lib/CodeGen/SelectionDAG/SelectionDAG.cpp

//===-- SelectionDAG.cpp - Implement the SelectionDAG data structures -----===//
// 
//                     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.
// 
//===----------------------------------------------------------------------===//
//
// This implements the SelectionDAG class.
//
//===----------------------------------------------------------------------===//

#include "llvm/CodeGen/SelectionDAG.h"
#include "llvm/Constants.h"
#include "llvm/GlobalValue.h"
#include "llvm/Assembly/Writer.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include <iostream>
#include <set>
#include <cmath>
#include <algorithm>
using namespace llvm;

static bool isCommutativeBinOp(unsigned Opcode) {
  switch (Opcode) {
  case ISD::ADD:
  case ISD::MUL:
  case ISD::AND:
  case ISD::OR:
  case ISD::XOR: return true;
  default: return false; // FIXME: Need commutative info for user ops!
  }
}

static bool isAssociativeBinOp(unsigned Opcode) {
  switch (Opcode) {
  case ISD::ADD:
  case ISD::MUL:
  case ISD::AND:
  case ISD::OR:
  case ISD::XOR: return true;
  default: return false; // FIXME: Need associative info for user ops!
  }
}

static unsigned ExactLog2(uint64_t Val) {
  unsigned Count = 0;
  while (Val != 1) {
    Val >>= 1;
    ++Count;
  }
  return Count;
}

// isInvertibleForFree - Return true if there is no cost to emitting the logical
// inverse of this node.
static bool isInvertibleForFree(SDOperand N) {
  if (isa<ConstantSDNode>(N.Val)) return true;
  if (isa<SetCCSDNode>(N.Val) && N.Val->hasOneUse())
    return true;
  return false;  
}


/// getSetCCSwappedOperands - Return the operation corresponding to (Y op X)
/// when given the operation for (X op Y).
ISD::CondCode ISD::getSetCCSwappedOperands(ISD::CondCode Operation) {
  // To perform this operation, we just need to swap the L and G bits of the
  // operation.
  unsigned OldL = (Operation >> 2) & 1;
  unsigned OldG = (Operation >> 1) & 1;
  return ISD::CondCode((Operation & ~6) |  // Keep the N, U, E bits
                       (OldL << 1) |       // New G bit
                       (OldG << 2));        // New L bit.
}

/// getSetCCInverse - Return the operation corresponding to !(X op Y), where
/// 'op' is a valid SetCC operation.
ISD::CondCode ISD::getSetCCInverse(ISD::CondCode Op, bool isInteger) {
  unsigned Operation = Op;
  if (isInteger)
    Operation ^= 7;   // Flip L, G, E bits, but not U.
  else
    Operation ^= 15;  // Flip all of the condition bits.
  if (Operation > ISD::SETTRUE2)
    Operation &= ~8;     // Don't let N and U bits get set.
  return ISD::CondCode(Operation);
}


/// isSignedOp - For an integer comparison, return 1 if the comparison is a
/// signed operation and 2 if the result is an unsigned comparison.  Return zero
/// if the operation does not depend on the sign of the input (setne and seteq).
static int isSignedOp(ISD::CondCode Opcode) {
  switch (Opcode) {
  default: assert(0 && "Illegal integer setcc operation!");
  case ISD::SETEQ:
  case ISD::SETNE: return 0;
  case ISD::SETLT:
  case ISD::SETLE:
  case ISD::SETGT:
  case ISD::SETGE: return 1;
  case ISD::SETULT:
  case ISD::SETULE:
  case ISD::SETUGT:
  case ISD::SETUGE: return 2;
  }
}

/// getSetCCOrOperation - Return the result of a logical OR between different
/// comparisons of identical values: ((X op1 Y) | (X op2 Y)).  This function
/// returns SETCC_INVALID if it is not possible to represent the resultant
/// comparison.
ISD::CondCode ISD::getSetCCOrOperation(ISD::CondCode Op1, ISD::CondCode Op2,
                                       bool isInteger) {
  if (isInteger && (isSignedOp(Op1) | isSignedOp(Op2)) == 3)
    // Cannot fold a signed integer setcc with an unsigned integer setcc.
    return ISD::SETCC_INVALID;
  
  unsigned Op = Op1 | Op2;  // Combine all of the condition bits.
  
  // If the N and U bits get set then the resultant comparison DOES suddenly
  // care about orderedness, and is true when ordered.
  if (Op > ISD::SETTRUE2)
    Op &= ~16;     // Clear the N bit.
  return ISD::CondCode(Op);
}

/// getSetCCAndOperation - Return the result of a logical AND between different
/// comparisons of identical values: ((X op1 Y) & (X op2 Y)).  This
/// function returns zero if it is not possible to represent the resultant
/// comparison.
ISD::CondCode ISD::getSetCCAndOperation(ISD::CondCode Op1, ISD::CondCode Op2,
                                        bool isInteger) {
  if (isInteger && (isSignedOp(Op1) | isSignedOp(Op2)) == 3)
    // Cannot fold a signed setcc with an unsigned setcc.
    return ISD::SETCC_INVALID; 

  // Combine all of the condition bits.
  return ISD::CondCode(Op1 & Op2);
}

/// RemoveDeadNodes - This method deletes all unreachable nodes in the
/// SelectionDAG, including nodes (like loads) that have uses of their token
/// chain but no other uses and no side effect.  If a node is passed in as an
/// argument, it is used as the seed for node deletion.
void SelectionDAG::RemoveDeadNodes(SDNode *N) {
  std::set<SDNode*> AllNodeSet(AllNodes.begin(), AllNodes.end());

  // Create a dummy node (which is not added to allnodes), that adds a reference
  // to the root node, preventing it from being deleted.
  SDNode *DummyNode = new SDNode(ISD::EntryToken, getRoot());

  DeleteNodeIfDead(N, &AllNodeSet);

 Restart:
  unsigned NumNodes = AllNodeSet.size();
  for (std::set<SDNode*>::iterator I = AllNodeSet.begin(), E = AllNodeSet.end();
       I != E; ++I) {
    // Try to delete this node.
    DeleteNodeIfDead(*I, &AllNodeSet);

