ScheduleDAG.cpp revision 4cb971ce1c8b254f29365c988b55f6dcfe86d21e 
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
29cl::opt<bool> StressSchedOpt(
30  "stress-sched", cl::Hidden, cl::init(false),
31  cl::desc("Stress test instruction scheduling"));
32#endif
33
34ScheduleDAG::ScheduleDAG(MachineFunction &mf)
35  : TM(mf.getTarget()),
36    TII(TM.getInstrInfo()),
37    TRI(TM.getRegisterInfo()),
38    MF(mf), MRI(mf.getRegInfo()),
39    EntrySU(), ExitSU() {
40#ifndef NDEBUG
41  StressSched = StressSchedOpt;
42#endif
43}
44
45ScheduleDAG::~ScheduleDAG() {}
46
47/// getInstrDesc helper to handle SDNodes.
48const TargetInstrDesc *ScheduleDAG::getNodeDesc(const SDNode *Node) const {
49  if (!Node || !Node->isMachineOpcode()) return NULL;
50  return &TII->get(Node->getMachineOpcode());
51}
52
53/// dump - dump the schedule.
54void ScheduleDAG::dumpSchedule() const {
55  for (unsigned i = 0, e = Sequence.size(); i != e; i++) {
56    if (SUnit *SU = Sequence[i])
57      SU->dump(this);
58    else
59      dbgs() << "**** NOOP ****\n";
60  }
61}
62
63
64/// Run - perform scheduling.
65///
66void ScheduleDAG::Run(MachineBasicBlock *bb,
67                      MachineBasicBlock::iterator insertPos) {
68  BB = bb;
69  InsertPos = insertPos;
70
71  SUnits.clear();
72  Sequence.clear();
73  EntrySU = SUnit();
74  ExitSU = SUnit();
75
76  Schedule();
77
78  DEBUG({
79      dbgs() << "*** Final schedule ***\n";
80      dumpSchedule();
81      dbgs() << '\n';
82    });
83}
84
85/// addPred - This adds the specified edge as a pred of the current node if
86/// not already.  It also adds the current node as a successor of the
87/// specified node.
88bool SUnit::addPred(const SDep &D) {
89  // If this node already has this depenence, don't add a redundant one.
90  for (SmallVector<SDep, 4>::const_iterator I = Preds.begin(), E = Preds.end();
91       I != E; ++I)
92    if (*I == D)
93      return false;
94  // Now add a corresponding succ to N.
95  SDep P = D;
96  P.setSUnit(this);
97  SUnit *N = D.getSUnit();
98  // Update the bookkeeping.
99  if (D.getKind() == SDep::Data) {
100    assert(NumPreds < UINT_MAX && "NumPreds will overflow!");
101    assert(N->NumSuccs < UINT_MAX && "NumSuccs will overflow!");
102    ++NumPreds;
103    ++N->NumSuccs;
104  }
105  if (!N->isScheduled) {
106    assert(NumPredsLeft < UINT_MAX && "NumPredsLeft will overflow!");
107    ++NumPredsLeft;
108  }
109  if (!isScheduled) {
110    assert(N->NumSuccsLeft < UINT_MAX && "NumSuccsLeft will overflow!");
111    ++N->NumSuccsLeft;
112  }
113  Preds.push_back(D);
114  N->Succs.push_back(P);
115  if (P.getLatency() != 0) {
116    this->setDepthDirty();
117    N->setHeightDirty();
118  }
119  return true;
120}
121
122/// removePred - This removes the specified edge as a pred of the current
123/// node if it exists.  It also removes the current node as a successor of
124/// the specified node.
125void SUnit::removePred(const SDep &D) {
126  // Find the matching predecessor.
127  for (SmallVector<SDep, 4>::iterator I = Preds.begin(), E = Preds.end();
128       I != E; ++I)
129    if (*I == D) {
130      bool FoundSucc = false;
131      // Find the corresponding successor in N.
132      SDep P = D;
133      P.setSUnit(this);
134      SUnit *N = D.getSUnit();
135      for (SmallVector<SDep, 4>::iterator II = N->Succs.begin(),
136             EE = N->Succs.end(); II != EE; ++II)
137        if (*II == P) {
138          FoundSucc = true;
139          N->Succs.erase(II);
140          break;
141        }
142      assert(FoundSucc && "Mismatching preds / succs lists!");
143      Preds.erase(I);
144      // Update the bookkeeping.
