[llvm] [CodeGen] Add laneBitmask as new MachineOperand type, utilised by newly defined COPY_LANEMASK instruction (PR #151944)

[Matt Arsenault via llvm-commits]

arsenm wrote:

My main concern with adding the new type of copy is making sure MachineInstr::getRegClassConstraint works correctly when a specific subclass is needed to represent the subregister copies. Right now with the expanded bundle, the subreg is applied when computing the effective class constraint but that will be hidden with the lane mask 

https://github.com/llvm/llvm-project/pull/151944