    // If we actually deleted any nodes, do not use invalid iterators in
    // AllNodeSet.
    if (AllNodeSet.size() != NumNodes)
      goto Restart;
  }

  // Restore AllNodes.
  if (AllNodes.size() != NumNodes)
    AllNodes.assign(AllNodeSet.begin(), AllNodeSet.end());

  // If the root changed (e.g. it was a dead load, update the root).
  setRoot(DummyNode->getOperand(0));

  // Now that we are done with the dummy node, delete it.
  DummyNode->getOperand(0).Val->removeUser(DummyNode);
  delete DummyNode;
}

void SelectionDAG::DeleteNodeIfDead(SDNode *N, void *NodeSet) {
  if (!N->use_empty())
    return;

  // Okay, we really are going to delete this node.  First take this out of the
  // appropriate CSE map.
  switch (N->getOpcode()) {
  case ISD::Constant:
    Constants.erase(std::make_pair(cast<ConstantSDNode>(N)->getValue(),
                                   N->getValueType(0)));
    break;
  case ISD::ConstantFP:
    ConstantFPs.erase(std::make_pair(cast<ConstantFPSDNode>(N)->getValue(),
                                     N->getValueType(0)));
    break;
  case ISD::GlobalAddress:
    GlobalValues.erase(cast<GlobalAddressSDNode>(N)->getGlobal());
    break;
  case ISD::FrameIndex:
    FrameIndices.erase(cast<FrameIndexSDNode>(N)->getIndex());
    break;
  case ISD::ConstantPool:
    ConstantPoolIndices.erase(cast<ConstantPoolSDNode>(N)->getIndex());
    break;
  case ISD::BasicBlock:
    BBNodes.erase(cast<BasicBlockSDNode>(N)->getBasicBlock());
    break;
  case ISD::ExternalSymbol:
    ExternalSymbols.erase(cast<ExternalSymbolSDNode>(N)->getSymbol());
    break;

  case ISD::LOAD:
    Loads.erase(std::make_pair(N->getOperand(1),
                               std::make_pair(N->getOperand(0),
                                              N->getValueType(0))));
    break;
  case ISD::SETCC:
    SetCCs.erase(std::make_pair(std::make_pair(N->getOperand(0),
                                               N->getOperand(1)),
                                cast<SetCCSDNode>(N)->getCondition()));
    break;
  case ISD::TRUNCSTORE:
  case ISD::SIGN_EXTEND_INREG:
  case ISD::ZERO_EXTEND_INREG:
  case ISD::FP_ROUND_INREG:
  case ISD::EXTLOAD:
  case ISD::SEXTLOAD:
  case ISD::ZEXTLOAD: {
    EVTStruct NN;
    NN.Opcode = ISD::TRUNCSTORE;
    NN.VT = N->getValueType(0);
    NN.EVT = cast<MVTSDNode>(N)->getExtraValueType();
    for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i)
      NN.Ops.push_back(N->getOperand(i));
    MVTSDNodes.erase(NN);
    break;
  }
  default:
    if (N->getNumOperands() == 1)
      UnaryOps.erase(std::make_pair(N->getOpcode(),
                                    std::make_pair(N->getOperand(0),
                                                   N->getValueType(0))));
    else if (N->getNumOperands() == 2)
      BinaryOps.erase(std::make_pair(N->getOpcode(),
                                     std::make_pair(N->getOperand(0),
                                                    N->getOperand(1))));
    break;
  }

  // Next, brutally remove the operand list.
  while (!N->Operands.empty()) {
    SDNode *O = N->Operands.back().Val;
    N->Operands.pop_back();
    O->removeUser(N);

    // Now that we removed this operand, see if there are no uses of it left.
    DeleteNodeIfDead(O, NodeSet);
  }
  
  // Remove the node from the nodes set and delete it.
  std::set<SDNode*> &AllNodeSet = *(std::set<SDNode*>*)NodeSet;
  AllNodeSet.erase(N);

  // Now that the node is gone, check to see if any of the operands of this node
  // are dead now.
  delete N;
}


SelectionDAG::~SelectionDAG() {
  for (unsigned i = 0, e = AllNodes.size(); i != e; ++i)
    delete AllNodes[i];
}

SDOperand SelectionDAG::getConstant(uint64_t Val, MVT::ValueType VT) {
  assert(MVT::isInteger(VT) && "Cannot create FP integer constant!");
  // Mask out any bits that are not valid for this constant.
  if (VT != MVT::i64)
    Val &= ((uint64_t)1 << MVT::getSizeInBits(VT)) - 1;
  
  SDNode *&N = Constants[std::make_pair(Val, VT)];
  if (N) return SDOperand(N, 0);
  N = new ConstantSDNode(Val, VT);
  AllNodes.push_back(N);
  return SDOperand(N, 0);
}

SDOperand SelectionDAG::getConstantFP(double Val, MVT::ValueType VT) {
  assert(MVT::isFloatingPoint(VT) && "Cannot create integer FP constant!");
  if (VT == MVT::f32)
    Val = (float)Val;  // Mask out extra precision.

  SDNode *&N = ConstantFPs[std::make_pair(Val, VT)];
  if (N) return SDOperand(N, 0);
  N = new ConstantFPSDNode(Val, VT);
  AllNodes.push_back(N);
  return SDOperand(N, 0);
}



SDOperand SelectionDAG::getGlobalAddress(const GlobalValue *GV,
                                         MVT::ValueType VT) {
  SDNode *&N = GlobalValues[GV];
  if (N) return SDOperand(N, 0);
  N = new GlobalAddressSDNode(GV,VT);
  AllNodes.push_back(N);
  return SDOperand(N, 0);
}

SDOperand SelectionDAG::getFrameIndex(int FI, MVT::ValueType VT) {
  SDNode *&N = FrameIndices[FI];
  if (N) return SDOperand(N, 0);
  N = new FrameIndexSDNode(FI, VT);
  AllNodes.push_back(N);
  return SDOperand(N, 0);
}

SDOperand SelectionDAG::getConstantPool(unsigned CPIdx, MVT::ValueType VT) {
  SDNode *N = ConstantPoolIndices[CPIdx];
  if (N) return SDOperand(N, 0);
  N = new ConstantPoolSDNode(CPIdx, VT);
  AllNodes.push_back(N);
  return SDOperand(N, 0);
}

