CoroFrame.cpp

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//===- CoroFrame.cpp - Builds and manipulates coroutine frame -------------===//
//
// 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 classes used to discover if for a particular value
// its definition precedes and its uses follow a suspend block. This is
// referred to as a suspend crossing value.
//
// Using the information discovered we form a Coroutine Frame structure to
// contain those values. All uses of those values are replaced with appropriate
// GEP + load from the coroutine frame. At the point of the definition we spill
// the value into the coroutine frame.
//===----------------------------------------------------------------------===//
 
#include "CoroInternal.h"
#include "llvm/ADT/ScopeExit.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/Analysis/StackLifetime.h"
#include "llvm/IR/DIBuilder.h"
#include "llvm/IR/DebugInfo.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/MDBuilder.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/ProfDataUtils.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/OptimizedStructLayout.h"
#include "llvm/Transforms/Coroutines/ABI.h"
#include "llvm/Transforms/Coroutines/CoroInstr.h"
#include "llvm/Transforms/Coroutines/MaterializationUtils.h"
#include "llvm/Transforms/Coroutines/SpillUtils.h"
#include "llvm/Transforms/Coroutines/SuspendCrossingInfo.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/PromoteMemToReg.h"
#include <algorithm>
#include <optional>
 
using namespace llvm;
 
namespace llvm {
extern cl::opt<bool> ProfcheckDisableMetadataFixes;
}
 
#define DEBUG_TYPE "coro-frame"
 
namespace {
class FrameTypeBuilder;
// Mapping from the to-be-spilled value to all the users that need reload.
struct FrameDataInfo {
  // All the values (that are not allocas) that needs to be spilled to the
  // frame.
  coro::SpillInfo &Spills;
  // Allocas contains all values defined as allocas that need to live in the
  // frame.
  SmallVectorImpl<coro::AllocaInfo> &Allocas;
 
  FrameDataInfo(coro::SpillInfo &Spills,
                SmallVectorImpl<coro::AllocaInfo> &Allocas)
      : Spills(Spills), Allocas(Allocas) {}
 
  SmallVector<Value *, 8> getAllDefs() const {
    SmallVector<Value *, 8> Defs;
    for (const auto &P : Spills)
      Defs.push_back(P.first);
    for (const auto &A : Allocas)
      Defs.push_back(A.Alloca);
    return Defs;
  }
 
  uint32_t getFieldIndex(Value *V) const {
    auto Itr = FieldIndexMap.find(V);
    assert(Itr != FieldIndexMap.end() &&
           "Value does not have a frame field index");
    return Itr->second;
  }
 
  void setFieldIndex(Value *V, uint32_t Index) {
    assert(FieldIndexMap.count(V) == 0 &&
           "Cannot set the index for the same field twice.");
    FieldIndexMap[V] = Index;
  }
 
  Align getAlign(Value *V) const {
    auto Iter = FieldAlignMap.find(V);
    assert(Iter != FieldAlignMap.end());
    return Iter->second;
  }
 
  void setAlign(Value *V, Align AL) {
    assert(FieldAlignMap.count(V) == 0);
    FieldAlignMap.insert({V, AL});
  }
 
  uint64_t getDynamicAlign(Value *V) const {
    auto Iter = FieldDynamicAlignMap.find(V);
    assert(Iter != FieldDynamicAlignMap.end());
    return Iter->second;
  }
 
  void setDynamicAlign(Value *V, uint64_t Align) {
    assert(FieldDynamicAlignMap.count(V) == 0);
    FieldDynamicAlignMap.insert({V, Align});
  }
 
  uint64_t getOffset(Value *V) const {
    auto Iter = FieldOffsetMap.find(V);
    assert(Iter != FieldOffsetMap.end());
    return Iter->second;
  }
 
  void setOffset(Value *V, uint64_t Offset) {
    assert(FieldOffsetMap.count(V) == 0);
    FieldOffsetMap.insert({V, Offset});
  }
 
  // Update field offset and alignment information from FrameTypeBuilder.
  void updateLayoutInfo(FrameTypeBuilder &B);
 
private:
  // Map from values to their slot indexes on the frame (insertion order).
  DenseMap<Value *, uint32_t> FieldIndexMap;
  // Map from values to their alignment on the frame. They would be set after
  // the frame is built.
  DenseMap<Value *, Align> FieldAlignMap;
  DenseMap<Value *, uint64_t> FieldDynamicAlignMap;
  // Map from values to their offset on the frame. They would be set after
  // the frame is built.
  DenseMap<Value *, uint64_t> FieldOffsetMap;
};
} // namespace
 
#ifndef NDEBUG
static void dumpSpills(StringRef Title, const coro::SpillInfo &Spills) {
  dbgs() << "------------- " << Title << " --------------\n";
  for (const auto &E : Spills) {
    E.first->dump();
    dbgs() << "   user: ";
    for (auto *I : E.second)
      I->dump();
  }
}
 
static void dumpAllocas(const SmallVectorImpl<coro::AllocaInfo> &Allocas) {
  dbgs() << "------------- Allocas --------------\n";
  for (const auto &A : Allocas) {
    A.Alloca->dump();
  }
}
#endif
 
namespace {
using FieldIDType = size_t;
// We cannot rely solely on natural alignment of a type when building a
// coroutine frame and if the alignment specified on the Alloca instruction
// differs from the natural alignment of the alloca type we will need to insert
// padding.
class FrameTypeBuilder {
private:
  struct Field {
    uint64_t Size;
    uint64_t Offset;
    Align Alignment;
    uint64_t DynamicAlignBuffer;
  };
 
  const DataLayout &DL;
  uint64_t StructSize = 0;
  Align StructAlign;
  bool IsFinished = false;
 
  std::optional<Align> MaxFrameAlignment;
 
  SmallVector<Field, 8> Fields;
  DenseMap<Value*, unsigned> FieldIndexByKey;
 
public:
  FrameTypeBuilder(const DataLayout &DL, std::optional<Align> MaxFrameAlignment)
      : DL(DL), MaxFrameAlignment(MaxFrameAlignment) {}
 
  /// Add a field to this structure for the storage of an `alloca`
  /// instruction.
  [[nodiscard]] FieldIDType addFieldForAlloca(AllocaInst *AI,
                                              bool IsHeader = false) {
    auto Size = AI->getAllocationSize(AI->getDataLayout());
    if (!Size || !Size->isFixed())
      report_fatal_error(
          "Coroutines cannot handle non static or vscale allocas yet");
    return addField(Size->getFixedValue(), AI->getAlign(), IsHeader);
  }
 
  /// We want to put the allocas whose lifetime-ranges are not overlapped
  /// into one slot of coroutine frame.
  /// Consider the example at:https://bugs.llvm.org/show_bug.cgi?id=45566
  ///
  ///     cppcoro::task<void> alternative_paths(bool cond) {
  ///         if (cond) {
  ///             big_structure a;
  ///             process(a);
  ///             co_await something();
  ///         } else {
  ///             big_structure b;
  ///             process2(b);
  ///             co_await something();
  ///         }
  ///     }
  ///
  /// We want to put variable a and variable b in the same slot to
  /// reduce the size of coroutine frame.
  ///
  /// This function use StackLifetime algorithm to partition the AllocaInsts in
  /// Spills to non-overlapped sets in order to put Alloca in the same
  /// non-overlapped set into the same slot in the Coroutine Frame. Then add
  /// field for the allocas in the same non-overlapped set by using the largest
  /// type as the field type.
  ///
  /// Side Effects: Because We sort the allocas, the order of allocas in the
  /// frame may be different with the order in the source code.
  void addFieldForAllocas(const Function &F, FrameDataInfo &FrameData,
                          coro::Shape &Shape, bool OptimizeFrame);
 
  /// Add a field to this structure for a spill.
  [[nodiscard]] FieldIDType addField(Type *Ty, MaybeAlign MaybeFieldAlignment,
                                     bool IsHeader = false,
                                     bool IsSpillOfValue = false) {
    assert(Ty && "must provide a type for a field");
    // The field size is the alloc size of the type.
    uint64_t FieldSize = DL.getTypeAllocSize(Ty);
    // The field alignment is usually the type alignment.
    // But if we are spilling values we don't need to worry about ABI alignment
    // concerns.
    Align ABIAlign = DL.getABITypeAlign(Ty);
    Align TyAlignment = ABIAlign;
    if (IsSpillOfValue && MaxFrameAlignment && *MaxFrameAlignment < ABIAlign)
      TyAlignment = *MaxFrameAlignment;
    Align FieldAlignment = MaybeFieldAlignment.value_or(TyAlignment);
    return addField(FieldSize, FieldAlignment, IsHeader);
  }
 
  /// Add a field to this structure.
  [[nodiscard]] FieldIDType addField(uint64_t FieldSize, Align FieldAlignment,
                                     bool IsHeader = false) {
    assert(!IsFinished && "adding fields to a finished builder");
 
    // For an alloca with size=0, we don't need to add a field and they
    // can just point to any index in the frame. Use index 0.
    if (FieldSize == 0)
      return 0;
 
    // The field alignment could be bigger than the max frame case, in that case
    // we request additional storage to be able to dynamically align the
    // pointer.
    uint64_t DynamicAlignBuffer = 0;
    if (MaxFrameAlignment && (FieldAlignment > *MaxFrameAlignment)) {
      DynamicAlignBuffer =
          offsetToAlignment(MaxFrameAlignment->value(), FieldAlignment);
      FieldAlignment = *MaxFrameAlignment;
      FieldSize = FieldSize + DynamicAlignBuffer;
    }
 
    // Lay out header fields immediately.
    uint64_t Offset;
    if (IsHeader) {
      Offset = alignTo(StructSize, FieldAlignment);
      StructSize = Offset + FieldSize;
 
      // Everything else has a flexible offset.
    } else {
      Offset = OptimizedStructLayoutField::FlexibleOffset;
    }
 
    Fields.push_back({FieldSize, Offset, FieldAlignment, DynamicAlignBuffer});
    return Fields.size() - 1;
  }
 
  /// Finish the layout and compute final size and alignment.
  void finish();
 
  uint64_t getStructSize() const {
    assert(IsFinished && "not yet finished!");
    return StructSize;
  }
 
  Align getStructAlign() const {
    assert(IsFinished && "not yet finished!");
    return StructAlign;
  }
 
  Field getLayoutField(FieldIDType Id) const {
    assert(IsFinished && "not yet finished!");
    return Fields[Id];
  }
};
} // namespace
 
void FrameDataInfo::updateLayoutInfo(FrameTypeBuilder &B) {
  auto Updater = [&](Value *I) {
    uint32_t FieldIndex = getFieldIndex(I);
    auto Field = B.getLayoutField(FieldIndex);
    setAlign(I, Field.Alignment);
    uint64_t dynamicAlign =
        Field.DynamicAlignBuffer
            ? Field.DynamicAlignBuffer + Field.Alignment.value()
            : 0;
    setDynamicAlign(I, dynamicAlign);
    setOffset(I, Field.Offset);
  };
  for (auto &S : Spills)
    Updater(S.first);
  for (const auto &A : Allocas)
    Updater(A.Alloca);
}
 
void FrameTypeBuilder::addFieldForAllocas(const Function &F,
                                          FrameDataInfo &FrameData,
                                          coro::Shape &Shape,
                                          bool OptimizeFrame) {
  using AllocaSetType = SmallVector<AllocaInst *, 4>;
  SmallVector<AllocaSetType, 4> NonOverlapedAllocas;
 
