lib/CodeGen/ScheduleDAG.cpp - llvm-project/llvm - Git at Google

 //===- ScheduleDAG.cpp - Implement the ScheduleDAG class ------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 /// \file Implements the ScheduleDAG class, which is a base class used by
 /// scheduling implementation classes.
 //
 //===----------------------------------------------------------------------===//

 #include "llvm/CodeGen/ScheduleDAG.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/ScheduleHazardRecognizer.h"
 #include "llvm/CodeGen/SelectionDAGNodes.h"
 #include "llvm/CodeGen/TargetInstrInfo.h"
 #include "llvm/CodeGen/TargetRegisterInfo.h"
 #include "llvm/CodeGen/TargetSubtargetInfo.h"
 #include "llvm/Config/llvm-config.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
 #include <cassert>
 #include <iterator>
 #include <limits>
 #include <utility>
 #include <vector>

 using namespace llvm;

 #define DEBUG_TYPE "pre-RA-sched"

 STATISTIC(NumNewPredsAdded, "Number of times a  single predecessor was added");
 STATISTIC(NumTopoInits,
           "Number of times the topological order has been recomputed");

 #ifndef NDEBUG
 static cl::opt<bool> StressSchedOpt(
   "stress-sched", cl::Hidden, cl::init(false),
   cl::desc("Stress test instruction scheduling"));
 #endif

 void SchedulingPriorityQueue::anchor() {}

 ScheduleDAG::ScheduleDAG(MachineFunction &mf)
     : TM(mf.getTarget()), TII(mf.getSubtarget().getInstrInfo()),
       TRI(mf.getSubtarget().getRegisterInfo()), MF(mf),
       MRI(mf.getRegInfo()) {
 #ifndef NDEBUG
   StressSched = StressSchedOpt;
 #endif
 }

 ScheduleDAG::~ScheduleDAG() = default;

 void ScheduleDAG::clearDAG() {
   SUnits.clear();
   EntrySU = SUnit();
   ExitSU = SUnit();
 }

 const MCInstrDesc *ScheduleDAG::getNodeDesc(const SDNode *Node) const {
   if (!Node || !Node->isMachineOpcode()) return nullptr;
   return &TII->get(Node->getMachineOpcode());
 }

 LLVM_DUMP_METHOD void SDep::dump(const TargetRegisterInfo *TRI) const {
   switch (getKind()) {
   case Data:   dbgs() << "Data"; break;
   case Anti:   dbgs() << "Anti"; break;
   case Output: dbgs() << "Out "; break;
   case Order:  dbgs() << "Ord "; break;
   }

   switch (getKind()) {
   case Data:
     dbgs() << " Latency=" << getLatency();
     if (TRI && isAssignedRegDep())
       dbgs() << " Reg=" << printReg(getReg(), TRI);
     break;
   case Anti:
   case Output:
     dbgs() << " Latency=" << getLatency();
     break;
   case Order:
     dbgs() << " Latency=" << getLatency();
     switch(Contents.OrdKind) {
     case Barrier:      dbgs() << " Barrier"; break;
     case MayAliasMem:
     case MustAliasMem: dbgs() << " Memory"; break;
     case Artificial:   dbgs() << " Artificial"; break;
     case Weak:         dbgs() << " Weak"; break;
     case Cluster:      dbgs() << " Cluster"; break;
     }
     break;
   }
 }

 bool SUnit::addPred(const SDep &D, bool Required) {
   // If this node already has this dependence, don't add a redundant one.
   for (SDep &PredDep : Preds) {
     // Zero-latency weak edges may be added purely for heuristic ordering. Don't
     // add them if another kind of edge already exists.
     if (!Required && PredDep.getSUnit() == D.getSUnit())
       return false;
     if (PredDep.overlaps(D)) {
       // Extend the latency if needed. Equivalent to
       // removePred(PredDep) + addPred(D).
       if (PredDep.getLatency() < D.getLatency()) {
         SUnit *PredSU = PredDep.getSUnit();
         // Find the corresponding successor in N.
         SDep ForwardD = PredDep;
         ForwardD.setSUnit(this);
         for (SDep &SuccDep : PredSU->Succs) {
           if (SuccDep == ForwardD) {
             SuccDep.setLatency(D.getLatency());
             break;
           }
         }
         PredDep.setLatency(D.getLatency());
       }
       return false;
     }
   }
   // Now add a corresponding succ to N.
   SDep P = D;
   P.setSUnit(this);
   SUnit *N = D.getSUnit();
   // Update the bookkeeping.
   if (D.getKind() == SDep::Data) {
     assert(NumPreds < std::numeric_limits<unsigned>::max() &&
            "NumPreds will overflow!");
     assert(N->NumSuccs < std::numeric_limits<unsigned>::max() &&
            "NumSuccs will overflow!");
     ++NumPreds;
     ++N->NumSuccs;
   }
   if (!N->isScheduled) {
     if (D.isWeak()) {
       ++WeakPredsLeft;
     }
     else {
       assert(NumPredsLeft < std::numeric_limits<unsigned>::max() &&
              "NumPredsLeft will overflow!");
       ++NumPredsLeft;
     }
   }
   if (!isScheduled) {
     if (D.isWeak()) {
       ++N->WeakSuccsLeft;
     }
     else {
       assert(N->NumSuccsLeft < std::numeric_limits<unsigned>::max() &&
              "NumSuccsLeft will overflow!");
       ++N->NumSuccsLeft;
     }
   }
   Preds.push_back(D);
   N->Succs.push_back(P);
   if (P.getLatency() != 0) {
     this->setDepthDirty();
     N->setHeightDirty();
   }
   return true;
 }

 void SUnit::removePred(const SDep &D) {
   // Find the matching predecessor.
   SmallVectorImpl<SDep>::iterator I = llvm::find(Preds, D);
   if (I == Preds.end())
     return;
   // Find the corresponding successor in N.
   SDep P = D;
   P.setSUnit(this);
   SUnit *N = D.getSUnit();
   SmallVectorImpl<SDep>::iterator Succ = llvm::find(N->Succs, P);
   assert(Succ != N->Succs.end() && "Mismatching preds / succs lists!");
   N->Succs.erase(Succ);
   Preds.erase(I);
   // Update the bookkeeping.
   if (P.getKind() == SDep::Data) {
     assert(NumPreds > 0 && "NumPreds will underflow!");
     assert(N->NumSuccs > 0 && "NumSuccs will underflow!");
     --NumPreds;
     --N->NumSuccs;
   }
   if (!N->isScheduled) {
     if (D.isWeak())
       --WeakPredsLeft;
     else {
       assert(NumPredsLeft > 0 && "NumPredsLeft will underflow!");
       --NumPredsLeft;
     }
   }
   if (!isScheduled) {
     if (D.isWeak())
       --N->WeakSuccsLeft;
     else {
       assert(N->NumSuccsLeft > 0 && "NumSuccsLeft will underflow!");
       --N->NumSuccsLeft;
     }
   }
   if (P.getLatency() != 0) {
     this->setDepthDirty();
     N->setHeightDirty();
   }
 }

