TargetLowering.h

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//===-- llvm/Target/TargetLowering.h - Target Lowering Info -----*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file describes how to lower LLVM code to machine code.  This has two
// main components:
//
//  1. Which ValueTypes are natively supported by the target.
//  2. Which operations are supported for supported ValueTypes.
//  3. Cost thresholds for alternative implementations of certain operations.
//
// In addition it has a few other components, like information about FP
// immediates.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_TARGET_TARGETLOWERING_H
#define LLVM_TARGET_TARGETLOWERING_H

#include "llvm/InlineAsm.h"
#include "llvm/CodeGen/SelectionDAGNodes.h"
#include "llvm/CodeGen/RuntimeLibcalls.h"
#include "llvm/ADT/APFloat.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/CodeGen/DebugLoc.h"
#include <climits>
#include <map>
#include <vector>

namespace llvm {
  class AllocaInst;
  class CallInst;
  class Function;
  class FastISel;
  class MachineBasicBlock;
  class MachineFunction;
  class MachineFrameInfo;
  class MachineInstr;
  class MachineModuleInfo;
  class DwarfWriter;
  class SDNode;
  class SDValue;
  class SelectionDAG;
  class TargetData;
  class TargetMachine;
  class TargetRegisterClass;
  class TargetSubtarget;
  class Value;

//===----------------------------------------------------------------------===//
/// TargetLowering - This class defines information used to lower LLVM code to
/// legal SelectionDAG operators that the target instruction selector can accept
/// natively.
///
/// This class also defines callbacks that targets must implement to lower
/// target-specific constructs to SelectionDAG operators.
///
class TargetLowering {
public:
  /// LegalizeAction - This enum indicates whether operations are valid for a
  /// target, and if not, what action should be used to make them valid.
  enum LegalizeAction {
    Legal,      // The target natively supports this operation.
    Promote,    // This operation should be executed in a larger type.
    Expand,     // Try to expand this to other ops, otherwise use a libcall.
    Custom      // Use the LowerOperation hook to implement custom lowering.
  };

  enum OutOfRangeShiftAmount {
    Undefined,  // Oversized shift amounts are undefined (default).
    Mask,       // Shift amounts are auto masked (anded) to value size.
    Extend      // Oversized shift pulls in zeros or sign bits.
  };

  enum BooleanContent { // How the target represents true/false values.
    UndefinedBooleanContent,    // Only bit 0 counts, the rest can hold garbage.
    ZeroOrOneBooleanContent,        // All bits zero except for bit 0.
    ZeroOrNegativeOneBooleanContent // All bits equal to bit 0.
  };

  enum SchedPreference {
    SchedulingForLatency,          // Scheduling for shortest total latency.
    SchedulingForRegPressure       // Scheduling for lowest register pressure.
  };

  explicit TargetLowering(TargetMachine &TM);
  virtual ~TargetLowering();

  TargetMachine &getTargetMachine() const { return TM; }
  const TargetData *getTargetData() const { return TD; }

  bool isBigEndian() const { return !IsLittleEndian; }
  bool isLittleEndian() const { return IsLittleEndian; }
  MVT getPointerTy() const { return PointerTy; }
  MVT getShiftAmountTy() const { return ShiftAmountTy; }
  OutOfRangeShiftAmount getShiftAmountFlavor() const {return ShiftAmtHandling; }

  /// usesGlobalOffsetTable - Return true if this target uses a GOT for PIC
  /// codegen.
  bool usesGlobalOffsetTable() const { return UsesGlobalOffsetTable; }

  /// isSelectExpensive - Return true if the select operation is expensive for
  /// this target.
  bool isSelectExpensive() const { return SelectIsExpensive; }
  
  /// isIntDivCheap() - Return true if integer divide is usually cheaper than
  /// a sequence of several shifts, adds, and multiplies for this target.
  bool isIntDivCheap() const { return IntDivIsCheap; }

  /// isPow2DivCheap() - Return true if pow2 div is cheaper than a chain of
  /// srl/add/sra.
  bool isPow2DivCheap() const { return Pow2DivIsCheap; }

  /// getSetCCResultType - Return the ValueType of the result of SETCC
  /// operations.  Also used to obtain the target's preferred type for
  /// the condition operand of SELECT and BRCOND nodes.  In the case of
  /// BRCOND the argument passed is MVT::Other since there are no other
  /// operands to get a type hint from.
  virtual MVT getSetCCResultType(MVT VT) const;

  /// getBooleanContents - For targets without i1 registers, this gives the
  /// nature of the high-bits of boolean values held in types wider than i1.
  /// "Boolean values" are special true/false values produced by nodes like
  /// SETCC and consumed (as the condition) by nodes like SELECT and BRCOND.
  /// Not to be confused with general values promoted from i1.
  BooleanContent getBooleanContents() const { return BooleanContents;}

  /// getSchedulingPreference - Return target scheduling preference.
  SchedPreference getSchedulingPreference() const {
    return SchedPreferenceInfo;
  }

  /// getRegClassFor - Return the register class that should be used for the
  /// specified value type.  This may only be called on legal types.
  TargetRegisterClass *getRegClassFor(MVT VT) const {
    assert((unsigned)VT.getSimpleVT() < array_lengthof(RegClassForVT));
    TargetRegisterClass *RC = RegClassForVT[VT.getSimpleVT()];
    assert(RC && "This value type is not natively supported!");
    return RC;
  }

  /// isTypeLegal - Return true if the target has native support for the
  /// specified value type.  This means that it has a register that directly
  /// holds it without promotions or expansions.
  bool isTypeLegal(MVT VT) const {
    assert(!VT.isSimple() ||
           (unsigned)VT.getSimpleVT() < array_lengthof(RegClassForVT));
    return VT.isSimple() && RegClassForVT[VT.getSimpleVT()] != 0;
  }

  class ValueTypeActionImpl {
    /// ValueTypeActions - This is a bitvector that contains two bits for each
    /// value type, where the two bits correspond to the LegalizeAction enum.
    /// This can be queried with "getTypeAction(VT)".
    uint32_t ValueTypeActions[2];
  public:
    ValueTypeActionImpl() {
      ValueTypeActions[0] = ValueTypeActions[1] = 0;
    }
    ValueTypeActionImpl(const ValueTypeActionImpl &RHS) {
      ValueTypeActions[0] = RHS.ValueTypeActions[0];
      ValueTypeActions[1] = RHS.ValueTypeActions[1];
    }
    
    LegalizeAction getTypeAction(MVT VT) const {
      if (VT.isExtended()) {
        if (VT.isVector()) {
          return VT.isPow2VectorType() ? Expand : Promote;
        }
        if (VT.isInteger())
          // First promote to a power-of-two size, then expand if necessary.
          return VT == VT.getRoundIntegerType() ? Expand : Promote;
        assert(0 && "Unsupported extended type!");
        return Legal;
      }
      unsigned I = VT.getSimpleVT();
      assert(I<4*array_lengthof(ValueTypeActions)*sizeof(ValueTypeActions[0]));
      return (LegalizeAction)((ValueTypeActions[I>>4] >> ((2*I) & 31)) & 3);
    }
    void setTypeAction(MVT VT, LegalizeAction Action) {
      unsigned I = VT.getSimpleVT();
      assert(I<4*array_lengthof(ValueTypeActions)*sizeof(ValueTypeActions[0]));
      ValueTypeActions[I>>4] |= Action << ((I*2) & 31);
    }
  };
  
  const ValueTypeActionImpl &getValueTypeActions() const {
    return ValueTypeActions;
  }

  /// getTypeAction - Return how we should legalize values of this type, either
  /// it is already legal (return 'Legal') or we need to promote it to a larger
  /// type (return 'Promote'), or we need to expand it into multiple registers
  /// of smaller integer type (return 'Expand').  'Custom' is not an option.
  LegalizeAction getTypeAction(MVT VT) const {
    return ValueTypeActions.getTypeAction(VT);
  }

  /// getTypeToTransformTo - For types supported by the target, this is an
  /// identity function.  For types that must be promoted to larger types, this
  /// returns the larger type to promote to.  For integer types that are larger
  /// than the largest integer register, this contains one step in the expansion
  /// to get to the smaller register. For illegal floating point types, this
  /// returns the integer type to transform to.
  MVT getTypeToTransformTo(MVT VT) const {
    if (VT.isSimple()) {
      assert((unsigned)VT.getSimpleVT() < array_lengthof(TransformToType));
      MVT NVT = TransformToType[VT.getSimpleVT()];
      assert(getTypeAction(NVT) != Promote &&
             "Promote may not follow Expand or Promote");
      return NVT;
    }

    if (VT.isVector()) {
      MVT NVT = VT.getPow2VectorType();
      if (NVT == VT) {
        // Vector length is a power of 2 - split to half the size.
        unsigned NumElts = VT.getVectorNumElements();
        MVT EltVT = VT.getVectorElementType();
        return (NumElts == 1) ? EltVT : MVT::getVectorVT(EltVT, NumElts / 2);
      }
      // Promote to a power of two size, avoiding multi-step promotion.
      return getTypeAction(NVT) == Promote ? getTypeToTransformTo(NVT) : NVT;
    } else if (VT.isInteger()) {
      MVT NVT = VT.getRoundIntegerType();
      if (NVT == VT)
        // Size is a power of two - expand to half the size.
        return MVT::getIntegerVT(VT.getSizeInBits() / 2);
      else
        // Promote to a power of two size, avoiding multi-step promotion.
        return getTypeAction(NVT) == Promote ? getTypeToTransformTo(NVT) : NVT;
    }
    assert(0 && "Unsupported extended type!");
    return MVT(); // Not reached
  }

