lib/CodeGen/ScheduleDAG.cpp

   1 //===---- ScheduleDAG.cpp - Implement the ScheduleDAG class ---------------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This implements the ScheduleDAG class, which is a base class used by
  11 // scheduling implementation classes.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #define DEBUG_TYPE "pre-RA-sched"
  16 #include "llvm/CodeGen/ScheduleDAG.h"
  17 #include "llvm/CodeGen/ScheduleHazardRecognizer.h"
  18 #include "llvm/CodeGen/SelectionDAGNodes.h"
  19 #include "llvm/Target/TargetMachine.h"
  20 #include "llvm/Target/TargetInstrInfo.h"
  21 #include "llvm/Target/TargetRegisterInfo.h"
  22 #include "llvm/Support/CommandLine.h"
  23 #include "llvm/Support/Debug.h"
  24 #include "llvm/Support/raw_ostream.h"
  25 #include <climits>
  26 using namespace llvm;
  27
  28 #ifndef NDEBUG
  29 cl::opt<bool> StressSchedOpt(
  30   "stress-sched", cl::Hidden, cl::init(false),
  31   cl::desc("Stress test instruction scheduling"));
  32 #endif
  33
  34 ScheduleDAG::ScheduleDAG(MachineFunction &mf)
  35   : TM(mf.getTarget()),
  36     TII(TM.getInstrInfo()),
  37     TRI(TM.getRegisterInfo()),
  38     MF(mf), MRI(mf.getRegInfo()),
  39     EntrySU(), ExitSU() {
  40 #ifndef NDEBUG
  41   StressSched = StressSchedOpt;
  42 #endif
  43 }
  44
  45 ScheduleDAG::~ScheduleDAG() {}
  46
  47 /// getInstrDesc helper to handle SDNodes.
  48 const MCInstrDesc *ScheduleDAG::getNodeDesc(const SDNode *Node) const {
  49   if (!Node || !Node->isMachineOpcode()) return NULL;
  50   return &TII->get(Node->getMachineOpcode());
  51 }
  52
  53 /// dump - dump the schedule.
  54 void ScheduleDAG::dumpSchedule() const {
  55   for (unsigned i = 0, e = Sequence.size(); i != e; i++) {
  56     if (SUnit *SU = Sequence[i])
  57       SU->dump(this);
  58     else
  59       dbgs() << "**** NOOP ****\n";
  60   }
  61 }
  62
  63
  64 /// Run - perform scheduling.
  65 ///
  66 void ScheduleDAG::Run(MachineBasicBlock *bb,
  67                       MachineBasicBlock::iterator insertPos) {
  68   BB = bb;
  69   InsertPos = insertPos;
  70
  71   SUnits.clear();
  72   Sequence.clear();
  73   EntrySU = SUnit();
  74   ExitSU = SUnit();
  75
  76   Schedule();
  77
  78   DEBUG({
  79       dbgs() << "*** Final schedule ***\n";
  80       dumpSchedule();
  81       dbgs() << '\n';
  82     });
  83 }
  84
  85 /// addPred - This adds the specified edge as a pred of the current node if
  86 /// not already.  It also adds the current node as a successor of the
  87 /// specified node.
  88 bool SUnit::addPred(const SDep &D) {
  89   // If this node already has this depenence, don't add a redundant one.
  90   for (SmallVector<SDep, 4>::const_iterator I = Preds.begin(), E = Preds.end();
  91        I != E; ++I)
  92     if (*I == D)
  93       return false;
  94   // Now add a corresponding succ to N.
  95   SDep P = D;
  96   P.setSUnit(this);
  97   SUnit *N = D.getSUnit();
  98   // Update the bookkeeping.
