lib/CodeGen/InstrSched/SchedGraph.cpp

//===- SchedGraph.cpp - Scheduling Graph Implementation -------------------===//
// 
//                     The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
// 
//===----------------------------------------------------------------------===//
//
// Scheduling graph based on SSA graph plus extra dependence edges capturing
// dependences due to machine resources (machine registers, CC registers, and
// any others).
//
//===----------------------------------------------------------------------===//

#include "SchedGraph.h"
#include "llvm/Function.h"
#include "llvm/iOther.h"
#include "llvm/CodeGen/MachineCodeForInstruction.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "../../Target/SparcV9/SparcV9RegInfo.h"
#include "Support/STLExtras.h"

namespace llvm {

//*********************** Internal Data Structures *************************/

// The following two types need to be classes, not typedefs, so we can use
// opaque declarations in SchedGraph.h
// 
struct RefVec: public std::vector<std::pair<SchedGraphNode*, int> > {
  typedef std::vector<std::pair<SchedGraphNode*,int> >::iterator iterator;
  typedef
  std::vector<std::pair<SchedGraphNode*,int> >::const_iterator const_iterator;
};

struct RegToRefVecMap: public hash_map<int, RefVec> {
  typedef hash_map<int, RefVec>::      iterator       iterator;
  typedef hash_map<int, RefVec>::const_iterator const_iterator;
};

struct ValueToDefVecMap: public hash_map<const Value*, RefVec> {
  typedef hash_map<const Value*, RefVec>::      iterator       iterator;
  typedef hash_map<const Value*, RefVec>::const_iterator const_iterator;
};


// 
// class SchedGraphNode
// 

SchedGraphNode::SchedGraphNode(unsigned NID, MachineBasicBlock *mbb,
                               int   indexInBB, const TargetMachine& Target)
  : SchedGraphNodeCommon(NID,indexInBB), MBB(mbb), MI(0) {
  if (mbb) {
    MachineBasicBlock::iterator I = MBB->begin();
    std::advance(I, indexInBB);
    MI = I;

    MachineOpCode mopCode = MI->getOpcode();
    latency = Target.getInstrInfo().hasResultInterlock(mopCode)
      ? Target.getInstrInfo().minLatency(mopCode)
      : Target.getInstrInfo().maxLatency(mopCode);
  }
}

//
// Method: SchedGraphNode Destructor
//
// Description:
//	Free memory allocated by the SchedGraphNode object.
//
// Notes:
//	Do not delete the edges here.  The base class will take care of that.
//	Only handle subclass specific stuff here (where currently there is
//	none).
//
SchedGraphNode::~SchedGraphNode() {
}

// 
// class SchedGraph
// 
SchedGraph::SchedGraph(MachineBasicBlock &mbb, const TargetMachine& target)
  : MBB(mbb) {
  buildGraph(target);
}

//
// Method: SchedGraph Destructor
//
// Description:
//	This method deletes memory allocated by the SchedGraph object.
//
// Notes:
//	Do not delete the graphRoot or graphLeaf here.  The base class handles
//	that bit of work.
//
SchedGraph::~SchedGraph() {
  for (const_iterator I = begin(); I != end(); ++I)
    delete I->second;
}

void SchedGraph::dump() const {
  std::cerr << "  Sched Graph for Basic Block: "
            << MBB.getBasicBlock()->getName()
            << " (" << MBB.getBasicBlock() << ")"
            << "\n\n    Actual Root nodes: ";
  for (SchedGraphNodeCommon::const_iterator I = graphRoot->beginOutEdges(),
                                            E = graphRoot->endOutEdges();
       I != E; ++I) {
    std::cerr << (*I)->getSink ()->getNodeId ();
    if (I + 1 != E) { std::cerr << ", "; }
  }
  std::cerr << "\n    Graph Nodes:\n";
  for (const_iterator I = begin(), E = end(); I != E; ++I)
    std::cerr << "\n" << *I->second;
  std::cerr << "\n";
}

void SchedGraph::addDummyEdges() {
  assert(graphRoot->getNumOutEdges() == 0);
  