  /// getTypeToExpandTo - For types supported by the target, this is an
  /// identity function.  For types that must be expanded (i.e. integer types
  /// that are larger than the largest integer register or illegal floating
  /// point types), this returns the largest legal type it will be expanded to.
  MVT getTypeToExpandTo(MVT VT) const {
    assert(!VT.isVector());
    while (true) {
      switch (getTypeAction(VT)) {
      case Legal:
        return VT;
      case Expand:
        VT = getTypeToTransformTo(VT);
        break;
      default:
        assert(false && "Type is not legal nor is it to be expanded!");
        return VT;
      }
    }
    return VT;
  }

  /// getVectorTypeBreakdown - Vector types are broken down into some number of
  /// legal first class types.  For example, MVT::v8f32 maps to 2 MVT::v4f32
  /// with Altivec or SSE1, or 8 promoted MVT::f64 values with the X86 FP stack.
  /// Similarly, MVT::v2i64 turns into 4 MVT::i32 values with both PPC and X86.
  ///
  /// This method returns the number of registers needed, and the VT for each
  /// register.  It also returns the VT and quantity of the intermediate values
  /// before they are promoted/expanded.
  ///
  unsigned getVectorTypeBreakdown(MVT VT,
                                  MVT &IntermediateVT,
                                  unsigned &NumIntermediates,
                                  MVT &RegisterVT) const;

  /// getTgtMemIntrinsic: Given an intrinsic, checks if on the target the
  /// intrinsic will need to map to a MemIntrinsicNode (touches memory). If
  /// this is the case, it returns true and store the intrinsic
  /// information into the IntrinsicInfo that was passed to the function.
  typedef struct IntrinsicInfo { 
    unsigned     opc;         // target opcode
    MVT          memVT;       // memory VT
    const Value* ptrVal;      // value representing memory location
    int          offset;      // offset off of ptrVal 
    unsigned     align;       // alignment
    bool         vol;         // is volatile?
    bool         readMem;     // reads memory?
    bool         writeMem;    // writes memory?
  } IntrinisicInfo;

  virtual bool getTgtMemIntrinsic(IntrinsicInfo& Info,
                                  CallInst &I, unsigned Intrinsic) {
    return false;
  }

  /// getWidenVectorType: given a vector type, returns the type to widen to
  /// (e.g., v7i8 to v8i8). If the vector type is legal, it returns itself.
  /// If there is no vector type that we want to widen to, returns MVT::Other
  /// When and were to widen is target dependent based on the cost of
  /// scalarizing vs using the wider vector type.
  virtual MVT getWidenVectorType(MVT VT) const;

  typedef std::vector<APFloat>::const_iterator legal_fpimm_iterator;
  legal_fpimm_iterator legal_fpimm_begin() const {
    return LegalFPImmediates.begin();
  }
  legal_fpimm_iterator legal_fpimm_end() const {
    return LegalFPImmediates.end();
  }
  
  /// isShuffleMaskLegal - Targets can use this to indicate that they only
  /// support *some* VECTOR_SHUFFLE operations, those with specific masks.
  /// By default, if a target supports the VECTOR_SHUFFLE node, all mask values
  /// are assumed to be legal.
  virtual bool isShuffleMaskLegal(SDValue Mask, MVT VT) const {
    return true;
  }

  /// isVectorClearMaskLegal - Similar to isShuffleMaskLegal. This is
  /// used by Targets can use this to indicate if there is a suitable
  /// VECTOR_SHUFFLE that can be used to replace a VAND with a constant
  /// pool entry.
  virtual bool isVectorClearMaskLegal(const std::vector<SDValue> &BVOps,
                                      MVT EVT,
                                      SelectionDAG &DAG) const {
    return false;
  }

  /// getOperationAction - Return how this operation should be treated: either
  /// it is legal, needs to be promoted to a larger size, needs to be
  /// expanded to some other code sequence, or the target has a custom expander
  /// for it.
  LegalizeAction getOperationAction(unsigned Op, MVT VT) const {
    if (VT.isExtended()) return Expand;
    assert(Op < array_lengthof(OpActions) &&
           (unsigned)VT.getSimpleVT() < sizeof(OpActions[0])*4 &&
           "Table isn't big enough!");
    return (LegalizeAction)((OpActions[Op] >> (2*VT.getSimpleVT())) & 3);
  }

  /// isOperationLegalOrCustom - Return true if the specified operation is
  /// legal on this target or can be made legal with custom lowering. This
  /// is used to help guide high-level lowering decisions.
  bool isOperationLegalOrCustom(unsigned Op, MVT VT) const {
    return (VT == MVT::Other || isTypeLegal(VT)) &&
      (getOperationAction(Op, VT) == Legal ||
       getOperationAction(Op, VT) == Custom);
  }

  /// isOperationLegal - Return true if the specified operation is legal on this
  /// target.
  bool isOperationLegal(unsigned Op, MVT VT) const {
    return (VT == MVT::Other || isTypeLegal(VT)) &&
           getOperationAction(Op, VT) == Legal;
  }

  /// getLoadExtAction - Return how this load with extension should be treated:
  /// either it is legal, needs to be promoted to a larger size, needs to be
  /// expanded to some other code sequence, or the target has a custom expander
  /// for it.
  LegalizeAction getLoadExtAction(unsigned LType, MVT VT) const {
    assert(LType < array_lengthof(LoadExtActions) &&
           (unsigned)VT.getSimpleVT() < sizeof(LoadExtActions[0])*4 &&
           "Table isn't big enough!");
    return (LegalizeAction)((LoadExtActions[LType] >> (2*VT.getSimpleVT())) & 3);
  }

  /// isLoadExtLegal - Return true if the specified load with extension is legal
  /// on this target.
  bool isLoadExtLegal(unsigned LType, MVT VT) const {
    return VT.isSimple() &&
      (getLoadExtAction(LType, VT) == Legal ||
       getLoadExtAction(LType, VT) == Custom);
  }

  /// getTruncStoreAction - Return how this store with truncation should be
  /// treated: either it is legal, needs to be promoted to a larger size, needs
  /// to be expanded to some other code sequence, or the target has a custom
  /// expander for it.
  LegalizeAction getTruncStoreAction(MVT ValVT,
                                     MVT MemVT) const {
    assert((unsigned)ValVT.getSimpleVT() < array_lengthof(TruncStoreActions) &&
           (unsigned)MemVT.getSimpleVT() < sizeof(TruncStoreActions[0])*4 &&
           "Table isn't big enough!");
    return (LegalizeAction)((TruncStoreActions[ValVT.getSimpleVT()] >>
                             (2*MemVT.getSimpleVT())) & 3);
  }

  /// isTruncStoreLegal - Return true if the specified store with truncation is
  /// legal on this target.
  bool isTruncStoreLegal(MVT ValVT, MVT MemVT) const {
    return isTypeLegal(ValVT) && MemVT.isSimple() &&
      (getTruncStoreAction(ValVT, MemVT) == Legal ||
       getTruncStoreAction(ValVT, MemVT) == Custom);
  }

  /// getIndexedLoadAction - Return how the indexed load should be treated:
  /// either it is legal, needs to be promoted to a larger size, needs to be
  /// expanded to some other code sequence, or the target has a custom expander
  /// for it.
  LegalizeAction
  getIndexedLoadAction(unsigned IdxMode, MVT VT) const {
    assert(IdxMode < array_lengthof(IndexedModeActions[0]) &&
           (unsigned)VT.getSimpleVT() < sizeof(IndexedModeActions[0][0])*4 &&
           "Table isn't big enough!");
    return (LegalizeAction)((IndexedModeActions[0][IdxMode] >>
                             (2*VT.getSimpleVT())) & 3);
  }

  /// isIndexedLoadLegal - Return true if the specified indexed load is legal
  /// on this target.
  bool isIndexedLoadLegal(unsigned IdxMode, MVT VT) const {
    return VT.isSimple() &&
      (getIndexedLoadAction(IdxMode, VT) == Legal ||
       getIndexedLoadAction(IdxMode, VT) == Custom);
  }

