[llvm] [AMDGPU] Add IR LiveReg type-based optimization (PR #66838)

[Matt Arsenault via llvm-commits]

arsenm wrote:

How does this compare to the usage of https://github.com/llvm/llvm-project/blob/3684a38d33d7643fe8c3a870006efa8677ac37f8/llvm/include/llvm/CodeGen/TargetLowering.h#L2869 in generic CodeGenPrepare? 

https://github.com/llvm/llvm-project/pull/66838