lib/CodeGen/ScheduleDAG.cpp - fp2-dev/platform/external/llvm - Gitiles

 //===---- ScheduleDAG.cpp - Implement the ScheduleDAG class ---------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This implements the ScheduleDAG class, which is a base class used by
 // scheduling implementation classes.
 //
 //===----------------------------------------------------------------------===//

 #define DEBUG_TYPE "pre-RA-sched"
 #include "llvm/CodeGen/ScheduleDAG.h"
 #include "llvm/Target/TargetMachine.h"
 #include "llvm/Target/TargetInstrInfo.h"
 #include "llvm/Target/TargetRegisterInfo.h"
 #include "llvm/Support/Debug.h"
 #include <climits>
 using namespace llvm;

 ScheduleDAG::ScheduleDAG(SelectionDAG *dag, MachineBasicBlock *bb,
                          const TargetMachine &tm)
   : DAG(dag), BB(bb), TM(tm), MRI(BB->getParent()->getRegInfo()) {
   TII = TM.getInstrInfo();
   MF  = BB->getParent();
   TRI = TM.getRegisterInfo();
   TLI = TM.getTargetLowering();
   ConstPool = MF->getConstantPool();
 }

 ScheduleDAG::~ScheduleDAG() {}

 /// CalculateDepths - compute depths using algorithms for the longest
 /// paths in the DAG
 void ScheduleDAG::CalculateDepths() {
   unsigned DAGSize = SUnits.size();
   std::vector<SUnit*> WorkList;
   WorkList.reserve(DAGSize);

   // Initialize the data structures
   for (unsigned i = 0, e = DAGSize; i != e; ++i) {
     SUnit *SU = &SUnits[i];
     unsigned Degree = SU->Preds.size();
     // Temporarily use the Depth field as scratch space for the degree count.
     SU->Depth = Degree;

     // Is it a node without dependencies?
     if (Degree == 0) {
       assert(SU->Preds.empty() && "SUnit should have no predecessors");
       // Collect leaf nodes
       WorkList.push_back(SU);
     }
   }

   // Process nodes in the topological order
   while (!WorkList.empty()) {
     SUnit *SU = WorkList.back();
     WorkList.pop_back();
     unsigned SUDepth = 0;

     // Use dynamic programming:
     // When current node is being processed, all of its dependencies
     // are already processed.
     // So, just iterate over all predecessors and take the longest path
     for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
          I != E; ++I) {
       unsigned PredDepth = I->getSUnit()->Depth;
       if (PredDepth+1 > SUDepth) {
         SUDepth = PredDepth + 1;
       }
     }

     SU->Depth = SUDepth;

     // Update degrees of all nodes depending on current SUnit
     for (SUnit::const_succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
          I != E; ++I) {
       SUnit *SU = I->getSUnit();
       if (!--SU->Depth)
         // If all dependencies of the node are processed already,
         // then the longest path for the node can be computed now
         WorkList.push_back(SU);
     }
   }
 }

 /// CalculateHeights - compute heights using algorithms for the longest
 /// paths in the DAG
 void ScheduleDAG::CalculateHeights() {
   unsigned DAGSize = SUnits.size();
   std::vector<SUnit*> WorkList;
   WorkList.reserve(DAGSize);

   // Initialize the data structures
   for (unsigned i = 0, e = DAGSize; i != e; ++i) {
     SUnit *SU = &SUnits[i];
     unsigned Degree = SU->Succs.size();
     // Temporarily use the Height field as scratch space for the degree count.
     SU->Height = Degree;

     // Is it a node without dependencies?
     if (Degree == 0) {
       assert(SU->Succs.empty() && "Something wrong");
       assert(WorkList.empty() && "Should be empty");
       // Collect leaf nodes
       WorkList.push_back(SU);
     }
   }

   // Process nodes in the topological order
   while (!WorkList.empty()) {
     SUnit *SU = WorkList.back();
     WorkList.pop_back();
     unsigned SUHeight = 0;

