clang/lib/CodeGen/CGCoroutine.cpp

   1 //===----- CGCoroutine.cpp - Emit LLVM Code for C++ coroutines ------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This contains code dealing with C++ code generation of coroutines.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "CGCleanup.h"
  14 #include "CodeGenFunction.h"
  15 #include "llvm/ADT/ScopeExit.h"
  16 #include "clang/AST/StmtCXX.h"
  17 #include "clang/AST/StmtVisitor.h"
  18
  19 using namespace clang;
  20 using namespace CodeGen;
  21
  22 using llvm::Value;
  23 using llvm::BasicBlock;
  24
  25 namespace {
  26 enum class AwaitKind { Init, Normal, Yield, Final };
  27 static constexpr llvm::StringLiteral AwaitKindStr[] = {"init", "await", "yield",
  28                                                        "final"};
  29 }
  30
  31 struct clang::CodeGen::CGCoroData {
  32   // What is the current await expression kind and how many
  33   // await/yield expressions were encountered so far.
  34   // These are used to generate pretty labels for await expressions in LLVM IR.
  35   AwaitKind CurrentAwaitKind = AwaitKind::Init;
  36   unsigned AwaitNum = 0;
  37   unsigned YieldNum = 0;
  38
  39   // How many co_return statements are in the coroutine. Used to decide whether
  40   // we need to add co_return; equivalent at the end of the user authored body.
  41   unsigned CoreturnCount = 0;
  42
  43   // A branch to this block is emitted when coroutine needs to suspend.
  44   llvm::BasicBlock *SuspendBB = nullptr;
  45
  46   // The promise type's 'unhandled_exception' handler, if it defines one.
  47   Stmt *ExceptionHandler = nullptr;
  48
  49   // A temporary i1 alloca that stores whether 'await_resume' threw an
  50   // exception. If it did, 'true' is stored in this variable, and the coroutine
  51   // body must be skipped. If the promise type does not define an exception
  52   // handler, this is null.
  53   llvm::Value *ResumeEHVar = nullptr;
  54
  55   // Stores the jump destination just before the coroutine memory is freed.
  56   // This is the destination that every suspend point jumps to for the cleanup
  57   // branch.
  58   CodeGenFunction::JumpDest CleanupJD;
  59
  60   // Stores the jump destination just before the final suspend. The co_return
  61   // statements jumps to this point after calling return_xxx promise member.
  62   CodeGenFunction::JumpDest FinalJD;
  63
  64   // Stores the llvm.coro.id emitted in the function so that we can supply it
  65   // as the first argument to coro.begin, coro.alloc and coro.free intrinsics.
  66   // Note: llvm.coro.id returns a token that cannot be directly expressed in a
  67   // builtin.
  68   llvm::CallInst *CoroId = nullptr;
  69
  70   // Stores the llvm.coro.begin emitted in the function so that we can replace
  71   // all coro.frame intrinsics with direct SSA value of coro.begin that returns
  72   // the address of the coroutine frame of the current coroutine.
  73   llvm::CallInst *CoroBegin = nullptr;
  74
  75   // Stores the last emitted coro.free for the deallocate expressions, we use it
  76   // to wrap dealloc code with if(auto mem = coro.free) dealloc(mem).
  77   llvm::CallInst *LastCoroFree = nullptr;
  78
  79   // If coro.id came from the builtin, remember the expression to give better
  80   // diagnostic. If CoroIdExpr is nullptr, the coro.id was created by
  81   // EmitCoroutineBody.
  82   CallExpr const *CoroIdExpr = nullptr;
  83 };
  84
  85 // Defining these here allows to keep CGCoroData private to this file.
  86 clang::CodeGen::CodeGenFunction::CGCoroInfo::CGCoroInfo() {}
  87 CodeGenFunction::CGCoroInfo::~CGCoroInfo() {}
  88
  89 static void createCoroData(CodeGenFunction &CGF,
  90                            CodeGenFunction::CGCoroInfo &CurCoro,
  91                            llvm::CallInst *CoroId,
  92                            CallExpr const *CoroIdExpr = nullptr) {
  93   if (CurCoro.Data) {
  94     if (CurCoro.Data->CoroIdExpr)
  95       CGF.CGM.Error(CoroIdExpr->getBeginLoc(),
  96                     "only one __builtin_coro_id can be used in a function");
  97     else if (CoroIdExpr)
  98       CGF.CGM.Error(CoroIdExpr->getBeginLoc(),
  99                     "__builtin_coro_id shall not be used in a C++ coroutine");
 100     else
 101       llvm_unreachable("EmitCoroutineBodyStatement called twice?");
 102
 103     return;
 104   }
 105
 106   CurCoro.Data = std::unique_ptr<CGCoroData>(new CGCoroData);
 107   CurCoro.Data->CoroId = CoroId;
 108   CurCoro.Data->CoroIdExpr = CoroIdExpr;
 109 }
 110
 111 // Synthesize a pretty name for a suspend point.
