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

[Michael Maitland via llvm-commits]

michaelmaitland wrote:

> 1. It prints out `LLT_invalid` when I have `-debug` flag on when running the test. The invalid information is printed [here](https://github.com/llvm/llvm-project/blob/75d6795e420274346b14aca8b6bd49bfe6030eeb/llvm/lib/CodeGen/LowLevelType.cpp#L47). Do you have any insight? Should it be in my scope of work?

If you could look into this, that would be nice. Do you know what the type *should* be? Why isn't it `isValid()` ? Maybe you can address this in another patch if it isn't too much work?

> What do you think to tackle with fractional `LMUL`?

You should test types that result in all the different LMULs. `<vscale x N x M>` encodes LMUL information in it. Check it out [here](https://github.com/llvm/llvm-project/blob/75d6795e420274346b14aca8b6bd49bfe6030eeb/llvm/lib/Target/RISCV/RISCVRegisterInfo.td#L257)

If you have tests for the relevant LLVM types, you end up testing all the LMUL values. It would be great if you can add tests  for all the types we want to legalize, and support legalization of those types.

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