  for (const_iterator I=begin(); I != end(); ++I) {
    SchedGraphNode* node = (*I).second;
    assert(node != graphRoot && node != graphLeaf);
    if (node->beginInEdges() == node->endInEdges())
      (void) new SchedGraphEdge(graphRoot, node, SchedGraphEdge::CtrlDep,
                                SchedGraphEdge::NonDataDep, 0);
    if (node->beginOutEdges() == node->endOutEdges())
      (void) new SchedGraphEdge(node, graphLeaf, SchedGraphEdge::CtrlDep,
                                SchedGraphEdge::NonDataDep, 0);
  }
}


void SchedGraph::addCDEdges(const TerminatorInst* term,
			    const TargetMachine& target) {
  const TargetInstrInfo& mii = target.getInstrInfo();
  MachineCodeForInstruction &termMvec = MachineCodeForInstruction::get(term);
  
  // Find the first branch instr in the sequence of machine instrs for term
  // 
  unsigned first = 0;
  while (! mii.isBranch(termMvec[first]->getOpcode()) &&
         ! mii.isReturn(termMvec[first]->getOpcode()))
    ++first;
  assert(first < termMvec.size() &&
	 "No branch instructions for terminator?  Ok, but weird!");
  if (first == termMvec.size())
    return;
  
  SchedGraphNode* firstBrNode = getGraphNodeForInstr(termMvec[first]);
  
  // Add CD edges from each instruction in the sequence to the
  // *last preceding* branch instr. in the sequence 
  // Use a latency of 0 because we only need to prevent out-of-order issue.
  // 
  for (unsigned i = termMvec.size(); i > first+1; --i) {
    SchedGraphNode* toNode = getGraphNodeForInstr(termMvec[i-1]);
    assert(toNode && "No node for instr generated for branch/ret?");
    
    for (unsigned j = i-1; j != 0; --j) 
      if (mii.isBranch(termMvec[j-1]->getOpcode()) ||
          mii.isReturn(termMvec[j-1]->getOpcode())) {
        SchedGraphNode* brNode = getGraphNodeForInstr(termMvec[j-1]);
        assert(brNode && "No node for instr generated for branch/ret?");
        (void) new SchedGraphEdge(brNode, toNode, SchedGraphEdge::CtrlDep,
                                  SchedGraphEdge::NonDataDep, 0);
        break;			// only one incoming edge is enough
      }
  }
  
  // Add CD edges from each instruction preceding the first branch
  // to the first branch.  Use a latency of 0 as above.
  // 
  for (unsigned i = first; i != 0; --i) {
    SchedGraphNode* fromNode = getGraphNodeForInstr(termMvec[i-1]);
    assert(fromNode && "No node for instr generated for branch?");
    (void) new SchedGraphEdge(fromNode, firstBrNode, SchedGraphEdge::CtrlDep,
                              SchedGraphEdge::NonDataDep, 0);
  }
  
  // Now add CD edges to the first branch instruction in the sequence from
  // all preceding instructions in the basic block.  Use 0 latency again.
  // 
  for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end(); I != E; ++I){
    if (&*I == termMvec[first])   // reached the first branch
      break;
    
    SchedGraphNode* fromNode = getGraphNodeForInstr(I);
    if (fromNode == NULL)
      continue;			// dummy instruction, e.g., PHI
    
    (void) new SchedGraphEdge(fromNode, firstBrNode,
                              SchedGraphEdge::CtrlDep,
                              SchedGraphEdge::NonDataDep, 0);
      
    // If we find any other machine instructions (other than due to
    // the terminator) that also have delay slots, add an outgoing edge
    // from the instruction to the instructions in the delay slots.
    // 
    unsigned d = mii.getNumDelaySlots(I->getOpcode());

    MachineBasicBlock::iterator J = I; ++J;
    for (unsigned j=1; j <= d; j++, ++J) {
      SchedGraphNode* toNode = this->getGraphNodeForInstr(J);
      assert(toNode && "No node for machine instr in delay slot?");
      (void) new SchedGraphEdge(fromNode, toNode,
                                SchedGraphEdge::CtrlDep,
                                SchedGraphEdge::NonDataDep, 0);
    }
  }
}

static const int SG_LOAD_REF  = 0;
static const int SG_STORE_REF = 1;
static const int SG_CALL_REF  = 2;

static const unsigned int SG_DepOrderArray[][3] = {
  { SchedGraphEdge::NonDataDep,
    SchedGraphEdge::AntiDep,
    SchedGraphEdge::AntiDep },
  { SchedGraphEdge::TrueDep,
    SchedGraphEdge::OutputDep,
    SchedGraphEdge::TrueDep | SchedGraphEdge::OutputDep },
  { SchedGraphEdge::TrueDep,
    SchedGraphEdge::AntiDep | SchedGraphEdge::OutputDep,
    SchedGraphEdge::TrueDep | SchedGraphEdge::AntiDep
    | SchedGraphEdge::OutputDep }
};


