Add a new "fast" scheduler. This is currently basically just a

copy of the BURRList scheduler, but with several parts ripped
out, such as backtracking, online topological sort maintenance
(needed by backtracking), the priority queue, and Sethi-Ullman
number computation and maintenance (needed by the priority
queue). As a result of all this, it generates somewhat lower
quality code, but that's its tradeoff for running about 30%
faster than list-burr in -fast mode in many cases.

This is somewhat experimental. Moving forward, major pieces of
this can be refactored with pieces in common with
ScheduleDAGRRList.cpp.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@56307 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/LinkAllCodegenComponents.h

@@ -44,6 +44,7 @@ namespace {
       (void) llvm::createBURRListDAGScheduler(NULL, NULL, NULL, false);
       (void) llvm::createTDRRListDAGScheduler(NULL, NULL, NULL, false);
       (void) llvm::createTDListDAGScheduler(NULL, NULL, NULL, false);
+      (void) llvm::createFastDAGScheduler(NULL, NULL, NULL, false);
       (void) llvm::createDefaultScheduler(NULL, NULL, NULL, false);
 
     }

include/llvm/CodeGen/ScheduleDAG.h

@@ -414,6 +414,13 @@ namespace llvm {
                                         MachineBasicBlock *BB,
                                         bool Fast);
                                         
+  /// createFastDAGScheduler - This creates a "fast" scheduler.
+  ///
+  ScheduleDAG *createFastDAGScheduler(SelectionDAGISel *IS,
+                                      SelectionDAG *DAG,
+                                      MachineBasicBlock *BB,
+                                      bool Fast);
+
   /// createDefaultScheduler - This creates an instruction scheduler appropriate
   /// for the target.
   ScheduleDAG* createDefaultScheduler(SelectionDAGISel *IS,

lib/CodeGen/SelectionDAG/ScheduleDAGFast.cpp

@@ -0,0 +1,654 @@
+//===----- ScheduleDAGFast.cpp - Fast poor list scheduler -----------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This implements a fast scheduler.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "pre-RA-sched"
+#include "llvm/CodeGen/ScheduleDAG.h"
+#include "llvm/CodeGen/SchedulerRegistry.h"
+#include "llvm/Target/TargetRegisterInfo.h"
+#include "llvm/Target/TargetData.h"
+#include "llvm/Target/TargetMachine.h"
+#include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/ADT/SmallSet.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/Support/CommandLine.h"
+using namespace llvm;
+
+STATISTIC(NumUnfolds,    "Number of nodes unfolded");
+STATISTIC(NumDups,       "Number of duplicated nodes");
+STATISTIC(NumCCCopies,   "Number of cross class copies");
+
+static RegisterScheduler
+  fastDAGScheduler("fast", "  Fast suboptimal list scheduling",
+                   createFastDAGScheduler);
+
+namespace {
+  /// FastPriorityQueue - A degenerate priority queue that considers
+  /// all nodes to have the same priority.
+  ///
+  struct VISIBILITY_HIDDEN FastPriorityQueue {
+    std::vector<SUnit *> Queue;
+
+    bool empty() const { return Queue.empty(); }
+    
+    void push(SUnit *U) {
+      Queue.push_back(U);
+    }
+
+    SUnit *pop() {
+      if (empty()) return NULL;
+      SUnit *V = Queue.back();
+      Queue.pop_back();
+      return V;
+    }
+  };
+
+//===----------------------------------------------------------------------===//
+/// ScheduleDAGFast - The actual "fast" list scheduler implementation.
+///
+class VISIBILITY_HIDDEN ScheduleDAGFast : public ScheduleDAG {
+private:
+  /// AvailableQueue - The priority queue to use for the available SUnits.
+  FastPriorityQueue AvailableQueue;
+
+  /// LiveRegs / LiveRegDefs - A set of physical registers and their definition
+  /// that are "live". These nodes must be scheduled before any other nodes that
+  /// modifies the registers can be scheduled.
+  SmallSet<unsigned, 4> LiveRegs;
+  std::vector<SUnit*> LiveRegDefs;
+  std::vector<unsigned> LiveRegCycles;
+
+public:
+  ScheduleDAGFast(SelectionDAG &dag, MachineBasicBlock *bb,
+                  const TargetMachine &tm)
+    : ScheduleDAG(dag, bb, tm) {}
+
+  void Schedule();
+
+  /// AddPred - This adds the specified node X as a predecessor of 
+  /// the current node Y if not already.
