Do some code refactoring on Jim's scheduler in preparation of the new list

scheduler.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@25493 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 891 insertions, 0 deletions

diff --git a/lib/CodeGen/SelectionDAG/ScheduleDAGSimple.cpp b/lib/CodeGen/SelectionDAG/ScheduleDAGSimple.cpp
new file mode 100644
index 0000000000..b22eae499a
--- /dev/null
+++ b/lib/CodeGen/SelectionDAG/ScheduleDAGSimple.cpp
@@ -0,0 +1,891 @@
+//===-- ScheduleDAGSimple.cpp - Implement a trivial DAG scheduler ---------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by James M. Laskey and is distributed under the
+// University of Illinois Open Source License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This implements a simple two pass scheduler.  The first pass attempts to push
+// backward any lengthy instructions and critical paths.  The second pass packs
+// instructions into semi-optimal time slots.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "sched"
+#include "llvm/CodeGen/ScheduleDAG.h"
+#include "llvm/CodeGen/SelectionDAG.h"
+#include "llvm/Target/TargetMachine.h"
+#include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include <iostream>
+#include <ios>
+#include <algorithm>
+using namespace llvm;
+
+namespace {
+  // Style of scheduling to use.
+  enum ScheduleChoices {
+    noScheduling,
+    simpleScheduling,
+    simpleNoItinScheduling
+  };
+} // namespace
+
+cl::opt<ScheduleChoices> ScheduleStyle("sched",
+  cl::desc("Choose scheduling style"),
+  cl::init(noScheduling),
+  cl::values(
+    clEnumValN(noScheduling, "none",
+              "Trivial emission with no analysis"),
+    clEnumValN(simpleScheduling, "simple",
+              "Minimize critical path and maximize processor utilization"),
+    clEnumValN(simpleNoItinScheduling, "simple-noitin",
+              "Same as simple except using generic latency"),
+   clEnumValEnd));
+
+
+namespace {
+//===----------------------------------------------------------------------===//
+///
+/// BitsIterator - Provides iteration through individual bits in a bit vector.
+///
+template<class T>
+class BitsIterator {
+private:
+  T Bits;                               // Bits left to iterate through
+
+public:
+  /// Ctor.
+  BitsIterator(T Initial) : Bits(Initial) {}
+  
+  /// Next - Returns the next bit set or zero if exhausted.
+  inline T Next() {
+    // Get the rightmost bit set
+    T Result = Bits & -Bits;
+    // Remove from rest
+    Bits &= ~Result;
+    // Return single bit or zero
+    return Result;
+  }
+};
+  
+//===----------------------------------------------------------------------===//
+
+
+//===----------------------------------------------------------------------===//
+///
+/// ResourceTally - Manages the use of resources over time intervals.  Each
+/// item (slot) in the tally vector represents the resources used at a given
+/// moment.  A bit set to 1 indicates that a resource is in use, otherwise
+/// available.  An assumption is made that the tally is large enough to schedule 
+/// all current instructions (asserts otherwise.)
+///
+template<class T>
+class ResourceTally {
+private:
+  std::vector<T> Tally;                 // Resources used per slot
+  typedef typename std::vector<T>::iterator Iter;
+                                        // Tally iterator 
+  
+  /// SlotsAvailable - Returns true if all units are available.
+	///
+  bool SlotsAvailable(Iter Begin, unsigned N, unsigned ResourceSet,
+                                              unsigned &Resource) {
+    assert(N && "Must check availability with N != 0");
+    // Determine end of interval
+    Iter End = Begin + N;
+    assert(End <= Tally.end() && "Tally is not large enough for schedule");
+    
+    // Iterate thru each resource
+    BitsIterator<T> Resources(ResourceSet & ~*Begin);
+    while (unsigned Res = Resources.Next()) {
+      // Check if resource is available for next N slots
+      Iter Interval = End;
+      do {
+        Interval--;
+        if (*Interval & Res) break;
+      } while (Interval != Begin);
+      
+      // If available for N
+      if (Interval == Begin) {
+        // Success
+        Resource = Res;
+        return true;
+      }
+    }
+    
+    // No luck
+    Resource = 0;
+    return false;
+  }
+	
+	/// RetrySlot - Finds a good candidate slot to retry search.
