ScheduleDAG.cpp revision 7a2bdde0a0eebcd2125055e0eacaca040f0b766c 
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/Debug.h"
23#include "llvm/Support/raw_ostream.h"
24#include <climits>
25using namespace llvm;
26
27ScheduleDAG::ScheduleDAG(MachineFunction &mf)
28  : TM(mf.getTarget()),
29    TII(TM.getInstrInfo()),
30    TRI(TM.getRegisterInfo()),
31    MF(mf), MRI(mf.getRegInfo()),
32    EntrySU(), ExitSU() {
33}
34
35ScheduleDAG::~ScheduleDAG() {}
36
37/// getInstrDesc helper to handle SDNodes.
38const TargetInstrDesc *ScheduleDAG::getNodeDesc(const SDNode *Node) const {
39  if (!Node || !Node->isMachineOpcode()) return NULL;
40  return &TII->get(Node->getMachineOpcode());
41}
42
43/// dump - dump the schedule.
44void ScheduleDAG::dumpSchedule() const {
45  for (unsigned i = 0, e = Sequence.size(); i != e; i++) {
46    if (SUnit *SU = Sequence[i])
47      SU->dump(this);
48    else
49      dbgs() << "**** NOOP ****\n";
50  }
51}
52
53
54/// Run - perform scheduling.
55///
56void ScheduleDAG::Run(MachineBasicBlock *bb,
57                      MachineBasicBlock::iterator insertPos) {
58  BB = bb;
59  InsertPos = insertPos;
60
61  SUnits.clear();
62  Sequence.clear();
63  EntrySU = SUnit();
64  ExitSU = SUnit();
65
66  Schedule();
67
68  DEBUG({
69      dbgs() << "*** Final schedule ***\n";
70      dumpSchedule();
71      dbgs() << '\n';
72    });
73}
74
75/// addPred - This adds the specified edge as a pred of the current node if
76/// not already.  It also adds the current node as a successor of the
77/// specified node.
78bool SUnit::addPred(const SDep &D) {
79  // If this node already has this depenence, don't add a redundant one.
80  for (SmallVector<SDep, 4>::const_iterator I = Preds.begin(), E = Preds.end();
81       I != E; ++I)
82    if (*I == D)
83      return false;
84  // Now add a corresponding succ to N.
85  SDep P = D;
86  P.setSUnit(this);
87  SUnit *N = D.getSUnit();
88  // Update the bookkeeping.
89  if (D.getKind() == SDep::Data) {
90    assert(NumPreds < UINT_MAX && "NumPreds will overflow!");
91    assert(N->NumSuccs < UINT_MAX && "NumSuccs will overflow!");
92    ++NumPreds;
93    ++N->NumSuccs;
94  }
95  if (!N->isScheduled) {
96    assert(NumPredsLeft < UINT_MAX && "NumPredsLeft will overflow!");
97    ++NumPredsLeft;
98  }
99  if (!isScheduled) {
100    assert(N->NumSuccsLeft < UINT_MAX && "NumSuccsLeft will overflow!");
101    ++N->NumSuccsLeft;
102  }
103  Preds.push_back(D);
104  N->Succs.push_back(P);
105  if (P.getLatency() != 0) {
106    this->setDepthDirty();
107    N->setHeightDirty();
108  }
109  return true;
110}
111
112/// removePred - This removes the specified edge as a pred of the current
113/// node if it exists.  It also removes the current node as a successor of
114/// the specified node.
115void SUnit::removePred(const SDep &D) {
116  // Find the matching predecessor.
117  for (SmallVector<SDep, 4>::iterator I = Preds.begin(), E = Preds.end();
118       I != E; ++I)
119    if (*I == D) {
120      bool FoundSucc = false;
121      // Find the corresponding successor in N.
122      SDep P = D;
123      P.setSUnit(this);
124      SUnit *N = D.getSUnit();
125      for (SmallVector<SDep, 4>::iterator II = N->Succs.begin(),
126             EE = N->Succs.end(); II != EE; ++II)
127        if (*II == P) {
128          FoundSucc = true;
129          N->Succs.erase(II);
130          break;
131        }
132      assert(FoundSucc && "Mismatching preds / succs lists!");
133      Preds.erase(I);
134      // Update the bookkeeping.
