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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>
26 using namespace llvm;
27 
28 #ifndef NDEBUG
29 static cl::opt<bool> StressSchedOpt(
30   "stress-sched", cl::Hidden, cl::init(false),
31   cl::desc("Stress test instruction scheduling"));
32 #endif
33 
ScheduleDAG(MachineFunction & mf)34 ScheduleDAG::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 
~ScheduleDAG()45 ScheduleDAG::~ScheduleDAG() {}
46 
47 /// getInstrDesc helper to handle SDNodes.
getNodeDesc(const SDNode * Node) const48 const MCInstrDesc *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.
dumpSchedule() const54 void 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 ///
Run(MachineBasicBlock * bb,MachineBasicBlock::iterator insertPos)66 void 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.
addPred(const SDep & D)88 bool 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.
removePred(const SDep & D)125 void 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       (void)FoundSucc;
144       Preds.erase(I);
145       // Update the bookkeeping.
146       if (P.getKind() == SDep::Data) {
147         assert(NumPreds > 0 && "NumPreds will underflow!");
148         assert(N->NumSuccs > 0 && "NumSuccs will underflow!");
149         --NumPreds;
150         --N->NumSuccs;
151       }
152       if (!N->isScheduled) {
153         assert(NumPredsLeft > 0 && "NumPredsLeft will underflow!");
154         --NumPredsLeft;
155       }
156       if (!isScheduled) {
157         assert(N->NumSuccsLeft > 0 && "NumSuccsLeft will underflow!");
158         --N->NumSuccsLeft;
159       }
160       if (P.getLatency() != 0) {
161         this->setDepthDirty();
162         N->setHeightDirty();
163       }
164       return;
165     }
166 }
167 
setDepthDirty()168 void SUnit::setDepthDirty() {
169   if (!isDepthCurrent) return;
170   SmallVector<SUnit*, 8> WorkList;
171   WorkList.push_back(this);
172   do {
173     SUnit *SU = WorkList.pop_back_val();
174     SU->isDepthCurrent = false;
175     for (SUnit::const_succ_iterator I = SU->Succs.begin(),
176          E = SU->Succs.end(); I != E; ++I) {
177       SUnit *SuccSU = I->getSUnit();
178       if (SuccSU->isDepthCurrent)
179         WorkList.push_back(SuccSU);
180     }
181   } while (!WorkList.empty());
182 }
183 
setHeightDirty()184 void SUnit::setHeightDirty() {
185   if (!isHeightCurrent) return;
186   SmallVector<SUnit*, 8> WorkList;
187   WorkList.push_back(this);
188   do {
189     SUnit *SU = WorkList.pop_back_val();
190     SU->isHeightCurrent = false;
191     for (SUnit::const_pred_iterator I = SU->Preds.begin(),
192          E = SU->Preds.end(); I != E; ++I) {
193       SUnit *PredSU = I->getSUnit();
194       if (PredSU->isHeightCurrent)
195         WorkList.push_back(PredSU);
196     }
197   } while (!WorkList.empty());
198 }
199 
200 /// setDepthToAtLeast - Update this node's successors to reflect the
201 /// fact that this node's depth just increased.
202 ///
setDepthToAtLeast(unsigned NewDepth)203 void SUnit::setDepthToAtLeast(unsigned NewDepth) {
204   if (NewDepth <= getDepth())
205     return;
206   setDepthDirty();
207   Depth = NewDepth;
208   isDepthCurrent = true;
209 }
210 
211 /// setHeightToAtLeast - Update this node's predecessors to reflect the
212 /// fact that this node's height just increased.
213 ///
setHeightToAtLeast(unsigned NewHeight)214 void SUnit::setHeightToAtLeast(unsigned NewHeight) {
215   if (NewHeight <= getHeight())
216     return;
217   setHeightDirty();
218   Height = NewHeight;
219   isHeightCurrent = true;
220 }
221 
222 /// ComputeDepth - Calculate the maximal path from the node to the exit.
