[llvm] [RISCV] Match mul_vl(v, (add_vl v1, splat 1)) to vmadd_vl (PR #71495)

[Liao Chunyu via llvm-commits]

ChunyuLiao wrote:

> Can we do this in DAGCombine? We already have a large MatcherTable now.
> And scalable tests are needed too.

Thanks, I can implement this feature in DAGCombine. I'd like to get more advice on which of these two ways is better.
But it seems a backend tends to use td? I can't find the source now.

https://github.com/llvm/llvm-project/pull/71495