[llvm] [RISCV][llvm-exegesis] Add missing operand frm for FCVT_D_W (PR #149989)

[Jim Lin via llvm-commits]

tclin914 wrote:

> It looks like before this produced a malformed instruction?
> 
> I would guess that the verifier should be catching an issue like this, which means that there are two reasons (assuming I'm understanding things correctly) this wasn't caught earlier:
> 
> 1. There isn't test coverage in exegesis that is actually exercising this code path and running the verifier over it. In that case we should add some.
> 2. The verifier isn't catching this. That would be weird though given this is a simple operand count mismatch and should be trivial to catch...

Thanks for the suggestion. I've added a test case that shows how the register setup code snippet looks to ensure the code path is verified.

https://github.com/llvm/llvm-project/pull/149989