  // We need to add field for allocas at the end of this function.
  llvm::scope_exit AddFieldForAllocasAtExit([&]() {
    for (auto AllocaList : NonOverlapedAllocas) {
      auto *LargestAI = *AllocaList.begin();
      FieldIDType Id = addFieldForAlloca(LargestAI);
      for (auto *Alloca : AllocaList)
        FrameData.setFieldIndex(Alloca, Id);
    }
  });
 
  if (!OptimizeFrame) {
    for (const auto &A : FrameData.Allocas) {
      AllocaInst *Alloca = A.Alloca;
      NonOverlapedAllocas.emplace_back(AllocaSetType(1, Alloca));
    }
    return;
  }
 
  // Because there are paths from the lifetime.start to coro.end
  // for each alloca, the liferanges for every alloca is overlaped
  // in the blocks who contain coro.end and the successor blocks.
  // So we choose to skip there blocks when we calculate the liferange
  // for each alloca. It should be reasonable since there shouldn't be uses
  // in these blocks and the coroutine frame shouldn't be used outside the
  // coroutine body.
  //
  // Note that the user of coro.suspend may not be SwitchInst. However, this
  // case seems too complex to handle. And it is harmless to skip these
  // patterns since it just prevend putting the allocas to live in the same
  // slot.
  DenseMap<SwitchInst *, BasicBlock *> DefaultSuspendDest;
  for (auto *CoroSuspendInst : Shape.CoroSuspends) {
    for (auto *U : CoroSuspendInst->users()) {
      if (auto *ConstSWI = dyn_cast<SwitchInst>(U)) {
        auto *SWI = const_cast<SwitchInst *>(ConstSWI);
        DefaultSuspendDest[SWI] = SWI->getDefaultDest();
        SWI->setDefaultDest(SWI->getSuccessor(1));
      }
    }
  }
 
  auto ExtractAllocas = [&]() {
    AllocaSetType Allocas;
    Allocas.reserve(FrameData.Allocas.size());
    for (const auto &A : FrameData.Allocas)
      Allocas.push_back(A.Alloca);
    return Allocas;
  };
  StackLifetime StackLifetimeAnalyzer(F, ExtractAllocas(),
                                      StackLifetime::LivenessType::May);
  StackLifetimeAnalyzer.run();
  auto DoAllocasInterfere = [&](const AllocaInst *AI1, const AllocaInst *AI2) {
    return StackLifetimeAnalyzer.getLiveRange(AI1).overlaps(
        StackLifetimeAnalyzer.getLiveRange(AI2));
  };
  auto GetAllocaSize = [&](const coro::AllocaInfo &A) {
    std::optional<TypeSize> RetSize = A.Alloca->getAllocationSize(DL);
    assert(RetSize && "Variable Length Arrays (VLA) are not supported.\n");
    assert(!RetSize->isScalable() && "Scalable vectors are not yet supported");
    return RetSize->getFixedValue();
  };
  // Put larger allocas in the front. So the larger allocas have higher
  // priority to merge, which can save more space potentially. Also each
  // AllocaSet would be ordered. So we can get the largest Alloca in one
  // AllocaSet easily.
  sort(FrameData.Allocas, [&](const auto &Iter1, const auto &Iter2) {
    return GetAllocaSize(Iter1) > GetAllocaSize(Iter2);
  });
  for (const auto &A : FrameData.Allocas) {
    AllocaInst *Alloca = A.Alloca;
    bool Merged = false;
    // Try to find if the Alloca does not interfere with any existing
    // NonOverlappedAllocaSet. If it is true, insert the alloca to that
    // NonOverlappedAllocaSet.
    for (auto &AllocaSet : NonOverlapedAllocas) {
      assert(!AllocaSet.empty() && "Processing Alloca Set is not empty.\n");
      bool NoInterference = none_of(AllocaSet, [&](auto Iter) {
        return DoAllocasInterfere(Alloca, Iter);
      });
      // If the alignment of A is multiple of the alignment of B, the address
      // of A should satisfy the requirement for aligning for B.
      //
      // There may be other more fine-grained strategies to handle the alignment
      // infomation during the merging process. But it seems hard to handle
      // these strategies and benefit little.
      bool Alignable = [&]() -> bool {
        auto *LargestAlloca = *AllocaSet.begin();
        return LargestAlloca->getAlign().value() % Alloca->getAlign().value() ==
               0;
      }();
      bool CouldMerge = NoInterference && Alignable;
      if (!CouldMerge)
        continue;
      AllocaSet.push_back(Alloca);
      Merged = true;
      break;
    }
    if (!Merged) {
      NonOverlapedAllocas.emplace_back(AllocaSetType(1, Alloca));
    }
  }
  // Recover the default target destination for each Switch statement
  // reserved.
  for (auto SwitchAndDefaultDest : DefaultSuspendDest) {
    SwitchInst *SWI = SwitchAndDefaultDest.first;
    BasicBlock *DestBB = SwitchAndDefaultDest.second;
    SWI->setDefaultDest(DestBB);
  }
  // This Debug Info could tell us which allocas are merged into one slot.
  LLVM_DEBUG(for (auto &AllocaSet
                  : NonOverlapedAllocas) {
    if (AllocaSet.size() > 1) {
      dbgs() << "In Function:" << F.getName() << "\n";
      dbgs() << "Find Union Set "
             << "\n";
      dbgs() << "\tAllocas are \n";
      for (auto Alloca : AllocaSet)
        dbgs() << "\t\t" << *Alloca << "\n";
    }
  });
}
 
void FrameTypeBuilder::finish() {
  assert(!IsFinished && "already finished!");
 
  // Prepare the optimal-layout field array.
  // The Id in the layout field is a pointer to our Field for it.
  SmallVector<OptimizedStructLayoutField, 8> LayoutFields;
  LayoutFields.reserve(Fields.size());
  for (auto &Field : Fields) {
    LayoutFields.emplace_back(&Field, Field.Size, Field.Alignment,
                              Field.Offset);
  }
 
  // Perform layout to compute size, alignment, and field offsets.
  auto SizeAndAlign = performOptimizedStructLayout(LayoutFields);
  StructSize = SizeAndAlign.first;
  StructAlign = SizeAndAlign.second;
 
  auto getField = [](const OptimizedStructLayoutField &LayoutField) -> Field & {
    return *static_cast<Field *>(const_cast<void*>(LayoutField.Id));
  };
 
  // Update field offsets from the computed layout.
  for (auto &LayoutField : LayoutFields) {
    auto &F = getField(LayoutField);
    F.Offset = LayoutField.Offset;
  }
 
  IsFinished = true;
}
 
static void cacheDIVar(FrameDataInfo &FrameData,
                       DenseMap<Value *, DILocalVariable *> &DIVarCache) {
  for (auto *V : FrameData.getAllDefs()) {
    if (DIVarCache.contains(V))
      continue;
 
    auto CacheIt = [&DIVarCache, V](const auto &Container) {
      auto *I = llvm::find_if(Container, [](auto *DDI) {
        return DDI->getExpression()->getNumElements() == 0;
      });
      if (I != Container.end())
        DIVarCache.insert({V, (*I)->getVariable()});
    };
    CacheIt(findDVRDeclares(V));
    CacheIt(findDVRDeclareValues(V));
  }
}
 
/// Create name for Type. It uses MDString to store new created string to
/// avoid memory leak.
static StringRef solveTypeName(Type *Ty) {
  if (Ty->isIntegerTy()) {
    // The longest name in common may be '__int_128', which has 9 bits.
    SmallString<16> Buffer;
    raw_svector_ostream OS(Buffer);
    OS << "__int_" << cast<IntegerType>(Ty)->getBitWidth();
    auto *MDName = MDString::get(Ty->getContext(), OS.str());
    return MDName->getString();
  }
 
  if (Ty->isFloatingPointTy()) {
    if (Ty->isFloatTy())
      return "__float_";
    if (Ty->isDoubleTy())
      return "__double_";
    return "__floating_type_";
  }
 
  if (Ty->isPointerTy())
    return "PointerType";
 
  if (Ty->isStructTy()) {
    if (!cast<StructType>(Ty)->hasName())
      return "__LiteralStructType_";
 
    auto Name = Ty->getStructName();
 
    SmallString<16> Buffer(Name);
    for (auto &Iter : Buffer)
      if (Iter == '.' || Iter == ':')
        Iter = '_';
    auto *MDName = MDString::get(Ty->getContext(), Buffer.str());
    return MDName->getString();
  }
 
  return "UnknownType";
}
 
static DIType *solveDIType(DIBuilder &Builder, Type *Ty,
                           const DataLayout &Layout, DIScope *Scope,
                           unsigned LineNum,
                           DenseMap<Type *, DIType *> &DITypeCache) {
  if (DIType *DT = DITypeCache.lookup(Ty))
    return DT;
 
  StringRef Name = solveTypeName(Ty);
 
  DIType *RetType = nullptr;
 
  if (Ty->isIntegerTy()) {
    auto BitWidth = cast<IntegerType>(Ty)->getBitWidth();
    RetType = Builder.createBasicType(Name, BitWidth, dwarf::DW_ATE_signed,
                                      llvm::DINode::FlagArtificial);
  } else if (Ty->isFloatingPointTy()) {
    RetType = Builder.createBasicType(Name, Layout.getTypeSizeInBits(Ty),
                                      dwarf::DW_ATE_float,
                                      llvm::DINode::FlagArtificial);
  } else if (Ty->isPointerTy()) {
    // Construct PointerType points to null (aka void *) instead of exploring
    // pointee type to avoid infinite search problem. For example, we would be
    // in trouble if we traverse recursively:
    //
    //  struct Node {
    //      Node* ptr;
    //  };
    RetType =
        Builder.createPointerType(nullptr, Layout.getTypeSizeInBits(Ty),
                                  Layout.getABITypeAlign(Ty).value() * CHAR_BIT,
                                  /*DWARFAddressSpace=*/std::nullopt, Name);
  } else if (Ty->isStructTy()) {
    auto *DIStruct = Builder.createStructType(
        Scope, Name, Scope->getFile(), LineNum, Layout.getTypeSizeInBits(Ty),
        Layout.getPrefTypeAlign(Ty).value() * CHAR_BIT,
        llvm::DINode::FlagArtificial, nullptr, llvm::DINodeArray());
 
    auto *StructTy = cast<StructType>(Ty);
    SmallVector<Metadata *, 16> Elements;
    for (unsigned I = 0; I < StructTy->getNumElements(); I++) {
      DIType *DITy = solveDIType(Builder, StructTy->getElementType(I), Layout,
                                 DIStruct, LineNum, DITypeCache);
      assert(DITy);
      Elements.push_back(Builder.createMemberType(
          DIStruct, DITy->getName(), DIStruct->getFile(), LineNum,
          DITy->getSizeInBits(), DITy->getAlignInBits(),
          Layout.getStructLayout(StructTy)->getElementOffsetInBits(I),
          llvm::DINode::FlagArtificial, DITy));
    }
 
