lib/CodeGen/SelectionDAG/ScheduleDAGFast.cpp

   1 //===----- ScheduleDAGFast.cpp - Fast poor list scheduler -----------------===//
   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 a fast scheduler.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "InstrEmitter.h"
  15 #include "ScheduleDAGSDNodes.h"
  16 #include "SDNodeDbgValue.h"
  17 #include "llvm/ADT/STLExtras.h"
  18 #include "llvm/ADT/SmallSet.h"
  19 #include "llvm/ADT/Statistic.h"
  20 #include "llvm/CodeGen/SchedulerRegistry.h"
  21 #include "llvm/CodeGen/SelectionDAGISel.h"
  22 #include "llvm/CodeGen/TargetInstrInfo.h"
  23 #include "llvm/CodeGen/TargetRegisterInfo.h"
  24 #include "llvm/IR/DataLayout.h"
  25 #include "llvm/IR/InlineAsm.h"
  26 #include "llvm/Support/Debug.h"
  27 #include "llvm/Support/ErrorHandling.h"
  28 #include "llvm/Support/raw_ostream.h"
  29 using namespace llvm;
  30
  31 #define DEBUG_TYPE "pre-RA-sched"
  32
  33 STATISTIC(NumUnfolds,    "Number of nodes unfolded");
  34 STATISTIC(NumDups,       "Number of duplicated nodes");
  35 STATISTIC(NumPRCopies,   "Number of physical copies");
  36
  37 static RegisterScheduler
  38   fastDAGScheduler("fast", "Fast suboptimal list scheduling",
  39                    createFastDAGScheduler);
  40 static RegisterScheduler
  41   linearizeDAGScheduler("linearize", "Linearize DAG, no scheduling",
  42                         createDAGLinearizer);
  43
  44
  45 namespace {
  46   /// FastPriorityQueue - A degenerate priority queue that considers
  47   /// all nodes to have the same priority.
  48   ///
  49   struct FastPriorityQueue {
  50     SmallVector<SUnit *, 16> Queue;
  51
  52     bool empty() const { return Queue.empty(); }
  53
  54     void push(SUnit *U) {
  55       Queue.push_back(U);
  56     }
  57
  58     SUnit *pop() {
  59       if (empty()) return nullptr;
  60       SUnit *V = Queue.back();
  61       Queue.pop_back();
  62       return V;
  63     }
  64   };
  65
  66 //===----------------------------------------------------------------------===//
  67 /// ScheduleDAGFast - The actual "fast" list scheduler implementation.
  68 ///
  69 class ScheduleDAGFast : public ScheduleDAGSDNodes {
  70 private:
  71   /// AvailableQueue - The priority queue to use for the available SUnits.
  72   FastPriorityQueue AvailableQueue;
  73
  74   /// LiveRegDefs - A set of physical registers and their definition
  75   /// that are "live". These nodes must be scheduled before any other nodes that
  76   /// modifies the registers can be scheduled.
  77   unsigned NumLiveRegs;
  78   std::vector<SUnit*> LiveRegDefs;
  79   std::vector<unsigned> LiveRegCycles;
  80
  81 public:
  82   ScheduleDAGFast(MachineFunction &mf)
  83     : ScheduleDAGSDNodes(mf) {}
  84
  85   void Schedule() override;
  86
  87   /// AddPred - adds a predecessor edge to SUnit SU.
  88   /// This returns true if this is a new predecessor.
  89   void AddPred(SUnit *SU, const SDep &D) {
  90     SU->addPred(D);
  91   }
  92
  93   /// RemovePred - removes a predecessor edge from SUnit SU.
  94   /// This returns true if an edge was removed.
  95   void RemovePred(SUnit *SU, const SDep &D) {
  96     SU->removePred(D);
  97   }
  98
  99 private:
 100   void ReleasePred(SUnit *SU, SDep *PredEdge);
 101   void ReleasePredecessors(SUnit *SU, unsigned CurCycle);
 102   void ScheduleNodeBottomUp(SUnit*, unsigned);
 103   SUnit *CopyAndMoveSuccessors(SUnit*);
 104   void InsertCopiesAndMoveSuccs(SUnit*, unsigned,
 105                                 const TargetRegisterClass*,
 106                                 const TargetRegisterClass*,
 107                                 SmallVectorImpl<SUnit*>&);
 108   bool DelayForLiveRegsBottomUp(SUnit*, SmallVectorImpl<unsigned>&);
 109   void ListScheduleBottomUp();
 110
 111   /// forceUnitLatencies - The fast scheduler doesn't care about real latencies.
