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
 205   if (SuspendRet != nullptr && SuspendRet->getType()->isIntegerTy(1)) {
 206     // Veto suspension if requested by bool returning await_suspend.
 207     BasicBlock *RealSuspendBlock =
 208         CGF.createBasicBlock(Prefix + Twine(".suspend.bool"));
 209     CGF.Builder.CreateCondBr(SuspendRet, RealSuspendBlock, ReadyBlock);
 210     CGF.EmitBlock(RealSuspendBlock);
 211   }
 212
 213   // Emit the suspend point.
 214   const bool IsFinalSuspend = (Kind == AwaitKind::Final);
 215   llvm::Function *CoroSuspend =
 216       CGF.CGM.getIntrinsic(llvm::Intrinsic::coro_suspend);
 217   auto *SuspendResult = Builder.CreateCall(
 218       CoroSuspend, {SaveCall, Builder.getInt1(IsFinalSuspend)});
 219
 220   // Create a switch capturing three possible continuations.
 221   auto *Switch = Builder.CreateSwitch(SuspendResult, Coro.SuspendBB, 2);
 222   Switch->addCase(Builder.getInt8(0), ReadyBlock);
 223   Switch->addCase(Builder.getInt8(1), CleanupBlock);
 224
 225   // Emit cleanup for this suspend point.
 226   CGF.EmitBlock(CleanupBlock);
 227   CGF.EmitBranchThroughCleanup(Coro.CleanupJD);
 228
 229   // Emit await_resume expression.
 230   CGF.EmitBlock(ReadyBlock);
 231
 232   // Exception handling requires additional IR. If the 'await_resume' function
 233   // is marked as 'noexcept', we avoid generating this additional IR.
 234   CXXTryStmt *TryStmt = nullptr;
 235   if (Coro.ExceptionHandler && Kind == AwaitKind::Init &&
 236       memberCallExpressionCanThrow(S.getResumeExpr())) {
 237     Coro.ResumeEHVar =
 238         CGF.CreateTempAlloca(Builder.getInt1Ty(), Prefix + Twine("resume.eh"));
 239     Builder.CreateFlagStore(true, Coro.ResumeEHVar);
 240
 241     auto Loc = S.getResumeExpr()->getExprLoc();
 242     auto *Catch = new (CGF.getContext())
 243         CXXCatchStmt(Loc, /*exDecl=*/nullptr, Coro.ExceptionHandler);
 244     auto *TryBody = CompoundStmt::Create(CGF.getContext(), S.getResumeExpr(),
 245                                          FPOptionsOverride(), Loc, Loc);
 246     TryStmt = CXXTryStmt::Create(CGF.getContext(), Loc, TryBody, Catch);
 247     CGF.EnterCXXTryStmt(*TryStmt);
 248   }
 249
 250   LValueOrRValue Res;
 251   if (forLValue)
 252     Res.LV = CGF.EmitLValue(S.getResumeExpr());
 253   else
 254     Res.RV = CGF.EmitAnyExpr(S.getResumeExpr(), aggSlot, ignoreResult);
 255
 256   if (TryStmt) {
 257     Builder.CreateFlagStore(false, Coro.ResumeEHVar);
 258     CGF.ExitCXXTryStmt(*TryStmt);
 259   }
 260
 261   return Res;
 262 }
 263
 264 RValue CodeGenFunction::EmitCoawaitExpr(const CoawaitExpr &E,
 265                                         AggValueSlot aggSlot,
 266                                         bool ignoreResult) {
 267   return emitSuspendExpression(*this, *CurCoro.Data, E,
 268                                CurCoro.Data->CurrentAwaitKind, aggSlot,
 269                                ignoreResult, /*forLValue*/false).RV;
 270 }
 271 RValue CodeGenFunction::EmitCoyieldExpr(const CoyieldExpr &E,
 272                                         AggValueSlot aggSlot,
 273                                         bool ignoreResult) {
 274   return emitSuspendExpression(*this, *CurCoro.Data, E, AwaitKind::Yield,
 275                                aggSlot, ignoreResult, /*forLValue*/false).RV;
 276 }
 277
 278 void CodeGenFunction::EmitCoreturnStmt(CoreturnStmt const &S) {
 279   ++CurCoro.Data->CoreturnCount;
 280   const Expr *RV = S.getOperand();
 281   if (RV && RV->getType()->isVoidType() && !isa<InitListExpr>(RV)) {
 282     // Make sure to evaluate the non initlist expression of a co_return
 283     // with a void expression for side effects.