135      if (P.getKind() == SDep::Data) {
136        assert(NumPreds > 0 && "NumPreds will underflow!");
137        assert(N->NumSuccs > 0 && "NumSuccs will underflow!");
138        --NumPreds;
139        --N->NumSuccs;
140      }
141      if (!N->isScheduled) {
142        assert(NumPredsLeft > 0 && "NumPredsLeft will underflow!");
143        --NumPredsLeft;
144      }
145      if (!isScheduled) {
146        assert(N->NumSuccsLeft > 0 && "NumSuccsLeft will underflow!");
147        --N->NumSuccsLeft;
148      }
149      if (P.getLatency() != 0) {
150        this->setDepthDirty();
151        N->setHeightDirty();
152      }
153      return;
154    }
155}
156
157void SUnit::setDepthDirty() {
158  if (!isDepthCurrent) return;
159  SmallVector<SUnit*, 8> WorkList;
160  WorkList.push_back(this);
161  do {
162    SUnit *SU = WorkList.pop_back_val();
163    SU->isDepthCurrent = false;
164    for (SUnit::const_succ_iterator I = SU->Succs.begin(),
165         E = SU->Succs.end(); I != E; ++I) {
166      SUnit *SuccSU = I->getSUnit();
167      if (SuccSU->isDepthCurrent)
168        WorkList.push_back(SuccSU);
169    }
170  } while (!WorkList.empty());
171}
172
173void SUnit::setHeightDirty() {
174  if (!isHeightCurrent) return;
175  SmallVector<SUnit*, 8> WorkList;
176  WorkList.push_back(this);
177  do {
178    SUnit *SU = WorkList.pop_back_val();
179    SU->isHeightCurrent = false;
180    for (SUnit::const_pred_iterator I = SU->Preds.begin(),
181         E = SU->Preds.end(); I != E; ++I) {
182      SUnit *PredSU = I->getSUnit();
183      if (PredSU->isHeightCurrent)
184        WorkList.push_back(PredSU);
185    }
186  } while (!WorkList.empty());
187}
188
189/// setDepthToAtLeast - Update this node's successors to reflect the
190/// fact that this node's depth just increased.
191///
192void SUnit::setDepthToAtLeast(unsigned NewDepth) {
193  if (NewDepth <= getDepth())
194    return;
195  setDepthDirty();
196  Depth = NewDepth;
197  isDepthCurrent = true;
198}
199
200/// setHeightToAtLeast - Update this node's predecessors to reflect the
201/// fact that this node's height just increased.
202///
203void SUnit::setHeightToAtLeast(unsigned NewHeight) {
204  if (NewHeight <= getHeight())
205    return;
206  setHeightDirty();
207  Height = NewHeight;
208  isHeightCurrent = true;
209}
210
211/// ComputeDepth - Calculate the maximal path from the node to the exit.
212///
213void SUnit::ComputeDepth() {
214  SmallVector<SUnit*, 8> WorkList;
215  WorkList.push_back(this);
216  do {
217    SUnit *Cur = WorkList.back();
218
219    bool Done = true;
220    unsigned MaxPredDepth = 0;
221    for (SUnit::const_pred_iterator I = Cur->Preds.begin(),
222         E = Cur->Preds.end(); I != E; ++I) {
223      SUnit *PredSU = I->getSUnit();
224      if (PredSU->isDepthCurrent)
225        MaxPredDepth = std::max(MaxPredDepth,
226                                PredSU->Depth + I->getLatency());
227      else {
228        Done = false;
229        WorkList.push_back(PredSU);
230      }
231    }
232
233    if (Done) {
234      WorkList.pop_back();
235      if (MaxPredDepth != Cur->Depth) {
236        Cur->setDepthDirty();
237        Cur->Depth = MaxPredDepth;
238      }
239      Cur->isDepthCurrent = true;
240    }
241  } while (!WorkList.empty());
242}
243
244/// ComputeHeight - Calculate the maximal path from the node to the entry.
245///
246void SUnit::ComputeHeight() {
247  SmallVector<SUnit*, 8> WorkList;
248  WorkList.push_back(this);
249  do {
250    SUnit *Cur = WorkList.back();
251
252    bool Done = true;
253    unsigned MaxSuccHeight = 0;
254    for (SUnit::const_succ_iterator I = Cur->Succs.begin(),
255         E = Cur->Succs.end(); I != E; ++I) {
256      SUnit *SuccSU = I->getSUnit();
257      if (SuccSU->isHeightCurrent)
258        MaxSuccHeight = std::max(MaxSuccHeight,
259                                 SuccSU->Height + I->getLatency());
260      else {
261        Done = false;
262        WorkList.push_back(SuccSU);
263      }
264    }
265
266    if (Done) {
267      WorkList.pop_back();
268      if (MaxSuccHeight != Cur->Height) {
269        Cur->setHeightDirty();
270        Cur->Height = MaxSuccHeight;
271      }
272      Cur->isHeightCurrent = true;
273    }
274  } while (!WorkList.empty());
275}
276
277/// SUnit - Scheduling unit. It's an wrapper around either a single SDNode or
278/// a group of nodes flagged together.
