//===----- CGCoroutine.cpp - Emit LLVM Code for C++ coroutines ------------===//

//

// 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 contains code dealing with C++ code generation of coroutines.

//

//===----------------------------------------------------------------------===//

#include "CGCleanup.h"

#include "CodeGenFunction.h"

#include "llvm/ADT/ScopeExit.h"

#include "clang/AST/StmtCXX.h"

#include "clang/AST/StmtVisitor.h"

using namespace clang;

using namespace CodeGen;

using llvm::Value;

using llvm::BasicBlock;

namespace {

enum class AwaitKind { Init, Normal, Yield, Final };

static constexpr llvm::StringLiteral AwaitKindStr[] = {"init", "await", "yield",

                                                       "final"};

}

struct clang::CodeGen::CGCoroData {

  // What is the current await expression kind and how many

  // await/yield expressions were encountered so far.

  // These are used to generate pretty labels for await expressions in LLVM IR.

  AwaitKind CurrentAwaitKind = AwaitKind::Init;

  unsigned AwaitNum = 0;

  unsigned YieldNum = 0;

  // How many co_return statements are in the coroutine. Used to decide whether

  // we need to add co_return; equivalent at the end of the user authored body.

  unsigned CoreturnCount = 0;

  // A branch to this block is emitted when coroutine needs to suspend.

  llvm::BasicBlock *SuspendBB = nullptr;

  // The promise type's 'unhandled_exception' handler, if it defines one.

  Stmt *ExceptionHandler = nullptr;

  // A temporary i1 alloca that stores whether 'await_resume' threw an

  // exception. If it did, 'true' is stored in this variable, and the coroutine

  // body must be skipped. If the promise type does not define an exception

  // handler, this is null.

  llvm::Value *ResumeEHVar = nullptr;

  // Stores the jump destination just before the coroutine memory is freed.

  // This is the destination that every suspend point jumps to for the cleanup

  // branch.

  CodeGenFunction::JumpDest CleanupJD;

  // Stores the jump destination just before the final suspend. The co_return

  // statements jumps to this point after calling return_xxx promise member.

  CodeGenFunction::JumpDest FinalJD;

  // Stores the llvm.coro.id emitted in the function so that we can supply it

  // as the first argument to coro.begin, coro.alloc and coro.free intrinsics.

  // Note: llvm.coro.id returns a token that cannot be directly expressed in a

  // builtin.

  llvm::CallInst *CoroId = nullptr;

  // Stores the llvm.coro.begin emitted in the function so that we can replace

  // all coro.frame intrinsics with direct SSA value of coro.begin that returns

  // the address of the coroutine frame of the current coroutine.

  llvm::CallInst *CoroBegin = nullptr;

  // Stores the last emitted coro.free for the deallocate expressions, we use it

  // to wrap dealloc code with if(auto mem = coro.free) dealloc(mem).

  llvm::CallInst *LastCoroFree = nullptr;

  // If coro.id came from the builtin, remember the expression to give better

  // diagnostic. If CoroIdExpr is nullptr, the coro.id was created by

  // EmitCoroutineBody.

  CallExpr const *CoroIdExpr = nullptr;

};

// Defining these here allows to keep CGCoroData private to this file.

clang::CodeGen::CodeGenFunction::CGCoroInfo::CGCoroInfo() {}

CodeGenFunction::CGCoroInfo::~CGCoroInfo() {}

static void createCoroData(CodeGenFunction &CGF,

                           CodeGenFunction::CGCoroInfo &CurCoro,

                           llvm::CallInst *CoroId,

                           CallExpr const *CoroIdExpr = nullptr) {

  if (CurCoro.Data) {

    if (CurCoro.Data->CoroIdExpr)

      CGF.CGM.Error(CoroIdExpr->getBeginLoc(),

                    "only one __builtin_coro_id can be used in a function");

    else if (CoroIdExpr)

      CGF.CGM.Error(CoroIdExpr->getBeginLoc(),

                    "__builtin_coro_id shall not be used in a C++ coroutine");

    else

      llvm_unreachable("EmitCoroutineBodyStatement called twice?");

    return;

