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

[Matt Arsenault via llvm-commits]

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@@ -430,28 +593,44 @@ bool GCNDownwardRPTracker::reset(const MachineInstr &MI,
   return true;
 }
 
-bool GCNDownwardRPTracker::advanceBeforeNext() {
+bool GCNDownwardRPTracker::advanceBeforeNext(MachineInstr *MI,
+                                             bool UseInternalIterator,
+                                             LiveIntervals *TheLIS) {
   assert(MRI && "call reset first");
-  if (!LastTrackedMI)
-    return NextMI == MBBEnd;
-
-  assert(NextMI == MBBEnd || !NextMI->isDebugInstr());
+  SlotIndex SI;
+  LiveIntervals *CurrLIS;
+  MachineInstr *CurrMI;
+  if (UseInternalIterator) {
+    if (!LastTrackedMI)
+      return NextMI == MBBEnd;
+
+    assert(NextMI == MBBEnd || !NextMI->isDebugInstr());
+    CurrLIS = const_cast<LiveIntervals *>(&LIS);
+    CurrMI = const_cast<MachineInstr *>(LastTrackedMI);
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arsenm wrote:

Can you avoid const_cast

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