    Builder.replaceArrays(DIStruct, Builder.getOrCreateArray(Elements));
 
    RetType = DIStruct;
  } else {
    LLVM_DEBUG(dbgs() << "Unresolved Type: " << *Ty << "\n");
    TypeSize Size = Layout.getTypeSizeInBits(Ty);
    auto *CharSizeType = Builder.createBasicType(
        Name, 8, dwarf::DW_ATE_unsigned_char, llvm::DINode::FlagArtificial);
 
    if (Size <= 8)
      RetType = CharSizeType;
    else {
      if (Size % 8 != 0)
        Size = TypeSize::getFixed(Size + 8 - (Size % 8));
 
      RetType = Builder.createArrayType(
          Size, Layout.getPrefTypeAlign(Ty).value(), CharSizeType,
          Builder.getOrCreateArray(Builder.getOrCreateSubrange(0, Size / 8)));
    }
  }
 
  DITypeCache.insert({Ty, RetType});
  return RetType;
}
 
/// Build artificial debug info for C++ coroutine frames to allow users to
/// inspect the contents of the frame directly
///
/// Create Debug information for coroutine frame with debug name "__coro_frame".
/// The debug information for the fields of coroutine frame is constructed from
/// the following way:
/// 1. For all the value in the Frame, we search the use of dbg.declare to find
///    the corresponding debug variables for the value. If we can find the
///    debug variable, we can get full and accurate debug information.
/// 2. If we can't get debug information in step 1 and 2, we could only try to
///    build the DIType by Type. We did this in solveDIType. We only handle
///    integer, float, double, integer type and struct type for now.
static void buildFrameDebugInfo(Function &F, coro::Shape &Shape,
                                FrameDataInfo &FrameData) {
  DISubprogram *DIS = F.getSubprogram();
  // If there is no DISubprogram for F, it implies the function is compiled
  // without debug info. So we also don't generate debug info for the frame.
 
  if (!DIS || !DIS->getUnit())
    return;
 
  if (!dwarf::isCPlusPlus(static_cast<llvm::dwarf::SourceLanguage>(
          DIS->getUnit()->getSourceLanguage().getUnversionedName())) ||
      DIS->getUnit()->getEmissionKind() !=
          DICompileUnit::DebugEmissionKind::FullDebug)
    return;
 
  assert(Shape.ABI == coro::ABI::Switch &&
         "We could only build debug infomation for C++ coroutine now.\n");
 
  DIBuilder DBuilder(*F.getParent(), /*AllowUnresolved*/ false);
 
  DIFile *DFile = DIS->getFile();
  unsigned LineNum = DIS->getLine();
 
  DICompositeType *FrameDITy = DBuilder.createStructType(
      DIS->getUnit(), Twine(F.getName() + ".coro_frame_ty").str(), DFile,
      LineNum, Shape.FrameSize * 8, Shape.FrameAlign.value() * 8,
      llvm::DINode::FlagArtificial, nullptr, llvm::DINodeArray());
  SmallVector<Metadata *, 16> Elements;
  DataLayout Layout = F.getDataLayout();
 
  DenseMap<Value *, DILocalVariable *> DIVarCache;
  cacheDIVar(FrameData, DIVarCache);
 
  // This counter is used to avoid same type names. e.g., there would be
  // many i32 and i64 types in one coroutine. And we would use i32_0 and
  // i32_1 to avoid the same type. Since it makes no sense the name of the
  // fields confilicts with each other.
  unsigned UnknownTypeNum = 0;
  DenseMap<Type *, DIType *> DITypeCache;
 
  auto addElement = [&](StringRef Name, uint64_t SizeInBits, uint64_t Alignment,
                        uint64_t Offset, DIType *DITy) {
    Elements.push_back(DBuilder.createMemberType(
        FrameDITy, Name, DFile, LineNum, SizeInBits, Alignment, Offset * 8,
        llvm::DINode::FlagArtificial, DITy));
  };
 
  auto addDIDef = [&](Value *V) {
    // Get the offset and alignment for this value.
    uint64_t Offset = FrameData.getOffset(V);
    Align Alignment = FrameData.getAlign(V);
 
    std::string Name;
    uint64_t SizeInBits;
    DIType *DITy = nullptr;
 
    auto It = DIVarCache.find(V);
    if (It != DIVarCache.end()) {
      // Get the type from the debug variable.
      Name = It->second->getName().str();
      DITy = It->second->getType();
    } else {
      if (auto AI = dyn_cast<AllocaInst>(V)) {
        // Frame alloca
        DITy = solveDIType(DBuilder, AI->getAllocatedType(), Layout, FrameDITy,
                           LineNum, DITypeCache);
      } else {
        // Spill
        DITy = solveDIType(DBuilder, V->getType(), Layout, FrameDITy, LineNum,
                           DITypeCache);
      }
      assert(DITy && "SolveDIType shouldn't return nullptr.\n");
      Name = DITy->getName().str();
      Name += "_" + std::to_string(UnknownTypeNum);
      UnknownTypeNum++;
    }
 
    if (auto AI = dyn_cast<AllocaInst>(V)) {
      // Lookup the total size of this alloca originally
      auto Size = AI->getAllocationSize(Layout);
      assert(Size && Size->isFixed() &&
             "unreachable due to addFieldForAlloca checks");
      SizeInBits = Size->getFixedValue() * 8;
    } else {
      // Compute the size of the active data of this member for this spill
      SizeInBits = Layout.getTypeSizeInBits(V->getType());
    }
 
    addElement(Name, SizeInBits, Alignment.value() * 8, Offset, DITy);
  };
 
  // For Switch ABI, add debug info for the added fields (resume, destroy).
  if (Shape.ABI == coro::ABI::Switch) {
    auto *FnPtrTy = Shape.getSwitchResumePointerType();
    uint64_t PtrSize = Layout.getPointerSizeInBits(FnPtrTy->getAddressSpace());
    uint64_t PtrAlign =
        Layout.getPointerABIAlignment(FnPtrTy->getAddressSpace()).value() * 8;
    auto *DIPtr = DBuilder.createPointerType(nullptr, PtrSize,
                                             FnPtrTy->getAddressSpace());
    addElement("__resume_fn", PtrSize, PtrAlign, 0, DIPtr);
    addElement("__destroy_fn", PtrSize, PtrAlign,
               Shape.SwitchLowering.DestroyOffset, DIPtr);
    uint64_t IndexSize =
        Layout.getTypeSizeInBits(Shape.getIndexType()).getFixedValue();
    addElement("__coro_index", IndexSize, Shape.SwitchLowering.IndexAlign * 8,
               Shape.SwitchLowering.IndexOffset,
               DBuilder.createBasicType("__coro_index",
                                        (IndexSize < 8) ? 8 : IndexSize,
                                        dwarf::DW_ATE_unsigned_char));
  }
  auto Defs = FrameData.getAllDefs();
  for (auto *V : Defs)
    addDIDef(V);
 
  DBuilder.replaceArrays(FrameDITy, DBuilder.getOrCreateArray(Elements));
 
  auto *FrameDIVar =
      DBuilder.createAutoVariable(DIS, "__coro_frame", DFile, LineNum,
                                  FrameDITy, true, DINode::FlagArtificial);
 
  // Subprogram would have ContainedNodes field which records the debug
  // variables it contained. So we need to add __coro_frame to the
  // ContainedNodes of it.
  //
  // If we don't add __coro_frame to the RetainedNodes, user may get
  // `no symbol __coro_frame in context` rather than `__coro_frame`
  // is optimized out, which is more precise.
  DIS->retainNodes(&FrameDIVar, &FrameDIVar + 1);
 
  // Construct the location for the frame debug variable. The column number
  // is fake but it should be fine.
  DILocation *DILoc =
      DILocation::get(DIS->getContext(), LineNum, /*Column=*/1, DIS);
  assert(FrameDIVar->isValidLocationForIntrinsic(DILoc));
 
  DbgVariableRecord *NewDVR =
      new DbgVariableRecord(ValueAsMetadata::get(Shape.FramePtr), FrameDIVar,
                            DBuilder.createExpression(), DILoc,
                            DbgVariableRecord::LocationType::Declare);
  BasicBlock::iterator It = Shape.getInsertPtAfterFramePtr();
  It->getParent()->insertDbgRecordBefore(NewDVR, It);
}
 
// If there is memory accessing to promise alloca before CoroBegin
static bool hasAccessingPromiseBeforeCB(const DominatorTree &DT,
                                        coro::Shape &Shape) {
  auto *PA = Shape.SwitchLowering.PromiseAlloca;
  return llvm::any_of(PA->uses(), [&](Use &U) {
    auto *Inst = dyn_cast<Instruction>(U.getUser());
    if (!Inst || DT.dominates(Shape.CoroBegin, Inst))
      return false;
 
    if (auto *CI = dyn_cast<CallInst>(Inst)) {
      // It is fine if the call wouldn't write to the Promise.
      // This is possible for @llvm.coro.id intrinsics, which
      // would take the promise as the second argument as a
      // marker.
      if (CI->onlyReadsMemory() || CI->onlyReadsMemory(CI->getArgOperandNo(&U)))
        return false;
      return true;
    }
 
    return isa<StoreInst>(Inst) ||
           // It may take too much time to track the uses.
           // Be conservative about the case the use may escape.
           isa<GetElementPtrInst>(Inst) ||
           // There would always be a bitcast for the promise alloca
           // before we enabled Opaque pointers. And now given
           // opaque pointers are enabled by default. This should be
           // fine.
           isa<BitCastInst>(Inst);
  });
}
// Build the coroutine frame type as a byte array.
// The frame layout includes:
//   - Resume function pointer at offset 0 (Switch ABI only)
//   - Destroy function pointer at offset ptrsize (Switch ABI only)
//   - Promise alloca (Switch ABI only, only if present)
//   - Suspend/Resume index
//   - Spilled values and allocas
static void buildFrameLayout(Function &F, const DominatorTree &DT,
                             coro::Shape &Shape, FrameDataInfo &FrameData,
                             bool OptimizeFrame) {
  const DataLayout &DL = F.getDataLayout();
 
  // We will use this value to cap the alignment of spilled values.
  std::optional<Align> MaxFrameAlignment;
  if (Shape.ABI == coro::ABI::Async)
    MaxFrameAlignment = Shape.AsyncLowering.getContextAlignment();
  FrameTypeBuilder B(DL, MaxFrameAlignment);
 