  }

  CurCoro.Data = std::unique_ptr<CGCoroData>(new CGCoroData);

  CurCoro.Data->CoroId = CoroId;

  CurCoro.Data->CoroIdExpr = CoroIdExpr;

}

// Synthesize a pretty name for a suspend point.

static SmallString<32> buildSuspendPrefixStr(CGCoroData &Coro, AwaitKind Kind) {

  unsigned No = 0;

  switch (Kind) {

  case AwaitKind::Init:

  case AwaitKind::Final:

    break;

  case AwaitKind::Normal:

    No = ++Coro.AwaitNum;

    break;

  case AwaitKind::Yield:

    No = ++Coro.YieldNum;

    break;

  }

  SmallString<32> Prefix(AwaitKindStr[static_cast<unsigned>(Kind)]);

  if (No > 1) {

    Twine(No).toVector(Prefix);

  }

  return Prefix;

}

static bool memberCallExpressionCanThrow(const Expr *E) {

  if (const auto *CE = dyn_cast<CXXMemberCallExpr>(E))

    if (const auto *Proto =

            CE->getMethodDecl()->getType()->getAs<FunctionProtoType>())

      if (isNoexceptExceptionSpec(Proto->getExceptionSpecType()) &&

          
Proto->canThrow() == CT_Cannot19
)

        return false;

  return true;

}

// Emit suspend expression which roughly looks like:

//

//   auto && x = CommonExpr();

//   if (!x.await_ready()) {

//      llvm_coro_save();

//      x.await_suspend(...);     (*)

//      llvm_coro_suspend(); (**)

//   }

//   x.await_resume();

//

// where the result of the entire expression is the result of x.await_resume()

//

//   (*) If x.await_suspend return type is bool, it allows to veto a suspend:

//      if (x.await_suspend(...))

//        llvm_coro_suspend();

//

//  (**) llvm_coro_suspend() encodes three possible continuations as

//       a switch instruction:

//

//  %where-to = call i8 @llvm.coro.suspend(...)

//  switch i8 %where-to, label %coro.ret [ ; jump to epilogue to suspend

//    i8 0, label %yield.ready   ; go here when resumed

//    i8 1, label %yield.cleanup ; go here when destroyed

//  ]

//

//  See llvm's docs/Coroutines.rst for more details.

//

namespace {

  struct LValueOrRValue {

    LValue LV;

    RValue RV;

  };

}

static LValueOrRValue emitSuspendExpression(CodeGenFunction &CGF, CGCoroData &Coro,

                                    CoroutineSuspendExpr const &S,

                                    AwaitKind Kind, AggValueSlot aggSlot,

                                    bool ignoreResult, bool forLValue) {

  auto *E = S.getCommonExpr();

  auto Binder =

      CodeGenFunction::OpaqueValueMappingData::bind(CGF, S.getOpaqueValue(), E);

  auto UnbindOnExit = llvm::make_scope_exit([&] { Binder.unbind(CGF); });

  auto Prefix = buildSuspendPrefixStr(Coro, Kind);

  BasicBlock *ReadyBlock = CGF.createBasicBlock(Prefix + Twine(".ready"));

  BasicBlock *SuspendBlock = CGF.createBasicBlock(Prefix + Twine(".suspend"));

  BasicBlock *CleanupBlock = CGF.createBasicBlock(Prefix + Twine(".cleanup"));

  // If expression is ready, no need to suspend.

  CGF.EmitBranchOnBoolExpr(S.getReadyExpr(), ReadyBlock, SuspendBlock, 0);

  // Otherwise, emit suspend logic.

  CGF.EmitBlock(SuspendBlock);

  auto &Builder = CGF.Builder;

  llvm::Function *CoroSave = CGF.CGM.getIntrinsic(llvm::Intrinsic::coro_save);

  auto *NullPtr = llvm::ConstantPointerNull::get(CGF.CGM.Int8PtrTy);

  auto *SaveCall = Builder.CreateCall(CoroSave, {NullPtr});

  auto *SuspendRet = CGF.EmitScalarExpr(S.getSuspendExpr());

  if (SuspendRet != nullptr && 
SuspendRet->getType()->isIntegerTy(1)20
) {

    // Veto suspension if requested by bool returning await_suspend.

