAmt,
                                          ShlAmtCI->getZExtValue() - AShrAmt);
          const SCEV *CompositeExpr =
              getMulExpr(AddTruncateExpr, getConstant(Mul));
          if (L->getOpcode() != Instruction::Shl)
            CompositeExpr = getAddExpr(CompositeExpr, AddConstant);
 
          return getSignExtendExpr(CompositeExpr, OuterTy);
        }
      }
      break;
    }
  }
 
  switch (U->getOpcode()) {
  case Instruction::Trunc:
    return getTruncateExpr(getSCEV(U->getOperand(0)), U->getType());
 
  case Instruction::ZExt:
    return getZeroExtendExpr(getSCEV(U->getOperand(0)), U->getType());
 
  case Instruction::SExt:
    if (auto BO = MatchBinaryOp(U->getOperand(0), getDataLayout(), AC, DT,
                                dyn_cast<Instruction>(V))) {
      // The NSW flag of a subtract does not always survive the conversion to
      // A + (-1)*B.  By pushing sign extension onto its operands we are much
      // more likely to preserve NSW and allow later AddRec optimisations.
      //
      // NOTE: This is effectively duplicating this logic from getSignExtend:
      //   sext((A + B + ...)<nsw>) --> (sext(A) + sext(B) + ...)<nsw>
      // but by that point the NSW information has potentially been lost.
      if (BO->Opcode == Instruction::Sub && BO->IsNSW) {
        Type *Ty = U->getType();
        auto *V1 = getSignExtendExpr(getSCEV(BO->LHS), Ty);
        auto *V2 = getSignExtendExpr(getSCEV(BO->RHS), Ty);
        return getMinusSCEV(V1, V2, SCEV::FlagNSW);
      }
    }
    return getSignExtendExpr(getSCEV(U->getOperand(0)), U->getType());
 
  case Instruction::BitCast:
    // BitCasts are no-op casts so we just eliminate the cast.
    if (isSCEVable(U->getType()) && isSCEVable(U->getOperand(0)->getType()))
      return getSCEV(U->getOperand(0));
    break;
 
  case Instruction::PtrToAddr: {
    const SCEV *IntOp = getPtrToAddrExpr(getSCEV(U->getOperand(0)));
    if (isa<SCEVCouldNotCompute>(IntOp))
      return getUnknown(V);
    return IntOp;
  }
 
  case Instruction::PtrToInt:
    // SCEV only models ptrtoaddr.
    return getUnknown(V);
 
  case Instruction::IntToPtr:
    // Just don't deal with inttoptr casts.
    return getUnknown(V);
 
  case Instruction::SDiv:
    // If both operands are non-negative, this is just an udiv.
    if (isKnownNonNegative(getSCEV(U->getOperand(0))) &&
        isKnownNonNegative(getSCEV(U->getOperand(1))))
      return getUDivExpr(getSCEV(U->getOperand(0)), getSCEV(U->getOperand(1)));
    break;
 
  case Instruction::SRem:
    // If both operands are non-negative, this is just an urem.
    if (isKnownNonNegative(getSCEV(U->getOperand(0))) &&
        isKnownNonNegative(getSCEV(U->getOperand(1))))
      return getURemExpr(getSCEV(U->getOperand(0)), getSCEV(U->getOperand(1)));
    break;
 
  case Instruction::GetElementPtr:
    return createNodeForGEP(cast<GEPOperator>(U));
 
  case Instruction::PHI:
    return createNodeForPHI(cast<PHINode>(U));
 
  case Instruction::Select:
    return createNodeForSelectOrPHI(U, U->getOperand(0), U->getOperand(1),
                                    U->getOperand(2));
 
  case Instruction::Call:
  case Instruction::Invoke:
    if (Value *RV = cast<CallBase>(U)->getReturnedArgOperand())
      return getSCEV(RV);
 
    if (auto *II = dyn_cast<IntrinsicInst>(U)) {
      switch (II->getIntrinsicID()) {
      case Intrinsic::abs:
        return getAbsExpr(
            getSCEV(II->getArgOperand(0)),
            /*IsNSW=*/cast<ConstantInt>(II->getArgOperand(1))->isOne());
      case Intrinsic::umax:
        LHS = getSCEV(II->getArgOperand(0));
        RHS = getSCEV(II->getArgOperand(1));
        return getUMaxExpr(LHS, RHS);
      case Intrinsic::umin:
        LHS = getSCEV(II->getArgOperand(0));
        RHS = getSCEV(II->getArgOperand(1));
        return getUMinExpr(LHS, RHS);
      case Intrinsic::smax:
        LHS = getSCEV(II->getArgOperand(0));
        RHS = getSCEV(II->getArgOperand(1));
        return getSMaxExpr(LHS, RHS);
      case Intrinsic::smin:
        LHS = getSCEV(II->getArgOperand(0));
        RHS = getSCEV(II->getArgOperand(1));
        return getSMinExpr(LHS, RHS);
      case Intrinsic::usub_sat: {
        const SCEV *X = getSCEV(II->getArgOperand(0));
        const SCEV *Y = getSCEV(II->getArgOperand(1));
        const SCEV *ClampedY = getUMinExpr(X, Y);
        return getMinusSCEV(X, ClampedY, SCEV::FlagNUW);
      }
      case Intrinsic::uadd_sat: {
        const SCEV *X = getSCEV(II->getArgOperand(0));
        const SCEV *Y = getSCEV(II->getArgOperand(1));
        const SCEV *ClampedX = getUMinExpr(X, getNotSCEV(Y));
        return getAddExpr(ClampedX, Y, SCEV::FlagNUW);
      }
      case Intrinsic::start_loop_iterations:
      case Intrinsic::annotation:
      case Intrinsic::ptr_annotation:
        // A start_loop_iterations or llvm.annotation or llvm.prt.annotation is
        // just eqivalent to the first operand for SCEV purposes.
        return getSCEV(II->getArgOperand(0));
      case Intrinsic::vscale:
        return getVScale(II->getType());
      default:
        break;
      }
    }
    break;
  }
 
  return getUnknown(V);
}
 
//===----------------------------------------------------------------------===//
//                   Iteration Count Computation Code
//
 
const SCEV *ScalarEvolution::getTripCountFromExitCount(const SCEV *ExitCount) {
  if (isa<SCEVCouldNotCompute>(ExitCount))
    return getCouldNotCompute();
 
  auto *ExitCountType = ExitCount->getType();
  assert(ExitCountType->isIntegerTy());
  auto *EvalTy = Type::getIntNTy(ExitCountType->getContext(),
                                 1 + ExitCountType->getScalarSizeInBits());
  return getTripCountFromExitCount(ExitCount, EvalTy, nullptr);
}
 
const SCEV *ScalarEvolution::getTripCountFromExitCount(const SCEV *ExitCount,
                                                       Type *EvalTy,
                                                       const Loop *L) {
  if (isa<SCEVCouldNotCompute>(ExitCount))
    return getCouldNotCompute();
 
  unsigned ExitCountSize = getTypeSizeInBits(ExitCount->getType());
  unsigned EvalSize = EvalTy->getPrimitiveSizeInBits();
 
  auto CanAddOneWithoutOverflow = [&]() {
    ConstantRange ExitCountRange =
      getRangeRef(ExitCount, RangeSignHint::HINT_RANGE_UNSIGNED);
    if (!ExitCountRange.contains(APInt::getMaxValue(ExitCountSize)))
      return true;
 
    return L && isLoopEntryGuardedByCond(L, ICmpInst::ICMP_NE, ExitCount,
                                         getMinusOne(ExitCount->getType()));
  };
 
  // If we need to zero extend the backedge count, check if we can add one to
  // it prior to zero extending without overflow. Provided this is safe, it
  // allows better simplification of the +1.
  if (EvalSize > ExitCountSize && CanAddOneWithoutOverflow())
    return getZeroExtendExpr(
        getAddExpr(ExitCount, getOne(ExitCount->getType())), EvalTy);
 
  // Get the total trip count from the count by adding 1.  This may wrap.
  return getAddExpr(getTruncateOrZeroExtend(ExitCount, EvalTy), getOne(EvalTy));
}
 
static unsigned getConstantTripCount(const SCEVConstant *ExitCount) {
  if (!ExitCount)
    return 0;
 
  ConstantInt *ExitConst = ExitCount->getValue();
 
  // Guard against huge trip counts.
  if (ExitConst->getValue().getActiveBits() > 32)
    return 0;
 
  // In case of integer overflow, this returns 0, which is correct.
  return ((unsigned)ExitConst->getZExtValue()) + 1;
}
 
unsigned ScalarEvolution::getSmallConstantTripCount(const Loop *L) {
  auto *ExitCount = dyn_cast<SCEVConstant>(getBackedgeTakenCount(L, Exact));
  return getConstantTripCount(ExitCount);
}
 
unsigned
ScalarEvolution::getSmallConstantTripCount(const Loop *L,
                                           const BasicBlock *ExitingBlock) {
  assert(ExitingBlock && "Must pass a non-null exiting block!");
  assert(L->isLoopExiting(ExitingBlock) &&
         "Exiting block must actually branch out of the loop!");
  const SCEVConstant *ExitCount =
      dyn_cast<SCEVConstant>(getExitCount(L, ExitingBlock));
  return getConstantTripCount(ExitCount);
}
 
unsigned ScalarEvolution::getSmallConstantMaxTripCount(
    const Loop *L, SmallVectorImpl<const SCEVPredicate *> *Predicates) {
 
  const auto *MaxExitCount =
      Predicates ? getPredicatedConstantMaxBackedgeTakenCount(L, *Predicates)
                 : getConstantMaxBackedgeTakenCount(L);
  return getConstantTripCount(dyn_cast<SCEVConstant>(MaxExitCount));
}
 
unsigned ScalarEvolution::getSmallConstantTripMultiple(const Loop *L) {
  SmallVector<BasicBlock *, 8> ExitingBlocks;
  L->getExitingBlocks(ExitingBlocks);
 
  // An exit with an uncomputable exit count makes the result 1.
  if (ExitingBlocks.empty() ||
      any_of(ExitingBlocks, [this, L](BasicBlock *ExitingBB) {
        return isa<SCEVCouldNotCompute>(getExitCount(L, ExitingBB));
      }))
    return 1;
 
  LoopGuards Guards = LoopGuards::collectOnDemand(L, *this);
  unsigned Res = 0;
  for (BasicBlock *ExitingBB : ExitingBlocks)
    Res = std::gcd(
        Res, getSmallConstantTripMultiple(getExitCount(L, ExitingBB), Guards));
  return Res;
}
 
unsigned ScalarEvolution::getSmallConstantTripMultiple(const SCEV *ExitCount,
                                                       LoopGuards &Guards) {
  assert(!isa<SCEVCouldNotCompute>(ExitCount) && "Must be computable!");
 
  // Get the trip count
  const SCEV *TCExpr =
      getTripCountFromExitCount(applyLoopGuards(ExitCount, Guards));
 
  APInt Multiple = getNonZeroConstantMultiple(TCExpr);
  // If a trip multiple is huge (>=2^32), the trip count is still divisible by
  // the greatest power of 2 divisor less than 2^32.
  return Multiple.getActiveBits() > 32
             ? 1U << std::min(31U, Multiple.countTrailingZeros())
             : (unsigned)Multiple.getZExtValue();
}
 
unsigned ScalarEvolution::getSmallConstantTripMultiple(const Loop *L,
                                                       const SCEV *ExitCount) {
  if (isa<SCEVCouldNotCompute>(ExitCount))
    return 1;
 
  LoopGuards Guards = LoopGuards::collectOnDemand(L, *this);
  return getSmallConstantTripMultiple(ExitCount, Guards);
}
 
/// Returns the largest constant divisor of the trip count of this loop as a
/// normal unsigned value, if possible. This means that the actual trip count is
/// always a multiple of the returned value (don't forget the trip count could
/// very well be zero as well!).
///
/// Returns 1 if the trip count is unknown or not guaranteed to be the
/// multiple of a constant (which is also the case if the trip count is simply
/// constant, use getSmallConstantTripCount for that case), Will also return 1
/// if the trip count is very large (>= 2^32).
///
/// As explained in the comments for getSmallConstantTripCount, this assumes
/// that control exits the loop via ExitingBlock.
unsigned
ScalarEvolution::getSmallConstantTripMultiple(const Loop *L,
                                              const BasicBlock *ExitingBlock) {
  assert(ExitingBlock && "Must pass a non-null exiting block!");
  assert(L->isLoopExiting(ExitingBlock) &&
         "Exiting block must actually branch out of the loop!");
  const SCEV *ExitCount = getExitCount(L, ExitingBlock);
  return getSmallConstantTripMultiple(L, ExitCount);
}
 
const SCEV *ScalarEvolution::getExitCount(const Loop *L,
                                          const BasicBlock *ExitingBlock,
                                          ExitCountKind Kind) {
  switch (Kind) {
  case Exact:
    return getBackedgeTakenInfo(L).getExact(ExitingBlock, this);
  case SymbolicMaximum:
    return getBackedgeTakenInfo(L).getSymbolicMax(ExitingBlock, this);
  case ConstantMaximum:
    return getBackedgeTakenInfo(L).getConstantMax(ExitingBlock, this);
  };
  llvm_unreachable("Invalid ExitCountKind!");
}
 
const SCEV *ScalarEvolution::getPredicatedExitCount(
    const Loop *L, const BasicBlock *ExitingBlock,
    SmallVectorImpl<const SCEVPredicate *> *Predicates, ExitCountKind Kind) {
  switch (Kind) {
  case Exact:
    return getPredicatedBackedgeTakenInfo(L).getExact(ExitingBlock, this,
                                                      Predicates);
  case SymbolicMaximum:
    return getPredicatedBackedgeTakenInfo(L).getSymbolicMax(ExitingBlock, this,
                                                            Predicates);
  case ConstantMaximum:
    return getPredicatedBackedgeTakenInfo(L).getConstantMax(ExitingBlock, this,
                                                            Predicates);
  };
  llvm_unreachable("Invalid ExitCountKind!");
}
 
const SCEV *ScalarEvolution::getPredicatedBackedgeTakenCount(
    const Loop *L, SmallVectorImpl<const SCEVPredicate *> &Preds) {
  return getPredicatedBackedgeTakenInfo(L).getExact(L, this, &Preds);
}
 
const SCEV *ScalarEvolution::getBackedgeTakenCount(const Loop *L,
                                                   ExitCountKind Kind) {
  switch (Kind) {
  case Exact:
    return getBackedgeTakenInfo(L).getExact(L, this);
  case ConstantMaximum:
    return getBackedgeTakenInfo(L).getConstantMax(this);
  case SymbolicMaximum:
    return getBackedgeTakenInfo(L).getSymbolicMax(L, this);
  };
  llvm_unreachable("Invalid ExitCountKind!");
}
 
const SCEV *ScalarEvolution::getPredicatedSymbolicMaxBackedgeTakenCount(
    const Loop *L, SmallVectorImpl<const SCEVPredicate *> &Preds) {
  return getPredicatedBackedgeTakenInfo(L).getSymbolicMax(L, this, &Preds);
}
 
const SCEV *ScalarEvolution::getPredicatedConstantMaxBackedgeTakenCount(
    const Loop *L, SmallVectorImpl<const SCEVPredicate *> &Preds) {
  return getPredicatedBackedgeTakenInfo(L).getConstantMax(this, &Preds);
}
 
bool ScalarEvolution::isBackedgeTakenCountMaxOrZero(const Loop *L) {
  return getBackedgeTakenInfo(L).isConstantMaxOrZero(this);
}
 
/// Push PHI nodes in the header of the given loop onto the given Worklist.
static void PushLoopPHIs(const Loop *L,
                         SmallVectorImpl<Instruction *> &Worklist,
                         SmallPtrSetImpl<Instruction *> &Visited) {
  BasicBlock *Header = L->getHeader();
 
  // Push all Loop-header PHIs onto the Worklist stack.
  for (PHINode &PN : Header->phis())
    if (Visited.insert(&PN).second)
      Worklist.push_back(&PN);
}
 
ScalarEvolution::BackedgeTakenInfo &
ScalarEvolution::getPredicatedBackedgeTakenInfo(const Loop *L) {
  auto &BTI = getBackedgeTakenInfo(L);
  if (BTI.hasFullInfo())
    return BTI;
 
  auto Pair = PredicatedBackedgeTakenCounts.try_emplace(L);
 
  if (!Pair.second)
    return Pair.first->second;
 
  BackedgeTakenInfo Result =
      computeBackedgeTakenCount(L, /*AllowPredicates=*/true);
 
  return PredicatedBackedgeTakenCounts.find(L)->second = std::move(Result);
}
 
ScalarEvolution::BackedgeTakenInfo &
ScalarEvolution::getBackedgeTakenInfo(const Loop *L) {
  // Initially insert an invalid entry for this loop. If the insertion
  // succeeds, proceed to actually compute a backedge-taken count and
  // update the value. The temporary CouldNotCompute value tells SCEV
  // code elsewhere that it shouldn't attempt to request a new
  // backedge-taken count, which could result in infinite recursion.
  std::pair<DenseMap<const Loop *, BackedgeTakenInfo>::iterator, bool> Pair =
      BackedgeTakenCounts.try_emplace(L);
  if (!Pair.second)
    return Pair.first->second;
 
  // computeBackedgeTakenCount may allocate memory for its result. Inserting it
  // into the BackedgeTakenCounts map transfers ownership. Otherwise, the result
  // must be cleared in this scope.
  BackedgeTakenInfo Result = computeBackedgeTakenCount(L);
 
  // Now that we know more about the trip count for this loop, forget any
  // existing SCEV values for PHI nodes in this loop since they are only
  // conservative estimates made without the benefit of trip count
  // information. This invalidation is not necessary for correctness, and is
  // only done to produce more precise results.
  if (Result.hasAnyInfo()) {
    // Invalidate any expression using an addrec in this loop.
    SmallVector<SCEVUse, 8> ToForget;
    auto LoopUsersIt = LoopUsers.find(L);
    if (LoopUsersIt != LoopUsers.end())
      append_range(ToForget, LoopUsersIt->second);
    forgetMemoizedResults(ToForget);
 
    // Invalidate constant-evolved loop header phis.
    for (PHINode &PN : L->getHeader()->phis())
      ConstantEvolutionLoopExitValue.erase(&PN);
  }
 
  // Re-lookup the insert position, since the call to
  // computeBackedgeTakenCount above could result in a
  // recusive call to getBackedgeTakenInfo (on a different
  // loop), which would invalidate the iterator computed
  // earlier.
  return BackedgeTakenCounts.find(L)->second = std::move(Result);
}
 
void ScalarEvolution::forgetAllLoops() {
  // This method is intended to forget all info about loops. It should
  // invalidate caches as if the following happened:
  // - The trip counts of all loops have changed arbitrarily
  // - Every llvm::Value has been updated in place to produce a different
  // result.
  BackedgeTakenCounts.clear();
  PredicatedBackedgeTakenCounts.clear();
  BECountUsers.clear();
  LoopPropertiesCache.clear();
  ConstantEvolutionLoopExitValue.clear();
  ValueExprMap.clear();
  ValuesAtScopes.clear();
  ValuesAtScopesUsers.clear();
  LoopDispositions.clear();
  BlockDispositions.clear();
  UnsignedRanges.clear();
  SignedRanges.clear();
  ExprValueMap.clear();
  HasRecMap.clear();
  ConstantMultipleCache.clear();
  PredicatedSCEVRewrites.clear();
  FoldCache.clear();
  FoldCacheUser.clear();
}
void ScalarEvolution::visitAndClearUsers(
    SmallVectorImpl<Instruction *> &Worklist,
    SmallPtrSetImpl<Instruction *> &Visited,
    SmallVectorImpl<SCEVUse> &ToForget) {
  // Nothing can be invalidated if no value has a SCEV yet.
  if (ValueExprMap.empty()) {
    Worklist.clear();
    return;
  }
  while (!Worklist.empty()) {
    Instruction *I = Worklist.pop_back_val();
    if (!isSCEVable(I->getType()) && !isa<WithOverflowInst>(I))
      continue;
 
    ValueExprMapType::iterator It =
        ValueExprMap.find_as(static_cast<Value *>(I));
    if (It != ValueExprMap.end()) {
      ToForget.push_back(It->second);
      eraseValueFromMap(It->first);
      if (PHINode *PN = dyn_cast<PHINode>(I))
        ConstantEvolutionLoopExitValue.erase(PN);
    }
 
    PushDefUseChildren(I, Worklist, Visited);
  }
}
 
void ScalarEvolution::forgetLoop(const Loop *L) {
  SmallVector<const Loop *, 16> LoopWorklist(1, L);
  SmallVector<Instruction *, 32> Worklist;
  SmallPtrSet<Instruction *, 16> Visited;
  SmallVector<SCEVUse, 16> ToForget;
 
  // Iterate over all the loops and sub-loops to drop SCEV information.
  while (!LoopWorklist.empty()) {
    auto *CurrL = LoopWorklist.pop_back_val();
 
    // Drop any stored trip count value.
    forgetBackedgeTakenCounts(CurrL, /* Predicated */ false);
    forgetBackedgeTakenCounts(CurrL, /* Predicated */ true);
 
    // Drop information about predicated SCEV rewrites for this loop.
    PredicatedSCEVRewrites.remove_if(
        [&](const auto &Entry) { return Entry.first.second == CurrL; });
 
    auto LoopUsersItr = LoopUsers.find(CurrL);
    if (LoopUsersItr != LoopUsers.end())
      llvm::append_range(ToForget, LoopUsersItr->second);
 
    // Drop information about expressions based on loop-header PHIs.
    PushLoopPHIs(CurrL, Worklist, Visited);
    visitAndClearUsers(Worklist, Visited, ToForget);
 
    LoopPropertiesCache.erase(CurrL);
    // Forget all contained loops too, to avoid dangling entries in the
    // ValuesAtScopes map.
    LoopWorklist.append(CurrL->begin(), CurrL->end());
  }
  forgetMemoizedResults(ToForget);
}
 
void ScalarEvolution::forgetTopmostLoop(const Loop *L) {
  forgetLoop(L->getOutermostLoop());
}
 
void ScalarEvolution::forgetValue(Value *V) {
  Instruction *I = dyn_cast<Instruction>(V);
  if (!I) return;
 
  // Drop information about expressions based on loop-header PHIs.
  SmallVector<Instruction *, 16> Worklist;
  SmallPtrSet<Instruction *, 8> Visited;
  SmallVector<SCEVUse, 8> ToForget;
  Worklist.push_back(I);
  Visited.insert(I);
  visitAndClearUsers(Worklist, Visited, ToForget);
 
  forgetMemoizedResults(ToForget);
}
 
void ScalarEvolution::forgetValues(ArrayRef<Value *> Values) {
  SmallVector<Instruction *, 16> Worklist;
  SmallPtrSet<Instruction *, 8> Visited;
  SmallVector<SCEVUse, 8> ToForget;
  for (Value *V : Values)
    if (auto *I = dyn_cast<Instruction>(V))
      if (Visited.insert(I).second)
        Worklist.push_back(I);
  visitAndClearUsers(Worklist, Visited, ToForget);
 
  forgetMemoizedResults(ToForget);
}
 
void ScalarEvolution::forgetLcssaPhiWithNewPredecessor(Loop *L, PHINode *V) {
  // If SCEV looked through a trivial LCSSA phi node, we might have SCEV's
  // directly using a SCEVUnknown/SCEVAddRec defined in the loop. After an
  // extra predecessor is added, this is no longer valid. Find all Unknowns and
  // AddRecs defined in the loop and invalidate any SCEV's making use of them.
  auto InvalidateValue = [&](Value *Val) {
    if (!isSCEVable(Val->getType()))
      return;
    if (const SCEV *S = getExistingSCEV(Val)) {
      struct InvalidationRootCollector {
        Loop *L;
        SmallVector<SCEVUse, 8> Roots;
 
        InvalidationRootCollector(Loop *L) : L(L) {}
 
        bool follow(const SCEV *S) {
          if (auto *SU = dyn_cast<SCEVUnknown>(S)) {
            if (auto *I = dyn_cast<Instruction>(SU->getValue()))
              if (L->contains(I))
                Roots.push_back(S);
          } else if (auto *AddRec = dyn_cast<SCEVAddRecExpr>(S)) {
            if (L->contains(AddRec->getLoop()))
              Roots.push_back(S);
          }
          return true;
        }
        bool isDone() const { return false; }
      };
 
      InvalidationRootCollector C(L);
      visitAll(S, C);
      forgetMemoizedResults(C.Roots);
    }
  };
 
  InvalidateValue(V);
 
  // If V has a non-SCEV-able type (e.g. {i64, i1} from a with.overflow
  // intrinsic), its users (e.g. extractvalue) may have stale SCEV
  // expressions referencing loop-internal values.
  if (!isSCEVable(V->getType()) &&
      any_of(V->incoming_values(), IsaPred<WithOverflowInst>))
    for (User *U : V->users())
      InvalidateValue(U);
  // Also perform the normal invalidation.
  forgetValue(V);
}
 
void ScalarEvolution::forgetLoopDispositions() { LoopDispositions.clear(); }
 
void ScalarEvolution::forgetBlockAndLoopDispositions(Value *V) {
  // Unless a specific value is passed to invalidation, completely clear both
  // caches.
  if (!V) {
    BlockDispositions.clear();
    LoopDispositions.clear();
    return;
  }
 
  if (!isSCEVable(V->getType()))
    return;
 
  const SCEV *S = getExistingSCEV(V);
  if (!S)
    return;
 
  // Invalidate the block and loop dispositions cached for S. Dispositions of
  // S's users may change if S's disposition changes (i.e. a user may change to
  // loop-invariant, if S changes to loop invariant), so also invalidate
  // dispositions of S's users recursively.
  SmallVector<SCEVUse, 8> Worklist = {S};
  SmallPtrSet<const SCEV *, 8> Seen = {S};
  while (!Worklist.empty()) {
    const SCEV *Curr = Worklist.pop_back_val();
    bool LoopDispoRemoved = LoopDispositions.erase(Curr);
    bool BlockDispoRemoved = BlockDispositions.erase(Curr);
    if (!LoopDispoRemoved && !BlockDispoRemoved)
      continue;
    auto Users = SCEVUsers.find(Curr);
    if (Users != SCEVUsers.end())
      for (const auto *User : Users->second)
        if (Seen.insert(User).second)
          Worklist.push_back(User);
  }
}
 
/// Get the exact loop backedge taken count considering all loop exits. A
/// computable result can only be returned for loops with all exiting blocks
/// dominating the latch. howFarToZero assumes that the limit of each loop test
/// is never skipped. This is a valid assumption as long as the loop exits via
/// that test. For precise results, it is the caller's responsibility to specify
/// the relevant loop exiting block using getExact(ExitingBlock, SE).
const SCEV *ScalarEvolution::BackedgeTakenInfo::getExact(
    const Loop *L, ScalarEvolution *SE,
    SmallVectorImpl<const SCEVPredicate *> *Preds) const {
  // If any exits were not computable, the loop is not computable.
  if (!isComplete() || ExitNotTaken.empty())
    return SE->getCouldNotCompute();
 
  const BasicBlock *Latch = L->getLoopLatch();
  // All exiting blocks we have collected must dominate the only backedge.
  if (!Latch)
    return SE->getCouldNotCompute();
 
  // All exiting blocks we have gathered dominate loop's latch, so exact trip
  // count is simply a minimum out of all these calculated exit counts.
  SmallVector<SCEVUse, 2> Ops;
  for (const auto &ENT : ExitNotTaken) {
    const SCEV *BECount = ENT.ExactNotTaken;
    assert(BECount != SE->getCouldNotCompute() && "Bad exit SCEV!");
    assert(SE->DT.dominates(ENT.ExitingBlock, Latch) &&
           "We should only have known counts for exiting blocks that dominate "
           "latch!");
 
    Ops.push_back(BECount);
 
    if (Preds)
      append_range(*Preds, ENT.Predicates);
 
    assert((Preds || ENT.hasAlwaysTruePredicate()) &&
           "Predicate should be always true!");
  }
 
  // If an earlier exit exits on the first iteration (exit count zero), then
  // a later poison exit count should not propagate into the result. This are
  // exactly the semantics provided by umin_seq.
  return SE->getUMinFromMismatchedTypes(Ops, /* Sequential */ true);
}
 
const ScalarEvolution::ExitNotTakenInfo *
ScalarEvolution::BackedgeTakenInfo::getExitNotTaken(
    const BasicBlock *ExitingBlock,
    SmallVectorImpl<const SCEVPredicate *> *Predicates) const {
  for (const auto &ENT : ExitNotTaken)
    if (ENT.ExitingBlock == ExitingBlock) {
      if (ENT.hasAlwaysTruePredicate())
        return &ENT;
      else if (Predicates) {
        append_range(*Predicates, ENT.Predicates);
        return &ENT;
      }
    }
 
  return nullptr;
}
 
/// getConstantMax - Get the constant max backedge taken count for the loop.
const SCEV *ScalarEvolution::BackedgeTakenInfo::getConstantMax(
    ScalarEvolution *SE,
    SmallVectorImpl<const SCEVPredicate *> *Predicates) const {
  if (!getConstantMax())
    return SE->getCouldNotCompute();
 
  for (const auto &ENT : ExitNotTaken)
    if (!ENT.hasAlwaysTruePredicate()) {
      if (!Predicates)
        return SE->getCouldNotCompute();
      append_range(*Predicates, ENT.Predicates);
    }
 
  assert((isa<SCEVCouldNotCompute>(getConstantMax()) ||
          isa<SCEVConstant>(getConstantMax())) &&
         "No point in having a non-constant max backedge taken count!");
  return getConstantMax();
}
 
const SCEV *ScalarEvolution::BackedgeTakenInfo::getSymbolicMax(
    const Loop *L, ScalarEvolution *SE,
    SmallVectorImpl<const SCEVPredicate *> *Predicates) {
  if (!SymbolicMax) {
    // Form an expression for the maximum exit count possible for this loop. We
    // merge the max and exact information to approximate a version of
    // getConstantMaxBackedgeTakenCount which isn't restricted to just
    // constants.
    SmallVector<SCEVUse, 4> ExitCounts;
 
    for (const auto &ENT : ExitNotTaken) {
      const SCEV *ExitCount = ENT.SymbolicMaxNotTaken;
      if (!isa<SCEVCouldNotCompute>(ExitCount)) {
        assert(SE->DT.dominates(ENT.ExitingBlock, L->getLoopLatch()) &&
               "We should only have known counts for exiting blocks that "
               "dominate latch!");
        ExitCounts.push_back(ExitCount);
        if (Predicates)
          append_range(*Predicates, ENT.Predicates);
 
        assert((Predicates || ENT.hasAlwaysTruePredicate()) &&
               "Predicate should be always true!");
      }
    }
    if (ExitCounts.empty())
      SymbolicMax = SE->getCouldNotCompute();
    else
      SymbolicMax =
          SE->getUMinFromMismatchedTypes(ExitCounts, /*Sequential*/ true);
  }
  return SymbolicMax;
}
 
bool ScalarEvolution::BackedgeTakenInfo::isConstantMaxOrZero(
    ScalarEvolution *SE) const {
  auto PredicateNotAlwaysTrue = [](const ExitNotTakenInfo &ENT) {
    return !ENT.hasAlwaysTruePredicate();
  };
  return MaxOrZero && !any_of(ExitNotTaken, PredicateNotAlwaysTrue);
}
 
ScalarEvolution::ExitLimit::ExitLimit(const SCEV *E)
    : ExitLimit(E, E, E, false) {}
 
ScalarEvolution::ExitLimit::ExitLimit(
    const SCEV *E, const SCEV *ConstantMaxNotTaken,
    const SCEV *SymbolicMaxNotTaken, bool MaxOrZero,
    ArrayRef<ArrayRef<const SCEVPredicate *>> PredLists)
    : ExactNotTaken(E), ConstantMaxNotTaken(ConstantMaxNotTaken),
      SymbolicMaxNotTaken(SymbolicMaxNotTaken), MaxOrZero(MaxOrZero) {
  // If we prove the max count is zero, so is the symbolic bound.  This happens
  // in practice due to differences in a) how context sensitive we've chosen
  // to be and b) how we reason about bounds implied by UB.
  if (ConstantMaxNotTaken->isZero()) {
    this->ExactNotTaken = E = ConstantMaxNotTaken;
    this->SymbolicMaxNotTaken = SymbolicMaxNotTaken = ConstantMaxNotTaken;
  }
 
  assert((isa<SCEVCouldNotCompute>(ExactNotTaken) ||
          !isa<SCEVCouldNotCompute>(ConstantMaxNotTaken)) &&
         "Exact is not allowed to be less precise than Constant Max");
  assert((isa<SCEVCouldNotCompute>(ExactNotTaken) ||
          !isa<SCEVCouldNotCompute>(SymbolicMaxNotTaken)) &&
         "Exact is not allowed to be less precise than Symbolic Max");
  assert((isa<SCEVCouldNotCompute>(SymbolicMaxNotTaken) ||
          !isa<SCEVCouldNotCompute>(ConstantMaxNotTaken)) &&
         "Symbolic Max is not allowed to be less precise than Constant Max");
  assert((isa<SCEVCouldNotCompute>(ConstantMaxNotTaken) ||
          isa<SCEVConstant>(ConstantMaxNotTaken)) &&
         "No point in having a non-constant max backedge taken count!");
  SmallPtrSet<const SCEVPredicate *, 4> SeenPreds;
  for (const auto PredList : PredLists)
    for (const auto *P : PredList) {
      if (SeenPreds.contains(P))
        continue;
      assert(!isa<SCEVUnionPredicate>(P) && "Only add leaf predicates here!");
      SeenPreds.insert(P);
      Predicates.push_back(P);
    }
  assert((isa<SCEVCouldNotCompute>(E) || !E->getType()->isPointerTy()) &&
         "Backedge count should be int");
  assert((isa<SCEVCouldNotCompute>(ConstantMaxNotTaken) ||
          !ConstantMaxNotTaken->getType()->isPointerTy()) &&
         "Max backedge count should be int");
}
 
ScalarEvolution::ExitLimit::ExitLimit(const SCEV *E,
                                      const SCEV *ConstantMaxNotTaken,
                                      const SCEV *SymbolicMaxNotTaken,
                                      bool MaxOrZero,
                                      ArrayRef<const SCEVPredicate *> PredList)
    : ExitLimit(E, ConstantMaxNotTaken, SymbolicMaxNotTaken, MaxOrZero,
                ArrayRef({PredList})) {}
 
/// Allocate memory for BackedgeTakenInfo and copy the not-taken count of each
/// computable exit into a persistent ExitNotTakenInfo array.
ScalarEvolution::BackedgeTakenInfo::BackedgeTakenInfo(
    ArrayRef<ScalarEvolution::BackedgeTakenInfo::EdgeExitInfo> ExitCounts,
    bool IsComplete, const SCEV *ConstantMax, bool MaxOrZero)
    : ConstantMax(ConstantMax), IsComplete(IsComplete), MaxOrZero(MaxOrZero) {
  using EdgeExitInfo = ScalarEvolution::BackedgeTakenInfo::EdgeExitInfo;
 
  ExitNotTaken.reserve(ExitCounts.size());
  std::transform(ExitCounts.begin(), ExitCounts.end(),
                 std::back_inserter(ExitNotTaken),
                 [&](const EdgeExitInfo &EEI) {
        BasicBlock *ExitBB = EEI.first;
        const ExitLimit &EL = EEI.second;
        return ExitNotTakenInfo(ExitBB, EL.ExactNotTaken,
                                EL.ConstantMaxNotTaken, EL.SymbolicMaxNotTaken,
                                EL.Predicates);
  });
  assert((isa<SCEVCouldNotCompute>(ConstantMax) ||
          isa<SCEVConstant>(ConstantMax)) &&
         "No point in having a non-constant max backedge taken count!");
}
 
/// Compute the number of times the backedge of the specified loop will execute.
ScalarEvolution::BackedgeTakenInfo
ScalarEvolution::computeBackedgeTakenCount(const Loop *L,
                                           bool AllowPredicates) {
  SmallVector<BasicBlock *, 8> ExitingBlocks;
  L->getExitingBlocks(ExitingBlocks);
 
  using EdgeExitInfo = ScalarEvolution::BackedgeTakenInfo::EdgeExitInfo;
 
  SmallVector<EdgeExitInfo, 4> ExitCounts;
  bool CouldComputeBECount = true;
  BasicBlock *Latch = L->getLoopLatch(); // may be NULL.
  const SCEV *MustExitMaxBECount = nullptr;
  const SCEV *MayExitMaxBECount = nullptr;
  bool MustExitMaxOrZero = false;
  bool IsOnlyExit = ExitingBlocks.size() == 1;
 
  // Compute the ExitLimit for each loop exit. Use this to populate ExitCounts
  // and compute maxBECount.
  // Do a union of all the predicates here.
  for (BasicBlock *ExitBB : ExitingBlocks) {
    // We canonicalize untaken exits to br (constant), ignore them so that
    // proving an exit untaken doesn't negatively impact our ability to reason
    // about the loop as whole.
    if (auto *BI = dyn_cast<CondBrInst>(ExitBB->getTerminator()))
      if (auto *CI = dyn_cast<ConstantInt>(BI->getCondition())) {
        bool ExitIfTrue = !L->contains(BI->getSuccessor(0));
        if (ExitIfTrue == CI->isZero())
          continue;
      }
 
    ExitLimit EL = computeExitLimit(L, ExitBB, IsOnlyExit, AllowPredicates);
 
    assert((AllowPredicates || EL.Predicates.empty()) &&
           "Predicated exit limit when predicates are not allowed!");
 
    // 1. For each exit that can be computed, add an entry to ExitCounts.
    // CouldComputeBECount is true only if all exits can be computed.
    if (EL.ExactNotTaken != getCouldNotCompute())
      ++NumExitCountsComputed;
    else
      // We couldn't compute an exact value for this exit, so
      // we won't be able to compute an exact value for the loop.
      CouldComputeBECount = false;
    // Remember exit count if either exact or symbolic is known. Because
    // Exact always implies symbolic, only check symbolic.
    if (EL.SymbolicMaxNotTaken != getCouldNotCompute())
      ExitCounts.emplace_back(ExitBB, EL);
    else {
      assert(EL.ExactNotTaken == getCouldNotCompute() &&
             "Exact is known but symbolic isn't?");
      ++NumExitCountsNotComputed;
    }
 
    // 2. Derive the loop's MaxBECount from each exit's max number of
    // non-exiting iterations. Partition the loop exits into two kinds:
    // LoopMustExits and LoopMayExits.
    //
    // If the exit dominates the loop latch, it is a LoopMustExit otherwise it
    // is a LoopMayExit.  If any computable LoopMustExit is found, then
    // MaxBECount is the minimum EL.ConstantMaxNotTaken of computable
    // LoopMustExits. Otherwise, MaxBECount is conservatively the maximum
    // EL.ConstantMaxNotTaken, where CouldNotCompute is considered greater than
    // any
    // computable EL.ConstantMaxNotTaken.
    if (EL.ConstantMaxNotTaken != getCouldNotCompute() && Latch &&
        DT.dominates(ExitBB, Latch)) {
      if (!MustExitMaxBECount) {
        MustExitMaxBECount = EL.ConstantMaxNotTaken;
        MustExitMaxOrZero = EL.MaxOrZero;
      } else {
        MustExitMaxBECount = getUMinFromMismatchedTypes(MustExitMaxBECount,
                                                        EL.ConstantMaxNotTaken);
      }
    } else if (MayExitMaxBECount != getCouldNotCompute()) {
      if (!MayExitMaxBECount || EL.ConstantMaxNotTaken == getCouldNotCompute())
        MayExitMaxBECount = EL.ConstantMaxNotTaken;
      else {
        MayExitMaxBECount = getUMaxFromMismatchedTypes(MayExitMaxBECount,
                                                       EL.ConstantMaxNotTaken);
      }
    }
  }
  const SCEV *MaxBECount = MustExitMaxBECount ? MustExitMaxBECount :
    (MayExitMaxBECount ? MayExitMaxBECount : getCouldNotCompute());
  // The loop backedge will be taken the maximum or zero times if there's
  // a single exit that must be taken the maximum or zero times.
  bool MaxOrZero = (MustExitMaxOrZero && ExitingBlocks.size() == 1);
 
  // Remember which SCEVs are used in exit limits for invalidation purposes.
  // We only care about non-constant SCEVs here, so we can ignore
  // EL.ConstantMaxNotTaken
  // and MaxBECount, which must be SCEVConstant.
  for (const auto &Pair : ExitCounts) {
    if (!isa<SCEVConstant>(Pair.second.ExactNotTaken))
      BECountUsers[Pair.second.ExactNotTaken].insert({L, AllowPredicates});
    if (!isa<SCEVConstant>(Pair.second.SymbolicMaxNotTaken))
      BECountUsers[Pair.second.SymbolicMaxNotTaken].insert(
          {L, AllowPredicates});
  }
  return BackedgeTakenInfo(std::move(ExitCounts), CouldComputeBECount,
                           MaxBECount, MaxOrZero);
}
 
ScalarEvolution::ExitLimit
ScalarEvolution::computeExitLimit(const Loop *L, BasicBlock *ExitingBlock,
                                  bool IsOnlyExit, bool AllowPredicates) {
  assert(L->contains(ExitingBlock) && "Exit count for non-loop block?");
  // If our exiting block does not dominate the latch, then its connection with
  // loop's exit limit may be far from trivial.
  const BasicBlock *Latch = L->getLoopLatch();
  if (!Latch || !DT.dominates(ExitingBlock, Latch))
    return getCouldNotCompute();
 
  Instruction *Term = ExitingBlock->getTerminator();
  if (CondBrInst *BI = dyn_cast<CondBrInst>(Term)) {
    bool ExitIfTrue = !L->contains(BI->getSuccessor(0));
    assert(ExitIfTrue == L->contains(BI->getSuccessor(1)) &&
           "It should have one successor in loop and one exit block!");
    // Proceed to the next level to examine the exit condition expression.
    return computeExitLimitFromCond(L, BI->getCondition(), ExitIfTrue,
                                    /*ControlsOnlyExit=*/IsOnlyExit,
                                    AllowPredicates);
  }
 
  if (SwitchInst *SI = dyn_cast<SwitchInst>(Term)) {
    // For switch, make sure that there is a single exit from the loop.
    BasicBlock *Exit = nullptr;
    for (auto *SBB : successors(ExitingBlock))
      if (!L->contains(SBB)) {
        if (Exit) // Multiple exit successors.
          return getCouldNotCompute();
        Exit = SBB;
      }
    assert(Exit && "Exiting block must have at least one exit");
    return computeExitLimitFromSingleExitSwitch(
        L, SI, Exit, /*ControlsOnlyExit=*/IsOnlyExit);
  }
 
  return getCouldNotCompute();
}
 
ScalarEvolution::ExitLimit ScalarEvolution::computeExitLimitFromCond(
    const Loop *L, Value *ExitCond, bool ExitIfTrue, bool ControlsOnlyExit,
    bool AllowPredicates) {
  ScalarEvolution::ExitLimitCacheTy Cache(L, ExitIfTrue, AllowPredicates);
  return computeExitLimitFromCondCached(Cache, L, ExitCond, ExitIfTrue,
                                        ControlsOnlyExit, AllowPredicates);
}
 
std::optional<ScalarEvolution::ExitLimit>
ScalarEvolution::ExitLimitCache::find(const Loop *L, Value *ExitCond,
                                      bool ExitIfTrue, bool ControlsOnlyExit,
                                      bool AllowPredicates) {
  (void)this->L;
  (void)this->ExitIfTrue;
  (void)this->AllowPredicates;
 
  assert(this->L == L && this->ExitIfTrue == ExitIfTrue &&
         this->AllowPredicates == AllowPredicates &&
         "Variance in assumed invariant key components!");
  auto Itr = TripCountMap.find({ExitCond, ControlsOnlyExit});
  if (Itr == TripCountMap.end())
    return std::nullopt;
  return Itr->second;
}
 
void ScalarEvolution::ExitLimitCache::insert(const Loop *L, Value *ExitCond,
                                             bool ExitIfTrue,
                                             bool ControlsOnlyExit,
                                             bool AllowPredicates,
                                             const ExitLimit &EL) {
  assert(this->L == L && this->ExitIfTrue == ExitIfTrue &&
         this->AllowPredicates == AllowPredicates &&
         "Variance in assumed invariant key components!");
 
  auto InsertResult = TripCountMap.insert({{ExitCond, ControlsOnlyExit}, EL});
  assert(InsertResult.second && "Expected successful insertion!");
  (void)InsertResult;
  (void)ExitIfTrue;
}
 
ScalarEvolution::ExitLimit ScalarEvolution::computeExitLimitFromCondCached(
    ExitLimitCacheTy &Cache, const Loop *L, Value *ExitCond, bool ExitIfTrue,
    bool ControlsOnlyExit, bool AllowPredicates) {
 
  if (auto MaybeEL = Cache.find(L, ExitCond, ExitIfTrue, ControlsOnlyExit,
                                AllowPredicates))
    return *MaybeEL;
 
  ExitLimit EL = computeExitLimitFromCondImpl(
      Cache, L, ExitCond, ExitIfTrue, ControlsOnlyExit, AllowPredicates);
  Cache.insert(L, ExitCond, ExitIfTrue, ControlsOnlyExit, AllowPredicates, EL);
  return EL;
}
 