145      if (P.getKind() == SDep::Data) {
146        assert(NumPreds > 0 && "NumPreds will underflow!");
147        assert(N->NumSuccs > 0 && "NumSuccs will underflow!");
148        --NumPreds;
149        --N->NumSuccs;
150      }
151      if (!N->isScheduled) {
152        assert(NumPredsLeft > 0 && "NumPredsLeft will underflow!");
153        --NumPredsLeft;
154      }
155      if (!isScheduled) {
156        assert(N->NumSuccsLeft > 0 && "NumSuccsLeft will underflow!");
157        --N->NumSuccsLeft;
158      }
159      if (P.getLatency() != 0) {
160        this->setDepthDirty();
161        N->setHeightDirty();
162      }
163      return;
164    }
165}
166
167void SUnit::setDepthDirty() {
168  if (!isDepthCurrent) return;
169  SmallVector<SUnit*, 8> WorkList;
170  WorkList.push_back(this);
171  do {
172    SUnit *SU = WorkList.pop_back_val();
173    SU->isDepthCurrent = false;
174    for (SUnit::const_succ_iterator I = SU->Succs.begin(),
175         E = SU->Succs.end(); I != E; ++I) {
176      SUnit *SuccSU = I->getSUnit();
177      if (SuccSU->isDepthCurrent)
178        WorkList.push_back(SuccSU);
179    }
180  } while (!WorkList.empty());
181}
182
183void SUnit::setHeightDirty() {
184  if (!isHeightCurrent) return;
185  SmallVector<SUnit*, 8> WorkList;
186  WorkList.push_back(this);
187  do {
188    SUnit *SU = WorkList.pop_back_val();
189    SU->isHeightCurrent = false;
190    for (SUnit::const_pred_iterator I = SU->Preds.begin(),
191         E = SU->Preds.end(); I != E; ++I) {
192      SUnit *PredSU = I->getSUnit();
193      if (PredSU->isHeightCurrent)
194        WorkList.push_back(PredSU);
195    }
196  } while (!WorkList.empty());
197}
198
199/// setDepthToAtLeast - Update this node's successors to reflect the
200/// fact that this node's depth just increased.
201///
202void SUnit::setDepthToAtLeast(unsigned NewDepth) {
203  if (NewDepth <= getDepth())
204    return;
205  setDepthDirty();
206  Depth = NewDepth;
207  isDepthCurrent = true;
208}
209
210/// setHeightToAtLeast - Update this node's predecessors to reflect the
211/// fact that this node's height just increased.
212///
213void SUnit::setHeightToAtLeast(unsigned NewHeight) {
214  if (NewHeight <= getHeight())
215    return;
216  setHeightDirty();
217  Height = NewHeight;
218  isHeightCurrent = true;
219}
220
221/// ComputeDepth - Calculate the maximal path from the node to the exit.
222///
223void SUnit::ComputeDepth() {
224  SmallVector<SUnit*, 8> WorkList;
225  WorkList.push_back(this);
226  do {
227    SUnit *Cur = WorkList.back();
228
229    bool Done = true;
230    unsigned MaxPredDepth = 0;
231    for (SUnit::const_pred_iterator I = Cur->Preds.begin(),
232         E = Cur->Preds.end(); I != E; ++I) {
233      SUnit *PredSU = I->getSUnit();
234      if (PredSU->isDepthCurrent)
235        MaxPredDepth = std::max(MaxPredDepth,
236                                PredSU->Depth + I->getLatency());
237      else {
238        Done = false;
239        WorkList.push_back(PredSU);
240      }
241    }
242
243    if (Done) {
244      WorkList.pop_back();
245      if (MaxPredDepth != Cur->Depth) {
246        Cur->setDepthDirty();
247        Cur->Depth = MaxPredDepth;
248      }
249      Cur->isDepthCurrent = true;
250    }
251  } while (!WorkList.empty());
252}
253
254/// ComputeHeight - Calculate the maximal path from the node to the entry.
255///
256void SUnit::ComputeHeight() {
257  SmallVector<SUnit*, 8> WorkList;
258  WorkList.push_back(this);
259  do {
260    SUnit *Cur = WorkList.back();
261
262    bool Done = true;
263    unsigned MaxSuccHeight = 0;
264    for (SUnit::const_succ_iterator I = Cur->Succs.begin(),
265         E = Cur->Succs.end(); I != E; ++I) {
266      SUnit *SuccSU = I->getSUnit();
267      if (SuccSU->isHeightCurrent)
268        MaxSuccHeight = std::max(MaxSuccHeight,
269                                 SuccSU->Height + I->getLatency());
270      else {
271        Done = false;
272        WorkList.push_back(SuccSU);
273      }
274    }
275
276    if (Done) {
277      WorkList.pop_back();
278      if (MaxSuccHeight != Cur->Height) {
279        Cur->setHeightDirty();
280        Cur->Height = MaxSuccHeight;
281      }
282      Cur->isHeightCurrent = true;
283    }
284  } while (!WorkList.empty());
285}
286
287/// SUnit - Scheduling unit. It's an wrapper around either a single SDNode or
288/// a group of nodes flagged together.