  AllocaInst *PromiseAlloca = Shape.getPromiseAlloca();
  std::optional<FieldIDType> SwitchIndexFieldId;
  IntegerType *SwitchIndexType = nullptr;
 
  if (Shape.ABI == coro::ABI::Switch) {
    auto *FnPtrTy = Shape.getSwitchResumePointerType();
 
    // Add header fields for the resume and destroy functions.
    // We can rely on these being perfectly packed.
    (void)B.addField(FnPtrTy, MaybeAlign(), /*header*/ true);
    (void)B.addField(FnPtrTy, MaybeAlign(), /*header*/ true);
 
    // PromiseAlloca field needs to be explicitly added here because it's
    // a header field with a fixed offset based on its alignment. Hence it
    // needs special handling.
    if (PromiseAlloca)
      FrameData.setFieldIndex(
          PromiseAlloca, B.addFieldForAlloca(PromiseAlloca, /*header*/ true));
 
    // Add a field to store the suspend index.  This doesn't need to
    // be in the header.
    unsigned IndexBits = std::max(1U, Log2_64_Ceil(Shape.CoroSuspends.size()));
    Type *LegalTy =
        F.getDataLayout().getSmallestLegalIntType(F.getContext(), IndexBits);
    SwitchIndexType = LegalTy ? cast<IntegerType>(LegalTy)
                              : Type::getIntNTy(F.getContext(), IndexBits);
 
    SwitchIndexFieldId = B.addField(SwitchIndexType, MaybeAlign());
  } else {
    assert(PromiseAlloca == nullptr && "lowering doesn't support promises");
  }
 
  // Because multiple allocas may own the same field slot,
  // we add allocas to field here.
  B.addFieldForAllocas(F, FrameData, Shape, OptimizeFrame);
  // Add PromiseAlloca to Allocas list so that
  // 1. updateLayoutIndex could update its index after
  // `performOptimizedStructLayout`
  // 2. it is processed in insertSpills.
  if (Shape.ABI == coro::ABI::Switch && PromiseAlloca) {
    // We assume that no alias will be create before CoroBegin.
    FrameData.Allocas.emplace_back(
        PromiseAlloca, DenseMap<Instruction *, std::optional<APInt>>{},
        hasAccessingPromiseBeforeCB(DT, Shape));
  }
  // Create an entry for every spilled value.
  for (auto &S : FrameData.Spills) {
    Type *FieldType = S.first->getType();
    MaybeAlign MA;
    // For byval arguments, we need to store the pointed value in the frame,
    // instead of the pointer itself.
    if (const Argument *A = dyn_cast<Argument>(S.first)) {
      if (A->hasByValAttr()) {
        FieldType = A->getParamByValType();
        MA = A->getParamAlign();
      }
    }
    FieldIDType Id =
        B.addField(FieldType, MA, false /*header*/, true /*IsSpillOfValue*/);
    FrameData.setFieldIndex(S.first, Id);
  }
 
  B.finish();
 
  FrameData.updateLayoutInfo(B);
  Shape.FrameAlign = B.getStructAlign();
  Shape.FrameSize = B.getStructSize();
 
  switch (Shape.ABI) {
  case coro::ABI::Switch: {
    // In the switch ABI, remember the function pointer and index field info.
    // Resume and Destroy function pointers are in the frame header.
    const DataLayout &DL = F.getDataLayout();
    Shape.SwitchLowering.DestroyOffset = DL.getPointerSize();
 
    auto IndexField = B.getLayoutField(*SwitchIndexFieldId);
    Shape.SwitchLowering.IndexType = SwitchIndexType;
    Shape.SwitchLowering.IndexAlign = IndexField.Alignment.value();
    Shape.SwitchLowering.IndexOffset = IndexField.Offset;
 
    // Also round the frame size up to a multiple of its alignment, as is
    // generally expected in C/C++.
    Shape.FrameSize = alignTo(Shape.FrameSize, Shape.FrameAlign);
    break;
  }
 
  // In the retcon ABI, remember whether the frame is inline in the storage.
  case coro::ABI::Retcon:
  case coro::ABI::RetconOnce: {
    auto Id = Shape.getRetconCoroId();
    Shape.RetconLowering.IsFrameInlineInStorage
      = (B.getStructSize() <= Id->getStorageSize() &&
         B.getStructAlign() <= Id->getStorageAlignment());
    break;
  }
  case coro::ABI::Async: {
    Shape.AsyncLowering.FrameOffset =
        alignTo(Shape.AsyncLowering.ContextHeaderSize, Shape.FrameAlign);
    // Also make the final context size a multiple of the context alignment to
    // make allocation easier for allocators.
    Shape.AsyncLowering.ContextSize =
        alignTo(Shape.AsyncLowering.FrameOffset + Shape.FrameSize,
                Shape.AsyncLowering.getContextAlignment());
    if (Shape.AsyncLowering.getContextAlignment() < Shape.FrameAlign) {
      report_fatal_error(
          "The alignment requirment of frame variables cannot be higher than "
          "the alignment of the async function context");
    }
    break;
  }
  }
}
 
/// If MaybeArgument is a byval Argument, return its byval type. Also removes
/// the captures attribute, so that the argument *value* may be stored directly
/// on the coroutine frame.
static Type *extractByvalIfArgument(Value *MaybeArgument) {
  if (auto *Arg = dyn_cast<Argument>(MaybeArgument)) {
    Arg->getParent()->removeParamAttr(Arg->getArgNo(), Attribute::Captures);
 
    if (Arg->hasByValAttr())
      return Arg->getParamByValType();
  }
  return nullptr;
}
 
/// Store Def into the coroutine frame.
static void createStoreIntoFrame(IRBuilder<> &Builder, Value *Def,
                                 Type *ByValTy, const coro::Shape &Shape,
                                 const FrameDataInfo &FrameData) {
  LLVMContext &Ctx = Shape.CoroBegin->getContext();
  uint64_t Offset = FrameData.getOffset(Def);
 
  Value *G = Shape.FramePtr;
  if (Offset != 0) {
    auto *OffsetVal = ConstantInt::get(Type::getInt64Ty(Ctx), Offset);
    G = Builder.CreateInBoundsPtrAdd(G, OffsetVal,
                                     Def->getName() + Twine(".spill.addr"));
  }
  auto SpillAlignment = Align(FrameData.getAlign(Def));
 
  // For byval arguments, copy the pointed-to value to the frame.
  if (ByValTy) {
    auto &DL = Builder.GetInsertBlock()->getDataLayout();
    auto Size = DL.getTypeStoreSize(ByValTy);
    // Def is a pointer to the byval argument
    Builder.CreateMemCpy(G, SpillAlignment, Def, SpillAlignment, Size);
  } else {
    Builder.CreateAlignedStore(Def, G, SpillAlignment);
  }
}
 
/// Returns a pointer into the coroutine frame at the offset where Orig is
/// located.
static Value *createGEPToFramePointer(const FrameDataInfo &FrameData,
                                      IRBuilder<> &Builder, coro::Shape &Shape,
                                      Value *Orig) {
  LLVMContext &Ctx = Shape.CoroBegin->getContext();
  uint64_t Offset = FrameData.getOffset(Orig);
  auto *OffsetVal = ConstantInt::get(Type::getInt64Ty(Ctx), Offset);
  Value *Ptr = Builder.CreateInBoundsPtrAdd(Shape.FramePtr, OffsetVal);
 
  if (auto *AI = dyn_cast<AllocaInst>(Orig)) {
    if (FrameData.getDynamicAlign(Orig) != 0) {
      assert(FrameData.getDynamicAlign(Orig) == AI->getAlign().value());
      auto *M = AI->getModule();
      auto *IntPtrTy = M->getDataLayout().getIntPtrType(AI->getType());
      auto *PtrValue = Builder.CreatePtrToInt(Ptr, IntPtrTy);
      auto *AlignMask = ConstantInt::get(IntPtrTy, AI->getAlign().value() - 1);
      PtrValue = Builder.CreateAdd(PtrValue, AlignMask);
      PtrValue = Builder.CreateAnd(PtrValue, Builder.CreateNot(AlignMask));
      return Builder.CreateIntToPtr(PtrValue, AI->getType());
    }
    // If the type of Ptr is not equal to the type of AllocaInst, it implies
    // that the AllocaInst may be reused in the Frame slot of other AllocaInst.
    // Note: If the strategy dealing with alignment changes, this cast must be
    // refined
    if (Ptr->getType() != Orig->getType())
      Ptr = Builder.CreateAddrSpaceCast(Ptr, Orig->getType(),
                                        Orig->getName() + Twine(".cast"));
  }
  return Ptr;
}
 
/// Find dbg.declare or dbg.declare_value records referencing `Def`. If none are
/// found, walk up the load chain to find one.
template <DbgVariableRecord::LocationType record_type>
static TinyPtrVector<DbgVariableRecord *>
findDbgRecordsThroughLoads(Function &F, Value *Def) {
  static_assert(record_type == DbgVariableRecord::LocationType::Declare ||
                record_type == DbgVariableRecord::LocationType::DeclareValue);
  constexpr auto FindFunc =
      record_type == DbgVariableRecord::LocationType::Declare
          ? findDVRDeclares
          : findDVRDeclareValues;
 
  TinyPtrVector<DbgVariableRecord *> Records = FindFunc(Def);
 
  if (!F.getSubprogram())
    return Records;
 
  Value *CurDef = Def;
  while (Records.empty() && isa<LoadInst>(CurDef)) {
    auto *LdInst = cast<LoadInst>(CurDef);
    if (!LdInst->getType()->isPointerTy())
      break;
    CurDef = LdInst->getPointerOperand();
    if (!isa<AllocaInst, LoadInst>(CurDef))
      break;
    Records = FindFunc(CurDef);
  }
 
  return Records;
}
 
// Helper function to handle allocas that may be accessed before CoroBegin.
// This creates a memcpy from the original alloca to the coroutine frame after
// CoroBegin, ensuring the frame has the correct initial values.
static void handleAccessBeforeCoroBegin(const FrameDataInfo &FrameData,
                                        coro::Shape &Shape,
                                        IRBuilder<> &Builder,
                                        AllocaInst *Alloca) {
  Value *Size = Builder.CreateAllocationSize(Builder.getInt64Ty(), Alloca);
  auto *G = createGEPToFramePointer(FrameData, Builder, Shape, Alloca);
  Builder.CreateMemCpy(G, FrameData.getAlign(Alloca), Alloca,
                       Alloca->getAlign(), Size);
}
 
// Replace all alloca and SSA values that are accessed across suspend points
// with GetElementPointer from coroutine frame + loads and stores. Create an
// AllocaSpillBB that will become the new entry block for the resume parts of
// the coroutine:
//
//    %hdl = coro.begin(...)
//    whatever
//
// becomes:
//
//    %hdl = coro.begin(...)
//    br label %AllocaSpillBB
//
//  AllocaSpillBB:
//    ; geps corresponding to allocas that were moved to coroutine frame
//    br label PostSpill
//
//  PostSpill:
//    whatever
//
//
static void insertSpills(const FrameDataInfo &FrameData, coro::Shape &Shape) {
  LLVMContext &C = Shape.CoroBegin->getContext();
  Function *F = Shape.CoroBegin->getFunction();
  IRBuilder<> Builder(C);
  DominatorTree DT(*F);
  SmallDenseMap<Argument *, AllocaInst *, 4> ArgToAllocaMap;
 
