[coroutines] Evaluate the operand of void `co_return` expressions.

[EricWF]

Summary

Previously Clang incorrectly ignored the expression of a void co_return. This patch addresses that bug.

I'm not quite sure if I got the code-gen right, but this patch is at least a start.

[GorNishanov]

LGTM

[rsmith]

test/CodeGenCoroutines/coro-ret-void.cpp

30

This seems like an extremely confusing way to format this statement. Maybe move the space left a bit?

[EricWF]

test/CodeGenCoroutines/coro-ret-void.cpp

30

Urg. git clang-format strikes again. I'm working on a patch to teach clang-format about coroutines. This is just more motivation :-)

I'll fix the formatting before committing.

lib/CodeGen/CGCoroutine.cpp

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()) {
+    // Make sure to evaluate the 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) {

test/CodeGenCoroutines/coro-ret-void.cpp

-// RUN: %clang_cc1 -std=c++14 -fcoroutines-ts -triple=x86_64-unknown-linux-gnu -emit-llvm %s -o - -disable-llvm-passes | FileCheck %s
+// RUN: %clang_cc1 -std=c++14 -fcoroutines-ts -munwind-tables -triple=x86_64-unknown-linux-gnu -emit-llvm %s -o - -disable-llvm-passes | FileCheck %s
 
 #include "Inputs/coroutine.h"
 
 namespace coro = std::experimental::coroutines_v1;
 
 struct coro1 {
   struct promise_type {
     coro1 get_return_object();
     coro::suspend_never initial_suspend();
     coro::suspend_never final_suspend();
     void return_void();
   };
 };
 
 coro1 f() {
   co_await coro::suspend_never{};
 }
 
 // CHECK-LABEL: define void @_Z1fv(
 // CHECK: call void @_ZNSt12experimental13coroutines_v113suspend_never12await_resumeEv(%"struct.std::experimental::coroutines_v1::suspend_never"*
 // CHECK: call void @_ZN5coro112promise_type11return_voidEv(%"struct.coro1::promise_type"* %__promise)
 
+struct A {
+  A();
+  ~A();
+};
+
+coro1 f2() {
+  co_return(void) A{};
+}
+
+// CHECK-LABEL: define void @_Z2f2v(
+// CHECK: call void @_ZN1AC1Ev(%struct.A* %[[AVar:.*]])
+// CHECK-NEXT: call void @_ZN1AD1Ev(%struct.A* %[[AVar]])
+// CHECK-NEXT: call void @_ZN5coro112promise_type11return_voidEv(%"struct.coro1::promise_type"*
+
 struct coro2 {
   struct promise_type {
     coro2 get_return_object();
     coro::suspend_never initial_suspend();
     coro::suspend_never final_suspend();
     void return_value(int);
   };
 };
 
 coro2 g() {
   co_return 42;
 }
 
 // CHECK-LABEL: define void @_Z1gv(
 // CHECK: call void @_ZNSt12experimental13coroutines_v113suspend_never12await_resumeEv(%"struct.std::experimental::coroutines_v1::suspend_never"*
 // CHECK: call void @_ZN5coro212promise_type12return_valueEi(%"struct.coro2::promise_type"* %__promise, i32 42)