[llvm] [GlobalISel] [AArch64] Skip redundant shift amount masking during isel (PR #223136)

[Deepak Shirke via llvm-commits]

deepakshirkem wrote:

@davemgreen I have  opened the PRs covering these cases. I also experimented with removing tryShiftAmountMod a few cases still remain, but they look achievable and could be handled incrementally.

Would you be open to landing these wins as they are now, or would you prefer I make sure the full removal works with no regressions before we proceed?

https://github.com/llvm/llvm-project/pull/223136