[llvm] [RISCV] Generalize (sub zext, zext) -> (sext (sub zext, zext)) to add (PR #86248)

[Craig Topper via llvm-commits]

topperc wrote:

> LGTM as well.
> 
> Minor, but what is the "ve" abbreviation you use everywhere? You should probably spell that out.

I think +ve means positive and -ve means negative. https://en.wiktionary.org/wiki/%2Bve

https://github.com/llvm/llvm-project/pull/86248