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