  99   if (D.getKind() == SDep::Data) {
 100     assert(NumPreds < UINT_MAX && "NumPreds will overflow!");
 101     assert(N->NumSuccs < UINT_MAX && "NumSuccs will overflow!");
 102     ++NumPreds;
 103     ++N->NumSuccs;
 104   }
 105   if (!N->isScheduled) {
 106     assert(NumPredsLeft < UINT_MAX && "NumPredsLeft will overflow!");
 107     ++NumPredsLeft;
 108   }
 109   if (!isScheduled) {
 110     assert(N->NumSuccsLeft < UINT_MAX && "NumSuccsLeft will overflow!");
 111     ++N->NumSuccsLeft;
 112   }
 113   Preds.push_back(D);
 114   N->Succs.push_back(P);
 115   if (P.getLatency() != 0) {
 116     this->setDepthDirty();
 117     N->setHeightDirty();
 118   }
 119   return true;
 120 }
 121
 122 /// removePred - This removes the specified edge as a pred of the current
 123 /// node if it exists.  It also removes the current node as a successor of
 124 /// the specified node.
 125 void SUnit::removePred(const SDep &D) {
 126   // Find the matching predecessor.
 127   for (SmallVector<SDep, 4>::iterator I = Preds.begin(), E = Preds.end();
 128        I != E; ++I)
 129     if (*I == D) {
 130       bool FoundSucc = false;
 131       // Find the corresponding successor in N.
 132       SDep P = D;
 133       P.setSUnit(this);
 134       SUnit *N = D.getSUnit();
 135       for (SmallVector<SDep, 4>::iterator II = N->Succs.begin(),
 136              EE = N->Succs.end(); II != EE; ++II)
 137         if (*II == P) {
 138           FoundSucc = true;
 139           N->Succs.erase(II);
 140           break;
 141         }
 142       assert(FoundSucc && "Mismatching preds / succs lists!");
 143       Preds.erase(I);
 144       // Update the bookkeeping.
 145       if (P.getKind() == SDep::Data) {
 146         assert(NumPreds > 0 && "NumPreds will underflow!");
 147         assert(N->NumSuccs > 0 && "NumSuccs will underflow!");
 148         --NumPreds;
 149         --N->NumSuccs;
 150       }
 151       if (!N->isScheduled) {
 152         assert(NumPredsLeft > 0 && "NumPredsLeft will underflow!");
 153         --NumPredsLeft;
 154       }
 155       if (!isScheduled) {
 156         assert(N->NumSuccsLeft > 0 && "NumSuccsLeft will underflow!");
 157         --N->NumSuccsLeft;
 158       }
 159       if (P.getLatency() != 0) {
 160         this->setDepthDirty();
 161         N->setHeightDirty();
 162       }
 163       return;
 164     }
 165 }
 166
 167 void SUnit::setDepthDirty() {
 168   if (!isDepthCurrent) return;
 169   SmallVector<SUnit*, 8> WorkList;
 170   WorkList.push_back(this);
 171   do {
 172     SUnit *SU = WorkList.pop_back_val();
 173     SU->isDepthCurrent = false;
 174     for (SUnit::const_succ_iterator I = SU->Succs.begin(),
 175          E = SU->Succs.end(); I != E; ++I) {
 176       SUnit *SuccSU = I->getSUnit();
 177       if (SuccSU->isDepthCurrent)
 178         WorkList.push_back(SuccSU);
 179     }
 180   } while (!WorkList.empty());
 181 }
 182
 183 void SUnit::setHeightDirty() {
 184   if (!isHeightCurrent) return;
 185   SmallVector<SUnit*, 8> WorkList;
 186   WorkList.push_back(this);
 187   do {
 188     SUnit *SU = WorkList.pop_back_val();
 189     SU->isHeightCurrent = false;
 190     for (SUnit::const_pred_iterator I = SU->Preds.begin(),
 191          E = SU->Preds.end(); I != E; ++I) {
 192       SUnit *PredSU = I->getSUnit();
 193       if (PredSU->isHeightCurrent)
 194         WorkList.push_back(PredSU);
 195     }
 196   } while (!WorkList.empty());
 197 }
 198
 199 /// setDepthToAtLeast - Update this node's successors to reflect the
 200 /// fact that this node's depth just increased.
 201 ///
 202 void SUnit::setDepthToAtLeast(unsigned NewDepth) {
 203   if (NewDepth <= getDepth())
 204     return;
 205   setDepthDirty();
 206   Depth = NewDepth;
 207   isDepthCurrent = true;
 208 }
 209
 210 /// setHeightToAtLeast - Update this node's predecessors to reflect the
 211 /// fact that this node's height just increased.