 void SUnit::setDepthDirty() {
   if (!isDepthCurrent) return;
   SmallVector<SUnit*, 8> WorkList;
   WorkList.push_back(this);
   do {
     SUnit *SU = WorkList.pop_back_val();
     SU->isDepthCurrent = false;
     for (SDep &SuccDep : SU->Succs) {
       SUnit *SuccSU = SuccDep.getSUnit();
       if (SuccSU->isDepthCurrent)
         WorkList.push_back(SuccSU);
     }
   } while (!WorkList.empty());
 }

 void SUnit::setHeightDirty() {
   if (!isHeightCurrent) return;
   SmallVector<SUnit*, 8> WorkList;
   WorkList.push_back(this);
   do {
     SUnit *SU = WorkList.pop_back_val();
     SU->isHeightCurrent = false;
     for (SDep &PredDep : SU->Preds) {
       SUnit *PredSU = PredDep.getSUnit();
       if (PredSU->isHeightCurrent)
         WorkList.push_back(PredSU);
     }
   } while (!WorkList.empty());
 }

 void SUnit::setDepthToAtLeast(unsigned NewDepth) {
   if (NewDepth <= getDepth())
     return;
   setDepthDirty();
   Depth = NewDepth;
   isDepthCurrent = true;
 }

 void SUnit::setHeightToAtLeast(unsigned NewHeight) {
   if (NewHeight <= getHeight())
     return;
   setHeightDirty();
   Height = NewHeight;
   isHeightCurrent = true;
 }

 /// Calculates the maximal path from the node to the exit.
 void SUnit::ComputeDepth() {
   SmallVector<SUnit*, 8> WorkList;
   WorkList.push_back(this);
   do {
     SUnit *Cur = WorkList.back();

     bool Done = true;
     unsigned MaxPredDepth = 0;
     for (const SDep &PredDep : Cur->Preds) {
       SUnit *PredSU = PredDep.getSUnit();
       if (PredSU->isDepthCurrent)
         MaxPredDepth = std::max(MaxPredDepth,
                                 PredSU->Depth + PredDep.getLatency());
       else {
         Done = false;
         WorkList.push_back(PredSU);
       }
     }

     if (Done) {
       WorkList.pop_back();
       if (MaxPredDepth != Cur->Depth) {
         Cur->setDepthDirty();
         Cur->Depth = MaxPredDepth;
       }
       Cur->isDepthCurrent = true;
     }
   } while (!WorkList.empty());
 }

 /// Calculates the maximal path from the node to the entry.
 void SUnit::ComputeHeight() {
   SmallVector<SUnit*, 8> WorkList;
   WorkList.push_back(this);
   do {
     SUnit *Cur = WorkList.back();

     bool Done = true;
     unsigned MaxSuccHeight = 0;
     for (const SDep &SuccDep : Cur->Succs) {
       SUnit *SuccSU = SuccDep.getSUnit();
       if (SuccSU->isHeightCurrent)
         MaxSuccHeight = std::max(MaxSuccHeight,
                                  SuccSU->Height + SuccDep.getLatency());
       else {
         Done = false;
         WorkList.push_back(SuccSU);
       }
     }

     if (Done) {
       WorkList.pop_back();
       if (MaxSuccHeight != Cur->Height) {
         Cur->setHeightDirty();
         Cur->Height = MaxSuccHeight;
       }
       Cur->isHeightCurrent = true;
     }
   } while (!WorkList.empty());
 }

 void SUnit::biasCriticalPath() {
   if (NumPreds < 2)
     return;

   SUnit::pred_iterator BestI = Preds.begin();
   unsigned MaxDepth = BestI->getSUnit()->getDepth();
   for (SUnit::pred_iterator I = std::next(BestI), E = Preds.end(); I != E;
        ++I) {
     if (I->getKind() == SDep::Data && I->getSUnit()->getDepth() > MaxDepth)
       BestI = I;
   }
   if (BestI != Preds.begin())
     std::swap(*Preds.begin(), *BestI);
 }

 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
 LLVM_DUMP_METHOD void SUnit::dumpAttributes() const {
   dbgs() << "  # preds left       : " << NumPredsLeft << "\n";
   dbgs() << "  # succs left       : " << NumSuccsLeft << "\n";
   if (WeakPredsLeft)
     dbgs() << "  # weak preds left  : " << WeakPredsLeft << "\n";
   if (WeakSuccsLeft)
     dbgs() << "  # weak succs left  : " << WeakSuccsLeft << "\n";
   dbgs() << "  # rdefs left       : " << NumRegDefsLeft << "\n";
   dbgs() << "  Latency            : " << Latency << "\n";
   dbgs() << "  Depth              : " << getDepth() << "\n";
   dbgs() << "  Height             : " << getHeight() << "\n";
 }

 LLVM_DUMP_METHOD void ScheduleDAG::dumpNodeName(const SUnit &SU) const {
   if (&SU == &EntrySU)
     dbgs() << "EntrySU";
   else if (&SU == &ExitSU)
     dbgs() << "ExitSU";
   else
     dbgs() << "SU(" << SU.NodeNum << ")";
 }

 LLVM_DUMP_METHOD void ScheduleDAG::dumpNodeAll(const SUnit &SU) const {
   dumpNode(SU);
   SU.dumpAttributes();
   if (SU.Preds.size() > 0) {
     dbgs() << "  Predecessors:\n";
     for (const SDep &Dep : SU.Preds) {
       dbgs() << "    ";
       dumpNodeName(*Dep.getSUnit());
       dbgs() << ": ";
       Dep.dump(TRI);
       dbgs() << '\n';
     }
   }
   if (SU.Succs.size() > 0) {
     dbgs() << "  Successors:\n";
     for (const SDep &Dep : SU.Succs) {
       dbgs() << "    ";
       dumpNodeName(*Dep.getSUnit());
       dbgs() << ": ";
       Dep.dump(TRI);
       dbgs() << '\n';
     }
   }
 }
 #endif

