[llvm] [AMDGPU] NFC: Provide RPTracker interface for external iterators (PR #93088)

[Jeffrey Byrnes via llvm-commits]

jrbyrnes wrote:

> > In the latest, I've ported over RP speculation code from the generic trackers to GCN Trackers. While this does introduce code duplication, I thought this to be the better approach than to try to support subreg liveness in generic speculation and introduce generic tracker copies per speculation.
> 
> The generic tracker really just should support subregister liveness

That is most likely the next step of this work. 

In order to enable the GCNTrackers by default, in order to save compile time, we would need to modify the scheduler to allow for a mode whcih enables RP tracking but disables the generic RPTracker. 

I think it probably makes more sense to just improve the accuracy of the generic trackers as you suggest. The purpose of this PR then is to provide access to the improvements while the longer term solution is being worked out.

https://github.com/llvm/llvm-project/pull/93088