public inbox for gcc-bugs@sourceware.org
help / color / mirror / Atom feed
From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/109626] forwprop introduces new signed multiplication UB
Date: Wed, 26 Apr 2023 06:36:45 +0000	[thread overview]
Message-ID: <bug-109626-4-7nJ5PGH3G5@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-109626-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109626

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
We apply from match.pd (-A) * (-B) -> A * B and -(A - B) -> B - A where
there are no constraints on overflow present for these patterns.

We go

(int) (v2_6(D) - _2) * (int) - v1_5(D)

-> (int) (- (v2_6(D) - _2)) * (int) v1_5(D)

-> (int) (_2 - v2_6(D)) * (int) v1_5(D)

I think the issue must be in (-A) * (-B) -> A * B, but I can't quite nail it.
To result in -1 * INT_MIN we'd have to come from 1 * INT_MIN but then the
negation of INT_MIN would already be problematic.

  reply	other threads:[~2023-04-26  6:36 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-04-25 21:53 [Bug tree-optimization/109626] New: " kristerw at gcc dot gnu.org
2023-04-26  6:36 ` rguenth at gcc dot gnu.org [this message]
2023-04-26  8:50 ` [Bug tree-optimization/109626] " mikael at gcc dot gnu.org

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=bug-109626-4-7nJ5PGH3G5@http.gcc.gnu.org/bugzilla/ \
    --to=gcc-bugzilla@gcc.gnu.org \
    --cc=gcc-bugs@gcc.gnu.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).