[llvm] [InstCombine] Use known bits to simplify mask in foldSelectICmpAnd (PR #128741)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

> Thanks, I incorporated the code comments. For the alive proof did you have a specific generalization in mind? I'm not quite sure how to use/represent known bits and `isPowerOf2` there.

You can use `@llvm.assume`:
```
%ctpop = call i32 @llvm.ctpop.i32(i32 %pow2)
%is_pow2 = icmp eq i32 %ctpop, 1
call void @llvm.assume(i1 %is_pow2)
```


https://github.com/llvm/llvm-project/pull/128741