[llvm] [RISCV] Use addi rather than addiw for immediates materialised by lui+addi(w) pairs when possible (PR #141663)

[Craig Topper via llvm-commits]

topperc wrote:

> > I think something like this should work.
> 
> Not sure if it makes sense to break out to a separate PR, but I've added this tentatively to this PR so at least we're all looking at the same thing. I can no longer see any cases of sext.w being introduced looking at the llvm-test-suite diff. I do see one or two odd cases where we end up with `lwu` but didn't before which I need to look into.
> 
> EDIT: the test-suite + SPEC just finished and I get failures on perlbench, so it seems there's a correctness issue here.

Does the failure only appear with my change to RISCVOptWInstrs?

https://github.com/llvm/llvm-project/pull/141663