+  /// This returns true if this is a new predecessor.
+  bool AddPred(SUnit *Y, SUnit *X, bool isCtrl, bool isSpecial,
+               unsigned PhyReg = 0, int Cost = 1);
+
+  /// RemovePred - This removes the specified node N from the predecessors of 
+  /// the current node M.
+  bool RemovePred(SUnit *M, SUnit *N, bool isCtrl, bool isSpecial);
+
+private:
+  void ReleasePred(SUnit*, bool, unsigned);
+  void ScheduleNodeBottomUp(SUnit*, unsigned);
+  SUnit *CopyAndMoveSuccessors(SUnit*);
+  void InsertCCCopiesAndMoveSuccs(SUnit*, unsigned,
+                                  const TargetRegisterClass*,
+                                  const TargetRegisterClass*,
+                                  SmallVector<SUnit*, 2>&);
+  bool DelayForLiveRegsBottomUp(SUnit*, SmallVector<unsigned, 4>&);
+  void ListScheduleBottomUp();
+
+  /// CreateNewSUnit - Creates a new SUnit and returns a pointer to it.
+  SUnit *CreateNewSUnit(SDNode *N) {
+    SUnit *NewNode = NewSUnit(N);
+    return NewNode;
+  }
+
+  /// CreateClone - Creates a new SUnit from an existing one.
+  SUnit *CreateClone(SUnit *N) {
+    SUnit *NewNode = Clone(N);
+    return NewNode;
+  }
+};
+}  // end anonymous namespace
+
+
+/// Schedule - Schedule the DAG using list scheduling.
+void ScheduleDAGFast::Schedule() {
+  DOUT << "********** List Scheduling **********\n";
+
+  LiveRegDefs.resize(TRI->getNumRegs(), NULL);  
+  LiveRegCycles.resize(TRI->getNumRegs(), 0);
+
+  // Build scheduling units.
+  BuildSchedUnits();
+
+  DEBUG(for (unsigned su = 0, e = SUnits.size(); su != e; ++su)
+          SUnits[su].dumpAll(&DAG));
+
+  // Execute the actual scheduling loop.
+  ListScheduleBottomUp();
+}
+
+//===----------------------------------------------------------------------===//
+//  Bottom-Up Scheduling
+//===----------------------------------------------------------------------===//
+
+/// ReleasePred - Decrement the NumSuccsLeft count of a predecessor. Add it to
+/// the AvailableQueue if the count reaches zero. Also update its cycle bound.
+void ScheduleDAGFast::ReleasePred(SUnit *PredSU, bool isChain, 
+                                  unsigned CurCycle) {
+  // FIXME: the distance between two nodes is not always == the predecessor's
+  // latency. For example, the reader can very well read the register written
+  // by the predecessor later than the issue cycle. It also depends on the
+  // interrupt model (drain vs. freeze).
+  PredSU->CycleBound = std::max(PredSU->CycleBound, CurCycle + PredSU->Latency);
+
+  --PredSU->NumSuccsLeft;
+  
+#ifndef NDEBUG
+  if (PredSU->NumSuccsLeft < 0) {
+    cerr << "*** List scheduling failed! ***\n";
+    PredSU->dump(&DAG);
+    cerr << " has been released too many times!\n";
+    assert(0);
+  }
+#endif
+  
+  if (PredSU->NumSuccsLeft == 0) {
+    PredSU->isAvailable = true;
+    AvailableQueue.push(PredSU);
+  }
+}
+
+/// ScheduleNodeBottomUp - Add the node to the schedule. Decrement the pending
+/// count of its predecessors. If a predecessor pending count is zero, add it to
+/// the Available queue.
+void ScheduleDAGFast::ScheduleNodeBottomUp(SUnit *SU, unsigned CurCycle) {
+  DOUT << "*** Scheduling [" << CurCycle << "]: ";
+  DEBUG(SU->dump(&DAG));
+  SU->Cycle = CurCycle;
+
+  // Bottom up: release predecessors
+  for (SUnit::pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
+       I != E; ++I) {
+    ReleasePred(I->Dep, I->isCtrl, CurCycle);
+    if (I->Cost < 0)  {
+      // This is a physical register dependency and it's impossible or
+      // expensive to copy the register. Make sure nothing that can 
+      // clobber the register is scheduled between the predecessor and
+      // this node.
