[llvm] [AMDGPU] NFC: Add BBLiveOutMap & LiveOut Cache (PR #93089)

[Matt Arsenault via llvm-commits]

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@@ -163,13 +163,43 @@ inline raw_ostream &operator<<(raw_ostream &OS, const ScheduleMetrics &Sm) {
   return OS;
 }
 
+class GCNScheduleDAGMILive;
+class RegionPressureMap {
+  GCNScheduleDAGMILive *DAG;
+  // The live in/out pressure as indexed by the first or last MI in the region
+  // before scheduling.
+  DenseMap<MachineInstr *, GCNRPTracker::LiveRegSet> BBLiveRegMap;
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arsenm wrote:

I'm worried this is making the pressure tracking even more complicated and expensive. LiveRegSet already felt wrong, and this adds another level on top of it? 

https://github.com/llvm/llvm-project/pull/93089