[coroutines] Add codegen for await and yield expressions

Details:

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
]

llvm-svn: 298784

clang/lib/CodeGen/CGCoroutine.cpp

@@ -12,35 +12,58 @@
 //===----------------------------------------------------------------------===//
 
 #include "CodeGenFunction.h"
+#include "llvm/ADT/ScopeExit.h"
 #include "clang/AST/StmtCXX.h"
 
 using namespace clang;
 using namespace CodeGen;
 
-namespace clang {
-namespace CodeGen {
+using llvm::Value;
+using llvm::BasicBlock;
 
-struct CGCoroData {
+namespace {
+enum class AwaitKind { Init, Normal, Yield, Final };
+static constexpr llvm::StringLiteral AwaitKindStr[] = {"init", "await", "yield",
+                                                       "final"};
+}
 
-  // Stores the jump destination just before the final suspend. Coreturn
-  // statements jumps to this point after calling return_xxx promise member.
-  CodeGenFunction::JumpDest FinalJD;
+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;
+
+  // 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;
+
   // 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() {}
 
@@ -66,6 +89,126 @@ static void createCoroData(CodeGenFunction &CGF,
   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;
+}
+
+// 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.
+//
+static RValue emitSuspendExpression(CodeGenFunction &CGF, CGCoroData &Coro,
+                                    CoroutineSuspendExpr const &S,
+                                    AwaitKind Kind, AggValueSlot aggSlot,
+                                    bool ignoreResult) {
+  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) {
+    // Veto suspension if requested by bool returning await_suspend.
+    assert(SuspendRet->getType()->isIntegerTy(1) &&
+           "Sema should have already checked that it is void or bool");
+    BasicBlock *RealSuspendBlock =
+        CGF.createBasicBlock(Prefix + Twine(".suspend.bool"));
+    CGF.Builder.CreateCondBr(SuspendRet, RealSuspendBlock, ReadyBlock);
+    SuspendBlock = RealSuspendBlock;
+    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);
+  return CGF.EmitAnyExpr(S.getResumeExpr(), aggSlot, ignoreResult);
+}
+
+RValue CodeGenFunction::EmitCoawaitExpr(const CoawaitExpr &E,
+                                        AggValueSlot aggSlot,
+                                        bool ignoreResult) {
+  return emitSuspendExpression(*this, *CurCoro.Data, E,
+                               CurCoro.Data->CurrentAwaitKind, aggSlot,
+                               ignoreResult);
+}
+RValue CodeGenFunction::EmitCoyieldExpr(const CoyieldExpr &E,
+                                        AggValueSlot aggSlot,
+                                        bool ignoreResult) {
+  return emitSuspendExpression(*this, *CurCoro.Data, E, AwaitKind::Yield,
+                               aggSlot, ignoreResult);
+}
+
 void CodeGenFunction::EmitCoreturnStmt(CoreturnStmt const &S) {
   ++CurCoro.Data->CoreturnCount;
   EmitStmt(S.getPromiseCall());
@@ -78,22 +221,26 @@ void CodeGenFunction::EmitCoroutineBody(const CoroutineBodyStmt &S) {
   unsigned NewAlign = TI.getNewAlign() / TI.getCharWidth();
 
   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;
 
   EmitScalarExpr(S.getAllocate());
 
   // FIXME: Setup cleanup scopes.
 
   EmitStmt(S.getPromiseDeclStmt());
 
+  CurCoro.Data->CleanupJD = getJumpDestInCurrentScope(RetBB);
   CurCoro.Data->FinalJD = getJumpDestInCurrentScope(FinalBB);
 
   // FIXME: Emit initial suspend and more before the body.
 