     // Use dynamic programming:
     // When current node is being processed, all of its dependencies
     // are already processed.
     // So, just iterate over all successors and take the longest path
     for (SUnit::const_succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
          I != E; ++I) {
       unsigned SuccHeight = I->getSUnit()->Height;
       if (SuccHeight+1 > SUHeight) {
         SUHeight = SuccHeight + 1;
       }
     }

     SU->Height = SUHeight;

     // Update degrees of all nodes depending on current SUnit
     for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
          I != E; ++I) {
       SUnit *SU = I->getSUnit();
       if (!--SU->Height)
         // If all dependencies of the node are processed already,
         // then the longest path for the node can be computed now
         WorkList.push_back(SU);
     }
   }
 }

 /// dump - dump the schedule.
 void ScheduleDAG::dumpSchedule() const {
   for (unsigned i = 0, e = Sequence.size(); i != e; i++) {
     if (SUnit *SU = Sequence[i])
       SU->dump(this);
     else
       cerr << "**** NOOP ****\n";
   }
 }


 /// Run - perform scheduling.
 ///
 void ScheduleDAG::Run() {
   Schedule();

   DOUT << "*** Final schedule ***\n";
   DEBUG(dumpSchedule());
   DOUT << "\n";
 }

 /// SUnit - Scheduling unit. It's an wrapper around either a single SDNode or
 /// a group of nodes flagged together.
 void SUnit::dump(const ScheduleDAG *G) const {
   cerr << "SU(" << NodeNum << "): ";
   G->dumpNode(this);
 }

 void SUnit::dumpAll(const ScheduleDAG *G) const {
   dump(G);

   cerr << "  # preds left       : " << NumPredsLeft << "\n";
   cerr << "  # succs left       : " << NumSuccsLeft << "\n";
   cerr << "  Latency            : " << Latency << "\n";
   cerr << "  Depth              : " << Depth << "\n";
   cerr << "  Height             : " << Height << "\n";

   if (Preds.size() != 0) {
     cerr << "  Predecessors:\n";
     for (SUnit::const_succ_iterator I = Preds.begin(), E = Preds.end();
          I != E; ++I) {
       cerr << "   ";
       switch (I->getKind()) {
       case SDep::Data:        cerr << "val "; break;
       case SDep::Anti:        cerr << "anti"; break;
       case SDep::Output:      cerr << "out "; break;
       case SDep::Order:       cerr << "ch  "; break;
       }
       cerr << "#";
       cerr << I->getSUnit() << " - SU(" << I->getSUnit()->NodeNum << ")";
       if (I->isArtificial())
         cerr << " *";
       cerr << "\n";
     }
   }
   if (Succs.size() != 0) {
     cerr << "  Successors:\n";
     for (SUnit::const_succ_iterator I = Succs.begin(), E = Succs.end();
          I != E; ++I) {
       cerr << "   ";
       switch (I->getKind()) {
       case SDep::Data:        cerr << "val "; break;
       case SDep::Anti:        cerr << "anti"; break;
       case SDep::Output:      cerr << "out "; break;
       case SDep::Order:       cerr << "ch  "; break;
       }
       cerr << "#";
       cerr << I->getSUnit() << " - SU(" << I->getSUnit()->NodeNum << ")";
       if (I->isArtificial())
         cerr << " *";
       cerr << "\n";
     }
   }
   cerr << "\n";
 }

 #ifndef NDEBUG
 /// VerifySchedule - Verify that all SUnits were scheduled and that
 /// their state is consistent.
 ///
 void ScheduleDAG::VerifySchedule(bool isBottomUp) {
   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 << "*** Scheduling failed! ***\n";
       SUnits[i].dump(this);
       cerr << "has not been scheduled!\n";
       AnyNotSched = true;
     }
     if (SUnits[i].isScheduled && SUnits[i].Cycle > (unsigned)INT_MAX) {
       if (!AnyNotSched)
         cerr << "*** Scheduling failed! ***\n";
       SUnits[i].dump(this);
       cerr << "has an unexpected Cycle value!\n";
       AnyNotSched = true;
     }
     if (isBottomUp) {
       if (SUnits[i].NumSuccsLeft != 0) {
         if (!AnyNotSched)
           cerr << "*** Scheduling failed! ***\n";
         SUnits[i].dump(this);
         cerr << "has successors left!\n";
         AnyNotSched = true;
       }
     } else {
       if (SUnits[i].NumPredsLeft != 0) {
         if (!AnyNotSched)
           cerr << "*** Scheduling failed! ***\n";
         SUnits[i].dump(this);
         cerr << "has predecessors 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

