Update NRVO logic to support early return (Attempt 2)

Summary:
This is the second attempt of r333500 (Update NRVO logic to support early return).
The previous one was reverted for a miscompilation for an incorrect NRVO set up on templates such as:
```
struct Foo {};

template <typename T>
T bar() {
  T t;
  if (false)
    return T();
  return t;
}
```

Where, `t` is marked as non-NRVO variable before its instantiation. However, while its instantiation, it's left an NRVO candidate, turned into an NRVO variable later.

Reviewers: rsmith

Reviewed By: rsmith

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D47586

llvm-svn: 335019

1 files changed, 3 insertions, 2 deletions

diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 68857d972b5..7e38dcc7959 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -740,12 +740,13 @@ Decl *TemplateDeclInstantiator::VisitVarDecl(VarDecl *D,
   SemaRef.BuildVariableInstantiation(Var, D, TemplateArgs, LateAttrs, Owner,
                                      StartingScope, InstantiatingVarTemplate);
 
+  bool NRVO = false;
   if (D->isNRVOVariable()) {
     QualType ReturnType = cast<FunctionDecl>(DC)->getReturnType();
     if (SemaRef.isCopyElisionCandidate(ReturnType, Var, Sema::CES_Strict))
-      Var->setNRVOVariable(true);
+      NRVO = true;
   }
-
+  Var->setNRVOVariable(NRVO);
   Var->setImplicit(D->isImplicit());
 
   return Var;