 112 static SmallString<32> buildSuspendPrefixStr(CGCoroData &Coro, AwaitKind Kind) {
 113   unsigned No = 0;
 114   switch (Kind) {
 115   case AwaitKind::Init:
 116   case AwaitKind::Final:
 117     break;
 118   case AwaitKind::Normal:
 119     No = ++Coro.AwaitNum;
 120     break;
 121   case AwaitKind::Yield:
 122     No = ++Coro.YieldNum;
 123     break;
 124   }
 125   SmallString<32> Prefix(AwaitKindStr[static_cast<unsigned>(Kind)]);
 126   if (No > 1) {
 127     Twine(No).toVector(Prefix);
 128   }
 129   return Prefix;
 130 }
 131
 132 static bool memberCallExpressionCanThrow(const Expr *E) {
 133   if (const auto *CE = dyn_cast<CXXMemberCallExpr>(E))
 134     if (const auto *Proto =
 135             CE->getMethodDecl()->getType()->getAs<FunctionProtoType>())
 136       if (isNoexceptExceptionSpec(Proto->getExceptionSpecType()) &&
 137           Proto->canThrow() == CT_Cannot)
 138         return false;
 139   return true;
 140 }
 141
 142 // Emit suspend expression which roughly looks like:
 143 //
 144 //   auto && x = CommonExpr();
 145 //   if (!x.await_ready()) {
 146 //      llvm_coro_save();
 147 //      x.await_suspend(...);     (*)
 148 //      llvm_coro_suspend(); (**)
 149 //   }
 150 //   x.await_resume();
 151 //
 152 // where the result of the entire expression is the result of x.await_resume()
 153 //
 154 //   (*) If x.await_suspend return type is bool, it allows to veto a suspend:
 155 //      if (x.await_suspend(...))
 156 //        llvm_coro_suspend();
 157 //
 158 //  (**) llvm_coro_suspend() encodes three possible continuations as
 159 //       a switch instruction:
 160 //
 161 //  %where-to = call i8 @llvm.coro.suspend(...)
 162 //  switch i8 %where-to, label %coro.ret [ ; jump to epilogue to suspend
 163 //    i8 0, label %yield.ready   ; go here when resumed
 164 //    i8 1, label %yield.cleanup ; go here when destroyed
 165 //  ]
 166 //
 167 //  See llvm's docs/Coroutines.rst for more details.
 168 //
 169 namespace {
 170   struct LValueOrRValue {
 171     LValue LV;
 172     RValue RV;
 173   };
 174 }
 175 static LValueOrRValue emitSuspendExpression(CodeGenFunction &CGF, CGCoroData &Coro,
 176                                     CoroutineSuspendExpr const &S,
 177                                     AwaitKind Kind, AggValueSlot aggSlot,
 178                                     bool ignoreResult, bool forLValue) {
 179   auto *E = S.getCommonExpr();
 180
 181   auto Binder =
 182       CodeGenFunction::OpaqueValueMappingData::bind(CGF, S.getOpaqueValue(), E);
 183   auto UnbindOnExit = llvm::make_scope_exit([&] { Binder.unbind(CGF); });
 184
 185   auto Prefix = buildSuspendPrefixStr(Coro, Kind);
 186   BasicBlock *ReadyBlock = CGF.createBasicBlock(Prefix + Twine(".ready"));
 187   BasicBlock *SuspendBlock = CGF.createBasicBlock(Prefix + Twine(".suspend"));
 188   BasicBlock *CleanupBlock = CGF.createBasicBlock(Prefix + Twine(".cleanup"));
 189
 190   // If expression is ready, no need to suspend.
 191   CGF.EmitBranchOnBoolExpr(S.getReadyExpr(), ReadyBlock, SuspendBlock, 0);
 192
 193   // Otherwise, emit suspend logic.
 194   CGF.EmitBlock(SuspendBlock);
 195
 196   auto &Builder = CGF.Builder;
 197   llvm::Function *CoroSave = CGF.CGM.getIntrinsic(llvm::Intrinsic::coro_save);
 198   auto *NullPtr = llvm::ConstantPointerNull::get(CGF.CGM.Int8PtrTy);
 199   auto *SaveCall = Builder.CreateCall(CoroSave, {NullPtr});
 200
 201   CGF.CurCoro.InSuspendBlock = true;
 202   auto *SuspendRet = CGF.EmitScalarExpr(S.getSuspendExpr());
 203   CGF.CurCoro.InSuspendBlock = false;
 204   if (SuspendRet != nullptr && SuspendRet->getType()->isIntegerTy(1)) {
 205     // Veto suspension if requested by bool returning await_suspend.
 206     BasicBlock *RealSuspendBlock =
 207         CGF.createBasicBlock(Prefix + Twine(".suspend.bool"));
 208     CGF.Builder.CreateCondBr(SuspendRet, RealSuspendBlock, ReadyBlock);
 209     CGF.EmitBlock(RealSuspendBlock);
 210   }
 211
 212   // Emit the suspend point.
 213   const bool IsFinalSuspend = (Kind == AwaitKind::Final);
 214   llvm::Function *CoroSuspend =
 215       CGF.CGM.getIntrinsic(llvm::Intrinsic::coro_suspend);
 216   auto *SuspendResult = Builder.CreateCall(
 217       CoroSuspend, {SaveCall, Builder.getInt1(IsFinalSuspend)});
 218
 219   // Create a switch capturing three possible continuations.
 220   auto *Switch = Builder.CreateSwitch(SuspendResult, Coro.SuspendBB, 2);
 221   Switch->addCase(Builder.getInt8(0), ReadyBlock);
 222   Switch->addCase(Builder.getInt8(1), CleanupBlock);
 223
 224   // Emit cleanup for this suspend point.
