re PR middle-end/70054 (GCC 6 gives a strict-aliasing warning on use of std::aligned_storage)

2016-03-04  Richard Biener  <rguenther@suse.de>

	PR c++/70054
	* c-common.c (strict_aliasing_warning): Use alias_set_subset_of
	instead of alias_sets_conflict_p.

	* g++.dg/warn/Wstrict-aliasing-bogus-union-2.C: New testcase.
	* gcc.dg/Wstrict-aliasing-struct-member.c: New testcase.

From-SVN: r233961

gcc/c-family/ChangeLog

+2016-03-04  Richard Biener  <rguenther@suse.de>
+
+	PR c++/70054
+	* c-common.c (strict_aliasing_warning): Use alias_set_subset_of
+	instead of alias_sets_conflict_p.
+
 2016-03-01  Marek Polacek  <polacek@redhat.com>
 
 	PR c++/69795

gcc/c-family/c-common.c

@@ -1568,7 +1568,7 @@ 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_sets_conflict_p (set1, set2)))
+	      && (set1 == 0 || !alias_set_subset_of (set2, set1)))
 	    {
 	      warning (OPT_Wstrict_aliasing, "dereferencing type-punned "
 		       "pointer will break strict-aliasing rules");

gcc/testsuite/ChangeLog

+2016-03-04  Richard Biener  <rguenther@suse.de>
+
+	PR c++/70054
+	* g++.dg/warn/Wstrict-aliasing-bogus-union-2.C: New testcase.
+	* gcc.dg/Wstrict-aliasing-struct-member.c: New testcase.
+
 2016-03-04  Dominik Vogt  <vogt@linux.vnet.ibm.com>
 
 	PR testsuite/69766

gcc/testsuite/g++.dg/warn/Wstrict-aliasing-bogus-union-2.C

+/* { dg-do compile { target c++11 } } */
+/* { dg-options "-Wstrict-aliasing=2 -O2 -Wall" } */
+
+#include <type_traits>
+
+struct foo
+{
+  std::aligned_storage<sizeof(long), alignof(long)>::type raw;
+
+  long& cooked()
+    {
+      return *static_cast<long*>(static_cast<void*>(&raw)); /* { dg-bogus "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" } */