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From: "i.nixman at autistici dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/107546] New: simd, redundant pcmpeqb and pxor
Date: Mon, 07 Nov 2022 06:39:28 +0000
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X-Bugzilla-Component: rtl-optimization
X-Bugzilla-Version: 12.2.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107546

            Bug ID: 107546
           Summary: simd, redundant pcmpeqb and pxor
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: i.nixman at autistici dot org
  Target Milestone: ---

Hello,

this code sample(https://godbolt.org/z/TnGMsfMs6):
```
#include <x86intrin.h>

auto foo(const char *p) {
    const auto substr =3D _mm_loadu_si128((const __m128i *)p);
    return _mm_cmplt_epi8(substr, _mm_set1_epi8('0'));
}

```
produces the following ASM code:
```
1: foo(char const*):
2:    movdqu  xmm0, XMMWORD PTR [rdi]
3:    pxor    xmm1, xmm1
4:    pcmpgtb xmm0, XMMWORD PTR .LC0[rip]
5:    pcmpeqb xmm0, xmm1
6:    ret
```
please look at line 5.
is there any reason for `pcmpeqb` and `pxor` instruction?

just for info, clang's output(https://godbolt.org/z/MPnvEMdhr):
```
1: foo(char const*):
2:    movdqu  xmm1, xmmword ptr [rdi]
3:    movdqa  xmm0, xmmword ptr [rip + .LCPI0_0]
4:    pcmpgtb xmm0, xmm1
5:    ret
```

it looks like the issue started at version 9 and up to the current trunk.=