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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/104551] [12 Regression] Wrong code with -O3
 for skylake-avx512, icelake-server, and sapphirerapids
Date: Tue, 15 Feb 2022 23:21:13 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104551

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
            Summary|Wrong code with -O3 for     |[12 Regression] Wrong code
                   |skylake-avx512,             |with -O3 for
                   |icelake-server, and         |skylake-avx512,
                   |sapphirerapids              |icelake-server, and
                   |                            |sapphirerapids
   Target Milestone|---                         |12.0
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2022-02-15

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed, single file version:
unsigned int var_11 =3D 16U;
unsigned int var_178 =3D 0;
unsigned char arr_492 [128];
[[gnu::noipa]]
void test() {
  for (bool a =3D 0; a < (bool)var_11; a =3D 2)
    for (unsigned b =3D 0; b < var_11;
         b +=3D 1)
      var_178 =3D arr_492[b] ? arr_492[b] : (char) b;
}
int main() {
    for (int i =3D 0; i < 128; ++i)
        arr_492 [i] =3D (unsigned char)128;
    test();
    __builtin_printf("%u\n", var_178);
    if (var_178 !=3D 128)
        __builtin_abort();
    return 0;
}

----- CUT -----

I increasing the array size to 128 allowed me to merge it, I don't know why
though; maybe because it allowed the code to be vectorize while 16 was not
going to.=