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 6EB413858D1E; Thu, 28 Mar 2024 18:09:23 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 6EB413858D1E
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1711649363;
	bh=FRwWG6gP17q68ymluqKHc2FAqyyyjiiHKYsYzj2kphk=;
	h=From:To:Subject:Date:From;
	b=ooT/seZ5EiN+g/qF7Vkn8dAF7gr+EFIf/i7q/oSY4JAKA+0mj1wjtE8iDjUViEDlW
	 g+VW6miPmS3IiXOb5KZv8W1MXD1GwQQIWjGiBI/2GsMUSEJ8HtsjSYn26pYlTp8x88
	 LFwuZbV3yVgLL7eG5OA99HB6nbBDmqmyovLkKg+g=
From: "goon.pri.low at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/114524] New: Use less expensive expression
 when expressions are equal
Date: Thu, 28 Mar 2024 18:09:23 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: rtl-optimization
X-Bugzilla-Version: 14.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: goon.pri.low 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-114524-4@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=3D114524

            Bug ID: 114524
           Summary: Use less expensive expression when expressions are
                    equal
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: goon.pri.low at gmail dot com
  Target Milestone: ---

When we know multiple expressions are equal, we should only evaluate the le=
ast
expensive one.

Example functions:

int a(int b, int *restrict c) {
    if (b !=3D *c) __builtin_unreachable();
    return *c;
}

int b(int b, int c) {
    if (b !=3D c + 1) __builtin_unreachable();
    return c + 1;
}

int c(int b, struct {int a; int b;} c) {
    if (b !=3D c.b) __builtin_unreachable();
    return c.b;
}

int d(int b, int c) {
    if (b * 44 !=3D c / 10) __builtin_unreachable();
    return c / 10;
}

Generated assembly:

a:
        mov     eax, DWORD PTR [rsi]
        ret
b:
        lea     eax, [rsi+1]
        ret
c:
        shr     rsi, 32
        mov     eax, esi
        ret
d:
        movsx   rax, esi
        sar     esi, 31
        imul    rax, rax, 1717986919
        sar     rax, 34
        sub     eax, esi
        ret

Optimal assembly (clang)

a:                                      # @a
        mov     eax, edi
        ret
b:                                      # @b
        mov     eax, edi
        ret
c:                                      # @c
        mov     eax, edi
        ret
d:                                      # @d
        imul    eax, edi, 44
        ret=