289void SUnit::dump(const ScheduleDAG *G) const {
290  dbgs() << "SU(" << NodeNum << "): ";
291  G->dumpNode(this);
292}
293
294void SUnit::dumpAll(const ScheduleDAG *G) const {
295  dump(G);
296
297  dbgs() << "  # preds left       : " << NumPredsLeft << "\n";
298  dbgs() << "  # succs left       : " << NumSuccsLeft << "\n";
299  dbgs() << "  # rdefs left       : " << NumRegDefsLeft << "\n";
300  dbgs() << "  Latency            : " << Latency << "\n";
301  dbgs() << "  Depth              : " << Depth << "\n";
302  dbgs() << "  Height             : " << Height << "\n";
303
304  if (Preds.size() != 0) {
305    dbgs() << "  Predecessors:\n";
306    for (SUnit::const_succ_iterator I = Preds.begin(), E = Preds.end();
307         I != E; ++I) {
308      dbgs() << "   ";
309      switch (I->getKind()) {
310      case SDep::Data:        dbgs() << "val "; break;
311      case SDep::Anti:        dbgs() << "anti"; break;
312      case SDep::Output:      dbgs() << "out "; break;
313      case SDep::Order:       dbgs() << "ch  "; break;
314      }
315      dbgs() << "#";
316      dbgs() << I->getSUnit() << " - SU(" << I->getSUnit()->NodeNum << ")";
317      if (I->isArtificial())
318        dbgs() << " *";
319      dbgs() << ": Latency=" << I->getLatency();
320      if (I->isAssignedRegDep())
321        dbgs() << " Reg=" << G->TRI->getName(I->getReg());
322      dbgs() << "\n";
323    }
324  }
325  if (Succs.size() != 0) {
326    dbgs() << "  Successors:\n";
327    for (SUnit::const_succ_iterator I = Succs.begin(), E = Succs.end();
328         I != E; ++I) {
329      dbgs() << "   ";
330      switch (I->getKind()) {
331      case SDep::Data:        dbgs() << "val "; break;
332      case SDep::Anti:        dbgs() << "anti"; break;
333      case SDep::Output:      dbgs() << "out "; break;
334      case SDep::Order:       dbgs() << "ch  "; break;
335      }
336      dbgs() << "#";
337      dbgs() << I->getSUnit() << " - SU(" << I->getSUnit()->NodeNum << ")";
338      if (I->isArtificial())
339        dbgs() << " *";
340      dbgs() << ": Latency=" << I->getLatency();
341      dbgs() << "\n";
342    }
343  }
344  dbgs() << "\n";
345}
346
347#ifndef NDEBUG
348/// VerifySchedule - Verify that all SUnits were scheduled and that
349/// their state is consistent.
350///
351void ScheduleDAG::VerifySchedule(bool isBottomUp) {
352  bool AnyNotSched = false;
353  unsigned DeadNodes = 0;
354  unsigned Noops = 0;
355  for (unsigned i = 0, e = SUnits.size(); i != e; ++i) {
356    if (!SUnits[i].isScheduled) {
357      if (SUnits[i].NumPreds == 0 && SUnits[i].NumSuccs == 0) {
358        ++DeadNodes;
359        continue;
360      }
361      if (!AnyNotSched)
362        dbgs() << "*** Scheduling failed! ***\n";
363      SUnits[i].dump(this);
364      dbgs() << "has not been scheduled!\n";
365      AnyNotSched = true;
366    }
367    if (SUnits[i].isScheduled &&
368        (isBottomUp ? SUnits[i].getHeight() : SUnits[i].getDepth()) >
369          unsigned(INT_MAX)) {
370      if (!AnyNotSched)
371        dbgs() << "*** Scheduling failed! ***\n";
372      SUnits[i].dump(this);
373      dbgs() << "has an unexpected "
374           << (isBottomUp ? "Height" : "Depth") << " value!\n";
375      AnyNotSched = true;
376    }
377    if (isBottomUp) {
378      if (SUnits[i].NumSuccsLeft != 0) {
379        if (!AnyNotSched)
380          dbgs() << "*** Scheduling failed! ***\n";
381        SUnits[i].dump(this);
382        dbgs() << "has successors left!\n";
383        AnyNotSched = true;
384      }
385    } else {
386      if (SUnits[i].NumPredsLeft != 0) {
387        if (!AnyNotSched)
388          dbgs() << "*** Scheduling failed! ***\n";
389        SUnits[i].dump(this);
390        dbgs() << "has predecessors left!\n";
391        AnyNotSched = true;
392      }
393    }
394  }
395  for (unsigned i = 0, e = Sequence.size(); i != e; ++i)
396    if (!Sequence[i])
397      ++Noops;
398  assert(!AnyNotSched);
399  assert(Sequence.size() + DeadNodes - Noops == SUnits.size() &&
400         "The number of nodes scheduled doesn't match the expected number!");
401}
402#endif
403
404/// InitDAGTopologicalSorting - create the initial topological
405/// ordering from the DAG to be scheduled.