 /// InitDAGTopologicalSorting - create the initial topological
 /// ordering from the DAG to be scheduled.
 ///
 /// The idea of the algorithm is taken from
 /// "Online algorithms for managing the topological order of
 /// a directed acyclic graph" by David J. Pearce and Paul H.J. Kelly
 /// This is the MNR algorithm, which was first introduced by
 /// A. Marchetti-Spaccamela, U. Nanni and H. Rohnert in
 /// "Maintaining a topological order under edge insertions".
 ///
 /// Short description of the algorithm:
 ///
 /// Topological ordering, ord, of a DAG maps each node to a topological
 /// index so that for all edges X->Y it is the case that ord(X) < ord(Y).
 ///
 /// This means that if there is a path from the node X to the node Z,
 /// then ord(X) < ord(Z).
 ///
 /// This property can be used to check for reachability of nodes:
 /// if Z is reachable from X, then an insertion of the edge Z->X would
 /// create a cycle.
 ///
 /// The algorithm first computes a topological ordering for the DAG by
 /// initializing the Index2Node and Node2Index arrays and then tries to keep
 /// the ordering up-to-date after edge insertions by reordering the DAG.
 ///
 /// On insertion of the edge X->Y, the algorithm first marks by calling DFS
 /// the nodes reachable from Y, and then shifts them using Shift to lie
 /// immediately after X in Index2Node.
 void ScheduleDAGTopologicalSort::InitDAGTopologicalSorting() {
   unsigned DAGSize = SUnits.size();
   std::vector<SUnit*> WorkList;
   WorkList.reserve(DAGSize);

   Index2Node.resize(DAGSize);
   Node2Index.resize(DAGSize);

   // Initialize the data structures.
   for (unsigned i = 0, e = DAGSize; i != e; ++i) {
     SUnit *SU = &SUnits[i];
     int NodeNum = SU->NodeNum;
     unsigned Degree = SU->Succs.size();
     // Temporarily use the Node2Index array as scratch space for degree counts.
     Node2Index[NodeNum] = Degree;

     // Is it a node without dependencies?
     if (Degree == 0) {
       assert(SU->Succs.empty() && "SUnit should have no successors");
       // Collect leaf nodes.
       WorkList.push_back(SU);
     }
   }

   int Id = DAGSize;
   while (!WorkList.empty()) {
     SUnit *SU = WorkList.back();
     WorkList.pop_back();
     Allocate(SU->NodeNum, --Id);
     for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
          I != E; ++I) {
       SUnit *SU = I->getSUnit();
       if (!--Node2Index[SU->NodeNum])
         // If all dependencies of the node are processed already,
         // then the node can be computed now.
         WorkList.push_back(SU);
     }
   }

   Visited.resize(DAGSize);

 #ifndef NDEBUG
   // Check correctness of the ordering
   for (unsigned i = 0, e = DAGSize; i != e; ++i) {
     SUnit *SU = &SUnits[i];
     for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
          I != E; ++I) {
       assert(Node2Index[SU->NodeNum] > Node2Index[I->getSUnit()->NodeNum] &&
       "Wrong topological sorting");
     }
   }
 #endif
 }

 /// AddPred - Updates the topological ordering to accomodate an edge
 /// to be added from SUnit X to SUnit Y.
 void ScheduleDAGTopologicalSort::AddPred(SUnit *Y, SUnit *X) {
   int UpperBound, LowerBound;
   LowerBound = Node2Index[Y->NodeNum];
   UpperBound = Node2Index[X->NodeNum];
   bool HasLoop = false;
   // Is Ord(X) < Ord(Y) ?
   if (LowerBound < UpperBound) {
     // Update the topological order.
     Visited.reset();
     DFS(Y, UpperBound, HasLoop);
     assert(!HasLoop && "Inserted edge creates a loop!");
     // Recompute topological indexes.
     Shift(Visited, LowerBound, UpperBound);
   }
 }