+  Iter RetrySlot(Iter Begin, unsigned N, unsigned ResourceSet) {
+    assert(N && "Must check availability with N != 0");
+    // Determine end of interval
+    Iter End = Begin + N;
+    assert(End <= Tally.end() && "Tally is not large enough for schedule");
+		
+		while (Begin != End--) {
+			// Clear units in use
+			ResourceSet &= ~*End;
+			// If no units left then we should go no further 
+			if (!ResourceSet) return End + 1;
+		}
+		// Made it all the way through
+		return Begin;
+	}
+  
+  /// FindAndReserveStages - Return true if the stages can be completed. If
+  /// so mark as busy.
+  bool FindAndReserveStages(Iter Begin,
+                            InstrStage *Stage, InstrStage *StageEnd) {
+    // If at last stage then we're done
+    if (Stage == StageEnd) return true;
+    // Get number of cycles for current stage
+    unsigned N = Stage->Cycles;
+    // Check to see if N slots are available, if not fail
+    unsigned Resource;
+    if (!SlotsAvailable(Begin, N, Stage->Units, Resource)) return false;
+    // Check to see if remaining stages are available, if not fail
+    if (!FindAndReserveStages(Begin + N, Stage + 1, StageEnd)) return false;
+    // Reserve resource
+    Reserve(Begin, N, Resource);
+    // Success
+    return true;
+  }
+
+  /// Reserve - Mark busy (set) the specified N slots.
+  void Reserve(Iter Begin, unsigned N, unsigned Resource) {
+    // Determine end of interval
+    Iter End = Begin + N;
+    assert(End <= Tally.end() && "Tally is not large enough for schedule");
+ 
+    // Set resource bit in each slot
+    for (; Begin < End; Begin++)
+      *Begin |= Resource;
+  }
+
+  /// FindSlots - Starting from Begin, locate consecutive slots where all stages
+  /// can be completed.  Returns the address of first slot.
+  Iter FindSlots(Iter Begin, InstrStage *StageBegin, InstrStage *StageEnd) {
+    // Track position      
+    Iter Cursor = Begin;
+    
+    // Try all possible slots forward
+    while (true) {
+      // Try at cursor, if successful return position.
+      if (FindAndReserveStages(Cursor, StageBegin, StageEnd)) return Cursor;
+      // Locate a better position
+			Cursor = RetrySlot(Cursor + 1, StageBegin->Cycles, StageBegin->Units);
+    }
+  }
+  
+public:
+  /// Initialize - Resize and zero the tally to the specified number of time
+  /// slots.
+  inline void Initialize(unsigned N) {
+    Tally.assign(N, 0);   // Initialize tally to all zeros.
+  }
+
+  // FindAndReserve - Locate an ideal slot for the specified stages and mark
+  // as busy.
+  unsigned FindAndReserve(unsigned Slot, InstrStage *StageBegin,
+                                         InstrStage *StageEnd) {
+		// Where to begin 
+		Iter Begin = Tally.begin() + Slot;
+		// Find a free slot
+		Iter Where = FindSlots(Begin, StageBegin, StageEnd);
+		// Distance is slot number
+		unsigned Final = Where - Tally.begin();
+    return Final;
+  }
+
+};
+
+//===----------------------------------------------------------------------===//
+///
+/// ScheduleDAGSimple - Simple two pass scheduler.
+///
+class ScheduleDAGSimple : public ScheduleDAG {
+private:
+  unsigned NodeCount;                   // Number of nodes in DAG
+  bool HasGroups;                       // True if there are any groups
+  NodeInfo *Info;                       // Info for nodes being scheduled
+  NIVector Ordering;                    // Emit ordering of nodes
+  ResourceTally<unsigned> Tally;        // Resource usage tally
+  unsigned NSlots;                      // Total latency
+  static const unsigned NotFound = ~0U; // Search marker
+  
+public:
+
+  // Ctor.
