[llvm] [AMDGPU] Add and optionally use GCNIterativeRPTrackers (PR #88797)

[Matt Arsenault via llvm-commits]

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@@ -343,6 +343,48 @@ void GCNRPTracker::reset(const MachineInstr &MI,
   MaxPressure = CurPressure = getRegPressure(*MRI, LiveRegs);
 }
 
+DenseMap<int, GCNRPTracker::LiveRegSet>
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arsenm wrote:

I'm not sure what the key is here. I'm also concerned by building maps for liveness info, that's already encoded in the LiveIntervals. Most of this code is also replicating logic from the generic tracker, and all of this is really hard to get correct. 

https://github.com/llvm/llvm-project/pull/88797