[llvm] [AMDGPU] Physical register tracking in GCN trackers. (PR #177223)

[Dhruva Chakrabarti via llvm-commits]

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dhruvachak wrote:

Callers of getLiveRegs probably expect only virtual registers, so if we unified the representation to contain both physical and virtual registers, the callers would have to be modified. It seemed cleaner to not have to touch existing code as much as possible.

https://github.com/llvm/llvm-project/pull/177223