  MDBuilder MDB(C);
  // Create a TBAA tag for accesses to certain coroutine frame slots, so that
  // subsequent alias analysis will understand they do not intersect with
  // user memory.
  // We do this only if a suitable TBAA root already exists in the module.
  MDNode *TBAATag = nullptr;
  if (auto *CppTBAAStr = MDString::getIfExists(C, "Simple C++ TBAA")) {
    auto *TBAARoot = MDNode::getIfExists(C, CppTBAAStr);
    // Create a "fake" scalar type; all other types defined in the source
    // language will be assumed non-aliasing with this type.
    MDNode *Scalar = MDB.createTBAAScalarTypeNode(
        (F->getName() + ".Frame Slot").str(), TBAARoot);
    TBAATag = MDB.createTBAAStructTagNode(Scalar, Scalar, 0);
  }
  for (auto const &E : FrameData.Spills) {
    Value *Def = E.first;
    Type *ByValTy = extractByvalIfArgument(Def);
 
    Builder.SetInsertPoint(coro::getSpillInsertionPt(Shape, Def, DT));
    createStoreIntoFrame(Builder, Def, ByValTy, Shape, FrameData);
 
    BasicBlock *CurrentBlock = nullptr;
    Value *CurrentReload = nullptr;
    for (auto *U : E.second) {
      // If we have not seen the use block, create a load instruction to reload
      // the spilled value from the coroutine frame. Populates the Value pointer
      // reference provided with the frame GEP.
      if (CurrentBlock != U->getParent()) {
        CurrentBlock = U->getParent();
        Builder.SetInsertPoint(CurrentBlock->getFirstInsertionPt());
 
        auto *GEP = createGEPToFramePointer(FrameData, Builder, Shape, E.first);
        GEP->setName(E.first->getName() + Twine(".reload.addr"));
        if (ByValTy) {
          CurrentReload = GEP;
        } else {
          auto SpillAlignment = Align(FrameData.getAlign(Def));
          auto *LI =
              Builder.CreateAlignedLoad(E.first->getType(), GEP, SpillAlignment,
                                        E.first->getName() + Twine(".reload"));
          if (TBAATag)
            LI->setMetadata(LLVMContext::MD_tbaa, TBAATag);
          CurrentReload = LI;
        }
 
        TinyPtrVector<DbgVariableRecord *> DVRs = findDbgRecordsThroughLoads<
            DbgVariableRecord::LocationType::Declare>(*F, Def);
 
        auto SalvageOne = [&](DbgVariableRecord *DDI) {
          // This dbg.declare is preserved for all coro-split function
          // fragments. It will be unreachable in the main function, and
          // processed by coro::salvageDebugInfo() by the Cloner.
          DbgVariableRecord *NewDVR = new DbgVariableRecord(
              ValueAsMetadata::get(CurrentReload), DDI->getVariable(),
              DDI->getExpression(), DDI->getDebugLoc(),
              DbgVariableRecord::LocationType::Declare);
          Builder.GetInsertPoint()->getParent()->insertDbgRecordBefore(
              NewDVR, Builder.GetInsertPoint());
          // This dbg.declare is for the main function entry point.  It
          // will be deleted in all coro-split functions.
          coro::salvageDebugInfo(ArgToAllocaMap, *DDI, false /*UseEntryValue*/);
        };
        for_each(DVRs, SalvageOne);
      }
 
      TinyPtrVector<DbgVariableRecord *> DVRDeclareValues =
          findDbgRecordsThroughLoads<
              DbgVariableRecord::LocationType::DeclareValue>(*F, Def);
 
      auto SalvageOneCoro = [&](auto *DDI) {
        // This dbg.declare_value is preserved for all coro-split function
        // fragments. It will be unreachable in the main function, and
        // processed by coro::salvageDebugInfo() by the Cloner. However, convert
        // it to a dbg.declare to make sure future passes don't have to deal
        // with a dbg.declare_value.
        auto *VAM = ValueAsMetadata::get(CurrentReload);
        Type *Ty = VAM->getValue()->getType();
        // If the metadata type is not a pointer, emit a dbg.value instead.
        DbgVariableRecord *NewDVR = new DbgVariableRecord(
            ValueAsMetadata::get(CurrentReload), DDI->getVariable(),
            DDI->getExpression(), DDI->getDebugLoc(),
            Ty->isPointerTy() ? DbgVariableRecord::LocationType::Declare
                              : DbgVariableRecord::LocationType::Value);
        Builder.GetInsertPoint()->getParent()->insertDbgRecordBefore(
            NewDVR, Builder.GetInsertPoint());
        // This dbg.declare_value is for the main function entry point.  It
        // will be deleted in all coro-split functions.
        coro::salvageDebugInfo(ArgToAllocaMap, *DDI, false /*UseEntryValue*/);
      };
      for_each(DVRDeclareValues, SalvageOneCoro);
 
      // If we have a single edge PHINode, remove it and replace it with a
      // reload from the coroutine frame. (We already took care of multi edge
      // PHINodes by normalizing them in the rewritePHIs function).
      if (auto *PN = dyn_cast<PHINode>(U)) {
        assert(PN->getNumIncomingValues() == 1 &&
               "unexpected number of incoming "
               "values in the PHINode");
        PN->replaceAllUsesWith(CurrentReload);
        PN->eraseFromParent();
        continue;
      }
 
      // Replace all uses of CurrentValue in the current instruction with
      // reload.
      U->replaceUsesOfWith(Def, CurrentReload);
      // Instructions are added to Def's user list if the attached
      // debug records use Def. Update those now.
      for (DbgVariableRecord &DVR : filterDbgVars(U->getDbgRecordRange()))
        DVR.replaceVariableLocationOp(Def, CurrentReload, true);
    }
  }
 
  BasicBlock *FramePtrBB = Shape.getInsertPtAfterFramePtr()->getParent();
 
  auto SpillBlock = FramePtrBB->splitBasicBlock(
      Shape.getInsertPtAfterFramePtr(), "AllocaSpillBB");
  SpillBlock->splitBasicBlock(&SpillBlock->front(), "PostSpill");
  Shape.AllocaSpillBlock = SpillBlock;
 
  // retcon and retcon.once lowering assumes all uses have been sunk.
  if (Shape.ABI == coro::ABI::Retcon || Shape.ABI == coro::ABI::RetconOnce ||
      Shape.ABI == coro::ABI::Async) {
    // If we found any allocas, replace all of their remaining uses with Geps.
    Builder.SetInsertPoint(SpillBlock->begin());
    for (const auto &P : FrameData.Allocas) {
      AllocaInst *Alloca = P.Alloca;
      auto *G = createGEPToFramePointer(FrameData, Builder, Shape, Alloca);
 
      // Remove any lifetime intrinsics, now that these are no longer allocas.
      for (User *U : make_early_inc_range(Alloca->users())) {
        auto *I = cast<Instruction>(U);
        if (I->isLifetimeStartOrEnd())
          I->eraseFromParent();
      }
 
      // We are not using ReplaceInstWithInst(P.first, cast<Instruction>(G))
      // here, as we are changing location of the instruction.
      G->takeName(Alloca);
      Alloca->replaceAllUsesWith(G);
      Alloca->eraseFromParent();
    }
    return;
  }
 
  // If we found any alloca, replace all of their remaining uses with GEP
  // instructions. To remain debugbility, we replace the uses of allocas for
  // dbg.declares and dbg.values with the reload from the frame.
  // Note: We cannot replace the alloca with GEP instructions indiscriminately,
  // as some of the uses may not be dominated by CoroBegin.
  Builder.SetInsertPoint(Shape.AllocaSpillBlock->begin());
  SmallVector<Instruction *, 4> UsersToUpdate;
  for (const auto &A : FrameData.Allocas) {
    AllocaInst *Alloca = A.Alloca;
    UsersToUpdate.clear();
    for (User *U : make_early_inc_range(Alloca->users())) {
      auto *I = cast<Instruction>(U);
      // It is meaningless to retain the lifetime intrinsics refer for the
      // member of coroutine frames and the meaningless lifetime intrinsics
      // are possible to block further optimizations.
      if (I->isLifetimeStartOrEnd())
        I->eraseFromParent();
      else if (DT.dominates(Shape.CoroBegin, I))
        UsersToUpdate.push_back(I);
    }
 
    if (UsersToUpdate.empty())
      continue;
    auto *G = createGEPToFramePointer(FrameData, Builder, Shape, Alloca);
    G->setName(Alloca->getName() + Twine(".reload.addr"));
 
    SmallVector<DbgVariableRecord *> DbgVariableRecords;
    findDbgUsers(Alloca, DbgVariableRecords);
    for (auto *DVR : DbgVariableRecords)
      DVR->replaceVariableLocationOp(Alloca, G);
 
    for (Instruction *I : UsersToUpdate)
      I->replaceUsesOfWith(Alloca, G);
 
    if (Alloca->user_empty())
      Alloca->eraseFromParent();
  }
  Builder.SetInsertPoint(&*Shape.getInsertPtAfterFramePtr());
  for (const auto &A : FrameData.Allocas) {
    AllocaInst *Alloca = A.Alloca;
    if (A.MayWriteBeforeCoroBegin) {
      // isEscaped really means potentially modified before CoroBegin.
      handleAccessBeforeCoroBegin(FrameData, Shape, Builder, Alloca);
    }
    // For each alias to Alloca created before CoroBegin but used after
    // CoroBegin, we recreate them after CoroBegin by applying the offset
    // to the pointer in the frame.
    for (const auto &Alias : A.Aliases) {
      auto *FramePtr =
          createGEPToFramePointer(FrameData, Builder, Shape, Alloca);
      auto &Value = *Alias.second;
      auto ITy = IntegerType::get(C, Value.getBitWidth());
      auto *AliasPtr =
          Builder.CreateInBoundsPtrAdd(FramePtr, ConstantInt::get(ITy, Value));
      Alias.first->replaceUsesWithIf(
          AliasPtr, [&](Use &U) { return DT.dominates(Shape.CoroBegin, U); });
    }
  }
}
 
// Moves the values in the PHIs in SuccBB that correspong to PredBB into a new
// PHI in InsertedBB.
static void movePHIValuesToInsertedBlock(BasicBlock *SuccBB,
                                         BasicBlock *InsertedBB,
                                         BasicBlock *PredBB,
                                         PHINode *UntilPHI = nullptr) {
  auto *PN = cast<PHINode>(&SuccBB->front());
  do {
    int Index = PN->getBasicBlockIndex(InsertedBB);
    Value *V = PN->getIncomingValue(Index);
    PHINode *InputV = PHINode::Create(
        V->getType(), 1, V->getName() + Twine(".") + SuccBB->getName());
    InputV->insertBefore(InsertedBB->begin());
    InputV->addIncoming(V, PredBB);
    PN->setIncomingValue(Index, InputV);
    PN = dyn_cast<PHINode>(PN->getNextNode());
  } while (PN != UntilPHI);
}
 