 112   bool forceUnitLatencies() const override { return true; }
 113 };
 114 }  // end anonymous namespace
 115
 116
 117 /// Schedule - Schedule the DAG using list scheduling.
 118 void ScheduleDAGFast::Schedule() {
 119   LLVM_DEBUG(dbgs() << "********** List Scheduling **********\n");
 120
 121   NumLiveRegs = 0;
 122   LiveRegDefs.resize(TRI->getNumRegs(), nullptr);
 123   LiveRegCycles.resize(TRI->getNumRegs(), 0);
 124
 125   // Build the scheduling graph.
 126   BuildSchedGraph(nullptr);
 127
 128   LLVM_DEBUG(dump());
 129
 130   // Execute the actual scheduling loop.
 131   ListScheduleBottomUp();
 132 }
 133
 134 //===----------------------------------------------------------------------===//
 135 //  Bottom-Up Scheduling
 136 //===----------------------------------------------------------------------===//
 137
 138 /// ReleasePred - Decrement the NumSuccsLeft count of a predecessor. Add it to
 139 /// the AvailableQueue if the count reaches zero. Also update its cycle bound.
 140 void ScheduleDAGFast::ReleasePred(SUnit *SU, SDep *PredEdge) {
 141   SUnit *PredSU = PredEdge->getSUnit();
 142
 143 #ifndef NDEBUG
 144   if (PredSU->NumSuccsLeft == 0) {
 145     dbgs() << "*** Scheduling failed! ***\n";
 146     dumpNode(*PredSU);
 147     dbgs() << " has been released too many times!\n";
 148     llvm_unreachable(nullptr);
 149   }
 150 #endif
 151   --PredSU->NumSuccsLeft;
 152
 153   // If all the node's successors are scheduled, this node is ready
 154   // to be scheduled. Ignore the special EntrySU node.
 155   if (PredSU->NumSuccsLeft == 0 && PredSU != &EntrySU) {
 156     PredSU->isAvailable = true;
 157     AvailableQueue.push(PredSU);
 158   }
 159 }
 160
 161 void ScheduleDAGFast::ReleasePredecessors(SUnit *SU, unsigned CurCycle) {
 162   // Bottom up: release predecessors
 163   for (SDep &Pred : SU->Preds) {
 164     ReleasePred(SU, &Pred);
 165     if (Pred.isAssignedRegDep()) {
 166       // This is a physical register dependency and it's impossible or
 167       // expensive to copy the register. Make sure nothing that can
 168       // clobber the register is scheduled between the predecessor and
 169       // this node.
 170       if (!LiveRegDefs[Pred.getReg()]) {
 171         ++NumLiveRegs;
 172         LiveRegDefs[Pred.getReg()] = Pred.getSUnit();
 173         LiveRegCycles[Pred.getReg()] = CurCycle;
 174       }
 175     }
 176   }
 177 }
 178
 179 /// ScheduleNodeBottomUp - Add the node to the schedule. Decrement the pending
 180 /// count of its predecessors. If a predecessor pending count is zero, add it to
 181 /// the Available queue.
 182 void ScheduleDAGFast::ScheduleNodeBottomUp(SUnit *SU, unsigned CurCycle) {
 183   LLVM_DEBUG(dbgs() << "*** Scheduling [" << CurCycle << "]: ");
 184   LLVM_DEBUG(dumpNode(*SU));
 185
 186   assert(CurCycle >= SU->getHeight() && "Node scheduled below its height!");
 187   SU->setHeightToAtLeast(CurCycle);
 188   Sequence.push_back(SU);
 189
 190   ReleasePredecessors(SU, CurCycle);
 191
 192   // Release all the implicit physical register defs that are live.
 193   for (SDep &Succ : SU->Succs) {
 194     if (Succ.isAssignedRegDep()) {
 195       if (LiveRegCycles[Succ.getReg()] == Succ.getSUnit()->getHeight()) {
 196         assert(NumLiveRegs > 0 && "NumLiveRegs is already zero!");
 197         assert(LiveRegDefs[Succ.getReg()] == SU &&
 198                "Physical register dependency violated?");
 199         --NumLiveRegs;
 200         LiveRegDefs[Succ.getReg()] = nullptr;
 201         LiveRegCycles[Succ.getReg()] = 0;
 202       }
 203     }
 204   }
 205
 206   SU->isScheduled = true;
 207 }
 208
 209 /// CopyAndMoveSuccessors - Clone the specified node and move its scheduled
 210 /// successors to the newly created node.