  /// getIndexedStoreAction - Return how the indexed store should be treated:
  /// either it is legal, needs to be promoted to a larger size, needs to be
  /// expanded to some other code sequence, or the target has a custom expander
  /// for it.
  LegalizeAction
  getIndexedStoreAction(unsigned IdxMode, MVT VT) const {
    assert(IdxMode < array_lengthof(IndexedModeActions[1]) &&
           (unsigned)VT.getSimpleVT() < sizeof(IndexedModeActions[1][0])*4 &&
           "Table isn't big enough!");
    return (LegalizeAction)((IndexedModeActions[1][IdxMode] >>
                             (2*VT.getSimpleVT())) & 3);
  }  

  /// isIndexedStoreLegal - Return true if the specified indexed load is legal
  /// on this target.
  bool isIndexedStoreLegal(unsigned IdxMode, MVT VT) const {
    return VT.isSimple() &&
      (getIndexedStoreAction(IdxMode, VT) == Legal ||
       getIndexedStoreAction(IdxMode, VT) == Custom);
  }

  /// getConvertAction - Return how the conversion should be treated:
  /// either it is legal, needs to be promoted to a larger size, needs to be
  /// expanded to some other code sequence, or the target has a custom expander
  /// for it.
  LegalizeAction
  getConvertAction(MVT FromVT, MVT ToVT) const {
    assert((unsigned)FromVT.getSimpleVT() < array_lengthof(ConvertActions) &&
           (unsigned)ToVT.getSimpleVT() < sizeof(ConvertActions[0])*4 &&
           "Table isn't big enough!");
    return (LegalizeAction)((ConvertActions[FromVT.getSimpleVT()] >>
                             (2*ToVT.getSimpleVT())) & 3);
  }

  /// isConvertLegal - Return true if the specified conversion is legal
  /// on this target.
  bool isConvertLegal(MVT FromVT, MVT ToVT) const {
    return isTypeLegal(FromVT) && isTypeLegal(ToVT) &&
      (getConvertAction(FromVT, ToVT) == Legal ||
       getConvertAction(FromVT, ToVT) == Custom);
  }

  /// getCondCodeAction - Return how the condition code should be treated:
  /// either it is legal, needs to be expanded to some other code sequence,
  /// or the target has a custom expander for it.
  LegalizeAction
  getCondCodeAction(ISD::CondCode CC, MVT VT) const {
    assert((unsigned)CC < array_lengthof(CondCodeActions) &&
           (unsigned)VT.getSimpleVT() < sizeof(CondCodeActions[0])*4 &&
           "Table isn't big enough!");
    LegalizeAction Action = (LegalizeAction)
      ((CondCodeActions[CC] >> (2*VT.getSimpleVT())) & 3);
    assert(Action != Promote && "Can't promote condition code!");
    return Action;
  }

  /// isCondCodeLegal - Return true if the specified condition code is legal
  /// on this target.
  bool isCondCodeLegal(ISD::CondCode CC, MVT VT) const {
    return getCondCodeAction(CC, VT) == Legal ||
           getCondCodeAction(CC, VT) == Custom;
  }


  /// getTypeToPromoteTo - If the action for this operation is to promote, this
  /// method returns the ValueType to promote to.
  MVT getTypeToPromoteTo(unsigned Op, MVT VT) const {
    assert(getOperationAction(Op, VT) == Promote &&
           "This operation isn't promoted!");

    // See if this has an explicit type specified.
    std::map<std::pair<unsigned, MVT::SimpleValueType>,
             MVT::SimpleValueType>::const_iterator PTTI =
      PromoteToType.find(std::make_pair(Op, VT.getSimpleVT()));
    if (PTTI != PromoteToType.end()) return PTTI->second;

    assert((VT.isInteger() || VT.isFloatingPoint()) &&
           "Cannot autopromote this type, add it with AddPromotedToType.");
    
    MVT NVT = VT;
    do {
      NVT = (MVT::SimpleValueType)(NVT.getSimpleVT()+1);
      assert(NVT.isInteger() == VT.isInteger() && NVT != MVT::isVoid &&
             "Didn't find type to promote to!");
    } while (!isTypeLegal(NVT) ||
              getOperationAction(Op, NVT) == Promote);
    return NVT;
  }

  /// getValueType - Return the MVT corresponding to this LLVM type.
  /// This is fixed by the LLVM operations except for the pointer size.  If
  /// AllowUnknown is true, this will return MVT::Other for types with no MVT
  /// counterpart (e.g. structs), otherwise it will assert.
  MVT getValueType(const Type *Ty, bool AllowUnknown = false) const {
    MVT VT = MVT::getMVT(Ty, AllowUnknown);
    return VT == MVT::iPTR ? PointerTy : VT;
  }

  /// getByValTypeAlignment - Return the desired alignment for ByVal aggregate
  /// function arguments in the caller parameter area.  This is the actual
  /// alignment, not its logarithm.
  virtual unsigned getByValTypeAlignment(const Type *Ty) const;
  
  /// getRegisterType - Return the type of registers that this ValueType will
  /// eventually require.
  MVT getRegisterType(MVT VT) const {
    if (VT.isSimple()) {
      assert((unsigned)VT.getSimpleVT() < array_lengthof(RegisterTypeForVT));
      return RegisterTypeForVT[VT.getSimpleVT()];
    }
    if (VT.isVector()) {
      MVT VT1, RegisterVT;
      unsigned NumIntermediates;
      (void)getVectorTypeBreakdown(VT, VT1, NumIntermediates, RegisterVT);
      return RegisterVT;
    }
    if (VT.isInteger()) {
      return getRegisterType(getTypeToTransformTo(VT));
    }
    assert(0 && "Unsupported extended type!");
    return MVT(); // Not reached
  }

  /// getNumRegisters - Return the number of registers that this ValueType will
  /// eventually require.  This is one for any types promoted to live in larger
  /// registers, but may be more than one for types (like i64) that are split
  /// into pieces.  For types like i140, which are first promoted then expanded,
  /// it is the number of registers needed to hold all the bits of the original
  /// type.  For an i140 on a 32 bit machine this means 5 registers.
  unsigned getNumRegisters(MVT VT) const {
    if (VT.isSimple()) {
      assert((unsigned)VT.getSimpleVT() < array_lengthof(NumRegistersForVT));
      return NumRegistersForVT[VT.getSimpleVT()];
    }
    if (VT.isVector()) {
      MVT VT1, VT2;
      unsigned NumIntermediates;
      return getVectorTypeBreakdown(VT, VT1, NumIntermediates, VT2);
    }
    if (VT.isInteger()) {
      unsigned BitWidth = VT.getSizeInBits();
      unsigned RegWidth = getRegisterType(VT).getSizeInBits();
      return (BitWidth + RegWidth - 1) / RegWidth;
    }
    assert(0 && "Unsupported extended type!");
    return 0; // Not reached
  }

  /// ShouldShrinkFPConstant - If true, then instruction selection should
  /// seek to shrink the FP constant of the specified type to a smaller type
  /// in order to save space and / or reduce runtime.
  virtual bool ShouldShrinkFPConstant(MVT VT) const { return true; }

  /// hasTargetDAGCombine - If true, the target has custom DAG combine
  /// transformations that it can perform for the specified node.
  bool hasTargetDAGCombine(ISD::NodeType NT) const {
    assert(unsigned(NT >> 3) < array_lengthof(TargetDAGCombineArray));
    return TargetDAGCombineArray[NT >> 3] & (1 << (NT&7));
  }

  /// This function returns the maximum number of store operations permitted
  /// to replace a call to llvm.memset. The value is set by the target at the
  /// performance threshold for such a replacement.
  /// @brief Get maximum # of store operations permitted for llvm.memset
  unsigned getMaxStoresPerMemset() const { return maxStoresPerMemset; }

  /// This function returns the maximum number of store operations permitted
  /// to replace a call to llvm.memcpy. The value is set by the target at the
  /// performance threshold for such a replacement.
  /// @brief Get maximum # of store operations permitted for llvm.memcpy
  unsigned getMaxStoresPerMemcpy() const { return maxStoresPerMemcpy; }

  /// This function returns the maximum number of store operations permitted
  /// to replace a call to llvm.memmove. The value is set by the target at the
  /// performance threshold for such a replacement.
  /// @brief Get maximum # of store operations permitted for llvm.memmove
  unsigned getMaxStoresPerMemmove() const { return maxStoresPerMemmove; }

  /// This function returns true if the target allows unaligned memory accesses.
  /// This is used, for example, in situations where an array copy/move/set is 
  /// converted to a sequence of store operations. It's use helps to ensure that
  /// such replacements don't generate code that causes an alignment error 
  /// (trap) on the target machine. 
  /// @brief Determine if the target supports unaligned memory accesses.
  bool allowsUnalignedMemoryAccesses() const {
    return allowUnalignedMemoryAccesses;
  }

