[llvm] [AArch64] Improve fixed vector lowering for cttz/ctlz when sve (PR #192427)

[Paul Walker via llvm-commits]

paulwalker-arm wrote:

Is it possible to split the PR into multiple commits so the first commit contains the tests. That will make it much easier to see the effect of the code changes.

https://github.com/llvm/llvm-project/pull/192427