[llvm] [WIP][AMDGPU][CopyPhysReg] Expand the COPY instructions using the encoded liveness mask. (PR #151124)

[Jay Foad via llvm-commits]

jayfoad wrote:

> That's the idea that if we ensure that each pass in-between can ensure the correct liveness update, this should hold true to be correct.

I don't see how this can work.

https://github.com/llvm/llvm-project/pull/151124