Exploit this-return of a callsite in a this-return function.

For constructors/desctructors that return 'this', if there exists a callsite
that returns 'this' and is immediately before the return instruction, make
sure we are using the return value from the callsite.

We don't need to keep 'this' alive through the callsite. It also enables
optimizations in the backend, such as tail call optimization.

rdar://12818789

llvm-svn: 177211

1 files changed, 3 insertions, 2 deletions

diff --git a/clang/lib/CodeGen/MicrosoftCXXABI.cpp b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
index fb6b86d8788..85d926023f3 100644
--- a/clang/lib/CodeGen/MicrosoftCXXABI.cpp
+++ b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
@@ -55,7 +55,7 @@ public:
 
   void EmitInstanceFunctionProlog(CodeGenFunction &CGF);
 
-  void EmitConstructorCall(CodeGenFunction &CGF,
+  llvm::Value *EmitConstructorCall(CodeGenFunction &CGF,
                            const CXXConstructorDecl *D,
                            CXXCtorType Type, bool ForVirtualBase,
                            bool Delegating,
@@ -238,7 +238,7 @@ void MicrosoftCXXABI::EmitInstanceFunctionProlog(CodeGenFunction &CGF) {
   }
 }
 
-void MicrosoftCXXABI::EmitConstructorCall(CodeGenFunction &CGF,
+llvm::Value *MicrosoftCXXABI::EmitConstructorCall(CodeGenFunction &CGF,
                                           const CXXConstructorDecl *D,
                                           CXXCtorType Type, bool ForVirtualBase,
                                           bool Delegating,
@@ -259,6 +259,7 @@ void MicrosoftCXXABI::EmitConstructorCall(CodeGenFunction &CGF,
   CGF.EmitCXXMemberCall(D, SourceLocation(), Callee, ReturnValueSlot(), This,
                         ImplicitParam, ImplicitParamTy,
                         ArgBeg, ArgEnd);
+  return Callee;
 }
 
 RValue MicrosoftCXXABI::EmitVirtualDestructorCall(CodeGenFunction &CGF,