    BasicBlock *RealSuspendBlock =

        CGF.createBasicBlock(Prefix + Twine(".suspend.bool"));

    CGF.Builder.CreateCondBr(SuspendRet, RealSuspendBlock, ReadyBlock);

    CGF.EmitBlock(RealSuspendBlock);

  }

  // Emit the suspend point.

  const bool IsFinalSuspend = (Kind == AwaitKind::Final);

  llvm::Function *CoroSuspend =

      CGF.CGM.getIntrinsic(llvm::Intrinsic::coro_suspend);

  auto *SuspendResult = Builder.CreateCall(

      CoroSuspend, {SaveCall, Builder.getInt1(IsFinalSuspend)});

  // Create a switch capturing three possible continuations.

  auto *Switch = Builder.CreateSwitch(SuspendResult, Coro.SuspendBB, 2);

  Switch->addCase(Builder.getInt8(0), ReadyBlock);

  Switch->addCase(Builder.getInt8(1), CleanupBlock);

  // Emit cleanup for this suspend point.

  CGF.EmitBlock(CleanupBlock);

  CGF.EmitBranchThroughCleanup(Coro.CleanupJD);

  // Emit await_resume expression.

  CGF.EmitBlock(ReadyBlock);

  // Exception handling requires additional IR. If the 'await_resume' function

  // is marked as 'noexcept', we avoid generating this additional IR.

  CXXTryStmt *TryStmt = nullptr;

  if (Coro.ExceptionHandler && 
Kind == AwaitKind::Init46
 &&

      
memberCallExpressionCanThrow(S.getResumeExpr())22
) {

    Coro.ResumeEHVar =

        CGF.CreateTempAlloca(Builder.getInt1Ty(), Prefix + Twine("resume.eh"));

    Builder.CreateFlagStore(true, Coro.ResumeEHVar);

    auto Loc = S.getResumeExpr()->getExprLoc();

    auto *Catch = new (CGF.getContext())

        CXXCatchStmt(Loc, /*exDecl=*/nullptr, Coro.ExceptionHandler);

    auto *TryBody =

        CompoundStmt::Create(CGF.getContext(), S.getResumeExpr(), Loc, Loc);

    TryStmt = CXXTryStmt::Create(CGF.getContext(), Loc, TryBody, Catch);

    CGF.EnterCXXTryStmt(*TryStmt);

  }

  LValueOrRValue Res;

  if (forLValue)

    Res.LV = CGF.EmitLValue(S.getResumeExpr());

  else

    Res.RV = CGF.EmitAnyExpr(S.getResumeExpr(), aggSlot, ignoreResult);

  if (TryStmt) {

    Builder.CreateFlagStore(false, Coro.ResumeEHVar);

    CGF.ExitCXXTryStmt(*TryStmt);

  }

  return Res;

}

RValue CodeGenFunction::EmitCoawaitExpr(const CoawaitExpr &E,

                                        AggValueSlot aggSlot,

                                        bool ignoreResult) {

  return emitSuspendExpression(*this, *CurCoro.Data, E,

                               CurCoro.Data->CurrentAwaitKind, aggSlot,

                               ignoreResult, /*forLValue*/false).RV;

}

RValue CodeGenFunction::EmitCoyieldExpr(const CoyieldExpr &E,

                                        AggValueSlot aggSlot,

                                        bool ignoreResult) {

  return emitSuspendExpression(*this, *CurCoro.Data, E, AwaitKind::Yield,

                               aggSlot, ignoreResult, /*forLValue*/false).RV;

}

void CodeGenFunction::EmitCoreturnStmt(CoreturnStmt const &S) {

  ++CurCoro.Data->CoreturnCount;

  const Expr *RV = S.getOperand();

  if (RV && 
RV->getType()->isVoidType()13
 && 
!isa<InitListExpr>(RV)4
) {

    // Make sure to evaluate the non initlist expression of a co_return

    // with a void expression for side effects.