 284     RunCleanupsScope cleanupScope(*this);
 285     EmitIgnoredExpr(RV);
 286   }
 287   EmitStmt(S.getPromiseCall());
 288   EmitBranchThroughCleanup(CurCoro.Data->FinalJD);
 289 }
 290
 291
 292 #ifndef NDEBUG
 293 static QualType getCoroutineSuspendExprReturnType(const ASTContext &Ctx,
 294   const CoroutineSuspendExpr *E) {
 295   const auto *RE = E->getResumeExpr();
 296   // Is it possible for RE to be a CXXBindTemporaryExpr wrapping
 297   // a MemberCallExpr?
 298   assert(isa<CallExpr>(RE) && "unexpected suspend expression type");
 299   return cast<CallExpr>(RE)->getCallReturnType(Ctx);
 300 }
 301 #endif
 302
 303 LValue
 304 CodeGenFunction::EmitCoawaitLValue(const CoawaitExpr *E) {
 305   assert(getCoroutineSuspendExprReturnType(getContext(), E)->isReferenceType() &&
 306          "Can't have a scalar return unless the return type is a "
 307          "reference type!");
 308   return emitSuspendExpression(*this, *CurCoro.Data, *E,
 309                                CurCoro.Data->CurrentAwaitKind, AggValueSlot::ignored(),
 310                                /*ignoreResult*/false, /*forLValue*/true).LV;
 311 }
 312
 313 LValue
 314 CodeGenFunction::EmitCoyieldLValue(const CoyieldExpr *E) {
 315   assert(getCoroutineSuspendExprReturnType(getContext(), E)->isReferenceType() &&
 316          "Can't have a scalar return unless the return type is a "
 317          "reference type!");
 318   return emitSuspendExpression(*this, *CurCoro.Data, *E,
 319                                AwaitKind::Yield, AggValueSlot::ignored(),
 320                                /*ignoreResult*/false, /*forLValue*/true).LV;
 321 }
 322
 323 // Hunts for the parameter reference in the parameter copy/move declaration.
 324 namespace {
 325 struct GetParamRef : public StmtVisitor<GetParamRef> {
 326 public:
 327   DeclRefExpr *Expr = nullptr;
 328   GetParamRef() {}
 329   void VisitDeclRefExpr(DeclRefExpr *E) {
 330     assert(Expr == nullptr && "multilple declref in param move");
 331     Expr = E;
 332   }
 333   void VisitStmt(Stmt *S) {
 334     for (auto *C : S->children()) {
 335       if (C)
 336         Visit(C);
 337     }
 338   }
 339 };
 340 }
 341
 342 // This class replaces references to parameters to their copies by changing
 343 // the addresses in CGF.LocalDeclMap and restoring back the original values in
 344 // its destructor.
 345
 346 namespace {
 347   struct ParamReferenceReplacerRAII {
 348     CodeGenFunction::DeclMapTy SavedLocals;
 349     CodeGenFunction::DeclMapTy& LocalDeclMap;
 350
 351     ParamReferenceReplacerRAII(CodeGenFunction::DeclMapTy &LocalDeclMap)
 352         : LocalDeclMap(LocalDeclMap) {}
 353
 354     void addCopy(DeclStmt const *PM) {
 355       // Figure out what param it refers to.
 356
 357       assert(PM->isSingleDecl());
 358       VarDecl const*VD = static_cast<VarDecl const*>(PM->getSingleDecl());
 359       Expr const *InitExpr = VD->getInit();
 360       GetParamRef Visitor;
 361       Visitor.Visit(const_cast<Expr*>(InitExpr));
 362       assert(Visitor.Expr);
 363       DeclRefExpr *DREOrig = Visitor.Expr;
 364       auto *PD = DREOrig->getDecl();
 365
 366       auto it = LocalDeclMap.find(PD);
 367       assert(it != LocalDeclMap.end() && "parameter is not found");
 368       SavedLocals.insert({ PD, it->second });
 369
 370       auto copyIt = LocalDeclMap.find(VD);
 371       assert(copyIt != LocalDeclMap.end() && "parameter copy is not found");
 372       it->second = copyIt->getSecond();
 373     }
 374
 375     ~ParamReferenceReplacerRAII() {
 376       for (auto&& SavedLocal : SavedLocals) {
 377         LocalDeclMap.insert({SavedLocal.first, SavedLocal.second});
 378       }
 379     }
 380   };
 381 }
 382
 383 // For WinEH exception representation backend needs to know what funclet coro.end
 384 // belongs to. That information is passed in a funclet bundle.