+      if (LiveRegs.insert(I->Reg)) {
+        LiveRegDefs[I->Reg] = I->Dep;
+        LiveRegCycles[I->Reg] = CurCycle;
+      }
+    }
+  }
+
+  // Release all the implicit physical register defs that are live.
+  for (SUnit::succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
+       I != E; ++I) {
+    if (I->Cost < 0)  {
+      if (LiveRegCycles[I->Reg] == I->Dep->Cycle) {
+        LiveRegs.erase(I->Reg);
+        assert(LiveRegDefs[I->Reg] == SU &&
+               "Physical register dependency violated?");
+        LiveRegDefs[I->Reg] = NULL;
+        LiveRegCycles[I->Reg] = 0;
+      }
+    }
+  }
+
+  SU->isScheduled = true;
+}
+
+/// AddPred - adds an edge from SUnit X to SUnit Y.
+bool ScheduleDAGFast::AddPred(SUnit *Y, SUnit *X, bool isCtrl, bool isSpecial,
+                              unsigned PhyReg, int Cost) {
+  return Y->addPred(X, isCtrl, isSpecial, PhyReg, Cost);
+}
+
+/// RemovePred - This removes the specified node N from the predecessors of 
+/// the current node M.
+bool ScheduleDAGFast::RemovePred(SUnit *M, SUnit *N, 
+                                 bool isCtrl, bool isSpecial) {
+  return M->removePred(N, isCtrl, isSpecial);
+}
+
+/// CopyAndMoveSuccessors - Clone the specified node and move its scheduled
+/// successors to the newly created node.
+SUnit *ScheduleDAGFast::CopyAndMoveSuccessors(SUnit *SU) {
+  if (SU->FlaggedNodes.size())
+    return NULL;
+
+  SDNode *N = SU->Node;
+  if (!N)
+    return NULL;
+
+  SUnit *NewSU;
+  bool TryUnfold = false;
+  for (unsigned i = 0, e = N->getNumValues(); i != e; ++i) {
+    MVT VT = N->getValueType(i);
+    if (VT == MVT::Flag)
+      return NULL;
+    else if (VT == MVT::Other)
+      TryUnfold = true;
+  }
+  for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i) {
+    const SDValue &Op = N->getOperand(i);
+    MVT VT = Op.getNode()->getValueType(Op.getResNo());
+    if (VT == MVT::Flag)
+      return NULL;
+  }
+
+  if (TryUnfold) {
+    SmallVector<SDNode*, 2> NewNodes;
+    if (!TII->unfoldMemoryOperand(DAG, N, NewNodes))
+      return NULL;
+
+    DOUT << "Unfolding SU # " << SU->NodeNum << "\n";
+    assert(NewNodes.size() == 2 && "Expected a load folding node!");
+
+    N = NewNodes[1];
+    SDNode *LoadNode = NewNodes[0];
+    unsigned NumVals = N->getNumValues();
+    unsigned OldNumVals = SU->Node->getNumValues();
+    for (unsigned i = 0; i != NumVals; ++i)
+      DAG.ReplaceAllUsesOfValueWith(SDValue(SU->Node, i), SDValue(N, i));
+    DAG.ReplaceAllUsesOfValueWith(SDValue(SU->Node, OldNumVals-1),
+                                  SDValue(LoadNode, 1));
+
+    SUnit *NewSU = CreateNewSUnit(N);
+    assert(N->getNodeId() == -1 && "Node already inserted!");
+    N->setNodeId(NewSU->NodeNum);
+      
+    const TargetInstrDesc &TID = TII->get(N->getMachineOpcode());
+    for (unsigned i = 0; i != TID.getNumOperands(); ++i) {
+      if (TID.getOperandConstraint(i, TOI::TIED_TO) != -1) {
+        NewSU->isTwoAddress = true;
+        break;
+      }
+    }
+    if (TID.isCommutable())
+      NewSU->isCommutable = true;
+    // FIXME: Calculate height / depth and propagate the changes?
