IRTranslator.h

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//===- llvm/CodeGen/GlobalISel/IRTranslator.h - IRTranslator ----*- C++ -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//
/// \file
/// This file declares the IRTranslator pass.
/// This pass is responsible for translating LLVM IR into MachineInstr.
/// It uses target hooks to lower the ABI but aside from that, the pass
/// generated code is generic. This is the default translator used for
/// GlobalISel.
///
/// \todo Replace the comments with actual doxygen comments.
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_CODEGEN_GLOBALISEL_IRTRANSLATOR_H
#define LLVM_CODEGEN_GLOBALISEL_IRTRANSLATOR_H
 
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/CodeGen/CodeGenCommonISel.h"
#include "llvm/CodeGen/FunctionLoweringInfo.h"
#include "llvm/CodeGen/GlobalISel/MachineIRBuilder.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/SwiftErrorValueTracking.h"
#include "llvm/CodeGen/SwitchLoweringUtils.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/CodeGen.h"
#include <memory>
#include <utility>
 
namespace llvm {
 
class AllocaInst;
class AssumptionCache;
class BasicBlock;
class CallInst;
class CallLowering;
class Constant;
class ConstrainedFPIntrinsic;
class DataLayout;
class Instruction;
class MachineBasicBlock;
class MachineFunction;
class MachineInstr;
class MachineRegisterInfo;
class OptimizationRemarkEmitter;
class PHINode;
class TargetLibraryInfo;
class TargetPassConfig;
class User;
class Value;
 
// Technically the pass should run on an hypothetical MachineModule,
// since it should translate Global into some sort of MachineGlobal.
// The MachineGlobal should ultimately just be a transfer of ownership of
// the interesting bits that are relevant to represent a global value.
// That being said, we could investigate what would it cost to just duplicate
// the information from the LLVM IR.
// The idea is that ultimately we would be able to free up the memory used
// by the LLVM IR as soon as the translation is over.
class IRTranslator : public MachineFunctionPass {
public:
  static char ID;
 
private:
  /// Interface used to lower the everything related to calls.
  const CallLowering *CLI;
 
  /// This class contains the mapping between the Values to vreg related data.
  class ValueToVRegInfo {
  public:
    ValueToVRegInfo() = default;
 
    using VRegListT = SmallVector<Register, 1>;
    using OffsetListT = SmallVector<uint64_t, 1>;
 
    using const_vreg_iterator =
        DenseMap<const Value *, VRegListT *>::const_iterator;
    using const_offset_iterator =
        DenseMap<const Value *, OffsetListT *>::const_iterator;
 
    inline const_vreg_iterator vregs_end() const { return ValToVRegs.end(); }
 
    VRegListT *getVRegs(const Value &V) {
      auto It = ValToVRegs.find(&V);
      if (It != ValToVRegs.end())
        return It->second;
 
      return insertVRegs(V);
    }
 
    OffsetListT *getOffsets(const Value &V) {
      auto It = TypeToOffsets.find(V.getType());
      if (It != TypeToOffsets.end())
        return It->second;
 
      return insertOffsets(V);
    }
 
    const_vreg_iterator findVRegs(const Value &V) const {
      return ValToVRegs.find(&V);
    }
 
    bool contains(const Value &V) const { return ValToVRegs.contains(&V); }
 
    void reset() {
      ValToVRegs.clear();
      TypeToOffsets.clear();
      VRegAlloc.DestroyAll();
      OffsetAlloc.DestroyAll();
    }
 
  private:
    VRegListT *insertVRegs(const Value &V) {
      assert(!ValToVRegs.contains(&V) && "Value already exists");
 
      // We placement new using our fast allocator since we never try to free
      // the vectors until translation is finished.
      auto *VRegList = new (VRegAlloc.Allocate()) VRegListT();
      ValToVRegs[&V] = VRegList;
      return VRegList;
    }
 
    OffsetListT *insertOffsets(const Value &V) {
      assert(!TypeToOffsets.contains(V.getType()) && "Type already exists");
 
      auto *OffsetList = new (OffsetAlloc.Allocate()) OffsetListT();
      TypeToOffsets[V.getType()] = OffsetList;
      return OffsetList;
    }
    SpecificBumpPtrAllocator<VRegListT> VRegAlloc;
    SpecificBumpPtrAllocator<OffsetListT> OffsetAlloc;
 