 385 static SmallVector<llvm::OperandBundleDef, 1>
 386 getBundlesForCoroEnd(CodeGenFunction &CGF) {
 387   SmallVector<llvm::OperandBundleDef, 1> BundleList;
 388
 389   if (llvm::Instruction *EHPad = CGF.CurrentFuncletPad)
 390     BundleList.emplace_back("funclet", EHPad);
 391
 392   return BundleList;
 393 }
 394
 395 namespace {
 396 // We will insert coro.end to cut any of the destructors for objects that
 397 // do not need to be destroyed once the coroutine is resumed.
 398 // See llvm/docs/Coroutines.rst for more details about coro.end.
 399 struct CallCoroEnd final : public EHScopeStack::Cleanup {
 400   void Emit(CodeGenFunction &CGF, Flags flags) override {
 401     auto &CGM = CGF.CGM;
 402     auto *NullPtr = llvm::ConstantPointerNull::get(CGF.Int8PtrTy);
 403     llvm::Function *CoroEndFn = CGM.getIntrinsic(llvm::Intrinsic::coro_end);
 404     // See if we have a funclet bundle to associate coro.end with. (WinEH)
 405     auto Bundles = getBundlesForCoroEnd(CGF);
 406     auto *CoroEnd =
 407       CGF.Builder.CreateCall(CoroEndFn,
 408                              {NullPtr, CGF.Builder.getTrue(),
 409                               llvm::ConstantTokenNone::get(CoroEndFn->getContext())},
 410                              Bundles);
 411     if (Bundles.empty()) {
 412       // Otherwise, (landingpad model), create a conditional branch that leads
 413       // either to a cleanup block or a block with EH resume instruction.
 414       auto *ResumeBB = CGF.getEHResumeBlock(/*isCleanup=*/true);
 415       auto *CleanupContBB = CGF.createBasicBlock("cleanup.cont");
 416       CGF.Builder.CreateCondBr(CoroEnd, ResumeBB, CleanupContBB);
 417       CGF.EmitBlock(CleanupContBB);
 418     }
 419   }
 420 };
 421 }
 422
 423 namespace {
 424 // Make sure to call coro.delete on scope exit.
 425 struct CallCoroDelete final : public EHScopeStack::Cleanup {
 426   Stmt *Deallocate;
 427
 428   // Emit "if (coro.free(CoroId, CoroBegin)) Deallocate;"
 429
 430   // Note: That deallocation will be emitted twice: once for a normal exit and
 431   // once for exceptional exit. This usage is safe because Deallocate does not
 432   // contain any declarations. The SubStmtBuilder::makeNewAndDeleteExpr()
 433   // builds a single call to a deallocation function which is safe to emit
 434   // multiple times.
 435   void Emit(CodeGenFunction &CGF, Flags) override {
 436     // Remember the current point, as we are going to emit deallocation code
 437     // first to get to coro.free instruction that is an argument to a delete
 438     // call.
 439     BasicBlock *SaveInsertBlock = CGF.Builder.GetInsertBlock();
 440
 441     auto *FreeBB = CGF.createBasicBlock("coro.free");
 442     CGF.EmitBlock(FreeBB);
 443     CGF.EmitStmt(Deallocate);
 444
 445     auto *AfterFreeBB = CGF.createBasicBlock("after.coro.free");
 446     CGF.EmitBlock(AfterFreeBB);
 447
 448     // We should have captured coro.free from the emission of deallocate.
 449     auto *CoroFree = CGF.CurCoro.Data->LastCoroFree;
 450     if (!CoroFree) {
 451       CGF.CGM.Error(Deallocate->getBeginLoc(),
 452                     "Deallocation expressoin does not refer to coro.free");
 453       return;
 454     }
 455
 456     // Get back to the block we were originally and move coro.free there.