+  ScheduleDAGSimple(SelectionDAG &dag, MachineBasicBlock *bb,
+                    const TargetMachine &tm)
+    : ScheduleDAG(dag, bb, tm),
+      NodeCount(0), HasGroups(false), Info(NULL), Tally(), NSlots(0) {
+    assert(&TII && "Target doesn't provide instr info?");
+    assert(&MRI && "Target doesn't provide register info?");
+  }
+
+  virtual ~ScheduleDAGSimple() {};
+
+private:
+  static bool isFlagDefiner(SDNode *A);
+  static bool isFlagUser(SDNode *A);
+  static bool isDefiner(NodeInfo *A, NodeInfo *B);
+  static bool isPassiveNode(SDNode *Node);
+  void IncludeNode(NodeInfo *NI);
+  void VisitAll();
+  void Schedule();
+  void IdentifyGroups();
+  void GatherSchedulingInfo();
+  void FakeGroupDominators(); 
+  void PrepareNodeInfo();
+  bool isStrongDependency(NodeInfo *A, NodeInfo *B);
+  bool isWeakDependency(NodeInfo *A, NodeInfo *B);
+  void ScheduleBackward();
+  void ScheduleForward();
+  void EmitAll();
+
+  void printChanges(unsigned Index);
+  void printSI(std::ostream &O, NodeInfo *NI) const;
+  void print(std::ostream &O) const;
+};
+
+
+//===----------------------------------------------------------------------===//
+/// Special case itineraries.
+///
+enum {
+  CallLatency = 40,          // To push calls back in time
+
+  RSInteger   = 0xC0000000,  // Two integer units
+  RSFloat     = 0x30000000,  // Two float units
+  RSLoadStore = 0x0C000000,  // Two load store units
+  RSBranch    = 0x02000000   // One branch unit
+};
+static InstrStage CallStage  = { CallLatency, RSBranch };
+static InstrStage LoadStage  = { 5, RSLoadStore };
+static InstrStage StoreStage = { 2, RSLoadStore };
+static InstrStage IntStage   = { 2, RSInteger };
+static InstrStage FloatStage = { 3, RSFloat };
+//===----------------------------------------------------------------------===//
+
+
+//===----------------------------------------------------------------------===//
+
+} // namespace
+
+//===----------------------------------------------------------------------===//
+
+
+//===----------------------------------------------------------------------===//
+/// Add - Adds a definer and user pair to a node group.
+///
+void NodeGroup::Add(NodeInfo *D, NodeInfo *U) {
+  // Get current groups
+  NodeGroup *DGroup = D->Group;
+  NodeGroup *UGroup = U->Group;
+  // If both are members of groups
+  if (DGroup && UGroup) {
+    // There may have been another edge connecting 
+    if (DGroup == UGroup) return;
+    // Add the pending users count
+    DGroup->addPending(UGroup->getPending());
+    // For each member of the users group
+    NodeGroupIterator UNGI(U);
+    while (NodeInfo *UNI = UNGI.next() ) {
+      // Change the group
+      UNI->Group = DGroup;
+      // For each member of the definers group
+      NodeGroupIterator DNGI(D);
+      while (NodeInfo *DNI = DNGI.next() ) {
+        // Remove internal edges
+        DGroup->addPending(-CountInternalUses(DNI, UNI));
+      }
+    }
+    // Merge the two lists
+    DGroup->group_insert(DGroup->group_end(),
+                         UGroup->group_begin(), UGroup->group_end());
+  } else if (DGroup) {
+    // Make user member of definers group
+    U->Group = DGroup;
+    // Add users uses to definers group pending
+    DGroup->addPending(U->Node->use_size());
+    // For each member of the definers group
+    NodeGroupIterator DNGI(D);
+    while (NodeInfo *DNI = DNGI.next() ) {
+      // Remove internal edges
+      DGroup->addPending(-CountInternalUses(DNI, U));
+    }
+    DGroup->group_push_back(U);
+  } else if (UGroup) {
+    // Make definer member of users group
+    D->Group = UGroup;
+    // Add definers uses to users group pending
+    UGroup->addPending(D->Node->use_size());
+    // For each member of the users group
+    NodeGroupIterator UNGI(U);
+    while (NodeInfo *UNI = UNGI.next() ) {
+      // Remove internal edges
+      UGroup->addPending(-CountInternalUses(D, UNI));
+    }
+    UGroup->group_insert(UGroup->group_begin(), D);
+  } else {
+    D->Group = U->Group = DGroup = new NodeGroup();
+    DGroup->addPending(D->Node->use_size() + U->Node->use_size() -
+                       CountInternalUses(D, U));
+    DGroup->group_push_back(D);
+    DGroup->group_push_back(U);
+  }
+}
+
+/// CountInternalUses - Returns the number of edges between the two nodes.
