[clang] [clang] Limit lifetimes of temporaries to the full expression (PR #170517)

[Eli Friedman via cfe-commits]

================
@@ -4947,7 +4948,23 @@ void CodeGenFunction::EmitCallArg(CallArgList &args, const Expr *E,
     return;
   }
 
-  args.add(EmitAnyExprToTemp(E), type);
+   AggValueSlot ArgSlot = AggValueSlot::ignored();
+  // If the callee returns a reference, skip this stack saving optimization;
----------------
efriedma-quic wrote:

I don't understand what "If the callee returns a reference" means, in this context.

The only way the address of the temporary created here could be user-visible is if we use it as the parameter address in the callee.

https://github.com/llvm/llvm-project/pull/170517