SDOperand SelectionDAG::getBasicBlock(MachineBasicBlock *MBB) {
  SDNode *&N = BBNodes[MBB];
  if (N) return SDOperand(N, 0);
  N = new BasicBlockSDNode(MBB);
  AllNodes.push_back(N);
  return SDOperand(N, 0);
}

SDOperand SelectionDAG::getExternalSymbol(const char *Sym, MVT::ValueType VT) {
  SDNode *&N = ExternalSymbols[Sym];
  if (N) return SDOperand(N, 0);
  N = new ExternalSymbolSDNode(Sym, VT);
  AllNodes.push_back(N);
  return SDOperand(N, 0);
}

SDOperand SelectionDAG::getSetCC(ISD::CondCode Cond, SDOperand N1,
                                 SDOperand N2) {
  // These setcc operations always fold.
  switch (Cond) {
  default: break;
  case ISD::SETFALSE:
  case ISD::SETFALSE2: return getConstant(0, MVT::i1);
  case ISD::SETTRUE:
  case ISD::SETTRUE2:  return getConstant(1, MVT::i1);
  }

  if (ConstantSDNode *N1C = dyn_cast<ConstantSDNode>(N1.Val))
    if (ConstantSDNode *N2C = dyn_cast<ConstantSDNode>(N2.Val)) {
      uint64_t C1 = N1C->getValue(), C2 = N2C->getValue();
      
      // Sign extend the operands if required
      if (ISD::isSignedIntSetCC(Cond)) {
        C1 = N1C->getSignExtended();
        C2 = N2C->getSignExtended();
      }

      switch (Cond) {
      default: assert(0 && "Unknown integer setcc!");
      case ISD::SETEQ:  return getConstant(C1 == C2, MVT::i1);
      case ISD::SETNE:  return getConstant(C1 != C2, MVT::i1);
      case ISD::SETULT: return getConstant(C1 <  C2, MVT::i1);
      case ISD::SETUGT: return getConstant(C1 >  C2, MVT::i1);
      case ISD::SETULE: return getConstant(C1 <= C2, MVT::i1);
      case ISD::SETUGE: return getConstant(C1 >= C2, MVT::i1);
      case ISD::SETLT:  return getConstant((int64_t)C1 <  (int64_t)C2, MVT::i1);
      case ISD::SETGT:  return getConstant((int64_t)C1 >  (int64_t)C2, MVT::i1);
      case ISD::SETLE:  return getConstant((int64_t)C1 <= (int64_t)C2, MVT::i1);
      case ISD::SETGE:  return getConstant((int64_t)C1 >= (int64_t)C2, MVT::i1);
      }
    } else {
      // Ensure that the constant occurs on the RHS.
      Cond = ISD::getSetCCSwappedOperands(Cond);
      std::swap(N1, N2);
    }

  if (ConstantFPSDNode *N1C = dyn_cast<ConstantFPSDNode>(N1.Val))
    if (ConstantFPSDNode *N2C = dyn_cast<ConstantFPSDNode>(N2.Val)) {
      double C1 = N1C->getValue(), C2 = N2C->getValue();
      
      switch (Cond) {
      default: break; // FIXME: Implement the rest of these!
      case ISD::SETEQ:  return getConstant(C1 == C2, MVT::i1);
      case ISD::SETNE:  return getConstant(C1 != C2, MVT::i1);
      case ISD::SETLT:  return getConstant((int64_t)C1 < (int64_t)C2, MVT::i1);
      case ISD::SETGT:  return getConstant((int64_t)C1 < (int64_t)C2, MVT::i1);
      case ISD::SETLE:  return getConstant((int64_t)C1 < (int64_t)C2, MVT::i1);
      case ISD::SETGE:  return getConstant((int64_t)C1 < (int64_t)C2, MVT::i1);
      }
    } else {
      // Ensure that the constant occurs on the RHS.
      Cond = ISD::getSetCCSwappedOperands(Cond);
      std::swap(N1, N2);
    }

  if (N1 == N2) {
    // We can always fold X == Y for integer setcc's.
    if (MVT::isInteger(N1.getValueType()))
      return getConstant(ISD::isTrueWhenEqual(Cond), MVT::i1);
    unsigned UOF = ISD::getUnorderedFlavor(Cond);
    if (UOF == 2)   // FP operators that are undefined on NaNs.
      return getConstant(ISD::isTrueWhenEqual(Cond), MVT::i1);
    if (UOF == ISD::isTrueWhenEqual(Cond))
      return getConstant(UOF, MVT::i1);
    // Otherwise, we can't fold it.  However, we can simplify it to SETUO/SETO
    // if it is not already.
    Cond = UOF == 0 ? ISD::SETUO : ISD::SETO;
  }

  if ((Cond == ISD::SETEQ || Cond == ISD::SETNE) &&
      MVT::isInteger(N1.getValueType())) {
    if (N1.getOpcode() == ISD::ADD || N1.getOpcode() == ISD::SUB ||
        N1.getOpcode() == ISD::XOR) {
      // Simplify (X+Y) == (X+Z) -->  Y == Z
      if (N1.getOpcode() == N2.getOpcode()) {
        if (N1.getOperand(0) == N2.getOperand(0))
          return getSetCC(Cond, N1.getOperand(1), N2.getOperand(1));
        if (N1.getOperand(1) == N2.getOperand(1))
          return getSetCC(Cond, N1.getOperand(0), N2.getOperand(0));
        if (isCommutativeBinOp(N1.getOpcode())) {
          // If X op Y == Y op X, try other combinations.
          if (N1.getOperand(0) == N2.getOperand(1))
            return getSetCC(Cond, N1.getOperand(1), N2.getOperand(0));
          if (N1.getOperand(1) == N2.getOperand(0))
            return getSetCC(Cond, N1.getOperand(1), N2.getOperand(1));
        }
      }
      