 457     auto *InsertPt = SaveInsertBlock->getTerminator();
 458     CoroFree->moveBefore(InsertPt);
 459     CGF.Builder.SetInsertPoint(InsertPt);
 460
 461     // Add if (auto *mem = coro.free) Deallocate;
 462     auto *NullPtr = llvm::ConstantPointerNull::get(CGF.Int8PtrTy);
 463     auto *Cond = CGF.Builder.CreateICmpNE(CoroFree, NullPtr);
 464     CGF.Builder.CreateCondBr(Cond, FreeBB, AfterFreeBB);
 465
 466     // No longer need old terminator.
 467     InsertPt->eraseFromParent();
 468     CGF.Builder.SetInsertPoint(AfterFreeBB);
 469   }
 470   explicit CallCoroDelete(Stmt *DeallocStmt) : Deallocate(DeallocStmt) {}
 471 };
 472 }
 473
 474 namespace {
 475 struct GetReturnObjectManager {
 476   CodeGenFunction &CGF;
 477   CGBuilderTy &Builder;
 478   const CoroutineBodyStmt &S;
 479   // When true, performs RVO for the return object.
 480   bool DirectEmit = false;
 481
 482   Address GroActiveFlag;
 483   CodeGenFunction::AutoVarEmission GroEmission;
 484
 485   GetReturnObjectManager(CodeGenFunction &CGF, const CoroutineBodyStmt &S)
 486       : CGF(CGF), Builder(CGF.Builder), S(S), GroActiveFlag(Address::invalid()),
 487         GroEmission(CodeGenFunction::AutoVarEmission::invalid()) {
 488     // The call to get_return_object is sequenced before the call to
 489     // initial_suspend and is invoked at most once, but there are caveats
 490     // regarding on whether the prvalue result object may be initialized
 491     // directly/eager or delayed, depending on the types involved.
 492     //
 493     // More info at https://github.com/cplusplus/papers/issues/1414
 494     //
 495     // The general cases:
 496     // 1. Same type of get_return_object and coroutine return type (direct
 497     // emission):
 498     //  - Constructed in the return slot.
 499     // 2. Different types (delayed emission):
 500     //  - Constructed temporary object prior to initial suspend initialized with
 501     //  a call to get_return_object()
 502     //  - When coroutine needs to to return to the caller and needs to construct
 503     //  return value for the coroutine it is initialized with expiring value of
 504     //  the temporary obtained above.
 505     //
 506     // Direct emission for void returning coroutines or GROs.
 507     DirectEmit = [&]() {
 508       auto *RVI = S.getReturnValueInit();
 509       assert(RVI && "expected RVI");
 510       auto GroType = RVI->getType();
 511       return CGF.getContext().hasSameType(GroType, CGF.FnRetTy);
 512     }();
 513   }
 514
 515   // The gro variable has to outlive coroutine frame and coroutine promise, but,
 516   // it can only be initialized after coroutine promise was created, thus, we
 517   // split its emission in two parts. EmitGroAlloca emits an alloca and sets up
 518   // cleanups. Later when coroutine promise is available we initialize the gro
 519   // and sets the flag that the cleanup is now active.
 520   void EmitGroAlloca() {
 521     if (DirectEmit)
 522       return;
 523
 524     auto *GroDeclStmt = dyn_cast_or_null<DeclStmt>(S.getResultDecl());
 525     if (!GroDeclStmt) {
 526       // If get_return_object returns void, no need to do an alloca.
 527       return;
 528     }
 529
 530     auto *GroVarDecl = cast<VarDecl>(GroDeclStmt->getSingleDecl());
 531
 532     // Set GRO flag that it is not initialized yet
 533     GroActiveFlag = CGF.CreateTempAlloca(Builder.getInt1Ty(), CharUnits::One(),
 534                                          "gro.active");
 535     Builder.CreateStore(Builder.getFalse(), GroActiveFlag);
 536
 537     GroEmission = CGF.EmitAutoVarAlloca(*GroVarDecl);
 538     auto *GroAlloca = dyn_cast_or_null<llvm::AllocaInst>(
 539         GroEmission.getOriginalAllocatedAddress().getPointer());
 540     assert(GroAlloca && "expected alloca to be emitted");
 541     GroAlloca->setMetadata(llvm::LLVMContext::MD_coro_outside_frame,
 542                            llvm::MDNode::get(CGF.CGM.getLLVMContext(), {}));
 543
 544     // Remember the top of EHStack before emitting the cleanup.