 211 SUnit *ScheduleDAGFast::CopyAndMoveSuccessors(SUnit *SU) {
 212   if (SU->getNode()->getGluedNode())
 213     return nullptr;
 214
 215   SDNode *N = SU->getNode();
 216   if (!N)
 217     return nullptr;
 218
 219   SUnit *NewSU;
 220   bool TryUnfold = false;
 221   for (unsigned i = 0, e = N->getNumValues(); i != e; ++i) {
 222     MVT VT = N->getSimpleValueType(i);
 223     if (VT == MVT::Glue)
 224       return nullptr;
 225     else if (VT == MVT::Other)
 226       TryUnfold = true;
 227   }
 228   for (const SDValue &Op : N->op_values()) {
 229     MVT VT = Op.getNode()->getSimpleValueType(Op.getResNo());
 230     if (VT == MVT::Glue)
 231       return nullptr;
 232   }
 233
 234   if (TryUnfold) {
 235     SmallVector<SDNode*, 2> NewNodes;
 236     if (!TII->unfoldMemoryOperand(*DAG, N, NewNodes))
 237       return nullptr;
 238
 239     LLVM_DEBUG(dbgs() << "Unfolding SU # " << SU->NodeNum << "\n");
 240     assert(NewNodes.size() == 2 && "Expected a load folding node!");
 241
 242     N = NewNodes[1];
 243     SDNode *LoadNode = NewNodes[0];
 244     unsigned NumVals = N->getNumValues();
 245     unsigned OldNumVals = SU->getNode()->getNumValues();
 246     for (unsigned i = 0; i != NumVals; ++i)
 247       DAG->ReplaceAllUsesOfValueWith(SDValue(SU->getNode(), i), SDValue(N, i));
 248     DAG->ReplaceAllUsesOfValueWith(SDValue(SU->getNode(), OldNumVals-1),
 249                                    SDValue(LoadNode, 1));
 250
 251     SUnit *NewSU = newSUnit(N);
 252     assert(N->getNodeId() == -1 && "Node already inserted!");
 253     N->setNodeId(NewSU->NodeNum);
 254
 255     const MCInstrDesc &MCID = TII->get(N->getMachineOpcode());
 256     for (unsigned i = 0; i != MCID.getNumOperands(); ++i) {
 257       if (MCID.getOperandConstraint(i, MCOI::TIED_TO) != -1) {
 258         NewSU->isTwoAddress = true;
 259         break;
 260       }
 261     }
 262     if (MCID.isCommutable())
 263       NewSU->isCommutable = true;
 264
 265     // LoadNode may already exist. This can happen when there is another
 266     // load from the same location and producing the same type of value
 267     // but it has different alignment or volatileness.
 268     bool isNewLoad = true;
 269     SUnit *LoadSU;
 270     if (LoadNode->getNodeId() != -1) {
 271       LoadSU = &SUnits[LoadNode->getNodeId()];
 272       isNewLoad = false;
 273     } else {
 274       LoadSU = newSUnit(LoadNode);
 275       LoadNode->setNodeId(LoadSU->NodeNum);
 276     }
 277
 278     SDep ChainPred;
 279     SmallVector<SDep, 4> ChainSuccs;
 280     SmallVector<SDep, 4> LoadPreds;
 281     SmallVector<SDep, 4> NodePreds;
 282     SmallVector<SDep, 4> NodeSuccs;
 283     for (SDep &Pred : SU->Preds) {
 284       if (Pred.isCtrl())
 285         ChainPred = Pred;
 286       else if (Pred.getSUnit()->getNode() &&
 287                Pred.getSUnit()->getNode()->isOperandOf(LoadNode))
 288         LoadPreds.push_back(Pred);
 289       else
 290         NodePreds.push_back(Pred);
 291     }
 292     for (SDep &Succ : SU->Succs) {
 293       if (Succ.isCtrl())
 294         ChainSuccs.push_back(Succ);
 295       else
 296         NodeSuccs.push_back(Succ);
 297     }
 298
 299     if (ChainPred.getSUnit()) {
 300       RemovePred(SU, ChainPred);
 301       if (isNewLoad)
 302         AddPred(LoadSU, ChainPred);
 303     }
 304     for (unsigned i = 0, e = LoadPreds.size(); i != e; ++i) {
 305       const SDep &Pred = LoadPreds[i];
 306       RemovePred(SU, Pred);
 307       if (isNewLoad) {
 308         AddPred(LoadSU, Pred);
 309       }
 310     }
 311     for (unsigned i = 0, e = NodePreds.size(); i != e; ++i) {
 312       const SDep &Pred = NodePreds[i];
 313       RemovePred(SU, Pred);
 314       AddPred(NewSU, Pred);
 315     }