 212 ///
 213 void SUnit::setHeightToAtLeast(unsigned NewHeight) {
 214   if (NewHeight <= getHeight())
 215     return;
 216   setHeightDirty();
 217   Height = NewHeight;
 218   isHeightCurrent = true;
 219 }
 220
 221 /// ComputeDepth - Calculate the maximal path from the node to the exit.
 222 ///
 223 void SUnit::ComputeDepth() {
 224   SmallVector<SUnit*, 8> WorkList;
 225   WorkList.push_back(this);
 226   do {
 227     SUnit *Cur = WorkList.back();
 228
 229     bool Done = true;
 230     unsigned MaxPredDepth = 0;
 231     for (SUnit::const_pred_iterator I = Cur->Preds.begin(),
 232          E = Cur->Preds.end(); I != E; ++I) {
 233       SUnit *PredSU = I->getSUnit();
 234       if (PredSU->isDepthCurrent)
 235         MaxPredDepth = std::max(MaxPredDepth,
 236                                 PredSU->Depth + I->getLatency());
 237       else {
 238         Done = false;
 239         WorkList.push_back(PredSU);
 240       }
 241     }
 242
 243     if (Done) {
 244       WorkList.pop_back();
 245       if (MaxPredDepth != Cur->Depth) {
 246         Cur->setDepthDirty();
 247         Cur->Depth = MaxPredDepth;
 248       }
 249       Cur->isDepthCurrent = true;
 250     }
 251   } while (!WorkList.empty());
 252 }
 253
 254 /// ComputeHeight - Calculate the maximal path from the node to the entry.
 255 ///
 256 void SUnit::ComputeHeight() {
 257   SmallVector<SUnit*, 8> WorkList;
 258   WorkList.push_back(this);
 259   do {
 260     SUnit *Cur = WorkList.back();
 261
 262     bool Done = true;
 263     unsigned MaxSuccHeight = 0;
 264     for (SUnit::const_succ_iterator I = Cur->Succs.begin(),
 265          E = Cur->Succs.end(); I != E; ++I) {
 266       SUnit *SuccSU = I->getSUnit();
 267       if (SuccSU->isHeightCurrent)
 268         MaxSuccHeight = std::max(MaxSuccHeight,
 269                                  SuccSU->Height + I->getLatency());
 270       else {
 271         Done = false;
 272         WorkList.push_back(SuccSU);
 273       }
 274     }
 275
 276     if (Done) {
 277       WorkList.pop_back();
 278       if (MaxSuccHeight != Cur->Height) {
 279         Cur->setHeightDirty();
 280         Cur->Height = MaxSuccHeight;
 281       }
 282       Cur->isHeightCurrent = true;
 283     }
 284   } while (!WorkList.empty());
 285 }
 286
 287 /// SUnit - Scheduling unit. It's an wrapper around either a single SDNode or
 288 /// a group of nodes flagged together.
 289 void SUnit::dump(const ScheduleDAG *G) const {
 290   dbgs() << "SU(" << NodeNum << "): ";
 291   G->dumpNode(this);
 292 }
 293
 294 void SUnit::dumpAll(const ScheduleDAG *G) const {
 295   dump(G);
 296
 297   dbgs() << "  # preds left       : " << NumPredsLeft << "\n";
 298   dbgs() << "  # succs left       : " << NumSuccsLeft << "\n";
 299   dbgs() << "  # rdefs left       : " << NumRegDefsLeft << "\n";
 300   dbgs() << "  Latency            : " << Latency << "\n";
 301   dbgs() << "  Depth              : " << Depth << "\n";
 302   dbgs() << "  Height             : " << Height << "\n";
 303
 304   if (Preds.size() != 0) {
 305     dbgs() << "  Predecessors:\n";
 306     for (SUnit::const_succ_iterator I = Preds.begin(), E = Preds.end();
 307          I != E; ++I) {
 308       dbgs() << "   ";
 309       switch (I->getKind()) {
 310       case SDep::Data:        dbgs() << "val "; break;
 311       case SDep::Anti:        dbgs() << "anti"; break;
 312       case SDep::Output:      dbgs() << "out "; break;
 313       case SDep::Order:       dbgs() << "ch  "; break;
 314       }
 315       dbgs() << "#";
 316       dbgs() << I->getSUnit() << " - SU(" << I->getSUnit()->NodeNum << ")";
