[llvm] [AMDGPU][Scheduler] Scoring system for rematerialization candidates (PR #153092)

[Lucas Ramirez via llvm-commits]

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@@ -2086,65 +2327,93 @@ void PreRARematStage::rematerialize() {
             assert((SR.LaneMask & UncoveredLanes).none());
         }
       }
+    }
 #endif
 
-      // The register is no longer a live-in in all regions but the one that
-      // contains the single use. In live-through regions, maximum register
-      // pressure decreases predictably so we can directly update it. In the
-      // using region, maximum RP may or may not decrease, so we will mark it
-      // for re-computation after all materializations have taken place.
-      LaneBitmask PrevMask = RegionLiveIns[Reg];
-      RegionLiveIns.erase(Reg);
-      RegMasks.insert({{I, Remat.RematMI->getOperand(0).getReg()}, PrevMask});
-      if (Remat.UseMI->getParent() != DAG.Regions[I].first->getParent())
-        DAG.Pressure[I].inc(Reg, PrevMask, LaneBitmask::getNone(), DAG.MRI);
-      else
-        RecomputeRP.insert(I);
+    // This save is guaranteed in regions in which the register is live-through
+    // and unused but optimistic in all other regions where the register is
+    // live.
+    RPTargets[I].saveReg(Reg, Remat.Mask, DAG.MRI);
+    DAG.LiveIns[I].erase(Reg);
+    DAG.RegionLiveOuts.getLiveRegsForRegionIdx(I).erase(Reg);
+    if (!Remat.isUnusedLiveThrough(I))
+      RecomputeRP.set(I);
+  }
+
+  DAG.deleteMI(Remat.DefRegion, &DefMI);
+  RescheduleRegions |= Remat.Live;
+}
+
+void PreRARematStage::rollback(const RollbackInfo &Rollback,
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lucas-rami wrote:

I am not finding a way to make the rematerialized MIs "transparent" to the scheduler during rescheduling post-remat. In particular, I don't think there is a way that I can make the unused defined register not contribute to RP, and this is causing regressions in some tests. Am I missing a way to do that cleanly?

https://github.com/llvm/llvm-project/pull/153092