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

[Craig Topper via llvm-commits]

topperc wrote:

> LGTM.

Are the results better now? Was that the only issue?

I'll add a test for that case before I commit.

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