c-common.c (shorten_compare): But look through macros from system headers.

	* c-common.c (shorten_compare): But look through macros from
	system headers.

From-SVN: r230665

gcc/c-family/ChangeLog

+2015-11-19  Jason Merrill  <jason@redhat.com>
+
+	* c-common.c (shorten_compare): But look through macros from
+	system headers.
+
 2015-11-18  Jason Merrill  <jason@redhat.com>
 
 	* c-common.c (shorten_compare): Don't -Wtype-limits if the

gcc/c-family/c-common.c

@@ -4651,8 +4651,10 @@ shorten_compare (location_t loc, tree *op0_ptr, tree *op1_ptr,
 	}
 
       if (TREE_CODE (primop0) != INTEGER_CST
-	  /* Don't warn if it's from a macro.  */
-	  && !from_macro_expansion_at (EXPR_LOCATION (primop0)))
+	  /* Don't warn if it's from a (non-system) macro.  */
+	  && !(from_macro_expansion_at
+	       (expansion_point_location_if_in_system_header
+		(EXPR_LOCATION (primop0)))))
 	{
 	  if (val == truthvalue_false_node)
 	    warning_at (loc, OPT_Wtype_limits,

gcc/testsuite/gcc.dg/Wtype-limits2.c

+/* { dg-do compile } */
+/* { dg-options "-Wtype-limits" } */
+/* { dg-require-effective-target sync_char_short } */
+
+#include <stdatomic.h>
+
+unsigned foo (unsigned char *x)
+{
+  if (atomic_load (x) > 1000) /* { dg-warning "comparison is always false due to limited range of data type" } */
+    return 0;
+  return 1;
+}