 316     for (unsigned i = 0, e = NodeSuccs.size(); i != e; ++i) {
 317       SDep D = NodeSuccs[i];
 318       SUnit *SuccDep = D.getSUnit();
 319       D.setSUnit(SU);
 320       RemovePred(SuccDep, D);
 321       D.setSUnit(NewSU);
 322       AddPred(SuccDep, D);
 323     }
 324     for (unsigned i = 0, e = ChainSuccs.size(); i != e; ++i) {
 325       SDep D = ChainSuccs[i];
 326       SUnit *SuccDep = D.getSUnit();
 327       D.setSUnit(SU);
 328       RemovePred(SuccDep, D);
 329       if (isNewLoad) {
 330         D.setSUnit(LoadSU);
 331         AddPred(SuccDep, D);
 332       }
 333     }
 334     if (isNewLoad) {
 335       SDep D(LoadSU, SDep::Barrier);
 336       D.setLatency(LoadSU->Latency);
 337       AddPred(NewSU, D);
 338     }
 339
 340     ++NumUnfolds;
 341
 342     if (NewSU->NumSuccsLeft == 0) {
 343       NewSU->isAvailable = true;
 344       return NewSU;
 345     }
 346     SU = NewSU;
 347   }
 348
 349   LLVM_DEBUG(dbgs() << "Duplicating SU # " << SU->NodeNum << "\n");
 350   NewSU = Clone(SU);
 351
 352   // New SUnit has the exact same predecessors.
 353   for (SDep &Pred : SU->Preds)
 354     if (!Pred.isArtificial())
 355       AddPred(NewSU, Pred);
 356
 357   // Only copy scheduled successors. Cut them from old node's successor
 358   // list and move them over.
 359   SmallVector<std::pair<SUnit *, SDep>, 4> DelDeps;
 360   for (SDep &Succ : SU->Succs) {
 361     if (Succ.isArtificial())
 362       continue;
 363     SUnit *SuccSU = Succ.getSUnit();
 364     if (SuccSU->isScheduled) {
 365       SDep D = Succ;
 366       D.setSUnit(NewSU);
 367       AddPred(SuccSU, D);
 368       D.setSUnit(SU);
 369       DelDeps.push_back(std::make_pair(SuccSU, D));
 370     }
 371   }
 372   for (unsigned i = 0, e = DelDeps.size(); i != e; ++i)
 373     RemovePred(DelDeps[i].first, DelDeps[i].second);
 374
 375   ++NumDups;
 376   return NewSU;
 377 }
 378
 379 /// InsertCopiesAndMoveSuccs - Insert register copies and move all
 380 /// scheduled successors of the given SUnit to the last copy.
 381 void ScheduleDAGFast::InsertCopiesAndMoveSuccs(SUnit *SU, unsigned Reg,
 382                                               const TargetRegisterClass *DestRC,
 383                                               const TargetRegisterClass *SrcRC,
 384                                               SmallVectorImpl<SUnit*> &Copies) {
 385   SUnit *CopyFromSU = newSUnit(static_cast<SDNode *>(nullptr));
 386   CopyFromSU->CopySrcRC = SrcRC;
 387   CopyFromSU->CopyDstRC = DestRC;
 388
 389   SUnit *CopyToSU = newSUnit(static_cast<SDNode *>(nullptr));
 390   CopyToSU->CopySrcRC = DestRC;
 391   CopyToSU->CopyDstRC = SrcRC;
 392
 393   // Only copy scheduled successors. Cut them from old node's successor
 394   // list and move them over.
 395   SmallVector<std::pair<SUnit *, SDep>, 4> DelDeps;
 396   for (SDep &Succ : SU->Succs) {
 397     if (Succ.isArtificial())
 398       continue;
 399     SUnit *SuccSU = Succ.getSUnit();
 400     if (SuccSU->isScheduled) {
 401       SDep D = Succ;
 402       D.setSUnit(CopyToSU);
 403       AddPred(SuccSU, D);
 404       DelDeps.push_back(std::make_pair(SuccSU, Succ));
 405     }
 406   }
 407   for (unsigned i = 0, e = DelDeps.size(); i != e; ++i) {
 408     RemovePred(DelDeps[i].first, DelDeps[i].second);
 409   }
 410   SDep FromDep(SU, SDep::Data, Reg);
 411   FromDep.setLatency(SU->Latency);
 412   AddPred(CopyFromSU, FromDep);
 413   SDep ToDep(CopyFromSU, SDep::Data, 0);
 414   ToDep.setLatency(CopyFromSU->Latency);
 415   AddPred(CopyToSU, ToDep);
 416
 417   Copies.push_back(CopyFromSU);
 418   Copies.push_back(CopyToSU);
 419
 420   ++NumPRCopies;
 421 }
 422
 423 /// getPhysicalRegisterVT - Returns the ValueType of the physical register
 424 /// definition of the specified node.
