ScheduleDAG.cpp revision 47c144505b9be28ed22c626b3a407c11dba2fec5 
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>::const_iterator I = Preds.begin(), E = Preds.end();
68       I != E; ++I)
69    if (*I == D)
70      return false;
71  // Now add a corresponding succ to N.
72  SDep P = D;
73  P.setSUnit(this);
74  SUnit *N = D.getSUnit();
75  // Update the bookkeeping.
76  if (D.getKind() == SDep::Data) {
77    assert(NumPreds < UINT_MAX && "NumPreds will overflow!");
78    assert(N->NumSuccs < UINT_MAX && "NumSuccs will overflow!");
79    ++NumPreds;
80    ++N->NumSuccs;
81  }
82  if (!N->isScheduled) {
83    assert(NumPredsLeft < UINT_MAX && "NumPredsLeft will overflow!");
84    ++NumPredsLeft;
85  }
86  if (!isScheduled) {
87    assert(N->NumSuccsLeft < UINT_MAX && "NumSuccsLeft will overflow!");
88    ++N->NumSuccsLeft;
89  }
90  Preds.push_back(D);
91  N->Succs.push_back(P);
92  if (P.getLatency() != 0) {
93    this->setDepthDirty();
94    N->setHeightDirty();
95  }
96  return true;
97}
98
99/// removePred - This removes the specified edge as a pred of the current
100/// node if it exists.  It also removes the current node as a successor of
101/// the specified node.
102void SUnit::removePred(const SDep &D) {
103  // Find the matching predecessor.
104  for (SmallVector<SDep, 4>::iterator I = Preds.begin(), E = Preds.end();
105       I != E; ++I)
106    if (*I == D) {
107      bool FoundSucc = false;
108      // Find the corresponding successor in N.
109      SDep P = D;
110      P.setSUnit(this);
111      SUnit *N = D.getSUnit();
112      for (SmallVector<SDep, 4>::iterator II = N->Succs.begin(),
113             EE = N->Succs.end(); II != EE; ++II)
114        if (*II == P) {
115          FoundSucc = true;
116          N->Succs.erase(II);
117          break;
118        }
119      assert(FoundSucc && "Mismatching preds / succs lists!");
120      (void)FoundSucc;
121      Preds.erase(I);
122      // Update the bookkeeping.
123      if (P.getKind() == SDep::Data) {
124        assert(NumPreds > 0 && "NumPreds will underflow!");
125        assert(N->NumSuccs > 0 && "NumSuccs will underflow!");
126        --NumPreds;
127        --N->NumSuccs;
128      }
129      if (!N->isScheduled) {
130        assert(NumPredsLeft > 0 && "NumPredsLeft will underflow!");
131        --NumPredsLeft;
132      }
133      if (!isScheduled) {
134        assert(N->NumSuccsLeft > 0 && "NumSuccsLeft will underflow!");
135        --N->NumSuccsLeft;
136      }
137      if (P.getLatency() != 0) {
138        this->setDepthDirty();
139        N->setHeightDirty();
140      }
141      return;
142    }
143}
144
145void SUnit::setDepthDirty() {
146  if (!isDepthCurrent) return;
147  SmallVector<SUnit*, 8> WorkList;
148  WorkList.push_back(this);
149  do {
150    SUnit *SU = WorkList.pop_back_val();
151    SU->isDepthCurrent = false;
152    for (SUnit::const_succ_iterator I = SU->Succs.begin(),
153         E = SU->Succs.end(); I != E; ++I) {
154      SUnit *SuccSU = I->getSUnit();
155      if (SuccSU->isDepthCurrent)
156        WorkList.push_back(SuccSU);
157    }
158  } while (!WorkList.empty());
159}
160
161void SUnit::setHeightDirty() {
162  if (!isHeightCurrent) return;
163  SmallVector<SUnit*, 8> WorkList;
164  WorkList.push_back(this);
165  do {
166    SUnit *SU = WorkList.pop_back_val();
167    SU->isHeightCurrent = false;
168    for (SUnit::const_pred_iterator I = SU->Preds.begin(),
169         E = SU->Preds.end(); I != E; ++I) {
170      SUnit *PredSU = I->getSUnit();
171      if (PredSU->isHeightCurrent)
172        WorkList.push_back(PredSU);
173    }
174  } while (!WorkList.empty());
175}
176
177/// setDepthToAtLeast - Update this node's successors to reflect the
178/// fact that this node's depth just increased.
