https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70143
--- Comment #7 from rguenther at suse dot de <rguenther at suse dot de> --- On Wed, 9 Mar 2016, jakub at gcc dot gnu.org wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70143 > > --- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> --- > (In reply to rguent...@suse.de from comment #5) > > Though that will FAIL the gcc.dg/Wstrict-aliasing-struct-member.c > > I added. > > > > Note that we then also don't warn for > > > > struct a { > > int i; > > int k; > > }; > > struct b { > > struct a a; > > int j; > > }; > > int main(void) { > > static struct b b; > > struct a *ap=(struct a *)&b; > > return ((struct b *)&ap->k)->j; > > } > > > > then either. Doing this kind of warnings strictly based on alias > > sets only is going to be "broken" - though I consider our strict-aliasing > > warnings broken anyway (and I don't think we can ever implement something > > sensible :/). > > The point of -Wstrict-aliasing=3 is to give very few false positives and still > catch lots of likely bugs. So, if there is INDIRECT_REF or *MEM_REF involved > and you can't analyze what it points to, we should err on the side that it > might be valid, people can still use -Wstrict-aliasing=2 that will warn even > about these. Ok, I'll remove the new test and test Index: gcc/c-family/c-common.c =================================================================== --- gcc/c-family/c-common.c (revision 234025) +++ gcc/c-family/c-common.c (working copy) @@ -1568,7 +1568,9 @@ strict_aliasing_warning (tree otype, tre 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"); then.