 225   CGF.EmitBlock(CleanupBlock);
 226   CGF.EmitBranchThroughCleanup(Coro.CleanupJD);
 227
 228   // Emit await_resume expression.
 229   CGF.EmitBlock(ReadyBlock);
 230
 231   // Exception handling requires additional IR. If the 'await_resume' function
 232   // is marked as 'noexcept', we avoid generating this additional IR.
 233   CXXTryStmt *TryStmt = nullptr;
 234   if (Coro.ExceptionHandler && Kind == AwaitKind::Init &&
 235       memberCallExpressionCanThrow(S.getResumeExpr())) {
 236     Coro.ResumeEHVar =
 237         CGF.CreateTempAlloca(Builder.getInt1Ty(), Prefix + Twine("resume.eh"));
 238     Builder.CreateFlagStore(true, Coro.ResumeEHVar);
 239
 240     auto Loc = S.getResumeExpr()->getExprLoc();
 241     auto *Catch = new (CGF.getContext())
 242         CXXCatchStmt(Loc, /*exDecl=*/nullptr, Coro.ExceptionHandler);
 243     auto *TryBody = CompoundStmt::Create(CGF.getContext(), S.getResumeExpr(),
 244                                          FPOptionsOverride(), Loc, Loc);
 245     TryStmt = CXXTryStmt::Create(CGF.getContext(), Loc, TryBody, Catch);
 246     CGF.EnterCXXTryStmt(*TryStmt);
 247   }
 248
 249   LValueOrRValue Res;
 250   if (forLValue)
 251     Res.LV = CGF.EmitLValue(S.getResumeExpr());
 252   else
 253     Res.RV = CGF.EmitAnyExpr(S.getResumeExpr(), aggSlot, ignoreResult);
 254
 255   if (TryStmt) {
 256     Builder.CreateFlagStore(false, Coro.ResumeEHVar);
 257     CGF.ExitCXXTryStmt(*TryStmt);
 258   }
 259
 260   return Res;
 261 }
 262
 263 RValue CodeGenFunction::EmitCoawaitExpr(const CoawaitExpr &E,
 264                                         AggValueSlot aggSlot,
 265                                         bool ignoreResult) {
 266   return emitSuspendExpression(*this, *CurCoro.Data, E,
 267                                CurCoro.Data->CurrentAwaitKind, aggSlot,
 268                                ignoreResult, /*forLValue*/false).RV;
 269 }
 270 RValue CodeGenFunction::EmitCoyieldExpr(const CoyieldExpr &E,
 271                                         AggValueSlot aggSlot,
 272                                         bool ignoreResult) {
 273   return emitSuspendExpression(*this, *CurCoro.Data, E, AwaitKind::Yield,
 274                                aggSlot, ignoreResult, /*forLValue*/false).RV;
 275 }
 276
 277 void CodeGenFunction::EmitCoreturnStmt(CoreturnStmt const &S) {
 278   ++CurCoro.Data->CoreturnCount;
 279   const Expr *RV = S.getOperand();
 280   if (RV && RV->getType()->isVoidType() && !isa<InitListExpr>(RV)) {
 281     // Make sure to evaluate the non initlist expression of a co_return
 282     // with a void expression for side effects.
 283     RunCleanupsScope cleanupScope(*this);
 284     EmitIgnoredExpr(RV);
 285   }
 286   EmitStmt(S.getPromiseCall());
 287   EmitBranchThroughCleanup(CurCoro.Data->FinalJD);
 288 }
 289
 290
 291 #ifndef NDEBUG
 292 static QualType getCoroutineSuspendExprReturnType(const ASTContext &Ctx,
 293   const CoroutineSuspendExpr *E) {
 294   const auto *RE = E->getResumeExpr();
 295   // Is it possible for RE to be a CXXBindTemporaryExpr wrapping
 296   // a MemberCallExpr?
 297   assert(isa<CallExpr>(RE) && "unexpected suspend expression type");
 298   return cast<CallExpr>(RE)->getCallReturnType(Ctx);
 299 }
 300 #endif
 301
 302 LValue
 303 CodeGenFunction::EmitCoawaitLValue(const CoawaitExpr *E) {
 304   assert(getCoroutineSuspendExprReturnType(getContext(), E)->isReferenceType() &&
 305          "Can't have a scalar return unless the return type is a "
 306          "reference type!");
 307   return emitSuspendExpression(*this, *CurCoro.Data, *E,
 308                                CurCoro.Data->CurrentAwaitKind, AggValueSlot::ignored(),
 309                                /*ignoreResult*/false, /*forLValue*/true).LV;
 310 }
 311
 312 LValue
 313 CodeGenFunction::EmitCoyieldLValue(const CoyieldExpr *E) {
 314   assert(getCoroutineSuspendExprReturnType(getContext(), E)->isReferenceType() &&
 315          "Can't have a scalar return unless the return type is a "
 316          "reference type!");
 317   return emitSuspendExpression(*this, *CurCoro.Data, *E,
 318                                AwaitKind::Yield, AggValueSlot::ignored(),
 319                                /*ignoreResult*/false, /*forLValue*/true).LV;
 320 }
 321
 322 // Hunts for the parameter reference in the parameter copy/move declaration.
