ScheduleDAG.cpp revision 4de099d8ca651e00fa5fac22bace4f4dba2d0292 
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/Target/TargetMachine.h"
19#include "llvm/Target/TargetInstrInfo.h"
20#include "llvm/Target/TargetRegisterInfo.h"
21#include "llvm/Support/Debug.h"
22#include "llvm/Support/raw_ostream.h"
23#include <climits>
24using namespace llvm;
25
26ScheduleDAG::ScheduleDAG(MachineFunction &mf)
27  : TM(mf.getTarget()),
28    TII(TM.getInstrInfo()),
29    TRI(TM.getRegisterInfo()),
30    TLI(TM.getTargetLowering()),
31    MF(mf), MRI(mf.getRegInfo()),
32    ConstPool(MF.getConstantPool()),
33    EntrySU(), ExitSU() {
34}
35
36ScheduleDAG::~ScheduleDAG() {}
37
38/// dump - dump the schedule.
39void ScheduleDAG::dumpSchedule() const {
40  for (unsigned i = 0, e = Sequence.size(); i != e; i++) {
41    if (SUnit *SU = Sequence[i])
42      SU->dump(this);
43    else
44      errs() << "**** NOOP ****\n";
45  }
46}
47
48
49/// Run - perform scheduling.
50///
51void ScheduleDAG::Run(MachineBasicBlock *bb,
52                      MachineBasicBlock::iterator insertPos) {
53  BB = bb;
54  InsertPos = insertPos;
55
56  SUnits.clear();
57  Sequence.clear();
58  EntrySU = SUnit();
59  ExitSU = SUnit();
60
61  Schedule();
62
63  DEBUG({
64      errs() << "*** Final schedule ***\n";
65      dumpSchedule();
66      errs() << '\n';
67    });
68}
69
70/// addPred - This adds the specified edge as a pred of the current node if
71/// not already.  It also adds the current node as a successor of the
72/// specified node.
73void SUnit::addPred(const SDep &D) {
74  // If this node already has this depenence, don't add a redundant one.
75  for (SmallVector<SDep, 4>::const_iterator I = Preds.begin(), E = Preds.end();
76       I != E; ++I)
77    if (*I == D)
78      return;
79  // Now add a corresponding succ to N.
80  SDep P = D;
81  P.setSUnit(this);
82  SUnit *N = D.getSUnit();
83  // Update the bookkeeping.
84  if (D.getKind() == SDep::Data) {
85    assert(NumPreds < UINT_MAX && "NumPreds will overflow!");
86    assert(N->NumSuccs < UINT_MAX && "NumSuccs will overflow!");
87    ++NumPreds;
88    ++N->NumSuccs;
89  }
90  if (!N->isScheduled) {
91    assert(NumPredsLeft < UINT_MAX && "NumPredsLeft will overflow!");
92    ++NumPredsLeft;
93  }
94  if (!isScheduled) {
95    assert(N->NumSuccsLeft < UINT_MAX && "NumSuccsLeft will overflow!");
96    ++N->NumSuccsLeft;
97  }
98  Preds.push_back(D);
99  N->Succs.push_back(P);
100  if (P.getLatency() != 0) {
101    this->setDepthDirty();
102    N->setHeightDirty();
103  }
104}
105
106/// removePred - This removes the specified edge as a pred of the current
107/// node if it exists.  It also removes the current node as a successor of
108/// the specified node.
109void SUnit::removePred(const SDep &D) {
110  // Find the matching predecessor.
111  for (SmallVector<SDep, 4>::iterator I = Preds.begin(), E = Preds.end();
112       I != E; ++I)
113    if (*I == D) {
114      bool FoundSucc = false;
115      // Find the corresponding successor in N.
116      SDep P = D;
117      P.setSUnit(this);
118      SUnit *N = D.getSUnit();
119      for (SmallVector<SDep, 4>::iterator II = N->Succs.begin(),
120             EE = N->Succs.end(); II != EE; ++II)
121        if (*II == P) {
122          FoundSucc = true;
123          N->Succs.erase(II);
124          break;
125        }
126      assert(FoundSucc && "Mismatching preds / succs lists!");
127      Preds.erase(I);
128      // Update the bookkeeping.