223 ///
ComputeDepth()224 void SUnit::ComputeDepth() {
225   SmallVector<SUnit*, 8> WorkList;
226   WorkList.push_back(this);
227   do {
228     SUnit *Cur = WorkList.back();
229 
230     bool Done = true;
231     unsigned MaxPredDepth = 0;
232     for (SUnit::const_pred_iterator I = Cur->Preds.begin(),
233          E = Cur->Preds.end(); I != E; ++I) {
234       SUnit *PredSU = I->getSUnit();
235       if (PredSU->isDepthCurrent)
236         MaxPredDepth = std::max(MaxPredDepth,
237                                 PredSU->Depth + I->getLatency());
238       else {
239         Done = false;
240         WorkList.push_back(PredSU);
241       }
242     }
243 
244     if (Done) {
245       WorkList.pop_back();
246       if (MaxPredDepth != Cur->Depth) {
247         Cur->setDepthDirty();
248         Cur->Depth = MaxPredDepth;
249       }
250       Cur->isDepthCurrent = true;
251     }
252   } while (!WorkList.empty());
253 }
254 
255 /// ComputeHeight - Calculate the maximal path from the node to the entry.
256 ///
ComputeHeight()257 void SUnit::ComputeHeight() {
258   SmallVector<SUnit*, 8> WorkList;
259   WorkList.push_back(this);
260   do {
261     SUnit *Cur = WorkList.back();
262 
263     bool Done = true;
264     unsigned MaxSuccHeight = 0;
265     for (SUnit::const_succ_iterator I = Cur->Succs.begin(),
266          E = Cur->Succs.end(); I != E; ++I) {
267       SUnit *SuccSU = I->getSUnit();
268       if (SuccSU->isHeightCurrent)
269         MaxSuccHeight = std::max(MaxSuccHeight,
270                                  SuccSU->Height + I->getLatency());
271       else {
272         Done = false;
273         WorkList.push_back(SuccSU);
274       }
275     }
276 
277     if (Done) {
278       WorkList.pop_back();
279       if (MaxSuccHeight != Cur->Height) {
280         Cur->setHeightDirty();
281         Cur->Height = MaxSuccHeight;
282       }
283       Cur->isHeightCurrent = true;
284     }
285   } while (!WorkList.empty());
286 }
287 
288 /// SUnit - Scheduling unit. It's an wrapper around either a single SDNode or
289 /// a group of nodes flagged together.
dump(const ScheduleDAG * G) const290 void SUnit::dump(const ScheduleDAG *G) const {
291   dbgs() << "SU(" << NodeNum << "): ";
292   G->dumpNode(this);
293 }
294 
dumpAll(const ScheduleDAG * G) const295 void SUnit::dumpAll(const ScheduleDAG *G) const {
296   dump(G);
297 
298   dbgs() << "  # preds left       : " << NumPredsLeft << "\n";
299   dbgs() << "  # succs left       : " << NumSuccsLeft << "\n";
300   dbgs() << "  # rdefs left       : " << NumRegDefsLeft << "\n";
301   dbgs() << "  Latency            : " << Latency << "\n";
302   dbgs() << "  Depth              : " << Depth << "\n";
303   dbgs() << "  Height             : " << Height << "\n";
304 
305   if (Preds.size() != 0) {
306     dbgs() << "  Predecessors:\n";
307     for (SUnit::const_succ_iterator I = Preds.begin(), E = Preds.end();
308          I != E; ++I) {
309       dbgs() << "   ";
310       switch (I->getKind()) {
311       case SDep::Data:        dbgs() << "val "; break;
312       case SDep::Anti:        dbgs() << "anti"; break;
313       case SDep::Output:      dbgs() << "out "; break;
314       case SDep::Order:       dbgs() << "ch  "; break;
315       }
316       dbgs() << "#";
317       dbgs() << I->getSUnit() << " - SU(" << I->getSUnit()->NodeNum << ")";
318       if (I->isArtificial())
319         dbgs() << " *";
320       dbgs() << ": Latency=" << I->getLatency();
321       if (I->isAssignedRegDep())
322         dbgs() << " Reg=" << G->TRI->getName(I->getReg());
323       dbgs() << "\n";
324     }
325   }
326   if (Succs.size() != 0) {
327     dbgs() << "  Successors:\n";
328     for (SUnit::const_succ_iterator I = Succs.begin(), E = Succs.end();
329          I != E; ++I) {
330       dbgs() << "   ";
331       switch (I->getKind()) {
332       case SDep::Data:        dbgs() << "val "; break;
333       case SDep::Anti:        dbgs() << "anti"; break;
334       case SDep::Output:      dbgs() << "out "; break;
335       case SDep::Order:       dbgs() << "ch  "; break;
336       }
337       dbgs() << "#";
338       dbgs() << I->getSUnit() << " - SU(" << I->getSUnit()->NodeNum << ")";
339       if (I->isArtificial())
340         dbgs() << " *";
341       dbgs() << ": Latency=" << I->getLatency();
342       dbgs() << "\n";
343     }
344   }
345   dbgs() << "\n";
346 }
347 
348 #ifndef NDEBUG
349 /// VerifySchedule - Verify that all SUnits were scheduled and that
350 /// their state is consistent.