 /// RemovePred - Updates the topological ordering to accomodate an
 /// an edge to be removed from the specified node N from the predecessors
 /// of the current node M.
 void ScheduleDAGTopologicalSort::RemovePred(SUnit *M, SUnit *N) {
   // InitDAGTopologicalSorting();
 }

 /// DFS - Make a DFS traversal to mark all nodes reachable from SU and mark
 /// all nodes affected by the edge insertion. These nodes will later get new
 /// topological indexes by means of the Shift method.
 void ScheduleDAGTopologicalSort::DFS(const SUnit *SU, int UpperBound,
                                      bool& HasLoop) {
   std::vector<const SUnit*> WorkList;
   WorkList.reserve(SUnits.size());

   WorkList.push_back(SU);
   while (!WorkList.empty()) {
     SU = WorkList.back();
     WorkList.pop_back();
     Visited.set(SU->NodeNum);
     for (int I = SU->Succs.size()-1; I >= 0; --I) {
       int s = SU->Succs[I].getSUnit()->NodeNum;
       if (Node2Index[s] == UpperBound) {
         HasLoop = true;
         return;
       }
       // Visit successors if not already and in affected region.
       if (!Visited.test(s) && Node2Index[s] < UpperBound) {
         WorkList.push_back(SU->Succs[I].getSUnit());
       }
     }
   }
 }

 /// Shift - Renumber the nodes so that the topological ordering is
 /// preserved.
 void ScheduleDAGTopologicalSort::Shift(BitVector& Visited, int LowerBound,
                                        int UpperBound) {
   std::vector<int> L;
   int shift = 0;
   int i;

   for (i = LowerBound; i <= UpperBound; ++i) {
     // w is node at topological index i.
     int w = Index2Node[i];
     if (Visited.test(w)) {
       // Unmark.
       Visited.reset(w);
       L.push_back(w);
       shift = shift + 1;
     } else {
       Allocate(w, i - shift);
     }
   }

   for (unsigned j = 0; j < L.size(); ++j) {
     Allocate(L[j], i - shift);
     i = i + 1;
   }
 }


 /// WillCreateCycle - Returns true if adding an edge from SU to TargetSU will
 /// create a cycle.
 bool ScheduleDAGTopologicalSort::WillCreateCycle(SUnit *SU, SUnit *TargetSU) {
   if (IsReachable(TargetSU, SU))
     return true;
   for (SUnit::pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
        I != E; ++I)
     if (I->isAssignedRegDep() &&
         IsReachable(TargetSU, I->getSUnit()))
       return true;
   return false;
 }

 /// IsReachable - Checks if SU is reachable from TargetSU.
 bool ScheduleDAGTopologicalSort::IsReachable(const SUnit *SU,
                                              const SUnit *TargetSU) {
   // If insertion of the edge SU->TargetSU would create a cycle
   // then there is a path from TargetSU to SU.
   int UpperBound, LowerBound;
   LowerBound = Node2Index[TargetSU->NodeNum];
   UpperBound = Node2Index[SU->NodeNum];
   bool HasLoop = false;
   // Is Ord(TargetSU) < Ord(SU) ?
   if (LowerBound < UpperBound) {
     Visited.reset();
     // There may be a path from TargetSU to SU. Check for it.
     DFS(TargetSU, UpperBound, HasLoop);
   }
   return HasLoop;
 }

 /// Allocate - assign the topological index to the node n.
 void ScheduleDAGTopologicalSort::Allocate(int n, int index) {
   Node2Index[n] = index;
   Index2Node[index] = n;
 }

