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