129      if (P.getKind() == SDep::Data) {
130        assert(NumPreds > 0 && "NumPreds will underflow!");
131        assert(N->NumSuccs > 0 && "NumSuccs will underflow!");
132        --NumPreds;
133        --N->NumSuccs;
134      }
135      if (!N->isScheduled) {
136        assert(NumPredsLeft > 0 && "NumPredsLeft will underflow!");
137        --NumPredsLeft;
138      }
139      if (!isScheduled) {
140        assert(N->NumSuccsLeft > 0 && "NumSuccsLeft will underflow!");
141        --N->NumSuccsLeft;
142      }
143      if (P.getLatency() != 0) {
144        this->setDepthDirty();
145        N->setHeightDirty();
146      }
147      return;
148    }
149}
150
151void SUnit::setDepthDirty() {
152  if (!isDepthCurrent) return;
153  SmallVector<SUnit*, 8> WorkList;
154  WorkList.push_back(this);
155  do {
156    SUnit *SU = WorkList.pop_back_val();
157    SU->isDepthCurrent = false;
158    for (SUnit::const_succ_iterator I = SU->Succs.begin(),
159         E = SU->Succs.end(); I != E; ++I) {
160      SUnit *SuccSU = I->getSUnit();
161      if (SuccSU->isDepthCurrent)
162        WorkList.push_back(SuccSU);
163    }
164  } while (!WorkList.empty());
165}
166
167void SUnit::setHeightDirty() {
168  if (!isHeightCurrent) return;
169  SmallVector<SUnit*, 8> WorkList;
170  WorkList.push_back(this);
171  do {
172    SUnit *SU = WorkList.pop_back_val();
173    SU->isHeightCurrent = false;
174    for (SUnit::const_pred_iterator I = SU->Preds.begin(),
175         E = SU->Preds.end(); I != E; ++I) {
176      SUnit *PredSU = I->getSUnit();
177      if (PredSU->isHeightCurrent)
178        WorkList.push_back(PredSU);
179    }
180  } while (!WorkList.empty());
181}
182
183/// setDepthToAtLeast - Update this node's successors to reflect the
184/// fact that this node's depth just increased.
185///
186void SUnit::setDepthToAtLeast(unsigned NewDepth, bool IgnoreAntiDep) {
187  if (NewDepth <= getDepth(IgnoreAntiDep))
188    return;
189  setDepthDirty();
190  Depth = NewDepth;
191  isDepthCurrent = true;
192}
193
194/// setHeightToAtLeast - Update this node's predecessors to reflect the
195/// fact that this node's height just increased.
196///
197void SUnit::setHeightToAtLeast(unsigned NewHeight, bool IgnoreAntiDep) {
198  if (NewHeight <= getHeight(IgnoreAntiDep))
199    return;
200  setHeightDirty();
201  Height = NewHeight;
202  isHeightCurrent = true;
203}
204
205/// ComputeDepth - Calculate the maximal path from the node to the exit.
206///
207void SUnit::ComputeDepth(bool IgnoreAntiDep) {
208  SmallVector<SUnit*, 8> WorkList;
209  WorkList.push_back(this);
210  do {
211    SUnit *Cur = WorkList.back();
212
213    bool Done = true;
214    unsigned MaxPredDepth = 0;
215    for (SUnit::const_pred_iterator I = Cur->Preds.begin(),
216         E = Cur->Preds.end(); I != E; ++I) {
217      if (IgnoreAntiDep && (I->getKind() == SDep::Anti)) continue;
218      SUnit *PredSU = I->getSUnit();
219      if (PredSU->isDepthCurrent)
220        MaxPredDepth = std::max(MaxPredDepth,
221                                PredSU->Depth + I->getLatency());
222      else {
223        Done = false;
224        WorkList.push_back(PredSU);
225      }
226    }
227
228    if (Done) {
229      WorkList.pop_back();
230      if (MaxPredDepth != Cur->Depth) {
231        Cur->setDepthDirty();
232        Cur->Depth = MaxPredDepth;
233      }
234      Cur->isDepthCurrent = true;
235    }
236  } while (!WorkList.empty());
237}
238
239/// ComputeHeight - Calculate the maximal path from the node to the entry.