 545     auto old_top = CGF.EHStack.stable_begin();
 546     CGF.EmitAutoVarCleanups(GroEmission);
 547     auto top = CGF.EHStack.stable_begin();
 548
 549     // Make the cleanup conditional on gro.active
 550     for (auto b = CGF.EHStack.find(top), e = CGF.EHStack.find(old_top); b != e;
 551          b++) {
 552       if (auto *Cleanup = dyn_cast<EHCleanupScope>(&*b)) {
 553         assert(!Cleanup->hasActiveFlag() && "cleanup already has active flag?");
 554         Cleanup->setActiveFlag(GroActiveFlag);
 555         Cleanup->setTestFlagInEHCleanup();
 556         Cleanup->setTestFlagInNormalCleanup();
 557       }
 558     }
 559   }
 560
 561   void EmitGroInit() {
 562     if (DirectEmit) {
 563       // ReturnValue should be valid as long as the coroutine's return type
 564       // is not void. The assertion could help us to reduce the check later.
 565       assert(CGF.ReturnValue.isValid() == (bool)S.getReturnStmt());
 566       // Now we have the promise, initialize the GRO.
 567       // We need to emit `get_return_object` first. According to:
 568       // [dcl.fct.def.coroutine]p7
 569       // The call to get_return_object is sequenced before the call to
 570       // initial_suspend and is invoked at most once.
 571       //
 572       // So we couldn't emit return value when we emit return statment,
 573       // otherwise the call to get_return_object wouldn't be in front
 574       // of initial_suspend.
 575       if (CGF.ReturnValue.isValid()) {
 576         CGF.EmitAnyExprToMem(S.getReturnValue(), CGF.ReturnValue,
 577                              S.getReturnValue()->getType().getQualifiers(),
 578                              /*IsInit*/ true);
 579       }
 580       return;
 581     }
 582
 583     if (!GroActiveFlag.isValid()) {
 584       // No Gro variable was allocated. Simply emit the call to
 585       // get_return_object.
 586       CGF.EmitStmt(S.getResultDecl());
 587       return;
 588     }
 589
 590     CGF.EmitAutoVarInit(GroEmission);
 591     Builder.CreateStore(Builder.getTrue(), GroActiveFlag);
 592   }
 593 };
 594 } // namespace
 595
 596 static void emitBodyAndFallthrough(CodeGenFunction &CGF,
 597                                    const CoroutineBodyStmt &S, Stmt *Body) {
 598   CGF.EmitStmt(Body);
 599   const bool CanFallthrough = CGF.Builder.GetInsertBlock();
 600   if (CanFallthrough)
 601     if (Stmt *OnFallthrough = S.getFallthroughHandler())
 602       CGF.EmitStmt(OnFallthrough);
 603 }
 604
 605 void CodeGenFunction::EmitCoroutineBody(const CoroutineBodyStmt &S) {
 606   auto *NullPtr = llvm::ConstantPointerNull::get(Builder.getPtrTy());
 607   auto &TI = CGM.getContext().getTargetInfo();
 608   unsigned NewAlign = TI.getNewAlign() / TI.getCharWidth();
 609
 610   auto *EntryBB = Builder.GetInsertBlock();
 611   auto *AllocBB = createBasicBlock("coro.alloc");
 612   auto *InitBB = createBasicBlock("coro.init");
 613   auto *FinalBB = createBasicBlock("coro.final");
 614   auto *RetBB = createBasicBlock("coro.ret");
 615
 616   auto *CoroId = Builder.CreateCall(
 617       CGM.getIntrinsic(llvm::Intrinsic::coro_id),
 618       {Builder.getInt32(NewAlign), NullPtr, NullPtr, NullPtr});
 619   createCoroData(*this, CurCoro, CoroId);
 620   CurCoro.Data->SuspendBB = RetBB;
 621   assert(ShouldEmitLifetimeMarkers &&
 622          "Must emit lifetime intrinsics for coroutines");
 623
 624   // Backend is allowed to elide memory allocations, to help it, emit
 625   // auto mem = coro.alloc() ? 0 : ... allocation code ...;
 626   auto *CoroAlloc = Builder.CreateCall(
 627       CGM.getIntrinsic(llvm::Intrinsic::coro_alloc), {CoroId});
 628
 629   Builder.CreateCondBr(CoroAlloc, AllocBB, InitBB);
 630
 631   EmitBlock(AllocBB);
 632   auto *AllocateCall = EmitScalarExpr(S.getAllocate());
 633   auto *AllocOrInvokeContBB = Builder.GetInsertBlock();
 634
 635   // Handle allocation failure if 'ReturnStmtOnAllocFailure' was provided.
