[llvm] [AMDGPU] Stop adding implicit def of superreg in copyPhysReg (PR #125255)

[Matt Arsenault via llvm-commits]

arsenm wrote:

I'm suspecting this is a difference in behavior between MachineVerifier with and without LiveIntervals available. It is significantly more permissive without LiveIntervals with respect to partially defined registers

Do you see any failures in conformance with -O0 and/or EXPENSIVE_ChECKS? 

https://github.com/llvm/llvm-project/pull/125255