[C++ PATCH] Fix -Wreturn-local-addr regression (PR c++/77591)

[Jakub Jelinek]

Hi!

Delayed folding caused following regression where we no longer warn about
returning reference to local variable.

Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux, ok for
trunk?

2016-11-24  Jakub Jelinek  <ja...@redhat.com>

        PR c++/77591
        * typeck.c (maybe_warn_about_returning_address_of_local): Optimize
        whats_returned through fold_for_warn.

        * g++.dg/cpp1y/pr77591.C: New test.

--- gcc/cp/typeck.c.jj  2016-11-15 09:57:00.000000000 +0100
+++ gcc/cp/typeck.c     2016-11-24 11:37:30.732109019 +0100
@@ -8612,7 +8612,7 @@ static bool
 maybe_warn_about_returning_address_of_local (tree retval)
 {
   tree valtype = TREE_TYPE (DECL_RESULT (current_function_decl));
-  tree whats_returned = retval;
+  tree whats_returned = fold_for_warn (retval);
 
   for (;;)
     {
--- gcc/testsuite/g++.dg/cpp1y/pr77591.C.jj     2016-11-24 11:41:03.867436090 
+0100
+++ gcc/testsuite/g++.dg/cpp1y/pr77591.C        2016-11-24 11:42:04.428676591 
+0100
@@ -0,0 +1,19 @@
+// PR c++/77591
+// { dg-do compile { target c++14 } }
+// { dg-options "-O0 -Wreturn-local-addr" }
+
+class A { };
+
+decltype(auto)
+foo ()
+{
+  A c;                 // { dg-warning "reference to local variable 'c' 
returned" }
+  return (c);
+}
+
+decltype(auto)
+bar ()
+{
+  A c;                 // { dg-warning "reference to local variable 'c' 
returned" }
+  return 1==1 ? c : c;
+}

        Jakub