179///
180void SUnit::setDepthToAtLeast(unsigned NewDepth) {
181  if (NewDepth <= getDepth())
182    return;
183  setDepthDirty();
184  Depth = NewDepth;
185  isDepthCurrent = true;
186}
187
188/// setHeightToAtLeast - Update this node's predecessors to reflect the
189/// fact that this node's height just increased.
190///
191void SUnit::setHeightToAtLeast(unsigned NewHeight) {
192  if (NewHeight <= getHeight())
193    return;
194  setHeightDirty();
195  Height = NewHeight;
196  isHeightCurrent = true;
197}
198
199/// ComputeDepth - Calculate the maximal path from the node to the exit.
200///
201void SUnit::ComputeDepth() {
202  SmallVector<SUnit*, 8> WorkList;
203  WorkList.push_back(this);
204  do {
205    SUnit *Cur = WorkList.back();
206
207    bool Done = true;
208    unsigned MaxPredDepth = 0;
209    for (SUnit::const_pred_iterator I = Cur->Preds.begin(),
210         E = Cur->Preds.end(); I != E; ++I) {
211      SUnit *PredSU = I->getSUnit();
212      if (PredSU->isDepthCurrent)
213        MaxPredDepth = std::max(MaxPredDepth,
214                                PredSU->Depth + I->getLatency());
215      else {
216        Done = false;
217        WorkList.push_back(PredSU);
218      }
219    }
220
221    if (Done) {
222      WorkList.pop_back();
223      if (MaxPredDepth != Cur->Depth) {
224        Cur->setDepthDirty();
225        Cur->Depth = MaxPredDepth;
226      }
227      Cur->isDepthCurrent = true;
228    }
229  } while (!WorkList.empty());
230}
231
232/// ComputeHeight - Calculate the maximal path from the node to the entry.
233///
234void SUnit::ComputeHeight() {
235  SmallVector<SUnit*, 8> WorkList;
236  WorkList.push_back(this);
237  do {
238    SUnit *Cur = WorkList.back();
239
240    bool Done = true;
241    unsigned MaxSuccHeight = 0;
242    for (SUnit::const_succ_iterator I = Cur->Succs.begin(),
243         E = Cur->Succs.end(); I != E; ++I) {
244      SUnit *SuccSU = I->getSUnit();
245      if (SuccSU->isHeightCurrent)
246        MaxSuccHeight = std::max(MaxSuccHeight,
247                                 SuccSU->Height + I->getLatency());
248      else {
249        Done = false;
250        WorkList.push_back(SuccSU);
251      }
252    }
253
254    if (Done) {
255      WorkList.pop_back();
256      if (MaxSuccHeight != Cur->Height) {
257        Cur->setHeightDirty();
258        Cur->Height = MaxSuccHeight;
259      }
260      Cur->isHeightCurrent = true;
261    }
262  } while (!WorkList.empty());
263}
264
265/// SUnit - Scheduling unit. It's an wrapper around either a single SDNode or
266/// a group of nodes flagged together.