    // We store pointers to vectors here since references may be invalidated
    // while we hold them if we stored the vectors directly.
    DenseMap<const Value *, VRegListT*> ValToVRegs;
    DenseMap<const Type *, OffsetListT*> TypeToOffsets;
  };
 
  /// Mapping of the values of the current LLVM IR function to the related
  /// virtual registers and offsets.
  ValueToVRegInfo VMap;
 
  // N.b. it's not completely obvious that this will be sufficient for every
  // LLVM IR construct (with "invoke" being the obvious candidate to mess up our
  // lives.
  DenseMap<const BasicBlock *, MachineBasicBlock *> BBToMBB;
 
  // One BasicBlock can be translated to multiple MachineBasicBlocks.  For such
  // BasicBlocks translated to multiple MachineBasicBlocks, MachinePreds retains
  // a mapping between the edges arriving at the BasicBlock to the corresponding
  // created MachineBasicBlocks. Some BasicBlocks that get translated to a
  // single MachineBasicBlock may also end up in this Map.
  using CFGEdge = std::pair<const BasicBlock *, const BasicBlock *>;
  DenseMap<CFGEdge, SmallVector<MachineBasicBlock *, 1>> MachinePreds;
 
  // List of stubbed PHI instructions, for values and basic blocks to be filled
  // in once all MachineBasicBlocks have been created.
  SmallVector<std::pair<const PHINode *, SmallVector<MachineInstr *, 1>>, 4>
      PendingPHIs;
 
  /// Record of what frame index has been allocated to specified allocas for
  /// this function.
  DenseMap<const AllocaInst *, int> FrameIndices;
 
  SwiftErrorValueTracking SwiftError;
 
  /// \name Methods for translating form LLVM IR to MachineInstr.
  /// \see ::translate for general information on the translate methods.
  /// @{
 
  /// Translate \p Inst into its corresponding MachineInstr instruction(s).
  /// Insert the newly translated instruction(s) right where the CurBuilder
  /// is set.
  ///
  /// The general algorithm is:
  /// 1. Look for a virtual register for each operand or
  ///    create one.
  /// 2 Update the VMap accordingly.
  /// 2.alt. For constant arguments, if they are compile time constants,
  ///   produce an immediate in the right operand and do not touch
  ///   ValToReg. Actually we will go with a virtual register for each
  ///   constants because it may be expensive to actually materialize the
  ///   constant. Moreover, if the constant spans on several instructions,
  ///   CSE may not catch them.
  ///   => Update ValToVReg and remember that we saw a constant in Constants.
  ///   We will materialize all the constants in finalize.
  /// Note: we would need to do something so that we can recognize such operand
  ///       as constants.
  /// 3. Create the generic instruction.
  ///
  /// \return true if the translation succeeded.
  bool translate(const Instruction &Inst);
 
  /// Materialize \p C into virtual-register \p Reg. The generic instructions
  /// performing this materialization will be inserted into the entry block of
  /// the function.
  ///
  /// \return true if the materialization succeeded.
  bool translate(const Constant &C, Register Reg);
 
  // Translate U as a copy of V.
  bool translateCopy(const User &U, const Value &V,
                     MachineIRBuilder &MIRBuilder);
 
  /// Translate an LLVM bitcast into generic IR. Either a COPY or a G_BITCAST is
  /// emitted.
  bool translateBitCast(const User &U, MachineIRBuilder &MIRBuilder);
 
  /// Translate an LLVM load instruction into generic IR.
  bool translateLoad(const User &U, MachineIRBuilder &MIRBuilder);
 
  /// Translate an LLVM store instruction into generic IR.
  bool translateStore(const User &U, MachineIRBuilder &MIRBuilder);
 
  /// Translate an LLVM string intrinsic (memcpy, memset, ...).
  bool translateMemFunc(const CallInst &CI, MachineIRBuilder &MIRBuilder,
                        unsigned Opcode);
 
  void getStackGuard(Register DstReg, MachineIRBuilder &MIRBuilder);
 
  bool translateOverflowIntrinsic(const CallInst &CI, unsigned Op,
                                  MachineIRBuilder &MIRBuilder);
  bool translateFixedPointIntrinsic(unsigned Op, const CallInst &CI,
                                    MachineIRBuilder &MIRBuilder);
 