 #ifndef NDEBUG
 unsigned ScheduleDAG::VerifyScheduledDAG(bool isBottomUp) {
   bool AnyNotSched = false;
   unsigned DeadNodes = 0;
   for (const SUnit &SUnit : SUnits) {
     if (!SUnit.isScheduled) {
       if (SUnit.NumPreds == 0 && SUnit.NumSuccs == 0) {
         ++DeadNodes;
         continue;
       }
       if (!AnyNotSched)
         dbgs() << "*** Scheduling failed! ***\n";
       dumpNode(SUnit);
       dbgs() << "has not been scheduled!\n";
       AnyNotSched = true;
     }
     if (SUnit.isScheduled &&
         (isBottomUp ? SUnit.getHeight() : SUnit.getDepth()) >
           unsigned(std::numeric_limits<int>::max())) {
       if (!AnyNotSched)
         dbgs() << "*** Scheduling failed! ***\n";
       dumpNode(SUnit);
       dbgs() << "has an unexpected "
            << (isBottomUp ? "Height" : "Depth") << " value!\n";
       AnyNotSched = true;
     }
     if (isBottomUp) {
       if (SUnit.NumSuccsLeft != 0) {
         if (!AnyNotSched)
           dbgs() << "*** Scheduling failed! ***\n";
         dumpNode(SUnit);
         dbgs() << "has successors left!\n";
         AnyNotSched = true;
       }
     } else {
       if (SUnit.NumPredsLeft != 0) {
         if (!AnyNotSched)
           dbgs() << "*** Scheduling failed! ***\n";
         dumpNode(SUnit);
         dbgs() << "has predecessors left!\n";
         AnyNotSched = true;
       }
     }
   }
   assert(!AnyNotSched);
   return SUnits.size() - DeadNodes;
 }
 #endif

 void ScheduleDAGTopologicalSort::InitDAGTopologicalSorting() {
   // The idea of the algorithm is taken from
   // "Online algorithms for managing the topological order of
   // a directed acyclic graph" by David J. Pearce and Paul H.J. Kelly
   // This is the MNR algorithm, which was first introduced by
   // A. Marchetti-Spaccamela, U. Nanni and H. Rohnert in
   // "Maintaining a topological order under edge insertions".
   //
   // Short description of the algorithm:
   //
   // Topological ordering, ord, of a DAG maps each node to a topological
   // index so that for all edges X->Y it is the case that ord(X) < ord(Y).
   //
   // This means that if there is a path from the node X to the node Z,
   // then ord(X) < ord(Z).
   //
   // This property can be used to check for reachability of nodes:
   // if Z is reachable from X, then an insertion of the edge Z->X would
   // create a cycle.
   //
   // The algorithm first computes a topological ordering for the DAG by
   // initializing the Index2Node and Node2Index arrays and then tries to keep
   // the ordering up-to-date after edge insertions by reordering the DAG.
   //
   // On insertion of the edge X->Y, the algorithm first marks by calling DFS
   // the nodes reachable from Y, and then shifts them using Shift to lie
   // immediately after X in Index2Node.

   // Cancel pending updates, mark as valid.
   Dirty = false;
   Updates.clear();

   unsigned DAGSize = SUnits.size();
   std::vector<SUnit*> WorkList;
   WorkList.reserve(DAGSize);

   Index2Node.resize(DAGSize);
   Node2Index.resize(DAGSize);

   // Initialize the data structures.
   if (ExitSU)
     WorkList.push_back(ExitSU);
   for (SUnit &SU : SUnits) {
     int NodeNum = SU.NodeNum;
     unsigned Degree = SU.Succs.size();
     // Temporarily use the Node2Index array as scratch space for degree counts.
     Node2Index[NodeNum] = Degree;

     // Is it a node without dependencies?
     if (Degree == 0) {
       assert(SU.Succs.empty() && "SUnit should have no successors");
       // Collect leaf nodes.
       WorkList.push_back(&SU);
     }
   }

   int Id = DAGSize;
   while (!WorkList.empty()) {
     SUnit *SU = WorkList.back();
     WorkList.pop_back();
     if (SU->NodeNum < DAGSize)
       Allocate(SU->NodeNum, --Id);
     for (const SDep &PredDep : SU->Preds) {
       SUnit *SU = PredDep.getSUnit();
       if (SU->NodeNum < DAGSize && !--Node2Index[SU->NodeNum])
         // If all dependencies of the node are processed already,
         // then the node can be computed now.
         WorkList.push_back(SU);
     }
   }

   Visited.resize(DAGSize);
   NumTopoInits++;

 #ifndef NDEBUG
   // Check correctness of the ordering
   for (SUnit &SU : SUnits)  {
     for (const SDep &PD : SU.Preds) {
       assert(Node2Index[SU.NodeNum] > Node2Index[PD.getSUnit()->NodeNum] &&
       "Wrong topological sorting");
     }
   }
 #endif
 }

 void ScheduleDAGTopologicalSort::FixOrder() {
   // Recompute from scratch after new nodes have been added.
   if (Dirty) {
     InitDAGTopologicalSorting();
     return;
   }

   // Otherwise apply updates one-by-one.
   for (auto &U : Updates)
     AddPred(U.first, U.second);
   Updates.clear();
 }

 void ScheduleDAGTopologicalSort::AddPredQueued(SUnit *Y, SUnit *X) {
   // Recomputing the order from scratch is likely more efficient than applying
   // updates one-by-one for too many updates. The current cut-off is arbitrarily
   // chosen.
   Dirty = Dirty || Updates.size() > 10;

   if (Dirty)
     return;

   Updates.emplace_back(Y, X);
 }

 void ScheduleDAGTopologicalSort::AddPred(SUnit *Y, SUnit *X) {
   int UpperBound, LowerBound;
   LowerBound = Node2Index[Y->NodeNum];
   UpperBound = Node2Index[X->NodeNum];
   bool HasLoop = false;
   // Is Ord(X) < Ord(Y) ?
   if (LowerBound < UpperBound) {
     // Update the topological order.
     Visited.reset();
     DFS(Y, UpperBound, HasLoop);
     assert(!HasLoop && "Inserted edge creates a loop!");
     // Recompute topological indexes.
     Shift(Visited, LowerBound, UpperBound);
   }

   NumNewPredsAdded++;
 }

 void ScheduleDAGTopologicalSort::RemovePred(SUnit *M, SUnit *N) {
   // InitDAGTopologicalSorting();
 }

 void ScheduleDAGTopologicalSort::DFS(const SUnit *SU, int UpperBound,
                                      bool &HasLoop) {
   std::vector<const SUnit*> WorkList;
   WorkList.reserve(SUnits.size());