 323 namespace {
 324 struct GetParamRef : public StmtVisitor<GetParamRef> {
 325 public:
 326   DeclRefExpr *Expr = nullptr;
 327   GetParamRef() {}
 328   void VisitDeclRefExpr(DeclRefExpr *E) {
 329     assert(Expr == nullptr && "multilple declref in param move");
 330     Expr = E;
 331   }
 332   void VisitStmt(Stmt *S) {
 333     for (auto *C : S->children()) {
 334       if (C)
 335         Visit(C);
 336     }
 337   }
 338 };
 339 }
 340
 341 // This class replaces references to parameters to their copies by changing
 342 // the addresses in CGF.LocalDeclMap and restoring back the original values in
 343 // its destructor.
 344
 345 namespace {
 346   struct ParamReferenceReplacerRAII {
 347     CodeGenFunction::DeclMapTy SavedLocals;
 348     CodeGenFunction::DeclMapTy& LocalDeclMap;
 349
 350     ParamReferenceReplacerRAII(CodeGenFunction::DeclMapTy &LocalDeclMap)
 351         : LocalDeclMap(LocalDeclMap) {}
 352
 353     void addCopy(DeclStmt const *PM) {
 354       // Figure out what param it refers to.
 355
 356       assert(PM->isSingleDecl());
 357       VarDecl const*VD = static_cast<VarDecl const*>(PM->getSingleDecl());
 358       Expr const *InitExpr = VD->getInit();
 359       GetParamRef Visitor;
 360       Visitor.Visit(const_cast<Expr*>(InitExpr));
 361       assert(Visitor.Expr);
 362       DeclRefExpr *DREOrig = Visitor.Expr;
 363       auto *PD = DREOrig->getDecl();
 364
 365       auto it = LocalDeclMap.find(PD);
 366       assert(it != LocalDeclMap.end() && "parameter is not found");
 367       SavedLocals.insert({ PD, it->second });
 368
 369       auto copyIt = LocalDeclMap.find(VD);
 370       assert(copyIt != LocalDeclMap.end() && "parameter copy is not found");
 371       it->second = copyIt->getSecond();
 372     }
 373
 374     ~ParamReferenceReplacerRAII() {
 375       for (auto&& SavedLocal : SavedLocals) {
 376         LocalDeclMap.insert({SavedLocal.first, SavedLocal.second});
 377       }
 378     }
 379   };
 380 }
 381
 382 // For WinEH exception representation backend needs to know what funclet coro.end
 383 // belongs to. That information is passed in a funclet bundle.
 384 static SmallVector<llvm::OperandBundleDef, 1>
 385 getBundlesForCoroEnd(CodeGenFunction &CGF) {
 386   SmallVector<llvm::OperandBundleDef, 1> BundleList;
 387
 388   if (llvm::Instruction *EHPad = CGF.CurrentFuncletPad)
 389     BundleList.emplace_back("funclet", EHPad);
 390
 391   return BundleList;
 392 }
 393
 394 namespace {
 395 // We will insert coro.end to cut any of the destructors for objects that
 396 // do not need to be destroyed once the coroutine is resumed.
 397 // See llvm/docs/Coroutines.rst for more details about coro.end.
 398 struct CallCoroEnd final : public EHScopeStack::Cleanup {
 399   void Emit(CodeGenFunction &CGF, Flags flags) override {
 400     auto &CGM = CGF.CGM;
 401     auto *NullPtr = llvm::ConstantPointerNull::get(CGF.Int8PtrTy);
 402     llvm::Function *CoroEndFn = CGM.getIntrinsic(llvm::Intrinsic::coro_end);
 403     // See if we have a funclet bundle to associate coro.end with. (WinEH)
 404     auto Bundles = getBundlesForCoroEnd(CGF);
 405     auto *CoroEnd = CGF.Builder.CreateCall(
 406         CoroEndFn, {NullPtr, CGF.Builder.getTrue()}, Bundles);
 407     if (Bundles.empty()) {
 408       // Otherwise, (landingpad model), create a conditional branch that leads
 409       // either to a cleanup block or a block with EH resume instruction.
 410       auto *ResumeBB = CGF.getEHResumeBlock(/*isCleanup=*/true);
 411       auto *CleanupContBB = CGF.createBasicBlock("cleanup.cont");
 412       CGF.Builder.CreateCondBr(CoroEnd, ResumeBB, CleanupContBB);
 413       CGF.EmitBlock(CleanupContBB);
 414     }
 415   }
 416 };
 417 }
 418
 419 namespace {
 420 // Make sure to call coro.delete on scope exit.
 421 struct CallCoroDelete final : public EHScopeStack::Cleanup {
 422   Stmt *Deallocate;
 423
 424   // Emit "if (coro.free(CoroId, CoroBegin)) Deallocate;"
 425
 426   // Note: That deallocation will be emitted twice: once for a normal exit and
 427   // once for exceptional exit. This usage is safe because Deallocate does not
 428   // contain any declarations. The SubStmtBuilder::makeNewAndDeleteExpr()
 429   // builds a single call to a deallocation function which is safe to emit
 430   // multiple times.