ScalarEvolution::ExitLimit ScalarEvolution::computeExitLimitFromCondImpl(
    ExitLimitCacheTy &Cache, const Loop *L, Value *ExitCond, bool ExitIfTrue,
    bool ControlsOnlyExit, bool AllowPredicates) {
  // Handle BinOp conditions (And, Or).
  if (auto LimitFromBinOp = computeExitLimitFromCondFromBinOp(
          Cache, L, ExitCond, ExitIfTrue, AllowPredicates))
    return *LimitFromBinOp;
 
  // With an icmp, it may be feasible to compute an exact backedge-taken count.
  // Proceed to the next level to examine the icmp.
  if (ICmpInst *ExitCondICmp = dyn_cast<ICmpInst>(ExitCond)) {
    ExitLimit EL =
        computeExitLimitFromICmp(L, ExitCondICmp, ExitIfTrue, ControlsOnlyExit);
    if (EL.hasFullInfo() || !AllowPredicates)
      return EL;
 
    // Try again, but use SCEV predicates this time.
    return computeExitLimitFromICmp(L, ExitCondICmp, ExitIfTrue,
                                    ControlsOnlyExit,
                                    /*AllowPredicates=*/true);
  }
 
  // Check for a constant condition. These are normally stripped out by
  // SimplifyCFG, but ScalarEvolution may be used by a pass which wishes to
  // preserve the CFG and is temporarily leaving constant conditions
  // in place.
  if (ConstantInt *CI = dyn_cast<ConstantInt>(ExitCond)) {
    if (ExitIfTrue == !CI->getZExtValue())
      // The backedge is always taken.
      return getCouldNotCompute();
    // The backedge is never taken.
    return getZero(CI->getType());
  }
 
  // If we're exiting based on the overflow flag of an x.with.overflow intrinsic
  // with a constant step, we can form an equivalent icmp predicate and figure
  // out how many iterations will be taken before we exit.
  const WithOverflowInst *WO;
  const APInt *C;
  if (match(ExitCond, m_ExtractValue<1>(m_WithOverflowInst(WO))) &&
      match(WO->getRHS(), m_APInt(C))) {
    ConstantRange NWR =
      ConstantRange::makeExactNoWrapRegion(WO->getBinaryOp(), *C,
                                           WO->getNoWrapKind());
    CmpInst::Predicate Pred;
    APInt NewRHSC, Offset;
    NWR.getEquivalentICmp(Pred, NewRHSC, Offset);
    if (!ExitIfTrue)
      Pred = ICmpInst::getInversePredicate(Pred);
    auto *LHS = getSCEV(WO->getLHS());
    if (Offset != 0)
      LHS = getAddExpr(LHS, getConstant(Offset));
    auto EL = computeExitLimitFromICmp(L, Pred, LHS, getConstant(NewRHSC),
                                       ControlsOnlyExit, AllowPredicates);
    if (EL.hasAnyInfo())
      return EL;
  }
 
  // If it's not an integer or pointer comparison then compute it the hard way.
  return computeExitCountExhaustively(L, ExitCond, ExitIfTrue);
}
 
std::optional<ScalarEvolution::ExitLimit>
ScalarEvolution::computeExitLimitFromCondFromBinOp(ExitLimitCacheTy &Cache,
                                                   const Loop *L,
                                                   Value *ExitCond,
                                                   bool ExitIfTrue,
                                                   bool AllowPredicates) {
  // Check if the controlling expression for this loop is an And or Or.
  Value *Op0, *Op1;
  bool IsAnd;
  if (match(ExitCond, m_LogicalAnd(m_Value(Op0), m_Value(Op1))))
    IsAnd = true;
  else if (match(ExitCond, m_LogicalOr(m_Value(Op0), m_Value(Op1))))
    IsAnd = false;
  else
    return std::nullopt;
 
  // A sub-condition of a non-trivial binop never solely controls the exit,
  // whether we exit always depends on both conditions.
  ExitLimit EL0 = computeExitLimitFromCondCached(
      Cache, L, Op0, ExitIfTrue, /*ControlsOnlyExit=*/false, AllowPredicates);
  ExitLimit EL1 = computeExitLimitFromCondCached(
      Cache, L, Op1, ExitIfTrue, /*ControlsOnlyExit=*/false, AllowPredicates);
 
  // EitherMayExit is true in these two cases:
  //   br (and Op0 Op1), loop, exit
  //   br (or  Op0 Op1), exit, loop
  bool EitherMayExit = IsAnd ^ ExitIfTrue;
 
  const SCEV *BECount = getCouldNotCompute();
  const SCEV *ConstantMaxBECount = getCouldNotCompute();
  const SCEV *SymbolicMaxBECount = getCouldNotCompute();
  if (EitherMayExit) {
    bool UseSequentialUMin = !isa<BinaryOperator>(ExitCond);
    // Both conditions must be same for the loop to continue executing.
    // Choose the less conservative count.
    if (EL0.ExactNotTaken != getCouldNotCompute() &&
        EL1.ExactNotTaken != getCouldNotCompute()) {
      BECount = getUMinFromMismatchedTypes(EL0.ExactNotTaken, EL1.ExactNotTaken,
                                           UseSequentialUMin);
    }
    if (EL0.ConstantMaxNotTaken == getCouldNotCompute())
      ConstantMaxBECount = EL1.ConstantMaxNotTaken;
    else if (EL1.ConstantMaxNotTaken == getCouldNotCompute())
      ConstantMaxBECount = EL0.ConstantMaxNotTaken;
    else
      ConstantMaxBECount = getUMinFromMismatchedTypes(EL0.ConstantMaxNotTaken,
                                                      EL1.ConstantMaxNotTaken);
    if (EL0.SymbolicMaxNotTaken == getCouldNotCompute())
      SymbolicMaxBECount = EL1.SymbolicMaxNotTaken;
    else if (EL1.SymbolicMaxNotTaken == getCouldNotCompute())
      SymbolicMaxBECount = EL0.SymbolicMaxNotTaken;
    else
      SymbolicMaxBECount = getUMinFromMismatchedTypes(
          EL0.SymbolicMaxNotTaken, EL1.SymbolicMaxNotTaken, UseSequentialUMin);
  } else {
    // Both conditions must be same at the same time for the loop to exit.
    // For now, be conservative.
    if (EL0.ExactNotTaken == EL1.ExactNotTaken)
      BECount = EL0.ExactNotTaken;
  }
 
  // There are cases (e.g. PR26207) where computeExitLimitFromCond is able
  // to be more aggressive when computing BECount than when computing
  // ConstantMaxBECount.  In these cases it is possible for EL0.ExactNotTaken
  // and
  // EL1.ExactNotTaken to match, but for EL0.ConstantMaxNotTaken and
  // EL1.ConstantMaxNotTaken to not.
  if (isa<SCEVCouldNotCompute>(ConstantMaxBECount) &&
      !isa<SCEVCouldNotCompute>(BECount))
    ConstantMaxBECount = getConstant(getUnsignedRangeMax(BECount));
  if (isa<SCEVCouldNotCompute>(SymbolicMaxBECount))
    SymbolicMaxBECount =
        isa<SCEVCouldNotCompute>(BECount) ? ConstantMaxBECount : BECount;
  return ExitLimit(BECount, ConstantMaxBECount, SymbolicMaxBECount, false,
                   {ArrayRef(EL0.Predicates), ArrayRef(EL1.Predicates)});
}
 
ScalarEvolution::ExitLimit ScalarEvolution::computeExitLimitFromICmp(
    const Loop *L, ICmpInst *ExitCond, bool ExitIfTrue, bool ControlsOnlyExit,
    bool AllowPredicates) {
  // If the condition was exit on true, convert the condition to exit on false
  CmpPredicate Pred;
  if (!ExitIfTrue)
    Pred = ExitCond->getCmpPredicate();
  else
    Pred = ExitCond->getInverseCmpPredicate();
  const ICmpInst::Predicate OriginalPred = Pred;
 
  const SCEV *LHS = getSCEV(ExitCond->getOperand(0));
  const SCEV *RHS = getSCEV(ExitCond->getOperand(1));
 
  ExitLimit EL = computeExitLimitFromICmp(L, Pred, LHS, RHS, ControlsOnlyExit,
                                          AllowPredicates);
  if (EL.hasAnyInfo())
    return EL;
 
  auto *ExhaustiveCount =
      computeExitCountExhaustively(L, ExitCond, ExitIfTrue);
 
  if (!isa<SCEVCouldNotCompute>(ExhaustiveCount))
    return ExhaustiveCount;
 
  return computeShiftCompareExitLimit(ExitCond->getOperand(0),
                                      ExitCond->getOperand(1), L, OriginalPred);
}
ScalarEvolution::ExitLimit ScalarEvolution::computeExitLimitFromICmp(
    const Loop *L, CmpPredicate Pred, SCEVUse LHS, SCEVUse RHS,
    bool ControlsOnlyExit, bool AllowPredicates) {
 
  // Try to evaluate any dependencies out of the loop.
  LHS = getSCEVAtScope(LHS, L);
  RHS = getSCEVAtScope(RHS, L);
 
  // At this point, we would like to compute how many iterations of the
  // loop the predicate will return true for these inputs.
  if (isLoopInvariant(LHS, L) && !isLoopInvariant(RHS, L)) {
    // If there is a loop-invariant, force it into the RHS.
    std::swap(LHS, RHS);
    Pred = ICmpInst::getSwappedCmpPredicate(Pred);
  }
 
  bool ControllingFiniteLoop = ControlsOnlyExit && loopHasNoAbnormalExits(L) &&
                               loopIsFiniteByAssumption(L);
  // Simplify the operands before analyzing them.
  (void)SimplifyICmpOperands(Pred, LHS, RHS, /*Depth=*/0);
 
  // If we have a comparison of a chrec against a constant, try to use value
  // ranges to answer this query.
  if (const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(RHS))
    if (const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(LHS))
      if (AddRec->getLoop() == L) {
        // Form the constant range.
        ConstantRange CompRange =
            ConstantRange::makeExactICmpRegion(Pred, RHSC->getAPInt());
 
        const SCEV *Ret = AddRec->getNumIterationsInRange(CompRange, *this);
        if (!isa<SCEVCouldNotCompute>(Ret)) return Ret;
      }
 
  // If this loop must exit based on this condition (or execute undefined
  // behaviour), see if we can improve wrap flags.  This is essentially
  // a must execute style proof.
  if (ControllingFiniteLoop && isLoopInvariant(RHS, L)) {
    // If we can prove the test sequence produced must repeat the same values
    // on self-wrap of the IV, then we can infer that IV doesn't self wrap
    // because if it did, we'd have an infinite (undefined) loop.
    // TODO: We can peel off any functions which are invertible *in L*.  Loop
    // invariant terms are effectively constants for our purposes here.
    SCEVUse InnerLHS = LHS;
    if (auto *ZExt = dyn_cast<SCEVZeroExtendExpr>(LHS))
      InnerLHS = ZExt->getOperand();
    if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(InnerLHS);
        AR && !AR->hasNoSelfWrap() && AR->getLoop() == L && AR->isAffine() &&
        isKnownToBeAPowerOfTwo(AR->getStepRecurrence(*this), /*OrZero=*/true,
                               /*OrNegative=*/true)) {
      auto Flags = AR->getNoWrapFlags();
      Flags = setFlags(Flags, SCEV::FlagNW);
      SmallVector<SCEVUse> Operands{AR->operands()};
      Flags = StrengthenNoWrapFlags(this, scAddRecExpr, Operands, Flags);
      setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR), Flags);
    }
 
    // For a slt/ult condition with a positive step, can we prove nsw/nuw?
    // From no-self-wrap, this follows trivially from the fact that every
    // (un)signed-wrapped, but not self-wrapped value must be LT than the
    // last value before (un)signed wrap.  Since we know that last value
    // didn't exit, nor will any smaller one.
    if (Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_ULT) {
      auto WrapType = Pred == ICmpInst::ICMP_SLT ? SCEV::FlagNSW : SCEV::FlagNUW;
      if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(LHS);
          AR && AR->getLoop() == L && AR->isAffine() &&
          !AR->getNoWrapFlags(WrapType) && AR->hasNoSelfWrap() &&
          isKnownPositive(AR->getStepRecurrence(*this))) {
        auto Flags = AR->getNoWrapFlags();
        Flags = setFlags(Flags, WrapType);
        SmallVector<SCEVUse> Operands{AR->operands()};
        Flags = StrengthenNoWrapFlags(this, scAddRecExpr, Operands, Flags);
        setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR), Flags);
      }
    }
  }
 
  switch (Pred) {
  case ICmpInst::ICMP_NE: {                     // while (X != Y)
    // Convert to: while (X-Y != 0)
    if (LHS->getType()->isPointerTy()) {
      LHS = getPtrToAddrExpr(LHS);
      if (isa<SCEVCouldNotCompute>(LHS))
        return LHS;
    }
    if (RHS->getType()->isPointerTy()) {
      RHS = getPtrToAddrExpr(RHS);
      if (isa<SCEVCouldNotCompute>(RHS))
        return RHS;
    }
    ExitLimit EL = howFarToZero(getMinusSCEV(LHS, RHS), L, ControlsOnlyExit,
                                AllowPredicates);
    if (EL.hasAnyInfo())
      return EL;
    break;
  }
  case ICmpInst::ICMP_EQ: {                     // while (X == Y)
    // Convert to: while (X-Y == 0)
    if (LHS->getType()->isPointerTy()) {
      LHS = getPtrToAddrExpr(LHS);
      if (isa<SCEVCouldNotCompute>(LHS))
        return LHS;
    }
    if (RHS->getType()->isPointerTy()) {
      RHS = getPtrToAddrExpr(RHS);
      if (isa<SCEVCouldNotCompute>(RHS))
        return RHS;
    }
    ExitLimit EL = howFarToNonZero(getMinusSCEV(LHS, RHS), L);
    if (EL.hasAnyInfo()) return EL;
    break;
  }
  case ICmpInst::ICMP_SLE:
  case ICmpInst::ICMP_ULE:
    // Since the loop is finite, an invariant RHS cannot include the boundary
    // value, otherwise it would loop forever.
    if (!EnableFiniteLoopControl || !ControllingFiniteLoop ||
        !isLoopInvariant(RHS, L)) {
      // Otherwise, perform the addition in a wider type, to avoid overflow.
      // If the LHS is an addrec with the appropriate nowrap flag, the
      // extension will be sunk into it and the exit count can be analyzed.
      auto *OldType = dyn_cast<IntegerType>(LHS->getType());
      if (!OldType)
        break;
      // Prefer doubling the bitwidth over adding a single bit to make it more
      // likely that we use a legal type.
      auto *NewType =
          Type::getIntNTy(OldType->getContext(), OldType->getBitWidth() * 2);
      if (ICmpInst::isSigned(Pred)) {
        LHS = getSignExtendExpr(LHS, NewType);
        RHS = getSignExtendExpr(RHS, NewType);
      } else {
        LHS = getZeroExtendExpr(LHS, NewType);
        RHS = getZeroExtendExpr(RHS, NewType);
      }
    }
    RHS = getAddExpr(getOne(RHS->getType()), RHS);
    [[fallthrough]];
  case ICmpInst::ICMP_SLT:
  case ICmpInst::ICMP_ULT: { // while (X < Y)
    bool IsSigned = ICmpInst::isSigned(Pred);
    ExitLimit EL = howManyLessThans(LHS, RHS, L, IsSigned, /*Invert=*/false,
                                    ControlsOnlyExit, AllowPredicates);
    if (EL.hasAnyInfo())
      return EL;
    break;
  }
  case ICmpInst::ICMP_SGE:
  case ICmpInst::ICMP_UGE:
    // Since the loop is finite, an invariant RHS cannot include the boundary
    // value, otherwise it would loop forever.
    if (!EnableFiniteLoopControl || !ControllingFiniteLoop ||
        !isLoopInvariant(RHS, L))
      break;
    RHS = getAddExpr(getMinusOne(RHS->getType()), RHS);
    [[fallthrough]];
  case ICmpInst::ICMP_SGT:
  case ICmpInst::ICMP_UGT: { // while (X > Y)
    // "X > Y" is analyzed as the equivalent "~X < ~Y".
    bool IsSigned = ICmpInst::isSigned(Pred);
    ExitLimit EL = howManyLessThans(LHS, RHS, L, IsSigned, /*Invert=*/true,
                                    ControlsOnlyExit, AllowPredicates);
    if (EL.hasAnyInfo())
      return EL;
    break;
  }
  default:
    break;
  }
 
  return getCouldNotCompute();
}
 
ScalarEvolution::ExitLimit
ScalarEvolution::computeExitLimitFromSingleExitSwitch(const Loop *L,
                                                      SwitchInst *Switch,
                                                      BasicBlock *ExitingBlock,
                                                      bool ControlsOnlyExit) {
  assert(!L->contains(ExitingBlock) && "Not an exiting block!");
 
  // Give up if the exit is the default dest of a switch.
  if (Switch->getDefaultDest() == ExitingBlock)
    return getCouldNotCompute();
 
  assert(L->contains(Switch->getDefaultDest()) &&
         "Default case must not exit the loop!");
  const SCEV *LHS = getSCEVAtScope(Switch->getCondition(), L);
  const SCEV *RHS = getConstant(Switch->findCaseDest(ExitingBlock));
 
  // while (X != Y) --> while (X-Y != 0)
  ExitLimit EL = howFarToZero(getMinusSCEV(LHS, RHS), L, ControlsOnlyExit);
  if (EL.hasAnyInfo())
    return EL;
 
  return getCouldNotCompute();
}
 
static ConstantInt *
EvaluateConstantChrecAtConstant(const SCEVAddRecExpr *AddRec, ConstantInt *C,
                                ScalarEvolution &SE) {
  const SCEV *InVal = SE.getConstant(C);
  const SCEV *Val = AddRec->evaluateAtIteration(InVal, SE);
  assert(isa<SCEVConstant>(Val) &&
         "Evaluation of SCEV at constant didn't fold correctly?");
  return cast<SCEVConstant>(Val)->getValue();
}
 
ScalarEvolution::ExitLimit ScalarEvolution::computeShiftCompareExitLimit(
    Value *LHS, Value *RHSV, const Loop *L, ICmpInst::Predicate Pred) {
  ConstantInt *RHS = dyn_cast<ConstantInt>(RHSV);
  if (!RHS)
    return getCouldNotCompute();
 
  const BasicBlock *Latch = L->getLoopLatch();
  if (!Latch)
    return getCouldNotCompute();
 
  const BasicBlock *Predecessor = L->getLoopPredecessor();
  if (!Predecessor)
    return getCouldNotCompute();
 
  // Return true if V is of the form "LHS `shift_op` <positive constant>".
  // Return LHS in OutLHS, shift_op in OutOpCode, and the shift amount in
  // OutShiftAmt.
  auto MatchPositiveShift = [](Value *V, Value *&OutLHS,
                               Instruction::BinaryOps &OutOpCode,
                               unsigned &OutShiftAmt) {
    using namespace PatternMatch;
 
    ConstantInt *ShiftAmt;
    if (match(V, m_LShr(m_Value(OutLHS), m_ConstantInt(ShiftAmt))))
      OutOpCode = Instruction::LShr;
    else if (match(V, m_AShr(m_Value(OutLHS), m_ConstantInt(ShiftAmt))))
      OutOpCode = Instruction::AShr;
    else if (match(V, m_Shl(m_Value(OutLHS), m_ConstantInt(ShiftAmt))))
      OutOpCode = Instruction::Shl;
    else
      return false;
 
    uint64_t Amt = ShiftAmt->getValue().getLimitedValue();
    if (Amt == 0 || Amt >= OutLHS->getType()->getScalarSizeInBits())
      return false;
    OutShiftAmt = Amt;
    return true;
  };
 
  // Recognize a "shift recurrence" either of the form %iv or of %iv.shifted in
  //
  // loop:
  //   %iv = phi i32 [ %iv.shifted, %loop ], [ %val, %preheader ]
  //   %iv.shifted = lshr i32 %iv, <positive constant>
  //
  // Return true on a successful match.  Return the corresponding PHI node (%iv
  // above) in PNOut, the opcode of the shift operation in OpCodeOut, and the
  // shift amount in ShiftAmtOut.
  auto MatchShiftRecurrence = [&](Value *V, PHINode *&PNOut,
                                  Instruction::BinaryOps &OpCodeOut,
                                  unsigned &ShiftAmtOut) {
    std::optional<Instruction::BinaryOps> PostShiftOpCode;
 
    {
      Instruction::BinaryOps OpC;
      Value *V;
      unsigned Amt;
 
      // If we encounter a shift instruction, "peel off" the shift operation,
      // and remember that we did so.  Later when we inspect %iv's backedge
      // value, we will make sure that the backedge value uses the same
      // operation.
      //
      // Note: the peeled shift operation does not have to be the same
      // instruction as the one feeding into the PHI's backedge value.  We only
      // really care about it being the same *kind* of shift instruction --
      // that's all that is required for our later inferences to hold.
      if (MatchPositiveShift(LHS, V, OpC, Amt)) {
        PostShiftOpCode = OpC;
        LHS = V;
      }
    }
 
    PNOut = dyn_cast<PHINode>(LHS);
    if (!PNOut || PNOut->getParent() != L->getHeader())
      return false;
 
    Value *BEValue = PNOut->getIncomingValueForBlock(Latch);
    Value *OpLHS;
 
    return
        // The backedge value for the PHI node must be a shift by a positive
        // amount
        MatchPositiveShift(BEValue, OpLHS, OpCodeOut, ShiftAmtOut) &&
 
        // of the PHI node itself
        OpLHS == PNOut &&
 
        // and the kind of shift should be match the kind of shift we peeled
        // off, if any.
        (!PostShiftOpCode || *PostShiftOpCode == OpCodeOut);
  };
 
  PHINode *PN;
  Instruction::BinaryOps OpCode;
  unsigned ShiftAmt;
  if (!MatchShiftRecurrence(LHS, PN, OpCode, ShiftAmt))
    return getCouldNotCompute();
 
  const DataLayout &DL = getDataLayout();
 
  // The key rationale for this optimization is that for some kinds of shift
  // recurrences, the value of the recurrence "stabilizes" to either 0 or -1
  // within a finite number of iterations.  If the condition guarding the
  // backedge (in the sense that the backedge is taken if the condition is true)
  // is false for the value the shift recurrence stabilizes to, then we know
  // that the backedge is taken only a finite number of times.
 
  ConstantInt *StableValue = nullptr;
  switch (OpCode) {
  default:
    llvm_unreachable("Impossible case!");
 
  case Instruction::AShr: {
    // {K,ashr,<positive-constant>} stabilizes to signum(K) in at most
    // bitwidth(K) iterations.
    Value *FirstValue = PN->getIncomingValueForBlock(Predecessor);
    KnownBits Known = computeKnownBits(FirstValue, DL, &AC,
                                       Predecessor->getTerminator(), &DT);
    auto *Ty = cast<IntegerType>(RHS->getType());
    if (Known.isNonNegative())
      StableValue = ConstantInt::get(Ty, 0);
    else if (Known.isNegative())
      StableValue = ConstantInt::get(Ty, -1, true);
    else
      return getCouldNotCompute();
 
    break;
  }
  case Instruction::LShr:
  case Instruction::Shl:
    // Both {K,lshr,<positive-constant>} and {K,shl,<positive-constant>}
    // stabilize to 0 in at most bitwidth(K) iterations.
    StableValue = ConstantInt::get(cast<IntegerType>(RHS->getType()), 0);
    break;
  }
 
  auto *Result =
      ConstantFoldCompareInstOperands(Pred, StableValue, RHS, DL, &TLI);
  assert(Result->getType()->isIntegerTy(1) &&
         "Otherwise cannot be an operand to a branch instruction");
 
  if (Result->isNullValue()) {
    unsigned BitWidth = getTypeSizeInBits(RHS->getType());
    unsigned MaxBTC = BitWidth;
 
    // For right-shift recurrences (lshr/ashr with non-negative start), we can
    // compute a tighter max backedge-taken count from the range of the start
    // value. After k shifts of ShiftAmt, value = start >> (k * ShiftAmt).
    // The value reaches 0 (the stable value) when k * ShiftAmt >=
    // activeBits(start), so max BTC = ceil(activeBits(maxStart) / ShiftAmt).
    if (OpCode == Instruction::LShr || OpCode == Instruction::AShr) {
      Value *StartValue = PN->getIncomingValueForBlock(Predecessor);
      const SCEV *StartSCEV = getSCEV(StartValue);
      APInt MaxStart = getUnsignedRangeMax(StartSCEV);
      if (MaxStart.isStrictlyPositive()) {
        unsigned ActiveBits = MaxStart.getActiveBits();
        unsigned RangeBTC = divideCeil(ActiveBits, ShiftAmt);
        MaxBTC = std::min(MaxBTC, RangeBTC);
      }
    }
 
    const SCEV *UpperBound =
        getConstant(getEffectiveSCEVType(RHS->getType()), MaxBTC);
    return ExitLimit(getCouldNotCompute(), UpperBound, UpperBound, false);
  }
 
  return getCouldNotCompute();
}
 
/// Return true if we can constant fold an instruction of the specified type,
/// assuming that all operands were constants.
static bool canConstantFold(const Instruction *I,
                            const TargetLibraryInfo *TLI) {
  if (isa<BinaryOperator, UnaryOperator, GEPOperator, FreezeInst, CmpInst,
          SelectInst, CastInst, LoadInst, ExtractElementInst, InsertElementInst,
          ExtractValueInst, InsertValueInst>(I))
    return true;
 
  if (const CallInst *CI = dyn_cast<CallInst>(I))
    if (const Function *F = CI->getCalledFunction())
      return canConstantFoldCallTo(CI, F, TLI);
  return false;
}
 
/// Determine whether this instruction can constant evolve within this loop
/// assuming its operands can all constant evolve.
static bool canConstantEvolve(Instruction *I, const Loop *L,
                              const TargetLibraryInfo *TLI) {
  // An instruction outside of the loop can't be derived from a loop PHI.
  if (!L->contains(I)) return false;
 
  if (isa<PHINode>(I)) {
    // We don't currently keep track of the control flow needed to evaluate
    // PHIs, so we cannot handle PHIs inside of loops.
    return L->getHeader() == I->getParent();
  }
 
  // If we won't be able to constant fold this expression even if the operands
  // are constants, bail early.
  return canConstantFold(I, TLI);
}
 
/// getConstantEvolvingPHIOperands - Implement getConstantEvolvingPHI by
/// recursing through each instruction operand until reaching a loop header phi.
static PHINode *
getConstantEvolvingPHIOperands(Instruction *UseInst, const Loop *L,
                               DenseMap<Instruction *, PHINode *> &PHIMap,
                               const TargetLibraryInfo *TLI, unsigned Depth) {
  if (Depth > MaxConstantEvolvingDepth)
    return nullptr;
 
  // Otherwise, we can evaluate this instruction if all of its operands are
  // constant or derived from a PHI node themselves.
  PHINode *PHI = nullptr;
  for (Value *Op : UseInst->operands()) {
    if (isa<Constant>(Op)) continue;
 
    Instruction *OpInst = dyn_cast<Instruction>(Op);
    if (!OpInst || !canConstantEvolve(OpInst, L, TLI))
      return nullptr;
 
    PHINode *P = dyn_cast<PHINode>(OpInst);
    if (!P)
      // If this operand is already visited, reuse the prior result.
      // We may have P != PHI if this is the deepest point at which the
      // inconsistent paths meet.
      P = PHIMap.lookup(OpInst);
    if (!P) {
      // Recurse and memoize the results, whether a phi is found or not.
      // This recursive call invalidates pointers into PHIMap.
      P = getConstantEvolvingPHIOperands(OpInst, L, PHIMap, TLI, Depth + 1);
      PHIMap[OpInst] = P;
    }
    if (!P)
      return nullptr;  // Not evolving from PHI
    if (PHI && PHI != P)
      return nullptr;  // Evolving from multiple different PHIs.
    PHI = P;
  }
  // This is a expression evolving from a constant PHI!
  return PHI;
}
 
/// getConstantEvolvingPHI - Given an LLVM value and a loop, return a PHI node
/// in the loop that V is derived from.  We allow arbitrary operations along the
/// way, but the operands of an operation must either be constants or a value
/// derived from a constant PHI.  If this expression does not fit with these
/// constraints, return null.
static PHINode *getConstantEvolvingPHI(Value *V, const Loop *L,
                                       const TargetLibraryInfo *TLI) {
  Instruction *I = dyn_cast<Instruction>(V);
  if (!I || !canConstantEvolve(I, L, TLI))
    return nullptr;
 
  if (PHINode *PN = dyn_cast<PHINode>(I))
    return PN;
 
  // Record non-constant instructions contained by the loop.
  DenseMap<Instruction *, PHINode *> PHIMap;
  return getConstantEvolvingPHIOperands(I, L, PHIMap, TLI, 0);
}
 
/// EvaluateExpression - Given an expression that passes the
/// getConstantEvolvingPHI predicate, evaluate its value assuming the PHI node
/// in the loop has the value PHIVal.  If we can't fold this expression for some
/// reason, return null.
static Constant *EvaluateExpression(Value *V, const Loop *L,
                                    DenseMap<Instruction *, Constant *> &Vals,
                                    const DataLayout &DL,
                                    const TargetLibraryInfo *TLI) {
  // Convenient constant check, but redundant for recursive calls.
  if (Constant *C = dyn_cast<Constant>(V)) return C;
  Instruction *I = dyn_cast<Instruction>(V);
  if (!I) return nullptr;
 
  if (Constant *C = Vals.lookup(I)) return C;
 
  // An instruction inside the loop depends on a value outside the loop that we
  // weren't given a mapping for, or a value such as a call inside the loop.
  if (!canConstantEvolve(I, L, TLI))
    return nullptr;
 
  // An unmapped PHI can be due to a branch or another loop inside this loop,
  // or due to this not being the initial iteration through a loop where we
  // couldn't compute the evolution of this particular PHI last time.
  if (isa<PHINode>(I)) return nullptr;
 
  std::vector<Constant*> Operands(I->getNumOperands());
 
  for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
    Instruction *Operand = dyn_cast<Instruction>(I->getOperand(i));
    if (!Operand) {
      Operands[i] = dyn_cast<Constant>(I->getOperand(i));
      if (!Operands[i]) return nullptr;
      continue;
    }
    Constant *C = EvaluateExpression(Operand, L, Vals, DL, TLI);
    Vals[Operand] = C;
    if (!C) return nullptr;
    Operands[i] = C;
  }
 
  return ConstantFoldInstOperands(I, Operands, DL, TLI,
                                  /*AllowNonDeterministic=*/false);
}
 
 
// If every incoming value to PN except the one for BB is a specific Constant,
// return that, else return nullptr.
static Constant *getOtherIncomingValue(PHINode *PN, BasicBlock *BB) {
  Constant *IncomingVal = nullptr;
 
  for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
    if (PN->getIncomingBlock(i) == BB)
      continue;
 
    auto *CurrentVal = dyn_cast<Constant>(PN->getIncomingValue(i));
    if (!CurrentVal)
      return nullptr;
 
    if (IncomingVal != CurrentVal) {
      if (IncomingVal)
        return nullptr;
      IncomingVal = CurrentVal;
    }
  }
 
  return IncomingVal;
}
 
/// getConstantEvolutionLoopExitValue - If we know that the specified Phi is
/// in the header of its containing loop, we know the loop executes a
/// constant number of times, and the PHI node is just a recurrence
/// involving constants, fold it.
Constant *
ScalarEvolution::getConstantEvolutionLoopExitValue(PHINode *PN,
                                                   const APInt &BEs,
                                                   const Loop *L) {
  auto [I, Inserted] = ConstantEvolutionLoopExitValue.try_emplace(PN);
  if (!Inserted)
    return I->second;
 
  if (BEs.ugt(MaxBruteForceIterations))
    return nullptr; // Not going to evaluate it.
 
  Constant *&RetVal = I->second;
 
  DenseMap<Instruction *, Constant *> CurrentIterVals;
  BasicBlock *Header = L->getHeader();
  assert(PN->getParent() == Header && "Can't evaluate PHI not in loop header!");
 
  BasicBlock *Latch = L->getLoopLatch();
  if (!Latch)
    return nullptr;
 
  for (PHINode &PHI : Header->phis()) {
    if (auto *StartCST = getOtherIncomingValue(&PHI, Latch))
      CurrentIterVals[&PHI] = StartCST;
  }
  if (!CurrentIterVals.count(PN))
    return RetVal = nullptr;
 
  Value *BEValue = PN->getIncomingValueForBlock(Latch);
 
  // Execute the loop symbolically to determine the exit value.
  assert(BEs.getActiveBits() < CHAR_BIT * sizeof(unsigned) &&
         "BEs is <= MaxBruteForceIterations which is an 'unsigned'!");
 
  unsigned NumIterations = BEs.getZExtValue(); // must be in range
  unsigned IterationNum = 0;
  const DataLayout &DL = getDataLayout();
  for (; ; ++IterationNum) {
    if (IterationNum == NumIterations)
      return RetVal = CurrentIterVals[PN];  // Got exit value!
 
    // Compute the value of the PHIs for the next iteration.
    // EvaluateExpression adds non-phi values to the CurrentIterVals map.
    DenseMap<Instruction *, Constant *> NextIterVals;
    Constant *NextPHI =
        EvaluateExpression(BEValue, L, CurrentIterVals, DL, &TLI);
    if (!NextPHI)
      return nullptr;        // Couldn't evaluate!
    NextIterVals[PN] = NextPHI;
 
    bool StoppedEvolving = NextPHI == CurrentIterVals[PN];
 
    // Also evaluate the other PHI nodes.  However, we don't get to stop if we
    // cease to be able to evaluate one of them or if they stop evolving,
    // because that doesn't necessarily prevent us from computing PN.
    SmallVector<std::pair<PHINode *, Constant *>, 8> PHIsToCompute;
    for (const auto &I : CurrentIterVals) {
      PHINode *PHI = dyn_cast<PHINode>(I.first);
      if (!PHI || PHI == PN || PHI->getParent() != Header) continue;
      PHIsToCompute.emplace_back(PHI, I.second);
    }
    // We use two distinct loops because EvaluateExpression may invalidate any
    // iterators into CurrentIterVals.
    for (const auto &I : PHIsToCompute) {
      PHINode *PHI = I.first;
      Constant *&NextPHI = NextIterVals[PHI];
      if (!NextPHI) {   // Not already computed.
        Value *BEValue = PHI->getIncomingValueForBlock(Latch);
        NextPHI = EvaluateExpression(BEValue, L, CurrentIterVals, DL, &TLI);
      }
      if (NextPHI != I.second)
        StoppedEvolving = false;
    }
 
    // If all entries in CurrentIterVals == NextIterVals then we can stop
    // iterating, the loop can't continue to change.
    if (StoppedEvolving)
      return RetVal = CurrentIterVals[PN];
 
    CurrentIterVals.swap(NextIterVals);
  }
}
 
const SCEV *ScalarEvolution::computeExitCountExhaustively(const Loop *L,
                                                          Value *Cond,
                                                          bool ExitWhen) {
  PHINode *PN = getConstantEvolvingPHI(Cond, L, &TLI);
  if (!PN) return getCouldNotCompute();
 
  // If the loop is canonicalized, the PHI will have exactly two entries.
  // That's the only form we support here.
  if (PN->getNumIncomingValues() != 2) return getCouldNotCompute();
 
  DenseMap<Instruction *, Constant *> CurrentIterVals;
  BasicBlock *Header = L->getHeader();
  assert(PN->getParent() == Header && "Can't evaluate PHI not in loop header!");
 
  BasicBlock *Latch = L->getLoopLatch();
  assert(Latch && "Should follow from NumIncomingValues == 2!");
 
  for (PHINode &PHI : Header->phis()) {
    if (auto *StartCST = getOtherIncomingValue(&PHI, Latch))
      CurrentIterVals[&PHI] = StartCST;
  }
  if (!CurrentIterVals.count(PN))
    return getCouldNotCompute();
 
  // Okay, we find a PHI node that defines the trip count of this loop.  Execute
  // the loop symbolically to determine when the condition gets a value of
  // "ExitWhen".
  unsigned MaxIterations = MaxBruteForceIterations;   // Limit analysis.
  const DataLayout &DL = getDataLayout();
  for (unsigned IterationNum = 0; IterationNum != MaxIterations;++IterationNum){
    auto *CondVal = dyn_cast_or_null<ConstantInt>(
        EvaluateExpression(Cond, L, CurrentIterVals, DL, &TLI));
 
    // Couldn't symbolically evaluate.
    if (!CondVal) return getCouldNotCompute();
 
    if (CondVal->getValue() == uint64_t(ExitWhen)) {
      ++NumBruteForceTripCountsComputed;
      return getConstant(Type::getInt32Ty(getContext()), IterationNum);
    }
 
    // Update all the PHI nodes for the next iteration.
    DenseMap<Instruction *, Constant *> NextIterVals;
 
    // Create a list of which PHIs we need to compute. We want to do this before
    // calling EvaluateExpression on them because that may invalidate iterators
    // into CurrentIterVals.
    SmallVector<PHINode *, 8> PHIsToCompute;
    for (const auto &I : CurrentIterVals) {
      PHINode *PHI = dyn_cast<PHINode>(I.first);
      if (!PHI || PHI->getParent() != Header) continue;
      PHIsToCompute.push_back(PHI);
    }
    for (PHINode *PHI : PHIsToCompute) {
      Constant *&NextPHI = NextIterVals[PHI];
      if (NextPHI) continue;    // Already computed!
 
      Value *BEValue = PHI->getIncomingValueForBlock(Latch);
      NextPHI = EvaluateExpression(BEValue, L, CurrentIterVals, DL, &TLI);
    }
    CurrentIterVals.swap(NextIterVals);
  }
 
  // Too many iterations were needed to evaluate.
  return getCouldNotCompute();
}
 
SCEVUse ScalarEvolution::getSCEVAtScope(const SCEV *V, const Loop *L) {
  if (isa<SCEVConstant>(V))
    return V;
 
  auto &Values = ValuesAtScopes[V];
  // Check to see if we've folded this expression at this loop before.
  for (auto &LS : Values)
    if (LS.first == L)
      return LS.second ? LS.second : SCEVUse(V);
 
  Values.emplace_back(L, nullptr);
 
  // Otherwise compute it.
  SCEVUse C = computeSCEVAtScope(V, L);
  for (auto &LS : reverse(ValuesAtScopes[V]))
    if (LS.first == L) {
      LS.second = C;
      // Record the dependency under the bare expression: invalidation walks
      // expressions, and any use flags on C do not change which expression
      // this is the value at scope of.
      if (!isa<SCEVConstant>(C))
        ValuesAtScopesUsers[C.getPointer()].push_back({L, V});
      break;
    }
  return C;
}
 
SCEVUse ScalarEvolution::getSCEVAtExit(const SCEV *V, const Loop *L,
                                       const BasicBlock *ExitingBlock) {
  SCEVUse ExitValue = getSCEVAtScope(V, L->getParentLoop());
  if (!isLoopInvariant(ExitValue, L)) {
    // If we failed to evaluate it in the outer scope, try to evaluate an
    // addrec for the specific exit.
    // TODO: Generalize this to other expressions.
    const SCEV *ExitCount = getExitCount(L, ExitingBlock);
    if (!isa<SCEVCouldNotCompute>(ExitCount))
      if (auto *AddRec = dyn_cast<SCEVAddRecExpr>(V))
        if (AddRec->getLoop() == L)
          ExitValue = AddRec->evaluateAtIteration(ExitCount, *this);
  }
  return ExitValue;
}
 
/// This builds up a Constant using the ConstantExpr interface.  That way, we
/// will return Constants for objects which aren't represented by a
/// SCEVConstant, because SCEVConstant is restricted to ConstantInt.
/// Returns NULL if the SCEV isn't representable as a Constant.
static Constant *BuildConstantFromSCEV(const SCEV *V) {
  switch (V->getSCEVType()) {
  case scCouldNotCompute:
  case scAddRecExpr:
  case scVScale:
    return nullptr;
  case scConstant:
    return cast<SCEVConstant>(V)->getValue();
  case scUnknown:
    return dyn_cast<Constant>(cast<SCEVUnknown>(V)->getValue());
  case scPtrToAddr: {
    const SCEVPtrToAddrExpr *P2I = cast<SCEVPtrToAddrExpr>(V);
    if (Constant *CastOp = BuildConstantFromSCEV(P2I->getOperand()))
      return ConstantExpr::getPtrToAddr(CastOp, P2I->getType());
 
    return nullptr;
  }
  case scTruncate: {
    const SCEVTruncateExpr *ST = cast<SCEVTruncateExpr>(V);
    if (Constant *CastOp = BuildConstantFromSCEV(ST->getOperand()))
      return ConstantExpr::getTrunc(CastOp, ST->getType());
    return nullptr;
  }
  case scAddExpr: {
    const SCEVAddExpr *SA = cast<SCEVAddExpr>(V);
    Constant *C = nullptr;
    for (const SCEV *Op : SA->operands()) {
      Constant *OpC = BuildConstantFromSCEV(Op);
      if (!OpC)
        return nullptr;
      if (!C) {
        C = OpC;
        continue;
      }
      assert(!C->getType()->isPointerTy() &&
             "Can only have one pointer, and it must be last");
      if (OpC->getType()->isPointerTy()) {
        // The offsets have been converted to bytes.  We can add bytes using
        // an i8 GEP.
        C = ConstantExpr::getPtrAdd(OpC, C);
      } else {
        C = ConstantExpr::getAdd(C, OpC);
      }
    }
    return C;
  }
  case scMulExpr:
  case scSignExtend:
  case scZeroExtend:
  case scUDivExpr:
  case scSMaxExpr:
  case scUMaxExpr:
  case scSMinExpr:
  case scUMinExpr:
  case scSequentialUMinExpr:
    return nullptr;
  }
  llvm_unreachable("Unknown SCEV kind!");
}
 
const SCEV *ScalarEvolution::getWithOperands(const SCEV *S,
                                             SmallVectorImpl<SCEVUse> &NewOps) {
  switch (S->getSCEVType()) {
  case scTruncate:
  case scZeroExtend:
  case scSignExtend:
  case scPtrToAddr:
    return getCastExpr(S->getSCEVType(), NewOps[0], S->getType());
  case scAddRecExpr: {
    auto *AddRec = cast<SCEVAddRecExpr>(S);
    return getAddRecExpr(NewOps, AddRec->getLoop(), AddRec->getNoWrapFlags());
  }
  case scAddExpr:
    return getAddExpr(NewOps, cast<SCEVAddExpr>(S)->getNoWrapFlags());
  case scMulExpr:
    return getMulExpr(NewOps, cast<SCEVMulExpr>(S)->getNoWrapFlags());
  case scUDivExpr:
    return getUDivExpr(NewOps[0], NewOps[1]);
  case scUMaxExpr:
  case scSMaxExpr:
  case scUMinExpr:
  case scSMinExpr:
    return getMinMaxExpr(S->getSCEVType(), NewOps);
  case scSequentialUMinExpr:
    return getSequentialMinMaxExpr(S->getSCEVType(), NewOps);
  case scConstant:
  case scVScale:
  case scUnknown:
    return S;
  case scCouldNotCompute:
    llvm_unreachable("Attempt to use a SCEVCouldNotCompute object!");
  }
  llvm_unreachable("Unknown SCEV kind!");
}
 
SCEVUse ScalarEvolution::computeSCEVAtScope(const SCEV *V, const Loop *L) {
  switch (V->getSCEVType()) {
  case scConstant:
  case scVScale:
    return V;
  case scAddRecExpr: {
    // If this is a loop recurrence for a loop that does not contain L, then we
    // are dealing with the final value computed by the loop.
    const SCEVAddRecExpr *AddRec = cast<SCEVAddRecExpr>(V);
    // First, attempt to evaluate each operand.
    // Avoid performing the look-up in the common case where the specified
    // expression has no loop-variant portions.
    for (unsigned i = 0, e = AddRec->getNumOperands(); i != e; ++i) {
      SCEVUse OpAtScope = getSCEVAtScope(AddRec->getOperand(i), L);
      if (OpAtScope == AddRec->getOperand(i))
        continue;
 
      // Okay, at least one of these operands is loop variant but might be
      // foldable.  Build a new instance of the folded commutative expression.
      SmallVector<SCEVUse, 8> NewOps;
      NewOps.reserve(AddRec->getNumOperands());
      append_range(NewOps, AddRec->operands().take_front(i));
      NewOps.push_back(OpAtScope);
      for (++i; i != e; ++i)
        NewOps.push_back(getSCEVAtScope(AddRec->getOperand(i), L));
 
      const SCEV *FoldedRec = getAddRecExpr(
          NewOps, AddRec->getLoop(), AddRec->getNoWrapFlags(SCEV::FlagNW));
      AddRec = dyn_cast<SCEVAddRecExpr>(FoldedRec);
      // The addrec may be folded to a nonrecurrence, for example, if the
      // induction variable is multiplied by zero after constant folding. Go
      // ahead and return the folded value.
      if (!AddRec)
        return FoldedRec;
      break;
    }
 
    // If the scope is outside the addrec's loop, evaluate it by using the
    // loop exit value of the addrec.
    if (!AddRec->getLoop()->contains(L)) {
      SCEVUse ExitValue = AddRec->getExitValue(*this);
      if (isa<SCEVCouldNotCompute>(ExitValue))
        return AddRec;
      return ExitValue;
    }
 
    return AddRec;
  }
  case scTruncate:
  case scZeroExtend:
  case scSignExtend:
  case scPtrToAddr:
  case scAddExpr:
  case scMulExpr:
  case scUDivExpr:
  case scUMaxExpr:
  case scSMaxExpr:
  case scUMinExpr:
  case scSMinExpr:
  case scSequentialUMinExpr: {
    ArrayRef<SCEVUse> Ops = V->operands();
    // Avoid performing the look-up in the common case where the specified
    // expression has no loop-variant portions.
    for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
      SCEVUse OpAtScope = getSCEVAtScope(Ops[i].getPointer(), L);
      if (OpAtScope != Ops[i].getPointer()) {
        // Okay, at least one of these operands is loop variant but might be
        // foldable.  Build a new instance of the folded commutative expression.
        SmallVector<SCEVUse, 8> NewOps;
        NewOps.reserve(Ops.size());
        append_range(NewOps, Ops.take_front(i));
        NewOps.push_back(OpAtScope);
 
        for (++i; i != e; ++i) {
          OpAtScope = getSCEVAtScope(Ops[i].getPointer(), L);
          NewOps.push_back(OpAtScope);
        }
 
        return getWithOperands(V, NewOps);
      }
    }
    // If we got here, all operands are loop invariant.
    return V;
  }
  case scUnknown: {
    // If this instruction is evolved from a constant-evolving PHI, compute the
    // exit value from the loop without using SCEVs.
    const SCEVUnknown *SU = cast<SCEVUnknown>(V);
    Instruction *I = dyn_cast<Instruction>(SU->getValue());
    if (!I)
      return V; // This is some other type of SCEVUnknown, just return it.
 
    if (PHINode *PN = dyn_cast<PHINode>(I)) {
      const Loop *CurrLoop = this->LI[I->getParent()];
      // Looking for loop exit value.
      if (CurrLoop && CurrLoop->getParentLoop() == L &&
          PN->getParent() == CurrLoop->getHeader()) {
        // Okay, there is no closed form solution for the PHI node.  Check
        // to see if the loop that contains it has a known backedge-taken
        // count.  If so, we may be able to force computation of the exit
        // value.
        const SCEV *BackedgeTakenCount = getBackedgeTakenCount(CurrLoop);
        // This trivial case can show up in some degenerate cases where
        // the incoming IR has not yet been fully simplified.
        if (BackedgeTakenCount->isZero()) {
          Value *InitValue = nullptr;
          bool MultipleInitValues = false;
          for (unsigned i = 0; i < PN->getNumIncomingValues(); i++) {
            if (!CurrLoop->contains(PN->getIncomingBlock(i))) {
              if (!InitValue)
                InitValue = PN->getIncomingValue(i);
              else if (InitValue != PN->getIncomingValue(i)) {
                MultipleInitValues = true;
                break;
              }
            }
          }
          if (!MultipleInitValues && InitValue)
            return getSCEV(InitValue);
        }
        // Do we have a loop invariant value flowing around the backedge
        // for a loop which must execute the backedge?
        if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount) &&
            isKnownNonZero(BackedgeTakenCount) &&
            PN->getNumIncomingValues() == 2) {
 
          unsigned InLoopPred =
              CurrLoop->contains(PN->getIncomingBlock(0)) ? 0 : 1;
          Value *BackedgeVal = PN->getIncomingValue(InLoopPred);
          if (CurrLoop->isLoopInvariant(BackedgeVal))
            return getSCEV(BackedgeVal);
        }
        if (auto *BTCC = dyn_cast<SCEVConstant>(BackedgeTakenCount)) {
          // Okay, we know how many times the containing loop executes.  If
          // this is a constant evolving PHI node, get the final value at
          // the specified iteration number.
          Constant *RV =
              getConstantEvolutionLoopExitValue(PN, BTCC->getAPInt(), CurrLoop);
          if (RV)
            return getSCEV(RV);
        }
      }
    }
 
    // Okay, this is an expression that we cannot symbolically evaluate
    // into a SCEV.  Check to see if it's possible to symbolically evaluate
    // the arguments into constants, and if so, try to constant propagate the
    // result.  This is particularly useful for computing loop exit values.
    if (!canConstantFold(I, &TLI))
      return V; // This is some other type of SCEVUnknown, just return it.
 