  /// Helper function for translateSimpleIntrinsic.
  /// \return The generic opcode for \p IntrinsicID if \p IntrinsicID is a
  /// simple intrinsic (ceil, fabs, etc.). Otherwise, returns
  /// Intrinsic::not_intrinsic.
  unsigned getSimpleIntrinsicOpcode(Intrinsic::ID ID);
 
  /// Translates the intrinsics defined in getSimpleIntrinsicOpcode.
  /// \return true if the translation succeeded.
  bool translateSimpleIntrinsic(const CallInst &CI, Intrinsic::ID ID,
                                MachineIRBuilder &MIRBuilder);
 
  bool translateConstrainedFPIntrinsic(const ConstrainedFPIntrinsic &FPI,
                                       MachineIRBuilder &MIRBuilder);
 
  bool translateKnownIntrinsic(const CallInst &CI, Intrinsic::ID ID,
                               MachineIRBuilder &MIRBuilder);
 
  bool translateInlineAsm(const CallBase &CB, MachineIRBuilder &MIRBuilder);
 
  /// Common code for translating normal calls or invokes.
  bool translateCallBase(const CallBase &CB, MachineIRBuilder &MIRBuilder);
 
  /// Translate call instruction.
  /// \pre \p U is a call instruction.
  bool translateCall(const User &U, MachineIRBuilder &MIRBuilder);
 
  /// When an invoke or a cleanupret unwinds to the next EH pad, there are
  /// many places it could ultimately go. In the IR, we have a single unwind
  /// destination, but in the machine CFG, we enumerate all the possible blocks.
  /// This function skips over imaginary basic blocks that hold catchswitch
  /// instructions, and finds all the "real" machine
  /// basic block destinations. As those destinations may not be successors of
  /// EHPadBB, here we also calculate the edge probability to those
  /// destinations. The passed-in Prob is the edge probability to EHPadBB.
  bool findUnwindDestinations(
      const BasicBlock *EHPadBB, BranchProbability Prob,
      SmallVectorImpl<std::pair<MachineBasicBlock *, BranchProbability>>
          &UnwindDests);
 
  bool translateInvoke(const User &U, MachineIRBuilder &MIRBuilder);
 
  bool translateCallBr(const User &U, MachineIRBuilder &MIRBuilder);
 
  bool translateLandingPad(const User &U, MachineIRBuilder &MIRBuilder);
 
  /// Translate one of LLVM's cast instructions into MachineInstrs, with the
  /// given generic Opcode.
  bool translateCast(unsigned Opcode, const User &U,
                     MachineIRBuilder &MIRBuilder);
 
  /// Translate a phi instruction.
  bool translatePHI(const User &U, MachineIRBuilder &MIRBuilder);
 
  /// Translate a comparison (icmp or fcmp) instruction or constant.
  bool translateCompare(const User &U, MachineIRBuilder &MIRBuilder);
 
  /// Translate an integer compare instruction (or constant).
  bool translateICmp(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateCompare(U, MIRBuilder);
  }
 
  /// Translate a floating-point compare instruction (or constant).
  bool translateFCmp(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateCompare(U, MIRBuilder);
  }
 
  /// Add remaining operands onto phis we've translated. Executed after all
  /// MachineBasicBlocks for the function have been created.
  void finishPendingPhis();
 
  /// Translate \p Inst into a unary operation \p Opcode.
  /// \pre \p U is a unary operation.
  bool translateUnaryOp(unsigned Opcode, const User &U,
                        MachineIRBuilder &MIRBuilder);
 
  /// Translate \p Inst into a binary operation \p Opcode.
  /// \pre \p U is a binary operation.
  bool translateBinaryOp(unsigned Opcode, const User &U,
                         MachineIRBuilder &MIRBuilder);
 
  /// If the set of cases should be emitted as a series of branches, return
  /// true. If we should emit this as a bunch of and/or'd together conditions,
  /// return false.
  bool shouldEmitAsBranches(const std::vector<SwitchCG::CaseBlock> &Cases);
  /// Helper method for findMergedConditions.
  /// This function emits a branch and is used at the leaves of an OR or an
  /// AND operator tree.
  void emitBranchForMergedCondition(const Value *Cond, MachineBasicBlock *TBB,
                                    MachineBasicBlock *FBB,
                                    MachineBasicBlock *CurBB,
                                    MachineBasicBlock *SwitchBB,
                                    BranchProbability TProb,
                                    BranchProbability FProb, bool InvertCond);
  /// Used during condbr translation to find trees of conditions that can be
  /// optimized.
  void findMergedConditions(const Value *Cond, MachineBasicBlock *TBB,
                            MachineBasicBlock *FBB, MachineBasicBlock *CurBB,
                            MachineBasicBlock *SwitchBB,
                            Instruction::BinaryOps Opc, BranchProbability TProb,
                            BranchProbability FProb, bool InvertCond);
 
