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From: "tilkax at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/104992] New: [missed optimization] x / y * y == x not optimized to x % y == 0
Date: Sun, 20 Mar 2022 15:19:25 +0000	[thread overview]
Message-ID: <bug-104992-4@http.gcc.gnu.org/bugzilla/> (raw)

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104992

            Bug ID: 104992
           Summary: [missed optimization] x / y * y == x not optimized to
                    x % y == 0
           Product: gcc
           Version: 11.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tilkax at gmail dot com
  Target Milestone: ---

This is especially helpful for constant y because checking
division-by-a-constant remainders against zero allows further optimization.

Repro case:

unsigned foo(unsigned x, unsigned y)
{
    return x / y * y == x;
}

GCC -O3:
        mov     eax, edi
        xor     edx, edx
        div     esi
        mov     eax, edi
        sub     eax, edx
        cmp     eax, edi
        sete    al
        movzx   eax, al
        ret

Clang -O3:
        mov     eax, edi
        xor     edx, edx
        div     esi
        xor     eax, eax
        test    edx, edx
        sete    al
        ret

             reply	other threads:[~2022-03-20 15:19 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-03-20 15:19 tilkax at gmail dot com [this message]
2022-03-20 20:25 ` [Bug tree-optimization/104992] " pinskia at gcc dot gnu.org
2022-03-21  9:37 ` rguenth at gcc dot gnu.org
2022-08-01 13:24 ` cvs-commit at gcc dot gnu.org
2022-08-03 16:00 ` seurer at gcc dot gnu.org
2022-08-11  8:29 ` cvs-commit at gcc dot gnu.org
2024-01-23 12:12 ` xry111 at gcc dot gnu.org

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