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 B94063858D37; Tue, 24 Oct 2023 06:01:49 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org B94063858D37
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1698127309;
	bh=q+ut59qv3m8yg6Mojqbq0byfKmLIhyy2vMt9o3qE/sQ=;
	h=From:To:Subject:Date:From;
	b=klOqjjCOddTV0+XM4jjl1eGOHYpZY7xFqdGODvaqy8evwa9U6gR+3X1Dd/M6YmERb
	 xwtoRpyTSsguKTjH0Z3nU/txjcGNhzNSf0Mi7ibhDHV8co4Urj7tjWtSNWuZD9qq2+
	 m/3AXX2rgsG0gFbBKZKSELsXUbnD+UWINCWJqCpg=
From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/111949] New: combine split points are not so good with
 targets that have (and (not x) y)
Date: Tue, 24 Oct 2023 06:01:49 +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: 14.0
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 cf_gcctarget
Message-ID: <bug-111949-4@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=3D111949

            Bug ID: 111949
           Summary: combine split points are not so good with targets that
                    have (and (not x) y)
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---
            Target: aarch64

Take:
```
bool f1(int a, bool b)
{
        int c =3D a & b;
        return (c ^ a)&1;
}
```
Currently GCC produces:
```
        and     w1, w1, 255
        bic     w0, w0, w1
        and     w0, w0, 1
```

Notice how there are 2 and.

If we look at combine dumps we will see:
Trying 3, 8 -> 10:
    3: r98:SI=3Dzero_extend(x1:QI)
      REG_DEAD x1:QI
    8: r101:SI=3D~r98:SI&r103:SI
      REG_DEAD r98:SI
      REG_DEAD r103:SI
   10: r102:SI=3Dr101:SI&0x1
      REG_DEAD r101:SI
Failed to match this instruction:
(set (reg:SI 102)
    (and:SI (and:SI (not:SI (reg:SI 1 x1 [ b ]))
            (reg:SI 103))
        (const_int 1 [0x1])))
Successfully matched this instruction:
(set (reg:SI 101)
    (not:SI (reg:SI 1 x1 [ b ])))
Failed to match this instruction:
(set (reg:SI 102)
    (and:SI (and:SI (reg:SI 101)
            (reg:SI 103))
        (const_int 1 [0x1])))

The first part is good but the second part is not so good and shows that
combine not finding a good split point and using:
(and:SI (not:SI (reg:SI 1 x1 [ b ])) (reg:SI 103))
as the point how to split the above instruction.

(note I don't know if this should be a generic change or a target specific =
one
off hand, just filing it to keep track of what missed optimization I found)=
.=