   WorkList.push_back(SU);
   do {
     SU = WorkList.back();
     WorkList.pop_back();
     Visited.set(SU->NodeNum);
     for (const SDep &SuccDep
          : make_range(SU->Succs.rbegin(), SU->Succs.rend())) {
       unsigned s = SuccDep.getSUnit()->NodeNum;
       // Edges to non-SUnits are allowed but ignored (e.g. ExitSU).
       if (s >= Node2Index.size())
         continue;
       if (Node2Index[s] == UpperBound) {
         HasLoop = true;
         return;
       }
       // Visit successors if not already and in affected region.
       if (!Visited.test(s) && Node2Index[s] < UpperBound) {
         WorkList.push_back(SuccDep.getSUnit());
       }
     }
   } while (!WorkList.empty());
 }

 std::vector<int> ScheduleDAGTopologicalSort::GetSubGraph(const SUnit &StartSU,
                                                          const SUnit &TargetSU,
                                                          bool &Success) {
   std::vector<const SUnit*> WorkList;
   int LowerBound = Node2Index[StartSU.NodeNum];
   int UpperBound = Node2Index[TargetSU.NodeNum];
   bool Found = false;
   BitVector VisitedBack;
   std::vector<int> Nodes;

   if (LowerBound > UpperBound) {
     Success = false;
     return Nodes;
   }

   WorkList.reserve(SUnits.size());
   Visited.reset();

   // Starting from StartSU, visit all successors up
   // to UpperBound.
   WorkList.push_back(&StartSU);
   do {
     const SUnit *SU = WorkList.back();
     WorkList.pop_back();
     for (int I = SU->Succs.size()-1; I >= 0; --I) {
       const SUnit *Succ = SU->Succs[I].getSUnit();
       unsigned s = Succ->NodeNum;
       // Edges to non-SUnits are allowed but ignored (e.g. ExitSU).
       if (Succ->isBoundaryNode())
         continue;
       if (Node2Index[s] == UpperBound) {
         Found = true;
         continue;
       }
       // Visit successors if not already and in affected region.
       if (!Visited.test(s) && Node2Index[s] < UpperBound) {
         Visited.set(s);
         WorkList.push_back(Succ);
       }
     }
   } while (!WorkList.empty());

   if (!Found) {
     Success = false;
     return Nodes;
   }

   WorkList.clear();
   VisitedBack.resize(SUnits.size());
   Found = false;

   // Starting from TargetSU, visit all predecessors up
   // to LowerBound. SUs that are visited by the two
   // passes are added to Nodes.
   WorkList.push_back(&TargetSU);
   do {
     const SUnit *SU = WorkList.back();
     WorkList.pop_back();
     for (int I = SU->Preds.size()-1; I >= 0; --I) {
       const SUnit *Pred = SU->Preds[I].getSUnit();
       unsigned s = Pred->NodeNum;
       // Edges to non-SUnits are allowed but ignored (e.g. EntrySU).
       if (Pred->isBoundaryNode())
         continue;
       if (Node2Index[s] == LowerBound) {
         Found = true;
         continue;
       }
       if (!VisitedBack.test(s) && Visited.test(s)) {
         VisitedBack.set(s);
         WorkList.push_back(Pred);
         Nodes.push_back(s);
       }
     }
   } while (!WorkList.empty());

   assert(Found && "Error in SUnit Graph!");
   Success = true;
   return Nodes;
 }

 void ScheduleDAGTopologicalSort::Shift(BitVector& Visited, int LowerBound,
                                        int UpperBound) {
   std::vector<int> L;
   int shift = 0;
   int i;

   for (i = LowerBound; i <= UpperBound; ++i) {
     // w is node at topological index i.
     int w = Index2Node[i];
     if (Visited.test(w)) {
       // Unmark.
       Visited.reset(w);
       L.push_back(w);
       shift = shift + 1;
     } else {
       Allocate(w, i - shift);
     }
   }

   for (unsigned LI : L) {
     Allocate(LI, i - shift);
     i = i + 1;
   }
 }

 bool ScheduleDAGTopologicalSort::WillCreateCycle(SUnit *TargetSU, SUnit *SU) {
   FixOrder();
   // Is SU reachable from TargetSU via successor edges?
   if (IsReachable(SU, TargetSU))
     return true;
   for (const SDep &PredDep : TargetSU->Preds)
     if (PredDep.isAssignedRegDep() &&
         IsReachable(SU, PredDep.getSUnit()))
       return true;
   return false;
 }

 void ScheduleDAGTopologicalSort::AddSUnitWithoutPredecessors(const SUnit *SU) {
   assert(SU->NodeNum == Index2Node.size() && "Node cannot be added at the end");
   assert(SU->NumPreds == 0 && "Can only add SU's with no predecessors");
   Node2Index.push_back(Index2Node.size());
   Index2Node.push_back(SU->NodeNum);
   Visited.resize(Node2Index.size());
 }

 bool ScheduleDAGTopologicalSort::IsReachable(const SUnit *SU,
                                              const SUnit *TargetSU) {
   FixOrder();
   // If insertion of the edge SU->TargetSU would create a cycle
   // then there is a path from TargetSU to SU.
   int UpperBound, LowerBound;
   LowerBound = Node2Index[TargetSU->NodeNum];
   UpperBound = Node2Index[SU->NodeNum];
   bool HasLoop = false;
   // Is Ord(TargetSU) < Ord(SU) ?
   if (LowerBound < UpperBound) {
     Visited.reset();
     // There may be a path from TargetSU to SU. Check for it.
     DFS(TargetSU, UpperBound, HasLoop);
   }
   return HasLoop;
 }

 void ScheduleDAGTopologicalSort::Allocate(int n, int index) {
   Node2Index[n] = index;
   Index2Node[index] = n;
 }

 ScheduleDAGTopologicalSort::
 ScheduleDAGTopologicalSort(std::vector<SUnit> &sunits, SUnit *exitsu)
   : SUnits(sunits), ExitSU(exitsu) {}

 ScheduleHazardRecognizer::~ScheduleHazardRecognizer() = default;
	//===- ScheduleDAG.cpp - Implement the ScheduleDAG class ------------------===//
	//
	// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
	// See https://llvm.org/LICENSE.txt for license information.
	// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
	//
	//===----------------------------------------------------------------------===//
	//
	/// \file Implements the ScheduleDAG class, which is a base class used by
	/// scheduling implementation classes.
	//
	//===----------------------------------------------------------------------===//