      // Simplify (X+Z) == X -->  Z == 0
      if (N1.getOperand(0) == N2)
        return getSetCC(Cond, N1.getOperand(1),
                        getConstant(0, N1.getValueType()));
      if (N1.getOperand(1) == N2) {
        if (isCommutativeBinOp(N1.getOpcode()))
          return getSetCC(Cond, N1.getOperand(0),
                          getConstant(0, N1.getValueType()));
        else {
          assert(N1.getOpcode() == ISD::SUB && "Unexpected operation!");
          // (Z-X) == X  --> Z == X<<1
          return getSetCC(Cond, N1.getOperand(0),
                          getNode(ISD::SHL, N2.getValueType(), 
                                  N2, getConstant(1, MVT::i8)));
        }
      }
    }

    if (N2.getOpcode() == ISD::ADD || N2.getOpcode() == ISD::SUB ||
        N2.getOpcode() == ISD::XOR) {
      // Simplify  X == (X+Z) -->  Z == 0
      if (N2.getOperand(0) == N1)
        return getSetCC(Cond, N2.getOperand(1),
                        getConstant(0, N2.getValueType()));
      else if (N2.getOperand(1) == N1)
        return getSetCC(Cond, N2.getOperand(0),
                        getConstant(0, N2.getValueType()));
    }
  }

  SetCCSDNode *&N = SetCCs[std::make_pair(std::make_pair(N1, N2), Cond)];
  if (N) return SDOperand(N, 0);
  N = new SetCCSDNode(Cond, N1, N2);
  AllNodes.push_back(N);
  return SDOperand(N, 0);
}



/// getNode - Gets or creates the specified node.
///
SDOperand SelectionDAG::getNode(unsigned Opcode, MVT::ValueType VT) {
  SDNode *N = new SDNode(Opcode, VT);
  AllNodes.push_back(N);
  return SDOperand(N, 0);
}

SDOperand SelectionDAG::getNode(unsigned Opcode, MVT::ValueType VT,
                                SDOperand Operand) {
  if (ConstantSDNode *C = dyn_cast<ConstantSDNode>(Operand.Val)) {
    uint64_t Val = C->getValue();
    switch (Opcode) {
    default: break;
    case ISD::SIGN_EXTEND: return getConstant(C->getSignExtended(), VT);
    case ISD::ZERO_EXTEND: return getConstant(Val, VT);
    case ISD::TRUNCATE:    return getConstant(Val, VT);
    case ISD::SINT_TO_FP:  return getConstantFP(C->getSignExtended(), VT);
    case ISD::UINT_TO_FP:  return getConstantFP(C->getValue(), VT);
    }
  }

  if (ConstantFPSDNode *C = dyn_cast<ConstantFPSDNode>(Operand.Val))
    switch (Opcode) {
    case ISD::FP_ROUND:
    case ISD::FP_EXTEND:
      return getConstantFP(C->getValue(), VT);
    case ISD::FP_TO_SINT:
      return getConstant((int64_t)C->getValue(), VT);
    case ISD::FP_TO_UINT:
      return getConstant((uint64_t)C->getValue(), VT);
    }

  unsigned OpOpcode = Operand.Val->getOpcode();
  switch (Opcode) {
  case ISD::SIGN_EXTEND:
    if (Operand.getValueType() == VT) return Operand;   // noop extension
    if (OpOpcode == ISD::SIGN_EXTEND || OpOpcode == ISD::ZERO_EXTEND)
      return getNode(OpOpcode, VT, Operand.Val->getOperand(0));
    break;
  case ISD::ZERO_EXTEND:
    if (Operand.getValueType() == VT) return Operand;   // noop extension
    if (OpOpcode == ISD::ZERO_EXTEND)
      return getNode(ISD::ZERO_EXTEND, VT, Operand.Val->getOperand(0));
    break;
  case ISD::TRUNCATE:
    if (Operand.getValueType() == VT) return Operand;   // noop truncate
    if (OpOpcode == ISD::TRUNCATE)
      return getNode(ISD::TRUNCATE, VT, Operand.Val->getOperand(0));
    else if (OpOpcode == ISD::ZERO_EXTEND || OpOpcode == ISD::SIGN_EXTEND) {
      // If the source is smaller than the dest, we still need an extend.
      if (Operand.Val->getOperand(0).getValueType() < VT)
        return getNode(OpOpcode, VT, Operand.Val->getOperand(0));
      else if (Operand.Val->getOperand(0).getValueType() > VT)
        return getNode(ISD::TRUNCATE, VT, Operand.Val->getOperand(0));
      else
        return Operand.Val->getOperand(0);
    }
    break;
  }

  SDNode *&N = UnaryOps[std::make_pair(Opcode, std::make_pair(Operand, VT))];
  if (N) return SDOperand(N, 0);
  N = new SDNode(Opcode, Operand);
  N->setValueTypes(VT);
  AllNodes.push_back(N);
  return SDOperand(N, 0);
}

SDOperand SelectionDAG::getNode(unsigned Opcode, MVT::ValueType VT,
                                SDOperand N1, SDOperand N2) {
  ConstantSDNode *N1C = dyn_cast<ConstantSDNode>(N1.Val);
  ConstantSDNode *N2C = dyn_cast<ConstantSDNode>(N2.Val);
  if (N1C) {
    if (N2C) {
      uint64_t C1 = N1C->getValue(), C2 = N2C->getValue();
      switch (Opcode) {
      case ISD::ADD: return getConstant(C1 + C2, VT);
      case ISD::SUB: return getConstant(C1 - C2, VT);
      case ISD::MUL: return getConstant(C1 * C2, VT);
      case ISD::UDIV:
        if (C2) return getConstant(C1 / C2, VT);
        break;
      case ISD::UREM :
        if (C2) return getConstant(C1 % C2, VT);
        break;
      case ISD::SDIV :
        if (C2) return getConstant(N1C->getSignExtended() /
                                   N2C->getSignExtended(), VT);
        break;
      case ISD::SREM :
        if (C2) return getConstant(N1C->getSignExtended() %
                                   N2C->getSignExtended(), VT);
        break;
      case ISD::AND  : return getConstant(C1 & C2, VT);
      case ISD::OR   : return getConstant(C1 | C2, VT);
      case ISD::XOR  : return getConstant(C1 ^ C2, VT);
      case ISD::SHL  : return getConstant(C1 << (int)C2, VT);
      case ISD::SRL  : return getConstant(C1 >> (unsigned)C2, VT);
      case ISD::SRA  : return getConstant(N1C->getSignExtended() >>(int)C2, VT);
      default: break;
      }

