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

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 commented:

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...

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