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

[Matt Arsenault via llvm-commits]

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@@ -616,11 +644,24 @@ GCNScheduleDAGMILive::getBBLiveInMap() const {
   return getLiveRegMap(BBStarters, false /*After*/, *LIS);
 }
 
+DenseMap<MachineInstr *, GCNRPTracker::LiveRegSet>
+GCNScheduleDAGMILive::getBBLiveOutMap() const {
+  assert(!Regions.empty());
+  std::vector<MachineInstr *> BBEnders;
+  BBEnders.reserve(Regions.size());
+  auto I = Regions.rbegin(), E = Regions.rend();
+  for (; I != E; I++)
+    BBEnders.push_back(getLastMIForRegion(I->first, I->second));
+
+  return getLiveRegMap(BBEnders, true /*After*/, *LIS);
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arsenm wrote:

```suggestion
  return getLiveRegMap(BBEnders, /*After=*/true, *LIS);
```

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