  /// getOptimalMemOpType - Returns the target specific optimal type for load
  /// and store operations as a result of memset, memcpy, and memmove lowering.
  /// It returns MVT::iAny if SelectionDAG should be responsible for
  /// determining it.
  virtual MVT getOptimalMemOpType(uint64_t Size, unsigned Align,
                                  bool isSrcConst, bool isSrcStr) const {
    return MVT::iAny;
  }
  
  /// usesUnderscoreSetJmp - Determine if we should use _setjmp or setjmp
  /// to implement llvm.setjmp.
  bool usesUnderscoreSetJmp() const {
    return UseUnderscoreSetJmp;
  }

  /// usesUnderscoreLongJmp - Determine if we should use _longjmp or longjmp
  /// to implement llvm.longjmp.
  bool usesUnderscoreLongJmp() const {
    return UseUnderscoreLongJmp;
  }

  /// getStackPointerRegisterToSaveRestore - If a physical register, this
  /// specifies the register that llvm.savestack/llvm.restorestack should save
  /// and restore.
  unsigned getStackPointerRegisterToSaveRestore() const {
    return StackPointerRegisterToSaveRestore;
  }

  /// getExceptionAddressRegister - If a physical register, this returns
  /// the register that receives the exception address on entry to a landing
  /// pad.
  unsigned getExceptionAddressRegister() const {
    return ExceptionPointerRegister;
  }

  /// getExceptionSelectorRegister - If a physical register, this returns
  /// the register that receives the exception typeid on entry to a landing
  /// pad.
  unsigned getExceptionSelectorRegister() const {
    return ExceptionSelectorRegister;
  }

  /// getJumpBufSize - returns the target's jmp_buf size in bytes (if never
  /// set, the default is 200)
  unsigned getJumpBufSize() const {
    return JumpBufSize;
  }

  /// getJumpBufAlignment - returns the target's jmp_buf alignment in bytes
  /// (if never set, the default is 0)
  unsigned getJumpBufAlignment() const {
    return JumpBufAlignment;
  }

  /// getIfCvtBlockLimit - returns the target specific if-conversion block size
  /// limit. Any block whose size is greater should not be predicated.
  unsigned getIfCvtBlockSizeLimit() const {
    return IfCvtBlockSizeLimit;
  }

  /// getIfCvtDupBlockLimit - returns the target specific size limit for a
  /// block to be considered for duplication. Any block whose size is greater
  /// should not be duplicated to facilitate its predication.
  unsigned getIfCvtDupBlockSizeLimit() const {
    return IfCvtDupBlockSizeLimit;
  }

  /// getPrefLoopAlignment - return the preferred loop alignment.
  ///
  unsigned getPrefLoopAlignment() const {
    return PrefLoopAlignment;
  }
  
  /// getPreIndexedAddressParts - returns true by value, base pointer and
  /// offset pointer and addressing mode by reference if the node's address
  /// can be legally represented as pre-indexed load / store address.
  virtual bool getPreIndexedAddressParts(SDNode *N, SDValue &Base,
                                         SDValue &Offset,
                                         ISD::MemIndexedMode &AM,
                                         SelectionDAG &DAG) const {
    return false;
  }
  
  /// getPostIndexedAddressParts - returns true by value, base pointer and
  /// offset pointer and addressing mode by reference if this node can be
  /// combined with a load / store to form a post-indexed load / store.
  virtual bool getPostIndexedAddressParts(SDNode *N, SDNode *Op,
                                          SDValue &Base, SDValue &Offset,
                                          ISD::MemIndexedMode &AM,
                                          SelectionDAG &DAG) const {
    return false;
  }
  
  /// getPICJumpTableRelocaBase - Returns relocation base for the given PIC
  /// jumptable.
  virtual SDValue getPICJumpTableRelocBase(SDValue Table,
                                             SelectionDAG &DAG) const;

  /// isOffsetFoldingLegal - Return true if folding a constant offset
  /// with the given GlobalAddress is legal.  It is frequently not legal in
  /// PIC relocation models.
  virtual bool isOffsetFoldingLegal(const GlobalAddressSDNode *GA) const;

  //===--------------------------------------------------------------------===//
  // TargetLowering Optimization Methods
  //
  
  /// TargetLoweringOpt - A convenience struct that encapsulates a DAG, and two
  /// SDValues for returning information from TargetLowering to its clients
  /// that want to combine 
  struct TargetLoweringOpt {
    SelectionDAG &DAG;
    SDValue Old;
    SDValue New;

    explicit TargetLoweringOpt(SelectionDAG &InDAG) : DAG(InDAG) {}
    
    bool CombineTo(SDValue O, SDValue N) { 
      Old = O; 
      New = N; 
      return true;
    }
    
    /// ShrinkDemandedConstant - Check to see if the specified operand of the 
    /// specified instruction is a constant integer.  If so, check to see if
    /// there are any bits set in the constant that are not demanded.  If so,
    /// shrink the constant and return true.
    bool ShrinkDemandedConstant(SDValue Op, const APInt &Demanded);
  };
                                                
  /// SimplifyDemandedBits - Look at Op.  At this point, we know that only the
  /// DemandedMask bits of the result of Op are ever used downstream.  If we can
  /// use this information to simplify Op, create a new simplified DAG node and
  /// return true, returning the original and new nodes in Old and New. 
  /// Otherwise, analyze the expression and return a mask of KnownOne and 
  /// KnownZero bits for the expression (used to simplify the caller).  
  /// The KnownZero/One bits may only be accurate for those bits in the 
  /// DemandedMask.
  bool SimplifyDemandedBits(SDValue Op, const APInt &DemandedMask, 
                            APInt &KnownZero, APInt &KnownOne,
                            TargetLoweringOpt &TLO, unsigned Depth = 0) const;
  
  /// computeMaskedBitsForTargetNode - Determine which of the bits specified in
  /// Mask are known to be either zero or one and return them in the 
  /// KnownZero/KnownOne bitsets.
  virtual void computeMaskedBitsForTargetNode(const SDValue Op,
                                              const APInt &Mask,
                                              APInt &KnownZero, 
                                              APInt &KnownOne,
                                              const SelectionDAG &DAG,
                                              unsigned Depth = 0) const;

  /// ComputeNumSignBitsForTargetNode - This method can be implemented by
  /// targets that want to expose additional information about sign bits to the
  /// DAG Combiner.
  virtual unsigned ComputeNumSignBitsForTargetNode(SDValue Op,
                                                   unsigned Depth = 0) const;
  
  struct DAGCombinerInfo {
    void *DC;  // The DAG Combiner object.
    bool BeforeLegalize;
    bool CalledByLegalizer;
  public:
    SelectionDAG &DAG;
    
    DAGCombinerInfo(SelectionDAG &dag, bool bl, bool cl, void *dc)
      : DC(dc), BeforeLegalize(bl), CalledByLegalizer(cl), DAG(dag) {}
    
    bool isBeforeLegalize() const { return BeforeLegalize; }
    bool isCalledByLegalizer() const { return CalledByLegalizer; }
    
    void AddToWorklist(SDNode *N);
    SDValue CombineTo(SDNode *N, const std::vector<SDValue> &To);
    SDValue CombineTo(SDNode *N, SDValue Res);
    SDValue CombineTo(SDNode *N, SDValue Res0, SDValue Res1);

    void CommitTargetLoweringOpt(const TargetLoweringOpt &TLO);
  };

  /// SimplifySetCC - Try to simplify a setcc built with the specified operands 
  /// and cc. If it is unable to simplify it, return a null SDValue.
  SDValue SimplifySetCC(MVT VT, SDValue N0, SDValue N1,
                          ISD::CondCode Cond, bool foldBooleans,
                          DAGCombinerInfo &DCI, DebugLoc dl) const;

  /// isGAPlusOffset - Returns true (and the GlobalValue and the offset) if the
  /// node is a GlobalAddress + offset.
  virtual bool
  isGAPlusOffset(SDNode *N, GlobalValue* &GA, int64_t &Offset) const;

  /// isConsecutiveLoad - Return true if LD (which must be a LoadSDNode) is
  /// loading 'Bytes' bytes from a location that is 'Dist' units away from the
  /// location that the 'Base' load is loading from.
  bool isConsecutiveLoad(SDNode *LD, SDNode *Base, unsigned Bytes, int Dist,
                         const MachineFrameInfo *MFI) const;