 431   void Emit(CodeGenFunction &CGF, Flags) override {
 432     // Remember the current point, as we are going to emit deallocation code
 433     // first to get to coro.free instruction that is an argument to a delete
 434     // call.
 435     BasicBlock *SaveInsertBlock = CGF.Builder.GetInsertBlock();
 436
 437     auto *FreeBB = CGF.createBasicBlock("coro.free");
 438     CGF.EmitBlock(FreeBB);
 439     CGF.EmitStmt(Deallocate);
 440
 441     auto *AfterFreeBB = CGF.createBasicBlock("after.coro.free");
 442     CGF.EmitBlock(AfterFreeBB);
 443
 444     // We should have captured coro.free from the emission of deallocate.
 445     auto *CoroFree = CGF.CurCoro.Data->LastCoroFree;
 446     if (!CoroFree) {
 447       CGF.CGM.Error(Deallocate->getBeginLoc(),
 448                     "Deallocation expressoin does not refer to coro.free");
 449       return;
 450     }
 451
 452     // Get back to the block we were originally and move coro.free there.
 453     auto *InsertPt = SaveInsertBlock->getTerminator();
 454     CoroFree->moveBefore(InsertPt);
 455     CGF.Builder.SetInsertPoint(InsertPt);
 456
 457     // Add if (auto *mem = coro.free) Deallocate;
 458     auto *NullPtr = llvm::ConstantPointerNull::get(CGF.Int8PtrTy);
 459     auto *Cond = CGF.Builder.CreateICmpNE(CoroFree, NullPtr);
 460     CGF.Builder.CreateCondBr(Cond, FreeBB, AfterFreeBB);
 461
 462     // No longer need old terminator.
 463     InsertPt->eraseFromParent();
 464     CGF.Builder.SetInsertPoint(AfterFreeBB);
 465   }
 466   explicit CallCoroDelete(Stmt *DeallocStmt) : Deallocate(DeallocStmt) {}
 467 };
 468 }
 469
 470 namespace {
 471 struct GetReturnObjectManager {
 472   CodeGenFunction &CGF;
 473   CGBuilderTy &Builder;
 474   const CoroutineBodyStmt &S;
 475   // When true, performs RVO for the return object.
 476   bool DirectEmit = false;
 477
 478   Address GroActiveFlag;
 479   CodeGenFunction::AutoVarEmission GroEmission;
 480
 481   GetReturnObjectManager(CodeGenFunction &CGF, const CoroutineBodyStmt &S)
 482       : CGF(CGF), Builder(CGF.Builder), S(S), GroActiveFlag(Address::invalid()),
 483         GroEmission(CodeGenFunction::AutoVarEmission::invalid()) {
 484     // The call to get_return_object is sequenced before the call to
 485     // initial_suspend and is invoked at most once, but there are caveats
 486     // regarding on whether the prvalue result object may be initialized
 487     // directly/eager or delayed, depending on the types involved.
 488     //
 489     // More info at https://github.com/cplusplus/papers/issues/1414
 490     //
 491     // The general cases:
 492     // 1. Same type of get_return_object and coroutine return type (direct
 493     // emission):
 494     //  - Constructed in the return slot.
 495     // 2. Different types (delayed emission):
 496     //  - Constructed temporary object prior to initial suspend initialized with
 497     //  a call to get_return_object()
 498     //  - When coroutine needs to to return to the caller and needs to construct
 499     //  return value for the coroutine it is initialized with expiring value of
 500     //  the temporary obtained above.
 501     //
 502     // Direct emission for void returning coroutines or GROs.
 503     DirectEmit = [&]() {
 504       auto *RVI = S.getReturnValueInit();
 505       assert(RVI && "expected RVI");
 506       auto GroType = RVI->getType();
 507       return CGF.getContext().hasSameType(GroType, CGF.FnRetTy);
 508     }();
 509   }
 510
 511   // The gro variable has to outlive coroutine frame and coroutine promise, but,
 512   // it can only be initialized after coroutine promise was created, thus, we
 513   // split its emission in two parts. EmitGroAlloca emits an alloca and sets up
 514   // cleanups. Later when coroutine promise is available we initialize the gro
 515   // and sets the flag that the cleanup is now active.
 516   void EmitGroAlloca() {
 517     if (DirectEmit)
 518       return;
 519
 520     auto *GroDeclStmt = dyn_cast_or_null<DeclStmt>(S.getResultDecl());
 521     if (!GroDeclStmt) {
 522       // If get_return_object returns void, no need to do an alloca.
 523       return;
 524     }
 525
 526     auto *GroVarDecl = cast<VarDecl>(GroDeclStmt->getSingleDecl());
 527
 528     // Set GRO flag that it is not initialized yet
 529     GroActiveFlag = CGF.CreateTempAlloca(Builder.getInt1Ty(), CharUnits::One(),
 530                                          "gro.active");
 531     Builder.CreateStore(Builder.getFalse(), GroActiveFlag);
 532
 533     GroEmission = CGF.EmitAutoVarAlloca(*GroVarDecl);
 534
 535     // Remember the top of EHStack before emitting the cleanup.
