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))
+ || (known_size_p (a.max_size)
+ && known_le (a.max_size, 0))))
+ {
+ 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?
Honza
