[llvm] [AMDGPU] Introduce Next-Use Analysis for SSA-based Register Allocation (PR #156079)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> heads up! this is going to be landed soon! @arsenm, @dstutt please let me know if you have any objections.

This shall not land without proper full review 

https://github.com/llvm/llvm-project/pull/156079