    RunCleanupsScope cleanupScope(*this);

    EmitIgnoredExpr(RV);

  }

  EmitStmt(S.getPromiseCall());

  EmitBranchThroughCleanup(CurCoro.Data->FinalJD);

}

#ifndef NDEBUG

static QualType getCoroutineSuspendExprReturnType(const ASTContext &Ctx,

  const CoroutineSuspendExpr *E) {

  const auto *RE = E->getResumeExpr();

  // Is it possible for RE to be a CXXBindTemporaryExpr wrapping

  // a MemberCallExpr?

  assert(isa<CallExpr>(RE) && "unexpected suspend expression type");

  return cast<CallExpr>(RE)->getCallReturnType(Ctx);

}

#endif

LValue

CodeGenFunction::EmitCoawaitLValue(const CoawaitExpr *E) {

  assert(getCoroutineSuspendExprReturnType(getContext(), E)->isReferenceType() &&

         "Can't have a scalar return unless the return type is a "

         "reference type!");

  return emitSuspendExpression(*this, *CurCoro.Data, *E,

                               CurCoro.Data->CurrentAwaitKind, AggValueSlot::ignored(),

                               /*ignoreResult*/false, /*forLValue*/true).LV;

}

LValue

CodeGenFunction::EmitCoyieldLValue(const CoyieldExpr *E) {

  assert(getCoroutineSuspendExprReturnType(getContext(), E)->isReferenceType() &&

         "Can't have a scalar return unless the return type is a "

         "reference type!");

  return emitSuspendExpression(*this, *CurCoro.Data, *E,

                               AwaitKind::Yield, AggValueSlot::ignored(),

                               /*ignoreResult*/false, /*forLValue*/true).LV;

}

// Hunts for the parameter reference in the parameter copy/move declaration.

namespace {

struct GetParamRef : public StmtVisitor<GetParamRef> {

public:

  DeclRefExpr *Expr = nullptr;

  GetParamRef() {}

  void VisitDeclRefExpr(DeclRefExpr *E) {

    assert(Expr == nullptr && "multilple declref in param move");

    Expr = E;

  }

  void VisitStmt(Stmt *S) {

    for (auto *C : S->children()) {

      if (C)

        Visit(C);

    }

  }

};

}

// This class replaces references to parameters to their copies by changing

// the addresses in CGF.LocalDeclMap and restoring back the original values in

// its destructor.

namespace {

  struct ParamReferenceReplacerRAII {

    CodeGenFunction::DeclMapTy SavedLocals;

    CodeGenFunction::DeclMapTy& LocalDeclMap;

    ParamReferenceReplacerRAII(CodeGenFunction::DeclMapTy &LocalDeclMap)

        : LocalDeclMap(LocalDeclMap) {}

    void addCopy(DeclStmt const *PM) {

      // Figure out what param it refers to.

      assert(PM->isSingleDecl());

      VarDecl const*VD = static_cast<VarDecl const*>(PM->getSingleDecl());

      Expr const *InitExpr = VD->getInit();

      GetParamRef Visitor;

      Visitor.Visit(const_cast<Expr*>(InitExpr));

      assert(Visitor.Expr);

      DeclRefExpr *DREOrig = Visitor.Expr;

      auto *PD = DREOrig->getDecl();

      auto it = LocalDeclMap.find(PD);

      assert(it != LocalDeclMap.end() && "parameter is not found");

      SavedLocals.insert({ PD, it->second });

      auto copyIt = LocalDeclMap.find(VD);

      assert(copyIt != LocalDeclMap.end() && "parameter copy is not found");

      it->second = copyIt->getSecond();

    }

    ~ParamReferenceReplacerRAII() {

      for (auto&& SavedLocal : SavedLocals) {

        LocalDeclMap.insert({SavedLocal.first, SavedLocal.second});

      }

    }

  };

}

// For WinEH exception representation backend needs to know what funclet coro.end

// belongs to. That information is passed in a funclet bundle.

static SmallVector<llvm::OperandBundleDef, 1>

getBundlesForCoroEnd(CodeGenFunction &CGF) {

  SmallVector<llvm::OperandBundleDef, 1> BundleList;

  if (llvm::Instruction *EHPad = CGF.CurrentFuncletPad)

    BundleList.emplace_back("funclet", EHPad);

  return BundleList;

}

namespace {

// We will insert coro.end to cut any of the destructors for objects that

// do not need to be destroyed once the coroutine is resumed.

