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

[Paul Kirth via cfe-commits]

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@@ -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;
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ilovepi wrote:

This was brought up in https://reviews.llvm.org/D74094. In a complex expression,  a reference to the temporary could be returned (e.g. passed in via a parameter and back out via return) and which is then used in another part of the expression. 

I left that logic (and comment) in place from the original patch, since it seems to be to be conservative w.r.t. preserving the status quo. 

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