+///
+unsigned NodeGroup::CountInternalUses(NodeInfo *D, NodeInfo *U) {
+  unsigned N = 0;
+  for (unsigned M = U->Node->getNumOperands(); 0 < M--;) {
+    SDOperand Op = U->Node->getOperand(M);
+    if (Op.Val == D->Node) N++;
+  }
+
+  return N;
+}
+//===----------------------------------------------------------------------===//
+
+
+//===----------------------------------------------------------------------===//
+/// isFlagDefiner - Returns true if the node defines a flag result.
+bool ScheduleDAGSimple::isFlagDefiner(SDNode *A) {
+  unsigned N = A->getNumValues();
+  return N && A->getValueType(N - 1) == MVT::Flag;
+}
+
+/// isFlagUser - Returns true if the node uses a flag result.
+///
+bool ScheduleDAGSimple::isFlagUser(SDNode *A) {
+  unsigned N = A->getNumOperands();
+  return N && A->getOperand(N - 1).getValueType() == MVT::Flag;
+}
+
+/// isDefiner - Return true if node A is a definer for B.
+///
+bool ScheduleDAGSimple::isDefiner(NodeInfo *A, NodeInfo *B) {
+  // While there are A nodes
+  NodeGroupIterator NII(A);
+  while (NodeInfo *NI = NII.next()) {
+    // Extract node
+    SDNode *Node = NI->Node;
+    // While there operands in nodes of B
+    NodeGroupOpIterator NGOI(B);
+    while (!NGOI.isEnd()) {
+      SDOperand Op = NGOI.next();
+      // If node from A defines a node in B
+      if (Node == Op.Val) return true;
+    }
+  }
+  return false;
+}
+
+/// isPassiveNode - Return true if the node is a non-scheduled leaf.
+///
+bool ScheduleDAGSimple::isPassiveNode(SDNode *Node) {
+  if (isa<ConstantSDNode>(Node))       return true;
+  if (isa<RegisterSDNode>(Node))       return true;
+  if (isa<GlobalAddressSDNode>(Node))  return true;
+  if (isa<BasicBlockSDNode>(Node))     return true;
+  if (isa<FrameIndexSDNode>(Node))     return true;
+  if (isa<ConstantPoolSDNode>(Node))   return true;
+  if (isa<ExternalSymbolSDNode>(Node)) return true;
+  return false;
+}
+
+/// IncludeNode - Add node to NodeInfo vector.
+///
+void ScheduleDAGSimple::IncludeNode(NodeInfo *NI) {
+  // Get node
+  SDNode *Node = NI->Node;
+  // Ignore entry node
+  if (Node->getOpcode() == ISD::EntryToken) return;
+  // Check current count for node
+  int Count = NI->getPending();
+  // If the node is already in list
+  if (Count < 0) return;
+  // Decrement count to indicate a visit
+  Count--;
+  // If count has gone to zero then add node to list
+  if (!Count) {
+    // Add node
+    if (NI->isInGroup()) {
+      Ordering.push_back(NI->Group->getDominator());
+    } else {
+      Ordering.push_back(NI);
+    }
+    // indicate node has been added
+    Count--;
+  }
+  // Mark as visited with new count 
+  NI->setPending(Count);
+}
+
+/// VisitAll - Visit each node breadth-wise to produce an initial ordering.
+/// Note that the ordering in the Nodes vector is reversed.