// See llvm/docs/Coroutines.rst for more details about coro.end.

struct CallCoroEnd final : public EHScopeStack::Cleanup {

  void Emit(CodeGenFunction &CGF, Flags flags) override {

    auto &CGM = CGF.CGM;

    auto *NullPtr = llvm::ConstantPointerNull::get(CGF.Int8PtrTy);

    llvm::Function *CoroEndFn = CGM.getIntrinsic(llvm::Intrinsic::coro_end);

    // See if we have a funclet bundle to associate coro.end with. (WinEH)

    auto Bundles = getBundlesForCoroEnd(CGF);

    auto *CoroEnd = CGF.Builder.CreateCall(

        CoroEndFn, {NullPtr, CGF.Builder.getTrue()}, Bundles);

    if (Bundles.empty()) {

      // Otherwise, (landingpad model), create a conditional branch that leads

      // either to a cleanup block or a block with EH resume instruction.

      auto *ResumeBB = CGF.getEHResumeBlock(/*isCleanup=*/true);

      auto *CleanupContBB = CGF.createBasicBlock("cleanup.cont");

      CGF.Builder.CreateCondBr(CoroEnd, ResumeBB, CleanupContBB);

      CGF.EmitBlock(CleanupContBB);

    }

  }

};

}

namespace {

// Make sure to call coro.delete on scope exit.

struct CallCoroDelete final : public EHScopeStack::Cleanup {

  Stmt *Deallocate;

  // Emit "if (coro.free(CoroId, CoroBegin)) Deallocate;"

  // Note: That deallocation will be emitted twice: once for a normal exit and

  // once for exceptional exit. This usage is safe because Deallocate does not

  // contain any declarations. The SubStmtBuilder::makeNewAndDeleteExpr()

  // builds a single call to a deallocation function which is safe to emit

  // multiple times.

  void Emit(CodeGenFunction &CGF, Flags) override {

    // Remember the current point, as we are going to emit deallocation code

    // first to get to coro.free instruction that is an argument to a delete

    // call.

    BasicBlock *SaveInsertBlock = CGF.Builder.GetInsertBlock();

    auto *FreeBB = CGF.createBasicBlock("coro.free");

    CGF.EmitBlock(FreeBB);

    CGF.EmitStmt(Deallocate);

    auto *AfterFreeBB = CGF.createBasicBlock("after.coro.free");

    CGF.EmitBlock(AfterFreeBB);

    // We should have captured coro.free from the emission of deallocate.

    auto *CoroFree = CGF.CurCoro.Data->LastCoroFree;

    if (!CoroFree) {

      CGF.CGM.Error(Deallocate->getBeginLoc(),

                    "Deallocation expressoin does not refer to coro.free");

      return;

    }

    // Get back to the block we were originally and move coro.free there.

    auto *InsertPt = SaveInsertBlock->getTerminator();

    CoroFree->moveBefore(InsertPt);

    CGF.Builder.SetInsertPoint(InsertPt);

    // Add if (auto *mem = coro.free) Deallocate;

    auto *NullPtr = llvm::ConstantPointerNull::get(CGF.Int8PtrTy);

    auto *Cond = CGF.Builder.CreateICmpNE(CoroFree, NullPtr);

    CGF.Builder.CreateCondBr(Cond, FreeBB, AfterFreeBB);

    // No longer need old terminator.

