[coroutines] Fix application of NRVO to Coroutine "Gro" or return object.

Summary:
Fix NRVO for Gro variable.

Previously, we only marked the GRO declaration as an NRVO variable
when its QualType and the function return's QualType matched exactly
(using operator==). However, this was incorrect for two reasons:

1. We were marking non-class types, such as ints, as being NRVO variables.

2. We failed to  handle cases where the canonical types were the same, but the actual `QualType` objects were different. For example, if  one was represented by a typedef. (Example: https://godbolt.org/g/3UFgsL)

This patch fixes these bugs by marking the Gro variable as supporting NRVO only
when `BuildReturnStmt` marks the Gro variable as a coroutine candidate.






Reviewers: rsmith, GorNishanov, nicholas

Reviewed By: GorNishanov

Subscribers: majnemer, cfe-commits

Differential Revision: https://reviews.llvm.org/D42343

llvm-svn: 323712

1 files changed, 2 insertions, 4 deletions

diff --git a/clang/lib/Sema/SemaCoroutine.cpp b/clang/lib/Sema/SemaCoroutine.cpp
index f05a94ebe0e..67c8b9b1a78 100644
--- a/clang/lib/Sema/SemaCoroutine.cpp
+++ b/clang/lib/Sema/SemaCoroutine.cpp
@@ -1316,10 +1316,6 @@ bool CoroutineStmtBuilder::makeGroDeclAndReturnStmt() {
   if (Res.isInvalid())
     return false;
 
-  if (GroType == FnRetType) {
-    GroDecl->setNRVOVariable(true);
-  }
-
   S.AddInitializerToDecl(GroDecl, Res.get(),
                          /*DirectInit=*/false);
 
@@ -1343,6 +1339,8 @@ bool CoroutineStmtBuilder::makeGroDeclAndReturnStmt() {
     noteMemberDeclaredHere(S, ReturnValue, Fn);
     return false;
   }
+  if (cast<clang::ReturnStmt>(ReturnStmt.get())->getNRVOCandidate() == GroDecl)
+    GroDecl->setNRVOVariable(true);
 
   this->ReturnStmt = ReturnStmt.get();
   return true;