  /// Translate branch (br) instruction.
  /// \pre \p U is a branch instruction.
  bool translateBr(const User &U, MachineIRBuilder &MIRBuilder);
 
  // Begin switch lowering functions.
  bool emitJumpTableHeader(SwitchCG::JumpTable &JT,
                           SwitchCG::JumpTableHeader &JTH,
                           MachineBasicBlock *HeaderBB);
  void emitJumpTable(SwitchCG::JumpTable &JT, MachineBasicBlock *MBB);
 
  void emitSwitchCase(SwitchCG::CaseBlock &CB, MachineBasicBlock *SwitchBB,
                      MachineIRBuilder &MIB);
 
  /// Generate for for the BitTest header block, which precedes each sequence of
  /// BitTestCases.
  void emitBitTestHeader(SwitchCG::BitTestBlock &BTB,
                         MachineBasicBlock *SwitchMBB);
  /// Generate code to produces one "bit test" for a given BitTestCase \p B.
  void emitBitTestCase(SwitchCG::BitTestBlock &BB, MachineBasicBlock *NextMBB,
                       BranchProbability BranchProbToNext, Register Reg,
                       SwitchCG::BitTestCase &B, MachineBasicBlock *SwitchBB);
 
  bool lowerJumpTableWorkItem(
      SwitchCG::SwitchWorkListItem W, MachineBasicBlock *SwitchMBB,
      MachineBasicBlock *CurMBB, MachineBasicBlock *DefaultMBB,
      MachineIRBuilder &MIB, MachineFunction::iterator BBI,
      BranchProbability UnhandledProbs, SwitchCG::CaseClusterIt I,
      MachineBasicBlock *Fallthrough, bool FallthroughUnreachable);
 
  bool lowerSwitchRangeWorkItem(SwitchCG::CaseClusterIt I, Value *Cond,
                                MachineBasicBlock *Fallthrough,
                                bool FallthroughUnreachable,
                                BranchProbability UnhandledProbs,
                                MachineBasicBlock *CurMBB,
                                MachineIRBuilder &MIB,
                                MachineBasicBlock *SwitchMBB);
 
  bool lowerBitTestWorkItem(
      SwitchCG::SwitchWorkListItem W, MachineBasicBlock *SwitchMBB,
      MachineBasicBlock *CurMBB, MachineBasicBlock *DefaultMBB,
      MachineIRBuilder &MIB, MachineFunction::iterator BBI,
      BranchProbability DefaultProb, BranchProbability UnhandledProbs,
      SwitchCG::CaseClusterIt I, MachineBasicBlock *Fallthrough,
      bool FallthroughUnreachable);
 
  bool lowerSwitchWorkItem(SwitchCG::SwitchWorkListItem W, Value *Cond,
                           MachineBasicBlock *SwitchMBB,
                           MachineBasicBlock *DefaultMBB,
                           MachineIRBuilder &MIB);
 
  bool translateSwitch(const User &U, MachineIRBuilder &MIRBuilder);
  // End switch lowering section.
 
  bool translateIndirectBr(const User &U, MachineIRBuilder &MIRBuilder);
 
  bool translateExtractValue(const User &U, MachineIRBuilder &MIRBuilder);
 
  bool translateInsertValue(const User &U, MachineIRBuilder &MIRBuilder);
 
  bool translateSelect(const User &U, MachineIRBuilder &MIRBuilder);
 
  bool translateGetElementPtr(const User &U, MachineIRBuilder &MIRBuilder);
 
  bool translateAlloca(const User &U, MachineIRBuilder &MIRBuilder);
 
