[gcc] GCC 4.5.0=>4.5.1

gcc/libgomp/config/linux/mutex.h

Index: gcc/libgomp/config/linux/mutex.h
diff --git a/gcc/libgomp/config/linux/mutex.h b/gcc/libgomp/config/linux/mutex.h
index 07a2156a462966818f5e4066a4573004df251ca1..1905ce012fde79b8b57ccc5a338be8f2b895eebf 100644
--- a/gcc/libgomp/config/linux/mutex.h
+++ b/gcc/libgomp/config/linux/mutex.h
@@ -48,6 +48,16 @@ static inline void gomp_mutex_lock (gomp_mutex_t *mutex)
 extern void gomp_mutex_unlock_slow (gomp_mutex_t *mutex);
 static inline void gomp_mutex_unlock (gomp_mutex_t *mutex)
 {
+  /* Warning: By definition __sync_lock_test_and_set() does not have
+     proper memory barrier semantics for a mutex unlock operation.
+     However, this default implementation is written assuming that it
+     does, which is true for some targets.
+
+     Targets that require additional memory barriers before
+     __sync_lock_test_and_set to achieve the release semantics of
+     mutex unlock, are encouraged to include
+     "config/linux/ia64/mutex.h" in a target specific mutex.h instead
+     of using this file.  */
   int val = __sync_lock_test_and_set (mutex, 0);
   if (__builtin_expect (val > 1, 0))
     gomp_mutex_unlock_slow (mutex);