 536     auto old_top = CGF.EHStack.stable_begin();
 537     CGF.EmitAutoVarCleanups(GroEmission);
 538     auto top = CGF.EHStack.stable_begin();
 539
 540     // Make the cleanup conditional on gro.active
 541     for (auto b = CGF.EHStack.find(top), e = CGF.EHStack.find(old_top); b != e;
 542          b++) {
 543       if (auto *Cleanup = dyn_cast<EHCleanupScope>(&*b)) {
 544         assert(!Cleanup->hasActiveFlag() && "cleanup already has active flag?");
 545         Cleanup->setActiveFlag(GroActiveFlag);
 546         Cleanup->setTestFlagInEHCleanup();
 547         Cleanup->setTestFlagInNormalCleanup();
 548       }
 549     }
 550   }
 551
 552   void EmitGroInit() {
 553     if (DirectEmit) {
 554       // ReturnValue should be valid as long as the coroutine's return type
 555       // is not void. The assertion could help us to reduce the check later.
 556       assert(CGF.ReturnValue.isValid() == (bool)S.getReturnStmt());
 557       // Now we have the promise, initialize the GRO.
 558       // We need to emit `get_return_object` first. According to:
 559       // [dcl.fct.def.coroutine]p7
 560       // The call to get_return_object is sequenced before the call to
 561       // initial_suspend and is invoked at most once.
 562       //
 563       // So we couldn't emit return value when we emit return statment,
 564       // otherwise the call to get_return_object wouldn't be in front
 565       // of initial_suspend.
 566       if (CGF.ReturnValue.isValid()) {
 567         CGF.EmitAnyExprToMem(S.getReturnValue(), CGF.ReturnValue,
 568                              S.getReturnValue()->getType().getQualifiers(),
 569                              /*IsInit*/ true);
 570       }
 571       return;
 572     }
 573
 574     if (!GroActiveFlag.isValid()) {
 575       // No Gro variable was allocated. Simply emit the call to
 576       // get_return_object.
 577       CGF.EmitStmt(S.getResultDecl());
 578       return;
 579     }
 580
 581     CGF.EmitAutoVarInit(GroEmission);
 582     Builder.CreateStore(Builder.getTrue(), GroActiveFlag);
 583   }
 584 };
 585 } // namespace
 586
 587 static void emitBodyAndFallthrough(CodeGenFunction &CGF,
 588                                    const CoroutineBodyStmt &S, Stmt *Body) {
 589   CGF.EmitStmt(Body);
 590   const bool CanFallthrough = CGF.Builder.GetInsertBlock();
 591   if (CanFallthrough)
 592     if (Stmt *OnFallthrough = S.getFallthroughHandler())
 593       CGF.EmitStmt(OnFallthrough);
 594 }
 595
 596 void CodeGenFunction::EmitCoroutineBody(const CoroutineBodyStmt &S) {
 597   auto *NullPtr = llvm::ConstantPointerNull::get(Builder.getInt8PtrTy());
 598   auto &TI = CGM.getContext().getTargetInfo();
 599   unsigned NewAlign = TI.getNewAlign() / TI.getCharWidth();
 600
 601   auto *EntryBB = Builder.GetInsertBlock();
 602   auto *AllocBB = createBasicBlock("coro.alloc");
 603   auto *InitBB = createBasicBlock("coro.init");
 604   auto *FinalBB = createBasicBlock("coro.final");
 605   auto *RetBB = createBasicBlock("coro.ret");
 606
 607   auto *CoroId = Builder.CreateCall(
 608       CGM.getIntrinsic(llvm::Intrinsic::coro_id),
 609       {Builder.getInt32(NewAlign), NullPtr, NullPtr, NullPtr});
 610   createCoroData(*this, CurCoro, CoroId);
 611   CurCoro.Data->SuspendBB = RetBB;
 612   assert(ShouldEmitLifetimeMarkers &&
 613          "Must emit lifetime intrinsics for coroutines");
 614
 615   // Backend is allowed to elide memory allocations, to help it, emit
 616   // auto mem = coro.alloc() ? 0 : ... allocation code ...;
 617   auto *CoroAlloc = Builder.CreateCall(
 618       CGM.getIntrinsic(llvm::Intrinsic::coro_alloc), {CoroId});
 619
 620   Builder.CreateCondBr(CoroAlloc, AllocBB, InitBB);
 621
 622   EmitBlock(AllocBB);
 623   auto *AllocateCall = EmitScalarExpr(S.getAllocate());
 624   auto *AllocOrInvokeContBB = Builder.GetInsertBlock();
 625
 626   // Handle allocation failure if 'ReturnStmtOnAllocFailure' was provided.
 627   if (auto *RetOnAllocFailure = S.getReturnStmtOnAllocFailure()) {
 628     auto *RetOnFailureBB = createBasicBlock("coro.ret.on.failure");
 629
 630     // See if allocation was successful.
 631     auto *NullPtr = llvm::ConstantPointerNull::get(Int8PtrTy);
 632     auto *Cond = Builder.CreateICmpNE(AllocateCall, NullPtr);
 633     Builder.CreateCondBr(Cond, InitBB, RetOnFailureBB);
 634
 635     // If not, return OnAllocFailure object.
 636     EmitBlock(RetOnFailureBB);
 637     EmitStmt(RetOnAllocFailure);
 638   }
 639   else {
 640     Builder.CreateBr(InitBB);
 641   }
 642
 643   EmitBlock(InitBB);
 644
 645   // Pass the result of the allocation to coro.begin.
