[llvm] [RISCV] Add isel special case for (and (shl X, c2), c1) -> (slli_uw (srli x, c4-c2), c4). (PR #91638)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

> > LGTM.
> 
> Are the results better now? Was that the only issue?
> 

Yeah, I confirmed that all regressions have been fixed :)
See https://github.com/dtcxzyw/llvm-codegen-benchmark/commit/5c1d00242e58f98cce06ff7e35137209e8f45bff


https://github.com/llvm/llvm-project/pull/91638