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 0C0FB3858D37; Wed,  2 Feb 2022 23:40:41 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 0C0FB3858D37
From: "gabravier at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/104357] New: [Aarch64] Failure to use csinv instead of
 mvn+csel where possible
Date: Wed, 02 Feb 2022 23:40:40 +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: 12.0
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-104357-4@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, 02 Feb 2022 23:40:41 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104357

            Bug ID: 104357
           Summary: [Aarch64] Failure to use csinv instead of mvn+csel
                    where possible
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gabravier at gmail dot com
  Target Milestone: ---

unsigned char stbi__clamp(int x)
{
   if ((unsigned)x > 255) {
      if (x < 0) return 0;
      if (x > 255) return 255;
   }
   return x;
}

With -O3, GCC outputs this (on aarch64):

stbi__clamp(int):
  mvn w1, w0
  cmp w0, 256
  and w0, w0, 255
  asr w1, w1, 31
  and w1, w1, 255
  csel w0, w0, w1, cc
  ret

LLVM instead outputs this:

stbi__clamp(int):
  asr w8, w0, #31
  cmp w0, #255
  csinv w0, w0, w8, ls
  ret

I don't know if the `and`s are there because of ABI differences, but it see=
ms
to me like the `mvn` can definitely be replaced by using `csinv` instead of
`csel`.=