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 25E143858D35; Mon, 30 Aug 2021 23:52:39 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 25E143858D35
From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/102138] New: t = a==0 and a = PHI<0, t>
 should be done earlier than PRE
Date: Mon, 30 Aug 2021 23:52:38 +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: 12.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: enhancement
X-Bugzilla-Who: pinskia at gcc dot gnu.org
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
 keywords bug_severity priority component assigned_to reporter
 target_milestone
Message-ID: <bug-102138-4@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: Mon, 30 Aug 2021 23:52:39 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102138

            Bug ID: 102138
           Summary: t =3D a=3D=3D0 and a =3D PHI<0, t> should be done earli=
er than
                    PRE
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

Take:
int len(int f, int l) {
 return l < f ? 0 : l - f + 1;
}

int lenzero(int f, int l) {
 return len(f, l) =3D=3D 0;
}

int g(); int h();
int lenzero1(int f, int l) {
 if ( len(f, l) =3D=3D 0)
   return g();
  return h();
}

we should be able to optimize lenzero at -O1 but don't.  lenzero1 is optimi=
zed
at -O1 because dom is able to jump thread.
The difference in IR is:
  # iftmp.0_9 =3D PHI <0(2), iftmp.0_8(3)>
  _2 =3D iftmp.0_9 =3D=3D 0;

vs:
  # iftmp.0_13 =3D PHI <0(2), iftmp.0_12(3)>
  if (iftmp.0_13 =3D=3D 0)

at -O2 PRE is enabled which does the optimization.
This is similar to spaceship_replacement in tree-ssa-phiopt but a more gene=
ral
statement of the problem.=