[llvm] [WIP][CodeGen] Encode liveness for COPY instructions after virtRegRewriter pass. (PR #151123)

[Vikash Gupta via llvm-commits]

vg0204 wrote:

> I've been thinking of introducing a COPY for a lanemask as a substitute for the copy bundles splitkit produces, but it should be a separate opcode instead of acting like an implicit operand on COPY.
> 
> I think you should introduce the new operand type first, then the opcode separately from touching VirtRegMap

Sure, could you review the next PR related to it (#151124 ), dealing with using this livenewss to expand COPYs!

https://github.com/llvm/llvm-project/pull/151123