re PR c/70143 (false strict-aliasing warning)

2016-03-09  Richard Biener  <rguenther@suse.de>

	c-family/
	PR c/70143
	* c-common.c (strict_aliasing_warning): Add back
	alias_sets_conflict_p check.

	* gcc.dg/Wstrict-aliasing-bogus-upcast.c: New testcase.
	* gcc.dg/Wstrict-aliasing-struct-with-char-member.c: Likewise.
	* gcc.dg/Wstrict-aliasing-struct-member.c: Remove again.

From-SVN: r234084

gcc/c-family/ChangeLog

+2016-03-09  Richard Biener  <rguenther@suse.de>
+
+	PR c/70143
+	* c-common.c (strict_aliasing_warning): Add back
+	alias_sets_conflict_p check.
+
 2016-03-08  Jason Merrill  <jason@redhat.com>
 
 	* c-opts.c (set_std_cxx1z): Don't enable concepts.

gcc/c-family/c-common.c

@@ -1568,7 +1568,9 @@ strict_aliasing_warning (tree otype, tree type, tree expr)
           alias_set_type set2 = get_alias_set (TREE_TYPE (type));
 
           if (set1 != set2 && set2 != 0
-	      && (set1 == 0 || !alias_set_subset_of (set2, set1)))
+	      && (set1 == 0
+		  || (!alias_set_subset_of (set2, set1)
+		      && !alias_sets_conflict_p (set1, set2))))
 	    {
 	      warning (OPT_Wstrict_aliasing, "dereferencing type-punned "
 		       "pointer will break strict-aliasing rules");

gcc/testsuite/ChangeLog

+2016-03-09  Richard Biener  <rguenther@suse.de>
+
+	PR c/70143
+	* gcc.dg/Wstrict-aliasing-bogus-upcast.c: New testcase.
+	* gcc.dg/Wstrict-aliasing-struct-with-char-member.c: Likewise.
+	* gcc.dg/Wstrict-aliasing-struct-member.c: Remove again.
+
 2016-03-09  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>
 
 	* gcc.dg/vect/bb-slp-34.c: Really don't xfail on aarch64-*-*,

gcc/testsuite/gcc.dg/Wstrict-aliasing-bogus-upcast.c

+/* { dg-do compile } */
+/* { dg-options "-O2 -Wall" } */
+
+struct a {
+    int i;
+};
+struct b {
+    struct a a;
+    int j;
+};
+int main(void)
+{
+  static struct b b;
+  struct a *ap=(struct a *)&b;
+  return ((struct b *)&ap->i)->j; /* { dg-bogus "will break strict-aliasing" } */
+}
+

gcc/testsuite/gcc.dg/Wstrict-aliasing-struct-member.c

-/* { dg-do compile } */
-/* { dg-options "-O2 -Wall" } */
-
-struct S { int i; long l; };
-long x;
-struct S foo () { return *(struct S *)&x; } /* { dg-warning "will break strict-aliasing" } */

gcc/testsuite/gcc.dg/Wstrict-aliasing-struct-with-char-member.c

+/* { dg-do compile } */
+/* { dg-options "-O2 -Wall" } */
+
+struct a {
+    int i;
+    char c;
+};
+struct b {
+    float f;
+    float g;
+};
+int main(void)
+{
+  static struct b b;
+  return ((struct a *)&b)->i; /* { dg-warning "will break strict-aliasing" } */
+}