[llvm] [RISCV] Add DAG combine for forming VAADDU_VL from VP intrinsics. (PR #124848)

[Luke Lau via llvm-commits]

lukel97 wrote:

> > LGTM
> > Could we also do this after legalization and try and match it on `TRUNCATE_VECTOR_VL`? That way we would also match fixed length vectors.
> 
> Don't we have a generic DAGCombine for fixed vectors using non-VP operations?

Yeah but this would be for fixed length VP operations. Just putting the idea out there

https://github.com/llvm/llvm-project/pull/124848