  /// PerformDAGCombine - This method will be invoked for all target nodes and
  /// for any target-independent nodes that the target has registered with
  /// invoke it for.
  ///
  /// The semantics are as follows:
  /// Return Value:
  ///   SDValue.Val == 0   - No change was made
  ///   SDValue.Val == N   - N was replaced, is dead, and is already handled.
  ///   otherwise          - N should be replaced by the returned Operand.
  ///
  /// In addition, methods provided by DAGCombinerInfo may be used to perform
  /// more complex transformations.
  ///
  virtual SDValue PerformDAGCombine(SDNode *N, DAGCombinerInfo &DCI) const;
  
  //===--------------------------------------------------------------------===//
  // TargetLowering Configuration Methods - These methods should be invoked by
  // the derived class constructor to configure this object for the target.
  //

protected:
  /// setUsesGlobalOffsetTable - Specify that this target does or doesn't use a
  /// GOT for PC-relative code.
  void setUsesGlobalOffsetTable(bool V) { UsesGlobalOffsetTable = V; }

  /// setShiftAmountType - Describe the type that should be used for shift
  /// amounts.  This type defaults to the pointer type.
  void setShiftAmountType(MVT VT) { ShiftAmountTy = VT; }

  /// setBooleanContents - Specify how the target extends the result of a
  /// boolean value from i1 to a wider type.  See getBooleanContents.
  void setBooleanContents(BooleanContent Ty) { BooleanContents = Ty; }

  /// setSchedulingPreference - Specify the target scheduling preference.
  void setSchedulingPreference(SchedPreference Pref) {
    SchedPreferenceInfo = Pref;
  }

  /// setShiftAmountFlavor - Describe how the target handles out of range shift
  /// amounts.
  void setShiftAmountFlavor(OutOfRangeShiftAmount OORSA) {
    ShiftAmtHandling = OORSA;
  }

  /// setUseUnderscoreSetJmp - Indicate whether this target prefers to
  /// use _setjmp to implement llvm.setjmp or the non _ version.
  /// Defaults to false.
  void setUseUnderscoreSetJmp(bool Val) {
    UseUnderscoreSetJmp = Val;
  }

  /// setUseUnderscoreLongJmp - Indicate whether this target prefers to
  /// use _longjmp to implement llvm.longjmp or the non _ version.
  /// Defaults to false.
  void setUseUnderscoreLongJmp(bool Val) {
    UseUnderscoreLongJmp = Val;
  }

  /// setStackPointerRegisterToSaveRestore - If set to a physical register, this
  /// specifies the register that llvm.savestack/llvm.restorestack should save
  /// and restore.
  void setStackPointerRegisterToSaveRestore(unsigned R) {
    StackPointerRegisterToSaveRestore = R;
  }
  
  /// setExceptionPointerRegister - If set to a physical register, this sets
  /// the register that receives the exception address on entry to a landing
  /// pad.
  void setExceptionPointerRegister(unsigned R) {
    ExceptionPointerRegister = R;
  }

  /// setExceptionSelectorRegister - If set to a physical register, this sets
  /// the register that receives the exception typeid on entry to a landing
  /// pad.
  void setExceptionSelectorRegister(unsigned R) {
    ExceptionSelectorRegister = R;
  }

  /// SelectIsExpensive - Tells the code generator not to expand operations
  /// into sequences that use the select operations if possible.
  void setSelectIsExpensive() { SelectIsExpensive = true; }

  /// setIntDivIsCheap - Tells the code generator that integer divide is
  /// expensive, and if possible, should be replaced by an alternate sequence
  /// of instructions not containing an integer divide.
  void setIntDivIsCheap(bool isCheap = true) { IntDivIsCheap = isCheap; }
  
  /// setPow2DivIsCheap - Tells the code generator that it shouldn't generate
  /// srl/add/sra for a signed divide by power of two, and let the target handle
  /// it.
  void setPow2DivIsCheap(bool isCheap = true) { Pow2DivIsCheap = isCheap; }
  
  /// addRegisterClass - Add the specified register class as an available
  /// regclass for the specified value type.  This indicates the selector can
  /// handle values of that class natively.
  void addRegisterClass(MVT VT, TargetRegisterClass *RC) {
    assert((unsigned)VT.getSimpleVT() < array_lengthof(RegClassForVT));
    AvailableRegClasses.push_back(std::make_pair(VT, RC));
    RegClassForVT[VT.getSimpleVT()] = RC;
  }

  /// computeRegisterProperties - Once all of the register classes are added,
  /// this allows us to compute derived properties we expose.
  void computeRegisterProperties();

  /// setOperationAction - Indicate that the specified operation does not work
  /// with the specified type and indicate what to do about it.
  void setOperationAction(unsigned Op, MVT VT,
                          LegalizeAction Action) {
    assert((unsigned)VT.getSimpleVT() < sizeof(OpActions[0])*4 &&
           Op < array_lengthof(OpActions) && "Table isn't big enough!");
    OpActions[Op] &= ~(uint64_t(3UL) << VT.getSimpleVT()*2);
    OpActions[Op] |= (uint64_t)Action << VT.getSimpleVT()*2;
  }
  
  /// setLoadExtAction - Indicate that the specified load with extension does
  /// not work with the with specified type and indicate what to do about it.
  void setLoadExtAction(unsigned ExtType, MVT VT,
                      LegalizeAction Action) {
    assert((unsigned)VT.getSimpleVT() < sizeof(LoadExtActions[0])*4 &&
           ExtType < array_lengthof(LoadExtActions) &&
           "Table isn't big enough!");
    LoadExtActions[ExtType] &= ~(uint64_t(3UL) << VT.getSimpleVT()*2);
    LoadExtActions[ExtType] |= (uint64_t)Action << VT.getSimpleVT()*2;
  }
  
  /// setTruncStoreAction - Indicate that the specified truncating store does
  /// not work with the with specified type and indicate what to do about it.
  void setTruncStoreAction(MVT ValVT, MVT MemVT,
                           LegalizeAction Action) {
    assert((unsigned)ValVT.getSimpleVT() < array_lengthof(TruncStoreActions) &&
           (unsigned)MemVT.getSimpleVT() < sizeof(TruncStoreActions[0])*4 &&
           "Table isn't big enough!");
    TruncStoreActions[ValVT.getSimpleVT()] &= ~(uint64_t(3UL) <<
                                                MemVT.getSimpleVT()*2);
    TruncStoreActions[ValVT.getSimpleVT()] |= (uint64_t)Action <<
      MemVT.getSimpleVT()*2;
  }

  /// setIndexedLoadAction - Indicate that the specified indexed load does or
  /// does not work with the with specified type and indicate what to do abort
  /// it. NOTE: All indexed mode loads are initialized to Expand in
  /// TargetLowering.cpp
  void setIndexedLoadAction(unsigned IdxMode, MVT VT,
                            LegalizeAction Action) {
    assert((unsigned)VT.getSimpleVT() < sizeof(IndexedModeActions[0])*4 &&
           IdxMode < array_lengthof(IndexedModeActions[0]) &&
           "Table isn't big enough!");
    IndexedModeActions[0][IdxMode] &= ~(uint64_t(3UL) << VT.getSimpleVT()*2);
    IndexedModeActions[0][IdxMode] |= (uint64_t)Action << VT.getSimpleVT()*2;
  }
  
  /// setIndexedStoreAction - Indicate that the specified indexed store does or
  /// does not work with the with specified type and indicate what to do about
  /// it. NOTE: All indexed mode stores are initialized to Expand in
  /// TargetLowering.cpp
  void setIndexedStoreAction(unsigned IdxMode, MVT VT,
                             LegalizeAction Action) {
    assert((unsigned)VT.getSimpleVT() < sizeof(IndexedModeActions[1][0])*4 &&
           IdxMode < array_lengthof(IndexedModeActions[1]) &&
           "Table isn't big enough!");
    IndexedModeActions[1][IdxMode] &= ~(uint64_t(3UL) << VT.getSimpleVT()*2);
    IndexedModeActions[1][IdxMode] |= (uint64_t)Action << VT.getSimpleVT()*2;
  }
  
  /// setConvertAction - Indicate that the specified conversion does or does
  /// not work with the with specified type and indicate what to do about it.
  void setConvertAction(MVT FromVT, MVT ToVT,
                        LegalizeAction Action) {
    assert((unsigned)FromVT.getSimpleVT() < array_lengthof(ConvertActions) &&
           (unsigned)ToVT.getSimpleVT() < sizeof(ConvertActions[0])*4 &&
           "Table isn't big enough!");
    ConvertActions[FromVT.getSimpleVT()] &= ~(uint64_t(3UL) <<
                                              ToVT.getSimpleVT()*2);
    ConvertActions[FromVT.getSimpleVT()] |= (uint64_t)Action <<
      ToVT.getSimpleVT()*2;
  }

