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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/113677] New: Missing `VEC_PERM_EXPR <{a,
 CST}, CST, {0, 1, 2, ...}>` optimization
Date: Wed, 31 Jan 2024 01:46:29 +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
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: enhancement
X-Bugzilla-Who: pinskia at gcc dot gnu.org
X-Bugzilla-Status: UNCONFIRMED
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113677

            Bug ID: 113677
           Summary: Missing `VEC_PERM_EXPR <{a, CST}, CST, {0, 1, 2,
                    ...}>` optimization
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

Take:
```
#define vect32 __attribute__((vector_size(4) ))
#define vect64 __attribute__((vector_size(8) ))

vect64 unsigned char f(vect32 unsigned char a)
{
  vect32 unsigned char zero=3D{0,0,0,0};
  return __builtin_shufflevector (a, zero, 0, 1, 2, 3, 4, 5, 6, 7);
}

```
On x86_64 this produces:
```
f:
        movd    xmm0, edi
        pxor    xmm1, xmm1
        punpckldq       xmm0, xmm1
        ret
```

We should just produce:
```
        movd    xmm0, edi
        ret
```

In .optimized we get:
```
  _1 =3D {a_2(D), { 0, 0, 0, 0 }};
  _3 =3D VEC_PERM_EXPR <_1, { 0, 0, 0, 0, 0, 0, 0, 0 }, { 0, 1, 2, 3, 8, 9,=
 10,
11 }>;
  return _3;
```


But _3 and _1 are the same ...=