// Add a dependence edge between every pair of machine load/store/call
// instructions, where at least one is a store or a call.
// Use latency 1 just to ensure that memory operations are ordered;
// latency does not otherwise matter (true dependences enforce that).
// 
void SchedGraph::addMemEdges(const std::vector<SchedGraphNode*>& memNodeVec,
			     const TargetMachine& target) {
  const TargetInstrInfo& mii = target.getInstrInfo();
  
  // Instructions in memNodeVec are in execution order within the basic block,
  // so simply look at all pairs <memNodeVec[i], memNodeVec[j: j > i]>.
  // 
  for (unsigned im=0, NM=memNodeVec.size(); im < NM; im++) {
    MachineOpCode fromOpCode = memNodeVec[im]->getOpcode();
    int fromType = (mii.isCall(fromOpCode)? SG_CALL_REF
                    : (mii.isLoad(fromOpCode)? SG_LOAD_REF
                       : SG_STORE_REF));
    for (unsigned jm=im+1; jm < NM; jm++) {
      MachineOpCode toOpCode = memNodeVec[jm]->getOpcode();
      int toType = (mii.isCall(toOpCode)? SG_CALL_REF
                    : (mii.isLoad(toOpCode)? SG_LOAD_REF
                       : SG_STORE_REF));
      
      if (fromType != SG_LOAD_REF || toType != SG_LOAD_REF)
        (void) new SchedGraphEdge(memNodeVec[im], memNodeVec[jm],
                                  SchedGraphEdge::MemoryDep,
                                  SG_DepOrderArray[fromType][toType], 1);
    }
  }
} 

// Add edges from/to CC reg instrs to/from call instrs.
// Essentially this prevents anything that sets or uses a CC reg from being
// reordered w.r.t. a call.
// Use a latency of 0 because we only need to prevent out-of-order issue,
// like with control dependences.
// 
void SchedGraph::addCallDepEdges(const std::vector<SchedGraphNode*>& callDepNodeVec,
				 const TargetMachine& target) {
  const TargetInstrInfo& mii = target.getInstrInfo();
  
  // Instructions in memNodeVec are in execution order within the basic block,
  // so simply look at all pairs <memNodeVec[i], memNodeVec[j: j > i]>.
  // 
  for (unsigned ic=0, NC=callDepNodeVec.size(); ic < NC; ic++)
    if (mii.isCall(callDepNodeVec[ic]->getOpcode())) {
      // Add SG_CALL_REF edges from all preds to this instruction.
      for (unsigned jc=0; jc < ic; jc++)
	(void) new SchedGraphEdge(callDepNodeVec[jc], callDepNodeVec[ic],
				  SchedGraphEdge::MachineRegister,
				  MachineIntRegsRID,  0);
      
      // And do the same from this instruction to all successors.
      for (unsigned jc=ic+1; jc < NC; jc++)
	(void) new SchedGraphEdge(callDepNodeVec[ic], callDepNodeVec[jc],
				  SchedGraphEdge::MachineRegister,
				  MachineIntRegsRID,  0);
    }
  
#ifdef CALL_DEP_NODE_VEC_CANNOT_WORK
  // Find the call instruction nodes and put them in a vector.
  std::vector<SchedGraphNode*> callNodeVec;
  for (unsigned im=0, NM=memNodeVec.size(); im < NM; im++)
    if (mii.isCall(memNodeVec[im]->getOpcode()))
      callNodeVec.push_back(memNodeVec[im]);
  
