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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/111257] new signed overflow after vectorizer Date: Thu, 31 Aug 2023 13:22:41 +0000 [thread overview] Message-ID: <bug-111257-4-QdwiWQe3XI@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-111257-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111257 Richard Biener <rguenth at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Ever confirmed|0 |1 Status|UNCONFIRMED |ASSIGNED Last reconfirmed| |2023-08-31 Assignee|unassigned at gcc dot gnu.org |rguenth at gcc dot gnu.org Keywords| |missed-optimization, | |wrong-code --- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> --- Yeah, we modify a copy of the scalar loop in-place, only removing original stmts that have side-effects, leaving dead code elimination to the followup DCE pass. Note we run that immediately after loop vectorization but for SLP vectorization there are quite some intermediate passes until we perform DCE, for example there's IVOPTS which might re-compute number of iterations and at least max_iteration estimate also looks at undefined behavior. OTOH with SLP vectorization we don't change any loop iteration which means the original stmts only compute the very original values (should, at least). That means there might be an actual issue for those cases but for loop vectorization the issue should be moot unless those stmts survive the DCE pass after it. I would suggest to "blacklist" analyzing the "vect" dump, the followup "dce" dump should be fine. For SLP I'm not sure, I guess no actual problems should show up but we should maybe try to use simple_dce_from_worklist with the root stmts original SSA uses (and defs in some cases), possibly the root stmt vectorization code generation code could gather relevant defs. So I think, correctness wise it should be a non-issue but it's a bit ugly also since some fuzzers like to disable DCE which then indeed would create wrong-code issues.
prev parent reply other threads:[~2023-08-31 13:22 UTC|newest] Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-08-31 11:48 [Bug tree-optimization/111257] New: " kristerw at gcc dot gnu.org 2023-08-31 13:22 ` rguenth at gcc dot gnu.org [this message]
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