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

[Matt Arsenault via llvm-commits]

arsenm wrote:

> What exactly is the `liveness verification` mentioned here and in the patch [e56e902](https://github.com/llvm/llvm-project/commit/e56e9022bc54c575ad8ecc3934e9cf84b8542e62)? Is there any codegen pass that verifies the liveness of tuple and their subregs when a Pseudo instruction for tuples is expanded into smaller chunks? 

It's just MachineVerifier 



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