267void SUnit::dump(const ScheduleDAG *G) const {
268  dbgs() << "SU(" << NodeNum << "): ";
269  G->dumpNode(this);
270}
271
272void SUnit::dumpAll(const ScheduleDAG *G) const {
273  dump(G);
274
275  dbgs() << "  # preds left       : " << NumPredsLeft << "\n";
276  dbgs() << "  # succs left       : " << NumSuccsLeft << "\n";
277  dbgs() << "  # rdefs left       : " << NumRegDefsLeft << "\n";
278  dbgs() << "  Latency            : " << Latency << "\n";
279  dbgs() << "  Depth              : " << Depth << "\n";
280  dbgs() << "  Height             : " << Height << "\n";
281
282  if (Preds.size() != 0) {
283    dbgs() << "  Predecessors:\n";
284    for (SUnit::const_succ_iterator I = Preds.begin(), E = Preds.end();
285         I != E; ++I) {
286      dbgs() << "   ";
287      switch (I->getKind()) {
288      case SDep::Data:        dbgs() << "val "; break;
289      case SDep::Anti:        dbgs() << "anti"; break;
290      case SDep::Output:      dbgs() << "out "; break;
291      case SDep::Order:       dbgs() << "ch  "; break;
292      }
293      dbgs() << "SU(" << I->getSUnit()->NodeNum << ")";
294      if (I->isArtificial())
295        dbgs() << " *";
296      dbgs() << ": Latency=" << I->getLatency();
297      if (I->isAssignedRegDep())
298        dbgs() << " Reg=" << PrintReg(I->getReg(), G->TRI);
299      dbgs() << "\n";
300    }
301  }
302  if (Succs.size() != 0) {
303    dbgs() << "  Successors:\n";
304    for (SUnit::const_succ_iterator I = Succs.begin(), E = Succs.end();
305         I != E; ++I) {
306      dbgs() << "   ";
307      switch (I->getKind()) {
308      case SDep::Data:        dbgs() << "val "; break;
309      case SDep::Anti:        dbgs() << "anti"; break;
310      case SDep::Output:      dbgs() << "out "; break;
311      case SDep::Order:       dbgs() << "ch  "; break;
312      }
313      dbgs() << "SU(" << I->getSUnit()->NodeNum << ")";
314      if (I->isArtificial())
315        dbgs() << " *";
316      dbgs() << ": Latency=" << I->getLatency();
317      dbgs() << "\n";
318    }
319  }
320  dbgs() << "\n";
321}
322
323#ifndef NDEBUG
324/// VerifyScheduledDAG - Verify that all SUnits were scheduled and that
325/// their state is consistent. Return the number of scheduled nodes.
326///
327unsigned ScheduleDAG::VerifyScheduledDAG(bool isBottomUp) {
328  bool AnyNotSched = false;
329  unsigned DeadNodes = 0;
330  for (unsigned i = 0, e = SUnits.size(); i != e; ++i) {
331    if (!SUnits[i].isScheduled) {
332      if (SUnits[i].NumPreds == 0 && SUnits[i].NumSuccs == 0) {
333        ++DeadNodes;
334        continue;
335      }
336      if (!AnyNotSched)
337        dbgs() << "*** Scheduling failed! ***\n";
338      SUnits[i].dump(this);
339      dbgs() << "has not been scheduled!\n";
340      AnyNotSched = true;
341    }
342    if (SUnits[i].isScheduled &&
343        (isBottomUp ? SUnits[i].getHeight() : SUnits[i].getDepth()) >
344          unsigned(INT_MAX)) {
345      if (!AnyNotSched)
346        dbgs() << "*** Scheduling failed! ***\n";
347      SUnits[i].dump(this);
348      dbgs() << "has an unexpected "
349           << (isBottomUp ? "Height" : "Depth") << " value!\n";
350      AnyNotSched = true;
351    }
352    if (isBottomUp) {
353      if (SUnits[i].NumSuccsLeft != 0) {
354        if (!AnyNotSched)
355          dbgs() << "*** Scheduling failed! ***\n";
356        SUnits[i].dump(this);
357        dbgs() << "has successors left!\n";
358        AnyNotSched = true;
359      }
360    } else {
361      if (SUnits[i].NumPredsLeft != 0) {
362        if (!AnyNotSched)
363          dbgs() << "*** Scheduling failed! ***\n";
364        SUnits[i].dump(this);
365        dbgs() << "has predecessors left!\n";
366        AnyNotSched = true;
367      }
368    }
369  }
370  assert(!AnyNotSched);
371  return SUnits.size() - DeadNodes;
372}
373#endif
374
375/// InitDAGTopologicalSorting - create the initial topological
376/// ordering from the DAG to be scheduled.