+void ScheduleDAGSimple::VisitAll() {
+  // Add first element to list
+  NodeInfo *NI = getNI(DAG.getRoot().Val);
+  if (NI->isInGroup()) {
+    Ordering.push_back(NI->Group->getDominator());
+  } else {
+    Ordering.push_back(NI);
+  }
+
+  // Iterate through all nodes that have been added
+  for (unsigned i = 0; i < Ordering.size(); i++) { // note: size() varies
+    // Visit all operands
+    NodeGroupOpIterator NGI(Ordering[i]);
+    while (!NGI.isEnd()) {
+      // Get next operand
+      SDOperand Op = NGI.next();
+      // Get node
+      SDNode *Node = Op.Val;
+      // Ignore passive nodes
+      if (isPassiveNode(Node)) continue;
+      // Check out node
+      IncludeNode(getNI(Node));
+    }
+  }
+
+  // Add entry node last (IncludeNode filters entry nodes)
+  if (DAG.getEntryNode().Val != DAG.getRoot().Val)
+    Ordering.push_back(getNI(DAG.getEntryNode().Val));
+    
+  // Reverse the order
+  std::reverse(Ordering.begin(), Ordering.end());
+}
+
+/// IdentifyGroups - Put flagged nodes into groups.
+///
+void ScheduleDAGSimple::IdentifyGroups() {
+  for (unsigned i = 0, N = NodeCount; i < N; i++) {
+    NodeInfo* NI = &Info[i];
+    SDNode *Node = NI->Node;
+
+    // For each operand (in reverse to only look at flags)
+    for (unsigned N = Node->getNumOperands(); 0 < N--;) {
+      // Get operand
+      SDOperand Op = Node->getOperand(N);
+      // No more flags to walk
+      if (Op.getValueType() != MVT::Flag) break;
+      // Add to node group
+      NodeGroup::Add(getNI(Op.Val), NI);
+      // Let evryone else know
+      HasGroups = true;
+    }
+  }
+}
+
+/// GatherSchedulingInfo - Get latency and resource information about each node.
+///
+void ScheduleDAGSimple::GatherSchedulingInfo() {
+  // Get instruction itineraries for the target
+  const InstrItineraryData InstrItins = TM.getInstrItineraryData();
+  
+  // For each node
+  for (unsigned i = 0, N = NodeCount; i < N; i++) {
+    // Get node info
+    NodeInfo* NI = &Info[i];
+    SDNode *Node = NI->Node;
+    
+    // If there are itineraries and it is a machine instruction
+    if (InstrItins.isEmpty() || ScheduleStyle == simpleNoItinScheduling) {
+      // If machine opcode
+      if (Node->isTargetOpcode()) {
+        // Get return type to guess which processing unit 
+        MVT::ValueType VT = Node->getValueType(0);
+        // Get machine opcode
+        MachineOpCode TOpc = Node->getTargetOpcode();
+        NI->IsCall = TII->isCall(TOpc);
+        NI->IsLoad = TII->isLoad(TOpc);
+        NI->IsStore = TII->isStore(TOpc);
+
+        if (TII->isLoad(TOpc))             NI->StageBegin = &LoadStage;
+        else if (TII->isStore(TOpc))       NI->StageBegin = &StoreStage;
+        else if (MVT::isInteger(VT))       NI->StageBegin = &IntStage;
+        else if (MVT::isFloatingPoint(VT)) NI->StageBegin = &FloatStage;
+        if (NI->StageBegin) NI->StageEnd = NI->StageBegin + 1;
+      }
+    } else if (Node->isTargetOpcode()) {
+      // get machine opcode
+      MachineOpCode TOpc = Node->getTargetOpcode();
+      // Check to see if it is a call
+      NI->IsCall = TII->isCall(TOpc);
+      // Get itinerary stages for instruction
+      unsigned II = TII->getSchedClass(TOpc);
+      NI->StageBegin = InstrItins.begin(II);
+      NI->StageEnd = InstrItins.end(II);
+    }
+    
+    // One slot for the instruction itself
+    NI->Latency = 1;
+    
+    // Add long latency for a call to push it back in time
+    if (NI->IsCall) NI->Latency += CallLatency;
+    
+    // Sum up all the latencies
+    for (InstrStage *Stage = NI->StageBegin, *E = NI->StageEnd;
+        Stage != E; Stage++) {
+      NI->Latency += Stage->Cycles;
+    }
+    
+    // Sum up all the latencies for max tally size
+    NSlots += NI->Latency;
+  }
+  
+  // Unify metrics if in a group
+  if (HasGroups) {
+    for (unsigned i = 0, N = NodeCount; i < N; i++) {
+      NodeInfo* NI = &Info[i];
+      
+      if (NI->isInGroup()) {
+        NodeGroup *Group = NI->Group;
+        
+        if (!Group->getDominator()) {
+          NIIterator NGI = Group->group_begin(), NGE = Group->group_end();
+          NodeInfo *Dominator = *NGI;
+          unsigned Latency = 0;
+          
+          for (NGI++; NGI != NGE; NGI++) {
+            NodeInfo* NGNI = *NGI;
+            Latency += NGNI->Latency;
+            if (Dominator->Latency < NGNI->Latency) Dominator = NGNI;
+          }
+          
+          Dominator->Latency = Latency;
+          Group->setDominator(Dominator);
+        }
+      }
+    }
+  }
+}
+
+/// FakeGroupDominators - Set dominators for non-scheduling.
