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From: "hugh at mimosa dot com" <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: Mon, 28 Sep 2015 18:18:00 -0000 [thread overview]
Message-ID: <bug-32667-4-5PedNh2zNF@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
D. Hugh Redelmeier <hugh at mimosa dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |hugh at mimosa dot com
--- Comment #12 from D. Hugh Redelmeier <hugh at mimosa dot com> ---
JJ in #11 is right.
The compiler should never generate calls to functions with names in the user's
space. That's because the user is allowed to (re)define anything with those
names and is not constrained to preserve expected semantics.
There should be a function in the reserved-to-system namespace that does what
is needed. GCC should then call this function.
Let's say that GCC uses __memcpy. The default standard definition of memcpy
could be a synonym (until redefinition) for __memcpy.
On the other hand, there are compile-time constraints on struct assignments
that could yield even better performance. For example, GCC might know that the
object is a multiple of 8 bytes, aligned on an 8-byte boundary. GCC would
certainly know that the struct's length is non-zero, conceptually eliminating
one test. This suggests implementing specialized variants, perhaps having
names starting with __struct_assign.
(I know GCC has an extension allowing 0 length objects. The assignment for
such objects could be eliminated.)
next prev parent reply other threads:[~2015-09-28 18:18 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 [this message]
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
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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