Recognize when the named return value optimization applies in a

"return" statement and mark the corresponding CXXConstructExpr as
elidable. Teach CodeGen that eliding a temporary is different from
eliding an object construction.

This is just a baby step toward NRVO.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@103849 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 6 insertions, 4 deletions

diff --git a/lib/CodeGen/CGExprCXX.cpp b/lib/CodeGen/CGExprCXX.cpp
index 3a2882e24b..22626fc519 100644
--- a/lib/CodeGen/CGExprCXX.cpp
+++ b/lib/CodeGen/CGExprCXX.cpp
@@ -321,11 +321,13 @@ CodeGenFunction::EmitCXXConstructExpr(llvm::Value *Dest,
       return;
   }
   // Code gen optimization to eliminate copy constructor and return
-  // its first argument instead.
+  // its first argument instead, if in fact that argument is a temporary 
+  // object.
   if (getContext().getLangOptions().ElideConstructors && E->isElidable()) {
-    const Expr *Arg = E->getArg(0)->getTemporaryObject();
-    EmitAggExpr(Arg, Dest, false);
-    return;
+    if (const Expr *Arg = E->getArg(0)->getTemporaryObject()) {
+      EmitAggExpr(Arg, Dest, false);
+      return;
+    }
   }
   if (Array) {
     QualType BaseElementTy = getContext().getBaseElementType(Array);