[llvm] [RISCV][GlobalISel] Vector Extension vadd Legalizer (PR #71400)

[Michael Maitland via llvm-commits]

michaelmaitland wrote:

> My main pet peeve with scalable vectors is that the binops only take two parameters and there is no space for masks resp. predicates today.
> 
> https://github.com/llvm/llvm-project/blob/521ac12a251e7cf88d3b304186081de31a7503be/llvm/include/llvm/Target/GenericOpcodes.td#L262

I don't think the `add` instruction has any ability for masking, so I'm not sure that this comment is relevant to this PR. When we want to lower `vp.add` though, then I think we will need to address this problem by either extending G_ADD to take VL and Mask, or to add a G_VP_ADD type opcode.

https://github.com/llvm/llvm-project/pull/71400