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 /// \file Implements the ScheduleDAG class, which is a base class used by
11 /// scheduling implementation classes.
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #include "llvm/CodeGen/ScheduleDAG.h"
16 #include "llvm/ADT/STLExtras.h"
17 #include "llvm/ADT/SmallVector.h"
18 #include "llvm/ADT/iterator_range.h"
19 #include "llvm/CodeGen/MachineFunction.h"
20 #include "llvm/CodeGen/ScheduleHazardRecognizer.h"
21 #include "llvm/CodeGen/SelectionDAGNodes.h"
22 #include "llvm/CodeGen/TargetInstrInfo.h"
23 #include "llvm/CodeGen/TargetRegisterInfo.h"
24 #include "llvm/CodeGen/TargetSubtargetInfo.h"
25 #include "llvm/Config/llvm-config.h"
26 #include "llvm/Support/CommandLine.h"
27 #include "llvm/Support/Compiler.h"
28 #include "llvm/Support/Debug.h"
29 #include "llvm/Support/raw_ostream.h"
30 #include <algorithm>
31 #include <cassert>
32 #include <iterator>
33 #include <limits>
34 #include <utility>
35 #include <vector>
36 
37 using namespace llvm;
38 
39 #define DEBUG_TYPE "pre-RA-sched"
40 
41 #ifndef NDEBUG
42 static cl::opt<bool> StressSchedOpt(
43   "stress-sched", cl::Hidden, cl::init(false),
44   cl::desc("Stress test instruction scheduling"));
45 #endif
46 
47 void SchedulingPriorityQueue::anchor() {}
48 
49 ScheduleDAG::ScheduleDAG(MachineFunction &mf)
50     : TM(mf.getTarget()), TII(mf.getSubtarget().getInstrInfo()),
51       TRI(mf.getSubtarget().getRegisterInfo()), MF(mf),
52       MRI(mf.getRegInfo()) {
53 #ifndef NDEBUG
54   StressSched = StressSchedOpt;
55 #endif
56 }
57 
58 ScheduleDAG::~ScheduleDAG() = default;
59 
60 void ScheduleDAG::clearDAG() {
61   SUnits.clear();
62   EntrySU = SUnit();
63   ExitSU = SUnit();
64 }
65 
66 const MCInstrDesc *ScheduleDAG::getNodeDesc(const SDNode *Node) const {
67   if (!Node || !Node->isMachineOpcode()) return nullptr;
68   return &TII->get(Node->getMachineOpcode());
69 }
70 
71 LLVM_DUMP_METHOD void SDep::dump(const TargetRegisterInfo *TRI) const {
72   switch (getKind()) {
73   case Data:   dbgs() << "Data"; break;
74   case Anti:   dbgs() << "Anti"; break;
75   case Output: dbgs() << "Out "; break;
76   case Order:  dbgs() << "Ord "; break;
77   }
78 
79   switch (getKind()) {
80   case Data:
81     dbgs() << " Latency=" << getLatency();
82     if (TRI && isAssignedRegDep())
83       dbgs() << " Reg=" << printReg(getReg(), TRI);
84     break;
85   case Anti:
86   case Output:
87     dbgs() << " Latency=" << getLatency();
88     break;
89   case Order:
90     dbgs() << " Latency=" << getLatency();
91     switch(Contents.OrdKind) {
92     case Barrier:      dbgs() << " Barrier"; break;
93     case MayAliasMem:
94     case MustAliasMem: dbgs() << " Memory"; break;
95     case Artificial:   dbgs() << " Artificial"; break;
96     case Weak:         dbgs() << " Weak"; break;
97     case Cluster:      dbgs() << " Cluster"; break;
98     }
99     break;
100   }
101 }
102 
103 bool SUnit::addPred(const SDep &D, bool Required) {
104   // If this node already has this dependence, don't add a redundant one.
105   for (SDep &PredDep : Preds) {
106     // Zero-latency weak edges may be added purely for heuristic ordering. Don't
107     // add them if another kind of edge already exists.
108     if (!Required && PredDep.getSUnit() == D.getSUnit())
109       return false;
110     if (PredDep.overlaps(D)) {
111       // Extend the latency if needed. Equivalent to
112       // removePred(PredDep) + addPred(D).
113       if (PredDep.getLatency() < D.getLatency()) {
114         SUnit *PredSU = PredDep.getSUnit();
115         // Find the corresponding successor in N.
