https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103073
--- Comment #11 from rguenther at suse dot de <rguenther at suse dot de> --- On Fri, 5 Nov 2021, hubicka at kam dot mff.cuni.cz wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103073 > > --- Comment #8 from hubicka at kam dot mff.cuni.cz --- > > Well, the usual thing to do is to check max_size_known_p () and > > if maybe_ne (max_size, size) then use [offset, max_size] for > > disambiguation. I think for modref you can do the same - if max size > > is known then use [offset, max_size], otherwise you have to punt. You > > shouldn't need 'size' at all, 'size' is when you are looking for > > must-defs. > > While disambiguating ref with decl we also check if size is greater than > size of decl and in that case we disambiguate. So tracking sizes helps > little bit even if not checking for kills. > > I plan to do also kills using modrefs. This helps to propagate clobber > inter-procedurally. One simply needs one extra flag tracking if store > must be executed before function returns (I have patch for this). > > Hoever still I am convinced I can simply ignore the range here since > from VRP we know it will be undefined if ever executed as follows: > > diff --git a/gcc/ipa-modref-tree.h b/gcc/ipa-modref-tree.h > index 9976e489697..1b51323175b 100644 > --- a/gcc/ipa-modref-tree.h > +++ b/gcc/ipa-modref-tree.h > @@ -813,6 +818,20 @@ struct GTY((user)) modref_tree > > bool changed = false; > > + /* We may end up with max_size being less than size for accesses past the > + end of array. Those are undefined and safe to ignore. */ > + if (a.range_info_useful_p () > + && ((known_size_p (a.size) && known_size_p (a.max_size) > + && known_lt (a.max_size, a.size)) What about maybe_lt? Well, you should know the ICEing place and whether it's sensitive to may or must ;) > + || (known_size_p (a.max_size) > + && known_le (a.max_size, 0)))) The known_size_p (a.max_size) && known_le (a.max_size, 0) should never be true (there's only the -1 special value denoting 'unknown'). > + { > + if (dump_file) > + fprintf (dump_file, > + " - Paradoxical ragne. Ignoring\n"); > + return false; > + } > + > /* No useful information tracked; collapse everything. */ > if (!base && !ref && !a.useful_p ()) > { > > Similarly we could detect this as undefined effect and turn to > trap/unreachable somewhere if we care. > > This bootstraps/regtests and fixes the testcase. Does it look sane to > you? Yeah, apart from the remark above.
