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From: "652023330028 at smail dot nju.edu.cn" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/114009] New: Missed optimization: (!a) * a =>
 0 when a=(a/2)*2
Date: Tue, 20 Feb 2024 10:16:58 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 14.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114009

            Bug ID: 114009
           Summary: Missed optimization: (!a) * a =3D> 0 when a=3D(a/2)*2
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: 652023330028 at smail dot nju.edu.cn
  Target Milestone: ---

Hello, we noticed that the code below can be optimized as stated in the tit=
le
((!a) * a =3D> 0), but gcc -O3 missed it.

Different from PR 113716, this example can be optimized under the option of=
 gcc
-O3 -fwrapv. At the same time, their patterns are different.

https://godbolt.org/z/GrPY1d6o3

int w;
void func(int a) {
    a =3D (a/2)*2;
    w =3D (!a) * a;
}

GCC -O3 :
func(int):
        mov     eax, edi
        xor     edx, edx
        shr     eax, 31
        add     eax, edi
        add     edi, 1
        sar     eax
        cmp     edi, 2
        cmova   eax, edx
        add     eax, eax
        mov     DWORD PTR w[rip], eax
        ret

Expected code (GCC -O3 -fwrapv):
func(int):
        mov     DWORD PTR w[rip], 0
        ret

Thank you very much for your time and effort! We look forward to hearing fr=
om
you.=