[llvm] [RISCV][GISel] Support G_MERGE_VALUES/G_UNMERGE_VALUES with Zfa. (PR #120379)

[Amara Emerson via llvm-commits]

aemerson wrote:

> I'm not sure if its a good idea to make GINodeEquiv between a target independent generic opcode and a target dependent SelectionDAG opcode. Similar is done on Mips. And I saw some G_LOAD/G_STORE equivalents in AMDGPU so maybe it's ok?

Is the general case of merge/unmerge really a 1-1 semantic mapping with your target node? If not I wouldn't advise going down this route, maybe lowering them into something more specific and then specifying the node equivalence would be a more precise route.

https://github.com/llvm/llvm-project/pull/120379