 317       if (I->isArtificial())
 318         dbgs() << " *";
 319       dbgs() << ": Latency=" << I->getLatency();
 320       if (I->isAssignedRegDep())
 321         dbgs() << " Reg=" << G->TRI->getName(I->getReg());
 322       dbgs() << "\n";
 323     }
 324   }
 325   if (Succs.size() != 0) {
 326     dbgs() << "  Successors:\n";
 327     for (SUnit::const_succ_iterator I = Succs.begin(), E = Succs.end();
 328          I != E; ++I) {
 329       dbgs() << "   ";
 330       switch (I->getKind()) {
 331       case SDep::Data:        dbgs() << "val "; break;
 332       case SDep::Anti:        dbgs() << "anti"; break;
 333       case SDep::Output:      dbgs() << "out "; break;
 334       case SDep::Order:       dbgs() << "ch  "; break;
 335       }
 336       dbgs() << "#";
 337       dbgs() << I->getSUnit() << " - SU(" << I->getSUnit()->NodeNum << ")";
 338       if (I->isArtificial())
 339         dbgs() << " *";
 340       dbgs() << ": Latency=" << I->getLatency();
 341       dbgs() << "\n";
 342     }
 343   }
 344   dbgs() << "\n";
 345 }
 346
 347 #ifndef NDEBUG
 348 /// VerifySchedule - Verify that all SUnits were scheduled and that
 349 /// their state is consistent.
 350 ///
 351 void ScheduleDAG::VerifySchedule(bool isBottomUp) {
 352   bool AnyNotSched = false;
 353   unsigned DeadNodes = 0;
 354   unsigned Noops = 0;
 355   for (unsigned i = 0, e = SUnits.size(); i != e; ++i) {
 356     if (!SUnits[i].isScheduled) {
 357       if (SUnits[i].NumPreds == 0 && SUnits[i].NumSuccs == 0) {
 358         ++DeadNodes;
 359         continue;
 360       }
 361       if (!AnyNotSched)
 362         dbgs() << "*** Scheduling failed! ***\n";
 363       SUnits[i].dump(this);
 364       dbgs() << "has not been scheduled!\n";
 365       AnyNotSched = true;
 366     }
 367     if (SUnits[i].isScheduled &&
 368         (isBottomUp ? SUnits[i].getHeight() : SUnits[i].getDepth()) >
 369           unsigned(INT_MAX)) {
 370       if (!AnyNotSched)
 371         dbgs() << "*** Scheduling failed! ***\n";
 372       SUnits[i].dump(this);
 373       dbgs() << "has an unexpected "
 374            << (isBottomUp ? "Height" : "Depth") << " value!\n";
 375       AnyNotSched = true;
 376     }
 377     if (isBottomUp) {
 378       if (SUnits[i].NumSuccsLeft != 0) {
 379         if (!AnyNotSched)
 380           dbgs() << "*** Scheduling failed! ***\n";
 381         SUnits[i].dump(this);
 382         dbgs() << "has successors left!\n";
 383         AnyNotSched = true;
 384       }
 385     } else {
 386       if (SUnits[i].NumPredsLeft != 0) {
 387         if (!AnyNotSched)
 388           dbgs() << "*** Scheduling failed! ***\n";
 389         SUnits[i].dump(this);
 390         dbgs() << "has predecessors left!\n";
 391         AnyNotSched = true;
 392       }
 393     }
 394   }
 395   for (unsigned i = 0, e = Sequence.size(); i != e; ++i)
 396     if (!Sequence[i])
 397       ++Noops;
 398   assert(!AnyNotSched);
 399   assert(Sequence.size() + DeadNodes - Noops == SUnits.size() &&
 400          "The number of nodes scheduled doesn't match the expected number!");
 401 }
 402 #endif
 403
 404 /// InitDAGTopologicalSorting - create the initial topological
 405 /// ordering from the DAG to be scheduled.
 406 ///
 407 /// The idea of the algorithm is taken from
 408 /// "Online algorithms for managing the topological order of
 409 /// a directed acyclic graph" by David J. Pearce and Paul H.J. Kelly
 410 /// This is the MNR algorithm, which was first introduced by
 411 /// A. Marchetti-Spaccamela, U. Nanni and H. Rohnert in
 412 /// "Maintaining a topological order under edge insertions".