406///
407/// The idea of the algorithm is taken from
408/// "Online algorithms for managing the topological order of
409/// a directed acyclic graph" by David J. Pearce and Paul H.J. Kelly
410/// This is the MNR algorithm, which was first introduced by
411/// A. Marchetti-Spaccamela, U. Nanni and H. Rohnert in
412/// "Maintaining a topological order under edge insertions".
413///
414/// Short description of the algorithm:
415///
416/// Topological ordering, ord, of a DAG maps each node to a topological
417/// index so that for all edges X->Y it is the case that ord(X) < ord(Y).
418///
419/// This means that if there is a path from the node X to the node Z,
420/// then ord(X) < ord(Z).
421///
422/// This property can be used to check for reachability of nodes:
423/// if Z is reachable from X, then an insertion of the edge Z->X would
424/// create a cycle.
425///
426/// The algorithm first computes a topological ordering for the DAG by
427/// initializing the Index2Node and Node2Index arrays and then tries to keep
428/// the ordering up-to-date after edge insertions by reordering the DAG.
429///
430/// On insertion of the edge X->Y, the algorithm first marks by calling DFS
431/// the nodes reachable from Y, and then shifts them using Shift to lie
432/// immediately after X in Index2Node.
433void ScheduleDAGTopologicalSort::InitDAGTopologicalSorting() {
434  unsigned DAGSize = SUnits.size();
435  std::vector<SUnit*> WorkList;
436  WorkList.reserve(DAGSize);
437
438  Index2Node.resize(DAGSize);
439  Node2Index.resize(DAGSize);
440
441  // Initialize the data structures.
442  for (unsigned i = 0, e = DAGSize; i != e; ++i) {
443    SUnit *SU = &SUnits[i];
444    int NodeNum = SU->NodeNum;
445    unsigned Degree = SU->Succs.size();
446    // Temporarily use the Node2Index array as scratch space for degree counts.
447    Node2Index[NodeNum] = Degree;
448
449    // Is it a node without dependencies?
450    if (Degree == 0) {
451      assert(SU->Succs.empty() && "SUnit should have no successors");
452      // Collect leaf nodes.
453      WorkList.push_back(SU);
454    }
455  }
456
457  int Id = DAGSize;
458  while (!WorkList.empty()) {
459    SUnit *SU = WorkList.back();
460    WorkList.pop_back();
461    Allocate(SU->NodeNum, --Id);
462    for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
463         I != E; ++I) {
464      SUnit *SU = I->getSUnit();
465      if (!--Node2Index[SU->NodeNum])
466        // If all dependencies of the node are processed already,
467        // then the node can be computed now.
468        WorkList.push_back(SU);
469    }
470  }
471
472  Visited.resize(DAGSize);
473
474#ifndef NDEBUG
475  // Check correctness of the ordering
476  for (unsigned i = 0, e = DAGSize; i != e; ++i) {
477    SUnit *SU = &SUnits[i];
478    for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
479         I != E; ++I) {
480      assert(Node2Index[SU->NodeNum] > Node2Index[I->getSUnit()->NodeNum] &&
481      "Wrong topological sorting");
482    }
483  }
484#endif
485}
486
487/// AddPred - Updates the topological ordering to accommodate an edge
488/// to be added from SUnit X to SUnit Y.
489void ScheduleDAGTopologicalSort::AddPred(SUnit *Y, SUnit *X) {
490  int UpperBound, LowerBound;
491  LowerBound = Node2Index[Y->NodeNum];
492  UpperBound = Node2Index[X->NodeNum];
493  bool HasLoop = false;
494  // Is Ord(X) < Ord(Y) ?
