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.

Updated from r177211.
rdar://12818789


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@177541 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 7 insertions, 0 deletions

diff --git a/lib/CodeGen/CodeGenFunction.cpp b/lib/CodeGen/CodeGenFunction.cpp
index 27ef65fa94..bd244355f0 100644
--- a/lib/CodeGen/CodeGenFunction.cpp
+++ b/lib/CodeGen/CodeGenFunction.cpp
@@ -564,6 +564,10 @@ void CodeGenFunction::GenerateCode(GlobalDecl GD, llvm::Function *Fn,
   SourceRange BodyRange;
   if (Stmt *Body = FD->getBody()) BodyRange = Body->getSourceRange();
 
+  // CalleeWithThisReturn keeps track of the last callee inside this function
+  // that returns 'this'. Before starting the function, we set it to null.
+  CalleeWithThisReturn = 0;
+
   // Emit the standard function prologue.
   StartFunction(GD, ResTy, Fn, FnInfo, Args, BodyRange.getBegin());
 
@@ -615,6 +619,9 @@ void CodeGenFunction::GenerateCode(GlobalDecl GD, llvm::Function *Fn,
 
   // Emit the standard function epilogue.
   FinishFunction(BodyRange.getEnd());
+  // CalleeWithThisReturn keeps track of the last callee inside this function
+  // that returns 'this'. After finishing the function, we set it to null.
+  CalleeWithThisReturn = 0;
 
   // If we haven't marked the function nothrow through other means, do
   // a quick pass now to see if we can.