    SmallVector<Constant *, 4> Operands;
    Operands.reserve(I->getNumOperands());
    bool MadeImprovement = false;
    for (Value *Op : I->operands()) {
      if (Constant *C = dyn_cast<Constant>(Op)) {
        Operands.push_back(C);
        continue;
      }
 
      // If any of the operands is non-constant and if they are
      // non-integer and non-pointer, don't even try to analyze them
      // with scev techniques.
      if (!isSCEVable(Op->getType()))
        return V;
 
      const SCEV *OrigV = getSCEV(Op);
      const SCEV *OpV = getSCEVAtScope(OrigV, L);
      MadeImprovement |= OrigV != OpV;
 
      Constant *C = BuildConstantFromSCEV(OpV);
      if (!C)
        return V;
      assert(C->getType() == Op->getType() && "Type mismatch");
      Operands.push_back(C);
    }
 
    // Check to see if getSCEVAtScope actually made an improvement.
    if (!MadeImprovement)
      return V; // This is some other type of SCEVUnknown, just return it.
 
    Constant *C = nullptr;
    const DataLayout &DL = getDataLayout();
    C = ConstantFoldInstOperands(I, Operands, DL, &TLI,
                                 /*AllowNonDeterministic=*/false);
    if (!C)
      return V;
    return getSCEV(C);
  }
  case scCouldNotCompute:
    llvm_unreachable("Attempt to use a SCEVCouldNotCompute object!");
  }
  llvm_unreachable("Unknown SCEV type!");
}
 
SCEVUse ScalarEvolution::getSCEVAtScope(Value *V, const Loop *L) {
  return getSCEVAtScope(getSCEV(V), L);
}
 
const SCEV *ScalarEvolution::stripInjectiveFunctions(const SCEV *S) const {
  if (const SCEVZeroExtendExpr *ZExt = dyn_cast<SCEVZeroExtendExpr>(S))
    return stripInjectiveFunctions(ZExt->getOperand());
  if (const SCEVSignExtendExpr *SExt = dyn_cast<SCEVSignExtendExpr>(S))
    return stripInjectiveFunctions(SExt->getOperand());
  return S;
}
 
/// Finds the minimum unsigned root of the following equation:
///
///     A * X = B (mod N)
///
/// where N = 2^BW and BW is the common bit width of A and B. The signedness of
/// A and B isn't important.
///
/// If the equation does not have a solution, SCEVCouldNotCompute is returned.
static const SCEV *
SolveLinEquationWithOverflow(const APInt &A, const SCEV *B,
                             SmallVectorImpl<const SCEVPredicate *> *Predicates,
                             ScalarEvolution &SE, const Loop *L) {
  uint32_t BW = A.getBitWidth();
  assert(BW == SE.getTypeSizeInBits(B->getType()));
  assert(A != 0 && "A must be non-zero.");
 
  // 1. D = gcd(A, N)
  //
  // The gcd of A and N may have only one prime factor: 2. The number of
  // trailing zeros in A is its multiplicity
  uint32_t Mult2 = A.countr_zero();
  // D = 2^Mult2
 
  // 2. Check if B is divisible by D.
  //
  // B is divisible by D if and only if the multiplicity of prime factor 2 for B
  // is not less than multiplicity of this prime factor for D.
  unsigned MinTZ = SE.getMinTrailingZeros(B);
  // Try again with the terminator of the loop predecessor for context-specific
  // result, if MinTZ s too small.
  if (MinTZ < Mult2 && L->getLoopPredecessor())
    MinTZ = SE.getMinTrailingZeros(B, L->getLoopPredecessor()->getTerminator());
  if (MinTZ < Mult2) {
    // Check if we can prove there's no remainder using URem.
    const SCEV *URem =
        SE.getURemExpr(B, SE.getConstant(APInt::getOneBitSet(BW, Mult2)));
    const SCEV *Zero = SE.getZero(B->getType());
    if (!SE.isKnownPredicate(CmpInst::ICMP_EQ, URem, Zero)) {
      // Try to add a predicate ensuring B is a multiple of 1 << Mult2.
      if (!Predicates)
        return SE.getCouldNotCompute();
 
      // Avoid adding a predicate that is known to be false.
      if (SE.isKnownPredicate(CmpInst::ICMP_NE, URem, Zero))
        return SE.getCouldNotCompute();
      Predicates->push_back(SE.getEqualPredicate(URem, Zero));
    }
  }
 
  // 3. Compute I: the multiplicative inverse of (A / D) in arithmetic
  // modulo (N / D).
  //
  // If D == 1, (N / D) == N == 2^BW, so we need one extra bit to represent
  // (N / D) in general. The inverse itself always fits into BW bits, though,
  // so we immediately truncate it.
  APInt AD = A.lshr(Mult2).trunc(BW - Mult2); // AD = A / D
  APInt I = AD.multiplicativeInverse().zext(BW);
 
  // 4. Compute the minimum unsigned root of the equation:
  // I * (B / D) mod (N / D)
  // To simplify the computation, we factor out the divide by D:
  // (I * B mod N) / D
  const SCEV *D = SE.getConstant(APInt::getOneBitSet(BW, Mult2));
  return SE.getUDivExactExpr(SE.getMulExpr(B, SE.getConstant(I)), D);
}
 
/// For a given quadratic addrec, generate coefficients of the corresponding
/// quadratic equation, multiplied by a common value to ensure that they are
/// integers.
/// The returned value is a tuple { A, B, C, M, BitWidth }, where
/// Ax^2 + Bx + C is the quadratic function, M is the value that A, B and C
/// were multiplied by, and BitWidth is the bit width of the original addrec
/// coefficients.
/// This function returns std::nullopt if the addrec coefficients are not
/// compile- time constants.
static std::optional<std::tuple<APInt, APInt, APInt, APInt, unsigned>>
GetQuadraticEquation(const SCEVAddRecExpr *AddRec) {
  assert(AddRec->getNumOperands() == 3 && "This is not a quadratic chrec!");
  const SCEVConstant *LC = dyn_cast<SCEVConstant>(AddRec->getOperand(0));
  const SCEVConstant *MC = dyn_cast<SCEVConstant>(AddRec->getOperand(1));
  const SCEVConstant *NC = dyn_cast<SCEVConstant>(AddRec->getOperand(2));
  LLVM_DEBUG(dbgs() << __func__ << ": analyzing quadratic addrec: "
                    << *AddRec << '\n');
 
  // We currently can only solve this if the coefficients are constants.
  if (!LC || !MC || !NC) {
    LLVM_DEBUG(dbgs() << __func__ << ": coefficients are not constant\n");
    return std::nullopt;
  }
 
  APInt L = LC->getAPInt();
  APInt M = MC->getAPInt();
  APInt N = NC->getAPInt();
  assert(!N.isZero() && "This is not a quadratic addrec");
 
  unsigned BitWidth = LC->getAPInt().getBitWidth();
  unsigned NewWidth = BitWidth + 1;
  LLVM_DEBUG(dbgs() << __func__ << ": addrec coeff bw: "
                    << BitWidth << '\n');
  // The sign-extension (as opposed to a zero-extension) here matches the
  // extension used in SolveQuadraticEquationWrap (with the same motivation).
  N = N.sext(NewWidth);
  M = M.sext(NewWidth);
  L = L.sext(NewWidth);
 
  // The increments are M, M+N, M+2N, ..., so the accumulated values are
  //   L+M, (L+M)+(M+N), (L+M)+(M+N)+(M+2N), ..., that is,
  //   L+M, L+2M+N, L+3M+3N, ...
  // After n iterations the accumulated value Acc is L + nM + n(n-1)/2 N.
  //
  // The equation Acc = 0 is then
  //   L + nM + n(n-1)/2 N = 0,  or  2L + 2M n + n(n-1) N = 0.
  // In a quadratic form it becomes:
  //   N n^2 + (2M-N) n + 2L = 0.
 
  APInt A = N;
  APInt B = 2 * M - A;
  APInt C = 2 * L;
  APInt T = APInt(NewWidth, 2);
  LLVM_DEBUG(dbgs() << __func__ << ": equation " << A << "x^2 + " << B
                    << "x + " << C << ", coeff bw: " << NewWidth
                    << ", multiplied by " << T << '\n');
  return std::make_tuple(A, B, C, T, BitWidth);
}
 
/// Helper function to compare optional APInts:
/// (a) if X and Y both exist, return min(X, Y),
/// (b) if neither X nor Y exist, return std::nullopt,
/// (c) if exactly one of X and Y exists, return that value.
static std::optional<APInt> MinOptional(std::optional<APInt> X,
                                        std::optional<APInt> Y) {
  if (X && Y) {
    unsigned W = std::max(X->getBitWidth(), Y->getBitWidth());
    APInt XW = X->sext(W);
    APInt YW = Y->sext(W);
    return XW.slt(YW) ? *X : *Y;
  }
  if (!X && !Y)
    return std::nullopt;
  return X ? *X : *Y;
}
 
/// Helper function to truncate an optional APInt to a given BitWidth.
/// When solving addrec-related equations, it is preferable to return a value
/// that has the same bit width as the original addrec's coefficients. If the
/// solution fits in the original bit width, truncate it (except for i1).
/// Returning a value of a different bit width may inhibit some optimizations.
///
/// In general, a solution to a quadratic equation generated from an addrec
/// may require BW+1 bits, where BW is the bit width of the addrec's
/// coefficients. The reason is that the coefficients of the quadratic
/// equation are BW+1 bits wide (to avoid truncation when converting from
/// the addrec to the equation).
static std::optional<APInt> TruncIfPossible(std::optional<APInt> X,
                                            unsigned BitWidth) {
  if (!X)
    return std::nullopt;
  unsigned W = X->getBitWidth();
  if (BitWidth > 1 && BitWidth < W && X->isIntN(BitWidth))
    return X->trunc(BitWidth);
  return X;
}
 
/// Let c(n) be the value of the quadratic chrec {L,+,M,+,N} after n
/// iterations. The values L, M, N are assumed to be signed, and they
/// should all have the same bit widths.
/// Find the least n >= 0 such that c(n) = 0 in the arithmetic modulo 2^BW,
/// where BW is the bit width of the addrec's coefficients.
/// If the calculated value is a BW-bit integer (for BW > 1), it will be
/// returned as such, otherwise the bit width of the returned value may
/// be greater than BW.
///
/// This function returns std::nullopt if
/// (a) the addrec coefficients are not constant, or
/// (b) SolveQuadraticEquationWrap was unable to find a solution. For cases
///     like x^2 = 5, no integer solutions exist, in other cases an integer
///     solution may exist, but SolveQuadraticEquationWrap may fail to find it.
static std::optional<APInt>
SolveQuadraticAddRecExact(const SCEVAddRecExpr *AddRec, ScalarEvolution &SE) {
  APInt A, B, C, M;
  unsigned BitWidth;
  auto T = GetQuadraticEquation(AddRec);
  if (!T)
    return std::nullopt;
 
  std::tie(A, B, C, M, BitWidth) = *T;
  LLVM_DEBUG(dbgs() << __func__ << ": solving for unsigned overflow\n");
  std::optional<APInt> X =
      APIntOps::SolveQuadraticEquationWrap(A, B, C, BitWidth + 1);
  if (!X)
    return std::nullopt;
 
  ConstantInt *CX = ConstantInt::get(SE.getContext(), *X);
  ConstantInt *V = EvaluateConstantChrecAtConstant(AddRec, CX, SE);
  if (!V->isZero())
    return std::nullopt;
 
  return TruncIfPossible(X, BitWidth);
}
 
/// Let c(n) be the value of the quadratic chrec {0,+,M,+,N} after n
/// iterations. The values M, N are assumed to be signed, and they
/// should all have the same bit widths.
/// Find the least n such that c(n) does not belong to the given range,
/// while c(n-1) does.
///
/// This function returns std::nullopt if
/// (a) the addrec coefficients are not constant, or
/// (b) SolveQuadraticEquationWrap was unable to find a solution for the
///     bounds of the range.
static std::optional<APInt>
SolveQuadraticAddRecRange(const SCEVAddRecExpr *AddRec,
                          const ConstantRange &Range, ScalarEvolution &SE) {
  assert(AddRec->getOperand(0)->isZero() &&
         "Starting value of addrec should be 0");
  LLVM_DEBUG(dbgs() << __func__ << ": solving boundary crossing for range "
                    << Range << ", addrec " << *AddRec << '\n');
  // This case is handled in getNumIterationsInRange. Here we can assume that
  // we start in the range.
  assert(Range.contains(APInt(SE.getTypeSizeInBits(AddRec->getType()), 0)) &&
         "Addrec's initial value should be in range");
 
  APInt A, B, C, M;
  unsigned BitWidth;
  auto T = GetQuadraticEquation(AddRec);
  if (!T)
    return std::nullopt;
 
  // Be careful about the return value: there can be two reasons for not
  // returning an actual number. First, if no solutions to the equations
  // were found, and second, if the solutions don't leave the given range.
  // The first case means that the actual solution is "unknown", the second
  // means that it's known, but not valid. If the solution is unknown, we
  // cannot make any conclusions.
  // Return a pair: the optional solution and a flag indicating if the
  // solution was found.
  auto SolveForBoundary =
      [&](APInt Bound) -> std::pair<std::optional<APInt>, bool> {
    // Solve for signed overflow and unsigned overflow, pick the lower
    // solution.
    LLVM_DEBUG(dbgs() << "SolveQuadraticAddRecRange: checking boundary "
                      << Bound << " (before multiplying by " << M << ")\n");
    Bound *= M; // The quadratic equation multiplier.
 
    std::optional<APInt> SO;
    if (BitWidth > 1) {
      LLVM_DEBUG(dbgs() << "SolveQuadraticAddRecRange: solving for "
                           "signed overflow\n");
      SO = APIntOps::SolveQuadraticEquationWrap(A, B, -Bound, BitWidth);
    }
    LLVM_DEBUG(dbgs() << "SolveQuadraticAddRecRange: solving for "
                         "unsigned overflow\n");
    std::optional<APInt> UO =
        APIntOps::SolveQuadraticEquationWrap(A, B, -Bound, BitWidth + 1);
 
    auto LeavesRange = [&] (const APInt &X) {
      ConstantInt *C0 = ConstantInt::get(SE.getContext(), X);
      ConstantInt *V0 = EvaluateConstantChrecAtConstant(AddRec, C0, SE);
      if (Range.contains(V0->getValue()))
        return false;
      // X should be at least 1, so X-1 is non-negative.
      ConstantInt *C1 = ConstantInt::get(SE.getContext(), X-1);
      ConstantInt *V1 = EvaluateConstantChrecAtConstant(AddRec, C1, SE);
      if (Range.contains(V1->getValue()))
        return true;
      return false;
    };
 
    // If SolveQuadraticEquationWrap returns std::nullopt, it means that there
    // can be a solution, but the function failed to find it. We cannot treat it
    // as "no solution".
    if (!SO || !UO)
      return {std::nullopt, false};
 
    // Check the smaller value first to see if it leaves the range.
    // At this point, both SO and UO must have values.
    std::optional<APInt> Min = MinOptional(SO, UO);
    if (LeavesRange(*Min))
      return { Min, true };
    std::optional<APInt> Max = Min == SO ? UO : SO;
    if (LeavesRange(*Max))
      return { Max, true };
 
    // Solutions were found, but were eliminated, hence the "true".
    return {std::nullopt, true};
  };
 
  std::tie(A, B, C, M, BitWidth) = *T;
  // Lower bound is inclusive, subtract 1 to represent the exiting value.
  APInt Lower = Range.getLower().sext(A.getBitWidth()) - 1;
  APInt Upper = Range.getUpper().sext(A.getBitWidth());
  auto SL = SolveForBoundary(Lower);
  auto SU = SolveForBoundary(Upper);
  // If any of the solutions was unknown, no meaninigful conclusions can
  // be made.
  if (!SL.second || !SU.second)
    return std::nullopt;
 
  // Claim: The correct solution is not some value between Min and Max.
  //
  // Justification: Assuming that Min and Max are different values, one of
  // them is when the first signed overflow happens, the other is when the
  // first unsigned overflow happens. Crossing the range boundary is only
  // possible via an overflow (treating 0 as a special case of it, modeling
  // an overflow as crossing k*2^W for some k).
  //
  // The interesting case here is when Min was eliminated as an invalid
  // solution, but Max was not. The argument is that if there was another
  // overflow between Min and Max, it would also have been eliminated if
  // it was considered.
  //
  // For a given boundary, it is possible to have two overflows of the same
  // type (signed/unsigned) without having the other type in between: this
  // can happen when the vertex of the parabola is between the iterations
  // corresponding to the overflows. This is only possible when the two
  // overflows cross k*2^W for the same k. In such case, if the second one
  // left the range (and was the first one to do so), the first overflow
  // would have to enter the range, which would mean that either we had left
  // the range before or that we started outside of it. Both of these cases
  // are contradictions.
  //
  // Claim: In the case where SolveForBoundary returns std::nullopt, the correct
  // solution is not some value between the Max for this boundary and the
  // Min of the other boundary.
  //
  // Justification: Assume that we had such Max_A and Min_B corresponding
  // to range boundaries A and B and such that Max_A < Min_B. If there was
  // a solution between Max_A and Min_B, it would have to be caused by an
  // overflow corresponding to either A or B. It cannot correspond to B,
  // since Min_B is the first occurrence of such an overflow. If it
  // corresponded to A, it would have to be either a signed or an unsigned
  // overflow that is larger than both eliminated overflows for A. But
  // between the eliminated overflows and this overflow, the values would
  // cover the entire value space, thus crossing the other boundary, which
  // is a contradiction.
 
  return TruncIfPossible(MinOptional(SL.first, SU.first), BitWidth);
}
 
ScalarEvolution::ExitLimit ScalarEvolution::howFarToZero(const SCEV *V,
                                                         const Loop *L,
                                                         bool ControlsOnlyExit,
                                                         bool AllowPredicates) {
 
  // This is only used for loops with a "x != y" exit test. The exit condition
  // is now expressed as a single expression, V = x-y. So the exit test is
  // effectively V != 0.  We know and take advantage of the fact that this
  // expression only being used in a comparison by zero context.
 
  SmallVector<const SCEVPredicate *> Predicates;
  // If the value is a constant
  if (const SCEVConstant *C = dyn_cast<SCEVConstant>(V)) {
    // If the value is already zero, the branch will execute zero times.
    if (C->getValue()->isZero()) return C;
    return getCouldNotCompute();  // Otherwise it will loop infinitely.
  }
 
  const SCEVAddRecExpr *AddRec =
      dyn_cast<SCEVAddRecExpr>(stripInjectiveFunctions(V));
 
  if (!AddRec && AllowPredicates)
    // Try to make this an AddRec using runtime tests, in the first X
    // iterations of this loop, where X is the SCEV expression found by the
    // algorithm below.
    AddRec = convertSCEVToAddRecWithPredicates(V, L, Predicates);
 
  if (!AddRec || AddRec->getLoop() != L)
    return getCouldNotCompute();
 
  // If this is a quadratic (3-term) AddRec {L,+,M,+,N}, find the roots of
  // the quadratic equation to solve it.
  if (AddRec->isQuadratic() && AddRec->getType()->isIntegerTy()) {
    // We can only use this value if the chrec ends up with an exact zero
    // value at this index.  When solving for "X*X != 5", for example, we
    // should not accept a root of 2.
    if (auto S = SolveQuadraticAddRecExact(AddRec, *this)) {
      const auto *R = cast<SCEVConstant>(getConstant(*S));
      return ExitLimit(R, R, R, false, Predicates);
    }
    return getCouldNotCompute();
  }
 
  // Otherwise we can only handle this if it is affine.
  if (!AddRec->isAffine())
    return getCouldNotCompute();
 
  // If this is an affine expression, the execution count of this branch is
  // the minimum unsigned root of the following equation:
  //
  //     Start + Step*N = 0 (mod 2^BW)
  //
  // equivalent to:
  //
  //             Step*N = -Start (mod 2^BW)
  //
  // where BW is the common bit width of Start and Step.
 
  // Get the initial value for the loop.
  const SCEV *Start = getSCEVAtScope(AddRec->getStart(), L->getParentLoop());
  const SCEV *Step = getSCEVAtScope(AddRec->getOperand(1), L->getParentLoop());
 
  if (!isLoopInvariant(Step, L))
    return getCouldNotCompute();
 
  LoopGuards Guards = LoopGuards::collectOnDemand(L, *this);
  // Specialize step for this loop so we get context sensitive facts below.
  const SCEV *StepWLG = applyLoopGuards(Step, Guards);
 
  // For positive steps (counting up until unsigned overflow):
  //   N = -Start/Step (as unsigned)
  // For negative steps (counting down to zero):
  //   N = Start/-Step
  // First compute the unsigned distance from zero in the direction of Step.
  bool CountDown = isKnownNegative(StepWLG);
  if (!CountDown && !isKnownNonNegative(StepWLG))
    return getCouldNotCompute();
 
  const SCEV *Distance = CountDown ? Start : getNegativeSCEV(Start);
  // Handle unitary steps, which cannot wraparound.
  // 1*N = -Start; -1*N = Start (mod 2^BW), so:
  //   N = Distance (as unsigned)
 
  if (match(Step, m_CombineOr(m_scev_One(), m_scev_AllOnes()))) {
    APInt MaxBECount = getUnsignedRangeMax(applyLoopGuards(Distance, Guards));
    MaxBECount = APIntOps::umin(MaxBECount, getUnsignedRangeMax(Distance));
 
    // When a loop like "for (int i = 0; i != n; ++i) { /* body */ }" is rotated,
    // we end up with a loop whose backedge-taken count is n - 1.  Detect this
    // case, and see if we can improve the bound.
    //
    // Explicitly handling this here is necessary because getUnsignedRange
    // isn't context-sensitive; it doesn't know that we only care about the
    // range inside the loop.
    const SCEV *Zero = getZero(Distance->getType());
    const SCEV *One = getOne(Distance->getType());
    const SCEV *DistancePlusOne = getAddExpr(Distance, One);
    if (isLoopEntryGuardedByCond(L, ICmpInst::ICMP_NE, DistancePlusOne, Zero)) {
      // If Distance + 1 doesn't overflow, we can compute the maximum distance
      // as "unsigned_max(Distance + 1) - 1". Also apply the loop guards to
      // Distance + 1; the range of Distance itself may be a wrapped set even
      // when the guards bound Distance + 1 tightly.
      APInt Max = APIntOps::umin(
          getUnsignedRangeMax(applyLoopGuards(DistancePlusOne, Guards)),
          getUnsignedRangeMax(DistancePlusOne));
      MaxBECount = APIntOps::umin(MaxBECount, Max - 1);
    }
    return ExitLimit(Distance, getConstant(MaxBECount), Distance, false,
                     Predicates);
  }
 
  // If the condition controls loop exit (the loop exits only if the expression
  // is true) and the addition is no-wrap we can use unsigned divide to
  // compute the backedge count.  In this case, the step may not divide the
  // distance, but we don't care because if the condition is "missed" the loop
  // will have undefined behavior due to wrapping.
  if (ControlsOnlyExit && AddRec->hasNoSelfWrap() &&
      loopHasNoAbnormalExits(AddRec->getLoop())) {
 
    // If the stride is zero and the start is non-zero, the loop must be
    // infinite. In C++, most loops are finite by assumption, in which case the
    // step being zero implies UB must execute if the loop is entered.
    if (!(loopIsFiniteByAssumption(L) && isKnownNonZero(Start)) &&
        !isKnownNonZero(StepWLG))
      return getCouldNotCompute();
 
    const SCEV *Exact =
        getUDivExpr(Distance, CountDown ? getNegativeSCEV(Step) : Step);
    const SCEV *ConstantMax = getCouldNotCompute();
    if (Exact != getCouldNotCompute()) {
      APInt MaxInt = getUnsignedRangeMax(applyLoopGuards(Exact, Guards));
      ConstantMax =
          getConstant(APIntOps::umin(MaxInt, getUnsignedRangeMax(Exact)));
    }
    const SCEV *SymbolicMax =
        isa<SCEVCouldNotCompute>(Exact) ? ConstantMax : Exact;
    return ExitLimit(Exact, ConstantMax, SymbolicMax, false, Predicates);
  }
 
  // Solve the general equation.
  const SCEVConstant *StepC = dyn_cast<SCEVConstant>(Step);
  if (!StepC || StepC->getValue()->isZero())
    return getCouldNotCompute();
  const SCEV *E = SolveLinEquationWithOverflow(
      StepC->getAPInt(), getNegativeSCEV(Start),
      AllowPredicates ? &Predicates : nullptr, *this, L);
 
  const SCEV *M = E;
  if (E != getCouldNotCompute()) {
    APInt MaxWithGuards = getUnsignedRangeMax(applyLoopGuards(E, Guards));
    M = getConstant(APIntOps::umin(MaxWithGuards, getUnsignedRangeMax(E)));
  }
  auto *S = isa<SCEVCouldNotCompute>(E) ? M : E;
  return ExitLimit(E, M, S, false, Predicates);
}
 
ScalarEvolution::ExitLimit
ScalarEvolution::howFarToNonZero(const SCEV *V, const Loop *L) {
  // Loops that look like: while (X == 0) are very strange indeed.  We don't
  // handle them yet except for the trivial case.  This could be expanded in the
  // future as needed.
 
  // If the value is a constant, check to see if it is known to be non-zero
  // already.  If so, the backedge will execute zero times.
  if (const SCEVConstant *C = dyn_cast<SCEVConstant>(V)) {
    if (!C->getValue()->isZero())
      return getZero(C->getType());
    return getCouldNotCompute();  // Otherwise it will loop infinitely.
  }
 
  // We could implement others, but I really doubt anyone writes loops like
  // this, and if they did, they would already be constant folded.
  return getCouldNotCompute();
}
 
std::pair<const BasicBlock *, const BasicBlock *>
ScalarEvolution::getPredecessorWithUniqueSuccessorForBB(const BasicBlock *BB)
    const {
  // If the block has a unique predecessor, then there is no path from the
  // predecessor to the block that does not go through the direct edge
  // from the predecessor to the block.
  if (const BasicBlock *Pred = BB->getSinglePredecessor())
    return {Pred, BB};
 
  // A loop's header is defined to be a block that dominates the loop.
  // If the header has a unique predecessor outside the loop, it must be
  // a block that has exactly one successor that can reach the loop.
  if (const Loop *L = LI.getLoopFor(BB))
    return {L->getLoopPredecessor(), L->getHeader()};
 
  return {nullptr, BB};
}
 
/// SCEV structural equivalence is usually sufficient for testing whether two
/// expressions are equal, however for the purposes of looking for a condition
/// guarding a loop, it can be useful to be a little more general, since a
/// front-end may have replicated the controlling expression.
static bool HasSameValue(const SCEV *A, const SCEV *B) {
  // Quick check to see if they are the same SCEV.
  if (A == B) return true;
 
  auto ComputesEqualValues = [](const Instruction *A, const Instruction *B) {
    // Not all instructions that are "identical" compute the same value.  For
    // instance, two distinct alloca instructions allocating the same type are
    // identical and do not read memory; but compute distinct values.
    return A->isIdenticalTo(B) && (isa<BinaryOperator>(A) || isa<GetElementPtrInst>(A));
  };
 
  // Otherwise, if they're both SCEVUnknown, it's possible that they hold
  // two different instructions with the same value. Check for this case.
  if (const SCEVUnknown *AU = dyn_cast<SCEVUnknown>(A))
    if (const SCEVUnknown *BU = dyn_cast<SCEVUnknown>(B))
      if (const Instruction *AI = dyn_cast<Instruction>(AU->getValue()))
        if (const Instruction *BI = dyn_cast<Instruction>(BU->getValue()))
          if (ComputesEqualValues(AI, BI))
            return true;
 
  // Otherwise assume they may have a different value.
  return false;
}
 
static bool MatchBinarySub(const SCEV *S, SCEVUse &LHS, SCEVUse &RHS) {
  const SCEV *Op0, *Op1;
  if (!match(S, m_scev_Add(m_SCEV(Op0), m_SCEV(Op1))))
    return false;
  if (match(Op0, m_scev_Mul(m_scev_AllOnes(), m_SCEV(RHS)))) {
    LHS = Op1;
    return true;
  }
  if (match(Op1, m_scev_Mul(m_scev_AllOnes(), m_SCEV(RHS)))) {
    LHS = Op0;
    return true;
  }
  return false;
}
 
bool ScalarEvolution::SimplifyICmpOperands(CmpPredicate &Pred, SCEVUse &LHS,
                                           SCEVUse &RHS, unsigned Depth) {
  bool Changed = false;
  // Simplifies ICMP to trivial true or false by turning it into '0 == 0' or
  // '0 != 0'.
  auto TrivialCase = [&](bool TriviallyTrue) {
    LHS = RHS = getConstant(ConstantInt::getFalse(getContext()));
    Pred = TriviallyTrue ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_NE;
    return true;
  };
  // If we hit the max recursion limit bail out.
  if (Depth >= 3)
    return false;
 
  const SCEV *NewLHS, *NewRHS;
  if (match(LHS, m_scev_c_Mul(m_SCEV(NewLHS), m_SCEVVScale())) &&
      match(RHS, m_scev_c_Mul(m_SCEV(NewRHS), m_SCEVVScale()))) {
    const SCEVMulExpr *LMul = cast<SCEVMulExpr>(LHS);
    const SCEVMulExpr *RMul = cast<SCEVMulExpr>(RHS);
 
    // (X * vscale) pred (Y * vscale) ==> X pred Y
    //     when both multiples are NSW.
    // (X * vscale) uicmp/eq/ne (Y * vscale) ==> X uicmp/eq/ne Y
    //     when both multiples are NUW.
    if ((LMul->hasNoSignedWrap() && RMul->hasNoSignedWrap()) ||
        (LMul->hasNoUnsignedWrap() && RMul->hasNoUnsignedWrap() &&
         !ICmpInst::isSigned(Pred))) {
      LHS = NewLHS;
      RHS = NewRHS;
      Changed = true;
    }
  }
 
  // Canonicalize a constant to the right side.
  if (const SCEVConstant *LHSC = dyn_cast<SCEVConstant>(LHS)) {
    // Check for both operands constant.
    if (const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(RHS)) {
      if (!ICmpInst::compare(LHSC->getAPInt(), RHSC->getAPInt(), Pred))
        return TrivialCase(false);
      return TrivialCase(true);
    }
    // Otherwise swap the operands to put the constant on the right.
    std::swap(LHS, RHS);
    Pred = ICmpInst::getSwappedCmpPredicate(Pred);
    Changed = true;
  }
 
  // (K + A) pred (K + B) --> A pred B
  // For equality, no flags are needed.
  // For signed, both adds must be NSW. For unsigned, both must be NUW.
  {
    const SCEVConstant *C = nullptr;
    if (match(LHS, m_scev_Add(m_SCEVConstant(C), m_SCEV(NewLHS))) &&
        match(RHS, m_scev_Add(m_scev_Specific(C), m_SCEV(NewRHS)))) {
      const auto *LAdd = cast<SCEVAddExpr>(LHS);
      const auto *RAdd = cast<SCEVAddExpr>(RHS);
      if (ICmpInst::isEquality(Pred) ||
          (ICmpInst::isSigned(Pred) && LAdd->hasNoSignedWrap() &&
           RAdd->hasNoSignedWrap()) ||
          (ICmpInst::isUnsigned(Pred) && LAdd->hasNoUnsignedWrap() &&
           RAdd->hasNoUnsignedWrap())) {
        LHS = NewLHS;
        RHS = NewRHS;
        Changed = true;
      }
    }
  }
 
  // (C * A) pred (C * B) --> A pred B
  // For equality predicates, both muls must be NUW or both must be NSW
  // (either suffices to make multiplication by C injective; C == 0 is
  // impossible because SCEV folds 0 * X to 0).
  // For signed ordering, C must be positive and both muls must be NSW.
  // For unsigned ordering, both muls must be NUW.
  {
    const SCEVConstant *C = nullptr;
    if (match(LHS, m_scev_Mul(m_SCEVConstant(C), m_SCEV(NewLHS))) &&
        match(RHS, m_scev_Mul(m_scev_Specific(C), m_SCEV(NewRHS)))) {
      const auto *LMul = cast<SCEVMulExpr>(LHS);
      const auto *RMul = cast<SCEVMulExpr>(RHS);
      bool BothNUW = LMul->hasNoUnsignedWrap() && RMul->hasNoUnsignedWrap();
      bool BothNSW = LMul->hasNoSignedWrap() && RMul->hasNoSignedWrap();
      if ((ICmpInst::isEquality(Pred) && (BothNUW || BothNSW)) ||
          (ICmpInst::isSigned(Pred) && BothNSW &&
           C->getAPInt().isStrictlyPositive()) ||
          (ICmpInst::isUnsigned(Pred) && BothNUW)) {
        LHS = NewLHS;
        RHS = NewRHS;
        Changed = true;
      }
    }
  }
 
  // If we're comparing an addrec with a value which is loop-invariant in the
  // addrec's loop, put the addrec on the left. Also make a dominance check,
  // as both operands could be addrecs loop-invariant in each other's loop.
  if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(RHS)) {
    const Loop *L = AR->getLoop();
    if (isLoopInvariant(LHS, L) && properlyDominates(LHS, L->getHeader())) {
      std::swap(LHS, RHS);
      Pred = ICmpInst::getSwappedCmpPredicate(Pred);
      Changed = true;
    }
  }
 
  // If there's a constant operand, canonicalize comparisons with boundary
  // cases, and canonicalize *-or-equal comparisons to regular comparisons.
  if (const SCEVConstant *RC = dyn_cast<SCEVConstant>(RHS)) {
    const APInt &RA = RC->getAPInt();
 
    bool SimplifiedByConstantRange = false;
 
    if (!ICmpInst::isEquality(Pred)) {
      ConstantRange ExactCR = ConstantRange::makeExactICmpRegion(Pred, RA);
      if (ExactCR.isFullSet())
        return TrivialCase(true);
      if (ExactCR.isEmptySet())
        return TrivialCase(false);
 
      APInt NewRHS;
      CmpInst::Predicate NewPred;
      if (ExactCR.getEquivalentICmp(NewPred, NewRHS) &&
          ICmpInst::isEquality(NewPred)) {
        // We were able to convert an inequality to an equality.
        Pred = NewPred;
        RHS = getConstant(NewRHS);
        Changed = SimplifiedByConstantRange = true;
      }
    }
 
    if (!SimplifiedByConstantRange) {
      switch (Pred) {
      default:
        break;
      case ICmpInst::ICMP_EQ:
      case ICmpInst::ICMP_NE:
        // Fold ((-1) * %a) + %b == 0 (equivalent to %b-%a == 0) into %a == %b.
        if (RA.isZero() && MatchBinarySub(LHS, LHS, RHS))
          Changed = true;
        break;
 
        // The "Should have been caught earlier!" messages refer to the fact
        // that the ExactCR.isFullSet() or ExactCR.isEmptySet() check above
        // should have fired on the corresponding cases, and canonicalized the
        // check to trivial case.
 
      case ICmpInst::ICMP_UGE:
        assert(!RA.isMinValue() && "Should have been caught earlier!");
        Pred = ICmpInst::ICMP_UGT;
        RHS = getConstant(RA - 1);
        Changed = true;
        break;
      case ICmpInst::ICMP_ULE:
        assert(!RA.isMaxValue() && "Should have been caught earlier!");
        Pred = ICmpInst::ICMP_ULT;
        RHS = getConstant(RA + 1);
        Changed = true;
        break;
      case ICmpInst::ICMP_SGE:
        assert(!RA.isMinSignedValue() && "Should have been caught earlier!");
        Pred = ICmpInst::ICMP_SGT;
        RHS = getConstant(RA - 1);
        Changed = true;
        break;
      case ICmpInst::ICMP_SLE:
        assert(!RA.isMaxSignedValue() && "Should have been caught earlier!");
        Pred = ICmpInst::ICMP_SLT;
        RHS = getConstant(RA + 1);
        Changed = true;
        break;
      }
    }
  }
 
  // a /u b == 0 => a < b
  // a /u b != 0 => a >= b
  if (ICmpInst::isEquality(Pred) && RHS->isZero() &&
      match(LHS, m_scev_UDiv(m_SCEV(LHS), m_SCEV(RHS)))) {
    Pred = Pred == ICmpInst::ICMP_EQ ? ICmpInst::ICMP_ULT : ICmpInst::ICMP_UGE;
    Changed = true;
  }
 
  // Check for obvious equality.
  if (HasSameValue(LHS, RHS)) {
    if (ICmpInst::isTrueWhenEqual(Pred))
      return TrivialCase(true);
    if (ICmpInst::isFalseWhenEqual(Pred))
      return TrivialCase(false);
  }
 
  // If possible, canonicalize GE/LE comparisons to GT/LT comparisons, by
  // adding or subtracting 1 from one of the operands.
  switch (Pred) {
  case ICmpInst::ICMP_SLE:
    if (!getSignedRangeMax(RHS).isMaxSignedValue()) {
      RHS = getAddExpr(getConstant(RHS->getType(), 1, true), RHS,
                       SCEV::FlagNSW);
      Pred = ICmpInst::ICMP_SLT;
      Changed = true;
    } else if (!getSignedRangeMin(LHS).isMinSignedValue()) {
      LHS = getAddExpr(getConstant(RHS->getType(), (uint64_t)-1, true), LHS,
                       SCEV::FlagNSW);
      Pred = ICmpInst::ICMP_SLT;
      Changed = true;
    }
    break;
  case ICmpInst::ICMP_SGE:
    if (!getSignedRangeMin(RHS).isMinSignedValue()) {
      RHS = getAddExpr(getConstant(RHS->getType(), (uint64_t)-1, true), RHS,
                       SCEV::FlagNSW);
      Pred = ICmpInst::ICMP_SGT;
      Changed = true;
    } else if (!getSignedRangeMax(LHS).isMaxSignedValue()) {
      LHS = getAddExpr(getConstant(RHS->getType(), 1, true), LHS,
                       SCEV::FlagNSW);
      Pred = ICmpInst::ICMP_SGT;
      Changed = true;
    }
    break;
  case ICmpInst::ICMP_ULE:
    if (!getUnsignedRangeMax(RHS).isMaxValue()) {
      RHS = getAddExpr(getConstant(RHS->getType(), 1, true), RHS,
                       SCEV::FlagNUW);
      Pred = ICmpInst::ICMP_ULT;
      Changed = true;
    } else if (!getUnsignedRangeMin(LHS).isMinValue()) {
      LHS = getAddExpr(getConstant(RHS->getType(), (uint64_t)-1, true), LHS);
      Pred = ICmpInst::ICMP_ULT;
      Changed = true;
    }
    break;
  case ICmpInst::ICMP_UGE:
    // If RHS is an op we can fold the -1, try that first.
    // Otherwise prefer LHS to preserve the nuw flag.
    if ((isa<SCEVConstant>(RHS) ||
         (isa<SCEVAddExpr, SCEVAddRecExpr>(RHS) &&
          isa<SCEVConstant>(cast<SCEVNAryExpr>(RHS)->getOperand(0)))) &&
        !getUnsignedRangeMin(RHS).isMinValue()) {
      RHS = getAddExpr(getConstant(RHS->getType(), (uint64_t)-1, true), RHS);
      Pred = ICmpInst::ICMP_UGT;
      Changed = true;
    } else if (!getUnsignedRangeMax(LHS).isMaxValue()) {
      LHS = getAddExpr(getConstant(RHS->getType(), 1, true), LHS,
                       SCEV::FlagNUW);
      Pred = ICmpInst::ICMP_UGT;
      Changed = true;
    } else if (!getUnsignedRangeMin(RHS).isMinValue()) {
      RHS = getAddExpr(getConstant(RHS->getType(), (uint64_t)-1, true), RHS);
      Pred = ICmpInst::ICMP_UGT;
      Changed = true;
    }
    break;
  default:
    break;
  }
 
  // TODO: More simplifications are possible here.
 
