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

[Vikash Gupta via llvm-commits]

vg0204 wrote:

> > > will be transformed into :
> > > liveins: $vgpr0_lo16, $vgpr0_hi16, $vgpr4, $vgpr5_hi16
> > > Does it make sense, along the line of my doubts just mentioned above?
> > 
> > This is the whole point, re-encode the live-ins in terms of register units
> 
> I think @vg0204's suggestion here was to store the liveins as a minimal covering set of physregs. This has some of the advantages of storing them as regunits, but without needing to implement serialization/deserialization of regunits themselves in MIR.

Not, exactly Jay, as it was the original thing that exists previously before the introduction of laneBitmask as part of liveIn. It conservatively will include those registers which are partially defined as when aimed to represent them as minimal set of physReg. What I really meant to take laneBitmask usage to next level to store only and only liveRegUnits (as MCPhysReg) in LiveIn list

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