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 1C76E3858D28; Wed,  8 Dec 2021 03:42:36 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 1C76E3858D28
From: "aoliva at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/103302] wrong code with -fharden-compares
Date: Wed, 08 Dec 2021 03:42:35 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: target
X-Bugzilla-Version: 12.0
X-Bugzilla-Keywords: wrong-code
X-Bugzilla-Severity: normal
X-Bugzilla-Who: aoliva at gcc dot gnu.org
X-Bugzilla-Status: ASSIGNED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: aoliva at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: attachments.created
Message-ID: <bug-103302-4-eM8D8pqxz7@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-103302-4@http.gcc.gnu.org/bugzilla/>
References: <bug-103302-4@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
X-BeenThere: gcc-bugs@gcc.gnu.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Gcc-bugs mailing list <gcc-bugs.gcc.gnu.org>
List-Unsubscribe: <https://gcc.gnu.org/mailman/options/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=unsubscribe>
List-Archive: <https://gcc.gnu.org/pipermail/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-request@gcc.gnu.org?subject=help>
List-Subscribe: <https://gcc.gnu.org/mailman/listinfo/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Wed, 08 Dec 2021 03:42:36 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103302

--- Comment #10 from Alexandre Oliva <aoliva at gcc dot gnu.org> ---
Created attachment 51947
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D51947&action=3Dedit
candidate patch under testing

Could the fix be as simple as this?

The resulting code is awful, with such stuff as loading and storing back ea=
ch
word of multi-word pseudos that end up assigned to memory, but at least we
don't clobber the asm outputs with these clobbers, which is what makes them
look dead.

Anyhow, comments at the top of emit_move_multi_word state:

   Note that you will get better code if you define such
   patterns, even if they must turn into multiple assembler instructions.=