  // Recursively simplify until we either hit a recursion limit or nothing
  // changes.
  if (Changed)
    (void)SimplifyICmpOperands(Pred, LHS, RHS, Depth + 1);
 
  return Changed;
}
 
bool ScalarEvolution::isKnownNegative(const SCEV *S) {
  return getSignedRangeMax(S).isNegative();
}
 
bool ScalarEvolution::isKnownPositive(const SCEV *S) {
  return getSignedRangeMin(S).isStrictlyPositive();
}
 
bool ScalarEvolution::isKnownNonNegative(const SCEV *S) {
  return !getSignedRangeMin(S).isNegative();
}
 
bool ScalarEvolution::isKnownNonPositive(const SCEV *S) {
  return !getSignedRangeMax(S).isStrictlyPositive();
}
 
bool ScalarEvolution::isKnownNonZero(const SCEV *S) {
  // Query push down for cases where the unsigned range is
  // less than sufficient.
  if (const auto *SExt = dyn_cast<SCEVSignExtendExpr>(S))
    return isKnownNonZero(SExt->getOperand(0));
  return getUnsignedRangeMin(S) != 0;
}
 
bool ScalarEvolution::isKnownToBeAPowerOfTwo(const SCEV *S, bool OrZero,
                                             bool OrNegative) {
  auto NonRecursive = [OrNegative](const SCEV *S) {
    if (auto *C = dyn_cast<SCEVConstant>(S))
      return C->getAPInt().isPowerOf2() ||
             (OrNegative && C->getAPInt().isNegatedPowerOf2());
 
    // vscale is a power-of-two.
    return isa<SCEVVScale>(S);
  };
 
  if (NonRecursive(S))
    return true;
 
  auto *Mul = dyn_cast<SCEVMulExpr>(S);
  if (!Mul)
    return false;
  return all_of(Mul->operands(), NonRecursive) && (OrZero || isKnownNonZero(S));
}
 
bool ScalarEvolution::isKnownMultipleOf(
    const SCEV *S, uint64_t M,
    SmallVectorImpl<const SCEVPredicate *> *Predicates) {
  if (M == 0)
    return false;
  if (M == 1)
    return true;
 
  // For a constant, check that "S % M == 0".
  if (auto *Cst = dyn_cast<SCEVConstant>(S)) {
    APInt C = Cst->getAPInt();
    return C.urem(M) == 0;
  }
 
  // Basic tests have failed.
  // Check "S % M == 0" at compile time and record runtime Assumptions.
  auto *STy = dyn_cast<IntegerType>(S->getType());
  const SCEV *SmodM =
      getURemExpr(S, getConstant(ConstantInt::get(STy, M, false)));
  const SCEV *Zero = getZero(STy);
 
  // Check whether "S % M == 0" is known at compile time.
  if (isKnownPredicate(ICmpInst::ICMP_EQ, SmodM, Zero))
    return true;
 
  // Check whether "S % M != 0" is known at compile time.
  if (isKnownPredicate(ICmpInst::ICMP_NE, SmodM, Zero))
    return false;
 
  if (!Predicates)
    return false;
 
  // Look through Add and AddRec expressions with nuw to improve the
  // precision of added predicates. S is a multiple of M if S starts with a
  // multiple of M and at every iteration step S only adds multiples of M.
  if (isa<SCEVAddExpr, SCEVAddRecExpr>(S) &&
      cast<SCEVNAryExpr>(S)->hasNoUnsignedWrap() &&
      all_of(S->operands(),
             [&](SCEVUse Op) { return isKnownMultipleOf(Op, M, Predicates); }))
    return true;
 
  // Similarly, look through Mul with nuw, where any operand being a
  // known-multiple is sufficient.
  if (auto *Mul = dyn_cast<SCEVMulExpr>(S))
    if (Mul->hasNoUnsignedWrap() && any_of(S->operands(), [&](SCEVUse Op) {
          return isKnownMultipleOf(Op, M, Predicates);
        }))
      return true;
 
  // Similarly, look through MinMax, with no wrapping arithmetic to consider.
  if (isa<SCEVMinMaxExpr>(S) && all_of(S->operands(), [&](SCEVUse Op) {
        return isKnownMultipleOf(Op, M, Predicates);
      }))
    return true;
 
  const SCEVPredicate *P = getComparePredicate(ICmpInst::ICMP_EQ, SmodM, Zero);
 
  // Detect redundant predicates.
  for (auto *A : *Predicates)
    if (A->implies(P, *this))
      return true;
 
  // Only record non-redundant predicates.
  Predicates->push_back(P);
  return true;
}
 
bool ScalarEvolution::haveSameSign(const SCEV *S1, const SCEV *S2) {
  return ((isKnownNonNegative(S1) && isKnownNonNegative(S2)) ||
          (isKnownNegative(S1) && isKnownNegative(S2)));
}
 
std::pair<const SCEV *, const SCEV *>
ScalarEvolution::SplitIntoInitAndPostInc(const Loop *L, const SCEV *S) {
  // Compute SCEV on entry of loop L.
  const SCEV *Start = SCEVInitRewriter::rewrite(S, L, *this);
  if (Start == getCouldNotCompute())
    return { Start, Start };
  // Compute post increment SCEV for loop L.
  const SCEV *PostInc = SCEVPostIncRewriter::rewrite(S, L, *this);
  assert(PostInc != getCouldNotCompute() && "Unexpected could not compute");
  return { Start, PostInc };
}
 
bool ScalarEvolution::isKnownViaInduction(CmpPredicate Pred, SCEVUse LHS,
                                          SCEVUse RHS) {
  // First collect all loops.
  SmallPtrSet<const Loop *, 8> LoopsUsed;
  getUsedLoops(LHS, LoopsUsed);
  getUsedLoops(RHS, LoopsUsed);
 
  if (LoopsUsed.empty())
    return false;
 
  // Domination relationship must be a linear order on collected loops.
#ifndef NDEBUG
  for (const auto *L1 : LoopsUsed)
    for (const auto *L2 : LoopsUsed)
      assert((DT.dominates(L1->getHeader(), L2->getHeader()) ||
              DT.dominates(L2->getHeader(), L1->getHeader())) &&
             "Domination relationship is not a linear order");
#endif
 
  const Loop *MDL =
      *llvm::max_element(LoopsUsed, [&](const Loop *L1, const Loop *L2) {
        return DT.properlyDominates(L1->getHeader(), L2->getHeader());
      });
 
  // Get init and post increment value for LHS.
  auto SplitLHS = SplitIntoInitAndPostInc(MDL, LHS);
  // if LHS contains unknown non-invariant SCEV then bail out.
  if (SplitLHS.first == getCouldNotCompute())
    return false;
  assert (SplitLHS.second != getCouldNotCompute() && "Unexpected CNC");
  // Get init and post increment value for RHS.
  auto SplitRHS = SplitIntoInitAndPostInc(MDL, RHS);
  // if RHS contains unknown non-invariant SCEV then bail out.
  if (SplitRHS.first == getCouldNotCompute())
    return false;
  assert (SplitRHS.second != getCouldNotCompute() && "Unexpected CNC");
  // It is possible that init SCEV contains an invariant load but it does
  // not dominate MDL and is not available at MDL loop entry, so we should
  // check it here.
  if (!isAvailableAtLoopEntry(SplitLHS.first, MDL) ||
      !isAvailableAtLoopEntry(SplitRHS.first, MDL))
    return false;
 
  // It seems backedge guard check is faster than entry one so in some cases
  // it can speed up whole estimation by short circuit
  return isLoopBackedgeGuardedByCond(MDL, Pred, SplitLHS.second,
                                     SplitRHS.second) &&
         isLoopEntryGuardedByCond(MDL, Pred, SplitLHS.first, SplitRHS.first);
}
 
bool ScalarEvolution::isKnownPredicate(CmpPredicate Pred, SCEVUse LHS,
                                       SCEVUse RHS) {
  // Canonicalize the inputs first.
  (void)SimplifyICmpOperands(Pred, LHS, RHS);
 
  return isKnownViaInduction(Pred, LHS, RHS) ||
         isKnownPredicateViaSplitting(Pred, LHS, RHS) ||
         isKnownViaNonRecursiveReasoning(Pred, LHS, RHS);
}
 
std::optional<bool> ScalarEvolution::evaluatePredicate(CmpPredicate Pred,
                                                       const SCEV *LHS,
                                                       const SCEV *RHS) {
  if (isKnownPredicate(Pred, LHS, RHS))
    return true;
  if (isKnownPredicate(ICmpInst::getInverseCmpPredicate(Pred), LHS, RHS))
    return false;
  return std::nullopt;
}
 
bool ScalarEvolution::isKnownPredicateAt(CmpPredicate Pred, const SCEV *LHS,
                                         const SCEV *RHS,
                                         const Instruction *CtxI) {
  // TODO: Analyze guards and assumes from Context's block.
  return isKnownPredicate(Pred, LHS, RHS) ||
         isBasicBlockEntryGuardedByCond(CtxI->getParent(), Pred, LHS, RHS);
}
 
std::optional<bool>
ScalarEvolution::evaluatePredicateAt(CmpPredicate Pred, const SCEV *LHS,
                                     const SCEV *RHS, const Instruction *CtxI) {
  std::optional<bool> KnownWithoutContext = evaluatePredicate(Pred, LHS, RHS);
  if (KnownWithoutContext)
    return KnownWithoutContext;
 
  if (isBasicBlockEntryGuardedByCond(CtxI->getParent(), Pred, LHS, RHS))
    return true;
  if (isBasicBlockEntryGuardedByCond(
          CtxI->getParent(), ICmpInst::getInverseCmpPredicate(Pred), LHS, RHS))
    return false;
  return std::nullopt;
}
 
bool ScalarEvolution::isKnownOnEveryIteration(CmpPredicate Pred,
                                              const SCEVAddRecExpr *LHS,
                                              const SCEV *RHS) {
  const Loop *L = LHS->getLoop();
  return isLoopEntryGuardedByCond(L, Pred, LHS->getStart(), RHS) &&
         isLoopBackedgeGuardedByCond(L, Pred, LHS->getPostIncExpr(*this), RHS);
}
 
std::optional<ScalarEvolution::MonotonicPredicateType>
ScalarEvolution::getMonotonicPredicateType(const SCEVAddRecExpr *LHS,
                                           ICmpInst::Predicate Pred) {
  auto Result = getMonotonicPredicateTypeImpl(LHS, Pred);
 
#ifndef NDEBUG
  // Verify an invariant: inverting the predicate should turn a monotonically
  // increasing change to a monotonically decreasing one, and vice versa.
  if (Result) {
    auto ResultSwapped =
        getMonotonicPredicateTypeImpl(LHS, ICmpInst::getSwappedPredicate(Pred));
 
    assert(*ResultSwapped != *Result &&
           "monotonicity should flip as we flip the predicate");
  }
#endif
 
  return Result;
}
 
std::optional<ScalarEvolution::MonotonicPredicateType>
ScalarEvolution::getMonotonicPredicateTypeImpl(const SCEVAddRecExpr *LHS,
                                               ICmpInst::Predicate Pred) {
  // A zero step value for LHS means the induction variable is essentially a
  // loop invariant value. We don't really depend on the predicate actually
  // flipping from false to true (for increasing predicates, and the other way
  // around for decreasing predicates), all we care about is that *if* the
  // predicate changes then it only changes from false to true.
  //
  // A zero step value in itself is not very useful, but there may be places
  // where SCEV can prove X >= 0 but not prove X > 0, so it is helpful to be
  // as general as possible.
 
  // Only handle LE/LT/GE/GT predicates.
  if (!ICmpInst::isRelational(Pred))
    return std::nullopt;
 
  bool IsGreater = ICmpInst::isGE(Pred) || ICmpInst::isGT(Pred);
  assert((IsGreater || ICmpInst::isLE(Pred) || ICmpInst::isLT(Pred)) &&
         "Should be greater or less!");
 
  // Check that AR does not wrap.
  if (ICmpInst::isUnsigned(Pred)) {
    if (!LHS->hasNoUnsignedWrap())
      return std::nullopt;
    return IsGreater ? MonotonicallyIncreasing : MonotonicallyDecreasing;
  }
  assert(ICmpInst::isSigned(Pred) &&
         "Relational predicate is either signed or unsigned!");
  if (!LHS->hasNoSignedWrap())
    return std::nullopt;
 
  const SCEV *Step = LHS->getStepRecurrence(*this);
 
  if (isKnownNonNegative(Step))
    return IsGreater ? MonotonicallyIncreasing : MonotonicallyDecreasing;
 
  if (isKnownNonPositive(Step))
    return !IsGreater ? MonotonicallyIncreasing : MonotonicallyDecreasing;
 
  return std::nullopt;
}
 
std::optional<ScalarEvolution::LoopInvariantPredicate>
ScalarEvolution::getLoopInvariantPredicate(CmpPredicate Pred, const SCEV *LHS,
                                           const SCEV *RHS, const Loop *L,
                                           const Instruction *CtxI) {
  // If there is a loop-invariant, force it into the RHS, otherwise bail out.
  if (!isLoopInvariant(RHS, L)) {
    if (!isLoopInvariant(LHS, L))
      return std::nullopt;
 
    std::swap(LHS, RHS);
    Pred = ICmpInst::getSwappedCmpPredicate(Pred);
  }
 
  const SCEVAddRecExpr *ArLHS = dyn_cast<SCEVAddRecExpr>(LHS);
  if (!ArLHS || ArLHS->getLoop() != L)
    return std::nullopt;
 
  auto MonotonicType = getMonotonicPredicateType(ArLHS, Pred);
  if (!MonotonicType)
    return std::nullopt;
  // If the predicate "ArLHS `Pred` RHS" monotonically increases from false to
  // true as the loop iterates, and the backedge is control dependent on
  // "ArLHS `Pred` RHS" == true then we can reason as follows:
  //
  //   * if the predicate was false in the first iteration then the predicate
  //     is never evaluated again, since the loop exits without taking the
  //     backedge.
  //   * if the predicate was true in the first iteration then it will
  //     continue to be true for all future iterations since it is
  //     monotonically increasing.
  //
  // For both the above possibilities, we can replace the loop varying
  // predicate with its value on the first iteration of the loop (which is
  // loop invariant).
  //
  // A similar reasoning applies for a monotonically decreasing predicate, by
  // replacing true with false and false with true in the above two bullets.
  bool Increasing = *MonotonicType == ScalarEvolution::MonotonicallyIncreasing;
  auto P = Increasing ? Pred : ICmpInst::getInverseCmpPredicate(Pred);
 
  if (isLoopBackedgeGuardedByCond(L, P, LHS, RHS))
    return ScalarEvolution::LoopInvariantPredicate(Pred, ArLHS->getStart(),
                                                   RHS);
 
  if (!CtxI)
    return std::nullopt;
  // Try to prove via context.
  // TODO: Support other cases.
  switch (Pred) {
  default:
    break;
  case ICmpInst::ICMP_ULE:
  case ICmpInst::ICMP_ULT: {
    assert(ArLHS->hasNoUnsignedWrap() && "Is a requirement of monotonicity!");
    // Given preconditions
    // (1) ArLHS does not cross the border of positive and negative parts of
    //     range because of:
    //     - Positive step; (TODO: lift this limitation)
    //     - nuw - does not cross zero boundary;
    //     - nsw - does not cross SINT_MAX boundary;
    // (2) ArLHS <s RHS
    // (3) RHS >=s 0
    // we can replace the loop variant ArLHS <u RHS condition with loop
    // invariant Start(ArLHS) <u RHS.
    //
    // Because of (1) there are two options:
    // - ArLHS is always negative. It means that ArLHS <u RHS is always false;
    // - ArLHS is always non-negative. Because of (3) RHS is also non-negative.
    //   It means that ArLHS <s RHS <=> ArLHS <u RHS.
    //   Because of (2) ArLHS <u RHS is trivially true.
    // All together it means that ArLHS <u RHS <=> Start(ArLHS) >=s 0.
    // We can strengthen this to Start(ArLHS) <u RHS.
    auto SignFlippedPred = ICmpInst::getFlippedSignednessPredicate(Pred);
    if (ArLHS->hasNoSignedWrap() && ArLHS->isAffine() &&
        isKnownPositive(ArLHS->getStepRecurrence(*this)) &&
        isKnownNonNegative(RHS) &&
        isKnownPredicateAt(SignFlippedPred, ArLHS, RHS, CtxI))
      return ScalarEvolution::LoopInvariantPredicate(Pred, ArLHS->getStart(),
                                                     RHS);
  }
  }
 
  return std::nullopt;
}
 
std::optional<ScalarEvolution::LoopInvariantPredicate>
ScalarEvolution::getLoopInvariantExitCondDuringFirstIterations(
    CmpPredicate Pred, const SCEV *LHS, const SCEV *RHS, const Loop *L,
    const Instruction *CtxI, const SCEV *MaxIter) {
  if (auto LIP = getLoopInvariantExitCondDuringFirstIterationsImpl(
          Pred, LHS, RHS, L, CtxI, MaxIter))
    return LIP;
  if (auto *UMin = dyn_cast<SCEVUMinExpr>(MaxIter))
    // Number of iterations expressed as UMIN isn't always great for expressing
    // the value on the last iteration. If the straightforward approach didn't
    // work, try the following trick: if the a predicate is invariant for X, it
    // is also invariant for umin(X, ...). So try to find something that works
    // among subexpressions of MaxIter expressed as umin.
    for (SCEVUse Op : UMin->operands())
      if (auto LIP = getLoopInvariantExitCondDuringFirstIterationsImpl(
              Pred, LHS, RHS, L, CtxI, Op))
        return LIP;
  return std::nullopt;
}
 
std::optional<ScalarEvolution::LoopInvariantPredicate>
ScalarEvolution::getLoopInvariantExitCondDuringFirstIterationsImpl(
    CmpPredicate Pred, const SCEV *LHS, const SCEV *RHS, const Loop *L,
    const Instruction *CtxI, const SCEV *MaxIter) {
  // Try to prove the following set of facts:
  // - The predicate is monotonic in the iteration space.
  // - If the check does not fail on the 1st iteration:
  //   - No overflow will happen during first MaxIter iterations;
  //   - It will not fail on the MaxIter'th iteration.
  // If the check does fail on the 1st iteration, we leave the loop and no
  // other checks matter.
 
  // If there is a loop-invariant, force it into the RHS, otherwise bail out.
  if (!isLoopInvariant(RHS, L)) {
    if (!isLoopInvariant(LHS, L))
      return std::nullopt;
 
    std::swap(LHS, RHS);
    Pred = ICmpInst::getSwappedCmpPredicate(Pred);
  }
 
  auto *AR = dyn_cast<SCEVAddRecExpr>(LHS);
  if (!AR || AR->getLoop() != L)
    return std::nullopt;
 
  // Even if both are valid, we need to consistently chose the unsigned or the
  // signed predicate below, not mixtures of both. For now, prefer the unsigned
  // predicate.
  Pred = Pred.dropSameSign();
 
  // The predicate must be relational (i.e. <, <=, >=, >).
  if (!ICmpInst::isRelational(Pred))
    return std::nullopt;
 
  // TODO: Support steps other than +/- 1.
  const SCEV *Step = AR->getStepRecurrence(*this);
  auto *One = getOne(Step->getType());
  auto *MinusOne = getNegativeSCEV(One);
  if (Step != One && Step != MinusOne)
    return std::nullopt;
 
  // Type mismatch here means that MaxIter is potentially larger than max
  // unsigned value in start type, which mean we cannot prove no wrap for the
  // indvar.
  if (AR->getType() != MaxIter->getType())
    return std::nullopt;
 
  // Value of IV on suggested last iteration.
  const SCEV *Last = AR->evaluateAtIteration(MaxIter, *this);
  // Does it still meet the requirement?
  if (!isLoopBackedgeGuardedByCond(L, Pred, Last, RHS))
    return std::nullopt;
  // Because step is +/- 1 and MaxIter has same type as Start (i.e. it does
  // not exceed max unsigned value of this type), this effectively proves
  // that there is no wrap during the iteration. To prove that there is no
  // signed/unsigned wrap, we need to check that
  // Start <= Last for step = 1 or Start >= Last for step = -1.
  ICmpInst::Predicate NoOverflowPred =
      CmpInst::isSigned(Pred) ? ICmpInst::ICMP_SLE : ICmpInst::ICMP_ULE;
  if (Step == MinusOne)
    NoOverflowPred = ICmpInst::getSwappedPredicate(NoOverflowPred);
  const SCEV *Start = AR->getStart();
  if (!isKnownPredicateAt(NoOverflowPred, Start, Last, CtxI))
    return std::nullopt;
 
  // Everything is fine.
  return ScalarEvolution::LoopInvariantPredicate(Pred, Start, RHS);
}
 
bool ScalarEvolution::isKnownPredicateViaConstantRanges(CmpPredicate Pred,
                                                        SCEVUse LHS,
                                                        SCEVUse RHS) {
  if (HasSameValue(LHS, RHS))
    return ICmpInst::isTrueWhenEqual(Pred);
 
  auto CheckRange = [&](bool IsSigned) {
    auto RangeLHS = IsSigned ? getSignedRange(LHS) : getUnsignedRange(LHS);
    auto RangeRHS = IsSigned ? getSignedRange(RHS) : getUnsignedRange(RHS);
    return RangeLHS.icmp(Pred, RangeRHS);
  };
 
  // The check at the top of the function catches the case where the values are
  // known to be equal.
  if (Pred == CmpInst::ICMP_EQ)
    return false;
 
  if (Pred == CmpInst::ICMP_NE) {
    if (CheckRange(true) || CheckRange(false))
      return true;
    auto *Diff = getMinusSCEV(LHS, RHS);
    return !isa<SCEVCouldNotCompute>(Diff) && isKnownNonZero(Diff);
  }
 
  return CheckRange(CmpInst::isSigned(Pred));
}
 
bool ScalarEvolution::isKnownPredicateViaNoOverflow(CmpPredicate Pred,
                                                    SCEVUse LHS, SCEVUse RHS) {
  // Match X to (A + C1)<ExpectedFlags> and Y to (A + C2)<ExpectedFlags>, where
  // C1 and C2 are constant integers. If either X or Y are not add expressions,
  // consider them as X + 0 and Y + 0 respectively. C1 and C2 are returned via
  // OutC1 and OutC2.
  auto MatchBinaryAddToConst = [this](SCEVUse X, SCEVUse Y, APInt &OutC1,
                                      APInt &OutC2, SCEVFlags ExpectedFlags) {
    SCEVUse XNonConstOp, XConstOp;
    SCEVUse YNonConstOp, YConstOp;
    SCEVFlags XFlagsPresent;
    SCEVFlags YFlagsPresent;
 
    // Use nullptr for 0, to avoid creating a zero SCEV.
    if (!splitBinaryAdd(X, XConstOp, XNonConstOp, XFlagsPresent)) {
      XConstOp = nullptr;
      XNonConstOp = X;
      XFlagsPresent = ExpectedFlags;
    }
    if (XConstOp && !isa<SCEVConstant>(XConstOp))
      return false;
 
    if (!splitBinaryAdd(Y, YConstOp, YNonConstOp, YFlagsPresent)) {
      YConstOp = nullptr;
      YNonConstOp = Y;
      YFlagsPresent = ExpectedFlags;
    }
 
    if (YNonConstOp != XNonConstOp)
      return false;
 
    if (YConstOp && !isa<SCEVConstant>(YConstOp))
      return false;
 
    // When matching ADDs with NUW flags (and unsigned predicates), only the
    // second ADD (with the larger constant) requires NUW.
    if ((YFlagsPresent & ExpectedFlags) != ExpectedFlags)
      return false;
    if (ExpectedFlags != SCEV::FlagNUW &&
        (XFlagsPresent & ExpectedFlags) != ExpectedFlags) {
      return false;
    }
 
    OutC1 = XConstOp ? cast<SCEVConstant>(XConstOp)->getAPInt()
                     : APInt::getZero(getTypeSizeInBits(X->getType()));
    OutC2 = YConstOp ? cast<SCEVConstant>(YConstOp)->getAPInt()
                     : APInt::getZero(getTypeSizeInBits(Y->getType()));
 
    return true;
  };
 
  APInt C1;
  APInt C2;
 
  switch (Pred) {
  default:
    break;
 
  case ICmpInst::ICMP_SGE:
    std::swap(LHS, RHS);
    [[fallthrough]];
  case ICmpInst::ICMP_SLE:
    // (X + C1)<nsw> s<= (X + C2)<nsw> if C1 s<= C2.
    if (MatchBinaryAddToConst(LHS, RHS, C1, C2, SCEV::FlagNSW) && C1.sle(C2))
      return true;
 
    break;
 
  case ICmpInst::ICMP_SGT:
    std::swap(LHS, RHS);
    [[fallthrough]];
  case ICmpInst::ICMP_SLT:
    // (X + C1)<nsw> s< (X + C2)<nsw> if C1 s< C2.
    if (MatchBinaryAddToConst(LHS, RHS, C1, C2, SCEV::FlagNSW) && C1.slt(C2))
      return true;
 
    break;
 
  case ICmpInst::ICMP_UGE:
    std::swap(LHS, RHS);
    [[fallthrough]];
  case ICmpInst::ICMP_ULE:
    // (X + C1) u<= (X + C2)<nuw> for C1 u<= C2.
    if (MatchBinaryAddToConst(LHS, RHS, C1, C2, SCEV::FlagNUW) && C1.ule(C2))
      return true;
 
    break;
 
  case ICmpInst::ICMP_UGT:
    std::swap(LHS, RHS);
    [[fallthrough]];
  case ICmpInst::ICMP_ULT:
    // (X + C1) u< (X + C2)<nuw> if C1 u< C2.
    if (MatchBinaryAddToConst(LHS, RHS, C1, C2, SCEV::FlagNUW) && C1.ult(C2))
      return true;
    break;
  }
 
  return false;
}
 
bool ScalarEvolution::isKnownPredicateViaSplitting(CmpPredicate Pred,
                                                   SCEVUse LHS, SCEVUse RHS) {
  if (Pred != ICmpInst::ICMP_ULT || ProvingSplitPredicate)
    return false;
 
  // Allowing arbitrary number of activations of isKnownPredicateViaSplitting on
  // the stack can result in exponential time complexity.
  SaveAndRestore Restore(ProvingSplitPredicate, true);
 
  // If L >= 0 then I `ult` L <=> I >= 0 && I `slt` L
  //
  // To prove L >= 0 we use isKnownNonNegative whereas to prove I >= 0 we use
  // isKnownPredicate.  isKnownPredicate is more powerful, but also more
  // expensive; and using isKnownNonNegative(RHS) is sufficient for most of the
  // interesting cases seen in practice.  We can consider "upgrading" L >= 0 to
  // use isKnownPredicate later if needed.
  return isKnownNonNegative(RHS) &&
         isKnownPredicate(CmpInst::ICMP_SGE, LHS, getZero(LHS->getType())) &&
         isKnownPredicate(CmpInst::ICMP_SLT, LHS, RHS);
}
 
bool ScalarEvolution::isImpliedViaGuard(const BasicBlock *BB, CmpPredicate Pred,
                                        const SCEV *LHS, const SCEV *RHS) {
  // No need to even try if we know the module has no guards.
  if (!HasGuards)
    return false;
 
  return any_of(*BB, [&](const Instruction &I) {
    using namespace llvm::PatternMatch;
 
    Value *Condition;
    return match(&I, m_Intrinsic<Intrinsic::experimental_guard>(
                         m_Value(Condition))) &&
           isImpliedCond(Pred, LHS, RHS, Condition, false);
  });
}
 
/// isLoopBackedgeGuardedByCond - Test whether the backedge of the loop is
/// protected by a conditional between LHS and RHS.  This is used to
/// to eliminate casts.
bool ScalarEvolution::isLoopBackedgeGuardedByCond(const Loop *L,
                                                  CmpPredicate Pred,
                                                  const SCEV *LHS,
                                                  const SCEV *RHS) {
  // Interpret a null as meaning no loop, where there is obviously no guard
  // (interprocedural conditions notwithstanding). Do not bother about
  // unreachable loops.
  if (!L || !DT.isReachableFromEntry(L->getHeader()))
    return true;
 
  if (VerifyIR)
    assert(!verifyFunction(*L->getHeader()->getParent(), &dbgs()) &&
           "This cannot be done on broken IR!");
 
 
  if (isKnownViaNonRecursiveReasoning(Pred, LHS, RHS))
    return true;
 
  BasicBlock *Latch = L->getLoopLatch();
  if (!Latch)
    return false;
 
  CondBrInst *LoopContinuePredicate =
      dyn_cast<CondBrInst>(Latch->getTerminator());
  if (LoopContinuePredicate &&
      isImpliedCond(Pred, LHS, RHS, LoopContinuePredicate->getCondition(),
                    LoopContinuePredicate->getSuccessor(0) != L->getHeader()))
    return true;
 
  // We don't want more than one activation of the following loops on the stack
  // -- that can lead to O(n!) time complexity.
  if (WalkingBEDominatingConds)
    return false;
 
  SaveAndRestore ClearOnExit(WalkingBEDominatingConds, true);
 
  // See if we can exploit a trip count to prove the predicate.
  const auto &BETakenInfo = getBackedgeTakenInfo(L);
  const SCEV *LatchBECount = BETakenInfo.getExact(Latch, this);
  if (LatchBECount != getCouldNotCompute()) {
    // We know that Latch branches back to the loop header exactly
    // LatchBECount times.  This means the backdege condition at Latch is
    // equivalent to  "{0,+,1} u< LatchBECount".
    Type *Ty = LatchBECount->getType();
    auto NoWrapFlags = SCEVFlags(SCEV::FlagNUW | SCEV::FlagNW);
    const SCEV *LoopCounter =
      getAddRecExpr(getZero(Ty), getOne(Ty), L, NoWrapFlags);
    if (isImpliedCond(Pred, LHS, RHS, ICmpInst::ICMP_ULT, LoopCounter,
                      LatchBECount))
      return true;
  }
 
  // Check conditions due to any @llvm.assume intrinsics.
  for (auto &AssumeVH : AC.assumptions()) {
    if (!AssumeVH)
      continue;
    auto *CI = cast<CallInst>(AssumeVH);
    if (!DT.dominates(CI, Latch->getTerminator()))
      continue;
 
    if (isImpliedCond(Pred, LHS, RHS, CI->getArgOperand(0), false))
      return true;
  }
 
  if (isImpliedViaGuard(Latch, Pred, LHS, RHS))
    return true;
 
  for (DomTreeNode *DTN = DT[Latch], *HeaderDTN = DT[L->getHeader()];
       DTN != HeaderDTN; DTN = DTN->getIDom()) {
    assert(DTN && "should reach the loop header before reaching the root!");
 
    BasicBlock *BB = DTN->getBlock();
    if (isImpliedViaGuard(BB, Pred, LHS, RHS))
      return true;
 
    BasicBlock *PBB = BB->getSinglePredecessor();
    if (!PBB)
      continue;
 
    CondBrInst *ContBr = dyn_cast<CondBrInst>(PBB->getTerminator());
    if (!ContBr || ContBr->getSuccessor(0) == ContBr->getSuccessor(1))
      continue;
 
    // If we have an edge `E` within the loop body that dominates the only
    // latch, the condition guarding `E` also guards the backedge.  This
    // reasoning works only for loops with a single latch.
    // We're constructively (and conservatively) enumerating edges within the
    // loop body that dominate the latch.  The dominator tree better agree
    // with us on this:
    assert(DT.dominates(BasicBlockEdge(PBB, BB), Latch) && "should be!");
    if (isImpliedCond(Pred, LHS, RHS, ContBr->getCondition(),
                      BB != ContBr->getSuccessor(0)))
      return true;
  }
 
  return false;
}
 
bool ScalarEvolution::isBasicBlockEntryGuardedByCond(const BasicBlock *BB,
                                                     CmpPredicate Pred,
                                                     const SCEV *LHS,
                                                     const SCEV *RHS) {
  // Do not bother proving facts for unreachable code.
  if (!DT.isReachableFromEntry(BB))
    return true;
  if (VerifyIR)
    assert(!verifyFunction(*BB->getParent(), &dbgs()) &&
           "This cannot be done on broken IR!");
 
  // If we cannot prove strict comparison (e.g. a > b), maybe we can prove
  // the facts (a >= b && a != b) separately. A typical situation is when the
  // non-strict comparison is known from ranges and non-equality is known from
  // dominating predicates. If we are proving strict comparison, we always try
  // to prove non-equality and non-strict comparison separately.
  CmpPredicate NonStrictPredicate = ICmpInst::getNonStrictCmpPredicate(Pred);
  const bool ProvingStrictComparison =
      Pred != NonStrictPredicate.dropSameSign();
  bool ProvedNonStrictComparison = false;
  bool ProvedNonEquality = false;
 
  auto SplitAndProve = [&](std::function<bool(CmpPredicate)> Fn) -> bool {
    if (!ProvedNonStrictComparison)
      ProvedNonStrictComparison = Fn(NonStrictPredicate);
    if (!ProvedNonEquality)
      ProvedNonEquality = Fn(ICmpInst::ICMP_NE);
    if (ProvedNonStrictComparison && ProvedNonEquality)
      return true;
    return false;
  };
 
  if (ProvingStrictComparison) {
    auto ProofFn = [&](CmpPredicate P) {
      return isKnownViaNonRecursiveReasoning(P, LHS, RHS);
    };
    if (SplitAndProve(ProofFn))
      return true;
  }
 
  // Try to prove (Pred, LHS, RHS) using isImpliedCond.
  auto ProveViaCond = [&](const Value *Condition, bool Inverse) {
    const Instruction *CtxI = &BB->front();
    if (isImpliedCond(Pred, LHS, RHS, Condition, Inverse, CtxI))
      return true;
    if (ProvingStrictComparison) {
      auto ProofFn = [&](CmpPredicate P) {
        return isImpliedCond(P, LHS, RHS, Condition, Inverse, CtxI);
      };
      if (SplitAndProve(ProofFn))
        return true;
    }
    return false;
  };
 
  // Starting at the block's predecessor, climb up the predecessor chain, as long
  // as there are predecessors that can be found that have unique successors
  // leading to the original block.
  const Loop *ContainingLoop = LI.getLoopFor(BB);
  const BasicBlock *PredBB;
  if (ContainingLoop && ContainingLoop->getHeader() == BB)
    PredBB = ContainingLoop->getLoopPredecessor();
  else
    PredBB = BB->getSinglePredecessor();
  for (std::pair<const BasicBlock *, const BasicBlock *> Pair(PredBB, BB);
       Pair.first; Pair = getPredecessorWithUniqueSuccessorForBB(Pair.first)) {
    const CondBrInst *BlockEntryPredicate =
        dyn_cast<CondBrInst>(Pair.first->getTerminator());
    if (!BlockEntryPredicate)
      continue;
 
    if (ProveViaCond(BlockEntryPredicate->getCondition(),
                     BlockEntryPredicate->getSuccessor(0) != Pair.second))
      return true;
  }
 
  // Check conditions due to any @llvm.assume intrinsics.
  for (auto &AssumeVH : AC.assumptions()) {
    if (!AssumeVH)
      continue;
    auto *CI = cast<CallInst>(AssumeVH);
    if (!DT.dominates(CI, BB))
      continue;
 
    if (ProveViaCond(CI->getArgOperand(0), false))
      return true;
  }
 
  // Check conditions due to any @llvm.experimental.guard intrinsics.
  auto *GuardDecl = Intrinsic::getDeclarationIfExists(
      F.getParent(), Intrinsic::experimental_guard);
  if (GuardDecl)
    for (const auto *GU : GuardDecl->users())
      if (const auto *Guard = dyn_cast<IntrinsicInst>(GU))
        if (Guard->getFunction() == BB->getParent() && DT.dominates(Guard, BB))
          if (ProveViaCond(Guard->getArgOperand(0), false))
            return true;
  return false;
}
 
bool ScalarEvolution::isLoopEntryGuardedByCond(const Loop *L, CmpPredicate Pred,
                                               const SCEV *LHS,
                                               const SCEV *RHS) {
  // Interpret a null as meaning no loop, where there is obviously no guard
  // (interprocedural conditions notwithstanding).
  if (!L)
    return false;
 
  // Both LHS and RHS must be available at loop entry.
  assert(isAvailableAtLoopEntry(LHS, L) &&
         "LHS is not available at Loop Entry");
  assert(isAvailableAtLoopEntry(RHS, L) &&
         "RHS is not available at Loop Entry");
 
  if (isKnownViaNonRecursiveReasoning(Pred, LHS, RHS))
    return true;
 
  return isBasicBlockEntryGuardedByCond(L->getHeader(), Pred, LHS, RHS);
}
 
bool ScalarEvolution::isImpliedCond(CmpPredicate Pred, const SCEV *LHS,
                                    const SCEV *RHS,
                                    const Value *FoundCondValue, bool Inverse,
                                    const Instruction *CtxI) {
  // False conditions implies anything. Do not bother analyzing it further.
  if (FoundCondValue ==
      ConstantInt::getBool(FoundCondValue->getContext(), Inverse))
    return true;
 
  if (!PendingLoopPredicates.insert(FoundCondValue).second)
    return false;
 
  llvm::scope_exit ClearOnExit(
      [&]() { PendingLoopPredicates.erase(FoundCondValue); });
 
  // Recursively handle And and Or conditions.
  const Value *Op0, *Op1;
  if (match(FoundCondValue, m_LogicalAnd(m_Value(Op0), m_Value(Op1)))) {
    if (!Inverse)
      return isImpliedCond(Pred, LHS, RHS, Op0, Inverse, CtxI) ||
             isImpliedCond(Pred, LHS, RHS, Op1, Inverse, CtxI);
  } else if (match(FoundCondValue, m_LogicalOr(m_Value(Op0), m_Value(Op1)))) {
    if (Inverse)
      return isImpliedCond(Pred, LHS, RHS, Op0, Inverse, CtxI) ||
             isImpliedCond(Pred, LHS, RHS, Op1, Inverse, CtxI);
  }
 
  const ICmpInst *ICI = dyn_cast<ICmpInst>(FoundCondValue);
  if (!ICI) return false;
 
  // Now that we found a conditional branch that dominates the loop or controls
  // the loop latch. Check to see if it is the comparison we are looking for.
  CmpPredicate FoundPred;
  if (Inverse)
    FoundPred = ICI->getInverseCmpPredicate();
  else
    FoundPred = ICI->getCmpPredicate();
 
  const SCEV *FoundLHS = getSCEV(ICI->getOperand(0));
  const SCEV *FoundRHS = getSCEV(ICI->getOperand(1));
 
  return isImpliedCond(Pred, LHS, RHS, FoundPred, FoundLHS, FoundRHS, CtxI);
}
 
bool ScalarEvolution::isImpliedCond(CmpPredicate Pred, const SCEV *LHS,
                                    const SCEV *RHS, CmpPredicate FoundPred,
                                    const SCEV *FoundLHS, const SCEV *FoundRHS,
                                    const Instruction *CtxI) {
  // Balance the types.
  if (getTypeSizeInBits(LHS->getType()) <
      getTypeSizeInBits(FoundLHS->getType())) {
    // For unsigned and equality predicates, try to prove that both found
    // operands fit into narrow unsigned range. If so, try to prove facts in
    // narrow types.
    if (!CmpInst::isSigned(FoundPred) && !FoundLHS->getType()->isPointerTy() &&
        !FoundRHS->getType()->isPointerTy()) {
      auto *NarrowType = LHS->getType();
      auto *WideType = FoundLHS->getType();
      auto BitWidth = getTypeSizeInBits(NarrowType);
      const SCEV *MaxValue = getZeroExtendExpr(
          getConstant(APInt::getMaxValue(BitWidth)), WideType);
      if (isKnownViaNonRecursiveReasoning(ICmpInst::ICMP_ULE, FoundLHS,
                                          MaxValue) &&
          isKnownViaNonRecursiveReasoning(ICmpInst::ICMP_ULE, FoundRHS,
                                          MaxValue)) {
        const SCEV *TruncFoundLHS = getTruncateExpr(FoundLHS, NarrowType);
        const SCEV *TruncFoundRHS = getTruncateExpr(FoundRHS, NarrowType);
        // We cannot preserve samesign after truncation.
        if (isImpliedCondBalancedTypes(Pred, LHS, RHS, FoundPred.dropSameSign(),
                                       TruncFoundLHS, TruncFoundRHS, CtxI))
          return true;
      }
    }
 
    if (LHS->getType()->isPointerTy() || RHS->getType()->isPointerTy())
      return false;
    if (CmpInst::isSigned(Pred)) {
      LHS = getSignExtendExpr(LHS, FoundLHS->getType());
      RHS = getSignExtendExpr(RHS, FoundLHS->getType());
    } else {
      LHS = getZeroExtendExpr(LHS, FoundLHS->getType());
      RHS = getZeroExtendExpr(RHS, FoundLHS->getType());
    }
  } else if (getTypeSizeInBits(LHS->getType()) >
      getTypeSizeInBits(FoundLHS->getType())) {
    if (FoundLHS->getType()->isPointerTy() || FoundRHS->getType()->isPointerTy())
      return false;
    if (CmpInst::isSigned(FoundPred)) {
      FoundLHS = getSignExtendExpr(FoundLHS, LHS->getType());
      FoundRHS = getSignExtendExpr(FoundRHS, LHS->getType());
    } else {
      FoundLHS = getZeroExtendExpr(FoundLHS, LHS->getType());
      FoundRHS = getZeroExtendExpr(FoundRHS, LHS->getType());
    }
  }
  return isImpliedCondBalancedTypes(Pred, LHS, RHS, FoundPred, FoundLHS,
                                    FoundRHS, CtxI);
}
 
bool ScalarEvolution::isImpliedCondBalancedTypes(
    CmpPredicate Pred, SCEVUse LHS, SCEVUse RHS, CmpPredicate FoundPred,
    SCEVUse FoundLHS, SCEVUse FoundRHS, const Instruction *CtxI) {
  assert(getTypeSizeInBits(LHS->getType()) ==
             getTypeSizeInBits(FoundLHS->getType()) &&
         "Types should be balanced!");
  // Canonicalize the query to match the way instcombine will have
  // canonicalized the comparison.
  if (SimplifyICmpOperands(Pred, LHS, RHS))
    if (LHS == RHS)
      return CmpInst::isTrueWhenEqual(Pred);
  if (SimplifyICmpOperands(FoundPred, FoundLHS, FoundRHS))
    if (FoundLHS == FoundRHS)
      return CmpInst::isFalseWhenEqual(FoundPred);
 
  // Check to see if we can make the LHS or RHS match.
  if (LHS == FoundRHS || RHS == FoundLHS) {
    if (isa<SCEVConstant>(RHS)) {
      std::swap(FoundLHS, FoundRHS);
      FoundPred = ICmpInst::getSwappedCmpPredicate(FoundPred);
    } else {
      std::swap(LHS, RHS);
      Pred = ICmpInst::getSwappedCmpPredicate(Pred);
    }
  }
 
  // Check whether the found predicate is the same as the desired predicate.
  if (auto P = CmpPredicate::getMatching(FoundPred, Pred))
    return isImpliedCondOperands(*P, LHS, RHS, FoundLHS, FoundRHS, CtxI);
 
  // Check whether swapping the found predicate makes it the same as the
  // desired predicate.
  if (auto P = CmpPredicate::getMatching(
          ICmpInst::getSwappedCmpPredicate(FoundPred), Pred)) {
    // We can write the implication
    // 0.  LHS Pred      RHS  <-   FoundLHS SwapPred  FoundRHS
    // using one of the following ways:
    // 1.  LHS Pred      RHS  <-   FoundRHS Pred      FoundLHS
    // 2.  RHS SwapPred  LHS  <-   FoundLHS SwapPred  FoundRHS
    // Both require swapping the operands of one condition. Don't do this if it
    // would break canonical constant/addrec ordering.
    if (!isa<SCEVConstant>(RHS) && !isa<SCEVAddRecExpr>(LHS))
      return isImpliedCondOperands(ICmpInst::getSwappedCmpPredicate(*P), RHS,
                                   LHS, FoundLHS, FoundRHS, CtxI);
    if (!isa<SCEVConstant>(FoundRHS) && !isa<SCEVAddRecExpr>(FoundLHS))
      return isImpliedCondOperands(*P, LHS, RHS, FoundRHS, FoundLHS, CtxI);
 
    return false;
  }
 
  // Try the query as is and with its operands swapped. E.g. "x >s -1" is
  // tried as "-1 <s x" too, to match the found condition "x <u y".
  auto IsSignFlippedPredicate = [](CmpInst::Predicate P1,
                                   CmpInst::Predicate P2) {
    return CmpInst::isRelational(P2) &&
           P1 == ICmpInst::getFlippedSignednessPredicate(P2);
  };
  if (IsSignFlippedPredicate(Pred, FoundPred) &&
      isImpliedCondViaSignFlippedPred(Pred, LHS, RHS, FoundLHS, FoundRHS, CtxI))
    return true;
  CmpPredicate SwappedPred = ICmpInst::getSwappedCmpPredicate(Pred);
  if (IsSignFlippedPredicate(SwappedPred, FoundPred) &&
      isImpliedCondViaSignFlippedPred(SwappedPred, RHS, LHS, FoundLHS, FoundRHS,
                                      CtxI))
    return true;
 
  // Check if we can make progress by sharpening ranges.
  if (FoundPred == ICmpInst::ICMP_NE &&
      (isa<SCEVConstant>(FoundLHS) || isa<SCEVConstant>(FoundRHS))) {
 
    const SCEVConstant *C = nullptr;
    const SCEV *V = nullptr;
 
    if (isa<SCEVConstant>(FoundLHS)) {
      C = cast<SCEVConstant>(FoundLHS);
      V = FoundRHS;
    } else {
      C = cast<SCEVConstant>(FoundRHS);
      V = FoundLHS;
    }
 
    // The guarding predicate tells us that C != V. If the known range
    // of V is [C, t), we can sharpen the range to [C + 1, t).  The
    // range we consider has to correspond to same signedness as the
    // predicate we're interested in folding.
 
    APInt Min = ICmpInst::isSigned(Pred) ?
        getSignedRangeMin(V) : getUnsignedRangeMin(V);
 
    if (Min == C->getAPInt()) {
      // Given (V >= Min && V != Min) we conclude V >= (Min + 1).
      // This is true even if (Min + 1) wraps around -- in case of
      // wraparound, (Min + 1) < Min, so (V >= Min => V >= (Min + 1)).
 
