public inbox for gcc-bugs@sourceware.org
help / color / mirror / Atom feed
From: "bugdal at aerifal dot cx" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/32667] block copy with exact overlap is expanded as memcpy
Date: Thu, 23 Nov 2023 18:55:59 +0000 [thread overview]
Message-ID: <bug-32667-4-BzzlDpyIwI@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-32667-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=32667
--- Comment #42 from Rich Felker <bugdal at aerifal dot cx> ---
> I'm not saying that such an implementation will be a good idea, but just a remark: You could, in fact, keep restrict for the arguments in this case, because the object pointed to by src and dest is not accessed at all when src==dest. So this is correct code according to the standard. (The exact semantics of restrict are a bit involved...)
Nope, UB is invoked as soon as you evaluate src==dest, even with no
dereferencing. The semantics of restrict are such that the behavior of the code
must be unchanged if the pointer were replaced to a pointer to a relocated copy
of the pointed-to object. Since this would alter the result of the == operator,
that constraint is not satisfied and thereby the behavior is undefined.
next prev parent reply other threads:[~2023-11-23 18:56 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <bug-32667-4@http.gcc.gnu.org/bugzilla/>
2011-12-05 17:00 ` [Bug middle-end/32667] builtin operator= generates memcpy with overlapping memory regions lu_zero at gentoo dot org
2011-12-05 20:38 ` mans at mansr dot com
2011-12-06 8:46 ` [Bug middle-end/32667] block copy with exact overlap is expanded as memcpy rguenth at gcc dot gnu.org
2015-02-12 5:38 ` pinskia at gcc dot gnu.org
2015-02-12 9:00 ` rguenth at gcc dot gnu.org
2015-02-12 9:42 ` jakub at gcc dot gnu.org
2015-09-28 18:18 ` hugh at mimosa dot com
2021-06-09 18:50 ` public at timruffing dot de
2021-06-10 6:36 ` rguenther at suse dot de
2023-01-05 8:53 ` pinskia at gcc dot gnu.org
2023-01-05 9:19 ` nyh at math dot technion.ac.il
2023-01-06 18:48 ` lopresti at gmail dot com
2023-10-28 10:04 ` post+gcc at ralfj dot de
2023-11-21 15:57 ` bugdal at aerifal dot cx
2023-11-22 7:33 ` rguenther at suse dot de
2023-11-22 14:57 ` bugdal at aerifal dot cx
2023-11-22 15:06 ` jakub at gcc dot gnu.org
2023-11-22 19:07 ` bugdal at aerifal dot cx
2023-11-23 0:00 ` lopresti at gmail dot com
2023-11-23 7:44 ` post+gcc at ralfj dot de
2023-11-23 7:58 ` rguenth at gcc dot gnu.org
2023-11-23 8:03 ` fw at gcc dot gnu.org
2023-11-23 8:08 ` rguenther at suse dot de
2023-11-23 8:32 ` cvs-commit at gcc dot gnu.org
2023-11-23 8:39 ` jakub at gcc dot gnu.org
2023-11-23 13:54 ` bugdal at aerifal dot cx
2023-11-23 13:57 ` bugdal at aerifal dot cx
2023-11-23 14:41 ` public at timruffing dot de
2023-11-23 15:00 ` public at timruffing dot de
2023-11-23 15:01 ` sjames at gcc dot gnu.org
2023-11-23 15:29 ` post+gcc at ralfj dot de
2023-11-23 18:55 ` bugdal at aerifal dot cx [this message]
2023-11-23 19:04 ` post+gcc at ralfj dot de
2023-11-23 20:27 ` bugdal at aerifal dot cx
2023-11-24 8:19 ` public at timruffing dot de
2023-11-24 9:29 ` rguenth at gcc dot gnu.org
2023-11-24 10:09 ` jakub at gcc dot gnu.org
2023-11-24 19:08 ` post+gcc at ralfj dot de
2023-11-27 14:12 ` post+gcc at ralfj dot de
2023-11-27 23:32 ` joseph at codesourcery dot com
2023-11-28 7:17 ` post+gcc at ralfj dot de
2023-11-28 7:20 ` post+gcc at ralfj dot de
2023-11-28 10:58 ` rguenther at suse dot de
2023-11-28 11:03 ` rguenth at gcc dot gnu.org
2023-11-28 11:07 ` fw at gcc dot gnu.org
2024-01-04 12:52 ` rearnsha at gcc dot gnu.org
2024-01-04 13:22 ` bugdal at aerifal dot cx
2024-01-04 13:37 ` jakub at gcc dot gnu.org
2024-01-04 14:28 ` rearnsha at gcc dot gnu.org
2024-01-04 14:29 ` bugdal at aerifal dot cx
2024-01-04 14:41 ` rearnsha at gcc dot gnu.org
2024-01-04 14:44 ` bugdal at aerifal dot cx
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-32667-4-BzzlDpyIwI@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).