116         SDep ForwardD = PredDep;
117         ForwardD.setSUnit(this);
118         for (SDep &SuccDep : PredSU->Succs) {
119           if (SuccDep == ForwardD) {
120             SuccDep.setLatency(D.getLatency());
121             break;
122           }
123         }
124         PredDep.setLatency(D.getLatency());
125       }
126       return false;
127     }
128   }
129   // Now add a corresponding succ to N.
130   SDep P = D;
131   P.setSUnit(this);
132   SUnit *N = D.getSUnit();
133   // Update the bookkeeping.
134   if (D.getKind() == SDep::Data) {
135     assert(NumPreds < std::numeric_limits<unsigned>::max() &&
136            "NumPreds will overflow!");
137     assert(N->NumSuccs < std::numeric_limits<unsigned>::max() &&
138            "NumSuccs will overflow!");
139     ++NumPreds;
140     ++N->NumSuccs;
141   }
142   if (!N->isScheduled) {
143     if (D.isWeak()) {
144       ++WeakPredsLeft;
145     }
146     else {
147       assert(NumPredsLeft < std::numeric_limits<unsigned>::max() &&
148              "NumPredsLeft will overflow!");
149       ++NumPredsLeft;
150     }
151   }
152   if (!isScheduled) {
153     if (D.isWeak()) {
154       ++N->WeakSuccsLeft;
155     }
156     else {
157       assert(N->NumSuccsLeft < std::numeric_limits<unsigned>::max() &&
158              "NumSuccsLeft will overflow!");
159       ++N->NumSuccsLeft;
160     }
161   }
162   Preds.push_back(D);
163   N->Succs.push_back(P);
164   if (P.getLatency() != 0) {
165     this->setDepthDirty();
166     N->setHeightDirty();
167   }
168   return true;
169 }
170 
171 void SUnit::removePred(const SDep &D) {
172   // Find the matching predecessor.
173   SmallVectorImpl<SDep>::iterator I = llvm::find(Preds, D);
174   if (I == Preds.end())
175     return;
176   // Find the corresponding successor in N.
177   SDep P = D;
178   P.setSUnit(this);
179   SUnit *N = D.getSUnit();
180   SmallVectorImpl<SDep>::iterator Succ = llvm::find(N->Succs, P);
181   assert(Succ != N->Succs.end() && "Mismatching preds / succs lists!");
182   N->Succs.erase(Succ);
183   Preds.erase(I);
184   // Update the bookkeeping.
185   if (P.getKind() == SDep::Data) {
186     assert(NumPreds > 0 && "NumPreds will underflow!");
187     assert(N->NumSuccs > 0 && "NumSuccs will underflow!");
188     --NumPreds;
189     --N->NumSuccs;
190   }
191   if (!N->isScheduled) {
192     if (D.isWeak())
193       --WeakPredsLeft;
194     else {
195       assert(NumPredsLeft > 0 && "NumPredsLeft will underflow!");
196       --NumPredsLeft;
197     }
198   }
199   if (!isScheduled) {
200     if (D.isWeak())
201       --N->WeakSuccsLeft;
202     else {
203       assert(N->NumSuccsLeft > 0 && "NumSuccsLeft will underflow!");
204       --N->NumSuccsLeft;
205     }
206   }
207   if (P.getLatency() != 0) {
208     this->setDepthDirty();
209     N->setHeightDirty();
210   }
211 }
212 
213 void SUnit::setDepthDirty() {
214   if (!isDepthCurrent) return;
215   SmallVector<SUnit*, 8> WorkList;
216   WorkList.push_back(this);
217   do {
218     SUnit *SU = WorkList.pop_back_val();
219     SU->isDepthCurrent = false;
220     for (SDep &SuccDep : SU->Succs) {
221       SUnit *SuccSU = SuccDep.getSUnit();
222       if (SuccSU->isDepthCurrent)
223         WorkList.push_back(SuccSU);
224     }
225   } while (!WorkList.empty());
226 }
227 
228 void SUnit::setHeightDirty() {
229   if (!isHeightCurrent) return;
230   SmallVector<SUnit*, 8> WorkList;
231   WorkList.push_back(this);
232   do {
233     SUnit *SU = WorkList.pop_back_val();
234     SU->isHeightCurrent = false;
235     for (SDep &PredDep : SU->Preds) {
236       SUnit *PredSU = PredDep.getSUnit();
237       if (PredSU->isHeightCurrent)
238         WorkList.push_back(PredSU);
239     }
240   } while (!WorkList.empty());
241 }
242 
243 void SUnit::setDepthToAtLeast(unsigned NewDepth) {
244   if (NewDepth <= getDepth())
245     return;
246   setDepthDirty();
247   Depth = NewDepth;
248   isDepthCurrent = true;
249 }
250 
251 void SUnit::setHeightToAtLeast(unsigned NewHeight) {
252   if (NewHeight <= getHeight())
253     return;
254   setHeightDirty();
255   Height = NewHeight;
256   isHeightCurrent = true;
257 }
258 
259 /// Calculates the maximal path from the node to the exit.
