[llvm] [CodeGen] Utilizing register units based liveIns tracking in MBB (PR #129847)

[Vikash Gupta via llvm-commits]

vg0204 wrote:

> This is missing most of the changes necessary to do this. We need a full migration away from the existing storage as reg + lane mask, to the register units. This requires MIR print and parsing changes, and I'm sure there will be downstream fallout in use sites

So, should I start this as separate task entirely? Also, don't we need MCphysReg mandatorily as part of liveIn representation too, as that is used entirely all over the llvm codegen, as regunits alone cannot hold that sense?

https://github.com/llvm/llvm-project/pull/129847