 413 ///
 414 /// Short description of the algorithm:
 415 ///
 416 /// Topological ordering, ord, of a DAG maps each node to a topological
 417 /// index so that for all edges X->Y it is the case that ord(X) < ord(Y).
 418 ///
 419 /// This means that if there is a path from the node X to the node Z,
 420 /// then ord(X) < ord(Z).
 421 ///
 422 /// This property can be used to check for reachability of nodes:
 423 /// if Z is reachable from X, then an insertion of the edge Z->X would
 424 /// create a cycle.
 425 ///
 426 /// The algorithm first computes a topological ordering for the DAG by
 427 /// initializing the Index2Node and Node2Index arrays and then tries to keep
 428 /// the ordering up-to-date after edge insertions by reordering the DAG.
 429 ///
 430 /// On insertion of the edge X->Y, the algorithm first marks by calling DFS
 431 /// the nodes reachable from Y, and then shifts them using Shift to lie
 432 /// immediately after X in Index2Node.
 433 void ScheduleDAGTopologicalSort::InitDAGTopologicalSorting() {
 434   unsigned DAGSize = SUnits.size();
 435   std::vector<SUnit*> WorkList;
 436   WorkList.reserve(DAGSize);
 437
 438   Index2Node.resize(DAGSize);
 439   Node2Index.resize(DAGSize);
 440
 441   // Initialize the data structures.
 442   for (unsigned i = 0, e = DAGSize; i != e; ++i) {
 443     SUnit *SU = &SUnits[i];
 444     int NodeNum = SU->NodeNum;
 445     unsigned Degree = SU->Succs.size();
 446     // Temporarily use the Node2Index array as scratch space for degree counts.
 447     Node2Index[NodeNum] = Degree;
 448
 449     // Is it a node without dependencies?
 450     if (Degree == 0) {
 451       assert(SU->Succs.empty() && "SUnit should have no successors");
 452       // Collect leaf nodes.
 453       WorkList.push_back(SU);
 454     }
 455   }
 456
 457   int Id = DAGSize;
 458   while (!WorkList.empty()) {
 459     SUnit *SU = WorkList.back();
 460     WorkList.pop_back();
 461     Allocate(SU->NodeNum, --Id);
 462     for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
 463          I != E; ++I) {
 464       SUnit *SU = I->getSUnit();
 465       if (!--Node2Index[SU->NodeNum])
 466         // If all dependencies of the node are processed already,
 467         // then the node can be computed now.
 468         WorkList.push_back(SU);
 469     }
 470   }
 471
 472   Visited.resize(DAGSize);
 473
 474 #ifndef NDEBUG
 475   // Check correctness of the ordering
 476   for (unsigned i = 0, e = DAGSize; i != e; ++i) {
 477     SUnit *SU = &SUnits[i];
 478     for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
 479          I != E; ++I) {
 480       assert(Node2Index[SU->NodeNum] > Node2Index[I->getSUnit()->NodeNum] &&
 481       "Wrong topological sorting");
 482     }
 483   }
 484 #endif
 485 }
 486
 487 /// AddPred - Updates the topological ordering to accommodate an edge
 488 /// to be added from SUnit X to SUnit Y.
 489 void ScheduleDAGTopologicalSort::AddPred(SUnit *Y, SUnit *X) {
 490   int UpperBound, LowerBound;
 491   LowerBound = Node2Index[Y->NodeNum];
 492   UpperBound = Node2Index[X->NodeNum];
 493   bool HasLoop = false;
 494   // Is Ord(X) < Ord(Y) ?
 495   if (LowerBound < UpperBound) {
 496     // Update the topological order.
 497     Visited.reset();
 498     DFS(Y, UpperBound, HasLoop);
 499     assert(!HasLoop && "Inserted edge creates a loop!");
 500     // Recompute topological indexes.
 501     Shift(Visited, LowerBound, UpperBound);
 502   }
 503 }
 504
 505 /// RemovePred - Updates the topological ordering to accommodate an
 506 /// an edge to be removed from the specified node N from the predecessors
 507 /// of the current node M.