+    NewSU->Depth = SU->Depth;
+    NewSU->Height = SU->Height;
+    ComputeLatency(NewSU);
+
+    // LoadNode may already exist. This can happen when there is another
+    // load from the same location and producing the same type of value
+    // but it has different alignment or volatileness.
+    bool isNewLoad = true;
+    SUnit *LoadSU;
+    if (LoadNode->getNodeId() != -1) {
+      LoadSU = &SUnits[LoadNode->getNodeId()];
+      isNewLoad = false;
+    } else {
+      LoadSU = CreateNewSUnit(LoadNode);
+      LoadNode->setNodeId(LoadSU->NodeNum);
+
+      LoadSU->Depth = SU->Depth;
+      LoadSU->Height = SU->Height;
+      ComputeLatency(LoadSU);
+    }
+
+    SUnit *ChainPred = NULL;
+    SmallVector<SDep, 4> ChainSuccs;
+    SmallVector<SDep, 4> LoadPreds;
+    SmallVector<SDep, 4> NodePreds;
+    SmallVector<SDep, 4> NodeSuccs;
+    for (SUnit::pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
+         I != E; ++I) {
+      if (I->isCtrl)
+        ChainPred = I->Dep;
+      else if (I->Dep->Node && I->Dep->Node->isOperandOf(LoadNode))
+        LoadPreds.push_back(SDep(I->Dep, I->Reg, I->Cost, false, false));
+      else
+        NodePreds.push_back(SDep(I->Dep, I->Reg, I->Cost, false, false));
+    }
+    for (SUnit::succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
+         I != E; ++I) {
+      if (I->isCtrl)
+        ChainSuccs.push_back(SDep(I->Dep, I->Reg, I->Cost,
+                                  I->isCtrl, I->isSpecial));
+      else
+        NodeSuccs.push_back(SDep(I->Dep, I->Reg, I->Cost,
+                                 I->isCtrl, I->isSpecial));
+    }
+
+    if (ChainPred) {
+      RemovePred(SU, ChainPred, true, false);
+      if (isNewLoad)
+        AddPred(LoadSU, ChainPred, true, false);
+    }
+    for (unsigned i = 0, e = LoadPreds.size(); i != e; ++i) {
+      SDep *Pred = &LoadPreds[i];
+      RemovePred(SU, Pred->Dep, Pred->isCtrl, Pred->isSpecial);
+      if (isNewLoad) {
+        AddPred(LoadSU, Pred->Dep, Pred->isCtrl, Pred->isSpecial,
+                Pred->Reg, Pred->Cost);
+      }
+    }
+    for (unsigned i = 0, e = NodePreds.size(); i != e; ++i) {
+      SDep *Pred = &NodePreds[i];
+      RemovePred(SU, Pred->Dep, Pred->isCtrl, Pred->isSpecial);
+      AddPred(NewSU, Pred->Dep, Pred->isCtrl, Pred->isSpecial,
+              Pred->Reg, Pred->Cost);
+    }
+    for (unsigned i = 0, e = NodeSuccs.size(); i != e; ++i) {
+      SDep *Succ = &NodeSuccs[i];
+      RemovePred(Succ->Dep, SU, Succ->isCtrl, Succ->isSpecial);
+      AddPred(Succ->Dep, NewSU, Succ->isCtrl, Succ->isSpecial,
+              Succ->Reg, Succ->Cost);
+    }
+    for (unsigned i = 0, e = ChainSuccs.size(); i != e; ++i) {
+      SDep *Succ = &ChainSuccs[i];
+      RemovePred(Succ->Dep, SU, Succ->isCtrl, Succ->isSpecial);
+      if (isNewLoad) {
+        AddPred(Succ->Dep, LoadSU, Succ->isCtrl, Succ->isSpecial,
+                Succ->Reg, Succ->Cost);
+      }
+    } 
+    if (isNewLoad) {
+      AddPred(NewSU, LoadSU, false, false);
+    }
+
+    ++NumUnfolds;
+
+    if (NewSU->NumSuccsLeft == 0) {
+      NewSU->isAvailable = true;
+      return NewSU;
+    }
+    SU = NewSU;
+  }
+
+  DOUT << "Duplicating SU # " << SU->NodeNum << "\n";
+  NewSU = CreateClone(SU);
+
+  // New SUnit has the exact same predecessors.