377///
378/// The idea of the algorithm is taken from
379/// "Online algorithms for managing the topological order of
380/// a directed acyclic graph" by David J. Pearce and Paul H.J. Kelly
381/// This is the MNR algorithm, which was first introduced by
382/// A. Marchetti-Spaccamela, U. Nanni and H. Rohnert in
383/// "Maintaining a topological order under edge insertions".
384///
385/// Short description of the algorithm:
386///
387/// Topological ordering, ord, of a DAG maps each node to a topological
388/// index so that for all edges X->Y it is the case that ord(X) < ord(Y).
389///
390/// This means that if there is a path from the node X to the node Z,
391/// then ord(X) < ord(Z).
392///
393/// This property can be used to check for reachability of nodes:
394/// if Z is reachable from X, then an insertion of the edge Z->X would
395/// create a cycle.
396///
397/// The algorithm first computes a topological ordering for the DAG by
398/// initializing the Index2Node and Node2Index arrays and then tries to keep
399/// the ordering up-to-date after edge insertions by reordering the DAG.
400///
401/// On insertion of the edge X->Y, the algorithm first marks by calling DFS
402/// the nodes reachable from Y, and then shifts them using Shift to lie
403/// immediately after X in Index2Node.
404void ScheduleDAGTopologicalSort::InitDAGTopologicalSorting() {
405  unsigned DAGSize = SUnits.size();
406  std::vector<SUnit*> WorkList;
407  WorkList.reserve(DAGSize);
408
409  Index2Node.resize(DAGSize);
410  Node2Index.resize(DAGSize);
411
412  // Initialize the data structures.
413  for (unsigned i = 0, e = DAGSize; i != e; ++i) {
414    SUnit *SU = &SUnits[i];
415    int NodeNum = SU->NodeNum;
416    unsigned Degree = SU->Succs.size();
417    // Temporarily use the Node2Index array as scratch space for degree counts.
418    Node2Index[NodeNum] = Degree;
419
420    // Is it a node without dependencies?
421    if (Degree == 0) {
422      assert(SU->Succs.empty() && "SUnit should have no successors");
423      // Collect leaf nodes.
424      WorkList.push_back(SU);
425    }
426  }
427
428  int Id = DAGSize;
429  while (!WorkList.empty()) {
430    SUnit *SU = WorkList.back();
431    WorkList.pop_back();
432    Allocate(SU->NodeNum, --Id);
433    for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
434         I != E; ++I) {
435      SUnit *SU = I->getSUnit();
436      if (!--Node2Index[SU->NodeNum])
437        // If all dependencies of the node are processed already,
438        // then the node can be computed now.
439        WorkList.push_back(SU);
440    }
441  }
442
443  Visited.resize(DAGSize);
444
445#ifndef NDEBUG
446  // Check correctness of the ordering
447  for (unsigned i = 0, e = DAGSize; i != e; ++i) {
448    SUnit *SU = &SUnits[i];
449    for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
450         I != E; ++I) {
451      assert(Node2Index[SU->NodeNum] > Node2Index[I->getSUnit()->NodeNum] &&
452      "Wrong topological sorting");
453    }
454  }
455#endif
456}
457
458/// AddPred - Updates the topological ordering to accommodate an edge
459/// to be added from SUnit X to SUnit Y.
460void ScheduleDAGTopologicalSort::AddPred(SUnit *Y, SUnit *X) {
461  int UpperBound, LowerBound;
462  LowerBound = Node2Index[Y->NodeNum];
463  UpperBound = Node2Index[X->NodeNum];
464  bool HasLoop = false;
465  // Is Ord(X) < Ord(Y) ?
466  if (LowerBound < UpperBound) {
467    // Update the topological order.
468    Visited.reset();
469    DFS(Y, UpperBound, HasLoop);
470    assert(!HasLoop && "Inserted edge creates a loop!");
471    // Recompute topological indexes.