351 ///
VerifySchedule(bool isBottomUp)352 void ScheduleDAG::VerifySchedule(bool isBottomUp) {
353   bool AnyNotSched = false;
354   unsigned DeadNodes = 0;
355   unsigned Noops = 0;
356   for (unsigned i = 0, e = SUnits.size(); i != e; ++i) {
357     if (!SUnits[i].isScheduled) {
358       if (SUnits[i].NumPreds == 0 && SUnits[i].NumSuccs == 0) {
359         ++DeadNodes;
360         continue;
361       }
362       if (!AnyNotSched)
363         dbgs() << "*** Scheduling failed! ***\n";
364       SUnits[i].dump(this);
365       dbgs() << "has not been scheduled!\n";
366       AnyNotSched = true;
367     }
368     if (SUnits[i].isScheduled &&
369         (isBottomUp ? SUnits[i].getHeight() : SUnits[i].getDepth()) >
370           unsigned(INT_MAX)) {
371       if (!AnyNotSched)
372         dbgs() << "*** Scheduling failed! ***\n";
373       SUnits[i].dump(this);
374       dbgs() << "has an unexpected "
375            << (isBottomUp ? "Height" : "Depth") << " value!\n";
376       AnyNotSched = true;
377     }
378     if (isBottomUp) {
379       if (SUnits[i].NumSuccsLeft != 0) {
380         if (!AnyNotSched)
381           dbgs() << "*** Scheduling failed! ***\n";
382         SUnits[i].dump(this);
383         dbgs() << "has successors left!\n";
384         AnyNotSched = true;
385       }
386     } else {
387       if (SUnits[i].NumPredsLeft != 0) {
388         if (!AnyNotSched)
389           dbgs() << "*** Scheduling failed! ***\n";
390         SUnits[i].dump(this);
391         dbgs() << "has predecessors left!\n";
392         AnyNotSched = true;
393       }
394     }
395   }
396   for (unsigned i = 0, e = Sequence.size(); i != e; ++i)
397     if (!Sequence[i])
398       ++Noops;
399   assert(!AnyNotSched);
400   assert(Sequence.size() + DeadNodes - Noops == SUnits.size() &&
401          "The number of nodes scheduled doesn't match the expected number!");
402 }
403 #endif
404 
405 /// InitDAGTopologicalSorting - create the initial topological
406 /// ordering from the DAG to be scheduled.
407 ///
408 /// The idea of the algorithm is taken from
409 /// "Online algorithms for managing the topological order of
410 /// a directed acyclic graph" by David J. Pearce and Paul H.J. Kelly
411 /// This is the MNR algorithm, which was first introduced by
412 /// A. Marchetti-Spaccamela, U. Nanni and H. Rohnert in
413 /// "Maintaining a topological order under edge insertions".
414 ///
415 /// Short description of the algorithm:
416 ///
417 /// Topological ordering, ord, of a DAG maps each node to a topological
418 /// index so that for all edges X->Y it is the case that ord(X) < ord(Y).
