[llvm] [AArch64] Signed comparison using CMN is safe when the subtraction is nsw (PR #141993)

[via llvm-commits]

AZero13 wrote:

When I remove the nsw check, tests fail, but for all those tests, alive2 says adding nsw to the sub causes no changes?

https://alive2.llvm.org/ce/z/rLPEWF

https://github.com/llvm/llvm-project/pull/141993