public inbox for gcc-bugs@sourceware.org
help / color / mirror / Atom feed
From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/111151] [12/13/14 Regression] Wrong code at -O0 on x86_64-pc-linux-gnu
Date: Fri, 22 Mar 2024 17:37:33 +0000 [thread overview]
Message-ID: <bug-111151-4-fqURnyoXih@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-111151-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111151
--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #5)
> but even when overflow is undefined we don't know whether we introduce
> additional overflow then. Consider MAX (INT_MIN, 0) * -1 where we compute
> 0 * -1 (fine) but after the transform we'd do MIN (INT_MIN * -1, 0)
> which isn't valid.
>
> And when overflow wraps consider MAX (UINT_MAX, 1) * 2 which
> will compute UINT_MAX * 2 == 0 while MAX (UINT_MAX * 2, 1 * 2) will compute
> 2.
>
> Unless I'm missing something.
You're right. So perhaps punt on this optimization for code == MULT_EXPR
altogether.
For the division/modulo, the problematic case is signed division by -1 (unless
we can prove that neither operand is signed type minimum), but c is constant
here, so we could as well just punt for code == MULT_EXPR || integer_minus_onep
(c)?
next prev parent reply other threads:[~2024-03-22 17:37 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-25 6:39 [Bug middle-end/111151] New: " jwzeng at nuaa dot edu.cn
2023-08-25 7:16 ` [Bug middle-end/111151] " rguenth at gcc dot gnu.org
2023-08-25 7:16 ` rguenth at gcc dot gnu.org
2023-08-25 11:51 ` mikpelinux at gmail dot com
2023-08-25 12:27 ` rguenth at gcc dot gnu.org
2023-08-25 12:28 ` rguenth at gcc dot gnu.org
2023-08-25 12:35 ` rguenth at gcc dot gnu.org
2023-08-26 3:27 ` pinskia at gcc dot gnu.org
2024-03-22 13:40 ` law at gcc dot gnu.org
2024-03-22 17:29 ` jakub at gcc dot gnu.org
2024-03-22 17:37 ` jakub at gcc dot gnu.org [this message]
2024-03-22 17:41 ` jakub at gcc dot gnu.org
2024-03-22 17:57 ` jakub at gcc dot gnu.org
2024-03-22 18:48 ` jakub at gcc dot gnu.org
2024-03-22 19:15 ` jakub at gcc dot gnu.org
2024-03-25 7:23 ` rguenth at gcc dot gnu.org
2024-03-25 11:01 ` jakub at gcc dot gnu.org
2024-03-25 12:45 ` rguenth at gcc dot gnu.org
2024-03-26 10:22 ` cvs-commit at gcc dot gnu.org
2024-03-26 10:32 ` [Bug middle-end/111151] [12/13 " jakub at gcc dot gnu.org
2024-03-26 15:43 ` cvs-commit at gcc dot gnu.org
2024-03-30 3:55 ` cvs-commit 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-111151-4-fqURnyoXih@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).