 636   if (auto *RetOnAllocFailure = S.getReturnStmtOnAllocFailure()) {
 637     auto *RetOnFailureBB = createBasicBlock("coro.ret.on.failure");
 638
 639     // See if allocation was successful.
 640     auto *NullPtr = llvm::ConstantPointerNull::get(Int8PtrTy);
 641     auto *Cond = Builder.CreateICmpNE(AllocateCall, NullPtr);
 642     // Expect the allocation to be successful.
 643     emitCondLikelihoodViaExpectIntrinsic(Cond, Stmt::LH_Likely);
 644     Builder.CreateCondBr(Cond, InitBB, RetOnFailureBB);
 645
 646     // If not, return OnAllocFailure object.
 647     EmitBlock(RetOnFailureBB);
 648     EmitStmt(RetOnAllocFailure);
 649   }
 650   else {
 651     Builder.CreateBr(InitBB);
 652   }
 653
 654   EmitBlock(InitBB);
 655
 656   // Pass the result of the allocation to coro.begin.
 657   auto *Phi = Builder.CreatePHI(VoidPtrTy, 2);
 658   Phi->addIncoming(NullPtr, EntryBB);
 659   Phi->addIncoming(AllocateCall, AllocOrInvokeContBB);
 660   auto *CoroBegin = Builder.CreateCall(
 661       CGM.getIntrinsic(llvm::Intrinsic::coro_begin), {CoroId, Phi});
 662   CurCoro.Data->CoroBegin = CoroBegin;
 663
 664   GetReturnObjectManager GroManager(*this, S);
 665   GroManager.EmitGroAlloca();
 666
 667   CurCoro.Data->CleanupJD = getJumpDestInCurrentScope(RetBB);
 668   {
 669     CGDebugInfo *DI = getDebugInfo();
 670     ParamReferenceReplacerRAII ParamReplacer(LocalDeclMap);
 671     CodeGenFunction::RunCleanupsScope ResumeScope(*this);
 672     EHStack.pushCleanup<CallCoroDelete>(NormalAndEHCleanup, S.getDeallocate());
 673
 674     // Create mapping between parameters and copy-params for coroutine function.
 675     llvm::ArrayRef<const Stmt *> ParamMoves = S.getParamMoves();
 676     assert(
 677         (ParamMoves.size() == 0 || (ParamMoves.size() == FnArgs.size())) &&
 678         "ParamMoves and FnArgs should be the same size for coroutine function");
 679     if (ParamMoves.size() == FnArgs.size() && DI)
 680       for (const auto Pair : llvm::zip(FnArgs, ParamMoves))
 681         DI->getCoroutineParameterMappings().insert(
 682             {std::get<0>(Pair), std::get<1>(Pair)});
 683
 684     // Create parameter copies. We do it before creating a promise, since an
 685     // evolution of coroutine TS may allow promise constructor to observe
 686     // parameter copies.
 687     for (auto *PM : S.getParamMoves()) {
 688       EmitStmt(PM);
 689       ParamReplacer.addCopy(cast<DeclStmt>(PM));
 690       // TODO: if(CoroParam(...)) need to surround ctor and dtor
 691       // for the copy, so that llvm can elide it if the copy is
 692       // not needed.
 693     }
 694
 695     EmitStmt(S.getPromiseDeclStmt());
 696
 697     Address PromiseAddr = GetAddrOfLocalVar(S.getPromiseDecl());
 698     auto *PromiseAddrVoidPtr =
 699         new llvm::BitCastInst(PromiseAddr.getPointer(), VoidPtrTy, "", CoroId);
 700     // Update CoroId to refer to the promise. We could not do it earlier because
 701     // promise local variable was not emitted yet.