 425 /// FIXME: Move to SelectionDAG?
 426 static MVT getPhysicalRegisterVT(SDNode *N, unsigned Reg,
 427                                  const TargetInstrInfo *TII) {
 428   unsigned NumRes;
 429   if (N->getOpcode() == ISD::CopyFromReg) {
 430     // CopyFromReg has: "chain, Val, glue" so operand 1 gives the type.
 431     NumRes = 1;
 432   } else {
 433     const MCInstrDesc &MCID = TII->get(N->getMachineOpcode());
 434     assert(MCID.ImplicitDefs && "Physical reg def must be in implicit def list!");
 435     NumRes = MCID.getNumDefs();
 436     for (const MCPhysReg *ImpDef = MCID.getImplicitDefs(); *ImpDef; ++ImpDef) {
 437       if (Reg == *ImpDef)
 438         break;
 439       ++NumRes;
 440     }
 441   }
 442   return N->getSimpleValueType(NumRes);
 443 }
 444
 445 /// CheckForLiveRegDef - Return true and update live register vector if the
 446 /// specified register def of the specified SUnit clobbers any "live" registers.
 447 static bool CheckForLiveRegDef(SUnit *SU, unsigned Reg,
 448                                std::vector<SUnit*> &LiveRegDefs,
 449                                SmallSet<unsigned, 4> &RegAdded,
 450                                SmallVectorImpl<unsigned> &LRegs,
 451                                const TargetRegisterInfo *TRI) {
 452   bool Added = false;
 453   for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) {
 454     if (LiveRegDefs[*AI] && LiveRegDefs[*AI] != SU) {
 455       if (RegAdded.insert(*AI).second) {
 456         LRegs.push_back(*AI);
 457         Added = true;
 458       }
 459     }
 460   }
 461   return Added;
 462 }
 463
 464 /// DelayForLiveRegsBottomUp - Returns true if it is necessary to delay
 465 /// scheduling of the given node to satisfy live physical register dependencies.
 466 /// If the specific node is the last one that's available to schedule, do
 467 /// whatever is necessary (i.e. backtracking or cloning) to make it possible.
 468 bool ScheduleDAGFast::DelayForLiveRegsBottomUp(SUnit *SU,
 469                                               SmallVectorImpl<unsigned> &LRegs){
 470   if (NumLiveRegs == 0)
 471     return false;
 472
 473   SmallSet<unsigned, 4> RegAdded;
 474   // If this node would clobber any "live" register, then it's not ready.
 475   for (SDep &Pred : SU->Preds) {
 476     if (Pred.isAssignedRegDep()) {
 477       CheckForLiveRegDef(Pred.getSUnit(), Pred.getReg(), LiveRegDefs,
 478                          RegAdded, LRegs, TRI);
 479     }
 480   }
 481
 482   for (SDNode *Node = SU->getNode(); Node; Node = Node->getGluedNode()) {
 483     if (Node->getOpcode() == ISD::INLINEASM) {
 484       // Inline asm can clobber physical defs.
 485       unsigned NumOps = Node->getNumOperands();
 486       if (Node->getOperand(NumOps-1).getValueType() == MVT::Glue)
 487         --NumOps;  // Ignore the glue operand.
 488
 489       for (unsigned i = InlineAsm::Op_FirstOperand; i != NumOps;) {
 490         unsigned Flags =
 491           cast<ConstantSDNode>(Node->getOperand(i))->getZExtValue();
 492         unsigned NumVals = InlineAsm::getNumOperandRegisters(Flags);
 493
 494         ++i; // Skip the ID value.
 495         if (InlineAsm::isRegDefKind(Flags) ||
 496             InlineAsm::isRegDefEarlyClobberKind(Flags) ||
 497             InlineAsm::isClobberKind(Flags)) {
 498           // Check for def of register or earlyclobber register.