// Rewrites the PHI Nodes in a cleanuppad.
static void rewritePHIsForCleanupPad(BasicBlock *CleanupPadBB,
                                     CleanupPadInst *CleanupPad) {
  // For every incoming edge to a CleanupPad we will create a new block holding
  // all incoming values in single-value PHI nodes. We will then create another
  // block to act as a dispather (as all unwind edges for related EH blocks
  // must be the same).
  //
  // cleanuppad:
  //    %2 = phi i32[%0, %catchswitch], [%1, %catch.1]
  //    %3 = cleanuppad within none []
  //
  // It will create:
  //
  // cleanuppad.corodispatch
  //    %2 = phi i8[0, %catchswitch], [1, %catch.1]
  //    %3 = cleanuppad within none []
  //    switch i8 % 2, label %unreachable
  //            [i8 0, label %cleanuppad.from.catchswitch
  //             i8 1, label %cleanuppad.from.catch.1]
  // cleanuppad.from.catchswitch:
  //    %4 = phi i32 [%0, %catchswitch]
  //    br %label cleanuppad
  // cleanuppad.from.catch.1:
  //    %6 = phi i32 [%1, %catch.1]
  //    br %label cleanuppad
  // cleanuppad:
  //    %8 = phi i32 [%4, %cleanuppad.from.catchswitch],
  //                 [%6, %cleanuppad.from.catch.1]
 
  // Unreachable BB, in case switching on an invalid value in the dispatcher.
  auto *UnreachBB = BasicBlock::Create(
      CleanupPadBB->getContext(), "unreachable", CleanupPadBB->getParent());
  IRBuilder<> Builder(UnreachBB);
  Builder.CreateUnreachable();
 
  // Create a new cleanuppad which will be the dispatcher.
  auto *NewCleanupPadBB =
      BasicBlock::Create(CleanupPadBB->getContext(),
                         CleanupPadBB->getName() + Twine(".corodispatch"),
                         CleanupPadBB->getParent(), CleanupPadBB);
  Builder.SetInsertPoint(NewCleanupPadBB);
  auto *SwitchType = Builder.getInt8Ty();
  auto *SetDispatchValuePN =
      Builder.CreatePHI(SwitchType, pred_size(CleanupPadBB));
  CleanupPad->removeFromParent();
  CleanupPad->insertAfter(SetDispatchValuePN->getIterator());
  auto *SwitchOnDispatch = Builder.CreateSwitch(SetDispatchValuePN, UnreachBB,
                                                pred_size(CleanupPadBB));
 
  int SwitchIndex = 0;
  SmallVector<BasicBlock *, 8> Preds(predecessors(CleanupPadBB));
  for (BasicBlock *Pred : Preds) {
    // Create a new cleanuppad and move the PHI values to there.
    auto *CaseBB = BasicBlock::Create(CleanupPadBB->getContext(),
                                      CleanupPadBB->getName() +
                                          Twine(".from.") + Pred->getName(),
                                      CleanupPadBB->getParent(), CleanupPadBB);
    updatePhiNodes(CleanupPadBB, Pred, CaseBB);
    CaseBB->setName(CleanupPadBB->getName() + Twine(".from.") +
                    Pred->getName());
    Builder.SetInsertPoint(CaseBB);
    Builder.CreateBr(CleanupPadBB);
    movePHIValuesToInsertedBlock(CleanupPadBB, CaseBB, NewCleanupPadBB);
 
    // Update this Pred to the new unwind point.
    setUnwindEdgeTo(Pred->getTerminator(), NewCleanupPadBB);
 
    // Setup the switch in the dispatcher.
    auto *SwitchConstant = ConstantInt::get(SwitchType, SwitchIndex);
    SetDispatchValuePN->addIncoming(SwitchConstant, Pred);
    SwitchOnDispatch->addCase(SwitchConstant, CaseBB);
    SwitchIndex++;
  }
 
  if (!ProfcheckDisableMetadataFixes) {
    // Add branch weights to SwitchOnDispatch, where branches are unreachable by
    // default. We mark all branches as having equal weights because they are
    // mutually exclusive.
    MDBuilder MDB(CleanupPadBB->getContext());
    SmallVector<uint32_t> Weights;
    Weights.push_back(0);
    for (int i = 0; i < SwitchIndex; ++i) {
      Weights.push_back(llvm::MDBuilder::kUnlikelyBranchWeight);
    }
    SwitchOnDispatch->setMetadata(LLVMContext::MD_prof,
                                  MDB.createBranchWeights(Weights));
  }
}
 
static void cleanupSinglePredPHIs(Function &F) {
  SmallVector<PHINode *, 32> Worklist;
  for (auto &BB : F) {
    for (auto &Phi : BB.phis()) {
      if (Phi.getNumIncomingValues() == 1) {
        Worklist.push_back(&Phi);
      } else
        break;
    }
  }
  while (!Worklist.empty()) {
    auto *Phi = Worklist.pop_back_val();
    auto *OriginalValue = Phi->getIncomingValue(0);
    Phi->replaceAllUsesWith(OriginalValue);
  }
}
 
static void rewritePHIs(BasicBlock &BB) {
  // For every incoming edge we will create a block holding all
  // incoming values in a single PHI nodes.
  //
  // loop:
  //    %n.val = phi i32[%n, %entry], [%inc, %loop]
  //
  // It will create:
  //
  // loop.from.entry:
  //    %n.loop.pre = phi i32 [%n, %entry]
  //    br %label loop
  // loop.from.loop:
  //    %inc.loop.pre = phi i32 [%inc, %loop]
  //    br %label loop
  //
  // After this rewrite, further analysis will ignore any phi nodes with more
  // than one incoming edge.
 
  // TODO: Simplify PHINodes in the basic block to remove duplicate
  // predecessors.
 
  // Special case for CleanupPad: all EH blocks must have the same unwind edge
  // so we need to create an additional "dispatcher" block.
  if (!BB.empty()) {
    if (auto *CleanupPad =
            dyn_cast_or_null<CleanupPadInst>(BB.getFirstNonPHIIt())) {
      SmallVector<BasicBlock *, 8> Preds(predecessors(&BB));
      for (BasicBlock *Pred : Preds) {
        if (CatchSwitchInst *CS =
                dyn_cast<CatchSwitchInst>(Pred->getTerminator())) {
          // CleanupPad with a CatchSwitch predecessor: therefore this is an
          // unwind destination that needs to be handle specially.
          assert(CS->getUnwindDest() == &BB);
          (void)CS;
          rewritePHIsForCleanupPad(&BB, CleanupPad);
          return;
        }
      }
    }
  }
 
  LandingPadInst *LandingPad = nullptr;
  PHINode *ReplPHI = nullptr;
  if (!BB.empty()) {
    if ((LandingPad =
             dyn_cast_or_null<LandingPadInst>(BB.getFirstNonPHIIt()))) {
      // ehAwareSplitEdge will clone the LandingPad in all the edge blocks.
      // We replace the original landing pad with a PHINode that will collect the
      // results from all of them.
      ReplPHI = PHINode::Create(LandingPad->getType(), 1, "");
      ReplPHI->insertBefore(LandingPad->getIterator());
      ReplPHI->takeName(LandingPad);
      LandingPad->replaceAllUsesWith(ReplPHI);
      // We will erase the original landing pad at the end of this function after
      // ehAwareSplitEdge cloned it in the transition blocks.
    }
  }
 
  SmallVector<BasicBlock *, 8> Preds(predecessors(&BB));
  for (BasicBlock *Pred : Preds) {
    auto *IncomingBB = ehAwareSplitEdge(Pred, &BB, LandingPad, ReplPHI);
    IncomingBB->setName(BB.getName() + Twine(".from.") + Pred->getName());
 
    // Stop the moving of values at ReplPHI, as this is either null or the PHI
    // that replaced the landing pad.
    movePHIValuesToInsertedBlock(&BB, IncomingBB, Pred, ReplPHI);
  }
 
  if (LandingPad) {
    // Calls to ehAwareSplitEdge function cloned the original lading pad.
    // No longer need it.
    LandingPad->eraseFromParent();
  }
}
 
static void rewritePHIs(Function &F) {
  SmallVector<BasicBlock *, 8> WorkList;
 
  for (BasicBlock &BB : F)
    if (auto *PN = dyn_cast<PHINode>(&BB.front()))
      if (PN->getNumIncomingValues() > 1)
        WorkList.push_back(&BB);
 
  for (BasicBlock *BB : WorkList)
    rewritePHIs(*BB);
}
 
// Splits the block at a particular instruction unless it is the first
// instruction in the block with a single predecessor.
static BasicBlock *splitBlockIfNotFirst(Instruction *I, const Twine &Name) {
  auto *BB = I->getParent();
  if (&BB->front() == I) {
    if (BB->getSinglePredecessor()) {
      BB->setName(Name);
      return BB;
    }
  }
  return BB->splitBasicBlock(I, Name);
}
 
// Split above and below a particular instruction so that it
// will be all alone by itself in a block.
static void splitAround(Instruction *I, const Twine &Name) {
  splitBlockIfNotFirst(I, Name);
  splitBlockIfNotFirst(I->getNextNode(), "After" + Name);
}
 
/// After we split the coroutine, will the given basic block be along
/// an obvious exit path for the resumption function?
static bool willLeaveFunctionImmediatelyAfter(BasicBlock *BB,
                                              unsigned depth = 3) {
  // If we've bottomed out our depth count, stop searching and assume
  // that the path might loop back.
  if (depth == 0) return false;
 
  // If this is a suspend block, we're about to exit the resumption function.
  if (coro::isSuspendBlock(BB))
    return true;
 
  // Recurse into the successors.
  for (auto *Succ : successors(BB)) {
    if (!willLeaveFunctionImmediatelyAfter(Succ, depth - 1))
      return false;
  }
 
  // If none of the successors leads back in a loop, we're on an exit/abort.
  return true;
}
 
static bool localAllocaNeedsStackSave(CoroAllocaAllocInst *AI) {
  // Look for a free that isn't sufficiently obviously followed by
  // either a suspend or a termination, i.e. something that will leave
  // the coro resumption frame.
  for (auto *U : AI->users()) {
    auto FI = dyn_cast<CoroAllocaFreeInst>(U);
    if (!FI) continue;
 
    if (!willLeaveFunctionImmediatelyAfter(FI->getParent()))
      return true;
  }
 
  // If we never found one, we don't need a stack save.
  return false;
}
 
/// Turn each of the given local allocas into a normal (dynamic) alloca
/// instruction.
static void lowerLocalAllocas(ArrayRef<CoroAllocaAllocInst*> LocalAllocas,
                              SmallVectorImpl<Instruction*> &DeadInsts) {
  for (auto *AI : LocalAllocas) {
    IRBuilder<> Builder(AI);
 