 ScheduleDAGTopologicalSort::ScheduleDAGTopologicalSort(
                                                      std::vector<SUnit> &sunits)
  : SUnits(sunits) {}
	//===---- ScheduleDAG.cpp - Implement the ScheduleDAG class ---------------===//
	//
	// The LLVM Compiler Infrastructure
	//
	// This file is distributed under the University of Illinois Open Source
	// License. See LICENSE.TXT for details.
	//
	//===----------------------------------------------------------------------===//
	//
	// This implements the ScheduleDAG class, which is a base class used by
	// scheduling implementation classes.
	//
	//===----------------------------------------------------------------------===//

	#define DEBUG_TYPE "pre-RA-sched"
	#include "llvm/CodeGen/ScheduleDAG.h"
	#include "llvm/Target/TargetMachine.h"
	#include "llvm/Target/TargetInstrInfo.h"
	#include "llvm/Target/TargetRegisterInfo.h"
	#include "llvm/Support/Debug.h"
	#include <climits>
	using namespace llvm;

	ScheduleDAG::ScheduleDAG(SelectionDAG dag, MachineBasicBlock bb,
	const TargetMachine &tm)
	: DAG(dag), BB(bb), TM(tm), MRI(BB->getParent()->getRegInfo()) {
	TII = TM.getInstrInfo();
	MF = BB->getParent();
	TRI = TM.getRegisterInfo();
	TLI = TM.getTargetLowering();
	ConstPool = MF->getConstantPool();
	}

	ScheduleDAG::~ScheduleDAG() {}

	/// CalculateDepths - compute depths using algorithms for the longest
	/// paths in the DAG
	void ScheduleDAG::CalculateDepths() {
	unsigned DAGSize = SUnits.size();
	std::vector<SUnit*> WorkList;
	WorkList.reserve(DAGSize);

	// Initialize the data structures
	for (unsigned i = 0, e = DAGSize; i != e; ++i) {
	SUnit *SU = &SUnits[i];
	unsigned Degree = SU->Preds.size();
	// Temporarily use the Depth field as scratch space for the degree count.
	SU->Depth = Degree;

	// Is it a node without dependencies?
	if (Degree == 0) {
	assert(SU->Preds.empty() && "SUnit should have no predecessors");
	// Collect leaf nodes
	WorkList.push_back(SU);
	}
	}

	// Process nodes in the topological order
	while (!WorkList.empty()) {
	SUnit *SU = WorkList.back();
	WorkList.pop_back();
	unsigned SUDepth = 0;

	// Use dynamic programming:
	// When current node is being processed, all of its dependencies
	// are already processed.
	// So, just iterate over all predecessors and take the longest path
	for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
	I != E; ++I) {
	unsigned PredDepth = I->getSUnit()->Depth;
	if (PredDepth+1 > SUDepth) {
	SUDepth = PredDepth + 1;
	}
	}

	SU->Depth = SUDepth;

	// Update degrees of all nodes depending on current SUnit
	for (SUnit::const_succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
	I != E; ++I) {
	SUnit *SU = I->getSUnit();
	if (!--SU->Depth)
	// If all dependencies of the node are processed already,
	// then the longest path for the node can be computed now
	WorkList.push_back(SU);
	}
	}
	}

	/// CalculateHeights - compute heights using algorithms for the longest
	/// paths in the DAG
	void ScheduleDAG::CalculateHeights() {
	unsigned DAGSize = SUnits.size();
	std::vector<SUnit*> WorkList;
	WorkList.reserve(DAGSize);

	// Initialize the data structures
	for (unsigned i = 0, e = DAGSize; i != e; ++i) {
	SUnit *SU = &SUnits[i];
	unsigned Degree = SU->Succs.size();
	// Temporarily use the Height field as scratch space for the degree count.
	SU->Height = Degree;

	// Is it a node without dependencies?
	if (Degree == 0) {
	assert(SU->Succs.empty() && "Something wrong");
	assert(WorkList.empty() && "Should be empty");
	// Collect leaf nodes
	WorkList.push_back(SU);
	}
	}

	// Process nodes in the topological order
	while (!WorkList.empty()) {
	SUnit *SU = WorkList.back();
	WorkList.pop_back();
	unsigned SUHeight = 0;