 702     CoroId->setArgOperand(1, PromiseAddrVoidPtr);
 703
 704     // Now we have the promise, initialize the GRO
 705     GroManager.EmitGroInit();
 706
 707     EHStack.pushCleanup<CallCoroEnd>(EHCleanup);
 708
 709     CurCoro.Data->CurrentAwaitKind = AwaitKind::Init;
 710     CurCoro.Data->ExceptionHandler = S.getExceptionHandler();
 711     EmitStmt(S.getInitSuspendStmt());
 712     CurCoro.Data->FinalJD = getJumpDestInCurrentScope(FinalBB);
 713
 714     CurCoro.Data->CurrentAwaitKind = AwaitKind::Normal;
 715
 716     if (CurCoro.Data->ExceptionHandler) {
 717       // If we generated IR to record whether an exception was thrown from
 718       // 'await_resume', then use that IR to determine whether the coroutine
 719       // body should be skipped.
 720       // If we didn't generate the IR (perhaps because 'await_resume' was marked
 721       // as 'noexcept'), then we skip this check.
 722       BasicBlock *ContBB = nullptr;
 723       if (CurCoro.Data->ResumeEHVar) {
 724         BasicBlock *BodyBB = createBasicBlock("coro.resumed.body");
 725         ContBB = createBasicBlock("coro.resumed.cont");
 726         Value *SkipBody = Builder.CreateFlagLoad(CurCoro.Data->ResumeEHVar,
 727                                                  "coro.resumed.eh");
 728         Builder.CreateCondBr(SkipBody, ContBB, BodyBB);
 729         EmitBlock(BodyBB);
 730       }
 731
 732       auto Loc = S.getBeginLoc();
 733       CXXCatchStmt Catch(Loc, /*exDecl=*/nullptr,
 734                          CurCoro.Data->ExceptionHandler);
 735       auto *TryStmt =
 736           CXXTryStmt::Create(getContext(), Loc, S.getBody(), &Catch);
 737
 738       EnterCXXTryStmt(*TryStmt);
 739       emitBodyAndFallthrough(*this, S, TryStmt->getTryBlock());
 740       ExitCXXTryStmt(*TryStmt);
 741
 742       if (ContBB)
 743         EmitBlock(ContBB);
 744     }
 745     else {
 746       emitBodyAndFallthrough(*this, S, S.getBody());
 747     }
 748
 749     // See if we need to generate final suspend.
 750     const bool CanFallthrough = Builder.GetInsertBlock();
 751     const bool HasCoreturns = CurCoro.Data->CoreturnCount > 0;
 752     if (CanFallthrough || HasCoreturns) {
 753       EmitBlock(FinalBB);
 754       CurCoro.Data->CurrentAwaitKind = AwaitKind::Final;
 755       EmitStmt(S.getFinalSuspendStmt());
 756     } else {
 757       // We don't need FinalBB. Emit it to make sure the block is deleted.
 758       EmitBlock(FinalBB, /*IsFinished=*/true);
 759     }
 760   }
 761
 762   EmitBlock(RetBB);
 763   // Emit coro.end before getReturnStmt (and parameter destructors), since
 764   // resume and destroy parts of the coroutine should not include them.
 765   llvm::Function *CoroEnd = CGM.getIntrinsic(llvm::Intrinsic::coro_end);
 766   Builder.CreateCall(CoroEnd,
 767                      {NullPtr, Builder.getFalse(),
 768                       llvm::ConstantTokenNone::get(CoroEnd->getContext())});
 769
 770   if (Stmt *Ret = S.getReturnStmt()) {
 771     // Since we already emitted the return value above, so we shouldn't
 772     // emit it again here.
 773     if (GroManager.DirectEmit)
 774       cast<ReturnStmt>(Ret)->setRetValue(nullptr);
 775     EmitStmt(Ret);
 776   }
 777
 778   // LLVM require the frontend to mark the coroutine.
 779   CurFn->setPresplitCoroutine();
 780 }
 781
 782 // Emit coroutine intrinsic and patch up arguments of the token type.