      APInt SharperMin = Min + 1;
 
      switch (Pred) {
        case ICmpInst::ICMP_SGE:
        case ICmpInst::ICMP_UGE:
          // We know V `Pred` SharperMin.  If this implies LHS `Pred`
          // RHS, we're done.
          if (isImpliedCondOperands(Pred, LHS, RHS, V, getConstant(SharperMin),
                                    CtxI))
            return true;
          [[fallthrough]];
 
        case ICmpInst::ICMP_SGT:
        case ICmpInst::ICMP_UGT:
          // We know from the range information that (V `Pred` Min ||
          // V == Min).  We know from the guarding condition that !(V
          // == Min).  This gives us
          //
          //       V `Pred` Min || V == Min && !(V == Min)
          //   =>  V `Pred` Min
          //
          // If V `Pred` Min implies LHS `Pred` RHS, we're done.
 
          if (isImpliedCondOperands(Pred, LHS, RHS, V, getConstant(Min), CtxI))
            return true;
          break;
 
        // `LHS < RHS` and `LHS <= RHS` are handled in the same way as `RHS > LHS` and `RHS >= LHS` respectively.
        case ICmpInst::ICMP_SLE:
        case ICmpInst::ICMP_ULE:
          if (isImpliedCondOperands(ICmpInst::getSwappedCmpPredicate(Pred), RHS,
                                    LHS, V, getConstant(SharperMin), CtxI))
            return true;
          [[fallthrough]];
 
        case ICmpInst::ICMP_SLT:
        case ICmpInst::ICMP_ULT:
          if (isImpliedCondOperands(ICmpInst::getSwappedCmpPredicate(Pred), RHS,
                                    LHS, V, getConstant(Min), CtxI))
            return true;
          break;
 
        default:
          // No change
          break;
      }
    }
  }
 
  // Check whether the actual condition is beyond sufficient.
  if (FoundPred == ICmpInst::ICMP_EQ)
    if (ICmpInst::isTrueWhenEqual(Pred))
      if (isImpliedCondOperands(Pred, LHS, RHS, FoundLHS, FoundRHS, CtxI))
        return true;
  if (Pred == ICmpInst::ICMP_NE)
    if (!ICmpInst::isTrueWhenEqual(FoundPred))
      if (isImpliedCondOperands(FoundPred, LHS, RHS, FoundLHS, FoundRHS, CtxI))
        return true;
 
  if (isImpliedCondOperandsViaRanges(Pred, LHS, RHS, FoundPred, FoundLHS, FoundRHS))
    return true;
 
  // Otherwise assume the worst.
  return false;
}
 
bool ScalarEvolution::isImpliedCondViaSignFlippedPred(
    CmpPredicate Pred, const SCEV *LHS, const SCEV *RHS, const SCEV *FoundLHS,
    const SCEV *FoundRHS, const Instruction *CtxI) {
  CmpPredicate FoundPred = ICmpInst::getFlippedSignednessPredicate(Pred);
  // Unsigned comparison is the same as signed comparison when both the
  // operands are non-negative or negative.
  if (haveSameSign(FoundLHS, FoundRHS) &&
      isImpliedCondOperands(Pred, LHS, RHS, FoundLHS, FoundRHS, CtxI))
    return true;
  // Canonicalize both conditions to "le/lt".
  if (ICmpInst::isGT(Pred) || ICmpInst::isGE(Pred)) {
    Pred = ICmpInst::getSwappedCmpPredicate(Pred);
    FoundPred = ICmpInst::getSwappedCmpPredicate(FoundPred);
    std::swap(LHS, RHS);
    std::swap(FoundLHS, FoundRHS);
  }
  assert((ICmpInst::isLT(Pred) || ICmpInst::isLE(Pred)) && "Must be!");
  assert((ICmpInst::isLT(FoundPred) || ICmpInst::isLE(FoundPred)) &&
         "Must be!");
  if (ICmpInst::isSigned(Pred)) {
    // Use implication:
    // x <u y && y <=u 2^(n-1) --> x >=s 0,
    // x <=u y && y <u 2^(n-1) --> x >=s 0,
    // where n is the bit width of x and y.
    // In both cases x <u 2^(n-1), so x >=s 0.
    // y <=u 2^(n-1) means y >=s 0 or y == INT_MIN.
    // If the implication's left part holds, try proving the query from x >=s
    // 0.
    Type *Ty = FoundLHS->getType();
    unsigned BitWidth = getTypeSizeInBits(Ty);
    const SCEV *SignedMin = getConstant(APInt::getSignedMinValue(BitWidth));
    CmpPredicate BoundPred =
        ICmpInst::isLT(FoundPred) ? ICmpInst::ICMP_ULE : ICmpInst::ICMP_ULT;
    if (isKnownViaNonRecursiveReasoning(BoundPred, FoundRHS, SignedMin)) {
      // x >=s 0, written as 0 <=s x, or as -1 <s x to match a strict query.
      const SCEV *Bound = ICmpInst::isLE(Pred) ? getZero(Ty) : getMinusOne(Ty);
      if (isImpliedCondOperands(Pred, LHS, RHS, Bound, FoundLHS, CtxI))
        return true;
    }
  }
  if (ICmpInst::isSigned(Pred) && isKnownNonNegative(RHS)) {
    // Use implication:
    // x <u y && y >=s 0 --> x <s y.
    // If we can prove the left part, the right part is also proven.
    if (isImpliedCondOperands(FoundPred, LHS, RHS, FoundLHS, FoundRHS))
      return true;
  }
  if (ICmpInst::isUnsigned(Pred) && isKnownNegative(RHS)) {
    // Use implication:
    // x <s y && y <s 0 --> x <u y.
    // If we can prove the left part, the right part is also proven.
    if (isImpliedCondOperands(FoundPred, LHS, RHS, FoundLHS, FoundRHS))
      return true;
  }
  return false;
}
 
bool ScalarEvolution::splitBinaryAdd(SCEVUse Expr, SCEVUse &L, SCEVUse &R,
                                     SCEVFlags &Flags) {
  if (!match(Expr, m_scev_Add(m_SCEV(L), m_SCEV(R))))
    return false;
 
  Flags = cast<SCEVAddExpr>(Expr)->getNoWrapFlags();
  return true;
}
 
std::optional<APInt>
ScalarEvolution::computeConstantDifference(const SCEV *More, const SCEV *Less) {
  // We avoid subtracting expressions here because this function is usually
  // fairly deep in the call stack (i.e. is called many times).
 
  unsigned BW = getTypeSizeInBits(More->getType());
  APInt Diff(BW, 0);
  APInt DiffMul(BW, 1);
  // Try various simplifications to reduce the difference to a constant. Limit
  // the number of allowed simplifications to keep compile-time low.
  for (unsigned I = 0; I < 8; ++I) {
    if (More == Less)
      return Diff;
 
    // Reduce addrecs with identical steps to their start value.
    if (isa<SCEVAddRecExpr>(Less) && isa<SCEVAddRecExpr>(More)) {
      const auto *LAR = cast<SCEVAddRecExpr>(Less);
      const auto *MAR = cast<SCEVAddRecExpr>(More);
 
      if (LAR->getLoop() != MAR->getLoop())
        return std::nullopt;
 
      // We look at affine expressions only; not for correctness but to keep
      // getStepRecurrence cheap.
      if (!LAR->isAffine() || !MAR->isAffine())
        return std::nullopt;
 
      if (LAR->getStepRecurrence(*this) != MAR->getStepRecurrence(*this))
        return std::nullopt;
 
      Less = LAR->getStart();
      More = MAR->getStart();
      continue;
    }
 
    // Try to match a common constant multiply.
    auto MatchConstMul =
        [](const SCEV *S) -> std::optional<std::pair<const SCEV *, APInt>> {
      const APInt *C;
      const SCEV *Op;
      if (match(S, m_scev_Mul(m_scev_APInt(C), m_SCEV(Op))))
        return {{Op, *C}};
      return std::nullopt;
    };
    if (auto MatchedMore = MatchConstMul(More)) {
      if (auto MatchedLess = MatchConstMul(Less)) {
        if (MatchedMore->second == MatchedLess->second) {
          More = MatchedMore->first;
          Less = MatchedLess->first;
          DiffMul *= MatchedMore->second;
          continue;
        }
      }
    }
 
    // Try to cancel out common factors in two add expressions.
    SmallDenseMap<const SCEV *, int, 8> Multiplicity;
    auto Add = [&](const SCEV *S, int Mul) {
      if (auto *C = dyn_cast<SCEVConstant>(S)) {
        if (Mul == 1) {
          Diff += C->getAPInt() * DiffMul;
        } else {
          assert(Mul == -1);
          Diff -= C->getAPInt() * DiffMul;
        }
      } else
        Multiplicity[S] += Mul;
    };
    auto Decompose = [&](const SCEV *S, int Mul) {
      if (isa<SCEVAddExpr>(S)) {
        for (const SCEV *Op : S->operands())
          Add(Op, Mul);
      } else
        Add(S, Mul);
    };
    Decompose(More, 1);
    Decompose(Less, -1);
 
    // Check whether all the non-constants cancel out, or reduce to new
    // More/Less values.
    const SCEV *NewMore = nullptr, *NewLess = nullptr;
    for (const auto &[S, Mul] : Multiplicity) {
      if (Mul == 0)
        continue;
      if (Mul == 1) {
        if (NewMore)
          return std::nullopt;
        NewMore = S;
      } else if (Mul == -1) {
        if (NewLess)
          return std::nullopt;
        NewLess = S;
      } else
        return std::nullopt;
    }
 
    // Values stayed the same, no point in trying further.
    if (NewMore == More || NewLess == Less)
      return std::nullopt;
 
    More = NewMore;
    Less = NewLess;
 
    // Reduced to constant.
    if (!More && !Less)
      return Diff;
 
    // Left with variable on only one side, bail out.
    if (!More || !Less)
      return std::nullopt;
  }
 
  // Did not reduce to constant.
  return std::nullopt;
}
 
bool ScalarEvolution::isImpliedCondOperandsViaAddRecStart(
    CmpPredicate Pred, const SCEV *LHS, const SCEV *RHS, const SCEV *FoundLHS,
    const SCEV *FoundRHS, const Instruction *CtxI) {
  // Try to recognize the following pattern:
  //
  //   FoundRHS = ...
  // ...
  // loop:
  //   FoundLHS = {Start,+,W}
  // context_bb: // Basic block from the same loop
  //   known(Pred, FoundLHS, FoundRHS)
  //
  // If some predicate is known in the context of a loop, it is also known on
  // each iteration of this loop, including the first iteration. Therefore, in
  // this case, `FoundLHS Pred FoundRHS` implies `Start Pred FoundRHS`. Try to
  // prove the original pred using this fact.
  if (!CtxI)
    return false;
  const BasicBlock *ContextBB = CtxI->getParent();
  // Make sure AR varies in the context block.
  if (auto *AR = dyn_cast<SCEVAddRecExpr>(FoundLHS)) {
    const Loop *L = AR->getLoop();
    const auto *Latch = L->getLoopLatch();
    // Make sure that context belongs to the loop and executes on 1st iteration
    // (if it ever executes at all).
    if (!L->contains(ContextBB) || !Latch || !DT.dominates(ContextBB, Latch))
      return false;
    if (!isAvailableAtLoopEntry(FoundRHS, AR->getLoop()))
      return false;
    return isImpliedCondOperands(Pred, LHS, RHS, AR->getStart(), FoundRHS);
  }
 
  if (auto *AR = dyn_cast<SCEVAddRecExpr>(FoundRHS)) {
    const Loop *L = AR->getLoop();
    const auto *Latch = L->getLoopLatch();
    // Make sure that context belongs to the loop and executes on 1st iteration
    // (if it ever executes at all).
    if (!L->contains(ContextBB) || !Latch || !DT.dominates(ContextBB, Latch))
      return false;
    if (!isAvailableAtLoopEntry(FoundLHS, AR->getLoop()))
      return false;
    return isImpliedCondOperands(Pred, LHS, RHS, FoundLHS, AR->getStart());
  }
 
  return false;
}
 
bool ScalarEvolution::isImpliedCondOperandsViaNoOverflow(CmpPredicate Pred,
                                                         const SCEV *LHS,
                                                         const SCEV *RHS,
                                                         const SCEV *FoundLHS,
                                                         const SCEV *FoundRHS) {
  if (Pred != CmpInst::ICMP_SLT && Pred != CmpInst::ICMP_ULT)
    return false;
 
  const auto *AddRecLHS = dyn_cast<SCEVAddRecExpr>(LHS);
  if (!AddRecLHS)
    return false;
 
  const auto *AddRecFoundLHS = dyn_cast<SCEVAddRecExpr>(FoundLHS);
  if (!AddRecFoundLHS)
    return false;
 
  // We'd like to let SCEV reason about control dependencies, so we constrain
  // both the inequalities to be about add recurrences on the same loop.  This
  // way we can use isLoopEntryGuardedByCond later.
 
  const Loop *L = AddRecFoundLHS->getLoop();
  if (L != AddRecLHS->getLoop())
    return false;
 
  //  FoundLHS u< FoundRHS u< -C =>  (FoundLHS + C) u< (FoundRHS + C) ... (1)
  //
  //  FoundLHS s< FoundRHS s< INT_MIN - C => (FoundLHS + C) s< (FoundRHS + C)
  //                                                                  ... (2)
  //
  // Informal proof for (2), assuming (1) [*]:
  //
  // We'll also assume (A s< B) <=> ((A + INT_MIN) u< (B + INT_MIN)) ... (3)[**]
  //
  // Then
  //
  //       FoundLHS s< FoundRHS s< INT_MIN - C
  // <=>  (FoundLHS + INT_MIN) u< (FoundRHS + INT_MIN) u< -C   [ using (3) ]
  // <=>  (FoundLHS + INT_MIN + C) u< (FoundRHS + INT_MIN + C) [ using (1) ]
  // <=>  (FoundLHS + INT_MIN + C + INT_MIN) s<
  //                        (FoundRHS + INT_MIN + C + INT_MIN) [ using (3) ]
  // <=>  FoundLHS + C s< FoundRHS + C
  //
  // [*]: (1) can be proved by ruling out overflow.
  //
  // [**]: This can be proved by analyzing all the four possibilities:
  //    (A s< 0, B s< 0), (A s< 0, B s>= 0), (A s>= 0, B s< 0) and
  //    (A s>= 0, B s>= 0).
  //
  // Note:
  // Despite (2), "FoundRHS s< INT_MIN - C" does not mean that "FoundRHS + C"
  // will not sign underflow.  For instance, say FoundLHS = (i8 -128), FoundRHS
  // = (i8 -127) and C = (i8 -100).  Then INT_MIN - C = (i8 -28), and FoundRHS
  // s< (INT_MIN - C).  Lack of sign overflow / underflow in "FoundRHS + C" is
  // neither necessary nor sufficient to prove "(FoundLHS + C) s< (FoundRHS +
  // C)".
 
  std::optional<APInt> LDiff = computeConstantDifference(LHS, FoundLHS);
  if (!LDiff)
    return false;
  std::optional<APInt> RDiff = computeConstantDifference(RHS, FoundRHS);
  if (!RDiff || *LDiff != *RDiff)
    return false;
 
  if (LDiff->isMinValue())
    return true;
 
  APInt FoundRHSLimit;
 
  if (Pred == CmpInst::ICMP_ULT) {
    FoundRHSLimit = -(*RDiff);
  } else {
    assert(Pred == CmpInst::ICMP_SLT && "Checked above!");
    FoundRHSLimit = APInt::getSignedMinValue(getTypeSizeInBits(RHS->getType())) - *RDiff;
  }
 
  // Try to prove (1) or (2), as needed.
  return isAvailableAtLoopEntry(FoundRHS, L) &&
         isLoopEntryGuardedByCond(L, Pred, FoundRHS,
                                  getConstant(FoundRHSLimit));
}
 
bool ScalarEvolution::isImpliedViaMerge(CmpPredicate Pred, const SCEV *LHS,
                                        const SCEV *RHS, const SCEV *FoundLHS,
                                        const SCEV *FoundRHS, unsigned Depth) {
  const PHINode *LPhi = nullptr, *RPhi = nullptr;
 
  llvm::scope_exit ClearOnExit([&]() {
    if (LPhi) {
      bool Erased = PendingMerges.erase(LPhi);
      assert(Erased && "Failed to erase LPhi!");
      (void)Erased;
    }
    if (RPhi) {
      bool Erased = PendingMerges.erase(RPhi);
      assert(Erased && "Failed to erase RPhi!");
      (void)Erased;
    }
  });
 
  // Find respective Phis and check that they are not being pending.
  if (const SCEVUnknown *LU = dyn_cast<SCEVUnknown>(LHS))
    if (auto *Phi = dyn_cast<PHINode>(LU->getValue())) {
      if (!PendingMerges.insert(Phi).second)
        return false;
      LPhi = Phi;
    }
  if (const SCEVUnknown *RU = dyn_cast<SCEVUnknown>(RHS))
    if (auto *Phi = dyn_cast<PHINode>(RU->getValue())) {
      // If we detect a loop of Phi nodes being processed by this method, for
      // example:
      //
      //   %a = phi i32 [ %some1, %preheader ], [ %b, %latch ]
      //   %b = phi i32 [ %some2, %preheader ], [ %a, %latch ]
      //
      // we don't want to deal with a case that complex, so return conservative
      // answer false.
      if (!PendingMerges.insert(Phi).second)
        return false;
      RPhi = Phi;
    }
 
  // If none of LHS, RHS is a Phi, nothing to do here.
  if (!LPhi && !RPhi)
    return false;
 
  // If there is a SCEVUnknown Phi we are interested in, make it left.
  if (!LPhi) {
    std::swap(LHS, RHS);
    std::swap(FoundLHS, FoundRHS);
    std::swap(LPhi, RPhi);
    Pred = ICmpInst::getSwappedCmpPredicate(Pred);
  }
 
  assert(LPhi && "LPhi should definitely be a SCEVUnknown Phi!");
  const BasicBlock *LBB = LPhi->getParent();
  const SCEVAddRecExpr *RAR = dyn_cast<SCEVAddRecExpr>(RHS);
 
  auto ProvedEasily = [&](const SCEV *S1, const SCEV *S2) {
    return isKnownViaNonRecursiveReasoning(Pred, S1, S2) ||
           isImpliedCondOperandsViaRanges(Pred, S1, S2, Pred, FoundLHS, FoundRHS) ||
           isImpliedViaOperations(Pred, S1, S2, FoundLHS, FoundRHS, Depth);
  };
 
  if (RPhi && RPhi->getParent() == LBB) {
    // Case one: RHS is also a SCEVUnknown Phi from the same basic block.
    // If we compare two Phis from the same block, and for each entry block
    // the predicate is true for incoming values from this block, then the
    // predicate is also true for the Phis.
    for (const BasicBlock *IncBB : predecessors(LBB)) {
      const SCEV *L = getSCEV(LPhi->getIncomingValueForBlock(IncBB));
      const SCEV *R = getSCEV(RPhi->getIncomingValueForBlock(IncBB));
      if (!ProvedEasily(L, R))
        return false;
    }
  } else if (RAR && RAR->getLoop()->getHeader() == LBB) {
    // Case two: RHS is also a Phi from the same basic block, and it is an
    // AddRec. It means that there is a loop which has both AddRec and Unknown
    // PHIs, for it we can compare incoming values of AddRec from above the loop
    // and latch with their respective incoming values of LPhi.
    // TODO: Generalize to handle loops with many inputs in a header.
    if (LPhi->getNumIncomingValues() != 2) return false;
 
    auto *RLoop = RAR->getLoop();
    auto *Predecessor = RLoop->getLoopPredecessor();
    assert(Predecessor && "Loop with AddRec with no predecessor?");
    const SCEV *L1 = getSCEV(LPhi->getIncomingValueForBlock(Predecessor));
    if (!ProvedEasily(L1, RAR->getStart()))
      return false;
    auto *Latch = RLoop->getLoopLatch();
    assert(Latch && "Loop with AddRec with no latch?");
    const SCEV *L2 = getSCEV(LPhi->getIncomingValueForBlock(Latch));
    if (!ProvedEasily(L2, RAR->getPostIncExpr(*this)))
      return false;
  } else {
    // In all other cases go over inputs of LHS and compare each of them to RHS,
    // the predicate is true for (LHS, RHS) if it is true for all such pairs.
    // At this point RHS is either a non-Phi, or it is a Phi from some block
    // different from LBB.
    for (const BasicBlock *IncBB : predecessors(LBB)) {
      // Check that RHS is available in this block.
      if (!dominates(RHS, IncBB))
        return false;
      const SCEV *L = getSCEV(LPhi->getIncomingValueForBlock(IncBB));
      // Make sure L does not refer to a value from a potentially previous
      // iteration of a loop.
      if (!properlyDominates(L, LBB))
        return false;
      // Addrecs are considered to properly dominate their loop, so are missed
      // by the previous check. Discard any values that have computable
      // evolution in this loop.
      if (auto *Loop = LI.getLoopFor(LBB))
        if (hasComputableLoopEvolution(L, Loop))
          return false;
      if (!ProvedEasily(L, RHS))
        return false;
    }
  }
  return true;
}
 
bool ScalarEvolution::isImpliedCondOperandsViaShift(CmpPredicate Pred,
                                                    const SCEV *LHS,
                                                    const SCEV *RHS,
                                                    const SCEV *FoundLHS,
                                                    const SCEV *FoundRHS) {
  // We want to imply LHS < RHS from LHS < (RHS >> shiftvalue).  First, make
  // sure that we are dealing with same LHS.
  if (RHS == FoundRHS) {
    std::swap(LHS, RHS);
    std::swap(FoundLHS, FoundRHS);
    Pred = ICmpInst::getSwappedCmpPredicate(Pred);
  }
  if (LHS != FoundLHS)
    return false;
 
  auto *SUFoundRHS = dyn_cast<SCEVUnknown>(FoundRHS);
  if (!SUFoundRHS)
    return false;
 
  Value *Shiftee, *ShiftValue;
 
  using namespace PatternMatch;
  if (match(SUFoundRHS->getValue(),
            m_LShr(m_Value(Shiftee), m_Value(ShiftValue)))) {
    auto *ShifteeS = getSCEV(Shiftee);
    // Prove one of the following:
    // LHS <u (shiftee >> shiftvalue) && shiftee <=u RHS ---> LHS <u RHS
    // LHS <=u (shiftee >> shiftvalue) && shiftee <=u RHS ---> LHS <=u RHS
    // LHS <s (shiftee >> shiftvalue) && shiftee <=s RHS && shiftee >=s 0
    //   ---> LHS <s RHS
    // LHS <=s (shiftee >> shiftvalue) && shiftee <=s RHS && shiftee >=s 0
    //   ---> LHS <=s RHS
    if (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_ULE)
      return isKnownPredicate(ICmpInst::ICMP_ULE, ShifteeS, RHS);
    if (Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_SLE)
      if (isKnownNonNegative(ShifteeS))
        return isKnownPredicate(ICmpInst::ICMP_SLE, ShifteeS, RHS);
  }
 
  return false;
}
 
bool ScalarEvolution::isImpliedCondOperandsViaMatchingDiff(
    CmpPredicate Pred, const SCEV *LHS, const SCEV *RHS, const SCEV *FoundLHS,
    const SCEV *FoundRHS) {
  // Only valid for equality predicates: (A == B) implies (C == D) when
  // the SCEV difference A - B equals C - D (they check the same
  // underlying relationship at every iteration).
  if (!ICmpInst::isEquality(Pred))
    return false;
 
  // Restrict to cases involving loop recurrences - that's where this
  // pattern arises (correlated IV comparisons). This avoids calling
  // getMinusSCEV on arbitrary non-loop expressions.
  if ((!isa<SCEVAddRecExpr>(LHS) && !isa<SCEVAddRecExpr>(RHS)) ||
      (!isa<SCEVAddRecExpr>(FoundLHS) && !isa<SCEVAddRecExpr>(FoundRHS)))
    return false;
 
  // AddRecs from different loops can never produce matching differences.
  const SCEVAddRecExpr *QueryAddRec = dyn_cast<SCEVAddRecExpr>(LHS);
  if (!QueryAddRec)
    QueryAddRec = cast<SCEVAddRecExpr>(RHS);
  const SCEVAddRecExpr *FoundAddRec = dyn_cast<SCEVAddRecExpr>(FoundLHS);
  if (!FoundAddRec)
    FoundAddRec = cast<SCEVAddRecExpr>(FoundRHS);
  if (QueryAddRec->getLoop() != FoundAddRec->getLoop())
    return false;
 
  // If the strides differ, the differences can never match.
  if (QueryAddRec->getStepRecurrence(*this) !=
      FoundAddRec->getStepRecurrence(*this))
    return false;
 
  // Compute differences. For pointer-typed operands sharing the same base,
  // getMinusSCEV strips the common base and returns an integer SCEV.
  // For example, {base,+,8} - (base+8*n) = {-8n,+,8}
  const SCEV *FoundDiff = getMinusSCEV(FoundLHS, FoundRHS);
  if (isa<SCEVCouldNotCompute>(FoundDiff))
    return false;
 
  const SCEV *Diff = getMinusSCEV(LHS, RHS);
  if (isa<SCEVCouldNotCompute>(Diff))
    return false;
 
  return Diff == FoundDiff;
}
 
bool ScalarEvolution::isImpliedCondOperands(CmpPredicate Pred, const SCEV *LHS,
                                            const SCEV *RHS,
                                            const SCEV *FoundLHS,
                                            const SCEV *FoundRHS,
                                            const Instruction *CtxI) {
  return isImpliedCondOperandsViaRanges(Pred, LHS, RHS, Pred, FoundLHS,
                                        FoundRHS) ||
         isImpliedCondOperandsViaNoOverflow(Pred, LHS, RHS, FoundLHS,
                                            FoundRHS) ||
         isImpliedCondOperandsViaShift(Pred, LHS, RHS, FoundLHS, FoundRHS) ||
         isImpliedCondOperandsViaAddRecStart(Pred, LHS, RHS, FoundLHS, FoundRHS,
                                             CtxI) ||
         isImpliedCondOperandsViaMatchingDiff(Pred, LHS, RHS, FoundLHS,
                                              FoundRHS) ||
         isImpliedCondOperandsHelper(Pred, LHS, RHS, FoundLHS, FoundRHS);
}
 
/// Is MaybeMinMaxExpr an (U|S)(Min|Max) of Candidate and some other values?
template <typename MinMaxExprType>
static bool IsMinMaxConsistingOf(const SCEV *MaybeMinMaxExpr,
                                 const SCEV *Candidate) {
  const MinMaxExprType *MinMaxExpr = dyn_cast<MinMaxExprType>(MaybeMinMaxExpr);
  if (!MinMaxExpr)
    return false;
 
  return is_contained(MinMaxExpr->operands(), Candidate);
}
 
static bool IsKnownPredicateViaAddRecStart(ScalarEvolution &SE,
                                           CmpPredicate Pred, const SCEV *LHS,
                                           const SCEV *RHS) {
  // If both sides are affine addrecs for the same loop, with equal
  // steps, and we know the recurrences don't wrap, then we only
  // need to check the predicate on the starting values.
 
  if (!ICmpInst::isRelational(Pred))
    return false;
 
  const SCEV *LStart, *RStart, *Step;
  const Loop *L;
  if (!match(LHS,
             m_scev_AffineAddRec(m_SCEV(LStart), m_SCEV(Step), m_Loop(L))) ||
      !match(RHS, m_scev_AffineAddRec(m_SCEV(RStart), m_scev_Specific(Step),
                                      m_SpecificLoop(L))))
    return false;
  const SCEVAddRecExpr *LAR = cast<SCEVAddRecExpr>(LHS);
  const SCEVAddRecExpr *RAR = cast<SCEVAddRecExpr>(RHS);
  SCEVFlags NW = ICmpInst::isSigned(Pred) ? SCEV::FlagNSW : SCEV::FlagNUW;
  if (!LAR->getNoWrapFlags(NW) || !RAR->getNoWrapFlags(NW))
    return false;
 
  return SE.isKnownPredicate(Pred, LStart, RStart);
}
 
/// Is LHS `Pred` RHS true because one of them is an AddRec that is known not to
/// go below its own start value?
static bool IsKnownPredicateViaAddRecMonotonicity(ScalarEvolution &SE,
                                                  CmpPredicate Pred,
                                                  const SCEV *LHS,
                                                  const SCEV *RHS) {
  // Normalize to (AddRec Pred Start).
  if (!isa<SCEVAddRecExpr>(LHS) && isa<SCEVAddRecExpr>(RHS)) {
    Pred = ICmpInst::getSwappedCmpPredicate(Pred);
    std::swap(LHS, RHS);
  }
 
  // The recurrence is equal to Start in the first iteration, so only the
  // non-strict predicate holds.
  if (Pred != ICmpInst::ICMP_UGE && Pred != ICmpInst::ICMP_SGE)
    return false;
 
  const auto *AR = dyn_cast<SCEVAddRecExpr>(LHS);
  if (!AR || AR->getStart() != RHS)
    return false;
 
  return SE.getMonotonicPredicateType(AR, Pred) ==
         ScalarEvolution::MonotonicallyIncreasing;
}
 
/// Is LHS `Pred` RHS true on the virtue of LHS or RHS being a Min or Max
/// expression?
static bool IsKnownPredicateViaMinOrMax(ScalarEvolution &SE, CmpPredicate Pred,
                                        const SCEV *LHS, const SCEV *RHS) {
  switch (Pred) {
  default:
    return false;
 
  case ICmpInst::ICMP_SGE:
    std::swap(LHS, RHS);
    [[fallthrough]];
  case ICmpInst::ICMP_SLE:
    return
        // min(A, ...) <= A
        IsMinMaxConsistingOf<SCEVSMinExpr>(LHS, RHS) ||
        // A <= max(A, ...)
        IsMinMaxConsistingOf<SCEVSMaxExpr>(RHS, LHS);
 
  case ICmpInst::ICMP_UGE:
    std::swap(LHS, RHS);
    [[fallthrough]];
  case ICmpInst::ICMP_ULE:
    return
        // min(A, ...) <= A
        // FIXME: what about umin_seq?
        IsMinMaxConsistingOf<SCEVUMinExpr>(LHS, RHS) ||
        // A <= max(A, ...)
        IsMinMaxConsistingOf<SCEVUMaxExpr>(RHS, LHS);
 
  case ICmpInst::ICMP_UGT:
    std::swap(LHS, RHS);
    [[fallthrough]];
  case ICmpInst::ICMP_ULT:
    // umin(Ops) u<= each Op, so proving Op u< RHS for any Op proves
    // umin(Ops) u< RHS.
    //
    // Use computeConstantDifference instead of the more powerful
    // isKnownPredicate to keep this check cheap: isKnownPredicateViaMinOrMax
    // is called from isKnownViaNonRecursiveReasoning, so recursing into
    // the full predicate prover would be expensive.
    if (const auto *Min = dyn_cast<SCEVUMinExpr>(LHS)) {
      for (SCEVUse Op : Min->operands()) {
        std::optional<APInt> Diff = SE.computeConstantDifference(RHS, Op);
        // When Op and RHS share a common base differing by a
        // constant offset D (RHS - Op = D), Op u< RHS holds iff D != 0 and
        // RHS >= D (unsigned), i.e. the subtraction doesn't underflow.
        if (Diff && !Diff->isZero() && SE.getUnsignedRangeMin(RHS).uge(*Diff))
          return true;
      }
    }
    return false;
  }
 
  llvm_unreachable("covered switch fell through?!");
}
 
bool ScalarEvolution::isImpliedViaOperations(CmpPredicate Pred, const SCEV *LHS,
                                             const SCEV *RHS,
                                             const SCEV *FoundLHS,
                                             const SCEV *FoundRHS,
                                             unsigned Depth) {
  assert(getTypeSizeInBits(LHS->getType()) ==
             getTypeSizeInBits(RHS->getType()) &&
         "LHS and RHS have different sizes?");
  assert(getTypeSizeInBits(FoundLHS->getType()) ==
             getTypeSizeInBits(FoundRHS->getType()) &&
         "FoundLHS and FoundRHS have different sizes?");
  // We want to avoid hurting the compile time with analysis of too big trees.
  if (Depth > MaxSCEVOperationsImplicationDepth)
    return false;
 
  // We only want to work with GT comparison so far.
  if (ICmpInst::isLT(Pred)) {
    Pred = ICmpInst::getSwappedCmpPredicate(Pred);
    std::swap(LHS, RHS);
    std::swap(FoundLHS, FoundRHS);
  }
 
  CmpInst::Predicate P = Pred.getPreferredSignedPredicate();
 
  // For unsigned, try to reduce it to corresponding signed comparison.
  if (P == ICmpInst::ICMP_UGT)
    // We can replace unsigned predicate with its signed counterpart if all
    // involved values are non-negative.
    // TODO: We could have better support for unsigned.
    if (isKnownNonNegative(FoundLHS) && isKnownNonNegative(FoundRHS)) {
      // Knowing that both FoundLHS and FoundRHS are non-negative, and knowing
      // FoundLHS >u FoundRHS, we also know that FoundLHS >s FoundRHS. Let us
      // use this fact to prove that LHS and RHS are non-negative.
      const SCEV *MinusOne = getMinusOne(LHS->getType());
      if (isImpliedCondOperands(ICmpInst::ICMP_SGT, LHS, MinusOne, FoundLHS,
                                FoundRHS) &&
          isImpliedCondOperands(ICmpInst::ICMP_SGT, RHS, MinusOne, FoundLHS,
                                FoundRHS))
        P = ICmpInst::ICMP_SGT;
    }
 
  if (P != ICmpInst::ICMP_SGT)
    return false;
 
  auto GetOpFromSExt = [&](const SCEV *S) -> const SCEV * {
    if (auto *Ext = dyn_cast<SCEVSignExtendExpr>(S))
      return Ext->getOperand();
    // TODO: If S is a SCEVConstant then you can cheaply "strip" the sext off
    // the constant in some cases.
    return S;
  };
 
  // Acquire values from extensions.
  auto *OrigLHS = LHS;
  auto *OrigFoundLHS = FoundLHS;
  LHS = GetOpFromSExt(LHS);
  FoundLHS = GetOpFromSExt(FoundLHS);
 
  // Is the SGT predicate can be proved trivially or using the found context.
  auto IsSGTViaContext = [&](const SCEV *S1, const SCEV *S2) {
    return isKnownViaNonRecursiveReasoning(ICmpInst::ICMP_SGT, S1, S2) ||
           isImpliedViaOperations(ICmpInst::ICMP_SGT, S1, S2, OrigFoundLHS,
                                  FoundRHS, Depth + 1);
  };
 
  if (auto *LHSAddExpr = dyn_cast<SCEVAddExpr>(LHS)) {
    // We want to avoid creation of any new non-constant SCEV. Since we are
    // going to compare the operands to RHS, we should be certain that we don't
    // need any size extensions for this. So let's decline all cases when the
    // sizes of types of LHS and RHS do not match.
    // TODO: Maybe try to get RHS from sext to catch more cases?
    if (getTypeSizeInBits(LHS->getType()) != getTypeSizeInBits(RHS->getType()))
      return false;
 
    // Should not overflow.
    if (!LHSAddExpr->hasNoSignedWrap())
      return false;
 
    SCEVUse LL = LHSAddExpr->getOperand(0);
    SCEVUse LR = LHSAddExpr->getOperand(1);
    auto *MinusOne = getMinusOne(RHS->getType());
 
    // Checks that S1 >= 0 && S2 > RHS, trivially or using the found context.
    auto IsSumGreaterThanRHS = [&](const SCEV *S1, const SCEV *S2) {
      return IsSGTViaContext(S1, MinusOne) && IsSGTViaContext(S2, RHS);
    };
    // Try to prove the following rule:
    // (LHS = LL + LR) && (LL >= 0) && (LR > RHS) => (LHS > RHS).
    // (LHS = LL + LR) && (LR >= 0) && (LL > RHS) => (LHS > RHS).
    if (IsSumGreaterThanRHS(LL, LR) || IsSumGreaterThanRHS(LR, LL))
      return true;
  } else if (auto *LHSUnknownExpr = dyn_cast<SCEVUnknown>(LHS)) {
    Value *LL, *LR;
    // FIXME: Once we have SDiv implemented, we can get rid of this matching.
 
    using namespace llvm::PatternMatch;
 
    if (match(LHSUnknownExpr->getValue(), m_SDiv(m_Value(LL), m_Value(LR)))) {
      // Rules for division.
      // We are going to perform some comparisons with Denominator and its
      // derivative expressions. In general case, creating a SCEV for it may
      // lead to a complex analysis of the entire graph, and in particular it
      // can request trip count recalculation for the same loop. This would
      // cache as SCEVCouldNotCompute to avoid the infinite recursion. To avoid
      // this, we only want to create SCEVs that are constants in this section.
      // So we bail if Denominator is not a constant.
      if (!isa<ConstantInt>(LR))
        return false;
 
      auto *Denominator = cast<SCEVConstant>(getSCEV(LR));
 
      // We want to make sure that LHS = FoundLHS / Denominator. If it is so,
      // then a SCEV for the numerator already exists and matches with FoundLHS.
      auto *Numerator = getExistingSCEV(LL);
      if (!Numerator || Numerator->getType() != FoundLHS->getType())
        return false;
 
      // Make sure that the numerator matches with FoundLHS and the denominator
      // is positive.
      if (!HasSameValue(Numerator, FoundLHS) || !isKnownPositive(Denominator))
        return false;
 
      auto *DTy = Denominator->getType();
      auto *FRHSTy = FoundRHS->getType();
      if (DTy->isPointerTy() != FRHSTy->isPointerTy())
        // One of types is a pointer and another one is not. We cannot extend
        // them properly to a wider type, so let us just reject this case.
        // TODO: Usage of getEffectiveSCEVType for DTy, FRHSTy etc should help
        // to avoid this check.
        return false;
 
      // Given that:
      // FoundLHS > FoundRHS, LHS = FoundLHS / Denominator, Denominator > 0.
      auto *WTy = getWiderType(DTy, FRHSTy);
      auto *DenominatorExt = getNoopOrSignExtend(Denominator, WTy);
      auto *FoundRHSExt = getNoopOrSignExtend(FoundRHS, WTy);
 
      // Try to prove the following rule:
      // (FoundRHS > Denominator - 2) && (RHS <= 0) => (LHS > RHS).
      // For example, given that FoundLHS > 2. It means that FoundLHS is at
      // least 3. If we divide it by Denominator < 4, we will have at least 1.
      auto *DenomMinusTwo = getMinusSCEV(DenominatorExt, getConstant(WTy, 2));
      if (isKnownNonPositive(RHS) &&
          IsSGTViaContext(FoundRHSExt, DenomMinusTwo))
        return true;
 
      // Try to prove the following rule:
      // (FoundRHS > -1 - Denominator) && (RHS < 0) => (LHS > RHS).
      // For example, given that FoundLHS > -3. Then FoundLHS is at least -2.
      // If we divide it by Denominator > 2, then:
      // 1. If FoundLHS is negative, then the result is 0.
      // 2. If FoundLHS is non-negative, then the result is non-negative.
      // Anyways, the result is non-negative.
      auto *MinusOne = getMinusOne(WTy);
      auto *NegDenomMinusOne = getMinusSCEV(MinusOne, DenominatorExt);
      if (isKnownNegative(RHS) &&
          IsSGTViaContext(FoundRHSExt, NegDenomMinusOne))
        return true;
    }
  }
 
  // If our expression contained SCEVUnknown Phis, and we split it down and now
  // need to prove something for them, try to prove the predicate for every
  // possible incoming values of those Phis.
  if (isImpliedViaMerge(Pred, OrigLHS, RHS, OrigFoundLHS, FoundRHS, Depth + 1))
    return true;
 
  return false;
}
 
static bool isKnownPredicateExtendIdiom(CmpPredicate Pred, const SCEV *LHS,
                                        const SCEV *RHS) {
  // zext x u<= sext x, sext x s<= zext x
  const SCEV *Op;
  switch (Pred) {
  case ICmpInst::ICMP_SGE:
    std::swap(LHS, RHS);
    [[fallthrough]];
  case ICmpInst::ICMP_SLE: {
    // If operand >=s 0 then ZExt == SExt. If operand <s 0 then SExt <s ZExt.
    return match(LHS, m_scev_SExt(m_SCEV(Op))) &&
           match(RHS, m_scev_ZExt(m_scev_Specific(Op)));
  }
  case ICmpInst::ICMP_UGE:
    std::swap(LHS, RHS);
    [[fallthrough]];
  case ICmpInst::ICMP_ULE: {
    // If operand >=u 0 then ZExt == SExt.  If operand <u 0 then ZExt <u SExt.
    return match(LHS, m_scev_ZExt(m_SCEV(Op))) &&
           match(RHS, m_scev_SExt(m_scev_Specific(Op)));
  }
  default:
    return false;
  };
  llvm_unreachable("unhandled case");
}
 
bool ScalarEvolution::isKnownViaNonRecursiveReasoning(CmpPredicate Pred,
                                                      SCEVUse LHS,
                                                      SCEVUse RHS) {
  return isKnownPredicateExtendIdiom(Pred, LHS, RHS) ||
         isKnownPredicateViaConstantRanges(Pred, LHS, RHS) ||
         IsKnownPredicateViaMinOrMax(*this, Pred, LHS, RHS) ||
         IsKnownPredicateViaAddRecStart(*this, Pred, LHS, RHS) ||
         IsKnownPredicateViaAddRecMonotonicity(*this, Pred, LHS, RHS) ||
         isKnownPredicateViaNoOverflow(Pred, LHS, RHS);
}
 
bool ScalarEvolution::isImpliedCondOperandsHelper(CmpPredicate Pred,
                                                  const SCEV *LHS,
                                                  const SCEV *RHS,
                                                  const SCEV *FoundLHS,
                                                  const SCEV *FoundRHS) {
  switch (Pred) {
  default:
    llvm_unreachable("Unexpected CmpPredicate value!");
  case ICmpInst::ICMP_EQ:
  case ICmpInst::ICMP_NE:
    if (HasSameValue(LHS, FoundLHS) && HasSameValue(RHS, FoundRHS))
      return true;
    break;
  case ICmpInst::ICMP_SLT:
  case ICmpInst::ICMP_SLE:
    if (isKnownViaNonRecursiveReasoning(ICmpInst::ICMP_SLE, LHS, FoundLHS) &&
        isKnownViaNonRecursiveReasoning(ICmpInst::ICMP_SGE, RHS, FoundRHS))
      return true;
    break;
  case ICmpInst::ICMP_SGT:
  case ICmpInst::ICMP_SGE:
    if (isKnownViaNonRecursiveReasoning(ICmpInst::ICMP_SGE, LHS, FoundLHS) &&
        isKnownViaNonRecursiveReasoning(ICmpInst::ICMP_SLE, RHS, FoundRHS))
      return true;
    break;
  case ICmpInst::ICMP_ULT:
  case ICmpInst::ICMP_ULE:
    if (isKnownViaNonRecursiveReasoning(ICmpInst::ICMP_ULE, LHS, FoundLHS) &&
        isKnownViaNonRecursiveReasoning(ICmpInst::ICMP_UGE, RHS, FoundRHS))
      return true;
    break;
  case ICmpInst::ICMP_UGT:
  case ICmpInst::ICMP_UGE:
    if (isKnownViaNonRecursiveReasoning(ICmpInst::ICMP_UGE, LHS, FoundLHS) &&
        isKnownViaNonRecursiveReasoning(ICmpInst::ICMP_ULE, RHS, FoundRHS))
      return true;
    break;
  }
 
  // Maybe it can be proved via operations?
  if (isImpliedViaOperations(Pred, LHS, RHS, FoundLHS, FoundRHS))
    return true;
 
  return false;
}
 
bool ScalarEvolution::isImpliedCondOperandsViaRanges(
    CmpPredicate Pred, const SCEV *LHS, const SCEV *RHS, CmpPredicate FoundPred,
    const SCEV *FoundLHS, const SCEV *FoundRHS) {
  if (!isa<SCEVConstant>(RHS) || !isa<SCEVConstant>(FoundRHS))
    // The restriction on `FoundRHS` be lifted easily -- it exists only to
    // reduce the compile time impact of this optimization.
    return false;
 
  std::optional<APInt> Addend = computeConstantDifference(LHS, FoundLHS);
  if (!Addend)
    return false;
 
  const APInt &ConstFoundRHS = cast<SCEVConstant>(FoundRHS)->getAPInt();
 
  // `FoundLHSRange` is the range we know `FoundLHS` to be in by virtue of the
  // antecedent "`FoundLHS` `FoundPred` `FoundRHS`".
  ConstantRange FoundLHSRange =
      ConstantRange::makeExactICmpRegion(FoundPred, ConstFoundRHS);
 
  // Since `LHS` is `FoundLHS` + `Addend`, we can compute a range for `LHS`:
  ConstantRange LHSRange = FoundLHSRange.add(ConstantRange(*Addend));
 
  // We can also compute the range of values for `LHS` that satisfy the
  // consequent, "`LHS` `Pred` `RHS`":
  const APInt &ConstRHS = cast<SCEVConstant>(RHS)->getAPInt();
  // The antecedent implies the consequent if every value of `LHS` that
  // satisfies the antecedent also satisfies the consequent.
  return LHSRange.icmp(Pred, ConstRHS);
}
 
bool ScalarEvolution::canIVOverflowOnLT(const SCEV *RHS, const SCEV *Stride,
                                        bool IsSigned, bool Invert) {
  assert(isKnownPositive(Stride) && "Positive stride expected!");
 
  unsigned BitWidth = getTypeSizeInBits(RHS->getType());
  const SCEV *One = getOne(Stride->getType());
 
  if (IsSigned) {
    APInt MaxRHS = getRangeMax(RHS, /*IsSigned=*/true, Invert);
    APInt MaxValue = APInt::getSignedMaxValue(BitWidth);
    APInt MaxStrideMinusOne = getSignedRangeMax(getMinusSCEV(Stride, One));
 
