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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] Missing `VEC_PERM_EXPR <{a, CST},
 CST, {0, 1, 2, ...}>` optimization
Date: Tue, 06 Feb 2024 17:05:46 +0000
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X-Bugzilla-Component: tree-optimization
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113677

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note it is not just about constants either.
Take:
```
#define vect64 __attribute__((vector_size(8) ))
#define vect128 __attribute__((vector_size(16) ))

vect128 unsigned int f(vect64 unsigned int a, vect64 unsigned int b)
{
  vect64 unsigned int zero=3D{0, 0};
  return __builtin_shufflevector (a, b, 0, 1, 2, 3);
}
```

We get:
```
  _1 =3D {a_3(D), { 0, 0 }};
  _2 =3D {b_4(D), { 0, 0 }};
  _5 =3D VEC_PERM_EXPR <_1, _2, { 0, 1, 4, 5 }>;
```

Which obvious could be done to just:
`_5 =3D {a_3(D), b_4(D)};`=