  // Now walk the entire basic block, looking for CC instructions *and*
  // call instructions, and keep track of the order of the instructions.
  // Use the call node vec to quickly find earlier and later call nodes
  // relative to the current CC instruction.
  // 
  int lastCallNodeIdx = -1;
  for (unsigned i=0, N=bbMvec.size(); i < N; i++)
    if (mii.isCall(bbMvec[i]->getOpcode())) {
      ++lastCallNodeIdx;
      for ( ; lastCallNodeIdx < (int)callNodeVec.size(); ++lastCallNodeIdx)
        if (callNodeVec[lastCallNodeIdx]->getMachineInstr() == bbMvec[i])
          break;
      assert(lastCallNodeIdx < (int)callNodeVec.size() && "Missed Call?");
    }
    else if (mii.isCCInstr(bbMvec[i]->getOpcode())) {
      // Add incoming/outgoing edges from/to preceding/later calls
      SchedGraphNode* ccNode = this->getGraphNodeForInstr(bbMvec[i]);
      int j=0;
      for ( ; j <= lastCallNodeIdx; j++)
        (void) new SchedGraphEdge(callNodeVec[j], ccNode,
                                  MachineCCRegsRID, 0);
      for ( ; j < (int) callNodeVec.size(); j++)
        (void) new SchedGraphEdge(ccNode, callNodeVec[j],
                                  MachineCCRegsRID, 0);
    }
#endif
}


void SchedGraph::addMachineRegEdges(RegToRefVecMap& regToRefVecMap,
				    const TargetMachine& target) {
  // This code assumes that two registers with different numbers are
  // not aliased!
  // 
  for (RegToRefVecMap::iterator I = regToRefVecMap.begin();
       I != regToRefVecMap.end(); ++I) {
    int regNum        = (*I).first;
    RefVec& regRefVec = (*I).second;
    
    // regRefVec is ordered by control flow order in the basic block
    for (unsigned i=0; i < regRefVec.size(); ++i) {
      SchedGraphNode* node = regRefVec[i].first;
      unsigned int opNum   = regRefVec[i].second;
      const MachineOperand& mop =
        node->getMachineInstr()->getExplOrImplOperand(opNum);
      bool isDef = mop.isDef() && !mop.isUse();
      bool isDefAndUse = mop.isDef() && mop.isUse();
          
      for (unsigned p=0; p < i; ++p) {
        SchedGraphNode* prevNode = regRefVec[p].first;
        if (prevNode != node) {
          unsigned int prevOpNum = regRefVec[p].second;
          const MachineOperand& prevMop =
            prevNode->getMachineInstr()->getExplOrImplOperand(prevOpNum);
          bool prevIsDef = prevMop.isDef() && !prevMop.isUse();
          bool prevIsDefAndUse = prevMop.isDef() && prevMop.isUse();
          if (isDef) {
            if (prevIsDef)
              new SchedGraphEdge(prevNode, node, regNum,
                                 SchedGraphEdge::OutputDep);
            if (!prevIsDef || prevIsDefAndUse)
              new SchedGraphEdge(prevNode, node, regNum,
                                 SchedGraphEdge::AntiDep);
          }
	  
          if (prevIsDef)
            if (!isDef || isDefAndUse)
              new SchedGraphEdge(prevNode, node, regNum,
                                 SchedGraphEdge::TrueDep);
        }
      }
    }
  }
}


// Adds dependences to/from refNode from/to all other defs
// in the basic block.  refNode may be a use, a def, or both.
// We do not consider other uses because we are not building use-use deps.
// 
void SchedGraph::addEdgesForValue(SchedGraphNode* refNode,
				  const RefVec& defVec,
				  const Value* defValue,
				  bool  refNodeIsDef,
				  bool  refNodeIsUse,
				  const TargetMachine& target) {
  // Add true or output dep edges from all def nodes before refNode in BB.
  // Add anti or output dep edges to all def nodes after refNode.
  for (RefVec::const_iterator I=defVec.begin(), E=defVec.end(); I != E; ++I) {
    if ((*I).first == refNode)
      continue;                       // Dont add any self-loops
    