472    Shift(Visited, LowerBound, UpperBound);
473  }
474}
475
476/// RemovePred - Updates the topological ordering to accommodate an
477/// an edge to be removed from the specified node N from the predecessors
478/// of the current node M.
479void ScheduleDAGTopologicalSort::RemovePred(SUnit *M, SUnit *N) {
480  // InitDAGTopologicalSorting();
481}
482
483/// DFS - Make a DFS traversal to mark all nodes reachable from SU and mark
484/// all nodes affected by the edge insertion. These nodes will later get new
485/// topological indexes by means of the Shift method.
486void ScheduleDAGTopologicalSort::DFS(const SUnit *SU, int UpperBound,
487                                     bool &HasLoop) {
488  std::vector<const SUnit*> WorkList;
489  WorkList.reserve(SUnits.size());
490
491  WorkList.push_back(SU);
492  do {
493    SU = WorkList.back();
494    WorkList.pop_back();
495    Visited.set(SU->NodeNum);
496    for (int I = SU->Succs.size()-1; I >= 0; --I) {
497      int s = SU->Succs[I].getSUnit()->NodeNum;
498      if (Node2Index[s] == UpperBound) {
499        HasLoop = true;
500        return;
501      }
502      // Visit successors if not already and in affected region.
503      if (!Visited.test(s) && Node2Index[s] < UpperBound) {
504        WorkList.push_back(SU->Succs[I].getSUnit());
505      }
506    }
507  } while (!WorkList.empty());
508}
509
510/// Shift - Renumber the nodes so that the topological ordering is
511/// preserved.
512void ScheduleDAGTopologicalSort::Shift(BitVector& Visited, int LowerBound,
513                                       int UpperBound) {
514  std::vector<int> L;
515  int shift = 0;
516  int i;
517
518  for (i = LowerBound; i <= UpperBound; ++i) {
519    // w is node at topological index i.
520    int w = Index2Node[i];
521    if (Visited.test(w)) {
522      // Unmark.
523      Visited.reset(w);
524      L.push_back(w);
525      shift = shift + 1;
526    } else {
527      Allocate(w, i - shift);
528    }
529  }
530
531  for (unsigned j = 0; j < L.size(); ++j) {
532    Allocate(L[j], i - shift);
533    i = i + 1;
534  }
535}
536
537
538/// WillCreateCycle - Returns true if adding an edge from SU to TargetSU will
539/// create a cycle.
540bool ScheduleDAGTopologicalSort::WillCreateCycle(SUnit *SU, SUnit *TargetSU) {
541  if (IsReachable(TargetSU, SU))
542    return true;
543  for (SUnit::pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
544       I != E; ++I)
545    if (I->isAssignedRegDep() &&
546        IsReachable(TargetSU, I->getSUnit()))
547      return true;
548  return false;
549}
550
551/// IsReachable - Checks if SU is reachable from TargetSU.
552bool ScheduleDAGTopologicalSort::IsReachable(const SUnit *SU,
553                                             const SUnit *TargetSU) {
554  // If insertion of the edge SU->TargetSU would create a cycle
555  // then there is a path from TargetSU to SU.
556  int UpperBound, LowerBound;
557  LowerBound = Node2Index[TargetSU->NodeNum];
558  UpperBound = Node2Index[SU->NodeNum];
559  bool HasLoop = false;
560  // Is Ord(TargetSU) < Ord(SU) ?
561  if (LowerBound < UpperBound) {
562    Visited.reset();
563    // There may be a path from TargetSU to SU. Check for it.
564    DFS(TargetSU, UpperBound, HasLoop);
565  }
566  return HasLoop;
567}
568
569/// Allocate - assign the topological index to the node n.
570void ScheduleDAGTopologicalSort::Allocate(int n, int index) {
571  Node2Index[n] = index;
572  Index2Node[index] = n;
573}
574
575ScheduleDAGTopologicalSort::
576ScheduleDAGTopologicalSort(std::vector<SUnit> &sunits) : SUnits(sunits) {}
577
578ScheduleHazardRecognizer::~ScheduleHazardRecognizer() {}
579