+/// 
+void ScheduleDAGSimple::FakeGroupDominators() {
+  for (unsigned i = 0, N = NodeCount; i < N; i++) {
+    NodeInfo* NI = &Info[i];
+    
+    if (NI->isInGroup()) {
+      NodeGroup *Group = NI->Group;
+      
+      if (!Group->getDominator()) {
+        Group->setDominator(NI);
+      }
+    }
+  }
+}
+
+/// PrepareNodeInfo - Set up the basic minimum node info for scheduling.
+/// 
+void ScheduleDAGSimple::PrepareNodeInfo() {
+  // Allocate node information
+  Info = new NodeInfo[NodeCount];
+
+  unsigned i = 0;
+  for (SelectionDAG::allnodes_iterator I = DAG.allnodes_begin(),
+       E = DAG.allnodes_end(); I != E; ++I, ++i) {
+    // Fast reference to node schedule info
+    NodeInfo* NI = &Info[i];
+    // Set up map
+    Map[I] = NI;
+    // Set node
+    NI->Node = I;
+    // Set pending visit count
+    NI->setPending(I->use_size());
+  }
+}
+
+/// isStrongDependency - Return true if node A has results used by node B. 
+/// I.E., B must wait for latency of A.
+bool ScheduleDAGSimple::isStrongDependency(NodeInfo *A, NodeInfo *B) {
+  // If A defines for B then it's a strong dependency or
+  // if a load follows a store (may be dependent but why take a chance.)
+  return isDefiner(A, B) || (A->IsStore && B->IsLoad);
+}
+
+/// isWeakDependency Return true if node A produces a result that will
+/// conflict with operands of B.  It is assumed that we have called
+/// isStrongDependency prior.
+bool ScheduleDAGSimple::isWeakDependency(NodeInfo *A, NodeInfo *B) {
+  // TODO check for conflicting real registers and aliases
+#if 0 // FIXME - Since we are in SSA form and not checking register aliasing
+  return A->Node->getOpcode() == ISD::EntryToken || isStrongDependency(B, A);
+#else
+  return A->Node->getOpcode() == ISD::EntryToken;
+#endif
+}
+
+/// ScheduleBackward - Schedule instructions so that any long latency
+/// instructions and the critical path get pushed back in time. Time is run in
+/// reverse to allow code reuse of the Tally and eliminate the overhead of
+/// biasing every slot indices against NSlots.
