[AArch64][SVE] Combine UXT[BHW] intrinsics to AND. (#137956)

This patch combines uxt[bhw] intrinsics to and_u when the governing
predicate is all-true or the passthrough is undef (e.g. in cases of
``unknown'' merging). This improves code gen as the latter can be
emitted as AND immediate instructions.

For example, given:
```cpp
svuint64_t foo(svuint64_t x) {
  return svextb_z(svptrue_b64(), x);
}
```

Currently:
```gas
foo:
  ptrue   p0.d
  movi    v1.2d, #0000000000000000
  uxtb    z0.d, p0/m, z0.d
  ret
```

Becomes:
```gas
foo:
  and     z0.d, z0.d, #0xff
  ret
```

0 files changed, 0 insertions, 0 deletions