  /// setCondCodeAction - Indicate that the specified condition code is or isn't
  /// supported on the target and indicate what to do about it.
  void setCondCodeAction(ISD::CondCode CC, MVT VT, LegalizeAction Action) {
    assert((unsigned)VT.getSimpleVT() < sizeof(CondCodeActions[0])*4 &&
           (unsigned)CC < array_lengthof(CondCodeActions) &&
           "Table isn't big enough!");
    CondCodeActions[(unsigned)CC] &= ~(uint64_t(3UL) << VT.getSimpleVT()*2);
    CondCodeActions[(unsigned)CC] |= (uint64_t)Action << VT.getSimpleVT()*2;
  }

  /// AddPromotedToType - If Opc/OrigVT is specified as being promoted, the
  /// promotion code defaults to trying a larger integer/fp until it can find
  /// one that works.  If that default is insufficient, this method can be used
  /// by the target to override the default.
  void AddPromotedToType(unsigned Opc, MVT OrigVT, MVT DestVT) {
    PromoteToType[std::make_pair(Opc, OrigVT.getSimpleVT())] =
      DestVT.getSimpleVT();
  }

  /// addLegalFPImmediate - Indicate that this target can instruction select
  /// the specified FP immediate natively.
  void addLegalFPImmediate(const APFloat& Imm) {
    LegalFPImmediates.push_back(Imm);
  }

  /// setTargetDAGCombine - Targets should invoke this method for each target
  /// independent node that they want to provide a custom DAG combiner for by
  /// implementing the PerformDAGCombine virtual method.
  void setTargetDAGCombine(ISD::NodeType NT) {
    assert(unsigned(NT >> 3) < array_lengthof(TargetDAGCombineArray));
    TargetDAGCombineArray[NT >> 3] |= 1 << (NT&7);
  }
  
  /// setJumpBufSize - Set the target's required jmp_buf buffer size (in
  /// bytes); default is 200
  void setJumpBufSize(unsigned Size) {
    JumpBufSize = Size;
  }

  /// setJumpBufAlignment - Set the target's required jmp_buf buffer
  /// alignment (in bytes); default is 0
  void setJumpBufAlignment(unsigned Align) {
    JumpBufAlignment = Align;
  }

  /// setIfCvtBlockSizeLimit - Set the target's if-conversion block size
  /// limit (in number of instructions); default is 2.
  void setIfCvtBlockSizeLimit(unsigned Limit) {
    IfCvtBlockSizeLimit = Limit;
  }
  
  /// setIfCvtDupBlockSizeLimit - Set the target's block size limit (in number
  /// of instructions) to be considered for code duplication during
  /// if-conversion; default is 2.
  void setIfCvtDupBlockSizeLimit(unsigned Limit) {
    IfCvtDupBlockSizeLimit = Limit;
  }

  /// setPrefLoopAlignment - Set the target's preferred loop alignment. Default
  /// alignment is zero, it means the target does not care about loop alignment.
  void setPrefLoopAlignment(unsigned Align) {
    PrefLoopAlignment = Align;
  }
  
public:

  virtual const TargetSubtarget *getSubtarget() {
    assert(0 && "Not Implemented");
    return NULL;    // this is here to silence compiler errors
  }
  //===--------------------------------------------------------------------===//
  // Lowering methods - These methods must be implemented by targets so that
  // the SelectionDAGLowering code knows how to lower these.
  //

  /// LowerArguments - This hook must be implemented to indicate how we should
  /// lower the arguments for the specified function, into the specified DAG.
  virtual void
  LowerArguments(Function &F, SelectionDAG &DAG,
                 SmallVectorImpl<SDValue>& ArgValues, DebugLoc dl);

  /// LowerCallTo - This hook lowers an abstract call to a function into an
  /// actual call.  This returns a pair of operands.  The first element is the
  /// return value for the function (if RetTy is not VoidTy).  The second
  /// element is the outgoing token chain.
  struct ArgListEntry {
    SDValue Node;
    const Type* Ty;
    bool isSExt  : 1;
    bool isZExt  : 1;
    bool isInReg : 1;
    bool isSRet  : 1;
    bool isNest  : 1;
    bool isByVal : 1;
    uint16_t Alignment;

    ArgListEntry() : isSExt(false), isZExt(false), isInReg(false),
      isSRet(false), isNest(false), isByVal(false), Alignment(0) { }
  };
  typedef std::vector<ArgListEntry> ArgListTy;
  virtual std::pair<SDValue, SDValue>
  LowerCallTo(SDValue Chain, const Type *RetTy, bool RetSExt, bool RetZExt,
              bool isVarArg, bool isInreg, unsigned CallingConv, 
              bool isTailCall, SDValue Callee, ArgListTy &Args, 
              SelectionDAG &DAG, DebugLoc dl);

  /// EmitTargetCodeForMemcpy - Emit target-specific code that performs a
  /// memcpy. This can be used by targets to provide code sequences for cases
  /// that don't fit the target's parameters for simple loads/stores and can be
  /// more efficient than using a library call. This function can return a null
  /// SDValue if the target declines to use custom code and a different
  /// lowering strategy should be used.
  /// 
  /// If AlwaysInline is true, the size is constant and the target should not
  /// emit any calls and is strongly encouraged to attempt to emit inline code
  /// even if it is beyond the usual threshold because this intrinsic is being
  /// expanded in a place where calls are not feasible (e.g. within the prologue
  /// for another call). If the target chooses to decline an AlwaysInline
  /// request here, legalize will resort to using simple loads and stores.
  virtual SDValue
  EmitTargetCodeForMemcpy(SelectionDAG &DAG,
                          SDValue Chain,
                          SDValue Op1, SDValue Op2,
                          SDValue Op3, unsigned Align,
                          bool AlwaysInline,
                          const Value *DstSV, uint64_t DstOff,
                          const Value *SrcSV, uint64_t SrcOff) {
    return SDValue();
  }

  /// EmitTargetCodeForMemmove - Emit target-specific code that performs a
  /// memmove. This can be used by targets to provide code sequences for cases
  /// that don't fit the target's parameters for simple loads/stores and can be
  /// more efficient than using a library call. This function can return a null
  /// SDValue if the target declines to use custom code and a different
  /// lowering strategy should be used.
  virtual SDValue
  EmitTargetCodeForMemmove(SelectionDAG &DAG,
                           SDValue Chain,
                           SDValue Op1, SDValue Op2,
                           SDValue Op3, unsigned Align,
                           const Value *DstSV, uint64_t DstOff,
                           const Value *SrcSV, uint64_t SrcOff) {
    return SDValue();
  }

  /// EmitTargetCodeForMemset - Emit target-specific code that performs a
  /// memset. This can be used by targets to provide code sequences for cases
  /// that don't fit the target's parameters for simple stores and can be more
  /// efficient than using a library call. This function can return a null
  /// SDValue if the target declines to use custom code and a different
  /// lowering strategy should be used.
  virtual SDValue
  EmitTargetCodeForMemset(SelectionDAG &DAG,
                          SDValue Chain,
                          SDValue Op1, SDValue Op2,
                          SDValue Op3, unsigned Align,
                          const Value *DstSV, uint64_t DstOff) {
    return SDValue();
  }

  /// LowerOperationWrapper - This callback is invoked by the type legalizer
  /// to legalize nodes with an illegal operand type but legal result types.
  /// It replaces the LowerOperation callback in the type Legalizer.
  /// The reason we can not do away with LowerOperation entirely is that
  /// LegalizeDAG isn't yet ready to use this callback.
  /// TODO: Consider merging with ReplaceNodeResults.

  /// The target places new result values for the node in Results (their number
  /// and types must exactly match those of the original return values of
  /// the node), or leaves Results empty, which indicates that the node is not
  /// to be custom lowered after all.
  /// The default implementation calls LowerOperation.
  virtual void LowerOperationWrapper(SDNode *N,
                                     SmallVectorImpl<SDValue> &Results,
                                     SelectionDAG &DAG);

  /// LowerOperation - This callback is invoked for operations that are 
  /// unsupported by the target, which are registered to use 'custom' lowering,
  /// and whose defined values are all legal.
  /// If the target has no operations that require custom lowering, it need not
  /// implement this.  The default implementation of this aborts.
  virtual SDValue LowerOperation(SDValue Op, SelectionDAG &DAG);

  /// ReplaceNodeResults - This callback is invoked when a node result type is
  /// illegal for the target, and the operation was registered to use 'custom'
  /// lowering for that result type.  The target places new result values for
  /// the node in Results (their number and types must exactly match those of
  /// the original return values of the node), or leaves Results empty, which
  /// indicates that the node is not to be custom lowered after all.
  ///
  /// If the target has no operations that require custom lowering, it need not
  /// implement this.  The default implementation aborts.
  virtual void ReplaceNodeResults(SDNode *N, SmallVectorImpl<SDValue> &Results,
                                  SelectionDAG &DAG) {
    assert(0 && "ReplaceNodeResults not implemented for this target!");
  }