    if ((*I).first->getOrigIndexInBB() < refNode->getOrigIndexInBB()) {
      // (*).first is before refNode
      if (refNodeIsDef && !refNodeIsUse)
        (void) new SchedGraphEdge((*I).first, refNode, defValue,
                                  SchedGraphEdge::OutputDep);
      if (refNodeIsUse)
        (void) new SchedGraphEdge((*I).first, refNode, defValue,
                                  SchedGraphEdge::TrueDep);
    } else {
      // (*).first is after refNode
      if (refNodeIsDef && !refNodeIsUse)
        (void) new SchedGraphEdge(refNode, (*I).first, defValue,
                                  SchedGraphEdge::OutputDep);
      if (refNodeIsUse)
        (void) new SchedGraphEdge(refNode, (*I).first, defValue,
                                  SchedGraphEdge::AntiDep);
    }
  }
}


void SchedGraph::addEdgesForInstruction(const MachineInstr& MI,
					const ValueToDefVecMap& valueToDefVecMap,
					const TargetMachine& target) {
  SchedGraphNode* node = getGraphNodeForInstr(&MI);
  if (node == NULL)
    return;
  
  // Add edges for all operands of the machine instruction.
  // 
  for (unsigned i = 0, numOps = MI.getNumOperands(); i != numOps; ++i) {
    switch (MI.getOperand(i).getType()) {
    case MachineOperand::MO_VirtualRegister:
    case MachineOperand::MO_CCRegister:
      if (const Value* srcI = MI.getOperand(i).getVRegValue()) {
        ValueToDefVecMap::const_iterator I = valueToDefVecMap.find(srcI);
        if (I != valueToDefVecMap.end())
          addEdgesForValue(node, I->second, srcI,
                           MI.getOperand(i).isDef(), MI.getOperand(i).isUse(),
                           target);
      }
      break;
      
    case MachineOperand::MO_MachineRegister:
      break; 
      
    case MachineOperand::MO_SignExtendedImmed:
    case MachineOperand::MO_UnextendedImmed:
    case MachineOperand::MO_PCRelativeDisp:
    case MachineOperand::MO_ConstantPoolIndex:
      break;	// nothing to do for immediate fields
      
    default:
      assert(0 && "Unknown machine operand type in SchedGraph builder");
      break;
    }
  }
  
  // Add edges for values implicitly used by the machine instruction.
  // Examples include function arguments to a Call instructions or the return
  // value of a Ret instruction.
  // 
  for (unsigned i=0, N=MI.getNumImplicitRefs(); i < N; ++i)
    if (MI.getImplicitOp(i).isUse())
      if (const Value* srcI = MI.getImplicitRef(i)) {
        ValueToDefVecMap::const_iterator I = valueToDefVecMap.find(srcI);
        if (I != valueToDefVecMap.end())
          addEdgesForValue(node, I->second, srcI,
                           MI.getImplicitOp(i).isDef(),
                           MI.getImplicitOp(i).isUse(), target);
      }
}


void SchedGraph::findDefUseInfoAtInstr(const TargetMachine& target,
				       SchedGraphNode* node,
				       std::vector<SchedGraphNode*>& memNodeVec,
				       std::vector<SchedGraphNode*>& callDepNodeVec,
				       RegToRefVecMap& regToRefVecMap,
				       ValueToDefVecMap& valueToDefVecMap) {
  const TargetInstrInfo& mii = target.getInstrInfo();
  
  MachineOpCode opCode = node->getOpcode();
  
  if (mii.isCall(opCode) || mii.isCCInstr(opCode))
    callDepNodeVec.push_back(node);
  
  if (mii.isLoad(opCode) || mii.isStore(opCode) || mii.isCall(opCode))
    memNodeVec.push_back(node);
  
  // Collect the register references and value defs. for explicit operands
  // 
  const MachineInstr& MI = *node->getMachineInstr();
  for (int i=0, numOps = (int) MI.getNumOperands(); i < numOps; i++) {
    const MachineOperand& mop = MI.getOperand(i);
    
    // if this references a register other than the hardwired
    // "zero" register, record the reference.
    if (mop.hasAllocatedReg()) {
      unsigned regNum = mop.getReg();
      
      // If this is not a dummy zero register, record the reference in order
      if (regNum != target.getRegInfo().getZeroRegNum())
        regToRefVecMap[mop.getReg()]
          .push_back(std::make_pair(node, i));