260 void SUnit::ComputeDepth() {
261   SmallVector<SUnit*, 8> WorkList;
262   WorkList.push_back(this);
263   do {
264     SUnit *Cur = WorkList.back();
265 
266     bool Done = true;
267     unsigned MaxPredDepth = 0;
268     for (const SDep &PredDep : Cur->Preds) {
269       SUnit *PredSU = PredDep.getSUnit();
270       if (PredSU->isDepthCurrent)
271         MaxPredDepth = std::max(MaxPredDepth,
272                                 PredSU->Depth + PredDep.getLatency());
273       else {
274         Done = false;
275         WorkList.push_back(PredSU);
276       }
277     }
278 
279     if (Done) {
280       WorkList.pop_back();
281       if (MaxPredDepth != Cur->Depth) {
282         Cur->setDepthDirty();
283         Cur->Depth = MaxPredDepth;
284       }
285       Cur->isDepthCurrent = true;
286     }
287   } while (!WorkList.empty());
288 }
289 
290 /// Calculates the maximal path from the node to the entry.
291 void SUnit::ComputeHeight() {
292   SmallVector<SUnit*, 8> WorkList;
293   WorkList.push_back(this);
294   do {
295     SUnit *Cur = WorkList.back();
296 
297     bool Done = true;
298     unsigned MaxSuccHeight = 0;
299     for (const SDep &SuccDep : Cur->Succs) {
300       SUnit *SuccSU = SuccDep.getSUnit();
301       if (SuccSU->isHeightCurrent)
302         MaxSuccHeight = std::max(MaxSuccHeight,
303                                  SuccSU->Height + SuccDep.getLatency());
304       else {
305         Done = false;
306         WorkList.push_back(SuccSU);
307       }
308     }
309 
310     if (Done) {
311       WorkList.pop_back();
312       if (MaxSuccHeight != Cur->Height) {
313         Cur->setHeightDirty();
314         Cur->Height = MaxSuccHeight;
315       }
316       Cur->isHeightCurrent = true;
317     }
318   } while (!WorkList.empty());
319 }
320 
321 void SUnit::biasCriticalPath() {
322   if (NumPreds < 2)
323     return;
324 
325   SUnit::pred_iterator BestI = Preds.begin();
326   unsigned MaxDepth = BestI->getSUnit()->getDepth();
327   for (SUnit::pred_iterator I = std::next(BestI), E = Preds.end(); I != E;
328        ++I) {
329     if (I->getKind() == SDep::Data && I->getSUnit()->getDepth() > MaxDepth)
330       BestI = I;
331   }
332   if (BestI != Preds.begin())
333     std::swap(*Preds.begin(), *BestI);
334 }
335 
336 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
337 LLVM_DUMP_METHOD void SUnit::dumpAttributes() const {
338   dbgs() << "  # preds left       : " << NumPredsLeft << "\n";
339   dbgs() << "  # succs left       : " << NumSuccsLeft << "\n";
340   if (WeakPredsLeft)
341     dbgs() << "  # weak preds left  : " << WeakPredsLeft << "\n";
342   if (WeakSuccsLeft)
343     dbgs() << "  # weak succs left  : " << WeakSuccsLeft << "\n";
344   dbgs() << "  # rdefs left       : " << NumRegDefsLeft << "\n";
345   dbgs() << "  Latency            : " << Latency << "\n";
346   dbgs() << "  Depth              : " << getDepth() << "\n";
347   dbgs() << "  Height             : " << getHeight() << "\n";
348 }
349 
350 LLVM_DUMP_METHOD void ScheduleDAG::dumpNodeName(const SUnit &SU) const {
351   if (&SU == &EntrySU)
352     dbgs() << "EntrySU";
353   else if (&SU == &ExitSU)
354     dbgs() << "ExitSU";
355   else
356     dbgs() << "SU(" << SU.NodeNum << ")";
357 }
358 
359 LLVM_DUMP_METHOD void ScheduleDAG::dumpNodeAll(const SUnit &SU) const {
360   dumpNode(SU);
361   SU.dumpAttributes();
362   if (SU.Preds.size() > 0) {
363     dbgs() << "  Predecessors:\n";
364     for (const SDep &Dep : SU.Preds) {
365       dbgs() << "    ";
366       dumpNodeName(*Dep.getSUnit());
367       dbgs() << ": ";
368       Dep.dump(TRI);
