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 8F2083858C56; Wed,  6 Dec 2023 16:47:54 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 8F2083858C56
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1701881274;
	bh=c5damMc93ZPM+3eIefYu80ubkwv9xAyERhXTWFUDy28=;
	h=From:To:Subject:Date:From;
	b=PPEjSSjJY12VFTdmG8Aomzr1LT6k39DZccarQ/58XjsecCY0yyU/txNPKpqR7O7Hi
	 cBwgUX4YRY1PHN6CzNctyqxTYZVWIf0kaLffq+le7Q5QpNXYI/7ePLLMBmDzmbWBuW
	 k+akROdY2TB332j04v8Dd6Y7BJyOPJSYfehl6ncQ=
From: "xxs_chy at outlook dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/112884] New: Missing optimization: fold
 a%2==0 ? a/2*2 : 0 to a%2==0 ? a : 0
Date: Wed, 06 Dec 2023 16:47:54 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 14.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: xxs_chy at outlook 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-112884-4@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=3D112884

            Bug ID: 112884
           Summary: Missing optimization: fold a%2=3D=3D0 ? a/2*2 : 0 to
                    a%2=3D=3D0 ? a : 0
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: xxs_chy at outlook dot com
  Target Milestone: ---

Godbolt example: https://godbolt.org/z/Ec1ax79r8

For the select arm "a / 2 * 2" in:

unsigned src(unsigned a) {
    return a % 2 =3D=3D 0 ? (a / 2 * 2) : 0;
}

it's equivalent to "a", so the program could be folded to:

unsigned tgt(unsigned a) {
    return a % 2 =3D=3D 0 ? a : 0;
}

Both GCC and LLVM missed such optimization in select arms.=