[llvm] [AArch64] Optimize vector slide shuffles with zeros to use shift instructions (PR #185170)

[David Green via llvm-commits]

davemgreen wrote:

Hello. I presume I meant because these are failing in the precommit CI and need updating:
LLVM.CodeGen/AArch64/ext-narrow-index.ll
LLVM.CodeGen/AArch64/fp-conversion-to-tbl.ll
If that is incorrect (or even if it is not), can you give it a rebase too?

https://github.com/llvm/llvm-project/pull/185170