	#include "llvm/CodeGen/ScheduleDAG.h"
	#include "llvm/ADT/STLExtras.h"
	#include "llvm/ADT/SmallVector.h"
	#include "llvm/ADT/Statistic.h"
	#include "llvm/ADT/iterator_range.h"
	#include "llvm/CodeGen/MachineFunction.h"
	#include "llvm/CodeGen/ScheduleHazardRecognizer.h"
	#include "llvm/CodeGen/SelectionDAGNodes.h"
	#include "llvm/CodeGen/TargetInstrInfo.h"
	#include "llvm/CodeGen/TargetRegisterInfo.h"
	#include "llvm/CodeGen/TargetSubtargetInfo.h"
	#include "llvm/Config/llvm-config.h"
	#include "llvm/Support/CommandLine.h"
	#include "llvm/Support/Compiler.h"
	#include "llvm/Support/Debug.h"
	#include "llvm/Support/raw_ostream.h"
	#include <algorithm>
	#include <cassert>
	#include <iterator>
	#include <limits>
	#include <utility>
	#include <vector>

	using namespace llvm;

	#define DEBUG_TYPE "pre-RA-sched"

	STATISTIC(NumNewPredsAdded, "Number of times a single predecessor was added");
	STATISTIC(NumTopoInits,
	"Number of times the topological order has been recomputed");

	#ifndef NDEBUG
	static cl::opt<bool> StressSchedOpt(
	"stress-sched", cl::Hidden, cl::init(false),
	cl::desc("Stress test instruction scheduling"));
	#endif

	void SchedulingPriorityQueue::anchor() {}

	ScheduleDAG::ScheduleDAG(MachineFunction &mf)
	: TM(mf.getTarget()), TII(mf.getSubtarget().getInstrInfo()),
	TRI(mf.getSubtarget().getRegisterInfo()), MF(mf),
	MRI(mf.getRegInfo()) {
	#ifndef NDEBUG
	StressSched = StressSchedOpt;
	#endif
	}

	ScheduleDAG::~ScheduleDAG() = default;

	void ScheduleDAG::clearDAG() {
	SUnits.clear();
	EntrySU = SUnit();
	ExitSU = SUnit();
	}

	const MCInstrDesc ScheduleDAG::getNodeDesc(const SDNode Node) const {
	if (!Node \|\| !Node->isMachineOpcode()) return nullptr;
	return &TII->get(Node->getMachineOpcode());
	}

	LLVM_DUMP_METHOD void SDep::dump(const TargetRegisterInfo *TRI) const {
	switch (getKind()) {
	case Data: dbgs() << "Data"; break;
	case Anti: dbgs() << "Anti"; break;
	case Output: dbgs() << "Out "; break;
	case Order: dbgs() << "Ord "; break;
	}

	switch (getKind()) {
	case Data:
	dbgs() << " Latency=" << getLatency();
	if (TRI && isAssignedRegDep())
	dbgs() << " Reg=" << printReg(getReg(), TRI);
	break;
	case Anti:
	case Output:
	dbgs() << " Latency=" << getLatency();
	break;
	case Order:
	dbgs() << " Latency=" << getLatency();
	switch(Contents.OrdKind) {
	case Barrier: dbgs() << " Barrier"; break;
	case MayAliasMem:
	case MustAliasMem: dbgs() << " Memory"; break;
	case Artificial: dbgs() << " Artificial"; break;
	case Weak: dbgs() << " Weak"; break;
	case Cluster: dbgs() << " Cluster"; break;
	}
	break;
	}
	}

	bool SUnit::addPred(const SDep &D, bool Required) {
	// If this node already has this dependence, don't add a redundant one.
	for (SDep &PredDep : Preds) {
	// Zero-latency weak edges may be added purely for heuristic ordering. Don't
	// add them if another kind of edge already exists.
	if (!Required && PredDep.getSUnit() == D.getSUnit())
	return false;
	if (PredDep.overlaps(D)) {
	// Extend the latency if needed. Equivalent to
	// removePred(PredDep) + addPred(D).
	if (PredDep.getLatency() < D.getLatency()) {
	SUnit *PredSU = PredDep.getSUnit();
	// Find the corresponding successor in N.
	SDep ForwardD = PredDep;
	ForwardD.setSUnit(this);
	for (SDep &SuccDep : PredSU->Succs) {
	if (SuccDep == ForwardD) {
	SuccDep.setLatency(D.getLatency());
	break;
	}
	}
	PredDep.setLatency(D.getLatency());
	}
	return false;
	}
	}
	// Now add a corresponding succ to N.
	SDep P = D;
	P.setSUnit(this);
	SUnit *N = D.getSUnit();
	// Update the bookkeeping.
	if (D.getKind() == SDep::Data) {
	assert(NumPreds < std::numeric_limits<unsigned>::max() &&
	"NumPreds will overflow!");
	assert(N->NumSuccs < std::numeric_limits<unsigned>::max() &&
	"NumSuccs will overflow!");
	++NumPreds;
	++N->NumSuccs;
	}
	if (!N->isScheduled) {
	if (D.isWeak()) {
	++WeakPredsLeft;
	}
	else {
	assert(NumPredsLeft < std::numeric_limits<unsigned>::max() &&
	"NumPredsLeft will overflow!");
	++NumPredsLeft;
	}
	}
	if (!isScheduled) {
	if (D.isWeak()) {
	++N->WeakSuccsLeft;
	}
	else {
	assert(N->NumSuccsLeft < std::numeric_limits<unsigned>::max() &&
	"NumSuccsLeft will overflow!");
	++N->NumSuccsLeft;
	}
	}
	Preds.push_back(D);
	N->Succs.push_back(P);
	if (P.getLatency() != 0) {
	this->setDepthDirty();
	N->setHeightDirty();
	}
	return true;
	}