  /// Translate return (ret) instruction.
  /// The target needs to implement CallLowering::lowerReturn for
  /// this to succeed.
  /// \pre \p U is a return instruction.
  bool translateRet(const User &U, MachineIRBuilder &MIRBuilder);
 
  bool translateFNeg(const User &U, MachineIRBuilder &MIRBuilder);
 
  bool translateAdd(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateBinaryOp(TargetOpcode::G_ADD, U, MIRBuilder);
  }
  bool translateSub(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateBinaryOp(TargetOpcode::G_SUB, U, MIRBuilder);
  }
  bool translateAnd(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateBinaryOp(TargetOpcode::G_AND, U, MIRBuilder);
  }
  bool translateMul(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateBinaryOp(TargetOpcode::G_MUL, U, MIRBuilder);
  }
  bool translateOr(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateBinaryOp(TargetOpcode::G_OR, U, MIRBuilder);
  }
  bool translateXor(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateBinaryOp(TargetOpcode::G_XOR, U, MIRBuilder);
  }
 
  bool translateUDiv(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateBinaryOp(TargetOpcode::G_UDIV, U, MIRBuilder);
  }
  bool translateSDiv(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateBinaryOp(TargetOpcode::G_SDIV, U, MIRBuilder);
  }
  bool translateURem(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateBinaryOp(TargetOpcode::G_UREM, U, MIRBuilder);
  }
  bool translateSRem(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateBinaryOp(TargetOpcode::G_SREM, U, MIRBuilder);
  }
  bool translateIntToPtr(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateCast(TargetOpcode::G_INTTOPTR, U, MIRBuilder);
  }
  bool translatePtrToInt(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateCast(TargetOpcode::G_PTRTOINT, U, MIRBuilder);
  }
  bool translateTrunc(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateCast(TargetOpcode::G_TRUNC, U, MIRBuilder);
  }
  bool translateFPTrunc(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateCast(TargetOpcode::G_FPTRUNC, U, MIRBuilder);
  }
  bool translateFPExt(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateCast(TargetOpcode::G_FPEXT, U, MIRBuilder);
  }
  bool translateFPToUI(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateCast(TargetOpcode::G_FPTOUI, U, MIRBuilder);
  }
  bool translateFPToSI(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateCast(TargetOpcode::G_FPTOSI, U, MIRBuilder);
  }
  bool translateUIToFP(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateCast(TargetOpcode::G_UITOFP, U, MIRBuilder);
  }
  bool translateSIToFP(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateCast(TargetOpcode::G_SITOFP, U, MIRBuilder);
  }
  bool translateUnreachable(const User &U, MachineIRBuilder &MIRBuilder);
 
  bool translateSExt(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateCast(TargetOpcode::G_SEXT, U, MIRBuilder);
  }
 
  bool translateZExt(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateCast(TargetOpcode::G_ZEXT, U, MIRBuilder);
  }
 
  bool translateShl(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateBinaryOp(TargetOpcode::G_SHL, U, MIRBuilder);
  }
  bool translateLShr(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateBinaryOp(TargetOpcode::G_LSHR, U, MIRBuilder);
  }
  bool translateAShr(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateBinaryOp(TargetOpcode::G_ASHR, U, MIRBuilder);
  }
 
  bool translateFAdd(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateBinaryOp(TargetOpcode::G_FADD, U, MIRBuilder);
  }
  bool translateFSub(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateBinaryOp(TargetOpcode::G_FSUB, U, MIRBuilder);
  }
  bool translateFMul(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateBinaryOp(TargetOpcode::G_FMUL, U, MIRBuilder);
  }
  bool translateFDiv(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateBinaryOp(TargetOpcode::G_FDIV, U, MIRBuilder);
  }
  bool translateFRem(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateBinaryOp(TargetOpcode::G_FREM, U, MIRBuilder);
  }
 
  bool translateVAArg(const User &U, MachineIRBuilder &MIRBuilder);
 
  bool translateInsertElement(const User &U, MachineIRBuilder &MIRBuilder);
 
  bool translateExtractElement(const User &U, MachineIRBuilder &MIRBuilder);
 
  bool translateShuffleVector(const User &U, MachineIRBuilder &MIRBuilder);
 
  bool translateAtomicCmpXchg(const User &U, MachineIRBuilder &MIRBuilder);
  bool translateAtomicRMW(const User &U, MachineIRBuilder &MIRBuilder);
  bool translateFence(const User &U, MachineIRBuilder &MIRBuilder);
  bool translateFreeze(const User &U, MachineIRBuilder &MIRBuilder);
 
