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From: "post+gcc at ralfj dot de" <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: Tue, 28 Nov 2023 07:20:18 +0000	[thread overview]
Message-ID: <bug-32667-4-DkKwoyP0OM@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 #52 from post+gcc at ralfj dot de ---
For the point discussed earlier with the `restrict` in the musl memcpy, I had
another look at the definition of `restrict` and it's not entirely clear to me
any more that there is UB here. The restrict rules only apply to objects that
are "also modified (by any means)". Now the question is, does "*X = *X" modify
the object? Is a write always a modification or only if the stores
representation changes or only if the stored value changes?

If it requires a representation change, then "memcpy(x, x, n)" does not modify
anything, and hence there is no UB from "restrict".

  parent reply	other threads:[~2023-11-28  7:20 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
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 [this message]
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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