240///
241void SUnit::ComputeHeight(bool IgnoreAntiDep) {
242  SmallVector<SUnit*, 8> WorkList;
243  WorkList.push_back(this);
244  do {
245    SUnit *Cur = WorkList.back();
246
247    bool Done = true;
248    unsigned MaxSuccHeight = 0;
249    for (SUnit::const_succ_iterator I = Cur->Succs.begin(),
250         E = Cur->Succs.end(); I != E; ++I) {
251      if (IgnoreAntiDep && (I->getKind() == SDep::Anti)) continue;
252      SUnit *SuccSU = I->getSUnit();
253      if (SuccSU->isHeightCurrent)
254        MaxSuccHeight = std::max(MaxSuccHeight,
255                                 SuccSU->Height + I->getLatency());
256      else {
257        Done = false;
258        WorkList.push_back(SuccSU);
259      }
260    }
261
262    if (Done) {
263      WorkList.pop_back();
264      if (MaxSuccHeight != Cur->Height) {
265        Cur->setHeightDirty();
266        Cur->Height = MaxSuccHeight;
267      }
268      Cur->isHeightCurrent = true;
269    }
270  } while (!WorkList.empty());
271}
272
273/// SUnit - Scheduling unit. It's an wrapper around either a single SDNode or
274/// a group of nodes flagged together.
275void SUnit::dump(const ScheduleDAG *G) const {
276  errs() << "SU(" << NodeNum << "): ";
277  G->dumpNode(this);
278}
279
280void SUnit::dumpAll(const ScheduleDAG *G) const {
281  dump(G);
282
283  errs() << "  # preds left       : " << NumPredsLeft << "\n";
284  errs() << "  # succs left       : " << NumSuccsLeft << "\n";
285  errs() << "  Latency            : " << Latency << "\n";
286  errs() << "  Depth              : " << Depth << "\n";
287  errs() << "  Height             : " << Height << "\n";
288
289  if (Preds.size() != 0) {
290    errs() << "  Predecessors:\n";
291    for (SUnit::const_succ_iterator I = Preds.begin(), E = Preds.end();
292         I != E; ++I) {
293      errs() << "   ";
294      switch (I->getKind()) {
295      case SDep::Data:        errs() << "val "; break;
296      case SDep::Anti:        errs() << "anti"; break;
297      case SDep::Output:      errs() << "out "; break;
298      case SDep::Order:       errs() << "ch  "; break;
299      }
300      errs() << "#";
301      errs() << I->getSUnit() << " - SU(" << I->getSUnit()->NodeNum << ")";
302      if (I->isArtificial())
303        errs() << " *";
304      errs() << ": Latency=" << I->getLatency();
305      errs() << "\n";
306    }
307  }
308  if (Succs.size() != 0) {
309    errs() << "  Successors:\n";
310    for (SUnit::const_succ_iterator I = Succs.begin(), E = Succs.end();
311         I != E; ++I) {
312      errs() << "   ";
313      switch (I->getKind()) {
314      case SDep::Data:        errs() << "val "; break;
315      case SDep::Anti:        errs() << "anti"; break;
316      case SDep::Output:      errs() << "out "; break;
317      case SDep::Order:       errs() << "ch  "; break;
318      }
319      errs() << "#";
320      errs() << I->getSUnit() << " - SU(" << I->getSUnit()->NodeNum << ")";
321      if (I->isArtificial())
322        errs() << " *";
323      errs() << ": Latency=" << I->getLatency();
324      errs() << "\n";
325    }
326  }
327  errs() << "\n";
328}
329
330#ifndef NDEBUG
331/// VerifySchedule - Verify that all SUnits were scheduled and that
332/// their state is consistent.
333///
334void ScheduleDAG::VerifySchedule(bool isBottomUp) {
335  bool AnyNotSched = false;
336  unsigned DeadNodes = 0;
337  unsigned Noops = 0;
338  for (unsigned i = 0, e = SUnits.size(); i != e; ++i) {
339    if (!SUnits[i].isScheduled) {
340      if (SUnits[i].NumPreds == 0 && SUnits[i].NumSuccs == 0) {
341        ++DeadNodes;
342        continue;
343      }
344      if (!AnyNotSched)
345        errs() << "*** Scheduling failed! ***\n";
346      SUnits[i].dump(this);
347      errs() << "has not been scheduled!\n";
348      AnyNotSched = true;
349    }
350    if (SUnits[i].isScheduled &&
351        (isBottomUp ? SUnits[i].getHeight() : SUnits[i].getDepth()) >
352          unsigned(INT_MAX)) {
353      if (!AnyNotSched)
354        errs() << "*** Scheduling failed! ***\n";
355      SUnits[i].dump(this);
356      errs() << "has an unexpected "
357           << (isBottomUp ? "Height" : "Depth") << " value!\n";
358      AnyNotSched = true;
359    }
360    if (isBottomUp) {
361      if (SUnits[i].NumSuccsLeft != 0) {
362        if (!AnyNotSched)
363          errs() << "*** Scheduling failed! ***\n";
364        SUnits[i].dump(this);
365        errs() << "has successors left!\n";
366        AnyNotSched = true;
367      }
368    } else {
369      if (SUnits[i].NumPredsLeft != 0) {
370        if (!AnyNotSched)
371          errs() << "*** Scheduling failed! ***\n";
372        SUnits[i].dump(this);
373        errs() << "has predecessors left!\n";
374        AnyNotSched = true;
375      }
376    }
377  }
378  for (unsigned i = 0, e = Sequence.size(); i != e; ++i)
379    if (!Sequence[i])
380      ++Noops;
381  assert(!AnyNotSched);
382  assert(Sequence.size() + DeadNodes - Noops == SUnits.size() &&
383         "The number of nodes scheduled doesn't match the expected number!");
384}
385#endif
386
387/// InitDAGTopologicalSorting - create the initial topological
388/// ordering from the DAG to be scheduled.
