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

[Paul Walker via llvm-commits]

paulwalker-arm wrote:

> * `llvm/test/Transforms/InstCombine/AArch64/sve-intrinsic-uxt.ll` introduces uses of `undef` because that's how ``don't care'' merging is lowered, e.g.: https://godbolt.org/z/6s3vY5f5x.

FYI: I have been investigating whether we can replace these uses of `undef` with `poison` but it's not entirely straightforward. I have a plan but there are several pieces that need completing before I can change clang because otherwise we're likely to see regression in generated code.

https://github.com/llvm/llvm-project/pull/137956