    InsertPt->eraseFromParent();

    CGF.Builder.SetInsertPoint(AfterFreeBB);

  }

  explicit CallCoroDelete(Stmt *DeallocStmt) : Deallocate(DeallocStmt) {}

};

}

static void emitBodyAndFallthrough(CodeGenFunction &CGF,

                                   const CoroutineBodyStmt &S, Stmt *Body) {

  CGF.EmitStmt(Body);

  const bool CanFallthrough = CGF.Builder.GetInsertBlock();

  if (CanFallthrough)

    if (Stmt *OnFallthrough = S.getFallthroughHandler())

      CGF.EmitStmt(OnFallthrough);

}

void CodeGenFunction::EmitCoroutineBody(const CoroutineBodyStmt &S) {

  auto *NullPtr = llvm::ConstantPointerNull::get(Builder.getInt8PtrTy());

  auto &TI = CGM.getContext().getTargetInfo();

  unsigned NewAlign = TI.getNewAlign() / TI.getCharWidth();

  auto *EntryBB = Builder.GetInsertBlock();

  auto *AllocBB = createBasicBlock("coro.alloc");

  auto *InitBB = createBasicBlock("coro.init");

  auto *FinalBB = createBasicBlock("coro.final");

  auto *RetBB = createBasicBlock("coro.ret");

  auto *CoroId = Builder.CreateCall(

      CGM.getIntrinsic(llvm::Intrinsic::coro_id),

      {Builder.getInt32(NewAlign), NullPtr, NullPtr, NullPtr});

  createCoroData(*this, CurCoro, CoroId);

  CurCoro.Data->SuspendBB = RetBB;

  assert(ShouldEmitLifetimeMarkers &&

         "Must emit lifetime intrinsics for coroutines");

  // Backend is allowed to elide memory allocations, to help it, emit

  // auto mem = coro.alloc() ? 0 : ... allocation code ...;

  auto *CoroAlloc = Builder.CreateCall(

      CGM.getIntrinsic(llvm::Intrinsic::coro_alloc), {CoroId});

  Builder.CreateCondBr(CoroAlloc, AllocBB, InitBB);

  EmitBlock(AllocBB);

  auto *AllocateCall = EmitScalarExpr(S.getAllocate());

  auto *AllocOrInvokeContBB = Builder.GetInsertBlock();

  // Handle allocation failure if 'ReturnStmtOnAllocFailure' was provided.

  if (auto *RetOnAllocFailure = S.getReturnStmtOnAllocFailure()) {

    auto *RetOnFailureBB = createBasicBlock("coro.ret.on.failure");

    // See if allocation was successful.

    auto *NullPtr = llvm::ConstantPointerNull::get(Int8PtrTy);

    auto *Cond = Builder.CreateICmpNE(AllocateCall, NullPtr);

    Builder.CreateCondBr(Cond, InitBB, RetOnFailureBB);

    // If not, return OnAllocFailure object.

    EmitBlock(RetOnFailureBB);

    EmitStmt(RetOnAllocFailure);

  }

  else {

    Builder.CreateBr(InitBB);

  }

  EmitBlock(InitBB);

  // Pass the result of the allocation to coro.begin.

  auto *Phi = Builder.CreatePHI(VoidPtrTy, 2);

  Phi->addIncoming(NullPtr, EntryBB);

  Phi->addIncoming(AllocateCall, AllocOrInvokeContBB);

  auto *CoroBegin = Builder.CreateCall(

      CGM.getIntrinsic(llvm::Intrinsic::coro_begin), {CoroId, Phi});

  CurCoro.Data->CoroBegin = CoroBegin;

  CurCoro.Data->CleanupJD = getJumpDestInCurrentScope(RetBB);

  {

    CGDebugInfo *DI = getDebugInfo();

    ParamReferenceReplacerRAII ParamReplacer(LocalDeclMap);

    CodeGenFunction::RunCleanupsScope ResumeScope(*this);

    EHStack.pushCleanup<CallCoroDelete>(NormalAndEHCleanup, S.getDeallocate());

    // Create mapping between parameters and copy-params for coroutine function.

    auto ParamMoves = S.getParamMoves();

    assert(

        (ParamMoves.size() == 0 || (ParamMoves.size() == FnArgs.size())) &&

        "ParamMoves and FnArgs should be the same size for coroutine function");

    if (ParamMoves.size() == FnArgs.size() && DI)

      for (const auto Pair : llvm::zip(FnArgs, ParamMoves))