	// Use dynamic programming:
	// When current node is being processed, all of its dependencies
	// are already processed.
	// So, just iterate over all successors and take the longest path
	for (SUnit::const_succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
	I != E; ++I) {
	unsigned SuccHeight = I->getSUnit()->Height;
	if (SuccHeight+1 > SUHeight) {
	SUHeight = SuccHeight + 1;
	}
	}

	SU->Height = SUHeight;

	// Update degrees of all nodes depending on current SUnit
	for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
	I != E; ++I) {
	SUnit *SU = I->getSUnit();
	if (!--SU->Height)
	// If all dependencies of the node are processed already,
	// then the longest path for the node can be computed now
	WorkList.push_back(SU);
	}
	}
	}

	/// dump - dump the schedule.
	void ScheduleDAG::dumpSchedule() const {
	for (unsigned i = 0, e = Sequence.size(); i != e; i++) {
	if (SUnit *SU = Sequence[i])
	SU->dump(this);
	else
	cerr << "** NOOP **\n";
	}
	}


	/// Run - perform scheduling.
	///
	void ScheduleDAG::Run() {
	Schedule();

	DOUT << "* Final schedule *\n";
	DEBUG(dumpSchedule());
	DOUT << "\n";
	}

	/// SUnit - Scheduling unit. It's an wrapper around either a single SDNode or
	/// a group of nodes flagged together.
	void SUnit::dump(const ScheduleDAG *G) const {
	cerr << "SU(" << NodeNum << "): ";
	G->dumpNode(this);
	}

	void SUnit::dumpAll(const ScheduleDAG *G) const {
	dump(G);

	cerr << " # preds left : " << NumPredsLeft << "\n";
	cerr << " # succs left : " << NumSuccsLeft << "\n";
	cerr << " Latency : " << Latency << "\n";
	cerr << " Depth : " << Depth << "\n";
	cerr << " Height : " << Height << "\n";

	if (Preds.size() != 0) {
	cerr << " Predecessors:\n";
	for (SUnit::const_succ_iterator I = Preds.begin(), E = Preds.end();
	I != E; ++I) {
	cerr << " ";
	switch (I->getKind()) {
	case SDep::Data: cerr << "val "; break;
	case SDep::Anti: cerr << "anti"; break;
	case SDep::Output: cerr << "out "; break;
	case SDep::Order: cerr << "ch "; break;
	}
	cerr << "#";
	cerr << I->getSUnit() << " - SU(" << I->getSUnit()->NodeNum << ")";
	if (I->isArtificial())
	cerr << " *";
	cerr << "\n";
	}
	}
	if (Succs.size() != 0) {
	cerr << " Successors:\n";
	for (SUnit::const_succ_iterator I = Succs.begin(), E = Succs.end();
	I != E; ++I) {
	cerr << " ";
	switch (I->getKind()) {
	case SDep::Data: cerr << "val "; break;
	case SDep::Anti: cerr << "anti"; break;
	case SDep::Output: cerr << "out "; break;
	case SDep::Order: cerr << "ch "; break;
	}
	cerr << "#";
	cerr << I->getSUnit() << " - SU(" << I->getSUnit()->NodeNum << ")";
	if (I->isArtificial())
	cerr << " *";
	cerr << "\n";
	}
	}
	cerr << "\n";
	}

	#ifndef NDEBUG
	/// VerifySchedule - Verify that all SUnits were scheduled and that
	/// their state is consistent.
	///
	void ScheduleDAG::VerifySchedule(bool isBottomUp) {
	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 << "* Scheduling failed! *\n";
	SUnits[i].dump(this);
	cerr << "has not been scheduled!\n";
	AnyNotSched = true;
	}
	if (SUnits[i].isScheduled && SUnits[i].Cycle > (unsigned)INT_MAX) {
	if (!AnyNotSched)
	cerr << "* Scheduling failed! *\n";
	SUnits[i].dump(this);
	cerr << "has an unexpected Cycle value!\n";
	AnyNotSched = true;
	}
	if (isBottomUp) {
	if (SUnits[i].NumSuccsLeft != 0) {
	if (!AnyNotSched)
	cerr << "* Scheduling failed! *\n";
	SUnits[i].dump(this);
	cerr << "has successors left!\n";
	AnyNotSched = true;
	}
	} else {
	if (SUnits[i].NumPredsLeft != 0) {
	if (!AnyNotSched)
	cerr << "* Scheduling failed! *\n";
	SUnits[i].dump(this);
	cerr << "has predecessors 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

