re PR c++/60272 (atomic<>::compare_exchange_weak has spurious store and can cause race conditions)

PR c++/60272

        * builtins.c (expand_builtin_atomic_compare_exchange): Always make
        a new pseudo for OLDVAL.

From-SVN: r207972

gcc/ChangeLog

+2014-02-20  Richard Henderson  <rth@redhat.com>
+
+	PR c++/60272
+	* builtins.c (expand_builtin_atomic_compare_exchange): Always make
+	a new pseudo for OLDVAL.
+
 2014-02-20  Jakub Jelinek  <jakub@redhat.com>
 
 	PR target/57896

gcc/builtins.c

@@ -5332,9 +5332,12 @@ expand_builtin_atomic_compare_exchange (enum machine_mode mode, tree exp,
 
   if (target == const0_rtx)
     target = NULL;
-  oldval = expect;
 
-  if (!expand_atomic_compare_and_swap (&target, &oldval, mem, oldval, desired,
+  /* Lest the rtl backend create a race condition with an imporoper store
+     to memory, always create a new pseudo for OLDVAL.  */
+  oldval = NULL;
+
+  if (!expand_atomic_compare_and_swap (&target, &oldval, mem, expect, desired,
 				       is_weak, success, failure))
     return NULL_RTX;