[llvm] [AMDGPU] GCNRegPressure printing pass for testing. (PR #70031)

[Valery Pykhtin via llvm-commits]

vpykhtin wrote:

Improved version:

* added live-through registers sets.
* added check if tracked live register set matches the set reported by LiveIntervals.
* debug values on BB boundaries are correctly skipped now.
* minimized special processing of empty basic blocks (I had to modify upward tracker interface).
* added testcase to illustrate LiveIntervals problem with undefined subregs,
  please take a look at upward_problem_lis_subregs_mismatch testcase.
* other review issues solved.

I decided to leave separate passes for upward and downward trackers.

This is close to the final version but I need to try running this pass with llc lit tests.

https://github.com/llvm/llvm-project/pull/70031