lib/CodeGen/ScheduleDAG.cpp

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