279void SUnit::dump(const ScheduleDAG *G) const {
280  dbgs() << "SU(" << NodeNum << "): ";
281  G->dumpNode(this);
282}
283
284void SUnit::dumpAll(const ScheduleDAG *G) const {
285  dump(G);
286
287  dbgs() << "  # preds left       : " << NumPredsLeft << "\n";
288  dbgs() << "  # succs left       : " << NumSuccsLeft << "\n";
289  dbgs() << "  # rdefs left       : " << NumRegDefsLeft << "\n";
290  dbgs() << "  Latency            : " << Latency << "\n";
291  dbgs() << "  Depth              : " << Depth << "\n";
292  dbgs() << "  Height             : " << Height << "\n";
293
294  if (Preds.size() != 0) {
295    dbgs() << "  Predecessors:\n";
296    for (SUnit::const_succ_iterator I = Preds.begin(), E = Preds.end();
297         I != E; ++I) {
298      dbgs() << "   ";
299      switch (I->getKind()) {
300      case SDep::Data:        dbgs() << "val "; break;
301      case SDep::Anti:        dbgs() << "anti"; break;
302      case SDep::Output:      dbgs() << "out "; break;
303      case SDep::Order:       dbgs() << "ch  "; break;
304      }
305      dbgs() << "#";
306      dbgs() << I->getSUnit() << " - SU(" << I->getSUnit()->NodeNum << ")";
307      if (I->isArtificial())
308        dbgs() << " *";
309      dbgs() << ": Latency=" << I->getLatency();
310      dbgs() << "\n";
311    }
312  }
313  if (Succs.size() != 0) {
314    dbgs() << "  Successors:\n";
315    for (SUnit::const_succ_iterator I = Succs.begin(), E = Succs.end();
316         I != E; ++I) {
317      dbgs() << "   ";
318      switch (I->getKind()) {
319      case SDep::Data:        dbgs() << "val "; break;
320      case SDep::Anti:        dbgs() << "anti"; break;
321      case SDep::Output:      dbgs() << "out "; break;
322      case SDep::Order:       dbgs() << "ch  "; break;
323      }
324      dbgs() << "#";
325      dbgs() << I->getSUnit() << " - SU(" << I->getSUnit()->NodeNum << ")";
326      if (I->isArtificial())
327        dbgs() << " *";
328      dbgs() << ": Latency=" << I->getLatency();
329      dbgs() << "\n";
330    }
331  }
332  dbgs() << "\n";
333}
334
335#ifndef NDEBUG
336/// VerifySchedule - Verify that all SUnits were scheduled and that
337/// their state is consistent.
338///
339void ScheduleDAG::VerifySchedule(bool isBottomUp) {
340  bool AnyNotSched = false;
341  unsigned DeadNodes = 0;
342  unsigned Noops = 0;
343  for (unsigned i = 0, e = SUnits.size(); i != e; ++i) {
344    if (!SUnits[i].isScheduled) {
345      if (SUnits[i].NumPreds == 0 && SUnits[i].NumSuccs == 0) {
346        ++DeadNodes;
347        continue;
348      }
349      if (!AnyNotSched)
350        dbgs() << "*** Scheduling failed! ***\n";
351      SUnits[i].dump(this);
352      dbgs() << "has not been scheduled!\n";
353      AnyNotSched = true;
354    }
355    if (SUnits[i].isScheduled &&
356        (isBottomUp ? SUnits[i].getHeight() : SUnits[i].getDepth()) >
357          unsigned(INT_MAX)) {
358      if (!AnyNotSched)
359        dbgs() << "*** Scheduling failed! ***\n";
360      SUnits[i].dump(this);
361      dbgs() << "has an unexpected "
362           << (isBottomUp ? "Height" : "Depth") << " value!\n";
363      AnyNotSched = true;
364    }
365    if (isBottomUp) {
366      if (SUnits[i].NumSuccsLeft != 0) {
367        if (!AnyNotSched)
368          dbgs() << "*** Scheduling failed! ***\n";
369        SUnits[i].dump(this);
370        dbgs() << "has successors left!\n";
371        AnyNotSched = true;
372      }
373    } else {
374      if (SUnits[i].NumPredsLeft != 0) {
375        if (!AnyNotSched)
376          dbgs() << "*** Scheduling failed! ***\n";
377        SUnits[i].dump(this);
378        dbgs() << "has predecessors left!\n";
379        AnyNotSched = true;
380      }
381    }
382  }
383  for (unsigned i = 0, e = Sequence.size(); i != e; ++i)
384    if (!Sequence[i])
385      ++Noops;
386  assert(!AnyNotSched);
387  assert(Sequence.size() + DeadNodes - Noops == SUnits.size() &&
388         "The number of nodes scheduled doesn't match the expected number!");
389}
390#endif
391
392/// InitDAGTopologicalSorting - create the initial topological
393/// ordering from the DAG to be scheduled.