	void SUnit::removePred(const SDep &D) {
	// Find the matching predecessor.
	SmallVectorImpl<SDep>::iterator I = llvm::find(Preds, D);
	if (I == Preds.end())
	return;
	// Find the corresponding successor in N.
	SDep P = D;
	P.setSUnit(this);
	SUnit *N = D.getSUnit();
	SmallVectorImpl<SDep>::iterator Succ = llvm::find(N->Succs, P);
	assert(Succ != N->Succs.end() && "Mismatching preds / succs lists!");
	N->Succs.erase(Succ);
	Preds.erase(I);
	// Update the bookkeeping.
	if (P.getKind() == SDep::Data) {
	assert(NumPreds > 0 && "NumPreds will underflow!");
	assert(N->NumSuccs > 0 && "NumSuccs will underflow!");
	--NumPreds;
	--N->NumSuccs;
	}
	if (!N->isScheduled) {
	if (D.isWeak())
	--WeakPredsLeft;
	else {
	assert(NumPredsLeft > 0 && "NumPredsLeft will underflow!");
	--NumPredsLeft;
	}
	}
	if (!isScheduled) {
	if (D.isWeak())
	--N->WeakSuccsLeft;
	else {
	assert(N->NumSuccsLeft > 0 && "NumSuccsLeft will underflow!");
	--N->NumSuccsLeft;
	}
	}
	if (P.getLatency() != 0) {
	this->setDepthDirty();
	N->setHeightDirty();
	}
	}

	void SUnit::setDepthDirty() {
	if (!isDepthCurrent) return;
	SmallVector<SUnit*, 8> WorkList;
	WorkList.push_back(this);
	do {
	SUnit *SU = WorkList.pop_back_val();
	SU->isDepthCurrent = false;
	for (SDep &SuccDep : SU->Succs) {
	SUnit *SuccSU = SuccDep.getSUnit();
	if (SuccSU->isDepthCurrent)
	WorkList.push_back(SuccSU);
	}
	} while (!WorkList.empty());
	}

	void SUnit::setHeightDirty() {
	if (!isHeightCurrent) return;
	SmallVector<SUnit*, 8> WorkList;
	WorkList.push_back(this);
	do {
	SUnit *SU = WorkList.pop_back_val();
	SU->isHeightCurrent = false;
	for (SDep &PredDep : SU->Preds) {
	SUnit *PredSU = PredDep.getSUnit();
	if (PredSU->isHeightCurrent)
	WorkList.push_back(PredSU);
	}
	} while (!WorkList.empty());
	}

	void SUnit::setDepthToAtLeast(unsigned NewDepth) {
	if (NewDepth <= getDepth())
	return;
	setDepthDirty();
	Depth = NewDepth;
	isDepthCurrent = true;
	}

	void SUnit::setHeightToAtLeast(unsigned NewHeight) {
	if (NewHeight <= getHeight())
	return;
	setHeightDirty();
	Height = NewHeight;
	isHeightCurrent = true;
	}

	/// Calculates the maximal path from the node to the exit.
	void SUnit::ComputeDepth() {
	SmallVector<SUnit*, 8> WorkList;
	WorkList.push_back(this);
	do {
	SUnit *Cur = WorkList.back();

	bool Done = true;
	unsigned MaxPredDepth = 0;
	for (const SDep &PredDep : Cur->Preds) {
	SUnit *PredSU = PredDep.getSUnit();
	if (PredSU->isDepthCurrent)
	MaxPredDepth = std::max(MaxPredDepth,
	PredSU->Depth + PredDep.getLatency());
	else {
	Done = false;
	WorkList.push_back(PredSU);
	}
	}

	if (Done) {
	WorkList.pop_back();
	if (MaxPredDepth != Cur->Depth) {
	Cur->setDepthDirty();
	Cur->Depth = MaxPredDepth;
	}
	Cur->isDepthCurrent = true;
	}
	} while (!WorkList.empty());
	}

	/// Calculates the maximal path from the node to the entry.
	void SUnit::ComputeHeight() {
	SmallVector<SUnit*, 8> WorkList;
	WorkList.push_back(this);
	do {
	SUnit *Cur = WorkList.back();

	bool Done = true;
	unsigned MaxSuccHeight = 0;
	for (const SDep &SuccDep : Cur->Succs) {
	SUnit *SuccSU = SuccDep.getSUnit();
	if (SuccSU->isHeightCurrent)
	MaxSuccHeight = std::max(MaxSuccHeight,
	SuccSU->Height + SuccDep.getLatency());
	else {
	Done = false;
	WorkList.push_back(SuccSU);
	}
	}

	if (Done) {
	WorkList.pop_back();
	if (MaxSuccHeight != Cur->Height) {
	Cur->setHeightDirty();
	Cur->Height = MaxSuccHeight;
	}
	Cur->isHeightCurrent = true;
	}
	} while (!WorkList.empty());
	}

	void SUnit::biasCriticalPath() {
	if (NumPreds < 2)
	return;

	SUnit::pred_iterator BestI = Preds.begin();
	unsigned MaxDepth = BestI->getSUnit()->getDepth();
	for (SUnit::pred_iterator I = std::next(BestI), E = Preds.end(); I != E;
	++I) {
	if (I->getKind() == SDep::Data && I->getSUnit()->getDepth() > MaxDepth)
	BestI = I;
	}
	if (BestI != Preds.begin())
	std::swap(Preds.begin(), BestI);
	}

	#if !defined(NDEBUG) \|\| defined(LLVM_ENABLE_DUMP)
	LLVM_DUMP_METHOD void SUnit::dumpAttributes() const {
	dbgs() << " # preds left : " << NumPredsLeft << "\n";
	dbgs() << " # succs left : " << NumSuccsLeft << "\n";
	if (WeakPredsLeft)
	dbgs() << " # weak preds left : " << WeakPredsLeft << "\n";
	if (WeakSuccsLeft)
	dbgs() << " # weak succs left : " << WeakSuccsLeft << "\n";
	dbgs() << " # rdefs left : " << NumRegDefsLeft << "\n";
	dbgs() << " Latency : " << Latency << "\n";
	dbgs() << " Depth : " << getDepth() << "\n";
	dbgs() << " Height : " << getHeight() << "\n";
	}

	LLVM_DUMP_METHOD void ScheduleDAG::dumpNodeName(const SUnit &SU) const {
	if (&SU == &EntrySU)
	dbgs() << "EntrySU";
	else if (&SU == &ExitSU)
	dbgs() << "ExitSU";
	else
	dbgs() << "SU(" << SU.NodeNum << ")";
	}

	LLVM_DUMP_METHOD void ScheduleDAG::dumpNodeAll(const SUnit &SU) const {
	dumpNode(SU);
	SU.dumpAttributes();
	if (SU.Preds.size() > 0) {
	dbgs() << " Predecessors:\n";
	for (const SDep &Dep : SU.Preds) {
	dbgs() << " ";
	dumpNodeName(*Dep.getSUnit());
	dbgs() << ": ";
	Dep.dump(TRI);
	dbgs() << '\n';
	}
	}
	if (SU.Succs.size() > 0) {
	dbgs() << " Successors:\n";
	for (const SDep &Dep : SU.Succs) {
	dbgs() << " ";
	dumpNodeName(*Dep.getSUnit());
	dbgs() << ": ";
	Dep.dump(TRI);
	dbgs() << '\n';
	}
	}
	}
	#endif

