[llvm] [GlobalISel][AArch64] Optimize shl, lshr, ashr (PR #213576)

[Yeongu Choe via llvm-commits]

YeonguChoe wrote:

@davemgreen 

Hi David

Please check if this is correct ISA wise. If you point me anything invalid, I will change the logic in the code.
If this looks okay, then I will update FileCheck comments in 50+ tests.

Thanks.

https://github.com/llvm/llvm-project/pull/213576