 499           for (; NumVals; --NumVals, ++i) {
 500             unsigned Reg = cast<RegisterSDNode>(Node->getOperand(i))->getReg();
 501             if (TargetRegisterInfo::isPhysicalRegister(Reg))
 502               CheckForLiveRegDef(SU, Reg, LiveRegDefs, RegAdded, LRegs, TRI);
 503           }
 504         } else
 505           i += NumVals;
 506       }
 507       continue;
 508     }
 509     if (!Node->isMachineOpcode())
 510       continue;
 511     const MCInstrDesc &MCID = TII->get(Node->getMachineOpcode());
 512     if (!MCID.ImplicitDefs)
 513       continue;
 514     for (const MCPhysReg *Reg = MCID.getImplicitDefs(); *Reg; ++Reg) {
 515       CheckForLiveRegDef(SU, *Reg, LiveRegDefs, RegAdded, LRegs, TRI);
 516     }
 517   }
 518   return !LRegs.empty();
 519 }
 520
 521
 522 /// ListScheduleBottomUp - The main loop of list scheduling for bottom-up
 523 /// schedulers.
 524 void ScheduleDAGFast::ListScheduleBottomUp() {
 525   unsigned CurCycle = 0;
 526
 527   // Release any predecessors of the special Exit node.
 528   ReleasePredecessors(&ExitSU, CurCycle);
 529
 530   // Add root to Available queue.
 531   if (!SUnits.empty()) {
 532     SUnit *RootSU = &SUnits[DAG->getRoot().getNode()->getNodeId()];
 533     assert(RootSU->Succs.empty() && "Graph root shouldn't have successors!");
 534     RootSU->isAvailable = true;
 535     AvailableQueue.push(RootSU);
 536   }
 537
 538   // While Available queue is not empty, grab the node with the highest
 539   // priority. If it is not ready put it back.  Schedule the node.
 540   SmallVector<SUnit*, 4> NotReady;
 541   DenseMap<SUnit*, SmallVector<unsigned, 4> > LRegsMap;
 542   Sequence.reserve(SUnits.size());
 543   while (!AvailableQueue.empty()) {
 544     bool Delayed = false;
 545     LRegsMap.clear();
 546     SUnit *CurSU = AvailableQueue.pop();
 547     while (CurSU) {
 548       SmallVector<unsigned, 4> LRegs;
 549       if (!DelayForLiveRegsBottomUp(CurSU, LRegs))
 550         break;
 551       Delayed = true;
 552       LRegsMap.insert(std::make_pair(CurSU, LRegs));
 553
 554       CurSU->isPending = true;  // This SU is not in AvailableQueue right now.
 555       NotReady.push_back(CurSU);
 556       CurSU = AvailableQueue.pop();
 557     }
 558
 559     // All candidates are delayed due to live physical reg dependencies.
 560     // Try code duplication or inserting cross class copies
 561     // to resolve it.
 562     if (Delayed && !CurSU) {
 563       if (!CurSU) {
 564         // Try duplicating the nodes that produces these
 565         // "expensive to copy" values to break the dependency. In case even
 566         // that doesn't work, insert cross class copies.
 567         SUnit *TrySU = NotReady[0];
 568         SmallVectorImpl<unsigned> &LRegs = LRegsMap[TrySU];
 569         assert(LRegs.size() == 1 && "Can't handle this yet!");
 570         unsigned Reg = LRegs[0];
 571         SUnit *LRDef = LiveRegDefs[Reg];
 572         MVT VT = getPhysicalRegisterVT(LRDef->getNode(), Reg, TII);
 573         const TargetRegisterClass *RC =
 574           TRI->getMinimalPhysRegClass(Reg, VT);
 575         const TargetRegisterClass *DestRC = TRI->getCrossCopyRegClass(RC);
 576
 577         // If cross copy register class is the same as RC, then it must be
 578         // possible copy the value directly. Do not try duplicate the def.
 579         // If cross copy register class is not the same as RC, then it's
 580         // possible to copy the value but it require cross register class copies
 581         // and it is expensive.
 582         // If cross copy register class is null, then it's not possible to copy
 583         // the value at all.
 584         SUnit *NewDef = nullptr;
 585         if (DestRC != RC) {
 586           NewDef = CopyAndMoveSuccessors(LRDef);
 587           if (!DestRC && !NewDef)
 588             report_fatal_error("Can't handle live physical "
 589                                "register dependency!");
 590         }
 591         if (!NewDef) {
 592           // Issue copies, these can be expensive cross register class copies.