+void ScheduleDAGSimple::ScheduleBackward() {
+  // Size and clear the resource tally
+  Tally.Initialize(NSlots);
+  // Get number of nodes to schedule
+  unsigned N = Ordering.size();
+  
+  // For each node being scheduled
+  for (unsigned i = N; 0 < i--;) {
+    NodeInfo *NI = Ordering[i];
+    // Track insertion
+    unsigned Slot = NotFound;
+    
+    // Compare against those previously scheduled nodes
+    unsigned j = i + 1;
+    for (; j < N; j++) {
+      // Get following instruction
+      NodeInfo *Other = Ordering[j];
+      
+      // Check dependency against previously inserted nodes
+      if (isStrongDependency(NI, Other)) {
+        Slot = Other->Slot + Other->Latency;
+        break;
+      } else if (isWeakDependency(NI, Other)) {
+        Slot = Other->Slot;
+        break;
+      }
+    }
+    
+    // If independent of others (or first entry)
+    if (Slot == NotFound) Slot = 0;
+    
+#if 0 // FIXME - measure later
+    // Find a slot where the needed resources are available
+    if (NI->StageBegin != NI->StageEnd)
+      Slot = Tally.FindAndReserve(Slot, NI->StageBegin, NI->StageEnd);
+#endif
+      
+    // Set node slot
+    NI->Slot = Slot;
+    
+    // Insert sort based on slot
+    j = i + 1;
+    for (; j < N; j++) {
+      // Get following instruction
+      NodeInfo *Other = Ordering[j];
+      // Should we look further (remember slots are in reverse time)
+      if (Slot >= Other->Slot) break;
+      // Shuffle other into ordering
+      Ordering[j - 1] = Other;
+    }
+    // Insert node in proper slot
+    if (j != i + 1) Ordering[j - 1] = NI;
+  }
+}
+
+/// ScheduleForward - Schedule instructions to maximize packing.
+///
+void ScheduleDAGSimple::ScheduleForward() {
+  // Size and clear the resource tally
+  Tally.Initialize(NSlots);
+  // Get number of nodes to schedule
+  unsigned N = Ordering.size();
+  
+  // For each node being scheduled
+  for (unsigned i = 0; i < N; i++) {
+    NodeInfo *NI = Ordering[i];
+    // Track insertion
+    unsigned Slot = NotFound;
+    
+    // Compare against those previously scheduled nodes
+    unsigned j = i;
+    for (; 0 < j--;) {
+      // Get following instruction
+      NodeInfo *Other = Ordering[j];
+      
+      // Check dependency against previously inserted nodes
+      if (isStrongDependency(Other, NI)) {
+        Slot = Other->Slot + Other->Latency;
+        break;
+      } else if (Other->IsCall || isWeakDependency(Other, NI)) {
+        Slot = Other->Slot;
+        break;
+      }
+    }
+    
+    // If independent of others (or first entry)
+    if (Slot == NotFound) Slot = 0;
+    
+    // Find a slot where the needed resources are available
+    if (NI->StageBegin != NI->StageEnd)
+      Slot = Tally.FindAndReserve(Slot, NI->StageBegin, NI->StageEnd);
+      
+    // Set node slot
+    NI->Slot = Slot;
+    
+    // Insert sort based on slot
+    j = i;
+    for (; 0 < j--;) {
+      // Get prior instruction
+      NodeInfo *Other = Ordering[j];
+      // Should we look further
+      if (Slot >= Other->Slot) break;
+      // Shuffle other into ordering
+      Ordering[j + 1] = Other;
+    }
+    // Insert node in proper slot
+    if (j != i) Ordering[j + 1] = NI;
+  }
+}
+
+/// EmitAll - Emit all nodes in schedule sorted order.
+///
+void ScheduleDAGSimple::EmitAll() {
+  // For each node in the ordering
+  for (unsigned i = 0, N = Ordering.size(); i < N; i++) {
+    // Get the scheduling info
+    NodeInfo *NI = Ordering[i];
+    if (NI->isInGroup()) {
+      NodeGroupIterator NGI(Ordering[i]);
+      while (NodeInfo *NI = NGI.next()) EmitNode(NI);
+    } else {
+      EmitNode(NI);
+    }
+  }
+}
+
+/// Schedule - Order nodes according to selected style.