369       dbgs() << '\n';
370     }
371   }
372   if (SU.Succs.size() > 0) {
373     dbgs() << "  Successors:\n";
374     for (const SDep &Dep : SU.Succs) {
375       dbgs() << "    ";
376       dumpNodeName(*Dep.getSUnit());
377       dbgs() << ": ";
378       Dep.dump(TRI);
379       dbgs() << '\n';
380     }
381   }
382 }
383 #endif
384 
385 #ifndef NDEBUG
386 unsigned ScheduleDAG::VerifyScheduledDAG(bool isBottomUp) {
387   bool AnyNotSched = false;
388   unsigned DeadNodes = 0;
389   for (const SUnit &SUnit : SUnits) {
390     if (!SUnit.isScheduled) {
391       if (SUnit.NumPreds == 0 && SUnit.NumSuccs == 0) {
392         ++DeadNodes;
393         continue;
394       }
395       if (!AnyNotSched)
396         dbgs() << "*** Scheduling failed! ***\n";
397       dumpNode(SUnit);
398       dbgs() << "has not been scheduled!\n";
399       AnyNotSched = true;
400     }
401     if (SUnit.isScheduled &&
402         (isBottomUp ? SUnit.getHeight() : SUnit.getDepth()) >
403           unsigned(std::numeric_limits<int>::max())) {
404       if (!AnyNotSched)
405         dbgs() << "*** Scheduling failed! ***\n";
406       dumpNode(SUnit);
407       dbgs() << "has an unexpected "
408            << (isBottomUp ? "Height" : "Depth") << " value!\n";
409       AnyNotSched = true;
410     }
411     if (isBottomUp) {
412       if (SUnit.NumSuccsLeft != 0) {
413         if (!AnyNotSched)
414           dbgs() << "*** Scheduling failed! ***\n";
415         dumpNode(SUnit);
416         dbgs() << "has successors left!\n";
417         AnyNotSched = true;
418       }
419     } else {
420       if (SUnit.NumPredsLeft != 0) {
421         if (!AnyNotSched)
422           dbgs() << "*** Scheduling failed! ***\n";
423         dumpNode(SUnit);
424         dbgs() << "has predecessors left!\n";
425         AnyNotSched = true;
426       }
427     }
428   }
429   assert(!AnyNotSched);
430   return SUnits.size() - DeadNodes;
431 }
432 #endif
433 
434 void ScheduleDAGTopologicalSort::InitDAGTopologicalSorting() {
435   // The idea of the algorithm is taken from
436   // "Online algorithms for managing the topological order of
437   // a directed acyclic graph" by David J. Pearce and Paul H.J. Kelly
438   // This is the MNR algorithm, which was first introduced by
439   // A. Marchetti-Spaccamela, U. Nanni and H. Rohnert in
440   // "Maintaining a topological order under edge insertions".
441   //
442   // Short description of the algorithm:
443   //
444   // Topological ordering, ord, of a DAG maps each node to a topological
445   // index so that for all edges X->Y it is the case that ord(X) < ord(Y).
446   //
447   // This means that if there is a path from the node X to the node Z,
448   // then ord(X) < ord(Z).
449   //
450   // This property can be used to check for reachability of nodes:
451   // if Z is reachable from X, then an insertion of the edge Z->X would
452   // create a cycle.
453   //
454   // The algorithm first computes a topological ordering for the DAG by
455   // initializing the Index2Node and Node2Index arrays and then tries to keep
456   // the ordering up-to-date after edge insertions by reordering the DAG.
457   //
458   // On insertion of the edge X->Y, the algorithm first marks by calling DFS
459   // the nodes reachable from Y, and then shifts them using Shift to lie
460   // immediately after X in Index2Node.
461   unsigned DAGSize = SUnits.size();
462   std::vector<SUnit*> WorkList;
463   WorkList.reserve(DAGSize);
464 
465   Index2Node.resize(DAGSize);
466   Node2Index.resize(DAGSize);
467 
468   // Initialize the data structures.
