[Bug target/113537] ext should be used more for __builtin_shufflevector

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113537

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
One gimple level thing I noticed is we produce:
```
  _1 = VEC_PERM_EXPR <a_2(D), a_2(D), { 1, 2, 3, 4, 5, 6, 7, 8, 8, 9, 10, 11,
12, 13, 14, 15 }>;
  _3 = BIT_FIELD_REF <_1, 64, 0>;
```

But Maybe that should just be:
```
_3 = VEC_PERM_EXPR <a_2(D), a_2(D), { 1, 2, 3, 4, 5, 6, 7, 8} >;
```

Which is what the vector might produce but maybe it is because
aarch64_vectorize_vec_perm_const does not know how to handle that ...