+  for (SUnit::pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
+       I != E; ++I)
+    if (!I->isSpecial) {
+      AddPred(NewSU, I->Dep, I->isCtrl, false, I->Reg, I->Cost);
+      NewSU->Depth = std::max(NewSU->Depth, I->Dep->Depth+1);
+    }
+
+  // Only copy scheduled successors. Cut them from old node's successor
+  // list and move them over.
+  SmallVector<std::pair<SUnit*, bool>, 4> DelDeps;
+  for (SUnit::succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
+       I != E; ++I) {
+    if (I->isSpecial)
+      continue;
+    if (I->Dep->isScheduled) {
+      NewSU->Height = std::max(NewSU->Height, I->Dep->Height+1);
+      AddPred(I->Dep, NewSU, I->isCtrl, false, I->Reg, I->Cost);
+      DelDeps.push_back(std::make_pair(I->Dep, I->isCtrl));
+    }
+  }
+  for (unsigned i = 0, e = DelDeps.size(); i != e; ++i) {
+    SUnit *Succ = DelDeps[i].first;
+    bool isCtrl = DelDeps[i].second;
+    RemovePred(Succ, SU, isCtrl, false);
+  }
+
+  ++NumDups;
+  return NewSU;
+}
+
+/// InsertCCCopiesAndMoveSuccs - Insert expensive cross register class copies
+/// and move all scheduled successors of the given SUnit to the last copy.
+void ScheduleDAGFast::InsertCCCopiesAndMoveSuccs(SUnit *SU, unsigned Reg,
+                                              const TargetRegisterClass *DestRC,
+                                              const TargetRegisterClass *SrcRC,
+                                               SmallVector<SUnit*, 2> &Copies) {
+  SUnit *CopyFromSU = CreateNewSUnit(NULL);
+  CopyFromSU->CopySrcRC = SrcRC;
+  CopyFromSU->CopyDstRC = DestRC;
+
+  SUnit *CopyToSU = CreateNewSUnit(NULL);
+  CopyToSU->CopySrcRC = DestRC;
+  CopyToSU->CopyDstRC = SrcRC;
+
+  // Only copy scheduled successors. Cut them from old node's successor
+  // list and move them over.
+  SmallVector<std::pair<SUnit*, bool>, 4> DelDeps;
+  for (SUnit::succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
+       I != E; ++I) {
+    if (I->isSpecial)
+      continue;
+    if (I->Dep->isScheduled) {
+      AddPred(I->Dep, CopyToSU, I->isCtrl, false, I->Reg, I->Cost);
+      DelDeps.push_back(std::make_pair(I->Dep, I->isCtrl));
+    }
+  }
+  for (unsigned i = 0, e = DelDeps.size(); i != e; ++i) {
+    SUnit *Succ = DelDeps[i].first;
+    bool isCtrl = DelDeps[i].second;
+    RemovePred(Succ, SU, isCtrl, false);
+  }
+
+  AddPred(CopyFromSU, SU, false, false, Reg, -1);
+  AddPred(CopyToSU, CopyFromSU, false, false, Reg, 1);
+
+  Copies.push_back(CopyFromSU);
+  Copies.push_back(CopyToSU);
+
+  ++NumCCCopies;
+}
+
+/// getPhysicalRegisterVT - Returns the ValueType of the physical register
+/// definition of the specified node.
+/// FIXME: Move to SelectionDAG?
+static MVT getPhysicalRegisterVT(SDNode *N, unsigned Reg,
+                                 const TargetInstrInfo *TII) {
+  const TargetInstrDesc &TID = TII->get(N->getMachineOpcode());
+  assert(TID.ImplicitDefs && "Physical reg def must be in implicit def list!");
+  unsigned NumRes = TID.getNumDefs();
+  for (const unsigned *ImpDef = TID.getImplicitDefs(); *ImpDef; ++ImpDef) {
+    if (Reg == *ImpDef)
+      break;
+    ++NumRes;
+  }
+  return N->getValueType(NumRes);
+}
+
+/// DelayForLiveRegsBottomUp - Returns true if it is necessary to delay
+/// scheduling of the given node to satisfy live physical register dependencies.
