[llvm] [AArch64] Take cmn into account when adjusting compare constants (PR #98634)

[via llvm-commits]

AtariDreams wrote:

> Sorry for the delay. I have been busy with some other things and this code isn't something I know super well. It sounds OK to me. Do you have any example of where it does reduce the number of instructions?

Yes but it can't be part of this PR because it requires another PR to be merged after this one to do that. 

The PR in question alone doesn't change anything without this. It's a different PR because that PR does additional cmn folds, whereas this just has more accurate profitability checks that reflect the changes to be made.

https://github.com/llvm/llvm-project/pull/98634