 508 void ScheduleDAGTopologicalSort::RemovePred(SUnit *M, SUnit *N) {
 509   // InitDAGTopologicalSorting();
 510 }
 511
 512 /// DFS - Make a DFS traversal to mark all nodes reachable from SU and mark
 513 /// all nodes affected by the edge insertion. These nodes will later get new
 514 /// topological indexes by means of the Shift method.
 515 void ScheduleDAGTopologicalSort::DFS(const SUnit *SU, int UpperBound,
 516                                      bool &HasLoop) {
 517   std::vector<const SUnit*> WorkList;
 518   WorkList.reserve(SUnits.size());
 519
 520   WorkList.push_back(SU);
 521   do {
 522     SU = WorkList.back();
 523     WorkList.pop_back();
 524     Visited.set(SU->NodeNum);
 525     for (int I = SU->Succs.size()-1; I >= 0; --I) {
 526       int s = SU->Succs[I].getSUnit()->NodeNum;
 527       if (Node2Index[s] == UpperBound) {
 528         HasLoop = true;
 529         return;
 530       }
 531       // Visit successors if not already and in affected region.
 532       if (!Visited.test(s) && Node2Index[s] < UpperBound) {
 533         WorkList.push_back(SU->Succs[I].getSUnit());
 534       }
 535     }
 536   } while (!WorkList.empty());
 537 }
 538
 539 /// Shift - Renumber the nodes so that the topological ordering is
 540 /// preserved.
 541 void ScheduleDAGTopologicalSort::Shift(BitVector& Visited, int LowerBound,
 542                                        int UpperBound) {
 543   std::vector<int> L;
 544   int shift = 0;
 545   int i;
 546
 547   for (i = LowerBound; i <= UpperBound; ++i) {
 548     // w is node at topological index i.
 549     int w = Index2Node[i];
 550     if (Visited.test(w)) {
 551       // Unmark.
 552       Visited.reset(w);
 553       L.push_back(w);
 554       shift = shift + 1;
 555     } else {
 556       Allocate(w, i - shift);
 557     }
 558   }
 559
 560   for (unsigned j = 0; j < L.size(); ++j) {
 561     Allocate(L[j], i - shift);
 562     i = i + 1;
 563   }
 564 }
 565
 566
 567 /// WillCreateCycle - Returns true if adding an edge from SU to TargetSU will
 568 /// create a cycle.
 569 bool ScheduleDAGTopologicalSort::WillCreateCycle(SUnit *SU, SUnit *TargetSU) {
 570   if (IsReachable(TargetSU, SU))
 571     return true;
 572   for (SUnit::pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
 573        I != E; ++I)
 574     if (I->isAssignedRegDep() &&
 575         IsReachable(TargetSU, I->getSUnit()))
 576       return true;
 577   return false;
 578 }
 579
 580 /// IsReachable - Checks if SU is reachable from TargetSU.
 581 bool ScheduleDAGTopologicalSort::IsReachable(const SUnit *SU,
 582                                              const SUnit *TargetSU) {
 583   // If insertion of the edge SU->TargetSU would create a cycle
 584   // then there is a path from TargetSU to SU.
 585   int UpperBound, LowerBound;
 586   LowerBound = Node2Index[TargetSU->NodeNum];
 587   UpperBound = Node2Index[SU->NodeNum];
 588   bool HasLoop = false;
 589   // Is Ord(TargetSU) < Ord(SU) ?
 590   if (LowerBound < UpperBound) {
 591     Visited.reset();
 592     // There may be a path from TargetSU to SU. Check for it.
 593     DFS(TargetSU, UpperBound, HasLoop);
 594   }
 595   return HasLoop;
 596 }
 597
 598 /// Allocate - assign the topological index to the node n.
 599 void ScheduleDAGTopologicalSort::Allocate(int n, int index) {
 600   Node2Index[n] = index;
 601   Index2Node[index] = n;
 602 }
 603
 604 ScheduleDAGTopologicalSort::
 605 ScheduleDAGTopologicalSort(std::vector<SUnit> &sunits) : SUnits(sunits) {}
 606
 607 ScheduleHazardRecognizer::~ScheduleHazardRecognizer() {}