  /// IsEligibleForTailCallOptimization - Check whether the call is eligible for
  /// tail call optimization. Targets which want to do tail call optimization
  /// should override this function. 
  virtual bool IsEligibleForTailCallOptimization(CallSDNode *Call, 
                                                 SDValue Ret, 
                                                 SelectionDAG &DAG) const {
    return false;
  }

  /// CheckTailCallReturnConstraints - Check whether CALL node immediatly
  /// preceeds the RET node and whether the return uses the result of the node
  /// or is a void return. This function can be used by the target to determine
  /// eligiblity of tail call optimization.
  static bool CheckTailCallReturnConstraints(CallSDNode *TheCall, SDValue Ret) {
    unsigned NumOps = Ret.getNumOperands();
    if ((NumOps == 1 &&
       (Ret.getOperand(0) == SDValue(TheCall,1) ||
        Ret.getOperand(0) == SDValue(TheCall,0))) ||
      (NumOps > 1 &&
       Ret.getOperand(0) == SDValue(TheCall,
                                    TheCall->getNumValues()-1) &&
       Ret.getOperand(1) == SDValue(TheCall,0)))
      return true;
    return false;
  }

  /// GetPossiblePreceedingTailCall - Get preceeding TailCallNodeOpCode node if
  /// it exists. Skip a possible ISD::TokenFactor.
  static SDValue GetPossiblePreceedingTailCall(SDValue Chain,
                                                 unsigned TailCallNodeOpCode) {
    if (Chain.getOpcode() == TailCallNodeOpCode) {
      return Chain;
    } else if (Chain.getOpcode() == ISD::TokenFactor) {
      if (Chain.getNumOperands() &&
          Chain.getOperand(0).getOpcode() == TailCallNodeOpCode)
        return Chain.getOperand(0);
    }
    return Chain;
  }

  /// getTargetNodeName() - This method returns the name of a target specific
  /// DAG node.
  virtual const char *getTargetNodeName(unsigned Opcode) const;

  /// createFastISel - This method returns a target specific FastISel object,
  /// or null if the target does not support "fast" ISel.
  virtual FastISel *
  createFastISel(MachineFunction &,
                 MachineModuleInfo *, DwarfWriter *,
                 DenseMap<const Value *, unsigned> &,
                 DenseMap<const BasicBlock *, MachineBasicBlock *> &,
                 DenseMap<const AllocaInst *, int> &
#ifndef NDEBUG
                 , SmallSet<Instruction*, 8> &CatchInfoLost
#endif
                 ) {
    return 0;
  }

  //===--------------------------------------------------------------------===//
  // Inline Asm Support hooks
  //
  
  enum ConstraintType {
    C_Register,            // Constraint represents specific register(s).
    C_RegisterClass,       // Constraint represents any of register(s) in class.
    C_Memory,              // Memory constraint.
    C_Other,               // Something else.
    C_Unknown              // Unsupported constraint.
  };
  
  /// AsmOperandInfo - This contains information for each constraint that we are
  /// lowering.
  struct AsmOperandInfo : public InlineAsm::ConstraintInfo {
    /// ConstraintCode - This contains the actual string for the code, like "m".
    /// TargetLowering picks the 'best' code from ConstraintInfo::Codes that
    /// most closely matches the operand.
    std::string ConstraintCode;

    /// ConstraintType - Information about the constraint code, e.g. Register,
    /// RegisterClass, Memory, Other, Unknown.
    TargetLowering::ConstraintType ConstraintType;
  
    /// CallOperandval - If this is the result output operand or a
    /// clobber, this is null, otherwise it is the incoming operand to the
    /// CallInst.  This gets modified as the asm is processed.
    Value *CallOperandVal;
  
    /// ConstraintVT - The ValueType for the operand value.
    MVT ConstraintVT;
    
    /// isMatchingInputConstraint - Return true of this is an input operand that
    /// is a matching constraint like "4".
    bool isMatchingInputConstraint() const;
    
    /// getMatchedOperand - If this is an input matching constraint, this method
    /// returns the output operand it matches.
    unsigned getMatchedOperand() const;
  
    AsmOperandInfo(const InlineAsm::ConstraintInfo &info)
      : InlineAsm::ConstraintInfo(info), 
        ConstraintType(TargetLowering::C_Unknown),
        CallOperandVal(0), ConstraintVT(MVT::Other) {
    }
  };

  /// ComputeConstraintToUse - Determines the constraint code and constraint
  /// type to use for the specific AsmOperandInfo, setting
  /// OpInfo.ConstraintCode and OpInfo.ConstraintType.  If the actual operand
  /// being passed in is available, it can be passed in as Op, otherwise an
  /// empty SDValue can be passed. If hasMemory is true it means one of the asm
  /// constraint of the inline asm instruction being processed is 'm'.
  virtual void ComputeConstraintToUse(AsmOperandInfo &OpInfo,
                                      SDValue Op,
                                      bool hasMemory,
                                      SelectionDAG *DAG = 0) const;
  
  /// getConstraintType - Given a constraint, return the type of constraint it
  /// is for this target.
  virtual ConstraintType getConstraintType(const std::string &Constraint) const;
  
  /// getRegClassForInlineAsmConstraint - Given a constraint letter (e.g. "r"),
  /// return a list of registers that can be used to satisfy the constraint.
  /// This should only be used for C_RegisterClass constraints.
  virtual std::vector<unsigned> 
  getRegClassForInlineAsmConstraint(const std::string &Constraint,
                                    MVT VT) const;

  /// getRegForInlineAsmConstraint - Given a physical register constraint (e.g.
  /// {edx}), return the register number and the register class for the
  /// register.
  ///
  /// Given a register class constraint, like 'r', if this corresponds directly
  /// to an LLVM register class, return a register of 0 and the register class
  /// pointer.
  ///
  /// This should only be used for C_Register constraints.  On error,
  /// this returns a register number of 0 and a null register class pointer..
  virtual std::pair<unsigned, const TargetRegisterClass*> 
    getRegForInlineAsmConstraint(const std::string &Constraint,
                                 MVT VT) const;
  
  /// LowerXConstraint - try to replace an X constraint, which matches anything,
  /// with another that has more specific requirements based on the type of the
  /// corresponding operand.  This returns null if there is no replacement to
  /// make.
  virtual const char *LowerXConstraint(MVT ConstraintVT) const;
  
  /// LowerAsmOperandForConstraint - Lower the specified operand into the Ops
  /// vector.  If it is invalid, don't add anything to Ops. If hasMemory is true
  /// it means one of the asm constraint of the inline asm instruction being
  /// processed is 'm'.
  virtual void LowerAsmOperandForConstraint(SDValue Op, char ConstraintLetter,
                                            bool hasMemory,
                                            std::vector<SDValue> &Ops,
                                            SelectionDAG &DAG) const;
  
  //===--------------------------------------------------------------------===//
  // Scheduler hooks
  //
  
  // EmitInstrWithCustomInserter - This method should be implemented by targets
  // that mark instructions with the 'usesCustomDAGSchedInserter' flag.  These
  // instructions are special in various ways, which require special support to
  // insert.  The specified MachineInstr is created but not inserted into any
  // basic blocks, and the scheduler passes ownership of it to this method.
  virtual MachineBasicBlock *EmitInstrWithCustomInserter(MachineInstr *MI,
                                                        MachineBasicBlock *MBB);

  //===--------------------------------------------------------------------===//
  // Addressing mode description hooks (used by LSR etc).
  //

  /// AddrMode - This represents an addressing mode of:
  ///    BaseGV + BaseOffs + BaseReg + Scale*ScaleReg
  /// If BaseGV is null,  there is no BaseGV.
  /// If BaseOffs is zero, there is no base offset.
  /// If HasBaseReg is false, there is no base register.
  /// If Scale is zero, there is no ScaleReg.  Scale of 1 indicates a reg with
  /// no scale.
  ///
  struct AddrMode {
    GlobalValue *BaseGV;
    int64_t      BaseOffs;
    bool         HasBaseReg;
    int64_t      Scale;
    AddrMode() : BaseGV(0), BaseOffs(0), HasBaseReg(false), Scale(0) {}
  };
  
  /// isLegalAddressingMode - Return true if the addressing mode represented by
  /// AM is legal for this target, for a load/store of the specified type.
  /// TODO: Handle pre/postinc as well.
  virtual bool isLegalAddressingMode(const AddrMode &AM, const Type *Ty) const;

  /// isTruncateFree - Return true if it's free to truncate a value of
  /// type Ty1 to type Ty2. e.g. On x86 it's free to truncate a i32 value in
  /// register EAX to i16 by referencing its sub-register AX.
  virtual bool isTruncateFree(const Type *Ty1, const Type *Ty2) const {
    return false;
  }

  virtual bool isTruncateFree(MVT VT1, MVT VT2) const {
    return false;
  }
  
  //===--------------------------------------------------------------------===//
  // Div utility functions
  //
  SDValue BuildSDIV(SDNode *N, SelectionDAG &DAG, 
                      std::vector<SDNode*>* Created) const;
  SDValue BuildUDIV(SDNode *N, SelectionDAG &DAG, 
                      std::vector<SDNode*>* Created) const;