	#ifndef NDEBUG
	unsigned ScheduleDAG::VerifyScheduledDAG(bool isBottomUp) {
	bool AnyNotSched = false;
	unsigned DeadNodes = 0;
	for (const SUnit &SUnit : SUnits) {
	if (!SUnit.isScheduled) {
	if (SUnit.NumPreds == 0 && SUnit.NumSuccs == 0) {
	++DeadNodes;
	continue;
	}
	if (!AnyNotSched)
	dbgs() << "* Scheduling failed! *\n";
	dumpNode(SUnit);
	dbgs() << "has not been scheduled!\n";
	AnyNotSched = true;
	}
	if (SUnit.isScheduled &&
	(isBottomUp ? SUnit.getHeight() : SUnit.getDepth()) >
	unsigned(std::numeric_limits<int>::max())) {
	if (!AnyNotSched)
	dbgs() << "* Scheduling failed! *\n";
	dumpNode(SUnit);
	dbgs() << "has an unexpected "
	<< (isBottomUp ? "Height" : "Depth") << " value!\n";
	AnyNotSched = true;
	}
	if (isBottomUp) {
	if (SUnit.NumSuccsLeft != 0) {
	if (!AnyNotSched)
	dbgs() << "* Scheduling failed! *\n";
	dumpNode(SUnit);
	dbgs() << "has successors left!\n";
	AnyNotSched = true;
	}
	} else {
	if (SUnit.NumPredsLeft != 0) {
	if (!AnyNotSched)
	dbgs() << "* Scheduling failed! *\n";
	dumpNode(SUnit);
	dbgs() << "has predecessors left!\n";
	AnyNotSched = true;
	}
	}
	}
	assert(!AnyNotSched);
	return SUnits.size() - DeadNodes;
	}
	#endif

	void ScheduleDAGTopologicalSort::InitDAGTopologicalSorting() {
	// The idea of the algorithm is taken from
	// "Online algorithms for managing the topological order of
	// a directed acyclic graph" by David J. Pearce and Paul H.J. Kelly
	// This is the MNR algorithm, which was first introduced by
	// A. Marchetti-Spaccamela, U. Nanni and H. Rohnert in
	// "Maintaining a topological order under edge insertions".
	//
	// Short description of the algorithm:
	//
	// Topological ordering, ord, of a DAG maps each node to a topological
	// index so that for all edges X->Y it is the case that ord(X) < ord(Y).
	//
	// This means that if there is a path from the node X to the node Z,
	// then ord(X) < ord(Z).
	//
	// This property can be used to check for reachability of nodes:
	// if Z is reachable from X, then an insertion of the edge Z->X would
	// create a cycle.
	//
	// The algorithm first computes a topological ordering for the DAG by
	// initializing the Index2Node and Node2Index arrays and then tries to keep
	// the ordering up-to-date after edge insertions by reordering the DAG.
	//
	// On insertion of the edge X->Y, the algorithm first marks by calling DFS
	// the nodes reachable from Y, and then shifts them using Shift to lie
	// immediately after X in Index2Node.

	// Cancel pending updates, mark as valid.
	Dirty = false;
	Updates.clear();

	unsigned DAGSize = SUnits.size();
	std::vector<SUnit*> WorkList;
	WorkList.reserve(DAGSize);

	Index2Node.resize(DAGSize);
	Node2Index.resize(DAGSize);

	// Initialize the data structures.
	if (ExitSU)
	WorkList.push_back(ExitSU);
	for (SUnit &SU : SUnits) {
	int NodeNum = SU.NodeNum;
	unsigned Degree = SU.Succs.size();
	// Temporarily use the Node2Index array as scratch space for degree counts.
	Node2Index[NodeNum] = Degree;

	// Is it a node without dependencies?
	if (Degree == 0) {
	assert(SU.Succs.empty() && "SUnit should have no successors");
	// Collect leaf nodes.
	WorkList.push_back(&SU);
	}
	}

	int Id = DAGSize;
	while (!WorkList.empty()) {
	SUnit *SU = WorkList.back();
	WorkList.pop_back();
	if (SU->NodeNum < DAGSize)
	Allocate(SU->NodeNum, --Id);
	for (const SDep &PredDep : SU->Preds) {
	SUnit *SU = PredDep.getSUnit();
	if (SU->NodeNum < DAGSize && !--Node2Index[SU->NodeNum])
	// If all dependencies of the node are processed already,
	// then the node can be computed now.
	WorkList.push_back(SU);
	}
	}

	Visited.resize(DAGSize);
	NumTopoInits++;

	#ifndef NDEBUG
	// Check correctness of the ordering
	for (SUnit &SU : SUnits) {
	for (const SDep &PD : SU.Preds) {
	assert(Node2Index[SU.NodeNum] > Node2Index[PD.getSUnit()->NodeNum] &&
	"Wrong topological sorting");
	}
	}
	#endif
	}

	void ScheduleDAGTopologicalSort::FixOrder() {
	// Recompute from scratch after new nodes have been added.
	if (Dirty) {
	InitDAGTopologicalSorting();
	return;
	}

	// Otherwise apply updates one-by-one.
	for (auto &U : Updates)
	AddPred(U.first, U.second);
	Updates.clear();
	}

	void ScheduleDAGTopologicalSort::AddPredQueued(SUnit Y, SUnit X) {
	// Recomputing the order from scratch is likely more efficient than applying
	// updates one-by-one for too many updates. The current cut-off is arbitrarily
	// chosen.
	Dirty = Dirty \|\| Updates.size() > 10;

	if (Dirty)
	return;

	Updates.emplace_back(Y, X);
	}

	void ScheduleDAGTopologicalSort::AddPred(SUnit Y, SUnit X) {
	int UpperBound, LowerBound;
	LowerBound = Node2Index[Y->NodeNum];
	UpperBound = Node2Index[X->NodeNum];
	bool HasLoop = false;
	// Is Ord(X) < Ord(Y) ?
	if (LowerBound < UpperBound) {
	// Update the topological order.
	Visited.reset();
	DFS(Y, UpperBound, HasLoop);
	assert(!HasLoop && "Inserted edge creates a loop!");
	// Recompute topological indexes.
	Shift(Visited, LowerBound, UpperBound);
	}