    // Save the stack depth.  Try to avoid doing this if the stackrestore
    // is going to immediately precede a return or something.
    Value *StackSave = nullptr;
    if (localAllocaNeedsStackSave(AI))
      StackSave = Builder.CreateStackSave();
 
    // Allocate memory.
    auto Alloca = Builder.CreateAlloca(Builder.getInt8Ty(), AI->getSize());
    Alloca->setAlignment(AI->getAlignment());
 
    for (auto *U : AI->users()) {
      // Replace gets with the allocation.
      if (isa<CoroAllocaGetInst>(U)) {
        U->replaceAllUsesWith(Alloca);
 
      // Replace frees with stackrestores.  This is safe because
      // alloca.alloc is required to obey a stack discipline, although we
      // don't enforce that structurally.
      } else {
        auto FI = cast<CoroAllocaFreeInst>(U);
        if (StackSave) {
          Builder.SetInsertPoint(FI);
          Builder.CreateStackRestore(StackSave);
        }
      }
      DeadInsts.push_back(cast<Instruction>(U));
    }
 
    DeadInsts.push_back(AI);
  }
}
 
/// Get the current swifterror value.
static Value *emitGetSwiftErrorValue(IRBuilder<> &Builder, Type *ValueTy,
                                     coro::Shape &Shape) {
  // Make a fake function pointer as a sort of intrinsic.
  auto FnTy = FunctionType::get(ValueTy, {}, false);
  auto Fn = ConstantPointerNull::get(Builder.getPtrTy());
 
  auto Call = Builder.CreateCall(FnTy, Fn, {});
  Shape.SwiftErrorOps.push_back(Call);
 
  return Call;
}
 
/// Set the given value as the current swifterror value.
///
/// Returns a slot that can be used as a swifterror slot.
static Value *emitSetSwiftErrorValue(IRBuilder<> &Builder, Value *V,
                                     coro::Shape &Shape) {
  // Make a fake function pointer as a sort of intrinsic.
  auto FnTy = FunctionType::get(Builder.getPtrTy(),
                                {V->getType()}, false);
  auto Fn = ConstantPointerNull::get(Builder.getPtrTy());
 
  auto Call = Builder.CreateCall(FnTy, Fn, { V });
  Shape.SwiftErrorOps.push_back(Call);
 
  return Call;
}
 
/// Set the swifterror value from the given alloca before a call,
/// then put in back in the alloca afterwards.
///
/// Returns an address that will stand in for the swifterror slot
/// until splitting.
static Value *emitSetAndGetSwiftErrorValueAround(Instruction *Call,
                                                 AllocaInst *Alloca,
                                                 coro::Shape &Shape) {
  auto ValueTy = Alloca->getAllocatedType();
  IRBuilder<> Builder(Call);
 
  // Load the current value from the alloca and set it as the
  // swifterror value.
  auto ValueBeforeCall = Builder.CreateLoad(ValueTy, Alloca);
  auto Addr = emitSetSwiftErrorValue(Builder, ValueBeforeCall, Shape);
 
  // Move to after the call.  Since swifterror only has a guaranteed
  // value on normal exits, we can ignore implicit and explicit unwind
  // edges.
  if (isa<CallInst>(Call)) {
    Builder.SetInsertPoint(Call->getNextNode());
  } else {
    auto Invoke = cast<InvokeInst>(Call);
    Builder.SetInsertPoint(Invoke->getNormalDest()->getFirstNonPHIOrDbg());
  }
 
  // Get the current swifterror value and store it to the alloca.
  auto ValueAfterCall = emitGetSwiftErrorValue(Builder, ValueTy, Shape);
  Builder.CreateStore(ValueAfterCall, Alloca);
 
  return Addr;
}
 
/// Eliminate a formerly-swifterror alloca by inserting the get/set
/// intrinsics and attempting to MemToReg the alloca away.
static void eliminateSwiftErrorAlloca(Function &F, AllocaInst *Alloca,
                                      coro::Shape &Shape) {
  for (Use &Use : llvm::make_early_inc_range(Alloca->uses())) {
    // swifterror values can only be used in very specific ways.
    // We take advantage of that here.
    auto User = Use.getUser();
    if (isa<LoadInst>(User) || isa<StoreInst>(User))
      continue;
 
    assert(isa<CallInst>(User) || isa<InvokeInst>(User));
    auto Call = cast<Instruction>(User);
 
    auto Addr = emitSetAndGetSwiftErrorValueAround(Call, Alloca, Shape);
 
    // Use the returned slot address as the call argument.
    Use.set(Addr);
  }
 
  // All the uses should be loads and stores now.
  assert(isAllocaPromotable(Alloca));
}
 
/// "Eliminate" a swifterror argument by reducing it to the alloca case
/// and then loading and storing in the prologue and epilog.
///
/// The argument keeps the swifterror flag.
static void eliminateSwiftErrorArgument(Function &F, Argument &Arg,
                                        coro::Shape &Shape,
                             SmallVectorImpl<AllocaInst*> &AllocasToPromote) {
  IRBuilder<> Builder(&F.getEntryBlock(),
                      F.getEntryBlock().getFirstNonPHIOrDbg());
 
  auto ArgTy = cast<PointerType>(Arg.getType());
  auto ValueTy = PointerType::getUnqual(F.getContext());
 
  // Reduce to the alloca case:
 
  // Create an alloca and replace all uses of the arg with it.
  auto Alloca = Builder.CreateAlloca(ValueTy, ArgTy->getAddressSpace());
  Arg.replaceAllUsesWith(Alloca);
 
  // Set an initial value in the alloca.  swifterror is always null on entry.
  auto InitialValue = Constant::getNullValue(ValueTy);
  Builder.CreateStore(InitialValue, Alloca);
 
  // Find all the suspends in the function and save and restore around them.
  for (auto *Suspend : Shape.CoroSuspends) {
    (void) emitSetAndGetSwiftErrorValueAround(Suspend, Alloca, Shape);
  }
 
  // Find all the coro.ends in the function and restore the error value.
  for (auto *End : Shape.CoroEnds) {
    Builder.SetInsertPoint(End);
    auto FinalValue = Builder.CreateLoad(ValueTy, Alloca);
    (void) emitSetSwiftErrorValue(Builder, FinalValue, Shape);
  }
 
  // Now we can use the alloca logic.
  AllocasToPromote.push_back(Alloca);
  eliminateSwiftErrorAlloca(F, Alloca, Shape);
}
 
/// Eliminate all problematic uses of swifterror arguments and allocas
/// from the function.  We'll fix them up later when splitting the function.
static void eliminateSwiftError(Function &F, coro::Shape &Shape) {
  SmallVector<AllocaInst*, 4> AllocasToPromote;
 
  // Look for a swifterror argument.
  for (auto &Arg : F.args()) {
    if (!Arg.hasSwiftErrorAttr()) continue;
 
    eliminateSwiftErrorArgument(F, Arg, Shape, AllocasToPromote);
    break;
  }
 
  // Look for swifterror allocas.
  for (auto &Inst : F.getEntryBlock()) {
    auto Alloca = dyn_cast<AllocaInst>(&Inst);
    if (!Alloca || !Alloca->isSwiftError()) continue;
 
    // Clear the swifterror flag.
    Alloca->setSwiftError(false);
 
    AllocasToPromote.push_back(Alloca);
    eliminateSwiftErrorAlloca(F, Alloca, Shape);
  }
 
  // If we have any allocas to promote, compute a dominator tree and
  // promote them en masse.
  if (!AllocasToPromote.empty()) {
    DominatorTree DT(F);
    PromoteMemToReg(AllocasToPromote, DT);
  }
}
 
/// For each local variable that all of its user are only used inside one of
/// suspended region, we sink their lifetime.start markers to the place where
/// after the suspend block. Doing so minimizes the lifetime of each variable,
/// hence minimizing the amount of data we end up putting on the frame.
static void sinkLifetimeStartMarkers(Function &F, coro::Shape &Shape,
                                     SuspendCrossingInfo &Checker,
                                     const DominatorTree &DT) {
  if (F.hasOptNone())
    return;
 
  // Collect all possible basic blocks which may dominate all uses of allocas.
  SmallPtrSet<BasicBlock *, 4> DomSet;
  DomSet.insert(&F.getEntryBlock());
  for (auto *CSI : Shape.CoroSuspends) {
    BasicBlock *SuspendBlock = CSI->getParent();
    assert(coro::isSuspendBlock(SuspendBlock) &&
           SuspendBlock->getSingleSuccessor() &&
           "should have split coro.suspend into its own block");
    DomSet.insert(SuspendBlock->getSingleSuccessor());
  }
 
  for (Instruction &I : instructions(F)) {
    AllocaInst* AI = dyn_cast<AllocaInst>(&I);
    if (!AI)
      continue;
 
    for (BasicBlock *DomBB : DomSet) {
      bool Valid = true;
      SmallVector<Instruction *, 1> Lifetimes;
 
      auto isLifetimeStart = [](Instruction* I) {
        if (auto* II = dyn_cast<IntrinsicInst>(I))
          return II->getIntrinsicID() == Intrinsic::lifetime_start;
        return false;
      };
 
      auto collectLifetimeStart = [&](Instruction *U, AllocaInst *AI) {
        if (isLifetimeStart(U)) {
          Lifetimes.push_back(U);
          return true;
        }
        if (!U->hasOneUse() || U->stripPointerCasts() != AI)
          return false;
        if (isLifetimeStart(U->user_back())) {
          Lifetimes.push_back(U->user_back());
          return true;
        }
        return false;
      };
 
      for (User *U : AI->users()) {
        Instruction *UI = cast<Instruction>(U);
        // For all users except lifetime.start markers, if they are all
        // dominated by one of the basic blocks and do not cross
        // suspend points as well, then there is no need to spill the
        // instruction.
        if (!DT.dominates(DomBB, UI->getParent()) ||
            Checker.isDefinitionAcrossSuspend(DomBB, UI)) {
          // Skip lifetime.start, GEP and bitcast used by lifetime.start
          // markers.
          if (collectLifetimeStart(UI, AI))
            continue;
          Valid = false;
          break;
        }
      }
      // Sink lifetime.start markers to dominate block when they are
      // only used outside the region.
      if (Valid && Lifetimes.size() != 0) {
        auto *NewLifetime = Lifetimes[0]->clone();
        NewLifetime->replaceUsesOfWith(NewLifetime->getOperand(0), AI);
        NewLifetime->insertBefore(DomBB->getTerminator()->getIterator());
 