389///
390/// The idea of the algorithm is taken from
391/// "Online algorithms for managing the topological order of
392/// a directed acyclic graph" by David J. Pearce and Paul H.J. Kelly
393/// This is the MNR algorithm, which was first introduced by
394/// A. Marchetti-Spaccamela, U. Nanni and H. Rohnert in
395/// "Maintaining a topological order under edge insertions".
396///
397/// Short description of the algorithm:
398///
399/// Topological ordering, ord, of a DAG maps each node to a topological
400/// index so that for all edges X->Y it is the case that ord(X) < ord(Y).
401///
402/// This means that if there is a path from the node X to the node Z,
403/// then ord(X) < ord(Z).
404///
405/// This property can be used to check for reachability of nodes:
406/// if Z is reachable from X, then an insertion of the edge Z->X would
407/// create a cycle.
408///
409/// The algorithm first computes a topological ordering for the DAG by
410/// initializing the Index2Node and Node2Index arrays and then tries to keep
411/// the ordering up-to-date after edge insertions by reordering the DAG.
412///
413/// On insertion of the edge X->Y, the algorithm first marks by calling DFS
414/// the nodes reachable from Y, and then shifts them using Shift to lie
415/// immediately after X in Index2Node.
416void ScheduleDAGTopologicalSort::InitDAGTopologicalSorting() {
417  unsigned DAGSize = SUnits.size();
418  std::vector<SUnit*> WorkList;
419  WorkList.reserve(DAGSize);
420
421  Index2Node.resize(DAGSize);
422  Node2Index.resize(DAGSize);
423
424  // Initialize the data structures.
425  for (unsigned i = 0, e = DAGSize; i != e; ++i) {
426    SUnit *SU = &SUnits[i];
427    int NodeNum = SU->NodeNum;
428    unsigned Degree = SU->Succs.size();
429    // Temporarily use the Node2Index array as scratch space for degree counts.
430    Node2Index[NodeNum] = Degree;
431
432    // Is it a node without dependencies?
433    if (Degree == 0) {
434      assert(SU->Succs.empty() && "SUnit should have no successors");
435      // Collect leaf nodes.
436      WorkList.push_back(SU);
437    }
438  }
439
440  int Id = DAGSize;
441  while (!WorkList.empty()) {
442    SUnit *SU = WorkList.back();
443    WorkList.pop_back();
444    Allocate(SU->NodeNum, --Id);
445    for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
446         I != E; ++I) {
447      SUnit *SU = I->getSUnit();
448      if (!--Node2Index[SU->NodeNum])
449        // If all dependencies of the node are processed already,
450        // then the node can be computed now.
451        WorkList.push_back(SU);
452    }
453  }
454
455  Visited.resize(DAGSize);
456
457#ifndef NDEBUG
458  // Check correctness of the ordering
459  for (unsigned i = 0, e = DAGSize; i != e; ++i) {
460    SUnit *SU = &SUnits[i];
461    for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
462         I != E; ++I) {
463      assert(Node2Index[SU->NodeNum] > Node2Index[I->getSUnit()->NodeNum] &&
464      "Wrong topological sorting");
465    }
466  }
467#endif
468}
469
470/// AddPred - Updates the topological ordering to accomodate an edge
471/// to be added from SUnit X to SUnit Y.
472void ScheduleDAGTopologicalSort::AddPred(SUnit *Y, SUnit *X) {
473  int UpperBound, LowerBound;
474  LowerBound = Node2Index[Y->NodeNum];
475  UpperBound = Node2Index[X->NodeNum];
476  bool HasLoop = false;
477  // Is Ord(X) < Ord(Y) ?