419 ///
420 /// This means that if there is a path from the node X to the node Z,
421 /// then ord(X) < ord(Z).
422 ///
423 /// This property can be used to check for reachability of nodes:
424 /// if Z is reachable from X, then an insertion of the edge Z->X would
425 /// create a cycle.
426 ///
427 /// The algorithm first computes a topological ordering for the DAG by
428 /// initializing the Index2Node and Node2Index arrays and then tries to keep
429 /// the ordering up-to-date after edge insertions by reordering the DAG.
430 ///
431 /// On insertion of the edge X->Y, the algorithm first marks by calling DFS
432 /// the nodes reachable from Y, and then shifts them using Shift to lie
433 /// immediately after X in Index2Node.
InitDAGTopologicalSorting()434 void ScheduleDAGTopologicalSort::InitDAGTopologicalSorting() {
435   unsigned DAGSize = SUnits.size();
436   std::vector<SUnit*> WorkList;
437   WorkList.reserve(DAGSize);
438 
439   Index2Node.resize(DAGSize);
440   Node2Index.resize(DAGSize);
441 
442   // Initialize the data structures.
443   for (unsigned i = 0, e = DAGSize; i != e; ++i) {
444     SUnit *SU = &SUnits[i];
445     int NodeNum = SU->NodeNum;
446     unsigned Degree = SU->Succs.size();
447     // Temporarily use the Node2Index array as scratch space for degree counts.
448     Node2Index[NodeNum] = Degree;
449 
450     // Is it a node without dependencies?
451     if (Degree == 0) {
452       assert(SU->Succs.empty() && "SUnit should have no successors");
453       // Collect leaf nodes.
454       WorkList.push_back(SU);
455     }
456   }
457 
458   int Id = DAGSize;
459   while (!WorkList.empty()) {
460     SUnit *SU = WorkList.back();
461     WorkList.pop_back();
462     Allocate(SU->NodeNum, --Id);
463     for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
464          I != E; ++I) {
465       SUnit *SU = I->getSUnit();
466       if (!--Node2Index[SU->NodeNum])
467         // If all dependencies of the node are processed already,
468         // then the node can be computed now.
469         WorkList.push_back(SU);
470     }
471   }
472 
473   Visited.resize(DAGSize);
474 
475 #ifndef NDEBUG
476   // Check correctness of the ordering
477   for (unsigned i = 0, e = DAGSize; i != e; ++i) {
478     SUnit *SU = &SUnits[i];
479     for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
480          I != E; ++I) {
481       assert(Node2Index[SU->NodeNum] > Node2Index[I->getSUnit()->NodeNum] &&
482       "Wrong topological sorting");
483     }
484   }
485 #endif
486 }
487 
488 /// AddPred - Updates the topological ordering to accommodate an edge
489 /// to be added from SUnit X to SUnit Y.
AddPred(SUnit * Y,SUnit * X)490 void ScheduleDAGTopologicalSort::AddPred(SUnit *Y, SUnit *X) {
491   int UpperBound, LowerBound;
492   LowerBound = Node2Index[Y->NodeNum];
493   UpperBound = Node2Index[X->NodeNum];
494   bool HasLoop = false;
495   // Is Ord(X) < Ord(Y) ?
496   if (LowerBound < UpperBound) {
497     // Update the topological order.
498     Visited.reset();
499     DFS(Y, UpperBound, HasLoop);
500     assert(!HasLoop && "Inserted edge creates a loop!");
501     // Recompute topological indexes.
502     Shift(Visited, LowerBound, UpperBound);
503   }
504 }
505 
506 /// RemovePred - Updates the topological ordering to accommodate an
507 /// an edge to be removed from the specified node N from the predecessors
508 /// of the current node M.
RemovePred(SUnit * M,SUnit * N)509 void ScheduleDAGTopologicalSort::RemovePred(SUnit *M, SUnit *N) {
510   // InitDAGTopologicalSorting();
511 }
512 
513 /// DFS - Make a DFS traversal to mark all nodes reachable from SU and mark
514 /// all nodes affected by the edge insertion. These nodes will later get new
515 /// topological indexes by means of the Shift method.
