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

[Lucas Ramirez via llvm-commits]

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@@ -369,6 +369,9 @@ class GCNSchedStage {
   // RP after scheduling the current region.
   GCNRegPressure PressureAfter;
 
+  // Whether checkScheduling reverted the schedule for the current region.
+  bool ScheduleReverted = false;
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lucas-rami wrote:

This is also removable after `PreRARematStage::RegionSchedRevert::AlreadyReverted` is deleted.

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