 593           SmallVector<SUnit*, 2> Copies;
 594           InsertCopiesAndMoveSuccs(LRDef, Reg, DestRC, RC, Copies);
 595           LLVM_DEBUG(dbgs() << "Adding an edge from SU # " << TrySU->NodeNum
 596                             << " to SU #" << Copies.front()->NodeNum << "\n");
 597           AddPred(TrySU, SDep(Copies.front(), SDep::Artificial));
 598           NewDef = Copies.back();
 599         }
 600
 601         LLVM_DEBUG(dbgs() << "Adding an edge from SU # " << NewDef->NodeNum
 602                           << " to SU #" << TrySU->NodeNum << "\n");
 603         LiveRegDefs[Reg] = NewDef;
 604         AddPred(NewDef, SDep(TrySU, SDep::Artificial));
 605         TrySU->isAvailable = false;
 606         CurSU = NewDef;
 607       }
 608
 609       if (!CurSU) {
 610         llvm_unreachable("Unable to resolve live physical register dependencies!");
 611       }
 612     }
 613
 614     // Add the nodes that aren't ready back onto the available list.
 615     for (unsigned i = 0, e = NotReady.size(); i != e; ++i) {
 616       NotReady[i]->isPending = false;
 617       // May no longer be available due to backtracking.
 618       if (NotReady[i]->isAvailable)
 619         AvailableQueue.push(NotReady[i]);
 620     }
 621     NotReady.clear();
 622
 623     if (CurSU)
 624       ScheduleNodeBottomUp(CurSU, CurCycle);
 625     ++CurCycle;
 626   }
 627
 628   // Reverse the order since it is bottom up.
 629   std::reverse(Sequence.begin(), Sequence.end());
 630
 631 #ifndef NDEBUG
 632   VerifyScheduledSequence(/*isBottomUp=*/true);
 633 #endif
 634 }
 635
 636
 637 namespace {
 638 //===----------------------------------------------------------------------===//
 639 // ScheduleDAGLinearize - No scheduling scheduler, it simply linearize the
 640 // DAG in topological order.
 641 // IMPORTANT: this may not work for targets with phyreg dependency.
 642 //
 643 class ScheduleDAGLinearize : public ScheduleDAGSDNodes {
 644 public:
 645   ScheduleDAGLinearize(MachineFunction &mf) : ScheduleDAGSDNodes(mf) {}
 646
 647   void Schedule() override;
 648
 649   MachineBasicBlock *
 650     EmitSchedule(MachineBasicBlock::iterator &InsertPos) override;
 651
 652 private:
 653   std::vector<SDNode*> Sequence;
 654   DenseMap<SDNode*, SDNode*> GluedMap;  // Cache glue to its user
 655
 656   void ScheduleNode(SDNode *N);
 657 };
 658 } // end anonymous namespace
 659
 660 void ScheduleDAGLinearize::ScheduleNode(SDNode *N) {
 661   if (N->getNodeId() != 0)
 662     llvm_unreachable(nullptr);
 663
 664   if (!N->isMachineOpcode() &&
 665       (N->getOpcode() == ISD::EntryToken || isPassiveNode(N)))
 666     // These nodes do not need to be translated into MIs.
 667     return;
 668
 669   LLVM_DEBUG(dbgs() << "\n*** Scheduling: ");
 670   LLVM_DEBUG(N->dump(DAG));
 671   Sequence.push_back(N);
 672
 673   unsigned NumOps = N->getNumOperands();
 674   if (unsigned NumLeft = NumOps) {
 675     SDNode *GluedOpN = nullptr;
 676     do {
 677       const SDValue &Op = N->getOperand(NumLeft-1);
 678       SDNode *OpN = Op.getNode();
 679
 680       if (NumLeft == NumOps && Op.getValueType() == MVT::Glue) {
 681         // Schedule glue operand right above N.
 682         GluedOpN = OpN;
 683         assert(OpN->getNodeId() != 0 && "Glue operand not ready?");
 684         OpN->setNodeId(0);
 685         ScheduleNode(OpN);
 686         continue;
 687       }
 688
 689       if (OpN == GluedOpN)
 690         // Glue operand is already scheduled.
 691         continue;
 692
 693       DenseMap<SDNode*, SDNode*>::iterator DI = GluedMap.find(OpN);
 694       if (DI != GluedMap.end() && DI->second != N)
 695         // Users of glues are counted against the glued users.