        DI->getCoroutineParameterMappings().insert(

            {std::get<0>(Pair), std::get<1>(Pair)});

    // Create parameter copies. We do it before creating a promise, since an

    // evolution of coroutine TS may allow promise constructor to observe

    // parameter copies.

    for (auto *PM : S.getParamMoves()) {

      EmitStmt(PM);

      ParamReplacer.addCopy(cast<DeclStmt>(PM));

      // TODO: if(CoroParam(...)) need to surround ctor and dtor

      // for the copy, so that llvm can elide it if the copy is

      // not needed.

    }

    EmitStmt(S.getPromiseDeclStmt());

    Address PromiseAddr = GetAddrOfLocalVar(S.getPromiseDecl());

    auto *PromiseAddrVoidPtr =

        new llvm::BitCastInst(PromiseAddr.getPointer(), VoidPtrTy, "", CoroId);

    // Update CoroId to refer to the promise. We could not do it earlier because

    // promise local variable was not emitted yet.

    CoroId->setArgOperand(1, PromiseAddrVoidPtr);

    // ReturnValue should be valid as long as the coroutine's return type

    // is not void. The assertion could help us to reduce the check later.

    assert(ReturnValue.isValid() == (bool)S.getReturnStmt());

    // Now we have the promise, initialize the GRO.

    // We need to emit `get_return_object` first. According to:

    // [dcl.fct.def.coroutine]p7

    // The call to get_return_­object is sequenced before the call to

    // initial_suspend and is invoked at most once.

    //

    // So we couldn't emit return value when we emit return statment,

    // otherwise the call to get_return_object wouldn't be in front

    // of initial_suspend.

    if (ReturnValue.isValid()) {

      EmitAnyExprToMem(S.getReturnValue(), ReturnValue,

                       S.getReturnValue()->getType().getQualifiers(),

                       /*IsInit*/ true);

    }

    EHStack.pushCleanup<CallCoroEnd>(EHCleanup);

    CurCoro.Data->CurrentAwaitKind = AwaitKind::Init;

    CurCoro.Data->ExceptionHandler = S.getExceptionHandler();

    EmitStmt(S.getInitSuspendStmt());

    CurCoro.Data->FinalJD = getJumpDestInCurrentScope(FinalBB);

    CurCoro.Data->CurrentAwaitKind = AwaitKind::Normal;

    if (CurCoro.Data->ExceptionHandler) {

      // If we generated IR to record whether an exception was thrown from

      // 'await_resume', then use that IR to determine whether the coroutine

      // body should be skipped.

      // If we didn't generate the IR (perhaps because 'await_resume' was marked

      // as 'noexcept'), then we skip this check.

      BasicBlock *ContBB = nullptr;

      if (CurCoro.Data->ResumeEHVar) {

        BasicBlock *BodyBB = createBasicBlock("coro.resumed.body");

        ContBB = createBasicBlock("coro.resumed.cont");

        Value *SkipBody = Builder.CreateFlagLoad(CurCoro.Data->ResumeEHVar,

                                                 "coro.resumed.eh");

        Builder.CreateCondBr(SkipBody, ContBB, BodyBB);

        EmitBlock(BodyBB);

      }

      auto Loc = S.getBeginLoc();

      CXXCatchStmt Catch(Loc, /*exDecl=*/nullptr,

                         CurCoro.Data->ExceptionHandler);

      auto *TryStmt =

          CXXTryStmt::Create(getContext(), Loc, S.getBody(), &Catch);

      EnterCXXTryStmt(*TryStmt);

      emitBodyAndFallthrough(*this, S, TryStmt->getTryBlock());

      ExitCXXTryStmt(*TryStmt);

      if (ContBB)

        EmitBlock(ContBB);

    }

    else {

      emitBodyAndFallthrough(*this, S, S.getBody());

    }

    // See if we need to generate final suspend.

    const bool CanFallthrough = Builder.GetInsertBlock();

    const bool HasCoreturns = CurCoro.Data->CoreturnCount > 0;

    if (CanFallthrough || 
HasCoreturns93
) {

      EmitBlock(FinalBB);

      CurCoro.Data->CurrentAwaitKind = AwaitKind::Final;

      EmitStmt(S.getFinalSuspendStmt());

    } else {

      // We don't need FinalBB. Emit it to make sure the block is deleted.

