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

[David Green via llvm-commits]

https://github.com/davemgreen commented:

> You're right that tryShiftAmountMod handles more complex cases. The current SelectShiftMask only handles the simple AND mask case. Replacing tryShiftAmountMod entirely with the ComplexPattern approach would require expanding SelectShiftMask to handle all those cases. Can this be done as a follow-up patch if that works for you?

Have you tried to implement this to make sure it works in all cases? I'm just trying to make sure we don't get half way into this and then figure out it doesn't work very well.

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