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