+  CurCoro.Data->CurrentAwaitKind = AwaitKind::Normal;
   EmitStmt(S.getBody());
 
   // See if we need to generate final suspend.
@@ -105,6 +252,8 @@ void CodeGenFunction::EmitCoroutineBody(const CoroutineBodyStmt &S) {
   }
   EmitStmt(S.getDeallocate());
 
+  EmitBlock(RetBB);
+
   // FIXME: Emit return for the coroutine return object.
 }
 

clang/lib/CodeGen/CGExprAgg.cpp

@@ -111,6 +111,13 @@ class AggExprEmitter : public StmtVisitor<AggExprEmitter> {
   void VisitGenericSelectionExpr(GenericSelectionExpr *GE) {
     Visit(GE->getResultExpr());
   }
+  void VisitCoawaitExpr(CoawaitExpr *E) {
+    CGF.EmitCoawaitExpr(*E, Dest, IsResultUnused);
+  }
+  void VisitCoyieldExpr(CoyieldExpr *E) {
+    CGF.EmitCoyieldExpr(*E, Dest, IsResultUnused);
+  }
+  void VisitUnaryCoawait(UnaryOperator *E) { Visit(E->getSubExpr()); }
   void VisitUnaryExtension(UnaryOperator *E) { Visit(E->getSubExpr()); }
   void VisitSubstNonTypeTemplateParmExpr(SubstNonTypeTemplateParmExpr *E) {
     return Visit(E->getReplacement());

clang/lib/CodeGen/CGExprComplex.cpp

@@ -110,6 +110,16 @@ class ComplexExprEmitter
   VisitSubstNonTypeTemplateParmExpr(SubstNonTypeTemplateParmExpr *PE) {
     return Visit(PE->getReplacement());
   }
+  ComplexPairTy VisitCoawaitExpr(CoawaitExpr *S) {
+    return CGF.EmitCoawaitExpr(*S).getComplexVal();
+  }
+  ComplexPairTy VisitCoyieldExpr(CoyieldExpr *S) {
+    return CGF.EmitCoyieldExpr(*S).getComplexVal();
+  }
+  ComplexPairTy VisitUnaryCoawait(const UnaryOperator *E) {
+    return Visit(E->getSubExpr());
+  }
+
 
   // l-values.
   ComplexPairTy VisitDeclRefExpr(DeclRefExpr *E) {

clang/lib/CodeGen/CGExprScalar.cpp

@@ -276,6 +276,15 @@ class ScalarExprEmitter
   Value *VisitGenericSelectionExpr(GenericSelectionExpr *GE) {
     return Visit(GE->getResultExpr());
   }
+  Value *VisitCoawaitExpr(CoawaitExpr *S) {
+    return CGF.EmitCoawaitExpr(*S).getScalarVal();
+  }
+  Value *VisitCoyieldExpr(CoyieldExpr *S) {
+    return CGF.EmitCoyieldExpr(*S).getScalarVal();
+  }
+  Value *VisitUnaryCoawait(const UnaryOperator *E) {
+    return Visit(E->getSubExpr());
+  }
 
   // Leaves.
   Value *VisitIntegerLiteral(const IntegerLiteral *E) {

clang/lib/CodeGen/CodeGenFunction.h

@@ -1986,7 +1986,7 @@ class CodeGenFunction : public CodeGenTypeCache {
   /// pointer to a char.
   Address EmitMSVAListRef(const Expr *E);
 
-  /// EmitAnyExprToTemp - Similary to EmitAnyExpr(), however, the result will
+  /// EmitAnyExprToTemp - Similarly to EmitAnyExpr(), however, the result will
   /// always be accessible even if no aggregate location is provided.
   RValue EmitAnyExprToTemp(const Expr *E);
 
@@ -2528,6 +2528,12 @@ class CodeGenFunction : public CodeGenTypeCache {
 
   void EmitCoroutineBody(const CoroutineBodyStmt &S);
   void EmitCoreturnStmt(const CoreturnStmt &S);
+  RValue EmitCoawaitExpr(const CoawaitExpr &E,
+                         AggValueSlot aggSlot = AggValueSlot::ignored(),
+                         bool ignoreResult = false);
+  RValue EmitCoyieldExpr(const CoyieldExpr &E,
+                         AggValueSlot aggSlot = AggValueSlot::ignored(),
+                         bool ignoreResult = false);
   RValue EmitCoroutineIntrinsic(const CallExpr *E, unsigned int IID);
 
   void EnterCXXTryStmt(const CXXTryStmt &S, bool IsFnTryBlock = false);