      // If this is a volatile register, add the instruction to callDepVec
      // (only if the node is not already on the callDepVec!)
      if (callDepNodeVec.size() == 0 || callDepNodeVec.back() != node)
        {
          unsigned rcid;
          int regInClass = target.getRegInfo().getClassRegNum(regNum, rcid);
          if (target.getRegInfo().getMachineRegClass(rcid)
              ->isRegVolatile(regInClass))
            callDepNodeVec.push_back(node);
        }
          
      continue;                     // nothing more to do
    }
    
    // ignore all other non-def operands
    if (!MI.getOperand(i).isDef())
      continue;
      
    // We must be defining a value.
    assert((mop.getType() == MachineOperand::MO_VirtualRegister ||
            mop.getType() == MachineOperand::MO_CCRegister)
           && "Do not expect any other kind of operand to be defined!");
    assert(mop.getVRegValue() != NULL && "Null value being defined?");
    
    valueToDefVecMap[mop.getVRegValue()].push_back(std::make_pair(node, i)); 
  }
  
  // 
  // Collect value defs. for implicit operands.  They may have allocated
  // physical registers also.
  // 
  for (unsigned i=0, N = MI.getNumImplicitRefs(); i != N; ++i) {
    const MachineOperand& mop = MI.getImplicitOp(i);
    if (mop.hasAllocatedReg()) {
      unsigned regNum = mop.getReg();
      if (regNum != target.getRegInfo().getZeroRegNum())
        regToRefVecMap[mop.getReg()]
          .push_back(std::make_pair(node, i + MI.getNumOperands()));
      continue;                     // nothing more to do
    }

    if (mop.isDef()) {
      assert(MI.getImplicitRef(i) != NULL && "Null value being defined?");
      valueToDefVecMap[MI.getImplicitRef(i)].push_back(
        std::make_pair(node, -i)); 
    }
  }
}


void SchedGraph::buildNodesForBB(const TargetMachine& target,
				 MachineBasicBlock& MBB,
				 std::vector<SchedGraphNode*>& memNodeVec,
				 std::vector<SchedGraphNode*>& callDepNodeVec,
				 RegToRefVecMap& regToRefVecMap,
				 ValueToDefVecMap& valueToDefVecMap) {
  const TargetInstrInfo& mii = target.getInstrInfo();
  
  // Build graph nodes for each VM instruction and gather def/use info.
  // Do both those together in a single pass over all machine instructions.
  unsigned i = 0;
  for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end(); I != E;
       ++I, ++i)
    if (!mii.isDummyPhiInstr(I->getOpcode())) {
      SchedGraphNode* node = new SchedGraphNode(getNumNodes(), &MBB, i, target);
      noteGraphNodeForInstr(I, node);
      
      // Remember all register references and value defs
      findDefUseInfoAtInstr(target, node, memNodeVec, callDepNodeVec,
                            regToRefVecMap, valueToDefVecMap);
    }
}


void SchedGraph::buildGraph(const TargetMachine& target) {
  // Use this data structure to note all machine operands that compute
  // ordinary LLVM values.  These must be computed defs (i.e., instructions). 
  // Note that there may be multiple machine instructions that define
  // each Value.
  ValueToDefVecMap valueToDefVecMap;
  
  // Use this data structure to note all memory instructions.
  // We use this to add memory dependence edges without a second full walk.
  std::vector<SchedGraphNode*> memNodeVec;

  // Use this data structure to note all instructions that access physical
  // registers that can be modified by a call (including call instructions)
  std::vector<SchedGraphNode*> callDepNodeVec;
  
  // Use this data structure to note any uses or definitions of
  // machine registers so we can add edges for those later without
  // extra passes over the nodes.
  // The vector holds an ordered list of references to the machine reg,
  // ordered according to control-flow order.  This only works for a
  // single basic block, hence the assertion.  Each reference is identified
  // by the pair: <node, operand-number>.
  // 
  RegToRefVecMap regToRefVecMap;
  
  // Make a dummy root node.  We'll add edges to the real roots later.
  graphRoot = new SchedGraphNode(0, NULL, -1, target);
  graphLeaf = new SchedGraphNode(1, NULL, -1, target);

  //----------------------------------------------------------------
  // First add nodes for all the machine instructions in the basic block
  // because this greatly simplifies identifying which edges to add.
  // Do this one VM instruction at a time since the SchedGraphNode needs that.
  // Also, remember the load/store instructions to add memory deps later.
  //----------------------------------------------------------------

  buildNodesForBB(target, MBB, memNodeVec, callDepNodeVec,
                  regToRefVecMap, valueToDefVecMap);
  