    } else {      // Cannonicalize constant to RHS if commutative
      if (isCommutativeBinOp(Opcode)) {
        std::swap(N1C, N2C);
        std::swap(N1, N2);
      }
    }
  }

  if (N2C) {
    uint64_t C2 = N2C->getValue();

    switch (Opcode) {
    case ISD::ADD:
      if (!C2) return N1;         // add X, 0 -> X
      break;
    case ISD::SUB:
      if (!C2) return N1;         // sub X, 0 -> X
      break;
    case ISD::MUL:
      if (!C2) return N2;         // mul X, 0 -> 0
      if (N2C->isAllOnesValue()) // mul X, -1 -> 0-X
        return getNode(ISD::SUB, VT, getConstant(0, VT), N1);

      // FIXME: This should only be done if the target supports shift
      // operations.
      if ((C2 & C2-1) == 0) {
        SDOperand ShAmt = getConstant(ExactLog2(C2), MVT::i8);
        return getNode(ISD::SHL, VT, N1, ShAmt);
      }
      break;

    case ISD::UDIV:
      // FIXME: This should only be done if the target supports shift
      // operations.
      if ((C2 & C2-1) == 0 && C2) {
        SDOperand ShAmt = getConstant(ExactLog2(C2), MVT::i8);
        return getNode(ISD::SRL, VT, N1, ShAmt);
      }
      break;

    case ISD::SHL:
    case ISD::SRL:
    case ISD::SRA:
      if (C2 == 0) return N1;
      break;

    case ISD::AND:
      if (!C2) return N2;         // X and 0 -> 0
      if (N2C->isAllOnesValue())
	return N1;                // X and -1 -> X
      break;
    case ISD::OR:
      if (!C2)return N1;          // X or 0 -> X
      if (N2C->isAllOnesValue())
	return N2;                // X or -1 -> -1
      break;
    case ISD::XOR:
      if (!C2) return N1;        // X xor 0 -> X
      if (N2C->isAllOnesValue()) {
        if (SetCCSDNode *SetCC = dyn_cast<SetCCSDNode>(N1.Val)){
          // !(X op Y) -> (X !op Y)
          bool isInteger = MVT::isInteger(SetCC->getOperand(0).getValueType());
          return getSetCC(ISD::getSetCCInverse(SetCC->getCondition(),isInteger),
                          SetCC->getOperand(0), SetCC->getOperand(1));
        } else if (N1.getOpcode() == ISD::AND || N1.getOpcode() == ISD::OR) {
          SDNode *Op = N1.Val;
          // !(X or Y) -> (!X and !Y) iff X or Y are freely invertible
          // !(X and Y) -> (!X or !Y) iff X or Y are freely invertible
          SDOperand LHS = Op->getOperand(0), RHS = Op->getOperand(1);
          if (isInvertibleForFree(RHS) || isInvertibleForFree(LHS)) {
            LHS = getNode(ISD::XOR, VT, LHS, N2);  // RHS = ~LHS
            RHS = getNode(ISD::XOR, VT, RHS, N2);  // RHS = ~RHS
            if (Op->getOpcode() == ISD::AND)
              return getNode(ISD::OR, VT, LHS, RHS);
            return getNode(ISD::AND, VT, LHS, RHS);
          }
        }
	// X xor -1 -> not(x)  ?
      }
      break;
    }

    // Reassociate ((X op C1) op C2) if possible.
    if (N1.getOpcode() == Opcode && isAssociativeBinOp(Opcode))
      if (ConstantSDNode *N3C = dyn_cast<ConstantSDNode>(N1.Val->getOperand(1)))
        return getNode(Opcode, VT, N1.Val->getOperand(0),
                       getNode(Opcode, VT, N2, N1.Val->getOperand(1)));
  }

  ConstantFPSDNode *N1CFP = dyn_cast<ConstantFPSDNode>(N1.Val);
  ConstantFPSDNode *N2CFP = dyn_cast<ConstantFPSDNode>(N2.Val);
  if (N1CFP)
    if (N2CFP) {
      double C1 = N1CFP->getValue(), C2 = N2CFP->getValue();
      switch (Opcode) {
      case ISD::ADD: return getConstantFP(C1 + C2, VT);
      case ISD::SUB: return getConstantFP(C1 - C2, VT);
      case ISD::MUL: return getConstantFP(C1 * C2, VT);
      case ISD::SDIV:
        if (C2) return getConstantFP(C1 / C2, VT);
        break;
      case ISD::SREM :
        if (C2) return getConstantFP(fmod(C1, C2), VT);
        break;
      default: break;
      }

    } else {      // Cannonicalize constant to RHS if commutative
      if (isCommutativeBinOp(Opcode)) {
        std::swap(N1CFP, N2CFP);
        std::swap(N1, N2);
      }
    }

  // Finally, fold operations that do not require constants.
  switch (Opcode) {
  case ISD::AND:
  case ISD::OR:
    if (SetCCSDNode *LHS = dyn_cast<SetCCSDNode>(N1.Val))
      if (SetCCSDNode *RHS = dyn_cast<SetCCSDNode>(N2.Val)) {
        SDOperand LL = LHS->getOperand(0), RL = RHS->getOperand(0);
        SDOperand LR = LHS->getOperand(1), RR = RHS->getOperand(1);
        ISD::CondCode Op2 = RHS->getCondition();

        // (X op1 Y) | (Y op2 X) -> (X op1 Y) | (X swapop2 Y)
        if (LL == RR && LR == RL) {
          Op2 = ISD::getSetCCSwappedOperands(Op2);
          goto MatchedBackwards;
        }
      
        if (LL == RL && LR == RR) {
        MatchedBackwards:
          ISD::CondCode Result;
          bool isInteger = MVT::isInteger(LL.getValueType());
          if (Opcode == ISD::OR)
            Result = ISD::getSetCCOrOperation(LHS->getCondition(), Op2,
                                              isInteger);
          else
            Result = ISD::getSetCCAndOperation(LHS->getCondition(), Op2,
                                               isInteger);
          if (Result != ISD::SETCC_INVALID)
            return getSetCC(Result, LL, LR);
        }
      }
    break;
  case ISD::XOR:
    if (N1 == N2) return getConstant(0, VT);  // xor X, Y -> 0
    break;
  case ISD::SUB:
    if (N1.getOpcode() == ISD::ADD) {
      if (N1.Val->getOperand(0) == N2)
        return N1.Val->getOperand(1);         // (A+B)-A == B
      if (N1.Val->getOperand(1) == N2)
        return N1.Val->getOperand(0);         // (A+B)-B == A
    }
    break;
  }

