[llvm] [AArch64] Enable cmp + csel fusion for Neoverse V2 (PR #94309)

[David Green via llvm-commits]

davemgreen wrote:

> One colleague and I are planning to run some microbenchmarks (including https://github.com/google/fleetbench) and one internal service (with FDO on) to evaluate both cmp + csel and cmp + bcc (already tracked in https://github.com/llvm/llvm-project/pull/90608). Meanwhile, please let us know if there are known reasons that cmp + csel isn't enabled in the first place, thanks!

I would be interested in any benchmark results you get. Yes I believe the reasons are much the same as #90608 - this makes a lot of sense on paper but sometimes LLVM's implementation of fusion is a bit too strong and can lead to problems in practice. Or it might just be noise.

Can you add a test case of some sort too?

https://github.com/llvm/llvm-project/pull/94309