  //----------------------------------------------------------------
  // Now add edges for the following (all are incoming edges except (4)):
  // (1) operands of the machine instruction, including hidden operands
  // (2) machine register dependences
  // (3) memory load/store dependences
  // (3) other resource dependences for the machine instruction, if any
  // (4) output dependences when multiple machine instructions define the
  //     same value; all must have been generated from a single VM instrn
  // (5) control dependences to branch instructions generated for the
  //     terminator instruction of the BB. Because of delay slots and
  //     2-way conditional branches, multiple CD edges are needed
  //     (see addCDEdges for details).
  // Also, note any uses or defs of machine registers.
  // 
  //----------------------------------------------------------------
      
  // First, add edges to the terminator instruction of the basic block.
  this->addCDEdges(MBB.getBasicBlock()->getTerminator(), target);
      
  // Then add memory dep edges: store->load, load->store, and store->store.
  // Call instructions are treated as both load and store.
  this->addMemEdges(memNodeVec, target);

  // Then add edges between call instructions and CC set/use instructions
  this->addCallDepEdges(callDepNodeVec, target);
  
  // Then add incoming def-use (SSA) edges for each machine instruction.
  for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end(); I != E; ++I)
    addEdgesForInstruction(*I, valueToDefVecMap, target);

  // Then add edges for dependences on machine registers
  this->addMachineRegEdges(regToRefVecMap, target);

  // Finally, add edges from the dummy root and to dummy leaf
  this->addDummyEdges();		
}


// 
// class SchedGraphSet
// 
SchedGraphSet::SchedGraphSet(const Function* _function,
			     const TargetMachine& target) :
  function(_function) {
  buildGraphsForMethod(function, target);
}

SchedGraphSet::~SchedGraphSet() {
  // delete all the graphs
  for(iterator I = begin(), E = end(); I != E; ++I)
    delete *I;  // destructor is a friend
}


void SchedGraphSet::dump() const {
  std::cerr << "======== Sched graphs for function `" << function->getName()
            << "' ========\n\n";
  
  for (const_iterator I=begin(); I != end(); ++I)
    (*I)->dump();
  
  std::cerr << "\n====== End graphs for function `" << function->getName()
            << "' ========\n\n";
}


void SchedGraphSet::buildGraphsForMethod(const Function *F,
					 const TargetMachine& target) {
  MachineFunction &MF = MachineFunction::get(F);
  for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
    addGraph(new SchedGraph(*I, target));
}


void SchedGraphEdge::print(std::ostream &os) const {
  os << "edge [" << src->getNodeId() << "] -> ["
     << sink->getNodeId() << "] : ";
  
  switch(depType) {
  case SchedGraphEdge::CtrlDep:		
    os<< "Control Dep"; 
    break;
  case SchedGraphEdge::ValueDep:        
    os<< "Reg Value " << val; 
    break;
  case SchedGraphEdge::MemoryDep:	
    os<< "Memory Dep"; 
    break;
  case SchedGraphEdge::MachineRegister: 
    os<< "Reg " << machineRegNum;
    break;
  case SchedGraphEdge::MachineResource:
    os<<"Resource "<< resourceId;
    break;
  default: 
    assert(0); 
    break;
  }
  
  os << " : delay = " << minDelay << "\n";
}

void SchedGraphNode::print(std::ostream &os) const {
  os << std::string(8, ' ')
     << "Node " << ID << " : "
     << "latency = " << latency << "\n" << std::string(12, ' ');
  
  if (getMachineInstr() == NULL)
    os << "(Dummy node)\n";
  else {
    os << *getMachineInstr() << "\n" << std::string(12, ' ');
    os << inEdges.size() << " Incoming Edges:\n";
    for (unsigned i=0, N = inEdges.size(); i < N; i++)
      os << std::string(16, ' ') << *inEdges[i];
  
    os << std::string(12, ' ') << outEdges.size()
       << " Outgoing Edges:\n";
    for (unsigned i=0, N= outEdges.size(); i < N; i++)
      os << std::string(16, ' ') << *outEdges[i];
  }
}

} // End llvm namespace