 646   auto *Phi = Builder.CreatePHI(VoidPtrTy, 2);
 647   Phi->addIncoming(NullPtr, EntryBB);
 648   Phi->addIncoming(AllocateCall, AllocOrInvokeContBB);
 649   auto *CoroBegin = Builder.CreateCall(
 650       CGM.getIntrinsic(llvm::Intrinsic::coro_begin), {CoroId, Phi});
 651   CurCoro.Data->CoroBegin = CoroBegin;
 652
 653   GetReturnObjectManager GroManager(*this, S);
 654   GroManager.EmitGroAlloca();
 655
 656   CurCoro.Data->CleanupJD = getJumpDestInCurrentScope(RetBB);
 657   {
 658     CGDebugInfo *DI = getDebugInfo();
 659     ParamReferenceReplacerRAII ParamReplacer(LocalDeclMap);
 660     CodeGenFunction::RunCleanupsScope ResumeScope(*this);
 661     EHStack.pushCleanup<CallCoroDelete>(NormalAndEHCleanup, S.getDeallocate());
 662
 663     // Create mapping between parameters and copy-params for coroutine function.
 664     llvm::ArrayRef<const Stmt *> ParamMoves = S.getParamMoves();
 665     assert(
 666         (ParamMoves.size() == 0 || (ParamMoves.size() == FnArgs.size())) &&
 667         "ParamMoves and FnArgs should be the same size for coroutine function");
 668     if (ParamMoves.size() == FnArgs.size() && DI)
 669       for (const auto Pair : llvm::zip(FnArgs, ParamMoves))
 670         DI->getCoroutineParameterMappings().insert(
 671             {std::get<0>(Pair), std::get<1>(Pair)});
 672
 673     // Create parameter copies. We do it before creating a promise, since an
 674     // evolution of coroutine TS may allow promise constructor to observe
 675     // parameter copies.
 676     for (auto *PM : S.getParamMoves()) {
 677       EmitStmt(PM);
 678       ParamReplacer.addCopy(cast<DeclStmt>(PM));
 679       // TODO: if(CoroParam(...)) need to surround ctor and dtor
 680       // for the copy, so that llvm can elide it if the copy is
 681       // not needed.
 682     }
 683
 684     EmitStmt(S.getPromiseDeclStmt());
 685
 686     Address PromiseAddr = GetAddrOfLocalVar(S.getPromiseDecl());
 687     auto *PromiseAddrVoidPtr =
 688         new llvm::BitCastInst(PromiseAddr.getPointer(), VoidPtrTy, "", CoroId);
 689     // Update CoroId to refer to the promise. We could not do it earlier because
 690     // promise local variable was not emitted yet.
 691     CoroId->setArgOperand(1, PromiseAddrVoidPtr);
 692
 693     // Now we have the promise, initialize the GRO
 694     GroManager.EmitGroInit();
 695
 696     EHStack.pushCleanup<CallCoroEnd>(EHCleanup);
 697
 698     CurCoro.Data->CurrentAwaitKind = AwaitKind::Init;
 699     CurCoro.Data->ExceptionHandler = S.getExceptionHandler();
 700     EmitStmt(S.getInitSuspendStmt());
 701     CurCoro.Data->FinalJD = getJumpDestInCurrentScope(FinalBB);
 702
 703     CurCoro.Data->CurrentAwaitKind = AwaitKind::Normal;
 704
 705     if (CurCoro.Data->ExceptionHandler) {
 706       // If we generated IR to record whether an exception was thrown from
 707       // 'await_resume', then use that IR to determine whether the coroutine
 708       // body should be skipped.
 709       // If we didn't generate the IR (perhaps because 'await_resume' was marked
 710       // as 'noexcept'), then we skip this check.
 711       BasicBlock *ContBB = nullptr;
 712       if (CurCoro.Data->ResumeEHVar) {
 713         BasicBlock *BodyBB = createBasicBlock("coro.resumed.body");
 714         ContBB = createBasicBlock("coro.resumed.cont");
 715         Value *SkipBody = Builder.CreateFlagLoad(CurCoro.Data->ResumeEHVar,
 716                                                  "coro.resumed.eh");
 717         Builder.CreateCondBr(SkipBody, ContBB, BodyBB);
 718         EmitBlock(BodyBB);
 719       }
 720
 721       auto Loc = S.getBeginLoc();
 722       CXXCatchStmt Catch(Loc, /*exDecl=*/nullptr,
 723                          CurCoro.Data->ExceptionHandler);
 724       auto *TryStmt =
 725           CXXTryStmt::Create(getContext(), Loc, S.getBody(), &Catch);
 726
 727       EnterCXXTryStmt(*TryStmt);
 728       emitBodyAndFallthrough(*this, S, TryStmt->getTryBlock());
 729       ExitCXXTryStmt(*TryStmt);
 730
 731       if (ContBB)
 732         EmitBlock(ContBB);
 733     }
 734     else {
 735       emitBodyAndFallthrough(*this, S, S.getBody());
 736     }
 737
 738     // See if we need to generate final suspend.
 739     const bool CanFallthrough = Builder.GetInsertBlock();
 740     const bool HasCoreturns = CurCoro.Data->CoreturnCount > 0;
 741     if (CanFallthrough || HasCoreturns) {
 742       EmitBlock(FinalBB);
 743       CurCoro.Data->CurrentAwaitKind = AwaitKind::Final;
 744       EmitStmt(S.getFinalSuspendStmt());
 745     } else {
 746       // We don't need FinalBB. Emit it to make sure the block is deleted.
