[llvm] [AMDGPU][Scheduler] Fix inconsistent MI slots after rematerialization revert (PR #180646)

[Dark Steve via llvm-commits]

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@@ -3109,30 +3085,66 @@ void PreRARematStage::finalizeGCNSchedStage() {
     commitRematerializations();
     return;
   }
+
+  // It is possible that re-scheduling lowers occupancy over the one achieved
+  // just through rematerializations, in which case we revert re-scheduling in
+  // all regions but do not roll back rematerializations.
+  const bool ShouldRollbackRemats = AchievedOcc < *TargetOcc;
+
+  // When we both need to revert re-scheduling and rollback rematerializations,
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PrasoonMishra wrote:

What about when we are not rolling back the remats but reverting re-scheduling? Won't DefMIs still be DBG_VALUE during the revert, leading to the stale slot issue?

https://github.com/llvm/llvm-project/pull/180646