      EmitBlock(FinalBB, /*IsFinished=*/true);

    }

  }

  EmitBlock(RetBB);

  // Emit coro.end before getReturnStmt (and parameter destructors), since

  // resume and destroy parts of the coroutine should not include them.

  llvm::Function *CoroEnd = CGM.getIntrinsic(llvm::Intrinsic::coro_end);

  Builder.CreateCall(CoroEnd, {NullPtr, Builder.getFalse()});

  if (Stmt *Ret = S.getReturnStmt()) {

    // Since we already emitted the return value above, so we shouldn't

    // emit it again here.

    cast<ReturnStmt>(Ret)->setRetValue(nullptr);

    EmitStmt(Ret);

  }

  // LLVM require the frontend to add the function attribute. See

  // Coroutines.rst.

  CurFn->addFnAttr("coroutine.presplit", "0");

}

// Emit coroutine intrinsic and patch up arguments of the token type.

RValue CodeGenFunction::EmitCoroutineIntrinsic(const CallExpr *E,

                                               unsigned int IID) {

  SmallVector<llvm::Value *, 8> Args;

  switch (IID) {

  default:

    break;

  // The coro.frame builtin is replaced with an SSA value of the coro.begin

  // intrinsic.

  case llvm::Intrinsic::coro_frame: {

    if (CurCoro.Data && CurCoro.Data->CoroBegin) {

      return RValue::get(CurCoro.Data->CoroBegin);

    }

    CGM.Error(E->getBeginLoc(), "this builtin expect that __builtin_coro_begin "

                                "has been used earlier in this function");

    auto NullPtr = llvm::ConstantPointerNull::get(Builder.getInt8PtrTy());

    return RValue::get(NullPtr);

  }

  // The following three intrinsics take a token parameter referring to a token

  // returned by earlier call to @llvm.coro.id. Since we cannot represent it in

  // builtins, we patch it up here.

  case llvm::Intrinsic::coro_alloc:

  case llvm::Intrinsic::coro_begin:

  case llvm::Intrinsic::coro_free: {

    if (CurCoro.Data && 
CurCoro.Data->CoroId144
) {

      Args.push_back(CurCoro.Data->CoroId);

      break;

    }

    CGM.Error(E->getBeginLoc(), "this builtin expect that __builtin_coro_id has"

                                " been used earlier in this function");

    // Fallthrough to the next case to add TokenNone as the first argument.

    LLVM_FALLTHROUGH;

  }

  // @llvm.coro.suspend takes a token parameter. Add token 'none' as the first

  // argument.

  case llvm::Intrinsic::coro_suspend:

    Args.push_back(llvm::ConstantTokenNone::get(getLLVMContext()));

    break;

  }

  for (const Expr *Arg : E->arguments())

    Args.push_back(EmitScalarExpr(Arg));

  llvm::Function *F = CGM.getIntrinsic(IID);

  llvm::CallInst *Call = Builder.CreateCall(F, Args);

  // Note: The following code is to enable to emit coro.id and coro.begin by

  // hand to experiment with coroutines in C.

  // If we see @llvm.coro.id remember it in the CoroData. We will update

  // coro.alloc, coro.begin and coro.free intrinsics to refer to it.

  if (IID == llvm::Intrinsic::coro_id) {

    createCoroData(*this, CurCoro, Call, E);

  }

  else if (IID == llvm::Intrinsic::coro_begin) {

    if (CurCoro.Data)

      CurCoro.Data->CoroBegin = Call;

  }

  else if (IID == llvm::Intrinsic::coro_free) {

    // Remember the last coro_free as we need it to build the conditional

    // deletion of the coroutine frame.

    if (CurCoro.Data)

      CurCoro.Data->LastCoroFree = Call;

  }

  return RValue::get(Call);

}