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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: Wed, 22 Nov 2023 14:57:19 +0000	[thread overview]
Message-ID: <bug-32667-4-VRY4ZlmPGe@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 #26 from Rich Felker <bugdal at aerifal dot cx> ---
> The only reasonable fix on the compiler side is to never emit memcpy but always use memmove.

No, it can literally just emit (equivalent at whatever intermediate form of):

cmp src,dst
je 1f
call memcpy
1:

in place of memcpy.

It can even optimize out that in the case where it's provable that they're not
equal, e.g. presence of restrict or one of the two objects not having had its
address taken/leaked.

  parent reply	other threads:[~2023-11-22 14:57 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 [this message]
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
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

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