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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/114277] New: Missed optimization: x*(x||b) =>
 x
Date: Fri, 08 Mar 2024 05:31:04 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 14.0
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X-Bugzilla-Severity: normal
X-Bugzilla-Who: 652023330028 at smail dot nju.edu.cn
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114277

            Bug ID: 114277
           Summary: Missed optimization: x*(x||b) =3D> x
           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
(x*(x||b) =3D> x), but gcc -O3 missed it.

https://godbolt.org/z/W8xYrGdej

int a,b;
void func(int x){
    a=3Dx*(x||b);
}

GCC -O3:
func(int):
        mov     eax, edi
        or      eax, DWORD PTR b[rip]
        mov     eax, 0
        cmove   edi, eax
        mov     DWORD PTR a[rip], edi
        ret

Expected code:
func(int):
        mov     DWORD PTR a[rip], edi
        ret

Surprisingly, GCC optimizes as expected for the following slightly more com=
plex
code:
int c;
void func2(int x){
    a=3Dx*(x||(b&&c));
}
func2(int):
        mov     DWORD PTR a[rip], edi
        ret

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