From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
	id BB09E3858423; Wed, 22 Nov 2023 15:06:02 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org BB09E3858423
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1700665562;
	bh=WayVrEL71zfXFzYb+avCTwRPkjisKPq/eC+LLxmGElw=;
	h=From:To:Subject:Date:In-Reply-To:References:From;
	b=MENMpUwSA+AG15ElpRiCDgrPvWb1ccP3fm4i9QTRhHk29+xbsiknZNoQuKX5E1igu
	 6YdG/G2cY1KFkgSl3OpcH4GlO+yZmv1zOAm7mLovZ7VXNYRrHnFcUEWObwHKMoc7Ls
	 Fr5iwFMjguwC/2y52lImCzHJHUGYcQrzzW1DTVog=
From: "jakub at gcc dot gnu.org" <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 15:06:02 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: middle-end
X-Bugzilla-Version: 4.2.0
X-Bugzilla-Keywords: wrong-code
X-Bugzilla-Severity: normal
X-Bugzilla-Who: jakub at gcc dot gnu.org
X-Bugzilla-Status: NEW
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-32667-4-z4YIjbcK3K@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-32667-4@http.gcc.gnu.org/bugzilla/>
References: <bug-32667-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
List-Id: <gcc-bugs.sourceware.org>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D32667

--- Comment #27 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Rich Felker from comment #26)
> > The only reasonable fix on the compiler side is to never emit memcpy bu=
t always use memmove.
>=20
> No, it can literally just emit (equivalent at whatever intermediate form =
of):
>=20
> cmp src,dst
> je 1f
> call memcpy
> 1:
>=20
> in place of memcpy.

No, that is not a reasonable fix, because it severely pessimizes common code
for a theoretical only problem.=