  SDNode *&N = BinaryOps[std::make_pair(Opcode, std::make_pair(N1, N2))];
  if (N) return SDOperand(N, 0);
  N = new SDNode(Opcode, N1, N2);
  N->setValueTypes(VT);

  AllNodes.push_back(N);
  return SDOperand(N, 0);
}

SDOperand SelectionDAG::getLoad(MVT::ValueType VT,
                                SDOperand Chain, SDOperand Ptr) {
  SDNode *&N = Loads[std::make_pair(Ptr, std::make_pair(Chain, VT))];
  if (N) return SDOperand(N, 0);
  N = new SDNode(ISD::LOAD, Chain, Ptr);

  // Loads have a token chain.
  N->setValueTypes(VT, MVT::Other);
  AllNodes.push_back(N);
  return SDOperand(N, 0);
}


SDOperand SelectionDAG::getNode(unsigned Opcode, MVT::ValueType VT,
                                SDOperand N1, SDOperand N2, SDOperand N3) {
  // Perform various simplifications.
  ConstantSDNode *N1C = dyn_cast<ConstantSDNode>(N1.Val);
  ConstantSDNode *N2C = dyn_cast<ConstantSDNode>(N2.Val);
  ConstantSDNode *N3C = dyn_cast<ConstantSDNode>(N3.Val);
  switch (Opcode) {
  case ISD::SELECT:
    if (N1C)
      if (N1C->getValue())
        return N2;             // select true, X, Y -> X
      else 
        return N3;             // select false, X, Y -> Y

    if (N2 == N3) return N2;   // select C, X, X -> X

    if (VT == MVT::i1) {  // Boolean SELECT
      if (N2C) {
        if (N3C) {
          if (N2C->getValue()) // select C, 1, 0 -> C
            return N1;
          return getNode(ISD::XOR, VT, N1, N3); // select C, 0, 1 -> ~C
        }

        if (N2C->getValue())   // select C, 1, X -> C | X
          return getNode(ISD::OR, VT, N1, N3);
        else                   // select C, 0, X -> ~C & X
          return getNode(ISD::AND, VT,
                         getNode(ISD::XOR, N1.getValueType(), N1,
                                 getConstant(1, N1.getValueType())), N3);
      } else if (N3C) {
        if (N3C->getValue())   // select C, X, 1 -> ~C | X
          return getNode(ISD::OR, VT,
                         getNode(ISD::XOR, N1.getValueType(), N1,
                                 getConstant(1, N1.getValueType())), N2);
        else                   // select C, X, 0 -> C & X
          return getNode(ISD::AND, VT, N1, N2);
      }
    }

    break;
  case ISD::BRCOND:
    if (N2C)
      if (N2C->getValue()) // Unconditional branch
        return getNode(ISD::BR, MVT::Other, N1, N3);
      else
        return N1;         // Never-taken branch
    break;
  }

  SDNode *N = new SDNode(Opcode, N1, N2, N3);
  switch (Opcode) {
  default: 
    N->setValueTypes(VT);
    break;
  case ISD::DYNAMIC_STACKALLOC: // DYNAMIC_STACKALLOC produces pointer and chain
    N->setValueTypes(VT, MVT::Other);
    break;
  }

  // FIXME: memoize NODES
  AllNodes.push_back(N);
  return SDOperand(N, 0);
}

SDOperand SelectionDAG::getNode(unsigned Opcode, MVT::ValueType VT,
                                std::vector<SDOperand> &Children) {
  switch (Children.size()) {
  case 0: return getNode(Opcode, VT);
  case 1: return getNode(Opcode, VT, Children[0]);
  case 2: return getNode(Opcode, VT, Children[0], Children[1]);
  case 3: return getNode(Opcode, VT, Children[0], Children[1], Children[2]);
  default:
    // FIXME: MEMOIZE!!
    SDNode *N = new SDNode(Opcode, Children);
    N->setValueTypes(VT);
    AllNodes.push_back(N);
    return SDOperand(N, 0);
  }
}

SDOperand SelectionDAG::getNode(unsigned Opcode, MVT::ValueType VT,SDOperand N1,
                                MVT::ValueType EVT) {

  switch (Opcode) {
  default: assert(0 && "Bad opcode for this accessor!");
  case ISD::FP_ROUND_INREG:
    assert(VT == N1.getValueType() && "Not an inreg round!");
    assert(MVT::isFloatingPoint(VT) && MVT::isFloatingPoint(EVT) &&
           "Cannot FP_ROUND_INREG integer types");
    if (EVT == VT) return N1;  // Not actually rounding
    assert(EVT < VT && "Not rounding down!");
    break;
  case ISD::ZERO_EXTEND_INREG:
  case ISD::SIGN_EXTEND_INREG:
    assert(VT == N1.getValueType() && "Not an inreg extend!");
    assert(MVT::isInteger(VT) && MVT::isInteger(EVT) &&
           "Cannot *_EXTEND_INREG FP types");
    if (EVT == VT) return N1;  // Not actually extending
    assert(EVT < VT && "Not extending!");

    // If we are sign extending an extension, use the original source.
    if (N1.getOpcode() == ISD::ZERO_EXTEND_INREG ||
        N1.getOpcode() == ISD::SIGN_EXTEND_INREG) {
      if (N1.getOpcode() == Opcode &&
          cast<MVTSDNode>(N1)->getExtraValueType() <= EVT)
        return N1;
    }

    break;
  }

  EVTStruct NN;
  NN.Opcode = Opcode;
  NN.VT = VT;
  NN.EVT = EVT;
  NN.Ops.push_back(N1);

  SDNode *&N = MVTSDNodes[NN];
  if (N) return SDOperand(N, 0);
  N = new MVTSDNode(Opcode, VT, N1, EVT);
  AllNodes.push_back(N);
  return SDOperand(N, 0);
}