    // SMaxRHS + SMaxStrideMinusOne > SMaxValue => overflow!
    return (std::move(MaxValue) - MaxStrideMinusOne).slt(MaxRHS);
  }
 
  APInt MaxRHS = getRangeMax(RHS, /*IsSigned=*/false, Invert);
  APInt MaxValue = APInt::getMaxValue(BitWidth);
  APInt MaxStrideMinusOne = getUnsignedRangeMax(getMinusSCEV(Stride, One));
 
  // UMaxRHS + UMaxStrideMinusOne > UMaxValue => overflow!
  return (std::move(MaxValue) - MaxStrideMinusOne).ult(MaxRHS);
}
 
const SCEV *ScalarEvolution::getUDivCeilSCEV(const SCEV *N, const SCEV *D) {
  // umin(N, 1) + floor((N - umin(N, 1)) / D)
  // This is equivalent to "1 + floor((N - 1) / D)" for N != 0. The umin
  // expression fixes the case of N=0.
  const SCEV *MinNOne = getUMinExpr(N, getOne(N->getType()));
  const SCEV *NMinusOne = getMinusSCEV(N, MinNOne);
  return getAddExpr(MinNOne, getUDivExpr(NMinusOne, D));
}
 
const SCEV *
ScalarEvolution::computeMaxBECountForLT(const SCEV *Start, const SCEV *Stride,
                                        const SCEV *End, unsigned BitWidth,
                                        bool IsSigned, bool Invert) {
  // The logic in this function assumes we can represent a positive stride.
  // If we can't, the backedge-taken count must be zero.
  if (IsSigned && BitWidth == 1)
    return getZero(Stride->getType());
 
  // This code below only been closely audited for negative strides in the
  // unsigned comparison case, it may be correct for signed comparison, but
  // that needs to be established.
  if (IsSigned && isKnownNegative(Stride))
    return getCouldNotCompute();
 
  // Calculate the maximum backedge count based on the range of values
  // permitted by Start, End, and Stride. If Invert is true, both Start and End
  // need inverting. Stride was already negated by the caller.
  APInt MinStart = getRangeMin(Start, IsSigned, Invert);
 
  APInt MinStride =
      IsSigned ? getSignedRangeMin(Stride) : getUnsignedRangeMin(Stride);
 
  // We assume either the stride is positive, or the backedge-taken count
  // is zero. So force StrideForMaxBECount to be at least one.
  APInt One(BitWidth, 1);
  APInt StrideForMaxBECount = IsSigned ? APIntOps::smax(One, MinStride)
                                       : APIntOps::umax(One, MinStride);
 
  APInt MaxValue = IsSigned ? APInt::getSignedMaxValue(BitWidth)
                            : APInt::getMaxValue(BitWidth);
  APInt Limit = MaxValue - (StrideForMaxBECount - 1);
 
  // Although End can be a MAX expression we estimate MaxEnd considering only
  // the case End = RHS of the loop termination condition. This is safe because
  // in the other case (End - Start) is zero, leading to a zero maximum backedge
  // taken count.
  APInt MaxEnd = getRangeMax(End, IsSigned, Invert);
  MaxEnd =
      IsSigned ? APIntOps::smin(MaxEnd, Limit) : APIntOps::umin(MaxEnd, Limit);
 
  // MaxBECount = ceil((max(MaxEnd, MinStart) - MinStart) / Stride)
  MaxEnd = IsSigned ? APIntOps::smax(MaxEnd, MinStart)
                    : APIntOps::umax(MaxEnd, MinStart);
 
  APInt Delta = MaxEnd - MinStart;
 
  // Try to refine Delta in case End - Start (or Start - End if Invert) gives a
  // tighter bound after folding.
  const SCEV *DeltaExpr =
      Invert ? getMinusSCEV(Start, End) : getMinusSCEV(End, Start);
  Delta = APIntOps::umin(Delta, getUnsignedRangeMax(DeltaExpr));
 
  return getUDivCeilSCEV(getConstant(Delta), getConstant(StrideForMaxBECount));
}
 
ScalarEvolution::ExitLimit
ScalarEvolution::howManyLessThans(const SCEV *LHS, const SCEV *RHS,
                                  const Loop *L, bool IsSigned, bool Invert,
                                  bool ControlsOnlyExit, bool AllowPredicates) {
  SmallVector<const SCEVPredicate *> Predicates;
 
  LoopGuards Guards = LoopGuards::collectOnDemand(L, *this);
 
  // FIXME: Extend the non-invariant RHS analysis to greater-than comparisons.
  if (Invert && !isLoopInvariant(RHS, L))
    return getCouldNotCompute();
 
  const SCEVAddRecExpr *IV = dyn_cast<SCEVAddRecExpr>(LHS);
  bool PredicatedIV = false;
  // FIXME: Generalize the NUW inference below to decreasing IVs.
  if (!IV && !Invert) {
    if (auto *ZExt = dyn_cast<SCEVZeroExtendExpr>(LHS)) {
      const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(ZExt->getOperand());
      if (AR && AR->getLoop() == L && AR->isAffine()) {
        auto canProveNUW = [&]() {
          // We can use the comparison to infer no-wrap flags only if it fully
          // controls the loop exit.
          if (!ControlsOnlyExit)
            return false;
 
          if (!isLoopInvariant(RHS, L))
            return false;
 
          if (!isKnownNonZero(AR->getStepRecurrence(*this)))
            // We need the sequence defined by AR to strictly increase in the
            // unsigned integer domain for the logic below to hold.
            return false;
 
          const unsigned InnerBitWidth = getTypeSizeInBits(AR->getType());
          const unsigned OuterBitWidth = getTypeSizeInBits(RHS->getType());
          // If RHS <=u Limit, then there must exist a value V in the sequence
          // defined by AR (e.g. {Start,+,Step}) such that V >u RHS, and
          // V <=u UINT_MAX.  Thus, we must exit the loop before unsigned
          // overflow occurs.  This limit also implies that a signed comparison
          // (in the wide bitwidth) is equivalent to an unsigned comparison as
          // the high bits on both sides must be zero.
          APInt StrideMax = getUnsignedRangeMax(AR->getStepRecurrence(*this));
          APInt Limit = APInt::getMaxValue(InnerBitWidth) - (StrideMax - 1);
          Limit = Limit.zext(OuterBitWidth);
          return getUnsignedRangeMax(applyLoopGuards(RHS, Guards)).ule(Limit);
        };
        auto Flags = AR->getNoWrapFlags();
        if (!hasFlags(Flags, SCEV::FlagNUW) && canProveNUW())
          Flags = setFlags(Flags, SCEV::FlagNUW);
 
        setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR), Flags);
        if (AR->hasNoUnsignedWrap()) {
          // Emulate what getZeroExtendExpr would have done during construction
          // if we'd been able to infer the fact just above at that time.
          const SCEV *Step = AR->getStepRecurrence(*this);
          Type *Ty = ZExt->getType();
          const SCEV *S = getAddRecExpr(
              getExtendAddRecStart<SCEVZeroExtendExpr>(AR, Ty, this, 0),
              getZeroExtendExpr(Step, Ty, 0), L, AR->getNoWrapFlags());
          IV = dyn_cast<SCEVAddRecExpr>(S);
        }
      }
    }
  }
 
  if (!IV && AllowPredicates) {
    // Try to make this an AddRec using runtime tests, in the first X
    // iterations of this loop, where X is the SCEV expression found by the
    // algorithm below.
    IV = convertSCEVToAddRecWithPredicates(LHS, L, Predicates);
    PredicatedIV = true;
  }
 
  // Avoid weird loops
  if (!IV || IV->getLoop() != L || !IV->isAffine())
    return getCouldNotCompute();
 
  // A precondition of this method is that the condition being analyzed
  // reaches an exiting branch which dominates the latch.  Given that, we can
  // assume that an increment which violates the nowrap specification and
  // produces poison must cause undefined behavior when the resulting poison
  // value is branched upon and thus we can conclude that the backedge is
  // taken no more often than would be required to produce that poison value.
  // Note that a well defined loop can exit on the iteration which violates
  // the nowrap specification if there is another exit (either explicit or
  // implicit/exceptional) which causes the loop to execute before the
  // exiting instruction we're analyzing would trigger UB.
  auto WrapType = IsSigned ? SCEV::FlagNSW : SCEV::FlagNUW;
  bool NoWrap = ControlsOnlyExit && any(IV->getNoWrapFlags(WrapType));
  // Reverse the ordering for greater-than comparisons.
  ICmpInst::Predicate Cond = IsSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT;
  if (Invert)
    Cond = ICmpInst::getSwappedPredicate(Cond);
 
  // The step of ~IV is the negated step of IV.
  const SCEV *Stride = IV->getStepRecurrence(*this);
  if (Invert)
    Stride = getNegativeSCEV(Stride);
  const SCEV *GuardedStride = Stride;
 
  // Whether the IV may reach the maximum (or minimum if inverted) value
  // before the exit is taken.
  bool IVMayOverflow = true;
 
  bool PositiveStride = isKnownPositive(Stride);
  // A dominating guard may prove the stride positive.
  if (!PositiveStride) {
    const SCEV *LoopGuardedStride = applyLoopGuards(Stride, Guards);
    if (isKnownPositive(LoopGuardedStride)) {
      GuardedStride = LoopGuardedStride;
      PositiveStride = true;
      // Encode the context-sensitive stride > 0 fact into the expression
      Stride = getUMaxExpr(Stride, getOne(Stride->getType()));
    }
  }
 
  // Avoid negative or zero stride values.
  if (!PositiveStride) {
    // FIXME: Generalize the unknown-stride analysis to decreasing IVs.
    if (Invert)
      return getCouldNotCompute();
 
    // We can compute the correct backedge taken count for loops with unknown
    // strides if we can prove that the loop is not an infinite loop with side
    // effects. Here's the loop structure we are trying to handle -
    //
    // i = start
    // do {
    //   A[i] = i;
    //   i += s;
    // } while (i < end);
    //
    // The backedge taken count for such loops is evaluated as -
    // (max(end, start + stride) - start - 1) /u stride
    //
    // The additional preconditions that we need to check to prove correctness
    // of the above formula is as follows -
    //
    // a) IV is either nuw or nsw depending upon signedness (indicated by the
    //    NoWrap flag).
    // b) the loop is guaranteed to be finite (e.g. is mustprogress and has
    // b) the loop is guaranteed to be finite (e.g. is mustprogress and has
    //    no side effects within the loop) or a predicate is added to ensure
    //    stride is positive.
    // c) loop has a single static exit (with no abnormal exits)
    //
    // Precondition a) implies that if the stride is negative, this is a single
    // trip loop. The backedge taken count formula reduces to zero in this case.
    //
    // Precondition b) and c) combine to imply that if rhs is invariant in L,
    // then a zero stride means the backedge can't be taken without executing
    // undefined behavior.
    //
    // The positive stride case is the same as isKnownPositive(Stride) returning
    // true (original behavior of the function).
    //
    if (PredicatedIV || !NoWrap || !loopHasNoAbnormalExits(L))
      return getCouldNotCompute();
 
    if (!loopIsFiniteByAssumption(L)) {
      // If the loop may be infinite, add a predicate ensuring Stride is
      // positive, to guarantee forward progress.
      if (!AllowPredicates || !isLoopInvariant(Stride, L))
        return getCouldNotCompute();
 
      const SCEV *Zero = getZero(Stride->getType());
      const SCEVPredicate *P =
          getComparePredicate(ICmpInst::ICMP_SGT, Stride, Zero);
      Predicates.push_back(P);
      // When the predicate holds (Stride > 0), umax(Stride, 1) == Stride,
      // so the result is unchanged. To prevent div by zero.
      Stride = getUMaxExpr(Stride, getOne(Stride->getType()));
    } else if (!isKnownNonZero(Stride)) {
      // If we have a step of zero, and RHS isn't invariant in L, we don't know
      // if it might eventually be greater than start and if so, on which
      // iteration.  We can't even produce a useful upper bound.
      if (!isLoopInvariant(RHS, L))
        return getCouldNotCompute();
 
      // We allow a potentially zero stride, but we need to divide by stride
      // below.  Since the loop can't be infinite and this check must control
      // the sole exit, we can infer the exit must be taken on the first
      // iteration (e.g. backedge count = 0) if the stride is zero.  Given that,
      // we know the numerator in the divides below must be zero, so we can
      // pick an arbitrary non-zero value for the denominator (e.g. stride)
      // and produce the right result.
      // FIXME: Handle the case where Stride is poison?
      auto wouldZeroStrideBeUB = [&]() {
        // Proof by contradiction.  Suppose the stride were zero.  If we can
        // prove that the backedge *is* taken on the first iteration, then since
        // we know this condition controls the sole exit, we must have an
        // infinite loop.  We can't have a (well defined) infinite loop per
        // check just above.
        // Note: The (Start - Stride) term is used to get the start' term from
        // (start' + stride,+,stride). Remember that we only care about the
        // result of this expression when stride == 0 at runtime.
        auto *StartIfZero = getMinusSCEV(IV->getStart(), Stride);
        return isLoopEntryGuardedByCond(L, Cond, StartIfZero, RHS);
      };
      if (!wouldZeroStrideBeUB()) {
        Stride = getUMaxExpr(Stride, getOne(Stride->getType()));
      }
    }
  } else {
    // Avoid proven overflow cases: this will ensure that the backedge taken
    // count will not generate any unsigned overflow.
    IVMayOverflow = canIVOverflowOnLT(RHS, GuardedStride, IsSigned, Invert) &&
                    canIVOverflowOnLT(applyLoopGuards(RHS, Guards),
                                      GuardedStride, IsSigned, Invert);
    if (IVMayOverflow && !NoWrap)
      return getCouldNotCompute();
  }
 
  // On all paths just preceeding, we established the following invariant:
  //   IV can be assumed not to overflow up to and including the exiting
  //   iteration.  We proved this in one of two ways:
  //   1) We can show overflow doesn't occur before the exiting iteration
  //      1a) canIVOverflowOnLT, and b) step of one
  //   2) We can show that if overflow occurs, the loop must execute UB
  //      before any possible exit.
  // Note that we have not yet proved RHS invariant (in general).
 
  const SCEV *Start = IV->getStart();
 
  // Preserve pointer-typed Start/RHS to pass to isLoopEntryGuardedByCond.
  // If we convert to integers, isLoopEntryGuardedByCond will miss some cases.
  // Use integer-typed versions for actual computation; we can't subtract
  // pointers in general.
  const SCEV *OrigStart = Start;
  const SCEV *OrigRHS = RHS;
  if (Start->getType()->isPointerTy()) {
    Start = getPtrToAddrExpr(Start);
    if (isa<SCEVCouldNotCompute>(Start))
      return Start;
  }
  if (RHS->getType()->isPointerTy()) {
    RHS = getPtrToAddrExpr(RHS);
    if (isa<SCEVCouldNotCompute>(RHS))
      return RHS;
  }
 
  const SCEV *End = nullptr, *BECount = getCouldNotCompute(),
             *BECountIfBackedgeTaken = getCouldNotCompute();
  if (!isLoopInvariant(RHS, L)) {
    assert(!Invert && "RHS must be loop-invariant for Invert");
    const auto *RHSAddRec = dyn_cast<SCEVAddRecExpr>(RHS);
    if (PositiveStride && RHSAddRec != nullptr && RHSAddRec->getLoop() == L &&
        any(RHSAddRec->getNoWrapFlags())) {
      // The structure of loop we are trying to calculate backedge count of:
      //
      //  left = left_start
      //  right = right_start
      //
      //  while(left < right){
      //    ... do something here ...
      //    left += s1; // stride of left is s1 (s1 > 0)
      //    right += s2; // stride of right is s2 (s2 < 0)
      //  }
      //
 
      const SCEV *RHSStart = RHSAddRec->getStart();
      const SCEV *RHSStride = RHSAddRec->getStepRecurrence(*this);
 
      // If Stride - RHSStride is positive and does not overflow, we can write
      // backedge count as ->
      //    ceil((End - Start) /u (Stride - RHSStride))
      //    Where, End = max(RHSStart, Start)
 
      // Check if RHSStride < 0 and Stride - RHSStride will not overflow.
      if (isKnownNegative(RHSStride) &&
          willNotOverflow(Instruction::Sub, /*Signed=*/true, Stride,
                          RHSStride)) {
 
        const SCEV *Denominator = getMinusSCEV(Stride, RHSStride);
        if (isKnownPositive(Denominator)) {
          End = IsSigned ? getSMaxExpr(RHSStart, Start)
                         : getUMaxExpr(RHSStart, Start);
 
          // We can do this because End >= Start, as End = max(RHSStart, Start)
          const SCEV *Delta = getMinusSCEV(End, Start);
 
          BECount = getUDivCeilSCEV(Delta, Denominator);
          BECountIfBackedgeTaken =
              getUDivCeilSCEV(getMinusSCEV(RHSStart, Start), Denominator);
        }
      }
    }
  } else {
    // Let End = max(RHS,Start).  We use the expression (End-Start)/Stride to
    // describe the backedge count: if the backedge is taken at least once then
    // End is RHS, and if not End is Start so we get a backedge count of zero.
    // Inverted, End is min(RHS, Start).
    //
    // AddingStrideMinusOneMayOverflow has the following preconditions:
    //
    // 1. Start <= End, signed if IsSigned (inverted: End <= Start)
    // 2. The index variable doesn't overflow.
    //
    // Therefore, we know N exists such that
    // (Start + Stride * N) >= End, and computing "(Start + Stride * N)"
    // doesn't overflow.
    //
    // Using this information, try to prove whether the addition in
    // "(End - Start) + (Stride - 1)" has unsigned overflow.
    //
    // If the IV cannot overflow, RHS is at least Stride - 1 below the maximum
    // value, so the distance End - Start is at most UMAX - (Stride - 1) and
    // the (Stride - 1) addition below cannot overflow.
    const SCEV *One = getOne(Stride->getType());
    bool AddingStrideMinusOneMayOverflow = IVMayOverflow && [&] {
      if (isKnownToBeAPowerOfTwo(Stride)) {
        // Suppose Stride is a power of two, and Start/End are unsigned
        // integers.  Let UMAX be the largest representable unsigned
        // integer.
        //
        // By the preconditions of this function, we know
        // "(Start + Stride * N) >= End", and this doesn't overflow.
        // As a formula:
        //
        //   End <= (Start + Stride * N) <= UMAX
        //
        // Subtracting Start from all the terms:
        //
        //   End - Start <= Stride * N <= UMAX - Start
        //
        // Since Start is unsigned, UMAX - Start <= UMAX.  Therefore:
        //
        //   End - Start <= Stride * N <= UMAX
        //
        // Stride * N is a multiple of Stride. Therefore,
        //
        //   End - Start <= Stride * N <= UMAX - (UMAX mod Stride)
        //
        // Since Stride is a power of two, UMAX + 1 is divisible by
        // Stride. Therefore, UMAX mod Stride == Stride - 1.  So we can
        // write:
        //
        //   End - Start <= Stride * N <= UMAX - Stride - 1
        //
        // Dropping the middle term:
        //
        //   End - Start <= UMAX - Stride - 1
        //
        // Adding Stride - 1 to both sides:
        //
        //   (End - Start) + (Stride - 1) <= UMAX
        //
        // In other words, the addition doesn't have unsigned overflow.
        //
        // A similar proof works if we treat Start/End as signed values.
        // Just rewrite steps before "End - Start <= Stride * N <= UMAX"
        // to use signed max instead of unsigned max. Note that we're
        // trying to prove a lack of unsigned overflow in either case.
        // Inverted: "Start - End <= Stride * N <= Start - MIN <= UMAX", same.
        return false;
      }
      if (!Invert && (Start == Stride || Start == getMinusSCEV(Stride, One))) {
        // If Start is equal to Stride, (End - Start) + (Stride - 1) == End
        // - 1. If !IsSigned, 0 <u Stride == Start <=u End; so 0 <u End - 1
        // <u End. If IsSigned, 0 <s Stride == Start <=s End; so 0 <s End -
        // 1 <s End.
        //
        // If Start is equal to Stride - 1, (End - Start) + Stride - 1 ==
        // End.
        //
        // Both need Start to be the smaller value, so neither applies inverted.
        return false;
      }
      return true;
    }();
 
    // If inverted, the analyzed values are complements: "~V - Offset" is "~(V +
    // Offset)" and "~To - ~From" is "From - To".
    auto StepBack = [&](const SCEV *V, const SCEV *Offset) -> const SCEV * {
      if (Invert)
        return getAddExpr(V, Offset);
      return getMinusSCEV(V, Offset);
    };
    auto Distance = [&](const SCEV *From, const SCEV *To) {
      return Invert ? getMinusSCEV(From, To) : getMinusSCEV(To, From);
    };
 
    const SCEV *OrigPrevStart = StepBack(OrigStart, Stride);
    assert(isAvailableAtLoopEntry(OrigPrevStart, L) && "Must be!");
    assert(isAvailableAtLoopEntry(OrigStart, L) && "Must be!");
    assert(isAvailableAtLoopEntry(OrigRHS, L) && "Must be!");
    // Can we prove Start - Stride < RHS, and either Start - Stride < Start or
    // (via !AddingStrideMinusOneMayOverflow) that (RHS - Start) + (Stride - 1)
    // does not overflow?
    if ((!AddingStrideMinusOneMayOverflow ||
         isLoopEntryGuardedByCond(L, Cond, OrigPrevStart, OrigStart)) &&
        isLoopEntryGuardedByCond(L, Cond, OrigPrevStart, OrigRHS)) {
      // In this case, we can use a refined formula for computing backedge
      // taken count.  The general formula remains:
      //   "End-Start /uceiling Stride"
      // We want to use the alternate formula:
      //   "((RHS - 1) - (Start - Stride)) /u Stride"
      // Let's do a quick case analysis to show these are equivalent under
      // our preconditions. When inverted, the proof uses complemented Start,
      // RHS and End; Stride remains positive.
      // * For RHS <= Start (End is Start), the backedge-taken count must be
      //   zero. Together with the precondition "Start - Stride < RHS", we have
      //   "Start - Stride < RHS <= Start". Subtracting Start - Stride from
      //   all sides we get "0 < RHS - (Start - Stride) <= Stride".
      //   Subtracting 1 we get "0 <= (RHS - 1) - (Start - Stride) < Stride".
      //   So dividing that by Stride gives zero.
      //
      // * For RHS > Start (End is RHS), the backedge count must be
      //   "RHS-Start /uceil Stride", so it is sufficient to show that the
      //   numerator "((RHS - 1) - (Start - Stride))" does not overflow.
      //
      //   If "Start - Stride < Start" holds, we have
      //   "RHS > Start > Start - Stride". As such
      //   "RHS - (Start - Stride) - 1" does not overflow, which is the
      //   reassociated numerator.
      //
      //   Otherwise !AddingStrideMinusOneMayOverflow guarantees that
      //   "(End - Start) + (Stride - 1)" does not overflow unsigned. Here
      //   "End" is "RHS", as "RHS > Start", so this is the reassociated
      //   numerator. Neither sub-term wraps unsigned: "RHS - Start"
      //   due to "RHS > Start", and "Stride - 1", as Stride is non-zero.
      const SCEV *Numerator =
          getMinusSCEV(Distance(StepBack(Start, Stride), RHS), One);
      BECount = getUDivExpr(Numerator, Stride);
    }
 
    if (isa<SCEVCouldNotCompute>(BECount)) {
      auto canProveRHSIsAtOrBeyondStart = [&]() {
        // Inverted, the claim is "Start >= RHS". Reverse the comparisons below
        // by swapping their operands rather than their predicates:
        // isLoopEntryGuardedByCond is sensitive to operand order and loses the
        // proof if the IV bound moves to the other side.
        auto SwapIfInverted = [&](const SCEV *A, const SCEV *B) {
          return Invert ? std::pair(B, A) : std::pair(A, B);
        };
 
        auto CondGE = IsSigned ? ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE;
        const SCEV *GuardedRHS = applyLoopGuards(OrigRHS, Guards);
        const SCEV *GuardedStart = applyLoopGuards(OrigStart, Guards);
        if (Invert)
          std::swap(GuardedRHS, GuardedStart);
 
        auto [GELHS, GERHS] = SwapIfInverted(OrigRHS, OrigStart);
        if (isLoopEntryGuardedByCond(L, CondGE, GELHS, GERHS) ||
            isKnownPredicate(CondGE, GuardedRHS, GuardedStart))
          return true;
 
        // (RHS > Start - 1) implies RHS >= Start.
        // * "RHS >= Start" is trivially equivalent to "RHS > Start - 1" if
        //   "Start - 1" doesn't overflow.
        // * For signed comparison, if Start - 1 does overflow, it's equal
        //   to INT_MAX, and "RHS >s INT_MAX" is trivially false.
        // * For unsigned comparison, if Start - 1 does overflow, it's equal
        //   to UINT_MAX, and "RHS >u UINT_MAX" is trivially false.
        //
        // FIXME: Should isLoopEntryGuardedByCond do this for us?
        auto CondGT = IsSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT;
        auto [GTLHS, GTRHS] = SwapIfInverted(OrigRHS, StepBack(OrigStart, One));
        return isLoopEntryGuardedByCond(L, CondGT, GTLHS, GTRHS);
      };
 
      // If we know that RHS >= Start in the context of loop, then we know
      // that max(RHS, Start) = RHS at this point.
      if (canProveRHSIsAtOrBeyondStart()) {
        End = RHS;
      } else {
        // If RHS < Start, the backedge will be taken zero times.  So in
        // general, we can write the backedge-taken count as:
        //
        //     RHS >= Start ? ceil(RHS - Start) / Stride : 0
        //
        // We convert it to the following to make it more convenient for SCEV:
        //
        //     ceil(max(RHS, Start) - Start) / Stride
        //
        // Inverted, this is ceil(Start - min(RHS, Start)) / Stride.
        if (Invert)
          End = IsSigned ? getSMinExpr(RHS, Start) : getUMinExpr(RHS, Start);
        else
          End = IsSigned ? getSMaxExpr(RHS, Start) : getUMaxExpr(RHS, Start);
 
        // See what would happen if we assume the backedge is taken. This is
        // used to compute MaxBECount.
        BECountIfBackedgeTaken = getUDivCeilSCEV(Distance(Start, RHS), Stride);
      }
 
      const SCEV *Delta = Distance(Start, End);
      if (!AddingStrideMinusOneMayOverflow) {
        // floor((D + (S - 1)) / S)
        // We prefer this formulation if it's legal because it's fewer
        // operations.
        BECount =
            getUDivExpr(getAddExpr(Delta, getMinusSCEV(Stride, One)), Stride);
      } else {
        BECount = getUDivCeilSCEV(Delta, Stride);
      }
    }
  }
 
  const SCEV *ConstantMaxBECount;
  bool MaxOrZero = false;
  if (isa<SCEVConstant>(BECount)) {
    ConstantMaxBECount = BECount;
  } else {
    ConstantMaxBECount = computeMaxBECountForLT(
        Start, Stride, RHS, getTypeSizeInBits(LHS->getType()), IsSigned,
        Invert);
    // If we know exactly how many times the backedge will be taken if it's
    // taken at least once, then the backedge count will either be that or
    // zero. If that count exceeds the range-based bound, the backedge can
    // never be taken.
    const APInt *IfTaken, *RangeMax;
    if (match(BECountIfBackedgeTaken, m_scev_APInt(IfTaken))) {
      if (match(ConstantMaxBECount, m_scev_APInt(RangeMax)) &&
          IfTaken->ugt(*RangeMax)) {
        ConstantMaxBECount = getZero(BECountIfBackedgeTaken->getType());
      } else {
        ConstantMaxBECount = BECountIfBackedgeTaken;
        MaxOrZero = true;
      }
    }
  }
 
  if (isa<SCEVCouldNotCompute>(ConstantMaxBECount) &&
      !isa<SCEVCouldNotCompute>(BECount))
    ConstantMaxBECount = getConstant(getUnsignedRangeMax(BECount));
 
  const SCEV *SymbolicMaxBECount =
      isa<SCEVCouldNotCompute>(BECount) ? ConstantMaxBECount : BECount;
  return ExitLimit(BECount, ConstantMaxBECount, SymbolicMaxBECount, MaxOrZero,
                   Predicates);
}
 
const SCEV *SCEVAddRecExpr::getNumIterationsInRange(const ConstantRange &Range,
                                                    ScalarEvolution &SE) const {
  if (Range.isFullSet())  // Infinite loop.
    return SE.getCouldNotCompute();
 
  // If the start is a non-zero constant, shift the range to simplify things.
  if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(getStart()))
    if (!SC->getValue()->isZero()) {
      SmallVector<SCEVUse, 4> Operands(operands());
      Operands[0] = SE.getZero(SC->getType());
      const SCEV *Shifted = SE.getAddRecExpr(Operands, getLoop(),
                                             getNoWrapFlags(FlagNW));
      if (const auto *ShiftedAddRec = dyn_cast<SCEVAddRecExpr>(Shifted))
        return ShiftedAddRec->getNumIterationsInRange(
            Range.subtract(SC->getAPInt()), SE);
      // This is strange and shouldn't happen.
      return SE.getCouldNotCompute();
    }
 
  // The only time we can solve this is when we have all constant indices.
  // Otherwise, we cannot determine the overflow conditions.
  if (!all_of(operands(), IsaPred<SCEVConstant>))
    return SE.getCouldNotCompute();
 
  // Okay at this point we know that all elements of the chrec are constants and
  // that the start element is zero.
 
  // First check to see if the range contains zero.  If not, the first
  // iteration exits.
  unsigned BitWidth = SE.getTypeSizeInBits(getType());
  if (!Range.contains(APInt(BitWidth, 0)))
    return SE.getZero(getType());
 
  if (isAffine()) {
    // If this is an affine expression then we have this situation:
    //   Solve {0,+,A} in Range  ===  Ax in Range
 
    // We know that zero is in the range.  If A is positive then we know that
    // the upper value of the range must be the first possible exit value.
    // If A is negative then the lower of the range is the last possible loop
    // value.  Also note that we already checked for a full range.
    APInt A = cast<SCEVConstant>(getOperand(1))->getAPInt();
    APInt End = A.sge(1) ? (Range.getUpper() - 1) : Range.getLower();
 
    // The exit value should be (End+A)/A.
    APInt ExitVal = (End + A).udiv(A);
    ConstantInt *ExitValue = ConstantInt::get(SE.getContext(), ExitVal);
 
    // Evaluate at the exit value.  If we really did fall out of the valid
    // range, then we computed our trip count, otherwise wrap around or other
    // things must have happened.
    ConstantInt *Val = EvaluateConstantChrecAtConstant(this, ExitValue, SE);
    if (Range.contains(Val->getValue()))
      return SE.getCouldNotCompute();  // Something strange happened
 
    // Ensure that the previous value is in the range.
    assert(Range.contains(
           EvaluateConstantChrecAtConstant(this,
           ConstantInt::get(SE.getContext(), ExitVal - 1), SE)->getValue()) &&
           "Linear scev computation is off in a bad way!");
    return SE.getConstant(ExitValue);
  }
 
  if (isQuadratic()) {
    if (auto S = SolveQuadraticAddRecRange(this, Range, SE))
      return SE.getConstant(*S);
  }
 
  return SE.getCouldNotCompute();
}
 
const SCEVAddRecExpr *
SCEVAddRecExpr::getPostIncExpr(ScalarEvolution &SE) const {
  assert(getNumOperands() > 1 && "AddRec with zero step?");
  // There is a temptation to just call getAddExpr(this, getStepRecurrence(SE)),
  // but in this case we cannot guarantee that the value returned will be an
  // AddRec because SCEV does not have a fixed point where it stops
  // simplification: it is legal to return ({rec1} + {rec2}). For example, it
  // may happen if we reach arithmetic depth limit while simplifying. So we
  // construct the returned value explicitly.
  SmallVector<SCEVUse, 3> Ops;
  // If this is {A,+,B,+,C,...,+,N}, then its step is {B,+,C,+,...,+,N}, and
  // (this + Step) is {A+B,+,B+C,+...,+,N}.
  for (unsigned i = 0, e = getNumOperands() - 1; i < e; ++i)
    Ops.push_back(SE.getAddExpr(getOperand(i), getOperand(i + 1)));
  // We know that the last operand is not a constant zero (otherwise it would
  // have been popped out earlier). This guarantees us that if the result has
  // the same last operand, then it will also not be popped out, meaning that
  // the returned value will be an AddRec.
  const SCEV *Last = getOperand(getNumOperands() - 1);
  assert(!Last->isZero() && "Recurrency with zero step?");
  Ops.push_back(Last);
  return cast<SCEVAddRecExpr>(SE.getAddRecExpr(Ops, getLoop(), SCEV::FlagNone));
}
 
// Return true when S contains at least an undef value.
bool ScalarEvolution::containsUndefs(const SCEV *S) const {
  return SCEVExprContains(
      S, [](const SCEV *S) { return match(S, m_scev_UndefOrPoison()); });
}
 
// Return true when S contains a value that is a nullptr.
bool ScalarEvolution::containsErasedValue(const SCEV *S) const {
  return SCEVExprContains(S, [](const SCEV *S) {
    if (const auto *SU = dyn_cast<SCEVUnknown>(S))
      return SU->getValue() == nullptr;
    return false;
  });
}
 
/// Return the size of an element read or written by Inst.
const SCEV *ScalarEvolution::getElementSize(Instruction *Inst) {
  if (!isa<LoadInst, StoreInst>(Inst))
    return nullptr;
  Type *ETy = getEffectiveSCEVType(getLoadStorePointerOperand(Inst)->getType());
  return getSizeOfExpr(ETy, getLoadStoreType(Inst));
}
 
//===----------------------------------------------------------------------===//
//                   SCEVCallbackVH Class Implementation
//===----------------------------------------------------------------------===//
 
void ScalarEvolution::SCEVCallbackVH::deleted() {
  assert(SE && "SCEVCallbackVH called with a null ScalarEvolution!");
  if (PHINode *PN = dyn_cast<PHINode>(getValPtr()))
    SE->ConstantEvolutionLoopExitValue.erase(PN);
  SE->eraseValueFromMap(getValPtr());
  // this now dangles!
}
 
void ScalarEvolution::SCEVCallbackVH::allUsesReplacedWith(Value *V) {
  assert(SE && "SCEVCallbackVH called with a null ScalarEvolution!");
 
  // Forget all the expressions associated with users of the old value,
  // so that future queries will recompute the expressions using the new
  // value.
  SE->forgetValue(getValPtr());
  // this now dangles!
}
 
ScalarEvolution::SCEVCallbackVH::SCEVCallbackVH(Value *V, ScalarEvolution *se)
  : CallbackVH(V), SE(se) {}
 
//===----------------------------------------------------------------------===//
//                   ScalarEvolution Class Implementation
//===----------------------------------------------------------------------===//
 
ScalarEvolution::ScalarEvolution(Function &F, TargetLibraryInfo &TLI,
                                 AssumptionCache &AC, DominatorTree &DT,
                                 LoopInfo &LI)
    : F(F), DL(F.getDataLayout()), TLI(TLI), AC(AC), DT(DT), LI(LI),
      CouldNotCompute(new SCEVCouldNotCompute()), ValuesAtScopes(64),
      LoopDispositions(64), BlockDispositions(64) {
  // To use guards for proving predicates, we need to scan every instruction in
  // relevant basic blocks, and not just terminators.  Doing this is a waste of
  // time if the IR does not actually contain any calls to
  // @llvm.experimental.guard, so do a quick check and remember this beforehand.
  //
  // This pessimizes the case where a pass that preserves ScalarEvolution wants
  // to _add_ guards to the module when there weren't any before, and wants
  // ScalarEvolution to optimize based on those guards.  For now we prefer to be
  // efficient in lieu of being smart in that rather obscure case.
 
  auto *GuardDecl = Intrinsic::getDeclarationIfExists(
      F.getParent(), Intrinsic::experimental_guard);
  HasGuards = GuardDecl && !GuardDecl->use_empty();
}
 
ScalarEvolution::ScalarEvolution(ScalarEvolution &&Arg)
    : F(Arg.F), DL(Arg.DL), HasGuards(Arg.HasGuards), TLI(Arg.TLI), AC(Arg.AC),
      DT(Arg.DT), LI(Arg.LI), CouldNotCompute(std::move(Arg.CouldNotCompute)),
      ValueExprMap(std::move(Arg.ValueExprMap)),
      PendingLoopPredicates(std::move(Arg.PendingLoopPredicates)),
      PendingMerges(std::move(Arg.PendingMerges)),
      ConstantMultipleCache(std::move(Arg.ConstantMultipleCache)),
      BackedgeTakenCounts(std::move(Arg.BackedgeTakenCounts)),
      PredicatedBackedgeTakenCounts(
          std::move(Arg.PredicatedBackedgeTakenCounts)),
      BECountUsers(std::move(Arg.BECountUsers)),
      ConstantEvolutionLoopExitValue(
          std::move(Arg.ConstantEvolutionLoopExitValue)),
      ValuesAtScopes(std::move(Arg.ValuesAtScopes)),
      ValuesAtScopesUsers(std::move(Arg.ValuesAtScopesUsers)),
      LoopDispositions(std::move(Arg.LoopDispositions)),
      LoopPropertiesCache(std::move(Arg.LoopPropertiesCache)),
      BlockDispositions(std::move(Arg.BlockDispositions)),
      SCEVUsers(std::move(Arg.SCEVUsers)),
      UnsignedRanges(std::move(Arg.UnsignedRanges)),
      SignedRanges(std::move(Arg.SignedRanges)),
      UniqueSCEVs(std::move(Arg.UniqueSCEVs)),
      UniquePreds(std::move(Arg.UniquePreds)),
      SCEVAllocator(std::move(Arg.SCEVAllocator)),
      ConstantSCEVs(std::move(Arg.ConstantSCEVs)),
      LoopUsers(std::move(Arg.LoopUsers)),
      PredicatedSCEVRewrites(std::move(Arg.PredicatedSCEVRewrites)),
      FirstUnknown(Arg.FirstUnknown),
      NextUnknownOrderID(Arg.NextUnknownOrderID) {
  Arg.FirstUnknown = nullptr;
}
 
ScalarEvolution::~ScalarEvolution() {
  // Iterate through all the SCEVUnknown instances and call their
  // destructors, so that they release their references to their values.
  for (SCEVUnknown *U = FirstUnknown; U;) {
    SCEVUnknown *Tmp = U;
    U = U->Next;
    Tmp->~SCEVUnknown();
  }
  FirstUnknown = nullptr;
 
  ExprValueMap.clear();
  ValueExprMap.clear();
  HasRecMap.clear();
  BackedgeTakenCounts.clear();
  PredicatedBackedgeTakenCounts.clear();
 
  assert(PendingLoopPredicates.empty() && "isImpliedCond garbage");
  assert(PendingMerges.empty() && "isImpliedViaMerge garbage");
  assert(!WalkingBEDominatingConds && "isLoopBackedgeGuardedByCond garbage!");
  assert(!ProvingSplitPredicate && "ProvingSplitPredicate garbage!");
}
 
bool ScalarEvolution::hasLoopInvariantBackedgeTakenCount(const Loop *L) {
  return !isa<SCEVCouldNotCompute>(getBackedgeTakenCount(L));
}
 
/// When printing a top-level SCEV for trip counts, it's helpful to include
/// a type for constants which are otherwise hard to disambiguate.
static void PrintSCEVWithTypeHint(raw_ostream &OS, const SCEV* S) {
  if (isa<SCEVConstant>(S))
    OS << *S->getType() << " ";
  OS << *S;
}
 
static void PrintLoopInfo(raw_ostream &OS, ScalarEvolution *SE,
                          const Loop *L) {
  // Print all inner loops first
  for (Loop *I : *L)
    PrintLoopInfo(OS, SE, I);
 
  OS << "Loop ";
  L->getHeader()->printAsOperand(OS, /*PrintType=*/false);
  OS << ": ";
 
  SmallVector<BasicBlock *, 8> ExitingBlocks;
  L->getExitingBlocks(ExitingBlocks);
  if (ExitingBlocks.size() != 1)
    OS << "<multiple exits> ";
 
  auto *BTC = SE->getBackedgeTakenCount(L);
  if (!isa<SCEVCouldNotCompute>(BTC)) {
    OS << "backedge-taken count is ";
    PrintSCEVWithTypeHint(OS, BTC);
  } else
    OS << "Unpredictable backedge-taken count.";
  OS << "\n";
 
  if (ExitingBlocks.size() > 1)
    for (BasicBlock *ExitingBlock : ExitingBlocks) {
      OS << "  exit count for " << ExitingBlock->getName() << ": ";
      const SCEV *EC = SE->getExitCount(L, ExitingBlock);
      PrintSCEVWithTypeHint(OS, EC);
      if (isa<SCEVCouldNotCompute>(EC)) {
        // Retry with predicates.
        SmallVector<const SCEVPredicate *> Predicates;
        EC = SE->getPredicatedExitCount(L, ExitingBlock, &Predicates);
        if (!isa<SCEVCouldNotCompute>(EC)) {
          OS << "\n  predicated exit count for " << ExitingBlock->getName()
             << ": ";
          PrintSCEVWithTypeHint(OS, EC);
          OS << "\n   Predicates:\n";
          for (const auto *P : Predicates)
            P->print(OS, 4);
        }
      }
      OS << "\n";
    }
 
  OS << "Loop ";
  L->getHeader()->printAsOperand(OS, /*PrintType=*/false);
  OS << ": ";
 
  auto *ConstantBTC = SE->getConstantMaxBackedgeTakenCount(L);
  if (!isa<SCEVCouldNotCompute>(ConstantBTC)) {
    OS << "constant max backedge-taken count is ";
    PrintSCEVWithTypeHint(OS, ConstantBTC);
    if (SE->isBackedgeTakenCountMaxOrZero(L))
      OS << ", actual taken count either this or zero.";
  } else {
    OS << "Unpredictable constant max backedge-taken count. ";
  }
 
  OS << "\n"
        "Loop ";
  L->getHeader()->printAsOperand(OS, /*PrintType=*/false);
  OS << ": ";
 
  auto *SymbolicBTC = SE->getSymbolicMaxBackedgeTakenCount(L);
  if (!isa<SCEVCouldNotCompute>(SymbolicBTC)) {
    OS << "symbolic max backedge-taken count is ";
    PrintSCEVWithTypeHint(OS, SymbolicBTC);
    if (SE->isBackedgeTakenCountMaxOrZero(L))
      OS << ", actual taken count either this or zero.";
  } else {
    OS << "Unpredictable symbolic max backedge-taken count. ";
  }
  OS << "\n";
 
  if (ExitingBlocks.size() > 1)
    for (BasicBlock *ExitingBlock : ExitingBlocks) {
      OS << "  symbolic max exit count for " << ExitingBlock->getName() << ": ";
      auto *ExitBTC = SE->getExitCount(L, ExitingBlock,
                                       ScalarEvolution::SymbolicMaximum);
      PrintSCEVWithTypeHint(OS, ExitBTC);
      if (isa<SCEVCouldNotCompute>(ExitBTC)) {
        // Retry with predicates.
        SmallVector<const SCEVPredicate *> Predicates;
        ExitBTC = SE->getPredicatedExitCount(L, ExitingBlock, &Predicates,
                                             ScalarEvolution::SymbolicMaximum);
        if (!isa<SCEVCouldNotCompute>(ExitBTC)) {
          OS << "\n  predicated symbolic max exit count for "
             << ExitingBlock->getName() << ": ";
          PrintSCEVWithTypeHint(OS, ExitBTC);
          OS << "\n   Predicates:\n";
          for (const auto *P : Predicates)
            P->print(OS, 4);
        }
      }
      OS << "\n";
    }
 
