[llvm] [AMDGPU][MISCHED] GCNBalancedSchedStrategy. (PR #66634)

[via llvm-commits]

================
@@ -981,193 +978,52 @@ void GCNSchedStage::checkScheduling() {
   }
 }
 
-unsigned
-GCNSchedStage::computeSUnitReadyCycle(const SUnit &SU, unsigned CurrCycle,
-                                      DenseMap<unsigned, unsigned> &ReadyCycles,
-                                      const TargetSchedModel &SM) {
-  unsigned ReadyCycle = CurrCycle;
-  for (auto &D : SU.Preds) {
-    if (D.isAssignedRegDep()) {
-      MachineInstr *DefMI = D.getSUnit()->getInstr();
-      unsigned Latency = SM.computeInstrLatency(DefMI);
-      unsigned DefReady = ReadyCycles[DAG.getSUnit(DefMI)->NodeNum];
-      ReadyCycle = std::max(ReadyCycle, DefReady + Latency);
-    }
-  }
-  ReadyCycles[SU.NodeNum] = ReadyCycle;
-  return ReadyCycle;
-}
-
-#ifndef NDEBUG
-struct EarlierIssuingCycle {
-  bool operator()(std::pair<MachineInstr *, unsigned> A,
-                  std::pair<MachineInstr *, unsigned> B) const {
-    return A.second < B.second;
-  }
-};
-
-static void printScheduleModel(std::set<std::pair<MachineInstr *, unsigned>,
-                                        EarlierIssuingCycle> &ReadyCycles) {
-  if (ReadyCycles.empty())
-    return;
-  unsigned BBNum = ReadyCycles.begin()->first->getParent()->getNumber();
-  dbgs() << "\n################## Schedule time ReadyCycles for MBB : " << BBNum
-         << " ##################\n# Cycle #\t\t\tInstruction          "
-            "             "
-            "                            \n";
-  unsigned IPrev = 1;
-  for (auto &I : ReadyCycles) {
-    if (I.second > IPrev + 1)
-      dbgs() << "****************************** BUBBLE OF " << I.second - IPrev
-             << " CYCLES DETECTED ******************************\n\n";
-    dbgs() << "[ " << I.second << " ]  :  " << *I.first << "\n";
-    IPrev = I.second;
-  }
-}
-#endif
-
-ScheduleMetrics
-GCNSchedStage::getScheduleMetrics(const std::vector<SUnit> &InputSchedule) {
-#ifndef NDEBUG
-  std::set<std::pair<MachineInstr *, unsigned>, EarlierIssuingCycle>
-      ReadyCyclesSorted;
-#endif
-  const TargetSchedModel &SM = ST.getInstrInfo()->getSchedModel();
-  unsigned SumBubbles = 0;
-  DenseMap<unsigned, unsigned> ReadyCycles;
-  unsigned CurrCycle = 0;
-  for (auto &SU : InputSchedule) {
-    unsigned ReadyCycle =
-        computeSUnitReadyCycle(SU, CurrCycle, ReadyCycles, SM);
-    SumBubbles += ReadyCycle - CurrCycle;
-#ifndef NDEBUG
-    ReadyCyclesSorted.insert(std::make_pair(SU.getInstr(), ReadyCycle));
-#endif
-    CurrCycle = ++ReadyCycle;
-  }
-#ifndef NDEBUG
-  LLVM_DEBUG(
-      printScheduleModel(ReadyCyclesSorted);
-      dbgs() << "\n\t"
-             << "Metric: "
-             << (SumBubbles
-                     ? (SumBubbles * ScheduleMetrics::ScaleFactor) / CurrCycle
-                     : 1)
-             << "\n\n");
-#endif
-
-  return ScheduleMetrics(CurrCycle, SumBubbles);
-}
-
-ScheduleMetrics
-GCNSchedStage::getScheduleMetrics(const GCNScheduleDAGMILive &DAG) {
-#ifndef NDEBUG
-  std::set<std::pair<MachineInstr *, unsigned>, EarlierIssuingCycle>
-      ReadyCyclesSorted;
-#endif
-  const TargetSchedModel &SM = ST.getInstrInfo()->getSchedModel();
-  unsigned SumBubbles = 0;
-  DenseMap<unsigned, unsigned> ReadyCycles;
-  unsigned CurrCycle = 0;
-  for (auto &MI : DAG) {
-    SUnit *SU = DAG.getSUnit(&MI);
-    if (!SU)
-      continue;
-    unsigned ReadyCycle =
-        computeSUnitReadyCycle(*SU, CurrCycle, ReadyCycles, SM);
-    SumBubbles += ReadyCycle - CurrCycle;
-#ifndef NDEBUG
-    ReadyCyclesSorted.insert(std::make_pair(SU->getInstr(), ReadyCycle));
-#endif
-    CurrCycle = ++ReadyCycle;
-  }
-#ifndef NDEBUG
-  LLVM_DEBUG(
-      printScheduleModel(ReadyCyclesSorted);
-      dbgs() << "\n\t"
-             << "Metric: "
-             << (SumBubbles
-                     ? (SumBubbles * ScheduleMetrics::ScaleFactor) / CurrCycle
-                     : 1)
-             << "\n\n");
-#endif
-
-  return ScheduleMetrics(CurrCycle, SumBubbles);
-}
-
-bool GCNSchedStage::shouldRevertScheduling(unsigned WavesAfter) {
+bool GCNSchedStage::shouldRevertScheduling(unsigned WavesAfter,
+                                           unsigned WavesBefore) {
   if (WavesAfter < DAG.MinOccupancy)
     return true;
 
   return false;
 }
 
-bool OccInitialScheduleStage::shouldRevertScheduling(unsigned WavesAfter) {
+bool OccInitialScheduleStage::shouldRevertScheduling(unsigned WavesAfter,
+                                                     unsigned WavesBefore) {
   if (PressureAfter == PressureBefore)
     return false;
 
-  if (GCNSchedStage::shouldRevertScheduling(WavesAfter))
----------------
alex-t wrote:

> We need to keep this in order to preserve MaxOccupancy scheduler's behavior, but it should not be the priority for the balanced scheduler. Maybe the balanced scheduler should just have a different initial stage entirely.

If we decide to exactly preserve the MaxOccupancy scheduler's behavior, we'd better write a completely new code for most things. We could try to have a separate set of stages for the balanced scheduler but it still has to communicate with interfaces that are focused on the occupancy. So, I agree that the approach to minimize the existing code changes could be not viable.


https://github.com/llvm/llvm-project/pull/66634