[llvm] [AMDGPU] Add AGPR pressure tracking (PR #214745)

[Romanov Vlad via llvm-commits]

romanovvlad wrote:

> AV pressure is kind of a parallel thing to A or V pressure; it should probably be separately tracked

This patch doesn't change how AV pressure is tracked. It only adds AGPR pressure tracking.
Please, let me know if you think the patch should be adjusted.

https://github.com/llvm/llvm-project/pull/214745