394///
395/// The idea of the algorithm is taken from
396/// "Online algorithms for managing the topological order of
397/// a directed acyclic graph" by David J. Pearce and Paul H.J. Kelly
398/// This is the MNR algorithm, which was first introduced by
399/// A. Marchetti-Spaccamela, U. Nanni and H. Rohnert in
400/// "Maintaining a topological order under edge insertions".
401///
402/// Short description of the algorithm:
403///
404/// Topological ordering, ord, of a DAG maps each node to a topological
405/// index so that for all edges X->Y it is the case that ord(X) < ord(Y).
406///
407/// This means that if there is a path from the node X to the node Z,
408/// then ord(X) < ord(Z).
409///
410/// This property can be used to check for reachability of nodes:
411/// if Z is reachable from X, then an insertion of the edge Z->X would
412/// create a cycle.
413///
414/// The algorithm first computes a topological ordering for the DAG by
415/// initializing the Index2Node and Node2Index arrays and then tries to keep
416/// the ordering up-to-date after edge insertions by reordering the DAG.
417///
418/// On insertion of the edge X->Y, the algorithm first marks by calling DFS
419/// the nodes reachable from Y, and then shifts them using Shift to lie
420/// immediately after X in Index2Node.
421void ScheduleDAGTopologicalSort::InitDAGTopologicalSorting() {
422  unsigned DAGSize = SUnits.size();
423  std::vector<SUnit*> WorkList;
424  WorkList.reserve(DAGSize);
425
426  Index2Node.resize(DAGSize);
427  Node2Index.resize(DAGSize);
428
429  // Initialize the data structures.
430  for (unsigned i = 0, e = DAGSize; i != e; ++i) {
431    SUnit *SU = &SUnits[i];
432    int NodeNum = SU->NodeNum;
433    unsigned Degree = SU->Succs.size();
434    // Temporarily use the Node2Index array as scratch space for degree counts.
435    Node2Index[NodeNum] = Degree;
436
437    // Is it a node without dependencies?
438    if (Degree == 0) {
439      assert(SU->Succs.empty() && "SUnit should have no successors");
440      // Collect leaf nodes.
441      WorkList.push_back(SU);
442    }
443  }
444
445  int Id = DAGSize;
446  while (!WorkList.empty()) {
447    SUnit *SU = WorkList.back();
448    WorkList.pop_back();
449    Allocate(SU->NodeNum, --Id);
450    for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
451         I != E; ++I) {
452      SUnit *SU = I->getSUnit();
453      if (!--Node2Index[SU->NodeNum])
454        // If all dependencies of the node are processed already,
455        // then the node can be computed now.
456        WorkList.push_back(SU);
457    }
458  }
459
460  Visited.resize(DAGSize);
461
462#ifndef NDEBUG
463  // Check correctness of the ordering
464  for (unsigned i = 0, e = DAGSize; i != e; ++i) {
465    SUnit *SU = &SUnits[i];
466    for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
467         I != E; ++I) {
468      assert(Node2Index[SU->NodeNum] > Node2Index[I->getSUnit()->NodeNum] &&
469      "Wrong topological sorting");
470    }
471  }
472#endif
473}
474
475/// AddPred - Updates the topological ordering to accommodate an edge
476/// to be added from SUnit X to SUnit Y.
477void ScheduleDAGTopologicalSort::AddPred(SUnit *Y, SUnit *X) {
478  int UpperBound, LowerBound;
479  LowerBound = Node2Index[Y->NodeNum];
480  UpperBound = Node2Index[X->NodeNum];
481  bool HasLoop = false;
482  // Is Ord(X) < Ord(Y) ?