495  if (LowerBound < UpperBound) {
496    // Update the topological order.
497    Visited.reset();
498    DFS(Y, UpperBound, HasLoop);
499    assert(!HasLoop && "Inserted edge creates a loop!");
500    // Recompute topological indexes.
501    Shift(Visited, LowerBound, UpperBound);
502  }
503}
504
505/// RemovePred - Updates the topological ordering to accommodate an
506/// an edge to be removed from the specified node N from the predecessors
507/// of the current node M.
508void ScheduleDAGTopologicalSort::RemovePred(SUnit *M, SUnit *N) {
509  // InitDAGTopologicalSorting();
510}
511
512/// DFS - Make a DFS traversal to mark all nodes reachable from SU and mark
513/// all nodes affected by the edge insertion. These nodes will later get new
514/// topological indexes by means of the Shift method.
515void ScheduleDAGTopologicalSort::DFS(const SUnit *SU, int UpperBound,
516                                     bool &HasLoop) {
517  std::vector<const SUnit*> WorkList;
518  WorkList.reserve(SUnits.size());
519
520  WorkList.push_back(SU);
521  do {
522    SU = WorkList.back();
523    WorkList.pop_back();
524    Visited.set(SU->NodeNum);
525    for (int I = SU->Succs.size()-1; I >= 0; --I) {
526      int s = SU->Succs[I].getSUnit()->NodeNum;
527      if (Node2Index[s] == UpperBound) {
528        HasLoop = true;
529        return;
530      }
531      // Visit successors if not already and in affected region.
532      if (!Visited.test(s) && Node2Index[s] < UpperBound) {
533        WorkList.push_back(SU->Succs[I].getSUnit());
534      }
535    }
536  } while (!WorkList.empty());
537}
538
539/// Shift - Renumber the nodes so that the topological ordering is
540/// preserved.
541void ScheduleDAGTopologicalSort::Shift(BitVector& Visited, int LowerBound,
542                                       int UpperBound) {
543  std::vector<int> L;
544  int shift = 0;
545  int i;
546
547  for (i = LowerBound; i <= UpperBound; ++i) {
548    // w is node at topological index i.
549    int w = Index2Node[i];
550    if (Visited.test(w)) {
551      // Unmark.
552      Visited.reset(w);
553      L.push_back(w);
554      shift = shift + 1;
555    } else {
556      Allocate(w, i - shift);
557    }
558  }
559
560  for (unsigned j = 0; j < L.size(); ++j) {
561    Allocate(L[j], i - shift);
562    i = i + 1;
563  }
564}
565
566
567/// WillCreateCycle - Returns true if adding an edge from SU to TargetSU will
568/// create a cycle.
569bool ScheduleDAGTopologicalSort::WillCreateCycle(SUnit *SU, SUnit *TargetSU) {
570  if (IsReachable(TargetSU, SU))
571    return true;
572  for (SUnit::pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
573       I != E; ++I)
574    if (I->isAssignedRegDep() &&
575        IsReachable(TargetSU, I->getSUnit()))
576      return true;
577  return false;
578}
579
580/// IsReachable - Checks if SU is reachable from TargetSU.
581bool ScheduleDAGTopologicalSort::IsReachable(const SUnit *SU,
582                                             const SUnit *TargetSU) {
583  // If insertion of the edge SU->TargetSU would create a cycle
584  // then there is a path from TargetSU to SU.
585  int UpperBound, LowerBound;
586  LowerBound = Node2Index[TargetSU->NodeNum];
587  UpperBound = Node2Index[SU->NodeNum];
588  bool HasLoop = false;
589  // Is Ord(TargetSU) < Ord(SU) ?
590  if (LowerBound < UpperBound) {
591    Visited.reset();
592    // There may be a path from TargetSU to SU. Check for it.
593    DFS(TargetSU, UpperBound, HasLoop);
594  }
595  return HasLoop;
596}
597
598/// Allocate - assign the topological index to the node n.
599void ScheduleDAGTopologicalSort::Allocate(int n, int index) {
600  Node2Index[n] = index;
601  Index2Node[index] = n;
602}
603
604ScheduleDAGTopologicalSort::
605ScheduleDAGTopologicalSort(std::vector<SUnit> &sunits) : SUnits(sunits) {}
606
607ScheduleHazardRecognizer::~ScheduleHazardRecognizer() {}
608