[llvm] [RISCV] Don't cost Fmv for Zfinx in isFPImmLegal. (PR #107361)

[Craig Topper via llvm-commits]

topperc wrote:

> LGTM
> 
> Though, I vaguely remember looking at this before and deciding not to do this because of some kind of negative interaction. Unfortunately, I don't remember details, and it's not a configuration I care much about, so it might not have been anything particularly major. I don't spot anything in the diffs now, so hopefully I'm just misremembering?

I didn't see anything in the diffs either. It's also not a config I care much about either. I'm looking into adding subregisters for 16 and 32 bit GPR sub-registers. Initially for Hinx/Finx, but I want to see if we can use 32-bit GPR sub-register for W instructions. Doing this lost some of the RISCVISD::FMV_X_ANYEXTH/FMV_X_ANYEXTW nodes that we recently added constant folding for. Lowering the cost helps preserve some cases.

https://github.com/llvm/llvm-project/pull/107361