469   if (ExitSU)
470     WorkList.push_back(ExitSU);
471   for (SUnit &SU : SUnits) {
472     int NodeNum = SU.NodeNum;
473     unsigned Degree = SU.Succs.size();
474     // Temporarily use the Node2Index array as scratch space for degree counts.
475     Node2Index[NodeNum] = Degree;
476 
477     // Is it a node without dependencies?
478     if (Degree == 0) {
479       assert(SU.Succs.empty() && "SUnit should have no successors");
480       // Collect leaf nodes.
481       WorkList.push_back(&SU);
482     }
483   }
484 
485   int Id = DAGSize;
486   while (!WorkList.empty()) {
487     SUnit *SU = WorkList.back();
488     WorkList.pop_back();
489     if (SU->NodeNum < DAGSize)
490       Allocate(SU->NodeNum, --Id);
491     for (const SDep &PredDep : SU->Preds) {
492       SUnit *SU = PredDep.getSUnit();
493       if (SU->NodeNum < DAGSize && !--Node2Index[SU->NodeNum])
494         // If all dependencies of the node are processed already,
495         // then the node can be computed now.
496         WorkList.push_back(SU);
497     }
498   }
499 
500   Visited.resize(DAGSize);
501 
502 #ifndef NDEBUG
503   // Check correctness of the ordering
504   for (SUnit &SU : SUnits)  {
505     for (const SDep &PD : SU.Preds) {
506       assert(Node2Index[SU.NodeNum] > Node2Index[PD.getSUnit()->NodeNum] &&
507       "Wrong topological sorting");
508     }
509   }
510 #endif
511 }
512 
513 void ScheduleDAGTopologicalSort::AddPred(SUnit *Y, SUnit *X) {
514   int UpperBound, LowerBound;
515   LowerBound = Node2Index[Y->NodeNum];
516   UpperBound = Node2Index[X->NodeNum];
517   bool HasLoop = false;
518   // Is Ord(X) < Ord(Y) ?
519   if (LowerBound < UpperBound) {
520     // Update the topological order.
521     Visited.reset();
522     DFS(Y, UpperBound, HasLoop);
523     assert(!HasLoop && "Inserted edge creates a loop!");
524     // Recompute topological indexes.
525     Shift(Visited, LowerBound, UpperBound);
526   }
527 }
528 
529 void ScheduleDAGTopologicalSort::RemovePred(SUnit *M, SUnit *N) {
530   // InitDAGTopologicalSorting();
531 }
532 
533 void ScheduleDAGTopologicalSort::DFS(const SUnit *SU, int UpperBound,
534                                      bool &HasLoop) {
535   std::vector<const SUnit*> WorkList;
536   WorkList.reserve(SUnits.size());
537 
538   WorkList.push_back(SU);
539   do {
540     SU = WorkList.back();
541     WorkList.pop_back();
542     Visited.set(SU->NodeNum);
543     for (const SDep &SuccDep
544          : make_range(SU->Succs.rbegin(), SU->Succs.rend())) {
545       unsigned s = SuccDep.getSUnit()->NodeNum;
546       // Edges to non-SUnits are allowed but ignored (e.g. ExitSU).
547       if (s >= Node2Index.size())
548         continue;
549       if (Node2Index[s] == UpperBound) {
550         HasLoop = true;
551         return;
552       }
553       // Visit successors if not already and in affected region.
554       if (!Visited.test(s) && Node2Index[s] < UpperBound) {
555         WorkList.push_back(SuccDep.getSUnit());
556       }
557     }
558   } while (!WorkList.empty());
559 }
560 
561 std::vector<int> ScheduleDAGTopologicalSort::GetSubGraph(const SUnit &StartSU,
562                                                          const SUnit &TargetSU,
563                                                          bool &Success) {
564   std::vector<const SUnit*> WorkList;
565   int LowerBound = Node2Index[StartSU.NodeNum];
566   int UpperBound = Node2Index[TargetSU.NodeNum];
567   bool Found = false;
568   BitVector VisitedBack;
569   std::vector<int> Nodes;
570 
571   if (LowerBound > UpperBound) {
572     Success = false;
573     return Nodes;
574   }
575 
576   WorkList.reserve(SUnits.size());
577   Visited.reset();
578 
579   // Starting from StartSU, visit all successors up
580   // to UpperBound.
