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 6B89D3857C5A; Sun, 12 Jul 2020 23:49:55 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 6B89D3857C5A
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
 s=default; t=1594597795;
 bh=kUgacZ4asRu1WsR9gkfvcc3PHBGTiQR16wFVEMLWF3I=;
 h=From:To:Subject:Date:From;
 b=ryf9JC5OiiOh9i4xcSDp8y8FXUgRQzsT0Vw9N6utyjX0ncHo9jj7FXuLyBfzAR6w2
 UBCvHKDkklKCMnpe0lvvnYAKyDW9ONerYZ7SnSIkxZ1zlAlyYr8MMCWmfBH4PIZGGp
 hnOvdvOHySUbOiABUSDzq3UYtMgwRPalWAdE5uAE=
From: "gabravier at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/96176] New: Failure to omit extraneous movzx in atomic
 compare exchange with unsigned char
Date: Sun, 12 Jul 2020 23:49:55 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: target
X-Bugzilla-Version: 11.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: gabravier at gmail dot com
X-Bugzilla-Status: UNCONFIRMED
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: bug_id short_desc product version bug_status
 bug_severity priority component assigned_to reporter target_milestone
Message-ID: <bug-96176-4@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: <http://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: <http://gcc.gnu.org/mailman/listinfo/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Sun, 12 Jul 2020 23:49:55 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96176

            Bug ID: 96176
           Summary: Failure to omit extraneous movzx in atomic compare
                    exchange with unsigned char
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gabravier at gmail dot com
  Target Milestone: ---

void f(unsigned char *addr, unsigned char old_val, unsigned char new_val)
{
    __atomic_compare_exchange_n(addr, &old_val, new_val, 0, 0, 0);
}

On x86 with -O3, LLVM generates this :

f(unsigned char*, unsigned char, unsigned char): # @f(unsigned char*, unsig=
ned
char, unsigned char)
  mov eax, esi
  lock cmpxchg byte ptr [rdi], dl
  ret

GCC generates this :

f(unsigned char*, unsigned char, unsigned char):
  mov eax, esi
  movzx edx, dl
  lock cmpxchg BYTE PTR [rdi], dl
  ret=