  SmallVector<const SCEVPredicate *, 4> Preds;
  auto *PBT = SE->getPredicatedBackedgeTakenCount(L, Preds);
  if (PBT != BTC) {
    OS << "Loop ";
    L->getHeader()->printAsOperand(OS, /*PrintType=*/false);
    OS << ": ";
    if (!isa<SCEVCouldNotCompute>(PBT)) {
      OS << "Predicated backedge-taken count is ";
      PrintSCEVWithTypeHint(OS, PBT);
    } else
      OS << "Unpredictable predicated backedge-taken count.";
    OS << "\n";
    OS << " Predicates:\n";
    for (const auto *P : Preds)
      P->print(OS, 4);
  }
  Preds.clear();
 
  auto *PredConstantMax =
      SE->getPredicatedConstantMaxBackedgeTakenCount(L, Preds);
  if (PredConstantMax != ConstantBTC) {
    OS << "Loop ";
    L->getHeader()->printAsOperand(OS, /*PrintType=*/false);
    OS << ": ";
    if (!isa<SCEVCouldNotCompute>(PredConstantMax)) {
      OS << "Predicated constant max backedge-taken count is ";
      PrintSCEVWithTypeHint(OS, PredConstantMax);
    } else
      OS << "Unpredictable predicated constant max backedge-taken count.";
    OS << "\n";
    OS << " Predicates:\n";
    for (const auto *P : Preds)
      P->print(OS, 4);
  }
  Preds.clear();
 
  auto *PredSymbolicMax =
      SE->getPredicatedSymbolicMaxBackedgeTakenCount(L, Preds);
  if (SymbolicBTC != PredSymbolicMax) {
    OS << "Loop ";
    L->getHeader()->printAsOperand(OS, /*PrintType=*/false);
    OS << ": ";
    if (!isa<SCEVCouldNotCompute>(PredSymbolicMax)) {
      OS << "Predicated symbolic max backedge-taken count is ";
      PrintSCEVWithTypeHint(OS, PredSymbolicMax);
    } else
      OS << "Unpredictable predicated symbolic max backedge-taken count.";
    OS << "\n";
    OS << " Predicates:\n";
    for (const auto *P : Preds)
      P->print(OS, 4);
  }
 
  if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
    OS << "Loop ";
    L->getHeader()->printAsOperand(OS, /*PrintType=*/false);
    OS << ": ";
    OS << "Trip multiple is " << SE->getSmallConstantTripMultiple(L) << "\n";
  }
}
 
namespace llvm {
// Note: these overloaded operators need to be in the llvm namespace for them
// to be resolved correctly. If we put them outside the llvm namespace, the
//
// OS << ": " << SE.getLoopDisposition(SV, InnerL);
//
// code below "breaks" and start printing raw enum values as opposed to the
// string values.
static raw_ostream &operator<<(raw_ostream &OS,
                               ScalarEvolution::LoopDisposition LD) {
  switch (LD) {
  case ScalarEvolution::LoopVariant:
    OS << "Variant";
    break;
  case ScalarEvolution::LoopInvariant:
    OS << "Invariant";
    break;
  case ScalarEvolution::LoopUniform:
    OS << "Uniform";
    break;
  case ScalarEvolution::LoopComputable:
    OS << "Computable";
    break;
  }
  return OS;
}
 
static raw_ostream &operator<<(raw_ostream &OS,
                               llvm::ScalarEvolution::BlockDisposition BD) {
  switch (BD) {
  case ScalarEvolution::DoesNotDominateBlock:
    OS << "DoesNotDominate";
    break;
  case ScalarEvolution::DominatesBlock:
    OS << "Dominates";
    break;
  case ScalarEvolution::ProperlyDominatesBlock:
    OS << "ProperlyDominates";
    break;
  }
  return OS;
}
} // namespace llvm
 
void ScalarEvolution::print(raw_ostream &OS) const {
  // ScalarEvolution's implementation of the print method is to print
  // out SCEV values of all instructions that are interesting. Doing
  // this potentially causes it to create new SCEV objects though,
  // which technically conflicts with the const qualifier. This isn't
  // observable from outside the class though, so casting away the
  // const isn't dangerous.
  ScalarEvolution &SE = *const_cast<ScalarEvolution *>(this);
 
  if (ClassifyExpressions) {
    OS << "Classifying expressions for: ";
    F.printAsOperand(OS, /*PrintType=*/false);
    OS << "\n";
    for (Instruction &I : instructions(F))
      if (isSCEVable(I.getType()) && !isa<CmpInst>(I)) {
        OS << I << '\n';
        OS << "  -->  ";
        const SCEV *SV = SE.getSCEV(&I);
        SV->print(OS);
        if (!isa<SCEVCouldNotCompute>(SV)) {
          OS << " U: ";
          SE.getUnsignedRange(SV).print(OS);
          OS << " S: ";
          SE.getSignedRange(SV).print(OS);
        }
 
        const Loop *L = LI.getLoopFor(I.getParent());
 
        SCEVUse AtUse = SE.getSCEVAtScope(SV, L);
        if (AtUse != SV) {
          OS << "  -->  ";
          OS << AtUse;
          if (!isa<SCEVCouldNotCompute>(AtUse)) {
            OS << " U: ";
            SE.getUnsignedRange(AtUse).print(OS);
            OS << " S: ";
            SE.getSignedRange(AtUse).print(OS);
          }
        }
 
        if (L) {
          OS << "\t\t" "Exits: ";
          SCEVUse ExitValue = SE.getSCEVAtScope(SV, L->getParentLoop());
          if (!SE.isLoopInvariant(ExitValue, L)) {
            OS << "<<Unknown>>";
          } else {
            OS << ExitValue;
          }
 
          ListSeparator LS(", ", "\t\tLoopDispositions: { ");
          for (const auto *Iter = L; Iter; Iter = Iter->getParentLoop()) {
            OS << LS;
            Iter->getHeader()->printAsOperand(OS, /*PrintType=*/false);
            OS << ": " << SE.getLoopDisposition(SV, Iter);
          }
 
          for (const auto *InnerL : depth_first(L)) {
            if (InnerL == L)
              continue;
            OS << LS;
            InnerL->getHeader()->printAsOperand(OS, /*PrintType=*/false);
            OS << ": " << SE.getLoopDisposition(SV, InnerL);
          }
 
          OS << " }";
        }
 
        OS << "\n";
      }
  }
 
  OS << "Determining loop execution counts for: ";
  F.printAsOperand(OS, /*PrintType=*/false);
  OS << "\n";
  for (Loop *I : LI)
    PrintLoopInfo(OS, &SE, I);
}
 
ScalarEvolution::LoopDisposition
ScalarEvolution::getLoopDisposition(const SCEV *S, const Loop *L) {
  if (isa<SCEVConstant>(S))
    return LoopInvariant;
 
  auto &Values = LoopDispositions[S];
  for (auto &V : Values) {
    if (V.getPointer() == L)
      return V.getInt();
  }
  Values.emplace_back(L, LoopVariant);
  LoopDisposition D = computeLoopDisposition(S, L);
  auto &Values2 = LoopDispositions[S];
  for (auto &V : llvm::reverse(Values2)) {
    if (V.getPointer() == L) {
      V.setInt(D);
      break;
    }
  }
  return D;
}
 
ScalarEvolution::LoopDisposition
ScalarEvolution::computeLoopDisposition(const SCEV *S, const Loop *L) {
  switch (S->getSCEVType()) {
  case scConstant:
  case scVScale:
    return LoopInvariant;
  case scAddRecExpr: {
    const SCEVAddRecExpr *AR = cast<SCEVAddRecExpr>(S);
 
    // If L is the addrec's loop, it's computable.
    if (AR->getLoop() == L)
      return LoopComputable;
 
    // Add recurrences are never invariant in the function-body (null loop).
    if (!L)
      return LoopVariant;
 
    // Everything that is not defined at loop entry is variant.
    if (DT.dominates(L->getHeader(), AR->getLoop()->getHeader())) {
      if (L->contains(AR->getLoop()) &&
          llvm::all_of(AR->operands(),
                       [&](const SCEV *Op) { return isLoopUniform(Op, L); }))
        return LoopUniform;
 
      return LoopVariant;
    }
    assert(!L->contains(AR->getLoop()) && "Containing loop's header does not"
           " dominate the contained loop's header?");
 
    // This recurrence is invariant w.r.t. L if AR's loop contains L.
    if (AR->getLoop()->contains(L))
      return LoopInvariant;
 
    // This recurrence is variant w.r.t. L if any of its operands
    // are variant.
    for (SCEVUse Op : AR->operands())
      if (!isLoopInvariant(Op, L))
        return LoopVariant;
 
    // Otherwise it's loop-invariant.
    return LoopInvariant;
  }
  case scTruncate:
  case scZeroExtend:
  case scSignExtend:
  case scPtrToAddr:
  case scAddExpr:
  case scMulExpr:
  case scUDivExpr:
  case scUMaxExpr:
  case scSMaxExpr:
  case scUMinExpr:
  case scSMinExpr:
  case scSequentialUMinExpr: {
    bool HasVarying = false;
    bool HasUniform = false;
    for (SCEVUse Op : S->operands()) {
      LoopDisposition D = getLoopDisposition(Op, L);
      if (D == LoopVariant)
        return LoopVariant;
      if (D == LoopComputable)
        HasVarying = true;
      if (D == LoopUniform)
        HasUniform = true;
    }
    return HasVarying ? (HasUniform ? LoopVariant : LoopComputable)
                      : (HasUniform ? LoopUniform : LoopInvariant);
  }
  case scUnknown:
    // All non-instruction values are loop invariant.  All instructions are loop
    // invariant if they are not contained in the specified loop.
    // Instructions are never considered invariant in the function body
    // (null loop) because they are defined within the "loop".
    if (auto *I = dyn_cast<Instruction>(cast<SCEVUnknown>(S)->getValue()))
      return (L && !L->contains(I)) ? LoopInvariant : LoopVariant;
    return LoopInvariant;
  case scCouldNotCompute:
    llvm_unreachable("Attempt to use a SCEVCouldNotCompute object!");
  }
  llvm_unreachable("Unknown SCEV kind!");
}
 
bool ScalarEvolution::isLoopUniform(const SCEV *S, const Loop *L) {
  LoopDisposition D = getLoopDisposition(S, L);
  return D == LoopUniform || D == LoopInvariant;
}
 
bool ScalarEvolution::isLoopInvariant(const SCEV *S, const Loop *L) {
  return getLoopDisposition(S, L) == LoopInvariant;
}
 
bool ScalarEvolution::hasComputableLoopEvolution(const SCEV *S, const Loop *L) {
  return getLoopDisposition(S, L) == LoopComputable;
}
 
ScalarEvolution::BlockDisposition
ScalarEvolution::getBlockDisposition(const SCEV *S, const BasicBlock *BB) {
  if (isa<SCEVConstant>(S))
    return ProperlyDominatesBlock;
 
  auto &Values = BlockDispositions[S];
  for (auto &V : Values) {
    if (V.getPointer() == BB)
      return V.getInt();
  }
  Values.emplace_back(BB, DoesNotDominateBlock);
  BlockDisposition D = computeBlockDisposition(S, BB);
  auto &Values2 = BlockDispositions[S];
  for (auto &V : llvm::reverse(Values2)) {
    if (V.getPointer() == BB) {
      V.setInt(D);
      break;
    }
  }
  return D;
}
 
ScalarEvolution::BlockDisposition
ScalarEvolution::computeBlockDisposition(const SCEV *S, const BasicBlock *BB) {
  switch (S->getSCEVType()) {
  case scConstant:
  case scVScale:
    return ProperlyDominatesBlock;
  case scAddRecExpr: {
    // This uses a "dominates" query instead of "properly dominates" query
    // to test for proper dominance too, because the instruction which
    // produces the addrec's value is a PHI, and a PHI effectively properly
    // dominates its entire containing block.
    const SCEVAddRecExpr *AR = cast<SCEVAddRecExpr>(S);
    if (!DT.dominates(AR->getLoop()->getHeader(), BB))
      return DoesNotDominateBlock;
 
    // Fall through into SCEVNAryExpr handling.
    [[fallthrough]];
  }
  case scTruncate:
  case scZeroExtend:
  case scSignExtend:
  case scPtrToAddr:
  case scAddExpr:
  case scMulExpr:
  case scUDivExpr:
  case scUMaxExpr:
  case scSMaxExpr:
  case scUMinExpr:
  case scSMinExpr:
  case scSequentialUMinExpr: {
    bool Proper = true;
    for (const SCEV *NAryOp : S->operands()) {
      BlockDisposition D = getBlockDisposition(NAryOp, BB);
      if (D == DoesNotDominateBlock)
        return DoesNotDominateBlock;
      if (D == DominatesBlock)
        Proper = false;
    }
    return Proper ? ProperlyDominatesBlock : DominatesBlock;
  }
  case scUnknown:
    if (Instruction *I =
          dyn_cast<Instruction>(cast<SCEVUnknown>(S)->getValue())) {
      if (I->getParent() == BB)
        return DominatesBlock;
      if (DT.properlyDominates(I->getParent(), BB))
        return ProperlyDominatesBlock;
      return DoesNotDominateBlock;
    }
    return ProperlyDominatesBlock;
  case scCouldNotCompute:
    llvm_unreachable("Attempt to use a SCEVCouldNotCompute object!");
  }
  llvm_unreachable("Unknown SCEV kind!");
}
 
bool ScalarEvolution::dominates(const SCEV *S, const BasicBlock *BB) {
  return getBlockDisposition(S, BB) >= DominatesBlock;
}
 
bool ScalarEvolution::properlyDominates(const SCEV *S, const BasicBlock *BB) {
  return getBlockDisposition(S, BB) == ProperlyDominatesBlock;
}
 
void ScalarEvolution::forgetBackedgeTakenCounts(const Loop *L,
                                                bool Predicated) {
  auto &BECounts =
      Predicated ? PredicatedBackedgeTakenCounts : BackedgeTakenCounts;
  auto It = BECounts.find(L);
  if (It != BECounts.end()) {
    for (const ExitNotTakenInfo &ENT : It->second.ExitNotTaken) {
      for (const SCEV *S : {ENT.ExactNotTaken, ENT.SymbolicMaxNotTaken}) {
        if (!isa<SCEVConstant>(S)) {
          auto UserIt = BECountUsers.find(S);
          assert(UserIt != BECountUsers.end());
          UserIt->second.erase({L, Predicated});
        }
      }
    }
    BECounts.erase(It);
  }
}
 
void ScalarEvolution::forgetMemoizedResults(ArrayRef<SCEVUse> SCEVs) {
  SmallPtrSet<const SCEV *, 8> ToForget(llvm::from_range, SCEVs);
  SmallVector<SCEVUse, 8> Worklist(ToForget.begin(), ToForget.end());
 
  while (!Worklist.empty()) {
    const SCEV *Curr = Worklist.pop_back_val();
    auto Users = SCEVUsers.find(Curr);
    if (Users != SCEVUsers.end())
      for (const auto *User : Users->second)
        if (ToForget.insert(User).second)
          Worklist.push_back(User);
  }
 
  for (const auto *S : ToForget)
    forgetMemoizedResultsImpl(S);
 
  PredicatedSCEVRewrites.remove_if(
      [&](const auto &Entry) { return ToForget.count(Entry.first.first); });
}
 
void ScalarEvolution::forgetMemoizedResultsImpl(const SCEV *S) {
  LoopDispositions.erase(S);
  BlockDispositions.erase(S);
  UnsignedRanges.erase(S);
  SignedRanges.erase(S);
  HasRecMap.erase(S);
  ConstantMultipleCache.erase(S);
 
  if (auto *AR = dyn_cast<SCEVAddRecExpr>(S)) {
    UnsignedWrapViaInductionTried.erase(AR);
    SignedWrapViaInductionTried.erase(AR);
  }
 
  auto ExprIt = ExprValueMap.find(S);
  if (ExprIt != ExprValueMap.end()) {
    for (Value *V : ExprIt->second) {
      auto ValueIt = ValueExprMap.find_as(V);
      if (ValueIt != ValueExprMap.end())
        ValueExprMap.erase(ValueIt);
    }
    ExprValueMap.erase(ExprIt);
  }
 
  auto ScopeIt = ValuesAtScopes.find(S);
  if (ScopeIt != ValuesAtScopes.end()) {
    for (const auto &Pair : ScopeIt->second)
      if (!isa_and_nonnull<SCEVConstant>(Pair.second))
        llvm::erase(ValuesAtScopesUsers[Pair.second.getPointer()],
                    std::make_pair(Pair.first, S));
    ValuesAtScopes.erase(ScopeIt);
  }
 
  auto ScopeUserIt = ValuesAtScopesUsers.find(S);
  if (ScopeUserIt != ValuesAtScopesUsers.end()) {
    for (const auto &Pair : ScopeUserIt->second)
      // The recorded value at scope is a use of S, which may carry no-wrap
      // flags that are not part of this key.
      llvm::erase_if(ValuesAtScopes[Pair.second], [&](const auto &LS) {
        return LS.first == Pair.first && LS.second.getPointer() == S;
      });
    ValuesAtScopesUsers.erase(ScopeUserIt);
  }
 
  auto BEUsersIt = BECountUsers.find(S);
  if (BEUsersIt != BECountUsers.end()) {
    // Work on a copy, as forgetBackedgeTakenCounts() will modify the original.
    auto Copy = BEUsersIt->second;
    for (const auto &Pair : Copy)
      forgetBackedgeTakenCounts(Pair.getPointer(), Pair.getInt());
    BECountUsers.erase(BEUsersIt);
  }
 
  auto FoldUser = FoldCacheUser.find(S);
  if (FoldUser != FoldCacheUser.end())
    for (auto &KV : FoldUser->second)
      FoldCache.erase(KV);
  FoldCacheUser.erase(S);
}
 
void
ScalarEvolution::getUsedLoops(const SCEV *S,
                              SmallPtrSetImpl<const Loop *> &LoopsUsed) {
  struct FindUsedLoops {
    FindUsedLoops(SmallPtrSetImpl<const Loop *> &LoopsUsed)
        : LoopsUsed(LoopsUsed) {}
    SmallPtrSetImpl<const Loop *> &LoopsUsed;
    bool follow(const SCEV *S) {
      if (auto *AR = dyn_cast<SCEVAddRecExpr>(S))
        LoopsUsed.insert(AR->getLoop());
      return true;
    }
 
    bool isDone() const { return false; }
  };
 
  FindUsedLoops F(LoopsUsed);
  SCEVTraversal<FindUsedLoops>(F).visitAll(S);
}
 
void ScalarEvolution::getReachableBlocks(
    SmallPtrSetImpl<BasicBlock *> &Reachable, Function &F) {
  SmallVector<BasicBlock *> Worklist;
  Worklist.push_back(&F.getEntryBlock());
  while (!Worklist.empty()) {
    BasicBlock *BB = Worklist.pop_back_val();
    if (!Reachable.insert(BB).second)
      continue;
 
    Value *Cond;
    BasicBlock *TrueBB, *FalseBB;
    if (match(BB->getTerminator(), m_Br(m_Value(Cond), m_BasicBlock(TrueBB),
                                        m_BasicBlock(FalseBB)))) {
      if (auto *C = dyn_cast<ConstantInt>(Cond)) {
        Worklist.push_back(C->isOne() ? TrueBB : FalseBB);
        continue;
      }
 
      if (auto *Cmp = dyn_cast<ICmpInst>(Cond)) {
        const SCEV *L = getSCEV(Cmp->getOperand(0));
        const SCEV *R = getSCEV(Cmp->getOperand(1));
        if (isKnownPredicateViaConstantRanges(Cmp->getCmpPredicate(), L, R)) {
          Worklist.push_back(TrueBB);
          continue;
        }
        if (isKnownPredicateViaConstantRanges(Cmp->getInverseCmpPredicate(), L,
                                              R)) {
          Worklist.push_back(FalseBB);
          continue;
        }
      }
    }
 
    append_range(Worklist, successors(BB));
  }
}
 
void ScalarEvolution::verify() const {
  ScalarEvolution &SE = *const_cast<ScalarEvolution *>(this);
  ScalarEvolution SE2(F, TLI, AC, DT, LI);
 
  SmallVector<Loop *, 8> LoopStack(LI.begin(), LI.end());
 
  // Map's SCEV expressions from one ScalarEvolution "universe" to another.
  struct SCEVMapper : public SCEVRewriteVisitor<SCEVMapper> {
    SCEVMapper(ScalarEvolution &SE) : SCEVRewriteVisitor<SCEVMapper>(SE) {}
 
    const SCEV *visitConstant(const SCEVConstant *Constant) {
      return SE.getConstant(Constant->getAPInt());
    }
 
    const SCEV *visitUnknown(const SCEVUnknown *Expr) {
      return SE.getUnknown(Expr->getValue());
    }
 
    const SCEV *visitCouldNotCompute(const SCEVCouldNotCompute *Expr) {
      return SE.getCouldNotCompute();
    }
  };
 
  SCEVMapper SCM(SE2);
  SmallPtrSet<BasicBlock *, 16> ReachableBlocks;
  SE2.getReachableBlocks(ReachableBlocks, F);
 
  auto GetDelta = [&](const SCEV *Old, const SCEV *New) -> const SCEV * {
    if (containsUndefs(Old) || containsUndefs(New)) {
      // SCEV treats "undef" as an unknown but consistent value (i.e. it does
      // not propagate undef aggressively).  This means we can (and do) fail
      // verification in cases where a transform makes a value go from "undef"
      // to "undef+1" (say).  The transform is fine, since in both cases the
      // result is "undef", but SCEV thinks the value increased by 1.
      return nullptr;
    }
 
    // Unless VerifySCEVStrict is set, we only compare constant deltas.
    const SCEV *Delta = SE2.getMinusSCEV(Old, New);
    if (!VerifySCEVStrict && !isa<SCEVConstant>(Delta))
      return nullptr;
 
    return Delta;
  };
 
  while (!LoopStack.empty()) {
    auto *L = LoopStack.pop_back_val();
    llvm::append_range(LoopStack, *L);
 
    // Only verify BECounts in reachable loops. For an unreachable loop,
    // any BECount is legal.
    if (!ReachableBlocks.contains(L->getHeader()))
      continue;
 
    // Only verify cached BECounts. Computing new BECounts may change the
    // results of subsequent SCEV uses.
    auto It = BackedgeTakenCounts.find(L);
    if (It == BackedgeTakenCounts.end())
      continue;
 
    auto *CurBECount =
        SCM.visit(It->second.getExact(L, const_cast<ScalarEvolution *>(this)));
    auto *NewBECount = SE2.getBackedgeTakenCount(L);
 
    if (CurBECount == SE2.getCouldNotCompute() ||
        NewBECount == SE2.getCouldNotCompute()) {
      // NB! This situation is legal, but is very suspicious -- whatever pass
      // change the loop to make a trip count go from could not compute to
      // computable or vice-versa *should have* invalidated SCEV.  However, we
      // choose not to assert here (for now) since we don't want false
      // positives.
      continue;
    }
 
    if (SE.getTypeSizeInBits(CurBECount->getType()) >
        SE.getTypeSizeInBits(NewBECount->getType()))
      NewBECount = SE2.getZeroExtendExpr(NewBECount, CurBECount->getType());
    else if (SE.getTypeSizeInBits(CurBECount->getType()) <
             SE.getTypeSizeInBits(NewBECount->getType()))
      CurBECount = SE2.getZeroExtendExpr(CurBECount, NewBECount->getType());
 
    const SCEV *Delta = GetDelta(CurBECount, NewBECount);
    if (Delta && !Delta->isZero()) {
      dbgs() << "Trip Count for " << *L << " Changed!\n";
      dbgs() << "Old: " << *CurBECount << "\n";
      dbgs() << "New: " << *NewBECount << "\n";
      dbgs() << "Delta: " << *Delta << "\n";
      std::abort();
    }
  }
 
  // Collect all valid loops currently in LoopInfo.
  SmallPtrSet<Loop *, 32> ValidLoops;
  SmallVector<Loop *, 32> Worklist(LI.begin(), LI.end());
  while (!Worklist.empty()) {
    Loop *L = Worklist.pop_back_val();
    if (ValidLoops.insert(L).second)
      Worklist.append(L->begin(), L->end());
  }
  for (const auto &KV : ValueExprMap) {
#ifndef NDEBUG
    // Check for SCEV expressions referencing invalid/deleted loops.
    if (auto *AR = dyn_cast<SCEVAddRecExpr>(KV.second)) {
      assert(ValidLoops.contains(AR->getLoop()) &&
             "AddRec references invalid loop");
    }
#endif
 
    // Check that the value is also part of the reverse map.
    auto It = ExprValueMap.find(KV.second);
    if (It == ExprValueMap.end() || !is_contained(It->second, KV.first)) {
      dbgs() << "Value " << *KV.first
             << " is in ValueExprMap but not in ExprValueMap\n";
      std::abort();
    }
 
    if (auto *I = dyn_cast<Instruction>(&*KV.first)) {
      if (!ReachableBlocks.contains(I->getParent()))
        continue;
      const SCEV *OldSCEV = SCM.visit(KV.second);
      const SCEV *NewSCEV = SE2.getSCEV(I);
      const SCEV *Delta = GetDelta(OldSCEV, NewSCEV);
      if (Delta && !Delta->isZero()) {
        dbgs() << "SCEV for value " << *I << " changed!\n"
               << "Old: " << *OldSCEV << "\n"
               << "New: " << *NewSCEV << "\n"
               << "Delta: " << *Delta << "\n";
        std::abort();
      }
    }
  }
 
  for (const auto &KV : ExprValueMap) {
    for (Value *V : KV.second) {
      const SCEV *S = ValueExprMap.lookup(V);
      if (!S) {
        dbgs() << "Value " << *V
               << " is in ExprValueMap but not in ValueExprMap\n";
        std::abort();
      }
      if (S != KV.first) {
        dbgs() << "Value " << *V << " mapped to " << *S << " rather than "
               << *KV.first << "\n";
        std::abort();
      }
    }
  }
 
  // Verify integrity of SCEV users.
  for (const auto &S : UniqueSCEVs) {
    for (SCEVUse Op : S.operands()) {
      // We do not store dependencies of constants.
      if (isa<SCEVConstant>(Op))
        continue;
      auto It = SCEVUsers.find(Op);
      if (It != SCEVUsers.end() && It->second.count(&S))
        continue;
      dbgs() << "Use of operand  " << *Op << " by user " << S
             << " is not being tracked!\n";
      std::abort();
    }
  }
 
  // Verify integrity of ValuesAtScopes users.
  for (const auto &ValueAndVec : ValuesAtScopes) {
    const SCEV *Value = ValueAndVec.first;
    for (const auto &LoopAndValueAtScope : ValueAndVec.second) {
      const Loop *L = LoopAndValueAtScope.first;
      SCEVUse ValueAtScope = LoopAndValueAtScope.second;
      if (!isa<SCEVConstant>(ValueAtScope)) {
        auto It = ValuesAtScopesUsers.find(ValueAtScope.getPointer());
        if (It != ValuesAtScopesUsers.end() &&
            is_contained(It->second, std::make_pair(L, Value)))
          continue;
        dbgs() << "Value: " << *Value << ", Loop: " << *L << ", ValueAtScope: "
               << *ValueAtScope << " missing in ValuesAtScopesUsers\n";
        std::abort();
      }
    }
  }
 
  for (const auto &ValueAtScopeAndVec : ValuesAtScopesUsers) {
    const SCEV *ValueAtScope = ValueAtScopeAndVec.first;
    for (const auto &LoopAndValue : ValueAtScopeAndVec.second) {
      const Loop *L = LoopAndValue.first;
      const SCEV *Value = LoopAndValue.second;
      assert(!isa<SCEVConstant>(Value));
      auto It = ValuesAtScopes.find(Value);
      // The recorded value at scope may carry no-wrap flags that are not part
      // of the key it is recorded under.
      if (It != ValuesAtScopes.end() && any_of(It->second, [&](const auto &LS) {
            return LS.first == L && LS.second.getPointer() == ValueAtScope;
          }))
        continue;
      dbgs() << "Value: " << *Value << ", Loop: " << *L << ", ValueAtScope: "
             << *ValueAtScope << " missing in ValuesAtScopes\n";
      std::abort();
    }
  }
 
  // Verify integrity of BECountUsers.
  auto VerifyBECountUsers = [&](bool Predicated) {
    auto &BECounts =
        Predicated ? PredicatedBackedgeTakenCounts : BackedgeTakenCounts;
    for (const auto &LoopAndBEInfo : BECounts) {
      for (const ExitNotTakenInfo &ENT : LoopAndBEInfo.second.ExitNotTaken) {
        for (const SCEV *S : {ENT.ExactNotTaken, ENT.SymbolicMaxNotTaken}) {
          if (!isa<SCEVConstant>(S)) {
            auto UserIt = BECountUsers.find(S);
            if (UserIt != BECountUsers.end() &&
                UserIt->second.contains({ LoopAndBEInfo.first, Predicated }))
              continue;
            dbgs() << "Value " << *S << " for loop " << *LoopAndBEInfo.first
                   << " missing from BECountUsers\n";
            std::abort();
          }
        }
      }
    }
  };
  VerifyBECountUsers(/* Predicated */ false);
  VerifyBECountUsers(/* Predicated */ true);
 
  // Verify intergity of loop disposition cache.
  for (auto &[S, Values] : LoopDispositions) {
    for (auto [Loop, CachedDisposition] : Values) {
      const auto RecomputedDisposition = SE2.getLoopDisposition(S, Loop);
      if (CachedDisposition != RecomputedDisposition) {
        dbgs() << "Cached disposition of " << *S << " for loop " << *Loop
               << " is incorrect: cached " << CachedDisposition << ", actual "
               << RecomputedDisposition << "\n";
        std::abort();
      }
    }
  }
 
  // Verify integrity of the block disposition cache.
  for (auto &[S, Values] : BlockDispositions) {
    for (auto [BB, CachedDisposition] : Values) {
      const auto RecomputedDisposition = SE2.getBlockDisposition(S, BB);
      if (CachedDisposition != RecomputedDisposition) {
        dbgs() << "Cached disposition of " << *S << " for block %"
               << BB->getName() << " is incorrect: cached " << CachedDisposition
               << ", actual " << RecomputedDisposition << "\n";
        std::abort();
      }
    }
  }
 
  // Verify FoldCache/FoldCacheUser caches.
  for (auto [FoldID, Expr] : FoldCache) {
    auto I = FoldCacheUser.find(Expr);
    if (I == FoldCacheUser.end()) {
      dbgs() << "Missing entry in FoldCacheUser for cached expression " << *Expr
             << "!\n";
      std::abort();
    }
    if (!is_contained(I->second, FoldID)) {
      dbgs() << "Missing FoldID in cached users of " << *Expr << "!\n";
      std::abort();
    }
  }
  for (auto [Expr, IDs] : FoldCacheUser) {
    for (auto &FoldID : IDs) {
      const SCEV *S = FoldCache.lookup(FoldID);
      if (!S) {
        dbgs() << "Missing entry in FoldCache for expression " << *Expr
               << "!\n";
        std::abort();
      }
      if (S != Expr) {
        dbgs() << "Entry in FoldCache doesn't match FoldCacheUser: " << *S
               << " != " << *Expr << "!\n";
        std::abort();
      }
    }
  }
 
  // Verify that ConstantMultipleCache computations are correct. We check that
  // cached multiples and recomputed multiples are multiples of each other to
  // verify correctness. It is possible that a recomputed multiple is different
  // from the cached multiple due to strengthened no wrap flags or changes in
  // KnownBits computations.
  for (auto [S, Multiple] : ConstantMultipleCache) {
    APInt RecomputedMultiple = SE2.getConstantMultiple(S);
    if ((Multiple != 0 && RecomputedMultiple != 0 &&
         Multiple.urem(RecomputedMultiple) != 0 &&
         RecomputedMultiple.urem(Multiple) != 0)) {
      dbgs() << "Incorrect cached computation in ConstantMultipleCache for "
             << *S << " : Computed " << RecomputedMultiple
             << " but cache contains " << Multiple << "!\n";
      std::abort();
    }
  }
}
 
bool ScalarEvolution::invalidate(
    Function &F, const PreservedAnalyses &PA,
    FunctionAnalysisManager::Invalidator &Inv) {
  // Invalidate the ScalarEvolution object whenever it isn't preserved or one
  // of its dependencies is invalidated.
  auto PAC = PA.getChecker<ScalarEvolutionAnalysis>();
  return !(PAC.preserved() || PAC.preservedSet<AllAnalysesOn<Function>>()) ||
         Inv.invalidate<AssumptionAnalysis>(F, PA) ||
         Inv.invalidate<DominatorTreeAnalysis>(F, PA) ||
         Inv.invalidate<LoopAnalysis>(F, PA);
}
 
AnalysisKey ScalarEvolutionAnalysis::Key;
 
ScalarEvolution ScalarEvolutionAnalysis::run(Function &F,
                                             FunctionAnalysisManager &AM) {
  auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
  auto &AC = AM.getResult<AssumptionAnalysis>(F);
  auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
  auto &LI = AM.getResult<LoopAnalysis>(F);
  return ScalarEvolution(F, TLI, AC, DT, LI);
}
 
PreservedAnalyses
ScalarEvolutionVerifierPass::run(Function &F, FunctionAnalysisManager &AM) {
  AM.getResult<ScalarEvolutionAnalysis>(F).verify();
  return PreservedAnalyses::all();
}
 
PreservedAnalyses
ScalarEvolutionPrinterPass::run(Function &F, FunctionAnalysisManager &AM) {
  // For compatibility with opt's -analyze feature under legacy pass manager
  // which was not ported to NPM. This keeps tests using
  // update_analyze_test_checks.py working.
  OS << "Printing analysis 'Scalar Evolution Analysis' for function '"
     << F.getName() << "':\n";
  AM.getResult<ScalarEvolutionAnalysis>(F).print(OS);
  return PreservedAnalyses::all();
}
 
INITIALIZE_PASS_BEGIN(ScalarEvolutionWrapperPass, "scalar-evolution",
                      "Scalar Evolution Analysis", false, true)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
INITIALIZE_PASS_END(ScalarEvolutionWrapperPass, "scalar-evolution",
                    "Scalar Evolution Analysis", false, true)
 
char ScalarEvolutionWrapperPass::ID = 0;
 
ScalarEvolutionWrapperPass::ScalarEvolutionWrapperPass() : FunctionPass(ID) {}
 
bool ScalarEvolutionWrapperPass::runOnFunction(Function &F) {
  SE.reset(new ScalarEvolution(
      F, getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F),
      getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F),
      getAnalysis<DominatorTreeWrapperPass>().getDomTree(),
      getAnalysis<LoopInfoWrapperPass>().getLoopInfo()));
  return false;
}
 
void ScalarEvolutionWrapperPass::releaseMemory() { SE.reset(); }
 
void ScalarEvolutionWrapperPass::print(raw_ostream &OS, const Module *) const {
  SE->print(OS);
}
 
void ScalarEvolutionWrapperPass::verifyAnalysis() const {
  if (!VerifySCEV)
    return;
 
  SE->verify();
}
 
void ScalarEvolutionWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
  AU.setPreservesAll();
  AU.addRequiredTransitive<AssumptionCacheTracker>();
  AU.addRequiredTransitive<LoopInfoWrapperPass>();
  AU.addRequiredTransitive<DominatorTreeWrapperPass>();
  AU.addRequiredTransitive<TargetLibraryInfoWrapperPass>();
}
 
const SCEVPredicate *ScalarEvolution::getEqualPredicate(const SCEV *LHS,
                                                        const SCEV *RHS) {
  return getComparePredicate(ICmpInst::ICMP_EQ, LHS, RHS);
}
 
const SCEVPredicate *
ScalarEvolution::getComparePredicate(const ICmpInst::Predicate Pred,
                                     const SCEV *LHS, const SCEV *RHS) {
  FoldingSetNodeID ID;
  assert(LHS->getType() == RHS->getType() &&
         "Type mismatch between LHS and RHS");
  // Unique this node based on the arguments
  ID.AddInteger(SCEVPredicate::P_Compare);
  ID.AddInteger(Pred);
  ID.AddPointer(LHS);
  ID.AddPointer(RHS);
  FoldingSetInsertToken Token;
  if (const auto *S = UniquePreds.lookup(ID, Token))
    return S;
  SCEVComparePredicate *Eq = new (SCEVAllocator)
    SCEVComparePredicate(ID.Intern(SCEVAllocator), Pred, LHS, RHS);
  UniquePreds.insert(Eq, Token);
  return Eq;
}
 
const SCEVPredicate *ScalarEvolution::getWrapPredicate(
    const SCEVAddRecExpr *AR,
    SCEVWrapPredicate::IncrementWrapFlags AddedFlags) {
  FoldingSetNodeID ID;
  // Unique this node based on the arguments
  ID.AddInteger(SCEVPredicate::P_Wrap);
  ID.AddPointer(AR);
  ID.AddInteger(AddedFlags);
  FoldingSetInsertToken Token;
  if (const auto *S = UniquePreds.lookup(ID, Token))
    return S;
  auto *OF = new (SCEVAllocator)
      SCEVWrapPredicate(ID.Intern(SCEVAllocator), AR, AddedFlags);
  UniquePreds.insert(OF, Token);
  return OF;
}
 
namespace {
 
class SCEVPredicateRewriter : public SCEVRewriteVisitor<SCEVPredicateRewriter> {
public:
 
  /// Rewrites \p S in the context of a loop L and the SCEV predication
  /// infrastructure.
  ///
  /// If \p Pred is non-null, the SCEV expression is rewritten to respect the
  /// equivalences present in \p Pred.
  ///
  /// If \p NewPreds is non-null, rewrite is free to add further predicates to
  /// \p NewPreds such that the result will be an AddRecExpr.
  static const SCEV *rewrite(const SCEV *S, const Loop *L, ScalarEvolution &SE,
                             SmallVectorImpl<const SCEVPredicate *> *NewPreds,
                             const SCEVPredicate *Pred) {
    SCEVPredicateRewriter Rewriter(L, SE, NewPreds, Pred);
    return Rewriter.visit(S);
  }
 
  const SCEV *visitUnknown(const SCEVUnknown *Expr) {
    if (Pred) {
      if (auto *U = dyn_cast<SCEVUnionPredicate>(Pred)) {
        for (const auto *Pred : U->getPredicates())
          if (const auto *IPred = dyn_cast<SCEVComparePredicate>(Pred))
            if (IPred->getLHS() == Expr &&
                IPred->getPredicate() == ICmpInst::ICMP_EQ)
              return IPred->getRHS();
      } else if (const auto *IPred = dyn_cast<SCEVComparePredicate>(Pred)) {
        if (IPred->getLHS() == Expr &&
            IPred->getPredicate() == ICmpInst::ICMP_EQ)
          return IPred->getRHS();
      }
    }
    return convertToAddRecWithPreds(Expr);
  }
 
  const SCEV *visitZeroExtendExpr(const SCEVZeroExtendExpr *Expr) {
    const SCEV *Operand = visit(Expr->getOperand());
    const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(Operand);
    if (AR && AR->getLoop() == L && AR->isAffine()) {
      // This couldn't be folded because the operand didn't have the nuw
      // flag. Add the nusw flag as an assumption that we could make.
      const SCEV *Step = AR->getStepRecurrence(SE);
      Type *Ty = Expr->getType();
      if (addOverflowAssumption(AR, SCEVWrapPredicate::IncrementNUSW))
        return SE.getAddRecExpr(SE.getZeroExtendExpr(AR->getStart(), Ty),
                                SE.getSignExtendExpr(Step, Ty), L,
                                AR->getNoWrapFlags());
    }
    return SE.getZeroExtendExpr(Operand, Expr->getType());
  }
 
  const SCEV *visitSignExtendExpr(const SCEVSignExtendExpr *Expr) {
    const SCEV *Operand = visit(Expr->getOperand());
    const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(Operand);
    if (AR && AR->getLoop() == L && AR->isAffine()) {
      // This couldn't be folded because the operand didn't have the nsw
      // flag. Add the nssw flag as an assumption that we could make.
      const SCEV *Step = AR->getStepRecurrence(SE);
      Type *Ty = Expr->getType();
      if (addOverflowAssumption(AR, SCEVWrapPredicate::IncrementNSSW))
        return SE.getAddRecExpr(SE.getSignExtendExpr(AR->getStart(), Ty),
                                SE.getSignExtendExpr(Step, Ty), L,
                                AR->getNoWrapFlags());
    }
    return SE.getSignExtendExpr(Operand, Expr->getType());
  }
 
private:
  explicit SCEVPredicateRewriter(
      const Loop *L, ScalarEvolution &SE,
      SmallVectorImpl<const SCEVPredicate *> *NewPreds,
      const SCEVPredicate *Pred)
      : SCEVRewriteVisitor(SE), NewPreds(NewPreds), Pred(Pred), L(L) {}
 
  bool addOverflowAssumption(const SCEVPredicate *P) {
    if (!NewPreds) {
      // Check if we've already made this assumption.
      return Pred && Pred->implies(P, SE);
    }
    NewPreds->push_back(P);
    return true;
  }
 
  bool addOverflowAssumption(const SCEVAddRecExpr *AR,
                             SCEVWrapPredicate::IncrementWrapFlags AddedFlags) {
    auto *A = SE.getWrapPredicate(AR, AddedFlags);
    return addOverflowAssumption(A);
  }
 
  // If \p Expr represents a PHINode, we try to see if it can be represented
  // as an AddRec, possibly under a predicate (PHISCEVPred). If it is possible
  // to add this predicate as a runtime overflow check, we return the AddRec.
  // If \p Expr does not meet these conditions (is not a PHI node, or we
  // couldn't create an AddRec for it, or couldn't add the predicate), we just
  // return \p Expr.
  const SCEV *convertToAddRecWithPreds(const SCEVUnknown *Expr) {
    if (!isa<PHINode>(Expr->getValue()))
      return Expr;
    std::optional<
        std::pair<const SCEV *, SmallVector<const SCEVPredicate *, 3>>>
        PredicatedRewrite = SE.createAddRecFromPHIWithCasts(Expr);
    if (!PredicatedRewrite)
      return Expr;
    for (const auto *P : PredicatedRewrite->second){
      // Wrap predicates from outer loops are not supported.
      if (auto *WP = dyn_cast<const SCEVWrapPredicate>(P)) {
        if (L != WP->getExpr()->getLoop())
          return Expr;
      }
      if (!addOverflowAssumption(P))
        return Expr;
    }
    return PredicatedRewrite->first;
  }
 
  SmallVectorImpl<const SCEVPredicate *> *NewPreds;
  const SCEVPredicate *Pred;
  const Loop *L;
};
 
} // end anonymous namespace
 
const SCEV *
ScalarEvolution::rewriteUsingPredicate(const SCEV *S, const Loop *L,
                                       const SCEVPredicate &Preds) {
  return SCEVPredicateRewriter::rewrite(S, L, *this, nullptr, &Preds);
}
 
const SCEVAddRecExpr *ScalarEvolution::convertSCEVToAddRecWithPredicates(
    const SCEV *S, const Loop *L,
    SmallVectorImpl<const SCEVPredicate *> &Preds) {
  SmallVector<const SCEVPredicate *> TransformPreds;
  S = SCEVPredicateRewriter::rewrite(S, L, *this, &TransformPreds, nullptr);
  auto *AddRec = dyn_cast<SCEVAddRecExpr>(S);
 
  if (!AddRec)
    return nullptr;
 
  // Check if any of the transformed predicates is known to be false. In that
  // case, it doesn't make sense to convert to a predicated AddRec, as the
  // versioned loop will never execute.
  for (const SCEVPredicate *Pred : TransformPreds) {
    auto *WrapPred = dyn_cast<SCEVWrapPredicate>(Pred);
    if (!WrapPred || WrapPred->getFlags() != SCEVWrapPredicate::IncrementNSSW)
      continue;
 
    const SCEVAddRecExpr *AddRecToCheck = WrapPred->getExpr();
    const SCEV *ExitCount = getBackedgeTakenCount(AddRecToCheck->getLoop());
    if (isa<SCEVCouldNotCompute>(ExitCount))
      continue;
 
    const SCEV *Step = AddRecToCheck->getStepRecurrence(*this);
    if (!Step->isOne())
      continue;
 
    ExitCount = getTruncateOrSignExtend(ExitCount, Step->getType());
    const SCEV *Add = getAddExpr(AddRecToCheck->getStart(), ExitCount);
    if (isKnownPredicate(CmpInst::ICMP_SLT, Add, AddRecToCheck->getStart()))
      return nullptr;
  }
 
  // Since the transformation was successful, we can now transfer the SCEV
  // predicates.
  Preds.append(TransformPreds.begin(), TransformPreds.end());
 
  return AddRec;
}
 
/// SCEV predicates
SCEVPredicate::SCEVPredicate(const FoldingSetNodeIDRef ID,
                             SCEVPredicateKind Kind)
    : FastID(ID), Kind(Kind) {}
 
SCEVComparePredicate::SCEVComparePredicate(const FoldingSetNodeIDRef ID,
                                   const ICmpInst::Predicate Pred,
                                   const SCEV *LHS, const SCEV *RHS)
  : SCEVPredicate(ID, P_Compare), Pred(Pred), LHS(LHS), RHS(RHS) {
  assert(LHS->getType() == RHS->getType() && "LHS and RHS types don't match");
  assert(LHS != RHS && "LHS and RHS are the same SCEV");
}
 
bool SCEVComparePredicate::implies(const SCEVPredicate *N,
                                   ScalarEvolution &SE) const {
  const auto *Op = dyn_cast<SCEVComparePredicate>(N);
 
  if (!Op)
    return false;
 
  if (Pred != ICmpInst::ICMP_EQ)
    return false;
 
  return Op->LHS == LHS && Op->RHS == RHS;
}
 
bool SCEVComparePredicate::isAlwaysTrue() const { return false; }
 
void SCEVComparePredicate::print(raw_ostream &OS, unsigned Depth) const {
  if (Pred == ICmpInst::ICMP_EQ)
    OS.indent(Depth) << "Equal predicate: " << *LHS << " == " << *RHS << "\n";
  else
    OS.indent(Depth) << "Compare predicate: " << *LHS << " " << Pred << ") "
                     << *RHS << "\n";
 