483  if (LowerBound < UpperBound) {
484    // Update the topological order.
485    Visited.reset();
486    DFS(Y, UpperBound, HasLoop);
487    assert(!HasLoop && "Inserted edge creates a loop!");
488    // Recompute topological indexes.
489    Shift(Visited, LowerBound, UpperBound);
490  }
491}
492
493/// RemovePred - Updates the topological ordering to accommodate an
494/// an edge to be removed from the specified node N from the predecessors
495/// of the current node M.
496void ScheduleDAGTopologicalSort::RemovePred(SUnit *M, SUnit *N) {
497  // InitDAGTopologicalSorting();
498}
499
500/// DFS - Make a DFS traversal to mark all nodes reachable from SU and mark
501/// all nodes affected by the edge insertion. These nodes will later get new
502/// topological indexes by means of the Shift method.
503void ScheduleDAGTopologicalSort::DFS(const SUnit *SU, int UpperBound,
504                                     bool &HasLoop) {
505  std::vector<const SUnit*> WorkList;
506  WorkList.reserve(SUnits.size());
507
508  WorkList.push_back(SU);
509  do {
510    SU = WorkList.back();
511    WorkList.pop_back();
512    Visited.set(SU->NodeNum);
513    for (int I = SU->Succs.size()-1; I >= 0; --I) {
514      int s = SU->Succs[I].getSUnit()->NodeNum;
515      if (Node2Index[s] == UpperBound) {
516        HasLoop = true;
517        return;
518      }
519      // Visit successors if not already and in affected region.
520      if (!Visited.test(s) && Node2Index[s] < UpperBound) {
521        WorkList.push_back(SU->Succs[I].getSUnit());
522      }
523    }
524  } while (!WorkList.empty());
525}
526
527/// Shift - Renumber the nodes so that the topological ordering is
528/// preserved.
529void ScheduleDAGTopologicalSort::Shift(BitVector& Visited, int LowerBound,
530                                       int UpperBound) {
531  std::vector<int> L;
532  int shift = 0;
533  int i;
534
535  for (i = LowerBound; i <= UpperBound; ++i) {
536    // w is node at topological index i.
537    int w = Index2Node[i];
538    if (Visited.test(w)) {
539      // Unmark.
540      Visited.reset(w);
541      L.push_back(w);
542      shift = shift + 1;
543    } else {
544      Allocate(w, i - shift);
545    }
546  }
547
548  for (unsigned j = 0; j < L.size(); ++j) {
549    Allocate(L[j], i - shift);
550    i = i + 1;
551  }
552}
553
554
555/// WillCreateCycle - Returns true if adding an edge from SU to TargetSU will
556/// create a cycle.
557bool ScheduleDAGTopologicalSort::WillCreateCycle(SUnit *SU, SUnit *TargetSU) {
558  if (IsReachable(TargetSU, SU))
559    return true;
560  for (SUnit::pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
561       I != E; ++I)
562    if (I->isAssignedRegDep() &&
563        IsReachable(TargetSU, I->getSUnit()))
564      return true;
565  return false;
566}
567
568/// IsReachable - Checks if SU is reachable from TargetSU.
569bool ScheduleDAGTopologicalSort::IsReachable(const SUnit *SU,
570                                             const SUnit *TargetSU) {
571  // If insertion of the edge SU->TargetSU would create a cycle
572  // then there is a path from TargetSU to SU.
573  int UpperBound, LowerBound;
574  LowerBound = Node2Index[TargetSU->NodeNum];
575  UpperBound = Node2Index[SU->NodeNum];
576  bool HasLoop = false;
577  // Is Ord(TargetSU) < Ord(SU) ?
578  if (LowerBound < UpperBound) {
579    Visited.reset();
580    // There may be a path from TargetSU to SU. Check for it.
581    DFS(TargetSU, UpperBound, HasLoop);
582  }
583  return HasLoop;
584}
585
586/// Allocate - assign the topological index to the node n.
587void ScheduleDAGTopologicalSort::Allocate(int n, int index) {
588  Node2Index[n] = index;
589  Index2Node[index] = n;
590}
591
592ScheduleDAGTopologicalSort::
593ScheduleDAGTopologicalSort(std::vector<SUnit> &sunits) : SUnits(sunits) {}
594
595ScheduleHazardRecognizer::~ScheduleHazardRecognizer() {}
596