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

[Craig Topper via llvm-commits]

topperc 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?

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