581   WorkList.push_back(&StartSU);
582   do {
583     const SUnit *SU = WorkList.back();
584     WorkList.pop_back();
585     for (int I = SU->Succs.size()-1; I >= 0; --I) {
586       const SUnit *Succ = SU->Succs[I].getSUnit();
587       unsigned s = Succ->NodeNum;
588       // Edges to non-SUnits are allowed but ignored (e.g. ExitSU).
589       if (Succ->isBoundaryNode())
590         continue;
591       if (Node2Index[s] == UpperBound) {
592         Found = true;
593         continue;
594       }
595       // Visit successors if not already and in affected region.
596       if (!Visited.test(s) && Node2Index[s] < UpperBound) {
597         Visited.set(s);
598         WorkList.push_back(Succ);
599       }
600     }
601   } while (!WorkList.empty());
602 
603   if (!Found) {
604     Success = false;
605     return Nodes;
606   }
607 
608   WorkList.clear();
609   VisitedBack.resize(SUnits.size());
610   Found = false;
611 
612   // Starting from TargetSU, visit all predecessors up
613   // to LowerBound. SUs that are visited by the two
614   // passes are added to Nodes.
615   WorkList.push_back(&TargetSU);
616   do {
617     const SUnit *SU = WorkList.back();
618     WorkList.pop_back();
619     for (int I = SU->Preds.size()-1; I >= 0; --I) {
620       const SUnit *Pred = SU->Preds[I].getSUnit();
621       unsigned s = Pred->NodeNum;
622       // Edges to non-SUnits are allowed but ignored (e.g. EntrySU).
623       if (Pred->isBoundaryNode())
624         continue;
625       if (Node2Index[s] == LowerBound) {
626         Found = true;
627         continue;
628       }
629       if (!VisitedBack.test(s) && Visited.test(s)) {
630         VisitedBack.set(s);
631         WorkList.push_back(Pred);
632         Nodes.push_back(s);
633       }
634     }
635   } while (!WorkList.empty());
636 
637   assert(Found && "Error in SUnit Graph!");
638   Success = true;
639   return Nodes;
640 }
641 
642 void ScheduleDAGTopologicalSort::Shift(BitVector& Visited, int LowerBound,
643                                        int UpperBound) {
644   std::vector<int> L;
645   int shift = 0;
646   int i;
647 
648   for (i = LowerBound; i <= UpperBound; ++i) {
649     // w is node at topological index i.
650     int w = Index2Node[i];
651     if (Visited.test(w)) {
652       // Unmark.
653       Visited.reset(w);
654       L.push_back(w);
655       shift = shift + 1;
656     } else {
657       Allocate(w, i - shift);
658     }
659   }
660 
661   for (unsigned LI : L) {
662     Allocate(LI, i - shift);
663     i = i + 1;
664   }
665 }
666 
667 bool ScheduleDAGTopologicalSort::WillCreateCycle(SUnit *TargetSU, SUnit *SU) {
668   // Is SU reachable from TargetSU via successor edges?
669   if (IsReachable(SU, TargetSU))
670     return true;
671   for (const SDep &PredDep : TargetSU->Preds)
672     if (PredDep.isAssignedRegDep() &&
673         IsReachable(SU, PredDep.getSUnit()))
674       return true;
675   return false;
676 }
677 
678 bool ScheduleDAGTopologicalSort::IsReachable(const SUnit *SU,
679                                              const SUnit *TargetSU) {
680   // If insertion of the edge SU->TargetSU would create a cycle
681   // then there is a path from TargetSU to SU.
682   int UpperBound, LowerBound;
683   LowerBound = Node2Index[TargetSU->NodeNum];
684   UpperBound = Node2Index[SU->NodeNum];
685   bool HasLoop = false;
686   // Is Ord(TargetSU) < Ord(SU) ?
687   if (LowerBound < UpperBound) {
688     Visited.reset();
689     // There may be a path from TargetSU to SU. Check for it.
690     DFS(TargetSU, UpperBound, HasLoop);
691   }
692   return HasLoop;
693 }
694 
695 void ScheduleDAGTopologicalSort::Allocate(int n, int index) {
696   Node2Index[n] = index;
697   Index2Node[index] = n;
698 }
699 
700 ScheduleDAGTopologicalSort::
701 ScheduleDAGTopologicalSort(std::vector<SUnit> &sunits, SUnit *exitsu)
702   : SUnits(sunits), ExitSU(exitsu) {}
703 
704 ScheduleHazardRecognizer::~ScheduleHazardRecognizer() = default;
705