        // All the outsided lifetime.start markers are no longer necessary.
        for (Instruction *S : Lifetimes)
          S->eraseFromParent();
 
        break;
      }
    }
  }
}
 
static std::optional<std::pair<Value &, DIExpression &>>
salvageDebugInfoImpl(SmallDenseMap<Argument *, AllocaInst *, 4> &ArgToAllocaMap,
                     bool UseEntryValue, Function *F, Value *Storage,
                     DIExpression *Expr, bool SkipOutermostLoad) {
  IRBuilder<> Builder(F->getContext());
  auto InsertPt = F->getEntryBlock().getFirstInsertionPt();
  while (isa<IntrinsicInst>(InsertPt))
    ++InsertPt;
  Builder.SetInsertPoint(InsertPt);
 
  while (auto *Inst = dyn_cast_or_null<Instruction>(Storage)) {
    if (auto *LdInst = dyn_cast<LoadInst>(Inst)) {
      Storage = LdInst->getPointerOperand();
      // FIXME: This is a heuristic that works around the fact that
      // LLVM IR debug intrinsics cannot yet distinguish between
      // memory and value locations: Because a dbg.declare(alloca) is
      // implicitly a memory location no DW_OP_deref operation for the
      // last direct load from an alloca is necessary.  This condition
      // effectively drops the *last* DW_OP_deref in the expression.
      if (!SkipOutermostLoad)
        Expr = DIExpression::prepend(Expr, DIExpression::DerefBefore);
    } else if (auto *StInst = dyn_cast<StoreInst>(Inst)) {
      Storage = StInst->getValueOperand();
    } else {
      SmallVector<uint64_t, 16> Ops;
      SmallVector<Value *, 0> AdditionalValues;
      Value *Op = llvm::salvageDebugInfoImpl(
          *Inst, Expr ? Expr->getNumLocationOperands() : 0, Ops,
          AdditionalValues);
      if (!Op || !AdditionalValues.empty()) {
        // If salvaging failed or salvaging produced more than one location
        // operand, give up.
        break;
      }
      Storage = Op;
      Expr = DIExpression::appendOpsToArg(Expr, Ops, 0, /*StackValue*/ false);
    }
    SkipOutermostLoad = false;
  }
  if (!Storage)
    return std::nullopt;
 
  auto *StorageAsArg = dyn_cast<Argument>(Storage);
 
  const bool IsSingleLocationExpression = Expr->isSingleLocationExpression();
  // Use an EntryValue when requested (UseEntryValue) for swift async Arguments.
  // Entry values in variadic expressions are not supported.
  const bool WillUseEntryValue =
      UseEntryValue && StorageAsArg &&
      StorageAsArg->hasAttribute(Attribute::SwiftAsync) &&
      !Expr->isEntryValue() && IsSingleLocationExpression;
 
  if (WillUseEntryValue)
    Expr = DIExpression::prepend(Expr, DIExpression::EntryValue);
 
  // If the coroutine frame is an Argument, store it in an alloca to improve
  // its availability (e.g. registers may be clobbered).
  // Avoid this if the value is guaranteed to be available through other means
  // (e.g. swift ABI guarantees).
  // Avoid this if multiple location expressions are involved, as LLVM does not
  // know how to prepend a deref in this scenario.
  if (StorageAsArg && !WillUseEntryValue && IsSingleLocationExpression) {
    auto &Cached = ArgToAllocaMap[StorageAsArg];
    if (!Cached) {
      Cached = Builder.CreateAlloca(Storage->getType(), 0, nullptr,
                                    Storage->getName() + ".debug");
      Builder.CreateStore(Storage, Cached);
    }
    Storage = Cached;
    // FIXME: LLVM lacks nuanced semantics to differentiate between
    // memory and direct locations at the IR level. The backend will
    // turn a dbg.declare(alloca, ..., DIExpression()) into a memory
    // location. Thus, if there are deref and offset operations in the
    // expression, we need to add a DW_OP_deref at the *start* of the
    // expression to first load the contents of the alloca before
    // adjusting it with the expression.
    Expr = DIExpression::prepend(Expr, DIExpression::DerefBefore);
  }
 
  Expr = Expr->foldConstantMath();
  return {{*Storage, *Expr}};
}
 
void coro::salvageDebugInfo(
    SmallDenseMap<Argument *, AllocaInst *, 4> &ArgToAllocaMap,
    DbgVariableRecord &DVR, bool UseEntryValue) {
 
  Function *F = DVR.getFunction();
  // Follow the pointer arithmetic all the way to the incoming
  // function argument and convert into a DIExpression.
  bool SkipOutermostLoad = DVR.isDbgDeclare() || DVR.isDbgDeclareValue();
  Value *OriginalStorage = DVR.getVariableLocationOp(0);
 
  auto SalvagedInfo =
      ::salvageDebugInfoImpl(ArgToAllocaMap, UseEntryValue, F, OriginalStorage,
                             DVR.getExpression(), SkipOutermostLoad);
  if (!SalvagedInfo)
    return;
 
  Value *Storage = &SalvagedInfo->first;
  DIExpression *Expr = &SalvagedInfo->second;
 
  DVR.replaceVariableLocationOp(OriginalStorage, Storage);
  DVR.setExpression(Expr);
  // We only hoist dbg.declare and dbg.declare_value today since it doesn't make
  // sense to hoist dbg.value since it does not have the same function wide
  // guarantees that dbg.declare does.
  if (DVR.getType() == DbgVariableRecord::LocationType::Declare ||
      DVR.getType() == DbgVariableRecord::LocationType::DeclareValue) {
    std::optional<BasicBlock::iterator> InsertPt;
    if (auto *I = dyn_cast<Instruction>(Storage)) {
      InsertPt = I->getInsertionPointAfterDef();
      // Update DILocation only if variable was not inlined.
      DebugLoc ILoc = I->getDebugLoc();
      DebugLoc DVRLoc = DVR.getDebugLoc();
      if (ILoc && DVRLoc &&
          DVRLoc->getScope()->getSubprogram() ==
              ILoc->getScope()->getSubprogram())
        DVR.setDebugLoc(ILoc);
    } else if (isa<Argument>(Storage))
      InsertPt = F->getEntryBlock().begin();
    if (InsertPt) {
      DVR.removeFromParent();
      // If there is a dbg.declare_value being reinserted, insert it as a
      // dbg.declare instead, so that subsequent passes don't have to deal with
      // a dbg.declare_value.
      if (DVR.getType() == DbgVariableRecord::LocationType::DeclareValue) {
        auto *MD = DVR.getRawLocation();
        if (auto *VAM = dyn_cast<ValueAsMetadata>(MD)) {
          Type *Ty = VAM->getValue()->getType();
          if (Ty->isPointerTy())
            DVR.Type = DbgVariableRecord::LocationType::Declare;
          else
            DVR.Type = DbgVariableRecord::LocationType::Value;
        }
      }
      (*InsertPt)->getParent()->insertDbgRecordBefore(&DVR, *InsertPt);
    }
  }
}
 
void coro::normalizeCoroutine(Function &F, coro::Shape &Shape,
                              TargetTransformInfo &TTI) {
  // Don't eliminate swifterror in async functions that won't be split.
  if (Shape.ABI != coro::ABI::Async || !Shape.CoroSuspends.empty())
    eliminateSwiftError(F, Shape);
 
  if (Shape.ABI == coro::ABI::Switch &&
      Shape.SwitchLowering.PromiseAlloca) {
    Shape.getSwitchCoroId()->clearPromise();
  }
 
  // Make sure that all coro.save, coro.suspend and the fallthrough coro.end
  // intrinsics are in their own blocks to simplify the logic of building up
  // SuspendCrossing data.
  for (auto *CSI : Shape.CoroSuspends) {
    if (auto *Save = CSI->getCoroSave())
      splitAround(Save, "CoroSave");
    splitAround(CSI, "CoroSuspend");
  }
 
  // Put CoroEnds into their own blocks.
  for (AnyCoroEndInst *CE : Shape.CoroEnds) {
    splitAround(CE, "CoroEnd");
 
    // Emit the musttail call function in a new block before the CoroEnd.
    // We do this here so that the right suspend crossing info is computed for
    // the uses of the musttail call function call. (Arguments to the coro.end
    // instructions would be ignored)
    if (auto *AsyncEnd = dyn_cast<CoroAsyncEndInst>(CE)) {
      auto *MustTailCallFn = AsyncEnd->getMustTailCallFunction();
      if (!MustTailCallFn)
        continue;
      IRBuilder<> Builder(AsyncEnd);
      SmallVector<Value *, 8> Args(AsyncEnd->args());
      auto Arguments = ArrayRef<Value *>(Args).drop_front(3);
      auto *Call = coro::createMustTailCall(
          AsyncEnd->getDebugLoc(), MustTailCallFn, TTI, Arguments, Builder);
      splitAround(Call, "MustTailCall.Before.CoroEnd");
    }
  }
 
  // Later code makes structural assumptions about single predecessors phis e.g
  // that they are not live across a suspend point.
  cleanupSinglePredPHIs(F);
 
  // Transforms multi-edge PHI Nodes, so that any value feeding into a PHI will
  // never have its definition separated from the PHI by the suspend point.
  rewritePHIs(F);
}
 
void coro::BaseABI::buildCoroutineFrame(bool OptimizeFrame) {
  SuspendCrossingInfo Checker(F, Shape);
  doRematerializations(F, Checker, IsMaterializable);
 
  const DominatorTree DT(F);
  if (Shape.ABI != coro::ABI::Async && Shape.ABI != coro::ABI::Retcon &&
      Shape.ABI != coro::ABI::RetconOnce)
    sinkLifetimeStartMarkers(F, Shape, Checker, DT);
 
  // All values (that are not allocas) that needs to be spilled to the frame.
  coro::SpillInfo Spills;
  // All values defined as allocas that need to live in the frame.
  SmallVector<coro::AllocaInfo, 8> Allocas;
 
  // Collect the spills for arguments and other not-materializable values.
  coro::collectSpillsFromArgs(Spills, F, Checker);
  SmallVector<Instruction *, 4> DeadInstructions;
  SmallVector<CoroAllocaAllocInst *, 4> LocalAllocas;
  coro::collectSpillsAndAllocasFromInsts(Spills, Allocas, DeadInstructions,
                                         LocalAllocas, F, Checker, DT, Shape);
  coro::collectSpillsFromDbgInfo(Spills, F, Checker);
 
  LLVM_DEBUG(dumpAllocas(Allocas));
  LLVM_DEBUG(dumpSpills("Spills", Spills));
 
  if (Shape.ABI == coro::ABI::Retcon || Shape.ABI == coro::ABI::RetconOnce ||
      Shape.ABI == coro::ABI::Async)
    sinkSpillUsesAfterCoroBegin(DT, Shape.CoroBegin, Spills, Allocas);
 
  // Build frame layout
  FrameDataInfo FrameData(Spills, Allocas);
  buildFrameLayout(F, DT, Shape, FrameData, OptimizeFrame);
  Shape.FramePtr = Shape.CoroBegin;
  // For now, this works for C++ programs only.
  buildFrameDebugInfo(F, Shape, FrameData);
  // Insert spills and reloads
  insertSpills(FrameData, Shape);
  lowerLocalAllocas(LocalAllocas, DeadInstructions);
 
  for (auto *I : DeadInstructions)
    I->eraseFromParent();
}