SDOperand SelectionDAG::getNode(unsigned Opcode, MVT::ValueType VT,SDOperand N1,
                                SDOperand N2, MVT::ValueType EVT) {
  switch (Opcode) {
  default:  assert(0 && "Bad opcode for this accessor!");
  case ISD::EXTLOAD:
  case ISD::SEXTLOAD:
  case ISD::ZEXTLOAD:
    // If they are asking for an extending loat from/to the same thing, return a
    // normal load.
    if (VT == EVT)
      return getNode(ISD::LOAD, VT, N1, N2);
    assert(EVT < VT && "Should only be an extending load, not truncating!");
    assert((Opcode == ISD::EXTLOAD || MVT::isInteger(VT)) && 
           "Cannot sign/zero extend a FP load!");
    assert(MVT::isInteger(VT) == MVT::isInteger(EVT) &&
           "Cannot convert from FP to Int or Int -> FP!");
    break;
  }

  EVTStruct NN;
  NN.Opcode = Opcode;
  NN.VT = VT;
  NN.EVT = EVT;
  NN.Ops.push_back(N1);
  NN.Ops.push_back(N2);

  SDNode *&N = MVTSDNodes[NN];
  if (N) return SDOperand(N, 0);
  N = new MVTSDNode(Opcode, VT, MVT::Other, N1, N2, EVT);
  AllNodes.push_back(N);
  return SDOperand(N, 0);
}

SDOperand SelectionDAG::getNode(unsigned Opcode, MVT::ValueType VT,SDOperand N1,
                                SDOperand N2, SDOperand N3, MVT::ValueType EVT) {
  switch (Opcode) {
  default:  assert(0 && "Bad opcode for this accessor!");
  case ISD::TRUNCSTORE:
#if 0 // FIXME: If the target supports EVT natively, convert to a truncate/store
    // If this is a truncating store of a constant, convert to the desired type
    // and store it instead.
    if (isa<Constant>(N1)) {
      SDOperand Op = getNode(ISD::TRUNCATE, EVT, N1);
      if (isa<Constant>(Op))
        N1 = Op;      
    }
    // Also for ConstantFP?
#endif
    if (N1.getValueType() == EVT)       // Normal store?
      return getNode(ISD::STORE, VT, N1, N2, N3);
    assert(N2.getValueType() > EVT && "Not a truncation?");
    assert(MVT::isInteger(N2.getValueType()) == MVT::isInteger(EVT) &&
           "Can't do FP-INT conversion!");
    break;
  }

  EVTStruct NN;
  NN.Opcode = Opcode;
  NN.VT = VT;
  NN.EVT = EVT;
  NN.Ops.push_back(N1);
  NN.Ops.push_back(N2);
  NN.Ops.push_back(N3);

  SDNode *&N = MVTSDNodes[NN];
  if (N) return SDOperand(N, 0);
  N = new MVTSDNode(Opcode, VT, N1, N2, N3, EVT);
  AllNodes.push_back(N);
  return SDOperand(N, 0);
}


/// hasNUsesOfValue - Return true if there are exactly NUSES uses of the
/// indicated value.  This method ignores uses of other values defined by this
/// operation.
bool SDNode::hasNUsesOfValue(unsigned NUses, unsigned Value) {
  assert(Value < getNumValues() && "Bad value!");

  // If there is only one value, this is easy.
  if (getNumValues() == 1)
    return use_size() == NUses;
  if (Uses.size() < NUses) return false;

  SDOperand TheValue(this, Value);

  std::set<SDNode*> UsersHandled;

  for (std::vector<SDNode*>::iterator UI = Uses.begin(), E = Uses.end();
       UI != E; ++UI) {
    SDNode *User = *UI;
    if (User->getNumOperands() == 1 ||
        UsersHandled.insert(User).second)     // First time we've seen this?
      for (unsigned i = 0, e = User->getNumOperands(); i != e; ++i)
        if (User->getOperand(i) == TheValue) {
          if (NUses == 0)
            return false;   // too many uses
          --NUses;
        }
  }

  // Found exactly the right number of uses?
  return NUses == 0;
}


const char *SDNode::getOperationName() const {
  switch (getOpcode()) {
  default: return "<<Unknown>>";
  case ISD::EntryToken:    return "EntryToken";
  case ISD::TokenFactor:   return "TokenFactor";
  case ISD::Constant:      return "Constant";
  case ISD::ConstantFP:    return "ConstantFP";
  case ISD::GlobalAddress: return "GlobalAddress";
  case ISD::FrameIndex:    return "FrameIndex";
  case ISD::BasicBlock:    return "BasicBlock";
  case ISD::ExternalSymbol: return "ExternalSymbol";
  case ISD::ConstantPool:  return "ConstantPoolIndex";
  case ISD::CopyToReg:     return "CopyToReg";
  case ISD::CopyFromReg:   return "CopyFromReg";
  case ISD::ImplicitDef:   return "ImplicitDef";

  case ISD::ADD:    return "add";
  case ISD::SUB:    return "sub";
  case ISD::MUL:    return "mul";
  case ISD::SDIV:   return "sdiv";
  case ISD::UDIV:   return "udiv";
  case ISD::SREM:   return "srem";
  case ISD::UREM:   return "urem";
  case ISD::AND:    return "and";
  case ISD::OR:     return "or";
  case ISD::XOR:    return "xor";
  case ISD::SHL:    return "shl";
  case ISD::SRA:    return "sra";
  case ISD::SRL:    return "srl";

  case ISD::SELECT: return "select";
  case ISD::ADDC:   return "addc";
  case ISD::SUBB:   return "subb";

    // Conversion operators.
  case ISD::SIGN_EXTEND: return "sign_extend";
  case ISD::ZERO_EXTEND: return "zero_extend";
  case ISD::SIGN_EXTEND_INREG: return "sign_extend_inreg";
  case ISD::ZERO_EXTEND_INREG: return "zero_extend_inreg";
  case ISD::TRUNCATE:    return "truncate";
  case ISD::FP_ROUND:    return "fp_round";
  case ISD::FP_ROUND_INREG: return "fp_round_inreg";
  case ISD::FP_EXTEND:   return "fp_extend";

  case ISD::SINT_TO_FP:  return "sint_to_fp";
  case ISD::UINT_TO_FP:  return "uint_to_fp";
  case ISD::FP_TO_SINT:  return "fp_to_sint";
  case ISD::FP_TO_UINT:  return "fp_to_uint";