DFS(const SUnit * SU,int UpperBound,bool & HasLoop)516 void ScheduleDAGTopologicalSort::DFS(const SUnit *SU, int UpperBound,
517                                      bool &HasLoop) {
518   std::vector<const SUnit*> WorkList;
519   WorkList.reserve(SUnits.size());
520 
521   WorkList.push_back(SU);
522   do {
523     SU = WorkList.back();
524     WorkList.pop_back();
525     Visited.set(SU->NodeNum);
526     for (int I = SU->Succs.size()-1; I >= 0; --I) {
527       int s = SU->Succs[I].getSUnit()->NodeNum;
528       if (Node2Index[s] == UpperBound) {
529         HasLoop = true;
530         return;
531       }
532       // Visit successors if not already and in affected region.
533       if (!Visited.test(s) && Node2Index[s] < UpperBound) {
534         WorkList.push_back(SU->Succs[I].getSUnit());
535       }
536     }
537   } while (!WorkList.empty());
538 }
539 
540 /// Shift - Renumber the nodes so that the topological ordering is
541 /// preserved.
Shift(BitVector & Visited,int LowerBound,int UpperBound)542 void ScheduleDAGTopologicalSort::Shift(BitVector& Visited, int LowerBound,
543                                        int UpperBound) {
544   std::vector<int> L;
545   int shift = 0;
546   int i;
547 
548   for (i = LowerBound; i <= UpperBound; ++i) {
549     // w is node at topological index i.
550     int w = Index2Node[i];
551     if (Visited.test(w)) {
552       // Unmark.
553       Visited.reset(w);
554       L.push_back(w);
555       shift = shift + 1;
556     } else {
557       Allocate(w, i - shift);
558     }
559   }
560 
561   for (unsigned j = 0; j < L.size(); ++j) {
562     Allocate(L[j], i - shift);
563     i = i + 1;
564   }
565 }
566 
567 
568 /// WillCreateCycle - Returns true if adding an edge from SU to TargetSU will
569 /// create a cycle.
WillCreateCycle(SUnit * SU,SUnit * TargetSU)570 bool ScheduleDAGTopologicalSort::WillCreateCycle(SUnit *SU, SUnit *TargetSU) {
571   if (IsReachable(TargetSU, SU))
572     return true;
573   for (SUnit::pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
574        I != E; ++I)
575     if (I->isAssignedRegDep() &&
576         IsReachable(TargetSU, I->getSUnit()))
577       return true;
578   return false;
579 }
580 
581 /// IsReachable - Checks if SU is reachable from TargetSU.
IsReachable(const SUnit * SU,const SUnit * TargetSU)582 bool ScheduleDAGTopologicalSort::IsReachable(const SUnit *SU,
583                                              const SUnit *TargetSU) {
584   // If insertion of the edge SU->TargetSU would create a cycle
585   // then there is a path from TargetSU to SU.
586   int UpperBound, LowerBound;
587   LowerBound = Node2Index[TargetSU->NodeNum];
588   UpperBound = Node2Index[SU->NodeNum];
589   bool HasLoop = false;
590   // Is Ord(TargetSU) < Ord(SU) ?
591   if (LowerBound < UpperBound) {
592     Visited.reset();
593     // There may be a path from TargetSU to SU. Check for it.
594     DFS(TargetSU, UpperBound, HasLoop);
595   }
596   return HasLoop;
597 }
598 
599 /// Allocate - assign the topological index to the node n.
Allocate(int n,int index)600 void ScheduleDAGTopologicalSort::Allocate(int n, int index) {
601   Node2Index[n] = index;
602   Index2Node[index] = n;
603 }
604 
605 ScheduleDAGTopologicalSort::
ScheduleDAGTopologicalSort(std::vector<SUnit> & sunits)606 ScheduleDAGTopologicalSort(std::vector<SUnit> &sunits) : SUnits(sunits) {}
607 
~ScheduleHazardRecognizer()608 ScheduleHazardRecognizer::~ScheduleHazardRecognizer() {}
609