 783 RValue CodeGenFunction::EmitCoroutineIntrinsic(const CallExpr *E,
 784                                                unsigned int IID) {
 785   SmallVector<llvm::Value *, 8> Args;
 786   switch (IID) {
 787   default:
 788     break;
 789   // The coro.frame builtin is replaced with an SSA value of the coro.begin
 790   // intrinsic.
 791   case llvm::Intrinsic::coro_frame: {
 792     if (CurCoro.Data && CurCoro.Data->CoroBegin) {
 793       return RValue::get(CurCoro.Data->CoroBegin);
 794     }
 795     CGM.Error(E->getBeginLoc(), "this builtin expect that __builtin_coro_begin "
 796                                 "has been used earlier in this function");
 797     auto *NullPtr = llvm::ConstantPointerNull::get(Builder.getPtrTy());
 798     return RValue::get(NullPtr);
 799   }
 800   case llvm::Intrinsic::coro_size: {
 801     auto &Context = getContext();
 802     CanQualType SizeTy = Context.getSizeType();
 803     llvm::IntegerType *T = Builder.getIntNTy(Context.getTypeSize(SizeTy));
 804     llvm::Function *F = CGM.getIntrinsic(llvm::Intrinsic::coro_size, T);
 805     return RValue::get(Builder.CreateCall(F));
 806   }
 807   case llvm::Intrinsic::coro_align: {
 808     auto &Context = getContext();
 809     CanQualType SizeTy = Context.getSizeType();
 810     llvm::IntegerType *T = Builder.getIntNTy(Context.getTypeSize(SizeTy));
 811     llvm::Function *F = CGM.getIntrinsic(llvm::Intrinsic::coro_align, T);
 812     return RValue::get(Builder.CreateCall(F));
 813   }
 814   // The following three intrinsics take a token parameter referring to a token
 815   // returned by earlier call to @llvm.coro.id. Since we cannot represent it in
 816   // builtins, we patch it up here.
 817   case llvm::Intrinsic::coro_alloc:
 818   case llvm::Intrinsic::coro_begin:
 819   case llvm::Intrinsic::coro_free: {
 820     if (CurCoro.Data && CurCoro.Data->CoroId) {
 821       Args.push_back(CurCoro.Data->CoroId);
 822       break;
 823     }
 824     CGM.Error(E->getBeginLoc(), "this builtin expect that __builtin_coro_id has"
 825                                 " been used earlier in this function");
 826     // Fallthrough to the next case to add TokenNone as the first argument.
 827     [[fallthrough]];
 828   }
 829   // @llvm.coro.suspend takes a token parameter. Add token 'none' as the first
 830   // argument.
 831   case llvm::Intrinsic::coro_suspend:
 832     Args.push_back(llvm::ConstantTokenNone::get(getLLVMContext()));
 833     break;
 834   }
 835   for (const Expr *Arg : E->arguments())
 836     Args.push_back(EmitScalarExpr(Arg));
 837   // @llvm.coro.end takes a token parameter. Add token 'none' as the last
 838   // argument.
 839   if (IID == llvm::Intrinsic::coro_end)
 840     Args.push_back(llvm::ConstantTokenNone::get(getLLVMContext()));
 841
 842   llvm::Function *F = CGM.getIntrinsic(IID);
 843   llvm::CallInst *Call = Builder.CreateCall(F, Args);
 844
 845   // Note: The following code is to enable to emit coro.id and coro.begin by
 846   // hand to experiment with coroutines in C.
 847   // If we see @llvm.coro.id remember it in the CoroData. We will update
 848   // coro.alloc, coro.begin and coro.free intrinsics to refer to it.
 849   if (IID == llvm::Intrinsic::coro_id) {
 850     createCoroData(*this, CurCoro, Call, E);
 851   }
 852   else if (IID == llvm::Intrinsic::coro_begin) {
 853     if (CurCoro.Data)
 854       CurCoro.Data->CoroBegin = Call;
 855   }
 856   else if (IID == llvm::Intrinsic::coro_free) {
 857     // Remember the last coro_free as we need it to build the conditional
 858     // deletion of the coroutine frame.
 859     if (CurCoro.Data)
 860       CurCoro.Data->LastCoroFree = Call;
 861   }
 862   return RValue::get(Call);
 863 }