478  if (LowerBound < UpperBound) {
479    // Update the topological order.
480    Visited.reset();
481    DFS(Y, UpperBound, HasLoop);
482    assert(!HasLoop && "Inserted edge creates a loop!");
483    // Recompute topological indexes.
484    Shift(Visited, LowerBound, UpperBound);
485  }
486}
487
488/// RemovePred - Updates the topological ordering to accomodate an
489/// an edge to be removed from the specified node N from the predecessors
490/// of the current node M.
491void ScheduleDAGTopologicalSort::RemovePred(SUnit *M, SUnit *N) {
492  // InitDAGTopologicalSorting();
493}
494
495/// DFS - Make a DFS traversal to mark all nodes reachable from SU and mark
496/// all nodes affected by the edge insertion. These nodes will later get new
497/// topological indexes by means of the Shift method.
498void ScheduleDAGTopologicalSort::DFS(const SUnit *SU, int UpperBound,
499                                     bool& HasLoop) {
500  std::vector<const SUnit*> WorkList;
501  WorkList.reserve(SUnits.size());
502
503  WorkList.push_back(SU);
504  do {
505    SU = WorkList.back();
506    WorkList.pop_back();
507    Visited.set(SU->NodeNum);
508    for (int I = SU->Succs.size()-1; I >= 0; --I) {
509      int s = SU->Succs[I].getSUnit()->NodeNum;
510      if (Node2Index[s] == UpperBound) {
511        HasLoop = true;
512        return;
513      }
514      // Visit successors if not already and in affected region.
515      if (!Visited.test(s) && Node2Index[s] < UpperBound) {
516        WorkList.push_back(SU->Succs[I].getSUnit());
517      }
518    }
519  } while (!WorkList.empty());
520}
521
522/// Shift - Renumber the nodes so that the topological ordering is
523/// preserved.
524void ScheduleDAGTopologicalSort::Shift(BitVector& Visited, int LowerBound,
525                                       int UpperBound) {
526  std::vector<int> L;
527  int shift = 0;
528  int i;
529
530  for (i = LowerBound; i <= UpperBound; ++i) {
531    // w is node at topological index i.
532    int w = Index2Node[i];
533    if (Visited.test(w)) {
534      // Unmark.
535      Visited.reset(w);
536      L.push_back(w);
537      shift = shift + 1;
538    } else {
539      Allocate(w, i - shift);
540    }
541  }
542
543  for (unsigned j = 0; j < L.size(); ++j) {
544    Allocate(L[j], i - shift);
545    i = i + 1;
546  }
547}
548
549
550/// WillCreateCycle - Returns true if adding an edge from SU to TargetSU will
551/// create a cycle.
552bool ScheduleDAGTopologicalSort::WillCreateCycle(SUnit *SU, SUnit *TargetSU) {
553  if (IsReachable(TargetSU, SU))
554    return true;
555  for (SUnit::pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
556       I != E; ++I)
557    if (I->isAssignedRegDep() &&
558        IsReachable(TargetSU, I->getSUnit()))
559      return true;
560  return false;
561}
562
563/// IsReachable - Checks if SU is reachable from TargetSU.
564bool ScheduleDAGTopologicalSort::IsReachable(const SUnit *SU,
565                                             const SUnit *TargetSU) {
566  // If insertion of the edge SU->TargetSU would create a cycle
567  // then there is a path from TargetSU to SU.
568  int UpperBound, LowerBound;
569  LowerBound = Node2Index[TargetSU->NodeNum];
570  UpperBound = Node2Index[SU->NodeNum];
571  bool HasLoop = false;
572  // Is Ord(TargetSU) < Ord(SU) ?
573  if (LowerBound < UpperBound) {
574    Visited.reset();
575    // There may be a path from TargetSU to SU. Check for it.
576    DFS(TargetSU, UpperBound, HasLoop);
577  }
578  return HasLoop;
579}
580
581/// Allocate - assign the topological index to the node n.
582void ScheduleDAGTopologicalSort::Allocate(int n, int index) {
583  Node2Index[n] = index;
584  Index2Node[index] = n;
585}
586
587ScheduleDAGTopologicalSort::ScheduleDAGTopologicalSort(
588                                                     std::vector<SUnit> &sunits)
589 : SUnits(sunits) {}
590
591ScheduleHazardRecognizer::~ScheduleHazardRecognizer() {}
592