The following patch adjusts strict_aliasing_warning to use
proper alias_set_subset_of instead of relying on alias_sets_conflict_p
as after the PR66110 fix aggregates with a char[] member do not
automatically behave like having alias-set zero. As a side-effect
the test will be somewhat stricter as well accessing a 'long' with
a struct { int i; long l; } * will now warn while it previously
didn't:
struct S { int i; long l; };
long x;
struct S foo () { return *(struct S *)&x; }
now warns:
t.c: In function ‘foo’:
t.c:3:35: warning: dereferencing type-punned pointer will break
strict-aliasing rules [-Wstrict-aliasing]
struct S foo () { return *(struct S *)&x; }
^
Bootstrap and regtest running on x86_64-unknown-linux-gnu, ok for trunk?
Thanks,
Richard.
2016-03-03 Richard Biener <rguent...@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.
Index: gcc/c-family/c-common.c
===================================================================
*** gcc/c-family/c-common.c (revision 233902)
--- gcc/c-family/c-common.c (working copy)
*************** strict_aliasing_warning (tree otype, tre
*** 1568,1574 ****
alias_set_type set2 = get_alias_set (TREE_TYPE (type));
if (set1 != set2 && set2 != 0
! && (set1 == 0 || !alias_sets_conflict_p (set1, set2)))
{
warning (OPT_Wstrict_aliasing, "dereferencing type-punned "
"pointer will break strict-aliasing rules");
--- 1568,1574 ----
alias_set_type set2 = get_alias_set (TREE_TYPE (type));
if (set1 != set2 && set2 != 0
! && (set1 == 0 || !alias_set_subset_of (set2, set1)))
{
warning (OPT_Wstrict_aliasing, "dereferencing type-punned "
"pointer will break strict-aliasing rules");
Index: gcc/testsuite/g++.dg/warn/Wstrict-aliasing-bogus-union-2.C
===================================================================
*** gcc/testsuite/g++.dg/warn/Wstrict-aliasing-bogus-union-2.C (revision 0)
--- gcc/testsuite/g++.dg/warn/Wstrict-aliasing-bogus-union-2.C (working copy)
***************
*** 0 ****
--- 1,14 ----
+ /* { 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" } */
+ }
+ };
Index: gcc/testsuite/gcc.dg/Wstrict-aliasing-struct-member.c
===================================================================
--- gcc/testsuite/gcc.dg/Wstrict-aliasing-struct-member.c (revision 0)
+++ gcc/testsuite/gcc.dg/Wstrict-aliasing-struct-member.c (working copy)
@@ -0,0 +1,6 @@
+/* { 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" } */