+/// If the specific node is the last one that's available to schedule, do
+/// whatever is necessary (i.e. backtracking or cloning) to make it possible.
+bool ScheduleDAGFast::DelayForLiveRegsBottomUp(SUnit *SU,
+                                               SmallVector<unsigned, 4> &LRegs){
+  if (LiveRegs.empty())
+    return false;
+
+  SmallSet<unsigned, 4> RegAdded;
+  // If this node would clobber any "live" register, then it's not ready.
+  for (SUnit::pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
+       I != E; ++I) {
+    if (I->Cost < 0)  {
+      unsigned Reg = I->Reg;
+      if (LiveRegs.count(Reg) && LiveRegDefs[Reg] != I->Dep) {
+        if (RegAdded.insert(Reg))
+          LRegs.push_back(Reg);
+      }
+      for (const unsigned *Alias = TRI->getAliasSet(Reg);
+           *Alias; ++Alias)
+        if (LiveRegs.count(*Alias) && LiveRegDefs[*Alias] != I->Dep) {
+          if (RegAdded.insert(*Alias))
+            LRegs.push_back(*Alias);
+        }
+    }
+  }
+
+  for (unsigned i = 0, e = SU->FlaggedNodes.size()+1; i != e; ++i) {
+    SDNode *Node = (i == 0) ? SU->Node : SU->FlaggedNodes[i-1];
+    if (!Node || !Node->isMachineOpcode())
+      continue;
+    const TargetInstrDesc &TID = TII->get(Node->getMachineOpcode());
+    if (!TID.ImplicitDefs)
+      continue;
+    for (const unsigned *Reg = TID.ImplicitDefs; *Reg; ++Reg) {
+      if (LiveRegs.count(*Reg) && LiveRegDefs[*Reg] != SU) {
+        if (RegAdded.insert(*Reg))
+          LRegs.push_back(*Reg);
+      }
+      for (const unsigned *Alias = TRI->getAliasSet(*Reg);
+           *Alias; ++Alias)
+        if (LiveRegs.count(*Alias) && LiveRegDefs[*Alias] != SU) {
+          if (RegAdded.insert(*Alias))
+            LRegs.push_back(*Alias);
+        }
+    }
+  }
+  return !LRegs.empty();
+}
+
+
+/// ListScheduleBottomUp - The main loop of list scheduling for bottom-up
+/// schedulers.
+void ScheduleDAGFast::ListScheduleBottomUp() {
+  unsigned CurCycle = 0;
+  // Add root to Available queue.
+  if (!SUnits.empty()) {
+    SUnit *RootSU = &SUnits[DAG.getRoot().getNode()->getNodeId()];
+    assert(RootSU->Succs.empty() && "Graph root shouldn't have successors!");
+    RootSU->isAvailable = true;
+    AvailableQueue.push(RootSU);
+  }
+
+  // While Available queue is not empty, grab the node with the highest
+  // priority. If it is not ready put it back.  Schedule the node.
+  SmallVector<SUnit*, 4> NotReady;
+  DenseMap<SUnit*, SmallVector<unsigned, 4> > LRegsMap;
+  Sequence.reserve(SUnits.size());
+  while (!AvailableQueue.empty()) {
+    bool Delayed = false;
+    LRegsMap.clear();
+    SUnit *CurSU = AvailableQueue.pop();
+    while (CurSU) {
+      if (CurSU->CycleBound <= CurCycle) {
+        SmallVector<unsigned, 4> LRegs;
+        if (!DelayForLiveRegsBottomUp(CurSU, LRegs))
+          break;
+        Delayed = true;
+        LRegsMap.insert(std::make_pair(CurSU, LRegs));
+      }
+
+      CurSU->isPending = true;  // This SU is not in AvailableQueue right now.
+      NotReady.push_back(CurSU);
+      CurSU = AvailableQueue.pop();
+    }
+
+    // All candidates are delayed due to live physical reg dependencies.
+    // Try code duplication or inserting cross class copies
+    // to resolve it.
+    if (Delayed && !CurSU) {
+      if (!CurSU) {
+        // Try duplicating the nodes that produces these
+        // "expensive to copy" values to break the dependency. In case even
+        // that doesn't work, insert cross class copies.