	NumNewPredsAdded++;
	}

	void ScheduleDAGTopologicalSort::RemovePred(SUnit M, SUnit N) {
	// InitDAGTopologicalSorting();
	}

	void ScheduleDAGTopologicalSort::DFS(const SUnit *SU, int UpperBound,
	bool &HasLoop) {
	std::vector<const SUnit*> WorkList;
	WorkList.reserve(SUnits.size());

	WorkList.push_back(SU);
	do {
	SU = WorkList.back();
	WorkList.pop_back();
	Visited.set(SU->NodeNum);
	for (const SDep &SuccDep
	: make_range(SU->Succs.rbegin(), SU->Succs.rend())) {
	unsigned s = SuccDep.getSUnit()->NodeNum;
	// Edges to non-SUnits are allowed but ignored (e.g. ExitSU).
	if (s >= Node2Index.size())
	continue;
	if (Node2Index[s] == UpperBound) {
	HasLoop = true;
	return;
	}
	// Visit successors if not already and in affected region.
	if (!Visited.test(s) && Node2Index[s] < UpperBound) {
	WorkList.push_back(SuccDep.getSUnit());
	}
	}
	} while (!WorkList.empty());
	}

	std::vector<int> ScheduleDAGTopologicalSort::GetSubGraph(const SUnit &StartSU,
	const SUnit &TargetSU,
	bool &Success) {
	std::vector<const SUnit*> WorkList;
	int LowerBound = Node2Index[StartSU.NodeNum];
	int UpperBound = Node2Index[TargetSU.NodeNum];
	bool Found = false;
	BitVector VisitedBack;
	std::vector<int> Nodes;

	if (LowerBound > UpperBound) {
	Success = false;
	return Nodes;
	}

	WorkList.reserve(SUnits.size());
	Visited.reset();

	// Starting from StartSU, visit all successors up
	// to UpperBound.
	WorkList.push_back(&StartSU);
	do {
	const SUnit *SU = WorkList.back();
	WorkList.pop_back();
	for (int I = SU->Succs.size()-1; I >= 0; --I) {
	const SUnit *Succ = SU->Succs[I].getSUnit();
	unsigned s = Succ->NodeNum;
	// Edges to non-SUnits are allowed but ignored (e.g. ExitSU).
	if (Succ->isBoundaryNode())
	continue;
	if (Node2Index[s] == UpperBound) {
	Found = true;
	continue;
	}
	// Visit successors if not already and in affected region.
	if (!Visited.test(s) && Node2Index[s] < UpperBound) {
	Visited.set(s);
	WorkList.push_back(Succ);
	}
	}
	} while (!WorkList.empty());

	if (!Found) {
	Success = false;
	return Nodes;
	}

	WorkList.clear();
	VisitedBack.resize(SUnits.size());
	Found = false;

	// Starting from TargetSU, visit all predecessors up
	// to LowerBound. SUs that are visited by the two
	// passes are added to Nodes.
	WorkList.push_back(&TargetSU);
	do {
	const SUnit *SU = WorkList.back();
	WorkList.pop_back();
	for (int I = SU->Preds.size()-1; I >= 0; --I) {
	const SUnit *Pred = SU->Preds[I].getSUnit();
	unsigned s = Pred->NodeNum;
	// Edges to non-SUnits are allowed but ignored (e.g. EntrySU).
	if (Pred->isBoundaryNode())
	continue;
	if (Node2Index[s] == LowerBound) {
	Found = true;
	continue;
	}
	if (!VisitedBack.test(s) && Visited.test(s)) {
	VisitedBack.set(s);
	WorkList.push_back(Pred);
	Nodes.push_back(s);
	}
	}
	} while (!WorkList.empty());

	assert(Found && "Error in SUnit Graph!");
	Success = true;
	return Nodes;
	}

	void ScheduleDAGTopologicalSort::Shift(BitVector& Visited, int LowerBound,
	int UpperBound) {
	std::vector<int> L;
	int shift = 0;
	int i;

	for (i = LowerBound; i <= UpperBound; ++i) {
	// w is node at topological index i.
	int w = Index2Node[i];
	if (Visited.test(w)) {
	// Unmark.
	Visited.reset(w);
	L.push_back(w);
	shift = shift + 1;
	} else {
	Allocate(w, i - shift);
	}
	}

	for (unsigned LI : L) {
	Allocate(LI, i - shift);
	i = i + 1;
	}
	}

	bool ScheduleDAGTopologicalSort::WillCreateCycle(SUnit TargetSU, SUnit SU) {
	FixOrder();
	// Is SU reachable from TargetSU via successor edges?
	if (IsReachable(SU, TargetSU))
	return true;
	for (const SDep &PredDep : TargetSU->Preds)
	if (PredDep.isAssignedRegDep() &&
	IsReachable(SU, PredDep.getSUnit()))
	return true;
	return false;
	}

	void ScheduleDAGTopologicalSort::AddSUnitWithoutPredecessors(const SUnit *SU) {
	assert(SU->NodeNum == Index2Node.size() && "Node cannot be added at the end");
	assert(SU->NumPreds == 0 && "Can only add SU's with no predecessors");
	Node2Index.push_back(Index2Node.size());
	Index2Node.push_back(SU->NodeNum);
	Visited.resize(Node2Index.size());
	}

	bool ScheduleDAGTopologicalSort::IsReachable(const SUnit *SU,
	const SUnit *TargetSU) {
	FixOrder();
	// If insertion of the edge SU->TargetSU would create a cycle
	// then there is a path from TargetSU to SU.
	int UpperBound, LowerBound;
	LowerBound = Node2Index[TargetSU->NodeNum];
	UpperBound = Node2Index[SU->NodeNum];
	bool HasLoop = false;
	// Is Ord(TargetSU) < Ord(SU) ?
	if (LowerBound < UpperBound) {
	Visited.reset();
	// There may be a path from TargetSU to SU. Check for it.
	DFS(TargetSU, UpperBound, HasLoop);
	}
	return HasLoop;
	}

	void ScheduleDAGTopologicalSort::Allocate(int n, int index) {
	Node2Index[n] = index;
	Index2Node[index] = n;
	}

	ScheduleDAGTopologicalSort::
	ScheduleDAGTopologicalSort(std::vector<SUnit> &sunits, SUnit *exitsu)
	: SUnits(sunits), ExitSU(exitsu) {}

	ScheduleHazardRecognizer::~ScheduleHazardRecognizer() = default;