[llvm] [GISEL][RISCV] Add G_VACOPY GISEL opcode and add lowering code for it. (PR #73066)

[Matt Arsenault via llvm-commits]

arsenm wrote:

I think every generic intrinsic and instruction should have a defined G_* opcode and not route through G_INTRINSIC*. G_INTRINSIC* is for target intrinsics 

https://github.com/llvm/llvm-project/pull/73066