	/// InitDAGTopologicalSorting - create the initial topological
	/// ordering from the DAG to be scheduled.
	///
	/// The idea of the algorithm is taken from
	/// "Online algorithms for managing the topological order of
	/// a directed acyclic graph" by David J. Pearce and Paul H.J. Kelly
	/// This is the MNR algorithm, which was first introduced by
	/// A. Marchetti-Spaccamela, U. Nanni and H. Rohnert in
	/// "Maintaining a topological order under edge insertions".
	///
	/// Short description of the algorithm:
	///
	/// Topological ordering, ord, of a DAG maps each node to a topological
	/// index so that for all edges X->Y it is the case that ord(X) < ord(Y).
	///
	/// This means that if there is a path from the node X to the node Z,
	/// then ord(X) < ord(Z).
	///
	/// This property can be used to check for reachability of nodes:
	/// if Z is reachable from X, then an insertion of the edge Z->X would
	/// create a cycle.
	///
	/// The algorithm first computes a topological ordering for the DAG by
	/// initializing the Index2Node and Node2Index arrays and then tries to keep
	/// the ordering up-to-date after edge insertions by reordering the DAG.
	///
	/// On insertion of the edge X->Y, the algorithm first marks by calling DFS
	/// the nodes reachable from Y, and then shifts them using Shift to lie
	/// immediately after X in Index2Node.
	void ScheduleDAGTopologicalSort::InitDAGTopologicalSorting() {
	unsigned DAGSize = SUnits.size();
	std::vector<SUnit*> WorkList;
	WorkList.reserve(DAGSize);

	Index2Node.resize(DAGSize);
	Node2Index.resize(DAGSize);

	// Initialize the data structures.
	for (unsigned i = 0, e = DAGSize; i != e; ++i) {
	SUnit *SU = &SUnits[i];
	int NodeNum = SU->NodeNum;
	unsigned Degree = SU->Succs.size();
	// Temporarily use the Node2Index array as scratch space for degree counts.
	Node2Index[NodeNum] = Degree;

	// Is it a node without dependencies?
	if (Degree == 0) {
	assert(SU->Succs.empty() && "SUnit should have no successors");
	// Collect leaf nodes.
	WorkList.push_back(SU);
	}
	}

	int Id = DAGSize;
	while (!WorkList.empty()) {
	SUnit *SU = WorkList.back();
	WorkList.pop_back();
	Allocate(SU->NodeNum, --Id);
	for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
	I != E; ++I) {
	SUnit *SU = I->getSUnit();
	if (!--Node2Index[SU->NodeNum])
	// If all dependencies of the node are processed already,
	// then the node can be computed now.
	WorkList.push_back(SU);
	}
	}

	Visited.resize(DAGSize);

	#ifndef NDEBUG
	// Check correctness of the ordering
	for (unsigned i = 0, e = DAGSize; i != e; ++i) {
	SUnit *SU = &SUnits[i];
	for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
	I != E; ++I) {
	assert(Node2Index[SU->NodeNum] > Node2Index[I->getSUnit()->NodeNum] &&
	"Wrong topological sorting");
	}
	}
	#endif
	}

	/// AddPred - Updates the topological ordering to accomodate an edge
	/// to be added from SUnit X to SUnit Y.
	void ScheduleDAGTopologicalSort::AddPred(SUnit Y, SUnit X) {
	int UpperBound, LowerBound;
	LowerBound = Node2Index[Y->NodeNum];
	UpperBound = Node2Index[X->NodeNum];
	bool HasLoop = false;
	// Is Ord(X) < Ord(Y) ?
	if (LowerBound < UpperBound) {
	// Update the topological order.
	Visited.reset();
	DFS(Y, UpperBound, HasLoop);
	assert(!HasLoop && "Inserted edge creates a loop!");
	// Recompute topological indexes.
	Shift(Visited, LowerBound, UpperBound);
	}
	}

