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 242B83858C60; Thu,  8 Feb 2024 17:37:04 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 242B83858C60
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1707413824;
	bh=z5NGtn7Rk7DZdsKKl2+ZF89Hmd/8Ps0wb0h7ksaZT+Q=;
	h=From:To:Subject:Date:From;
	b=NbBWIvxdHaBo6it+OzUR4RT0exK2MPGWkarVpXyVt9odkoVp67Uf4cP4jfSFE78iM
	 5TJdzlCNmB9og7e35GUCU8En6SPyTw4QFlksW8H8KzpJ5Nst97JYrT3EjujA3iarfZ
	 YbRXZyFRbPRcXDarPQkZ8lp6LgLCVSjeC6L3nswY=
From: "absoler at smail dot nju.edu.cn" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/113838] New: regression of redundant load
 operation introduced by -fno-tree-forwprop introduce
Date: Thu, 08 Feb 2024 17:37:03 +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: 13.2.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: absoler at smail dot nju.edu.cn
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-113838-4@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=3D113838

            Bug ID: 113838
           Summary: regression of redundant load operation introduced by
                    -fno-tree-forwprop introduce
           Product: gcc
           Version: 13.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: absoler at smail dot nju.edu.cn
  Target Milestone: ---

hi, I have found for the following code, with -O2 option, gcc-10.2.0 will
generate a redundant load, and gcc-13.2.0 won't. However, with an extra fla=
g "
-fno-tree-forwprop", gcc-13.2.0 will produce the same bad code

full code https://godbolt.org/z/objsWGnY6

```
func_37() ...

    l_50[1] =3D &g_51;
    if (((*l_50[1]) ^=3D g_26[5][3][0]))
    { /* block id: 13 */
        int32_t **l_52[5] =3D {&l_50[2],&l_50[2],&l_50[2],&l_50[2],&l_50[2]=
};
        int i;
        (*l_52[4]) =3D (((void*)0 !=3D &g_51) , &g_36[3][4]);
        return p_39;
    }
    else
    { /* block id: 16 */
        int32_t *l_53 =3D &g_54[0][1][1];
        return l_53;
    }
```
```
func_37():
  401d74:       mov    0x364e(%rip),%edx        # 4053c8 <g_26+0x1a8>
func_11():
  401d7a:       mov    %al,0x33d9(%rip)        # 405159 <g_44+0x9>
func_37():
  401d80:       mov    0x33c2(%rip),%eax        # 405148 <g_51>
  401d86:       xor    %eax,%edx
  401d88:       cmp    0x363a(%rip),%eax        # 4053c8 <g_26+0x1a8>
  401d8e:       mov    $0x40510c,%eax
  401d93:       mov    %edx,0x33af(%rip)        # 405148 <g_51>
  401d99:       mov    $0x4051a4,%edx
  401d9e:       cmovne %rdx,%rax
```

the second load of g_26[5][3][0], i.e. "cmp    0x363a(%rip),%eax" can be
optimized away. The better code generated by gcc-13.2.0 is:
```
func_37():
  401e40:       mov    0x3582(%rip),%eax        # 4053c8 <g_26+0x1a8>
  401e46:       mov    %edx,%ecx
  401e48:       xor    %eax,%ecx
  401e4a:       cmp    %eax,%edx
  401e4c:       mov    $0x40510c,%edx
  401e51:       mov    $0x4051a4,%eax
  401e56:       cmove  %rdx,%rax
```=