}
 
SCEVWrapPredicate::SCEVWrapPredicate(const FoldingSetNodeIDRef ID,
                                     const SCEVAddRecExpr *AR,
                                     IncrementWrapFlags Flags)
    : SCEVPredicate(ID, P_Wrap), AR(AR), Flags(Flags) {}
 
const SCEVAddRecExpr *SCEVWrapPredicate::getExpr() const { return AR; }
 
bool SCEVWrapPredicate::implies(const SCEVPredicate *N,
                                ScalarEvolution &SE) const {
  const auto *Op = dyn_cast<SCEVWrapPredicate>(N);
  if (!Op || setFlags(Flags, Op->Flags) != Flags)
    return false;
 
  if (Op->AR == AR)
    return true;
 
  if (Flags != SCEVWrapPredicate::IncrementNSSW &&
      Flags != SCEVWrapPredicate::IncrementNUSW)
    return false;
 
  const SCEV *Start = AR->getStart();
  const SCEV *OpStart = Op->AR->getStart();
  if (Start->getType()->isPointerTy() != OpStart->getType()->isPointerTy())
    return false;
 
  // Reject pointers to different address spaces.
  if (Start->getType()->isPointerTy() && Start->getType() != OpStart->getType())
    return false;
 
  // NUSW/NSSW on a wider-type AddRec does not imply the same on a
  // narrower-type AddRec.
  if (SE.getTypeSizeInBits(AR->getType()) >
      SE.getTypeSizeInBits(Op->AR->getType()))
    return false;
 
  const SCEV *Step = AR->getStepRecurrence(SE);
  const SCEV *OpStep = Op->AR->getStepRecurrence(SE);
  if (!SE.isKnownPositive(Step) || !SE.isKnownPositive(OpStep))
    return false;
 
  // If both steps are positive, this implies N, if N's start and step are
  // ULE/SLE (for NSUW/NSSW) than this'.
  Type *WiderTy = SE.getWiderType(Step->getType(), OpStep->getType());
  Step = SE.getNoopOrZeroExtend(Step, WiderTy);
  OpStep = SE.getNoopOrZeroExtend(OpStep, WiderTy);
 
  bool IsNUW = Flags == SCEVWrapPredicate::IncrementNUSW;
  OpStart = IsNUW ? SE.getNoopOrZeroExtend(OpStart, WiderTy)
                  : SE.getNoopOrSignExtend(OpStart, WiderTy);
  Start = IsNUW ? SE.getNoopOrZeroExtend(Start, WiderTy)
                : SE.getNoopOrSignExtend(Start, WiderTy);
  CmpInst::Predicate Pred = IsNUW ? CmpInst::ICMP_ULE : CmpInst::ICMP_SLE;
  return SE.isKnownPredicate(Pred, OpStep, Step) &&
         SE.isKnownPredicate(Pred, OpStart, Start);
}
 
bool SCEVWrapPredicate::isAlwaysTrue() const {
  SCEVFlags ScevFlags = AR->getNoWrapFlags();
  IncrementWrapFlags IFlags = Flags;
 
  if (ScalarEvolution::setFlags(ScevFlags, SCEV::FlagNSW) == ScevFlags)
    IFlags = clearFlags(IFlags, IncrementNSSW);
 
  return IFlags == IncrementAnyWrap;
}
 
void SCEVWrapPredicate::print(raw_ostream &OS, unsigned Depth) const {
  OS.indent(Depth) << *getExpr() << " Added Flags: ";
  if (SCEVWrapPredicate::IncrementNUSW & getFlags())
    OS << "<nusw>";
  if (SCEVWrapPredicate::IncrementNSSW & getFlags())
    OS << "<nssw>";
  OS << "\n";
}
 
/// Union predicates don't get cached so create a dummy set ID for it.
SCEVUnionPredicate::SCEVUnionPredicate(ArrayRef<const SCEVPredicate *> Preds,
                                       ScalarEvolution &SE)
    : SCEVPredicate(FoldingSetNodeIDRef(), P_Union) {
  for (const auto *P : Preds)
    add(P, SE);
}
 
bool SCEVUnionPredicate::isAlwaysTrue() const {
  return all_of(Preds,
                [](const SCEVPredicate *I) { return I->isAlwaysTrue(); });
}
 
bool SCEVUnionPredicate::implies(const SCEVPredicate *N,
                                 ScalarEvolution &SE) const {
  if (const auto *Set = dyn_cast<SCEVUnionPredicate>(N))
    return all_of(Set->Preds, [this, &SE](const SCEVPredicate *I) {
      return this->implies(I, SE);
    });
 
  if (any_of(Preds,
             [N, &SE](const SCEVPredicate *I) { return I->implies(N, SE); }))
    return true;
 
  // A wrap predicate may be implied by a wrap predicate in Preds after applying
  // equal predicates.
  const auto *NWrap = dyn_cast<SCEVWrapPredicate>(N);
  if (!NWrap)
    return false;
  const Loop *L = NWrap->getExpr()->getLoop();
  return any_of(Preds, [&](const SCEVPredicate *I) {
    const auto *IWrap = dyn_cast<SCEVWrapPredicate>(I);
    if (!IWrap)
      return false;
    const auto *RewrittenAR = dyn_cast<SCEVAddRecExpr>(
        SE.rewriteUsingPredicate(IWrap->getExpr(), L, *this));
    return RewrittenAR &&
           SE.getWrapPredicate(RewrittenAR, IWrap->getFlags())->implies(N, SE);
  });
}
 
void SCEVUnionPredicate::print(raw_ostream &OS, unsigned Depth) const {
  for (const auto *Pred : Preds)
    Pred->print(OS, Depth);
}
 
void SCEVUnionPredicate::add(const SCEVPredicate *N, ScalarEvolution &SE) {
  if (const auto *Set = dyn_cast<SCEVUnionPredicate>(N)) {
    for (const auto *Pred : Set->Preds)
      add(Pred, SE);
    return;
  }
 
  // Implication checks are quadratic in the number of predicates. Stop doing
  // them if there are many predicates, as they should be too expensive to use
  // anyway at that point.
  bool CheckImplies = Preds.size() < 16;
 
  // Only add predicate if it is not already implied by this union predicate.
  if (CheckImplies && implies(N, SE))
    return;
 
  // Build a new vector containing the current predicates, except the ones that
  // are implied by the new predicate N.
  SmallVector<const SCEVPredicate *> PrunedPreds;
  for (auto *P : Preds) {
    if (CheckImplies && N->implies(P, SE))
      continue;
    PrunedPreds.push_back(P);
  }
  Preds = std::move(PrunedPreds);
  Preds.push_back(N);
}
 
PredicatedScalarEvolution::PredicatedScalarEvolution(ScalarEvolution &SE,
                                                     Loop &L)
    : SE(SE), L(L) {
  SmallVector<const SCEVPredicate*, 4> Empty;
  Preds = std::make_unique<SCEVUnionPredicate>(Empty, SE);
}
 
void ScalarEvolution::registerUser(const SCEV *User, ArrayRef<SCEVUse> Ops) {
  for (const SCEV *Op : Ops)
    // We do not expect that forgetting cached data for SCEVConstants will ever
    // open any prospects for sharpening or introduce any correctness issues,
    // so we don't bother storing their dependencies.
    if (!isa<SCEVConstant>(Op))
      SCEVUsers[Op].insert(User);
}
 
const SCEV *PredicatedScalarEvolution::getSCEV(Value *V) {
  const SCEV *Expr = SE.getSCEV(V);
  return getPredicatedSCEV(Expr);
}
 
const SCEV *PredicatedScalarEvolution::getPredicatedSCEV(const SCEV *Expr) {
  RewriteEntry &Entry = RewriteMap[Expr];
 
  // If we already have an entry and the version matches, return it.
  if (Entry.second && Generation == Entry.first)
    return Entry.second;
 
  // We found an entry but it's stale. Rewrite the stale entry
  // according to the current predicate.
  if (Entry.second)
    Expr = Entry.second;
 
  const SCEV *NewSCEV = SE.rewriteUsingPredicate(Expr, &L, *Preds);
  Entry = {Generation, NewSCEV};
 
  return NewSCEV;
}
 
const SCEV *PredicatedScalarEvolution::getBackedgeTakenCount() {
  if (!BackedgeCount) {
    SmallVector<const SCEVPredicate *, 4> Preds;
    BackedgeCount = SE.getPredicatedBackedgeTakenCount(&L, Preds);
    for (const auto *P : Preds)
      addPredicate(*P);
  }
  return BackedgeCount;
}
 
const SCEV *PredicatedScalarEvolution::getSymbolicMaxBackedgeTakenCount() {
  if (!SymbolicMaxBackedgeCount) {
    SmallVector<const SCEVPredicate *, 4> Preds;
    SymbolicMaxBackedgeCount =
        SE.getPredicatedSymbolicMaxBackedgeTakenCount(&L, Preds);
    for (const auto *P : Preds)
      addPredicate(*P);
  }
  return SymbolicMaxBackedgeCount;
}
 
unsigned PredicatedScalarEvolution::getSmallConstantMaxTripCount() {
  if (!SmallConstantMaxTripCount) {
    SmallVector<const SCEVPredicate *, 4> Preds;
    SmallConstantMaxTripCount = SE.getSmallConstantMaxTripCount(&L, &Preds);
    for (const auto *P : Preds)
      addPredicate(*P);
  }
  return *SmallConstantMaxTripCount;
}
 
void PredicatedScalarEvolution::addPredicate(const SCEVPredicate &Pred) {
  if (Preds->implies(&Pred, SE))
    return;
 
  Preds = std::make_unique<SCEVUnionPredicate>(Preds->getUnionWith(&Pred, SE));
  updateGeneration();
}
 
void PredicatedScalarEvolution::addPredicates(
    ArrayRef<const SCEVPredicate *> Preds) {
  for (const SCEVPredicate *P : Preds)
    addPredicate(*P);
}
 
const SCEVPredicate &PredicatedScalarEvolution::getPredicate() const {
  return *Preds;
}
 
void PredicatedScalarEvolution::updateGeneration() {
  // If the generation number wrapped recompute everything.
  if (++Generation == 0) {
    for (auto &II : RewriteMap) {
      const SCEV *Rewritten = II.second.second;
      II.second = {Generation, SE.rewriteUsingPredicate(Rewritten, &L, *Preds)};
    }
  }
}
 
const SCEVAddRecExpr *PredicatedScalarEvolution::getAsAddRec(
    Value *V, SmallVectorImpl<const SCEVPredicate *> *ExtraPreds) {
  const SCEV *Expr = this->getSCEV(V);
  SmallVector<const SCEVPredicate *, 4> NewPreds;
  auto *New = SE.convertSCEVToAddRecWithPredicates(Expr, &L, NewPreds);
 
  if (!New)
    return nullptr;
 
  if (ExtraPreds) {
    ExtraPreds->append(NewPreds);
    return New;
  }
 
  addPredicates(NewPreds);
 
  RewriteMap[SE.getSCEV(V)] = {Generation, New};
  return New;
}
 
PredicatedScalarEvolution::PredicatedScalarEvolution(
    const PredicatedScalarEvolution &Init)
    : RewriteMap(Init.RewriteMap), SE(Init.SE), L(Init.L),
      Preds(std::make_unique<SCEVUnionPredicate>(*Init.Preds)),
      Generation(Init.Generation), BackedgeCount(Init.BackedgeCount) {}
 
void PredicatedScalarEvolution::print(raw_ostream &OS, unsigned Depth) const {
  // For each block.
  for (auto *BB : L.getBlocks())
    for (auto &I : *BB) {
      if (!SE.isSCEVable(I.getType()))
        continue;
 
      auto *Expr = SE.getSCEV(&I);
      auto II = RewriteMap.find(Expr);
 
      if (II == RewriteMap.end())
        continue;
 
      // Don't print things that are not interesting.
      if (II->second.second == Expr)
        continue;
 
      OS.indent(Depth) << "[PSE]" << I << ":\n";
      OS.indent(Depth + 2) << *Expr << "\n";
      OS.indent(Depth + 2) << "--> " << *II->second.second << "\n";
    }
}
 
void ScalarEvolution::LoopGuards::collectPending() {
  const Loop *L = PendingLoop;
  if (!L)
    return;
  PendingLoop = nullptr;
  BasicBlock *Pred = L->getLoopPredecessor();
  if (!Pred)
    return;
  SmallPtrSet<const BasicBlock *, 8> VisitedBlocks;
  collectFromBlock(SE, *this, L->getHeader(), Pred, VisitedBlocks);
}
 
void ScalarEvolution::LoopGuards::collectFromPHI(
    ScalarEvolution &SE, ScalarEvolution::LoopGuards &Guards,
    const PHINode &Phi, SmallPtrSetImpl<const BasicBlock *> &VisitedBlocks,
    SmallDenseMap<const BasicBlock *, LoopGuards> &IncomingGuards,
    unsigned Depth) {
  if (!SE.isSCEVable(Phi.getType()))
    return;
 
  using MinMaxPattern = std::pair<const SCEVConstant *, SCEVTypes>;
  auto GetMinMaxConst = [&](unsigned IncomingIdx) -> MinMaxPattern {
    const BasicBlock *InBlock = Phi.getIncomingBlock(IncomingIdx);
    if (!VisitedBlocks.insert(InBlock).second)
      return {nullptr, scCouldNotCompute};
 
    // Avoid analyzing unreachable blocks so that we don't get trapped
    // traversing cycles with ill-formed dominance or infinite cycles
    if (!SE.DT.isReachableFromEntry(InBlock))
      return {nullptr, scCouldNotCompute};
 
    auto [G, Inserted] = IncomingGuards.try_emplace(InBlock, LoopGuards(SE));
    if (Inserted)
      collectFromBlock(SE, G->second, Phi.getParent(), InBlock, VisitedBlocks,
                       Depth + 1);
    auto &RewriteMap = G->second.RewriteMap;
    if (RewriteMap.empty())
      return {nullptr, scCouldNotCompute};
    auto S = RewriteMap.find(SE.getSCEV(Phi.getIncomingValue(IncomingIdx)));
    if (S == RewriteMap.end())
      return {nullptr, scCouldNotCompute};
    auto *SM = dyn_cast_if_present<SCEVMinMaxExpr>(S->second);
    if (!SM)
      return {nullptr, scCouldNotCompute};
    if (const SCEVConstant *C0 = dyn_cast<SCEVConstant>(SM->getOperand(0)))
      return {C0, SM->getSCEVType()};
    return {nullptr, scCouldNotCompute};
  };
  auto MergeMinMaxConst = [](MinMaxPattern P1,
                             MinMaxPattern P2) -> MinMaxPattern {
    auto [C1, T1] = P1;
    auto [C2, T2] = P2;
    if (!C1 || !C2 || T1 != T2)
      return {nullptr, scCouldNotCompute};
    switch (T1) {
    case scUMaxExpr:
      return {C1->getAPInt().ult(C2->getAPInt()) ? C1 : C2, T1};
    case scSMaxExpr:
      return {C1->getAPInt().slt(C2->getAPInt()) ? C1 : C2, T1};
    case scUMinExpr:
      return {C1->getAPInt().ugt(C2->getAPInt()) ? C1 : C2, T1};
    case scSMinExpr:
      return {C1->getAPInt().sgt(C2->getAPInt()) ? C1 : C2, T1};
    default:
      llvm_unreachable("Trying to merge non-MinMaxExpr SCEVs.");
    }
  };
  auto P = GetMinMaxConst(0);
  for (unsigned int In = 1; In < Phi.getNumIncomingValues(); In++) {
    if (!P.first)
      break;
    P = MergeMinMaxConst(P, GetMinMaxConst(In));
  }
  if (P.first) {
    const SCEV *LHS = SE.getSCEV(const_cast<PHINode *>(&Phi));
    SmallVector<SCEVUse, 2> Ops({P.first, LHS});
    const SCEV *RHS = SE.getMinMaxExpr(P.second, Ops);
    Guards.RewriteMap.insert({LHS, RHS});
  }
}
 
// Return a new SCEV that modifies \p Expr to the closest number divides by
// \p Divisor and less or equal than Expr. For now, only handle constant
// Expr.
static const SCEV *getPreviousSCEVDivisibleByDivisor(const SCEV *Expr,
                                                     const APInt &DivisorVal,
                                                     ScalarEvolution &SE) {
  const APInt *ExprVal;
  if (!match(Expr, m_scev_APInt(ExprVal)) || ExprVal->isNegative() ||
      DivisorVal.isNonPositive())
    return Expr;
  APInt Rem = ExprVal->urem(DivisorVal);
  // return the SCEV: Expr - Expr % Divisor
  return SE.getConstant(*ExprVal - Rem);
}
 
// Return a new SCEV that modifies \p Expr to the closest number divides by
// \p Divisor and greater or equal than Expr. For now, only handle constant
// Expr.
static const SCEV *getNextSCEVDivisibleByDivisor(const SCEV *Expr,
                                                 const APInt &DivisorVal,
                                                 ScalarEvolution &SE) {
  const APInt *ExprVal;
  if (!match(Expr, m_scev_APInt(ExprVal)) || ExprVal->isNegative() ||
      DivisorVal.isNonPositive())
    return Expr;
  APInt Rem = ExprVal->urem(DivisorVal);
  if (Rem.isZero())
    return Expr;
  // return the SCEV: Expr + Divisor - Expr % Divisor
  return SE.getConstant(*ExprVal + DivisorVal - Rem);
}
 
static bool collectDivisibilityInformation(
    ICmpInst::Predicate Predicate, const SCEV *LHS, const SCEV *RHS,
    DenseMap<const SCEV *, const SCEV *> &DivInfo,
    DenseMap<const SCEV *, APInt> &Multiples, ScalarEvolution &SE) {
  // If we have LHS == 0, check if LHS is computing a property of some unknown
  // SCEV %v which we can rewrite %v to express explicitly.
  if (Predicate != CmpInst::ICMP_EQ || !match(RHS, m_scev_Zero()))
    return false;
  // If LHS is A % B, i.e. A % B == 0, rewrite A to (A /u B) * B to
  // explicitly express that.
  const SCEVUnknown *URemLHS = nullptr;
  const SCEV *URemRHS = nullptr;
  if (!match(LHS, m_scev_URem(m_SCEVUnknown(URemLHS), m_SCEV(URemRHS), SE)))
    return false;
 
  const SCEV *Multiple =
      SE.getMulExpr(SE.getUDivExpr(URemLHS, URemRHS), URemRHS);
  DivInfo[URemLHS] = Multiple;
  if (auto *C = dyn_cast<SCEVConstant>(URemRHS))
    Multiples[URemLHS] = C->getAPInt();
  return true;
}
 
// Check if the condition is a divisibility guard (A % B == 0).
static bool isDivisibilityGuard(const SCEV *LHS, const SCEV *RHS,
                                ScalarEvolution &SE) {
  const SCEV *X, *Y;
  return match(LHS, m_scev_URem(m_SCEV(X), m_SCEV(Y), SE)) && RHS->isZero();
}
 
// Apply divisibility by \p Divisor on MinMaxExpr with constant values,
// recursively. This is done by aligning up/down the constant value to the
// Divisor.
static const SCEV *applyDivisibilityOnMinMaxExpr(const SCEV *MinMaxExpr,
                                                 APInt Divisor,
                                                 ScalarEvolution &SE) {
  // Return true if \p Expr is a MinMax SCEV expression with a non-negative
  // constant operand. If so, return in \p SCTy the SCEV type and in \p RHS
  // the non-constant operand and in \p LHS the constant operand.
  auto IsMinMaxSCEVWithNonNegativeConstant =
      [&](const SCEV *Expr, SCEVTypes &SCTy, const SCEV *&LHS,
          const SCEV *&RHS) {
        if (auto *MinMax = dyn_cast<SCEVMinMaxExpr>(Expr)) {
          if (MinMax->getNumOperands() != 2)
            return false;
          if (auto *C = dyn_cast<SCEVConstant>(MinMax->getOperand(0))) {
            if (C->getAPInt().isNegative())
              return false;
            SCTy = MinMax->getSCEVType();
            LHS = MinMax->getOperand(0);
            RHS = MinMax->getOperand(1);
            return true;
          }
        }
        return false;
      };
 
  const SCEV *MinMaxLHS = nullptr, *MinMaxRHS = nullptr;
  SCEVTypes SCTy;
  if (!IsMinMaxSCEVWithNonNegativeConstant(MinMaxExpr, SCTy, MinMaxLHS,
                                           MinMaxRHS))
    return MinMaxExpr;
  auto IsMin = isa<SCEVSMinExpr>(MinMaxExpr) || isa<SCEVUMinExpr>(MinMaxExpr);
  assert(SE.isKnownNonNegative(MinMaxLHS) && "Expected non-negative operand!");
  auto *DivisibleExpr =
      IsMin ? getPreviousSCEVDivisibleByDivisor(MinMaxLHS, Divisor, SE)
            : getNextSCEVDivisibleByDivisor(MinMaxLHS, Divisor, SE);
  SmallVector<SCEVUse> Ops = {
      applyDivisibilityOnMinMaxExpr(MinMaxRHS, Divisor, SE), DivisibleExpr};
  return SE.getMinMaxExpr(SCTy, Ops);
}
 
void ScalarEvolution::LoopGuards::collectFromBlock(
    ScalarEvolution &SE, ScalarEvolution::LoopGuards &Guards,
    const BasicBlock *Block, const BasicBlock *Pred,
    SmallPtrSetImpl<const BasicBlock *> &VisitedBlocks, unsigned Depth) {
 
  assert(SE.DT.isReachableFromEntry(Block) && SE.DT.isReachableFromEntry(Pred));
 
  SmallVector<SCEVUse> ExprsToRewrite;
  auto CollectCondition = [&](ICmpInst::Predicate Predicate, const SCEV *LHS,
                              const SCEV *RHS,
                              DenseMap<const SCEV *, const SCEV *> &RewriteMap,
                              const LoopGuards &DivGuards) {
    // WARNING: It is generally unsound to apply any wrap flags to the proposed
    // replacement SCEV which isn't directly implied by the structure of that
    // SCEV.  In particular, using contextual facts to imply flags is *NOT*
    // legal.  See the scoping rules for flags in the header to understand why.
 
    // Puts rewrite rule \p From -> \p To into the rewrite map. Also if \p From
    // and \p FromRewritten are the same (i.e. there has been no rewrite
    // registered for \p From), then puts this value in the list of rewritten
    // expressions.
    auto AddRewrite = [&](const SCEV *From, const SCEV *FromRewritten,
                          const SCEV *To) {
      if (From == FromRewritten)
        ExprsToRewrite.push_back(From);
      RewriteMap[From] = To;
    };
 
    // Checks whether \p S has already been rewritten. In that case returns the
    // existing rewrite because we want to chain further rewrites onto the
    // already rewritten value. Otherwise returns \p S.
    auto GetMaybeRewritten = [&](const SCEV *S) {
      return RewriteMap.lookup_or(S, S);
    };
 
    // Check for a condition of the form (-C1 + X < C2).  InstCombine will
    // create this form when combining two checks of the form (X u< C2 + C1) and
    // (X >=u C1).
    auto MatchRangeCheckIdiom = [&](ICmpInst::Predicate Pred,
                                    const SCEV *MatchLHS,
                                    const SCEV *MatchRHS) {
      const SCEVConstant *C1;
      const SCEVUnknown *LHSUnknown;
      auto *C2 = dyn_cast<SCEVConstant>(MatchRHS);
      if (!match(MatchLHS,
                 m_scev_Add(m_SCEVConstant(C1), m_SCEVUnknown(LHSUnknown))) ||
          !C2)
        return false;
 
      auto ExactRegion =
          ConstantRange::makeExactICmpRegion(Pred, C2->getAPInt())
              .sub(C1->getAPInt());
 
      // Tighten the raw range with what we already know about LHSUnknown
      // from prior guards recorded in RewriteMap, or from SCEV's own range
      // analysis.
      const SCEV *RewrittenLHS = GetMaybeRewritten(LHSUnknown);
      ExactRegion = ExactRegion.intersectWith(SE.getUnsignedRange(RewrittenLHS),
                                              ConstantRange::Unsigned);
 
      // Bail if the guard is inconsistent with prior facts, or if the range
      // is still not a monotonic non-wrapping interval after tightening.
      if (ExactRegion.isEmptySet() || ExactRegion.isWrappedSet() ||
          ExactRegion.isFullSet())
        return false;
 
      const SCEV *RegionMin = SE.getConstant(ExactRegion.getUnsignedMin());
      const SCEV *RegionMax = SE.getConstant(ExactRegion.getUnsignedMax());
      const SCEV *ClampedLHS =
          SE.getUMaxExpr(RegionMin, SE.getUMinExpr(RewrittenLHS, RegionMax));
      AddRewrite(LHSUnknown, RewrittenLHS, ClampedLHS);
      return true;
    };
    if (MatchRangeCheckIdiom(Predicate, LHS, RHS))
      return;
 
    // Do not apply information for constants or if RHS contains an AddRec.
    if (isa<SCEVConstant>(LHS) || SE.containsAddRecurrence(RHS))
      return;
 
    // If RHS is SCEVUnknown, make sure the information is applied to it.
    if (!isa<SCEVUnknown>(LHS) && isa<SCEVUnknown>(RHS)) {
      std::swap(LHS, RHS);
      Predicate = CmpInst::getSwappedPredicate(Predicate);
    }
 
    const SCEV *RewrittenLHS = GetMaybeRewritten(LHS);
    // Apply divisibility information when computing the constant multiple.
    const APInt &DividesBy =
        SE.getConstantMultiple(DivGuards.rewrite(RewrittenLHS));
 
    // Collect rewrites for LHS and its transitive operands based on the
    // condition.
    // For min/max expressions, also apply the guard to its operands:
    //  'min(a, b) >= c'   ->   '(a >= c) and (b >= c)',
    //  'min(a, b) >  c'   ->   '(a >  c) and (b >  c)',
    //  'max(a, b) <= c'   ->   '(a <= c) and (b <= c)',
    //  'max(a, b) <  c'   ->   '(a <  c) and (b <  c)'.
 
    // We cannot express strict predicates in SCEV, so instead we replace them
    // with non-strict ones against plus or minus one of RHS depending on the
    // predicate.
    const SCEV *One = SE.getOne(RHS->getType());
    switch (Predicate) {
    case CmpInst::ICMP_ULT:
      if (RHS->getType()->isPointerTy())
        return;
      RHS = SE.getUMaxExpr(RHS, One);
      [[fallthrough]];
    case CmpInst::ICMP_SLT: {
      RHS = SE.getMinusSCEV(RHS, One);
      RHS = getPreviousSCEVDivisibleByDivisor(RHS, DividesBy, SE);
      break;
    }
    case CmpInst::ICMP_UGT:
    case CmpInst::ICMP_SGT:
      RHS = SE.getAddExpr(RHS, One);
      RHS = getNextSCEVDivisibleByDivisor(RHS, DividesBy, SE);
      break;
    case CmpInst::ICMP_ULE:
    case CmpInst::ICMP_SLE:
      RHS = getPreviousSCEVDivisibleByDivisor(RHS, DividesBy, SE);
      break;
    case CmpInst::ICMP_UGE:
    case CmpInst::ICMP_SGE:
      RHS = getNextSCEVDivisibleByDivisor(RHS, DividesBy, SE);
      break;
    default:
      break;
    }
 
    SmallVector<SCEVUse, 16> Worklist(1, LHS);
    SmallPtrSet<const SCEV *, 16> Visited;
 
    auto EnqueueOperands = [&Worklist](const SCEVNAryExpr *S) {
      append_range(Worklist, S->operands());
    };
 
    while (!Worklist.empty()) {
      const SCEV *From = Worklist.pop_back_val();
      if (isa<SCEVConstant>(From))
        continue;
      if (!Visited.insert(From).second)
        continue;
      const SCEV *FromRewritten = GetMaybeRewritten(From);
      const SCEV *To = nullptr;
 
      switch (Predicate) {
      case CmpInst::ICMP_ULT:
      case CmpInst::ICMP_ULE:
        To = SE.getUMinExpr(FromRewritten, RHS);
        if (auto *UMax = dyn_cast<SCEVUMaxExpr>(FromRewritten))
          EnqueueOperands(UMax);
        break;
      case CmpInst::ICMP_SLT:
      case CmpInst::ICMP_SLE:
        To = SE.getSMinExpr(FromRewritten, RHS);
        if (auto *SMax = dyn_cast<SCEVSMaxExpr>(FromRewritten))
          EnqueueOperands(SMax);
        break;
      case CmpInst::ICMP_UGT:
      case CmpInst::ICMP_UGE:
        To = SE.getUMaxExpr(FromRewritten, RHS);
        if (auto *UMin = dyn_cast<SCEVUMinExpr>(FromRewritten))
          EnqueueOperands(UMin);
        break;
      case CmpInst::ICMP_SGT:
      case CmpInst::ICMP_SGE:
        To = SE.getSMaxExpr(FromRewritten, RHS);
        if (auto *SMin = dyn_cast<SCEVSMinExpr>(FromRewritten))
          EnqueueOperands(SMin);
        break;
      case CmpInst::ICMP_EQ:
        if (isa<SCEVConstant>(RHS))
          To = RHS;
        break;
      case CmpInst::ICMP_NE:
        if (match(RHS, m_scev_Zero())) {
          const SCEV *OneAlignedUp =
              getNextSCEVDivisibleByDivisor(One, DividesBy, SE);
          To = SE.getUMaxExpr(FromRewritten, OneAlignedUp);
        } else {
          // LHS != RHS can be rewritten as (LHS - RHS) = UMax(1, LHS - RHS),
          // but creating the subtraction eagerly is expensive. Track the
          // inequalities in a separate map, and materialize the rewrite lazily
          // when encountering a suitable subtraction while re-writing.
          if (LHS->getType()->isPointerTy()) {
            LHS = SE.getPtrToAddrExpr(LHS);
            RHS = SE.getPtrToAddrExpr(RHS);
            if (isa<SCEVCouldNotCompute>(LHS) || isa<SCEVCouldNotCompute>(RHS))
              break;
          }
          const SCEVConstant *C;
          const SCEV *A, *B;
          if (match(RHS, m_scev_Add(m_SCEVConstant(C), m_SCEV(A))) &&
              match(LHS, m_scev_Add(m_scev_Specific(C), m_SCEV(B)))) {
            RHS = A;
            LHS = B;
          }
          if (LHS > RHS)
            std::swap(LHS, RHS);
          Guards.NotEqual.insert({LHS, RHS});
          continue;
        }
        break;
      default:
        break;
      }
 
      if (To)
        AddRewrite(From, FromRewritten, To);
    }
  };
 
  SmallVector<PointerIntPair<Value *, 1, bool>> Terms;
  // First, collect information from assumptions dominating the loop.
  for (auto &AssumeVH : SE.AC.assumptions()) {
    if (!AssumeVH)
      continue;
    auto *AssumeI = cast<CallInst>(AssumeVH);
    if (!SE.DT.dominates(AssumeI, Block))
      continue;
    Terms.emplace_back(AssumeI->getOperand(0), true);
  }
 
  // Second, collect information from llvm.experimental.guards dominating the loop.
  auto *GuardDecl = Intrinsic::getDeclarationIfExists(
      SE.F.getParent(), Intrinsic::experimental_guard);
  if (GuardDecl)
    for (const auto *GU : GuardDecl->users())
      if (const auto *Guard = dyn_cast<IntrinsicInst>(GU))
        if (Guard->getFunction() == Block->getParent() &&
            SE.DT.dominates(Guard, Block))
          Terms.emplace_back(Guard->getArgOperand(0), true);
 
  // Third, collect conditions from dominating branches. Starting at the loop
  // predecessor, climb up the predecessor chain, as long as there are
  // predecessors that can be found that have unique successors leading to the
  // original header. If there is no such predecessor, continue at the
  // immediate dominator.
  // TODO: share this logic with isLoopEntryGuardedByCond.
  unsigned NumCollectedConditions = 0;
  unsigned NumDomTreeSteps = 0;
  VisitedBlocks.insert(Block);
  std::pair<const BasicBlock *, const BasicBlock *> Pair(Pred, Block);
  for (;; Pair = SE.getPredecessorWithUniqueSuccessorForBB(Pair.first)) {
    if (!Pair.first) {
      // At the first block without a unique predecessor, try to build
      // conditions for its phis by merging those of their incoming blocks.
      if (!NumDomTreeSteps && Depth < MaxLoopGuardCollectionDepth) {
        SmallDenseMap<const BasicBlock *, LoopGuards> IncomingGuards;
        for (auto &Phi : Pair.second->phis())
          collectFromPHI(SE, Guards, Phi, VisitedBlocks, IncomingGuards, Depth);
      }
      const DomTreeNode *IDom = SE.DT.getNode(Pair.second)->getIDom();
      if (!IDom || ++NumDomTreeSteps > MaxGuardDomTreeSteps)
        break;
      Pair.first = IDom->getBlock();
      continue;
    }
    VisitedBlocks.insert(Pair.second);
    const CondBrInst *LoopEntryPredicate =
        dyn_cast<CondBrInst>(Pair.first->getTerminator());
    if (!LoopEntryPredicate)
      continue;
 
    Terms.emplace_back(LoopEntryPredicate->getCondition(),
                       LoopEntryPredicate->getSuccessor(0) == Pair.second);
    NumCollectedConditions++;
 
    // If we are recursively collecting guards stop after 2
    // conditions to limit compile-time impact for now.
    if (Depth > 0 && NumCollectedConditions == 2)
      break;
  }
 
  // Now apply the information from the collected conditions to
  // Guards.RewriteMap. Conditions are processed in reverse order, so the
  // earliest conditions is processed first, except guards with divisibility
  // information, which are moved to the back. This ensures the SCEVs with the
  // shortest dependency chains are constructed first.
  SmallVector<std::tuple<CmpInst::Predicate, const SCEV *, const SCEV *>>
      GuardsToProcess;
  for (auto [Term, EnterIfTrue] : reverse(Terms)) {
    SmallVector<Value *, 8> Worklist;
    SmallPtrSet<Value *, 8> Visited;
    Worklist.push_back(Term);
    while (!Worklist.empty()) {
      Value *Cond = Worklist.pop_back_val();
      if (!Visited.insert(Cond).second)
        continue;
 
      if (auto *Cmp = dyn_cast<ICmpInst>(Cond)) {
        auto Predicate =
            EnterIfTrue ? Cmp->getPredicate() : Cmp->getInversePredicate();
        const auto *LHS = SE.getSCEV(Cmp->getOperand(0));
        const auto *RHS = SE.getSCEV(Cmp->getOperand(1));
        // If LHS is a constant, apply information to the other expression.
        // TODO: If LHS is not a constant, check if using CompareSCEVComplexity
        // can improve results.
        if (isa<SCEVConstant>(LHS)) {
          std::swap(LHS, RHS);
          Predicate = CmpInst::getSwappedPredicate(Predicate);
        }
        GuardsToProcess.emplace_back(Predicate, LHS, RHS);
        continue;
      }
 
      Value *L, *R;
      if (EnterIfTrue ? match(Cond, m_LogicalAnd(m_Value(L), m_Value(R)))
                      : match(Cond, m_LogicalOr(m_Value(L), m_Value(R)))) {
        Worklist.push_back(L);
        Worklist.push_back(R);
      }
    }
  }
 
  // Process divisibility guards in reverse order to populate DivGuards early.
  DenseMap<const SCEV *, APInt> Multiples;
  LoopGuards DivGuards(SE);
  for (const auto &[Predicate, LHS, RHS] : GuardsToProcess) {
    if (!isDivisibilityGuard(LHS, RHS, SE))
      continue;
    collectDivisibilityInformation(Predicate, LHS, RHS, DivGuards.RewriteMap,
                                   Multiples, SE);
  }
 
  for (const auto &[Predicate, LHS, RHS] : GuardsToProcess)
    CollectCondition(Predicate, LHS, RHS, Guards.RewriteMap, DivGuards);
 
  // Apply divisibility information last. This ensures it is applied to the
  // outermost expression after other rewrites for the given value.
  for (const auto &[K, Divisor] : Multiples) {
    const SCEV *DivisorSCEV = SE.getConstant(Divisor);
    Guards.RewriteMap[K] =
        SE.getMulExpr(SE.getUDivExpr(applyDivisibilityOnMinMaxExpr(
                                         Guards.rewrite(K), Divisor, SE),
                                     DivisorSCEV),
                      DivisorSCEV);
    ExprsToRewrite.push_back(K);
  }
 
  // Let the rewriter preserve NUW/NSW flags if the unsigned/signed ranges of
  // the replacement expressions are contained in the ranges of the replaced
  // expressions.
  Guards.PreserveNUW = true;
  Guards.PreserveNSW = true;
  for (const SCEV *Expr : ExprsToRewrite) {
    const SCEV *RewriteTo = Guards.RewriteMap[Expr];
    Guards.PreserveNUW &=
        SE.getUnsignedRange(Expr).contains(SE.getUnsignedRange(RewriteTo));
    Guards.PreserveNSW &=
        SE.getSignedRange(Expr).contains(SE.getSignedRange(RewriteTo));
  }
 
  // Now that all rewrite information is collect, rewrite the collected
  // expressions with the information in the map. This applies information to
  // sub-expressions.
  if (ExprsToRewrite.size() > 1) {
    for (const SCEV *Expr : ExprsToRewrite) {
      const SCEV *RewriteTo = Guards.RewriteMap[Expr];
      Guards.RewriteMap.erase(Expr);
      Guards.RewriteMap.insert({Expr, Guards.rewrite(RewriteTo)});
    }
  }
}
 
const SCEV *ScalarEvolution::LoopGuards::rewrite(const SCEV *Expr) const {
  /// A rewriter to replace SCEV expressions in Map with the corresponding entry
  /// in the map. It skips AddRecExpr because we cannot guarantee that the
  /// replacement is loop invariant in the loop of the AddRec.
  class SCEVLoopGuardRewriter
      : public SCEVRewriteVisitor<SCEVLoopGuardRewriter> {
    const DenseMap<const SCEV *, const SCEV *> &Map;
    const SmallDenseSet<std::pair<const SCEV *, const SCEV *>> &NotEqual;
 
    SCEVFlags FlagMask = SCEV::FlagNone;
 
  public:
    SCEVLoopGuardRewriter(ScalarEvolution &SE,
                          const ScalarEvolution::LoopGuards &Guards)
        : SCEVRewriteVisitor(SE), Map(Guards.RewriteMap),
          NotEqual(Guards.NotEqual) {
      if (Guards.PreserveNUW)
        FlagMask = ScalarEvolution::setFlags(FlagMask, SCEV::FlagNUW);
      if (Guards.PreserveNSW)
        FlagMask = ScalarEvolution::setFlags(FlagMask, SCEV::FlagNSW);
    }
 
    const SCEV *visitAddRecExpr(const SCEVAddRecExpr *Expr) { return Expr; }
 
    const SCEV *visitUnknown(const SCEVUnknown *Expr) {
      return Map.lookup_or(Expr, Expr);
    }
 
    const SCEV *visitPtrToAddrExpr(const SCEVPtrToAddrExpr *Expr) {
      if (const SCEV *S = Map.lookup(Expr))
        return S;
      return SCEVRewriteVisitor<SCEVLoopGuardRewriter>::visitPtrToAddrExpr(
          Expr);
    }
 
    const SCEV *visitZeroExtendExpr(const SCEVZeroExtendExpr *Expr) {
      if (const SCEV *S = Map.lookup(Expr))
        return S;
 
      // If we didn't find the extact ZExt expr in the map, check if there's
      // an entry for a smaller ZExt we can use instead.
      Type *Ty = Expr->getType();
      const SCEV *Op = Expr->getOperand(0);
      unsigned Bitwidth = Ty->getScalarSizeInBits() / 2;
      while (Bitwidth % 8 == 0 && Bitwidth >= 8 &&
             Bitwidth > Op->getType()->getScalarSizeInBits()) {
        Type *NarrowTy = IntegerType::get(SE.getContext(), Bitwidth);
        auto *NarrowExt = SE.getZeroExtendExpr(Op, NarrowTy);
        if (const SCEV *S = Map.lookup(NarrowExt))
          return SE.getZeroExtendExpr(S, Ty);
        Bitwidth = Bitwidth / 2;
      }
 
      return SCEVRewriteVisitor<SCEVLoopGuardRewriter>::visitZeroExtendExpr(
          Expr);
    }
 
    const SCEV *visitSignExtendExpr(const SCEVSignExtendExpr *Expr) {
      if (const SCEV *S = Map.lookup(Expr))
        return S;
      return SCEVRewriteVisitor<SCEVLoopGuardRewriter>::visitSignExtendExpr(
          Expr);
    }
 
    const SCEV *visitUMinExpr(const SCEVUMinExpr *Expr) {
      if (const SCEV *S = Map.lookup(Expr))
        return S;
      return SCEVRewriteVisitor<SCEVLoopGuardRewriter>::visitUMinExpr(Expr);
    }
 
    const SCEV *visitSMinExpr(const SCEVSMinExpr *Expr) {
      if (const SCEV *S = Map.lookup(Expr))
        return S;
      return SCEVRewriteVisitor<SCEVLoopGuardRewriter>::visitSMinExpr(Expr);
    }
 
    const SCEV *visitAddExpr(const SCEVAddExpr *Expr) {
      if (const SCEV *S = Map.lookup(Expr))
        return S;
 
      // Helper to check if S is a subtraction (A - B) where A != B, and if so,
      // return UMax(S, 1).
      auto RewriteSubtraction = [&](const SCEV *S) -> const SCEV * {
        SCEVUse LHS, RHS;
        if (MatchBinarySub(S, LHS, RHS)) {
          if (LHS > RHS)
            std::swap(LHS, RHS);
          if (NotEqual.contains({LHS, RHS})) {
            const SCEV *OneAlignedUp = getNextSCEVDivisibleByDivisor(
                SE.getOne(S->getType()), SE.getConstantMultiple(S), SE);
            return SE.getUMaxExpr(OneAlignedUp, S);
          }
        }
        return nullptr;
      };
 
      // Check if Expr itself is a subtraction pattern with guard info.
      if (const SCEV *Rewritten = RewriteSubtraction(Expr))
        return Rewritten;
 
      // Trip count expressions sometimes consist of adding 3 operands, i.e.
      // (Const + A + B). There may be guard info for A + B, and if so, apply
      // it.
      // TODO: Could more generally apply guards to Add sub-expressions.
      if (isa<SCEVConstant>(Expr->getOperand(0))) {
        if (Expr->getNumOperands() == 3) {
          const SCEV *Add =
              SE.getAddExpr(Expr->getOperand(1), Expr->getOperand(2));
          if (const SCEV *Rewritten = RewriteSubtraction(Add))
            return SE.getAddExpr(
                Expr->getOperand(0), Rewritten,
                ScalarEvolution::maskFlags(Expr->getNoWrapFlags(), FlagMask));
          if (const SCEV *S = Map.lookup(Add))
            return SE.getAddExpr(Expr->getOperand(0), S);
        }
 
        // For expressions of the form (Const + A), check if we have guard info
        // for (Const + 1 + A), and rewrite to ((Const + 1 + A) - 1). This makes
        // sure we don't lose information when rewriting expressions based on
        // back-edge taken counts in some cases.
        if (Expr->getNumOperands() == 2) {
          const SCEV *S = nullptr;
          // Handle (-1 + 1 + A) without constructing SCEVs.
          if (match(Expr->getOperand(0), m_scev_AllOnes())) {
            S = Map.lookup(Expr->getOperand(1));
          } else {
            const SCEV *NewC =
                SE.getAddExpr(Expr->getOperand(0), SE.getOne(Expr->getType()));
            S = Map.lookup(SE.getAddExpr(NewC, Expr->getOperand(1)));
          }
          if (S)
            return SE.getAddExpr(S, SE.getMinusOne(Expr->getType()));
        }
      }
      SmallVector<SCEVUse, 2> Operands;
      bool Changed = false;
      for (SCEVUse Op : Expr->operands()) {
        Operands.push_back(
            SCEVRewriteVisitor<SCEVLoopGuardRewriter>::visit(Op));
        Changed |= Op != Operands.back();
      }
      // We are only replacing operands with equivalent values, so transfer the
      // flags from the original expression.
      return !Changed ? Expr
                      : SE.getAddExpr(Operands,
                                      ScalarEvolution::maskFlags(
                                          Expr->getNoWrapFlags(), FlagMask));
    }
 
    const SCEV *visitMulExpr(const SCEVMulExpr *Expr) {
      SmallVector<SCEVUse, 2> Operands;
      bool Changed = false;
      for (SCEVUse Op : Expr->operands()) {
        Operands.push_back(
            SCEVRewriteVisitor<SCEVLoopGuardRewriter>::visit(Op));
        Changed |= Op != Operands.back();
      }
      // We are only replacing operands with equivalent values, so transfer the
      // flags from the original expression.
      return !Changed ? Expr
                      : SE.getMulExpr(Operands,
                                      ScalarEvolution::maskFlags(
                                          Expr->getNoWrapFlags(), FlagMask));
    }
  };
 
  if (RewriteMap.empty() && NotEqual.empty())
    return Expr;
 
  SCEVLoopGuardRewriter Rewriter(SE, *this);
  return Rewriter.visit(Expr);
}
 
const SCEV *ScalarEvolution::applyLoopGuards(const SCEV *Expr, const Loop *L) {
  LoopGuards Guards = LoopGuards::collectOnDemand(L, *this);
  return applyLoopGuards(Expr, Guards);
}
 
const SCEV *ScalarEvolution::applyLoopGuards(const SCEV *Expr,
                                             LoopGuards &Guards) {
  // Loop guards never rewrite constants and AddRecs, so there is no need to
  // collect pending guards for them.
  if (isa<SCEVConstant, SCEVAddRecExpr>(Expr))
    return Expr;
  if (Guards.PendingLoop)
    Guards.collectPending();
  return Guards.rewrite(Expr);
}