 696         OpN = DI->second;
 697
 698       unsigned Degree = OpN->getNodeId();
 699       assert(Degree > 0 && "Predecessor over-released!");
 700       OpN->setNodeId(--Degree);
 701       if (Degree == 0)
 702         ScheduleNode(OpN);
 703     } while (--NumLeft);
 704   }
 705 }
 706
 707 /// findGluedUser - Find the representative use of a glue value by walking
 708 /// the use chain.
 709 static SDNode *findGluedUser(SDNode *N) {
 710   while (SDNode *Glued = N->getGluedUser())
 711     N = Glued;
 712   return N;
 713 }
 714
 715 void ScheduleDAGLinearize::Schedule() {
 716   LLVM_DEBUG(dbgs() << "********** DAG Linearization **********\n");
 717
 718   SmallVector<SDNode*, 8> Glues;
 719   unsigned DAGSize = 0;
 720   for (SDNode &Node : DAG->allnodes()) {
 721     SDNode *N = &Node;
 722
 723     // Use node id to record degree.
 724     unsigned Degree = N->use_size();
 725     N->setNodeId(Degree);
 726     unsigned NumVals = N->getNumValues();
 727     if (NumVals && N->getValueType(NumVals-1) == MVT::Glue &&
 728         N->hasAnyUseOfValue(NumVals-1)) {
 729       SDNode *User = findGluedUser(N);
 730       if (User) {
 731         Glues.push_back(N);
 732         GluedMap.insert(std::make_pair(N, User));
 733       }
 734     }
 735
 736     if (N->isMachineOpcode() ||
 737         (N->getOpcode() != ISD::EntryToken && !isPassiveNode(N)))
 738       ++DAGSize;
 739   }
 740
 741   for (unsigned i = 0, e = Glues.size(); i != e; ++i) {
 742     SDNode *Glue = Glues[i];
 743     SDNode *GUser = GluedMap[Glue];
 744     unsigned Degree = Glue->getNodeId();
 745     unsigned UDegree = GUser->getNodeId();
 746
 747     // Glue user must be scheduled together with the glue operand. So other
 748     // users of the glue operand must be treated as its users.
 749     SDNode *ImmGUser = Glue->getGluedUser();
 750     for (const SDNode *U : Glue->uses())
 751       if (U == ImmGUser)
 752         --Degree;
 753     GUser->setNodeId(UDegree + Degree);
 754     Glue->setNodeId(1);
 755   }
 756
 757   Sequence.reserve(DAGSize);
 758   ScheduleNode(DAG->getRoot().getNode());
 759 }
 760
 761 MachineBasicBlock*
 762 ScheduleDAGLinearize::EmitSchedule(MachineBasicBlock::iterator &InsertPos) {
 763   InstrEmitter Emitter(BB, InsertPos);
 764   DenseMap<SDValue, unsigned> VRBaseMap;
 765
 766   LLVM_DEBUG({ dbgs() << "\n*** Final schedule ***\n"; });
 767
 768   unsigned NumNodes = Sequence.size();
 769   MachineBasicBlock *BB = Emitter.getBlock();
 770   for (unsigned i = 0; i != NumNodes; ++i) {
 771     SDNode *N = Sequence[NumNodes-i-1];
 772     LLVM_DEBUG(N->dump(DAG));
 773     Emitter.EmitNode(N, false, false, VRBaseMap);
 774
 775     // Emit any debug values associated with the node.
 776     if (N->getHasDebugValue()) {
 777       MachineBasicBlock::iterator InsertPos = Emitter.getInsertPos();
 778       for (auto DV : DAG->GetDbgValues(N)) {
 779         if (DV->isInvalidated())
 780           continue;
 781         if (auto *DbgMI = Emitter.EmitDbgValue(DV, VRBaseMap))
 782           BB->insert(InsertPos, DbgMI);
 783         DV->setIsInvalidated();
 784       }
 785     }
 786   }
 787
 788   LLVM_DEBUG(dbgs() << '\n');
 789
 790   InsertPos = Emitter.getInsertPos();
 791   return Emitter.getBlock();
 792 }
 793
 794 //===----------------------------------------------------------------------===//
 795 //                         Public Constructor Functions
 796 //===----------------------------------------------------------------------===//
 797
 798 llvm::ScheduleDAGSDNodes *
 799 llvm::createFastDAGScheduler(SelectionDAGISel *IS, CodeGenOpt::Level) {
 800   return new ScheduleDAGFast(*IS->MF);
 801 }
 802
 803 llvm::ScheduleDAGSDNodes *
 804 llvm::createDAGLinearizer(SelectionDAGISel *IS, CodeGenOpt::Level) {
 805   return new ScheduleDAGLinearize(*IS->MF);
 806 }