  // Stubs to keep the compiler happy while we implement the rest of the
  // translation.
  bool translateResume(const User &U, MachineIRBuilder &MIRBuilder) {
    return false;
  }
  bool translateCleanupRet(const User &U, MachineIRBuilder &MIRBuilder) {
    return false;
  }
  bool translateCatchRet(const User &U, MachineIRBuilder &MIRBuilder) {
    return false;
  }
  bool translateCatchSwitch(const User &U, MachineIRBuilder &MIRBuilder) {
    return false;
  }
  bool translateAddrSpaceCast(const User &U, MachineIRBuilder &MIRBuilder) {
    return translateCast(TargetOpcode::G_ADDRSPACE_CAST, U, MIRBuilder);
  }
  bool translateCleanupPad(const User &U, MachineIRBuilder &MIRBuilder) {
    return false;
  }
  bool translateCatchPad(const User &U, MachineIRBuilder &MIRBuilder) {
    return false;
  }
  bool translateUserOp1(const User &U, MachineIRBuilder &MIRBuilder) {
    return false;
  }
  bool translateUserOp2(const User &U, MachineIRBuilder &MIRBuilder) {
    return false;
  }
 
  /// @}
 
  // Builder for machine instruction a la IRBuilder.
  // I.e., compared to regular MIBuilder, this one also inserts the instruction
  // in the current block, it can creates block, etc., basically a kind of
  // IRBuilder, but for Machine IR.
  // CSEMIRBuilder CurBuilder;
  std::unique_ptr<MachineIRBuilder> CurBuilder;
 
  // Builder set to the entry block (just after ABI lowering instructions). Used
  // as a convenient location for Constants.
  // CSEMIRBuilder EntryBuilder;
  std::unique_ptr<MachineIRBuilder> EntryBuilder;
 
  // The MachineFunction currently being translated.
  MachineFunction *MF;
 
  /// MachineRegisterInfo used to create virtual registers.
  MachineRegisterInfo *MRI = nullptr;
 
  const DataLayout *DL;
 
  /// Current target configuration. Controls how the pass handles errors.
  const TargetPassConfig *TPC;
 
  CodeGenOpt::Level OptLevel;
 
  /// Current optimization remark emitter. Used to report failures.
  std::unique_ptr<OptimizationRemarkEmitter> ORE;
 
  AAResults *AA;
  AssumptionCache *AC;
  const TargetLibraryInfo *LibInfo;
  FunctionLoweringInfo FuncInfo;
 
  // True when either the Target Machine specifies no optimizations or the
  // function has the optnone attribute.
  bool EnableOpts = false;
 
  /// True when the block contains a tail call. This allows the IRTranslator to
  /// stop translating such blocks early.
  bool HasTailCall = false;
 
  StackProtectorDescriptor SPDescriptor;
 
  /// Switch analysis and optimization.
  class GISelSwitchLowering : public SwitchCG::SwitchLowering {
  public:
    GISelSwitchLowering(IRTranslator *irt, FunctionLoweringInfo &funcinfo)
        : SwitchLowering(funcinfo), IRT(irt) {
      assert(irt && "irt is null!");
    }
 
    void addSuccessorWithProb(
        MachineBasicBlock *Src, MachineBasicBlock *Dst,
        BranchProbability Prob = BranchProbability::getUnknown()) override {
      IRT->addSuccessorWithProb(Src, Dst, Prob);
    }
 
    virtual ~GISelSwitchLowering() = default;
 
  private:
    IRTranslator *IRT;
  };
 
  std::unique_ptr<GISelSwitchLowering> SL;
 
  // * Insert all the code needed to materialize the constants
  // at the proper place. E.g., Entry block or dominator block
  // of each constant depending on how fancy we want to be.
  // * Clear the different maps.
  void finalizeFunction();
 
  // Processing steps done per block. E.g. emitting jump tables, stack
  // protectors etc. Returns true if no errors, false if there was a problem
  // that caused an abort.
  bool finalizeBasicBlock(const BasicBlock &BB, MachineBasicBlock &MBB);
 
  /// Codegen a new tail for a stack protector check ParentMBB which has had its
  /// tail spliced into a stack protector check success bb.
  ///
  /// For a high level explanation of how this fits into the stack protector
  /// generation see the comment on the declaration of class
  /// StackProtectorDescriptor.
  ///
  /// \return true if there were no problems.
  bool emitSPDescriptorParent(StackProtectorDescriptor &SPD,
                              MachineBasicBlock *ParentBB);
 
