[llvm] [AMDGPU][Scheduler] Fix non-monotonic SlotIndex after schedule revert (PR #192039)

[via llvm-commits]

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@@ -2210,6 +2213,18 @@ void GCNSchedStage::modifyRegionSchedule(unsigned RegionIdx,
       if (NonDebugReordered)
         DAG.LIS->handleMove(*MI, true);
     } else {
+      // MI is already at the expected position. However, earlier splices in
+      // this loop may have changed neighboring slot indices, so this MI's
+      // slot index can become non-monotonic w.r.t. the physical MBB order.
+      // Only re-seat when monotonicity is actually violated to avoid
+      // unnecessary LiveInterval changes that could perturb scheduling.
+      if (!MI->isDebugInstr() && !MI->isBundled() &&
+          DAG.LIS->getSlotIndexes()->hasIndex(*MI)) {
+        SlotIndex MI_Idx = DAG.LIS->getInstructionIndex(*MI);
+        SlotIndex PrevIdx = DAG.LIS->getSlotIndexes()->getIndexBefore(*MI);
+        if (PrevIdx >= MI_Idx)
+          DAG.LIS->handleMove(*MI, true);
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michaelselehov wrote:

Done

https://github.com/llvm/llvm-project/pull/192039