    // Control flow instructions
  case ISD::BR:      return "br";
  case ISD::BRCOND:  return "brcond";
  case ISD::RET:     return "ret";
  case ISD::CALL:    return "call";
  case ISD::ADJCALLSTACKDOWN:  return "adjcallstackdown";
  case ISD::ADJCALLSTACKUP:    return "adjcallstackup";

    // Other operators
  case ISD::LOAD:    return "load";
  case ISD::STORE:   return "store";
  case ISD::EXTLOAD:    return "extload";
  case ISD::SEXTLOAD:   return "sextload";
  case ISD::ZEXTLOAD:   return "zextload";
  case ISD::TRUNCSTORE: return "truncstore";

  case ISD::DYNAMIC_STACKALLOC: return "dynamic_stackalloc";
  case ISD::EXTRACT_ELEMENT: return "extract_element";
  case ISD::BUILD_PAIR: return "build_pair";
  case ISD::MEMSET:  return "memset";
  case ISD::MEMCPY:  return "memcpy";
  case ISD::MEMMOVE: return "memmove";

  case ISD::SETCC:
    const SetCCSDNode *SetCC = cast<SetCCSDNode>(this);
    switch (SetCC->getCondition()) {
    default: assert(0 && "Unknown setcc condition!");
    case ISD::SETOEQ:  return "setcc:setoeq";
    case ISD::SETOGT:  return "setcc:setogt";
    case ISD::SETOGE:  return "setcc:setoge";
    case ISD::SETOLT:  return "setcc:setolt";
    case ISD::SETOLE:  return "setcc:setole";
    case ISD::SETONE:  return "setcc:setone";
      
    case ISD::SETO:    return "setcc:seto"; 
    case ISD::SETUO:   return "setcc:setuo";
    case ISD::SETUEQ:  return "setcc:setue";
    case ISD::SETUGT:  return "setcc:setugt";
    case ISD::SETUGE:  return "setcc:setuge";
    case ISD::SETULT:  return "setcc:setult";
    case ISD::SETULE:  return "setcc:setule";
    case ISD::SETUNE:  return "setcc:setune";
      
    case ISD::SETEQ:   return "setcc:seteq";
    case ISD::SETGT:   return "setcc:setgt";
    case ISD::SETGE:   return "setcc:setge";
    case ISD::SETLT:   return "setcc:setlt";
    case ISD::SETLE:   return "setcc:setle";
    case ISD::SETNE:   return "setcc:setne";
    }
  }
}

void SDNode::dump() const {
  std::cerr << (void*)this << ": ";

  for (unsigned i = 0, e = getNumValues(); i != e; ++i) {
    if (i) std::cerr << ",";
    if (getValueType(i) == MVT::Other)
      std::cerr << "ch";
    else
      std::cerr << MVT::getValueTypeString(getValueType(i));
  }
  std::cerr << " = " << getOperationName();

  std::cerr << " ";
  for (unsigned i = 0, e = getNumOperands(); i != e; ++i) {
    if (i) std::cerr << ", ";
    std::cerr << (void*)getOperand(i).Val;
    if (unsigned RN = getOperand(i).ResNo)
      std::cerr << ":" << RN;
  }

  if (const ConstantSDNode *CSDN = dyn_cast<ConstantSDNode>(this)) {
    std::cerr << "<" << CSDN->getValue() << ">";
  } else if (const ConstantFPSDNode *CSDN = dyn_cast<ConstantFPSDNode>(this)) {
    std::cerr << "<" << CSDN->getValue() << ">";
  } else if (const GlobalAddressSDNode *GADN = 
             dyn_cast<GlobalAddressSDNode>(this)) {
    std::cerr << "<";
    WriteAsOperand(std::cerr, GADN->getGlobal()) << ">";
  } else if (const FrameIndexSDNode *FIDN =
	     dyn_cast<FrameIndexSDNode>(this)) {
    std::cerr << "<" << FIDN->getIndex() << ">";
  } else if (const ConstantPoolSDNode *CP = dyn_cast<ConstantPoolSDNode>(this)){
    std::cerr << "<" << CP->getIndex() << ">";
  } else if (const BasicBlockSDNode *BBDN = 
	     dyn_cast<BasicBlockSDNode>(this)) {
    std::cerr << "<";
    const Value *LBB = (const Value*)BBDN->getBasicBlock()->getBasicBlock();
    if (LBB)
      std::cerr << LBB->getName() << " ";
    std::cerr << (const void*)BBDN->getBasicBlock() << ">";
  } else if (const RegSDNode *C2V = dyn_cast<RegSDNode>(this)) {
    std::cerr << "<reg #" << C2V->getReg() << ">";
  } else if (const ExternalSymbolSDNode *ES =
             dyn_cast<ExternalSymbolSDNode>(this)) {
    std::cerr << "'" << ES->getSymbol() << "'";
  } else if (const MVTSDNode *M = dyn_cast<MVTSDNode>(this)) {
    std::cerr << " - Ty = " << MVT::getValueTypeString(M->getExtraValueType());
  }
}

static void DumpNodes(SDNode *N, unsigned indent) {
  for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i)
    if (N->getOperand(i).Val->hasOneUse())
      DumpNodes(N->getOperand(i).Val, indent+2);
    else
      std::cerr << "\n" << std::string(indent+2, ' ')
                << (void*)N->getOperand(i).Val << ": <multiple use>";
    

  std::cerr << "\n" << std::string(indent, ' ');
  N->dump();
}

void SelectionDAG::dump() const {
  std::cerr << "SelectionDAG has " << AllNodes.size() << " nodes:";
  std::vector<SDNode*> Nodes(AllNodes);
  std::sort(Nodes.begin(), Nodes.end());

  for (unsigned i = 0, e = Nodes.size(); i != e; ++i) {
    if (!Nodes[i]->hasOneUse() && Nodes[i] != getRoot().Val)
      DumpNodes(Nodes[i], 2);
  }

  DumpNodes(getRoot().Val, 2);

  std::cerr << "\n\n";
}