	/// RemovePred - Updates the topological ordering to accomodate an
	/// an edge to be removed from the specified node N from the predecessors
	/// of the current node M.
	void ScheduleDAGTopologicalSort::RemovePred(SUnit M, SUnit N) {
	// InitDAGTopologicalSorting();
	}

	/// DFS - Make a DFS traversal to mark all nodes reachable from SU and mark
	/// all nodes affected by the edge insertion. These nodes will later get new
	/// topological indexes by means of the Shift method.
	void ScheduleDAGTopologicalSort::DFS(const SUnit *SU, int UpperBound,
	bool& HasLoop) {
	std::vector<const SUnit*> WorkList;
	WorkList.reserve(SUnits.size());

	WorkList.push_back(SU);
	while (!WorkList.empty()) {
	SU = WorkList.back();
	WorkList.pop_back();
	Visited.set(SU->NodeNum);
	for (int I = SU->Succs.size()-1; I >= 0; --I) {
	int s = SU->Succs[I].getSUnit()->NodeNum;
	if (Node2Index[s] == UpperBound) {
	HasLoop = true;
	return;
	}
	// Visit successors if not already and in affected region.
	if (!Visited.test(s) && Node2Index[s] < UpperBound) {
	WorkList.push_back(SU->Succs[I].getSUnit());
	}
	}
	}
	}

	/// Shift - Renumber the nodes so that the topological ordering is
	/// preserved.
	void ScheduleDAGTopologicalSort::Shift(BitVector& Visited, int LowerBound,
	int UpperBound) {
	std::vector<int> L;
	int shift = 0;
	int i;

	for (i = LowerBound; i <= UpperBound; ++i) {
	// w is node at topological index i.
	int w = Index2Node[i];
	if (Visited.test(w)) {
	// Unmark.
	Visited.reset(w);
	L.push_back(w);
	shift = shift + 1;
	} else {
	Allocate(w, i - shift);
	}
	}

	for (unsigned j = 0; j < L.size(); ++j) {
	Allocate(L[j], i - shift);
	i = i + 1;
	}
	}


	/// WillCreateCycle - Returns true if adding an edge from SU to TargetSU will
	/// create a cycle.
	bool ScheduleDAGTopologicalSort::WillCreateCycle(SUnit SU, SUnit TargetSU) {
	if (IsReachable(TargetSU, SU))
	return true;
	for (SUnit::pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
	I != E; ++I)
	if (I->isAssignedRegDep() &&
	IsReachable(TargetSU, I->getSUnit()))
	return true;
	return false;
	}

	/// IsReachable - Checks if SU is reachable from TargetSU.
	bool ScheduleDAGTopologicalSort::IsReachable(const SUnit *SU,
	const SUnit *TargetSU) {
	// If insertion of the edge SU->TargetSU would create a cycle
	// then there is a path from TargetSU to SU.
	int UpperBound, LowerBound;
	LowerBound = Node2Index[TargetSU->NodeNum];
	UpperBound = Node2Index[SU->NodeNum];
	bool HasLoop = false;
	// Is Ord(TargetSU) < Ord(SU) ?
	if (LowerBound < UpperBound) {
	Visited.reset();
	// There may be a path from TargetSU to SU. Check for it.
	DFS(TargetSU, UpperBound, HasLoop);
	}
	return HasLoop;
	}

	/// Allocate - assign the topological index to the node n.
	void ScheduleDAGTopologicalSort::Allocate(int n, int index) {
	Node2Index[n] = index;
	Index2Node[index] = n;
	}

	ScheduleDAGTopologicalSort::ScheduleDAGTopologicalSort(
	std::vector<SUnit> &sunits)
	: SUnits(sunits) {}