[llvm] [RISCV][VLOPT] Add support for vfmerge.vfm and vfmv.v.f (PR #146692)

[Luke Lau via llvm-commits]

lukel97 wrote:

> I have a list of enums from the x60 scheduling model and just did a diff of the enums in isSupportedInstr. I got the following list:

Thanks for compiling that, a lot of those we can't support for correctness like VCOMPRESS and the reductions, but yeah there's some that we should be able to support e.g. VFREC7_V and VRGATHER?

I also think we can do VSLIDEUP/VSLIDEDOWN/VSLIDE1UP, but not VSLIDE1DOWN. I'll work on a patch for those next because those show up with fixed order recurrences in EVL tail folding in the loop vectorizer.

https://github.com/llvm/llvm-project/pull/146692