  /// Codegen the failure basic block for a stack protector check.
  ///
  /// A failure stack protector machine basic block consists simply of a call to
  /// __stack_chk_fail().
  ///
  /// For a high level explanation of how this fits into the stack protector
  /// generation see the comment on the declaration of class
  /// StackProtectorDescriptor.
  ///
  /// \return true if there were no problems.
  bool emitSPDescriptorFailure(StackProtectorDescriptor &SPD,
                               MachineBasicBlock *FailureBB);
 
  /// Get the VRegs that represent \p Val.
  /// Non-aggregate types have just one corresponding VReg and the list can be
  /// used as a single "unsigned". Aggregates get flattened. If such VRegs do
  /// not exist, they are created.
  ArrayRef<Register> getOrCreateVRegs(const Value &Val);
 
  Register getOrCreateVReg(const Value &Val) {
    auto Regs = getOrCreateVRegs(Val);
    if (Regs.empty())
      return 0;
    assert(Regs.size() == 1 &&
           "attempt to get single VReg for aggregate or void");
    return Regs[0];
  }
 
  /// Allocate some vregs and offsets in the VMap. Then populate just the
  /// offsets while leaving the vregs empty.
  ValueToVRegInfo::VRegListT &allocateVRegs(const Value &Val);
 
  /// Get the frame index that represents \p Val.
  /// If such VReg does not exist, it is created.
  int getOrCreateFrameIndex(const AllocaInst &AI);
 
  /// Get the alignment of the given memory operation instruction. This will
  /// either be the explicitly specified value or the ABI-required alignment for
  /// the type being accessed (according to the Module's DataLayout).
  Align getMemOpAlign(const Instruction &I);
 
  /// Get the MachineBasicBlock that represents \p BB. Specifically, the block
  /// returned will be the head of the translated block (suitable for branch
  /// destinations).
  MachineBasicBlock &getMBB(const BasicBlock &BB);
 
  /// Record \p NewPred as a Machine predecessor to `Edge.second`, corresponding
  /// to `Edge.first` at the IR level. This is used when IRTranslation creates
  /// multiple MachineBasicBlocks for a given IR block and the CFG is no longer
  /// represented simply by the IR-level CFG.
  void addMachineCFGPred(CFGEdge Edge, MachineBasicBlock *NewPred);
 
  /// Returns the Machine IR predecessors for the given IR CFG edge. Usually
  /// this is just the single MachineBasicBlock corresponding to the predecessor
  /// in the IR. More complex lowering can result in multiple MachineBasicBlocks
  /// preceding the original though (e.g. switch instructions).
  SmallVector<MachineBasicBlock *, 1> getMachinePredBBs(CFGEdge Edge) {
    auto RemappedEdge = MachinePreds.find(Edge);
    if (RemappedEdge != MachinePreds.end())
      return RemappedEdge->second;
    return SmallVector<MachineBasicBlock *, 4>(1, &getMBB(*Edge.first));
  }
 
  /// Return branch probability calculated by BranchProbabilityInfo for IR
  /// blocks.
  BranchProbability getEdgeProbability(const MachineBasicBlock *Src,
                                       const MachineBasicBlock *Dst) const;
 
  void addSuccessorWithProb(
      MachineBasicBlock *Src, MachineBasicBlock *Dst,
      BranchProbability Prob = BranchProbability::getUnknown());
 
public:
  IRTranslator(CodeGenOpt::Level OptLevel = CodeGenOpt::None);
 
  StringRef getPassName() const override { return "IRTranslator"; }
 
  void getAnalysisUsage(AnalysisUsage &AU) const override;
 
  // Algo:
  //   CallLowering = MF.subtarget.getCallLowering()
  //   F = MF.getParent()
  //   MIRBuilder.reset(MF)
  //   getMBB(F.getEntryBB())
  //   CallLowering->translateArguments(MIRBuilder, F, ValToVReg)
  //   for each bb in F
  //     getMBB(bb)
  //     for each inst in bb
  //       if (!translate(MIRBuilder, inst, ValToVReg, ConstantToSequence))
  //         report_fatal_error("Don't know how to translate input");
  //   finalize()
  bool runOnMachineFunction(MachineFunction &MF) override;
};
 
} // end namespace llvm
 
#endif // LLVM_CODEGEN_GLOBALISEL_IRTRANSLATOR_H