 747       EmitBlock(FinalBB, /*IsFinished=*/true);
 748     }
 749   }
 750
 751   EmitBlock(RetBB);
 752   // Emit coro.end before getReturnStmt (and parameter destructors), since
 753   // resume and destroy parts of the coroutine should not include them.
 754   llvm::Function *CoroEnd = CGM.getIntrinsic(llvm::Intrinsic::coro_end);
 755   Builder.CreateCall(CoroEnd, {NullPtr, Builder.getFalse()});
 756
 757   if (Stmt *Ret = S.getReturnStmt()) {
 758     // Since we already emitted the return value above, so we shouldn't
 759     // emit it again here.
 760     if (GroManager.DirectEmit)
 761       cast<ReturnStmt>(Ret)->setRetValue(nullptr);
 762     EmitStmt(Ret);
 763   }
 764
 765   // LLVM require the frontend to mark the coroutine.
 766   CurFn->setPresplitCoroutine();
 767 }
 768
 769 // Emit coroutine intrinsic and patch up arguments of the token type.
 770 RValue CodeGenFunction::EmitCoroutineIntrinsic(const CallExpr *E,
 771                                                unsigned int IID) {
 772   SmallVector<llvm::Value *, 8> Args;
 773   switch (IID) {
 774   default:
 775     break;
 776   // The coro.frame builtin is replaced with an SSA value of the coro.begin
 777   // intrinsic.
 778   case llvm::Intrinsic::coro_frame: {
 779     if (CurCoro.Data && CurCoro.Data->CoroBegin) {
 780       return RValue::get(CurCoro.Data->CoroBegin);
 781     }
 782     CGM.Error(E->getBeginLoc(), "this builtin expect that __builtin_coro_begin "
 783                                 "has been used earlier in this function");
 784     auto *NullPtr = llvm::ConstantPointerNull::get(Builder.getInt8PtrTy());
 785     return RValue::get(NullPtr);
 786   }
 787   case llvm::Intrinsic::coro_size: {
 788     auto &Context = getContext();
 789     CanQualType SizeTy = Context.getSizeType();
 790     llvm::IntegerType *T = Builder.getIntNTy(Context.getTypeSize(SizeTy));
 791     llvm::Function *F = CGM.getIntrinsic(llvm::Intrinsic::coro_size, T);
 792     return RValue::get(Builder.CreateCall(F));
 793   }
 794   case llvm::Intrinsic::coro_align: {
 795     auto &Context = getContext();
 796     CanQualType SizeTy = Context.getSizeType();
 797     llvm::IntegerType *T = Builder.getIntNTy(Context.getTypeSize(SizeTy));
 798     llvm::Function *F = CGM.getIntrinsic(llvm::Intrinsic::coro_align, T);
 799     return RValue::get(Builder.CreateCall(F));
 800   }
 801   // The following three intrinsics take a token parameter referring to a token
 802   // returned by earlier call to @llvm.coro.id. Since we cannot represent it in
 803   // builtins, we patch it up here.
 804   case llvm::Intrinsic::coro_alloc:
 805   case llvm::Intrinsic::coro_begin:
 806   case llvm::Intrinsic::coro_free: {
 807     if (CurCoro.Data && CurCoro.Data->CoroId) {
 808       Args.push_back(CurCoro.Data->CoroId);
 809       break;
 810     }
 811     CGM.Error(E->getBeginLoc(), "this builtin expect that __builtin_coro_id has"
 812                                 " been used earlier in this function");
 813     // Fallthrough to the next case to add TokenNone as the first argument.
 814     [[fallthrough]];
 815   }
 816   // @llvm.coro.suspend takes a token parameter. Add token 'none' as the first
 817   // argument.
 818   case llvm::Intrinsic::coro_suspend:
 819     Args.push_back(llvm::ConstantTokenNone::get(getLLVMContext()));
 820     break;
 821   }
 822   for (const Expr *Arg : E->arguments())
 823     Args.push_back(EmitScalarExpr(Arg));
 824
 825   llvm::Function *F = CGM.getIntrinsic(IID);
 826   llvm::CallInst *Call = Builder.CreateCall(F, Args);
 827
 828   // Note: The following code is to enable to emit coro.id and coro.begin by
 829   // hand to experiment with coroutines in C.
 830   // If we see @llvm.coro.id remember it in the CoroData. We will update
 831   // coro.alloc, coro.begin and coro.free intrinsics to refer to it.
 832   if (IID == llvm::Intrinsic::coro_id) {
 833     createCoroData(*this, CurCoro, Call, E);
 834   }
 835   else if (IID == llvm::Intrinsic::coro_begin) {
 836     if (CurCoro.Data)
 837       CurCoro.Data->CoroBegin = Call;
 838   }
 839   else if (IID == llvm::Intrinsic::coro_free) {
 840     // Remember the last coro_free as we need it to build the conditional
 841     // deletion of the coroutine frame.
 842     if (CurCoro.Data)
 843       CurCoro.Data->LastCoroFree = Call;
 844   }
 845   return RValue::get(Call);
 846 }