+        SUnit *TrySU = NotReady[0];
+        SmallVector<unsigned, 4> &LRegs = LRegsMap[TrySU];
+        assert(LRegs.size() == 1 && "Can't handle this yet!");
+        unsigned Reg = LRegs[0];
+        SUnit *LRDef = LiveRegDefs[Reg];
+        SUnit *NewDef = CopyAndMoveSuccessors(LRDef);
+        if (!NewDef) {
+          // Issue expensive cross register class copies.
+          MVT VT = getPhysicalRegisterVT(LRDef->Node, Reg, TII);
+          const TargetRegisterClass *RC =
+            TRI->getPhysicalRegisterRegClass(Reg, VT);
+          const TargetRegisterClass *DestRC = TRI->getCrossCopyRegClass(RC);
+          if (!DestRC) {
+            assert(false && "Don't know how to copy this physical register!");
+            abort();
+          }
+          SmallVector<SUnit*, 2> Copies;
+          InsertCCCopiesAndMoveSuccs(LRDef, Reg, DestRC, RC, Copies);
+          DOUT << "Adding an edge from SU # " << TrySU->NodeNum
+               << " to SU #" << Copies.front()->NodeNum << "\n";
+          AddPred(TrySU, Copies.front(), true, true);
+          NewDef = Copies.back();
+        }
+
+        DOUT << "Adding an edge from SU # " << NewDef->NodeNum
+             << " to SU #" << TrySU->NodeNum << "\n";
+        LiveRegDefs[Reg] = NewDef;
+        AddPred(NewDef, TrySU, true, true);
+        TrySU->isAvailable = false;
+        CurSU = NewDef;
+      }
+
+      if (!CurSU) {
+        assert(false && "Unable to resolve live physical register dependencies!");
+        abort();
+      }
+    }
+
+    // Add the nodes that aren't ready back onto the available list.
+    for (unsigned i = 0, e = NotReady.size(); i != e; ++i) {
+      NotReady[i]->isPending = false;
+      // May no longer be available due to backtracking.
+      if (NotReady[i]->isAvailable)
+        AvailableQueue.push(NotReady[i]);
+    }
+    NotReady.clear();
+
+    if (!CurSU)
+      Sequence.push_back(0);
+    else {
+      ScheduleNodeBottomUp(CurSU, CurCycle);
+      Sequence.push_back(CurSU);
+    }
+    ++CurCycle;
+  }
+
+  // Reverse the order if it is bottom up.
+  std::reverse(Sequence.begin(), Sequence.end());
+  
+  
+#ifndef NDEBUG
+  // Verify that all SUnits were scheduled.
+  bool AnyNotSched = false;
+  unsigned DeadNodes = 0;
+  unsigned Noops = 0;
+  for (unsigned i = 0, e = SUnits.size(); i != e; ++i) {
+    if (!SUnits[i].isScheduled) {
+      if (SUnits[i].NumPreds == 0 && SUnits[i].NumSuccs == 0) {
+        ++DeadNodes;
+        continue;
+      }
+      if (!AnyNotSched)
+        cerr << "*** List scheduling failed! ***\n";
+      SUnits[i].dump(&DAG);
+      cerr << "has not been scheduled!\n";
+      AnyNotSched = true;
+    }
+    if (SUnits[i].NumSuccsLeft != 0) {
+      if (!AnyNotSched)
+        cerr << "*** List scheduling failed! ***\n";
+      SUnits[i].dump(&DAG);
+      cerr << "has successors left!\n";
+      AnyNotSched = true;
+    }
+  }
+  for (unsigned i = 0, e = Sequence.size(); i != e; ++i)
+    if (!Sequence[i])
+      ++Noops;
+  assert(!AnyNotSched);
+  assert(Sequence.size() + DeadNodes - Noops == SUnits.size() &&
+         "The number of nodes scheduled doesn't match the expected number!");
+#endif
+}
+
+//===----------------------------------------------------------------------===//
+//                         Public Constructor Functions
+//===----------------------------------------------------------------------===//
+
+llvm::ScheduleDAG* llvm::createFastDAGScheduler(SelectionDAGISel *IS,
+                                                SelectionDAG *DAG,
+                                                MachineBasicBlock *BB, bool) {
+  return new ScheduleDAGFast(*DAG, BB, DAG->getTarget());
+}