+///
+void ScheduleDAGSimple::Schedule() {
+  // Number the nodes
+  NodeCount = std::distance(DAG.allnodes_begin(), DAG.allnodes_end());
+  // Test to see if scheduling should occur
+  bool ShouldSchedule = NodeCount > 3 && ScheduleStyle != noScheduling;
+  // Set up minimum info for scheduling
+  PrepareNodeInfo();
+  // Construct node groups for flagged nodes
+  IdentifyGroups();
+
+  // Don't waste time if is only entry and return
+  if (ShouldSchedule) {
+    // Get latency and resource requirements
+    GatherSchedulingInfo();
+  } else if (HasGroups) {
+    // Make sure all the groups have dominators
+    FakeGroupDominators();
+  }
+
+  // Breadth first walk of DAG
+  VisitAll();
+
+#ifndef NDEBUG
+  static unsigned Count = 0;
+  Count++;
+  for (unsigned i = 0, N = Ordering.size(); i < N; i++) {
+    NodeInfo *NI = Ordering[i];
+    NI->Preorder = i;
+  }
+#endif  
+  
+  // Don't waste time if is only entry and return
+  if (ShouldSchedule) {
+    // Push back long instructions and critical path
+    ScheduleBackward();
+    
+    // Pack instructions to maximize resource utilization
+    ScheduleForward();
+  }
+  
+  DEBUG(printChanges(Count));
+  
+  // Emit in scheduled order
+  EmitAll();
+}
+
+/// printChanges - Hilight changes in order caused by scheduling.
+///
+void ScheduleDAGSimple::printChanges(unsigned Index) {
+#ifndef NDEBUG
+  // Get the ordered node count
+  unsigned N = Ordering.size();
+  // Determine if any changes
+  unsigned i = 0;
+  for (; i < N; i++) {
+    NodeInfo *NI = Ordering[i];
+    if (NI->Preorder != i) break;
+  }
+  
+  if (i < N) {
+    std::cerr << Index << ". New Ordering\n";
+    
+    for (i = 0; i < N; i++) {
+      NodeInfo *NI = Ordering[i];
+      std::cerr << "  " << NI->Preorder << ". ";
+      printSI(std::cerr, NI);
+      std::cerr << "\n";
+      if (NI->isGroupDominator()) {
+        NodeGroup *Group = NI->Group;
+        for (NIIterator NII = Group->group_begin(), E = Group->group_end();
+             NII != E; NII++) {
+          std::cerr << "          ";
+          printSI(std::cerr, *NII);
+          std::cerr << "\n";
+        }
+      }
+    }
+  } else {
+    std::cerr << Index << ". No Changes\n";
+  }
+#endif
+}
+
+/// printSI - Print schedule info.
+///
+void ScheduleDAGSimple::printSI(std::ostream &O, NodeInfo *NI) const {
+#ifndef NDEBUG
+  SDNode *Node = NI->Node;
+  O << " "
+    << std::hex << Node << std::dec
+    << ", Lat=" << NI->Latency
+    << ", Slot=" << NI->Slot
+    << ", ARITY=(" << Node->getNumOperands() << ","
+                   << Node->getNumValues() << ")"
+    << " " << Node->getOperationName(&DAG);
+  if (isFlagDefiner(Node)) O << "<#";
+  if (isFlagUser(Node)) O << ">#";
+#endif
+}
+
+/// print - Print ordering to specified output stream.
+///
+void ScheduleDAGSimple::print(std::ostream &O) const {
+#ifndef NDEBUG
+  using namespace std;
+  O << "Ordering\n";
+  for (unsigned i = 0, N = Ordering.size(); i < N; i++) {
+    NodeInfo *NI = Ordering[i];
+    printSI(O, NI);
+    O << "\n";
+    if (NI->isGroupDominator()) {
+      NodeGroup *Group = NI->Group;
+      for (NIIterator NII = Group->group_begin(), E = Group->group_end();
+           NII != E; NII++) {
+        O << "    ";
+        printSI(O, *NII);
+        O << "\n";
+      }
+    }
+  }
+#endif
+}
+
+/// createSimpleDAGScheduler - This creates a simple two pass instruction
+/// scheduler.
+llvm::ScheduleDAG* llvm::createSimpleDAGScheduler(SelectionDAG &DAG,
+                                                  MachineBasicBlock *BB) {
+  return new ScheduleDAGSimple(DAG, BB, DAG.getTarget());
+}