  //===--------------------------------------------------------------------===//
  // Runtime Library hooks
  //

  /// setLibcallName - Rename the default libcall routine name for the specified
  /// libcall.
  void setLibcallName(RTLIB::Libcall Call, const char *Name) {
    LibcallRoutineNames[Call] = Name;
  }

  /// getLibcallName - Get the libcall routine name for the specified libcall.
  ///
  const char *getLibcallName(RTLIB::Libcall Call) const {
    return LibcallRoutineNames[Call];
  }

  /// setCmpLibcallCC - Override the default CondCode to be used to test the
  /// result of the comparison libcall against zero.
  void setCmpLibcallCC(RTLIB::Libcall Call, ISD::CondCode CC) {
    CmpLibcallCCs[Call] = CC;
  }

  /// getCmpLibcallCC - Get the CondCode that's to be used to test the result of
  /// the comparison libcall against zero.
  ISD::CondCode getCmpLibcallCC(RTLIB::Libcall Call) const {
    return CmpLibcallCCs[Call];
  }

private:
  TargetMachine &TM;
  const TargetData *TD;

  /// PointerTy - The type to use for pointers, usually i32 or i64.
  ///
  MVT PointerTy;

  /// IsLittleEndian - True if this is a little endian target.
  ///
  bool IsLittleEndian;

  /// UsesGlobalOffsetTable - True if this target uses a GOT for PIC codegen.
  ///
  bool UsesGlobalOffsetTable;
  
  /// SelectIsExpensive - Tells the code generator not to expand operations
  /// into sequences that use the select operations if possible.
  bool SelectIsExpensive;

  /// IntDivIsCheap - Tells the code generator not to expand integer divides by
  /// constants into a sequence of muls, adds, and shifts.  This is a hack until
  /// a real cost model is in place.  If we ever optimize for size, this will be
  /// set to true unconditionally.
  bool IntDivIsCheap;
  
  /// Pow2DivIsCheap - Tells the code generator that it shouldn't generate
  /// srl/add/sra for a signed divide by power of two, and let the target handle
  /// it.
  bool Pow2DivIsCheap;
  
  /// UseUnderscoreSetJmp - This target prefers to use _setjmp to implement
  /// llvm.setjmp.  Defaults to false.
  bool UseUnderscoreSetJmp;

  /// UseUnderscoreLongJmp - This target prefers to use _longjmp to implement
  /// llvm.longjmp.  Defaults to false.
  bool UseUnderscoreLongJmp;

  /// ShiftAmountTy - The type to use for shift amounts, usually i8 or whatever
  /// PointerTy is.
  MVT ShiftAmountTy;

  OutOfRangeShiftAmount ShiftAmtHandling;

  /// BooleanContents - Information about the contents of the high-bits in
  /// boolean values held in a type wider than i1.  See getBooleanContents.
  BooleanContent BooleanContents;

  /// SchedPreferenceInfo - The target scheduling preference: shortest possible
  /// total cycles or lowest register usage.
  SchedPreference SchedPreferenceInfo;
  
  /// JumpBufSize - The size, in bytes, of the target's jmp_buf buffers
  unsigned JumpBufSize;
  
  /// JumpBufAlignment - The alignment, in bytes, of the target's jmp_buf
  /// buffers
  unsigned JumpBufAlignment;

  /// IfCvtBlockSizeLimit - The maximum allowed size for a block to be
  /// if-converted.
  unsigned IfCvtBlockSizeLimit;
  
  /// IfCvtDupBlockSizeLimit - The maximum allowed size for a block to be
  /// duplicated during if-conversion.
  unsigned IfCvtDupBlockSizeLimit;

  /// PrefLoopAlignment - The perferred loop alignment.
  ///
  unsigned PrefLoopAlignment;

  /// StackPointerRegisterToSaveRestore - If set to a physical register, this
  /// specifies the register that llvm.savestack/llvm.restorestack should save
  /// and restore.
  unsigned StackPointerRegisterToSaveRestore;

  /// ExceptionPointerRegister - If set to a physical register, this specifies
  /// the register that receives the exception address on entry to a landing
  /// pad.
  unsigned ExceptionPointerRegister;

  /// ExceptionSelectorRegister - If set to a physical register, this specifies
  /// the register that receives the exception typeid on entry to a landing
  /// pad.
  unsigned ExceptionSelectorRegister;

  /// RegClassForVT - This indicates the default register class to use for
  /// each ValueType the target supports natively.
  TargetRegisterClass *RegClassForVT[MVT::LAST_VALUETYPE];
  unsigned char NumRegistersForVT[MVT::LAST_VALUETYPE];
  MVT RegisterTypeForVT[MVT::LAST_VALUETYPE];

  /// TransformToType - For any value types we are promoting or expanding, this
  /// contains the value type that we are changing to.  For Expanded types, this
  /// contains one step of the expand (e.g. i64 -> i32), even if there are
  /// multiple steps required (e.g. i64 -> i16).  For types natively supported
  /// by the system, this holds the same type (e.g. i32 -> i32).
  MVT TransformToType[MVT::LAST_VALUETYPE];

  /// OpActions - For each operation and each value type, keep a LegalizeAction
  /// that indicates how instruction selection should deal with the operation.
  /// Most operations are Legal (aka, supported natively by the target), but
  /// operations that are not should be described.  Note that operations on
  /// non-legal value types are not described here.
  uint64_t OpActions[ISD::BUILTIN_OP_END];
  
  /// LoadExtActions - For each load of load extension type and each value type,
  /// keep a LegalizeAction that indicates how instruction selection should deal
  /// with the load.
  uint64_t LoadExtActions[ISD::LAST_LOADEXT_TYPE];
  
  /// TruncStoreActions - For each truncating store, keep a LegalizeAction that
  /// indicates how instruction selection should deal with the store.
  uint64_t TruncStoreActions[MVT::LAST_VALUETYPE];

  /// IndexedModeActions - For each indexed mode and each value type, keep a
  /// pair of LegalizeAction that indicates how instruction selection should
  /// deal with the load / store.
  uint64_t IndexedModeActions[2][ISD::LAST_INDEXED_MODE];
  
  /// ConvertActions - For each conversion from source type to destination type,
  /// keep a LegalizeAction that indicates how instruction selection should
  /// deal with the conversion.
  /// Currently, this is used only for floating->floating conversions
  /// (FP_EXTEND and FP_ROUND).
  uint64_t ConvertActions[MVT::LAST_VALUETYPE];

  /// CondCodeActions - For each condition code (ISD::CondCode) keep a
  /// LegalizeAction that indicates how instruction selection should
  /// deal with the condition code.
  uint64_t CondCodeActions[ISD::SETCC_INVALID];

  ValueTypeActionImpl ValueTypeActions;

  std::vector<APFloat> LegalFPImmediates;

  std::vector<std::pair<MVT, TargetRegisterClass*> > AvailableRegClasses;

  /// TargetDAGCombineArray - Targets can specify ISD nodes that they would
  /// like PerformDAGCombine callbacks for by calling setTargetDAGCombine(),
  /// which sets a bit in this array.
  unsigned char
  TargetDAGCombineArray[(ISD::BUILTIN_OP_END+CHAR_BIT-1)/CHAR_BIT];
  
  /// PromoteToType - For operations that must be promoted to a specific type,
  /// this holds the destination type.  This map should be sparse, so don't hold
  /// it as an array.
  ///
  /// Targets add entries to this map with AddPromotedToType(..), clients access
  /// this with getTypeToPromoteTo(..).
  std::map<std::pair<unsigned, MVT::SimpleValueType>, MVT::SimpleValueType>
    PromoteToType;

  /// LibcallRoutineNames - Stores the name each libcall.
  ///
  const char *LibcallRoutineNames[RTLIB::UNKNOWN_LIBCALL];

  /// CmpLibcallCCs - The ISD::CondCode that should be used to test the result
  /// of each of the comparison libcall against zero.
  ISD::CondCode CmpLibcallCCs[RTLIB::UNKNOWN_LIBCALL];

protected:
  /// When lowering @llvm.memset this field specifies the maximum number of
  /// store operations that may be substituted for the call to memset. Targets
  /// must set this value based on the cost threshold for that target. Targets
  /// should assume that the memset will be done using as many of the largest
  /// store operations first, followed by smaller ones, if necessary, per
  /// alignment restrictions. For example, storing 9 bytes on a 32-bit machine
  /// with 16-bit alignment would result in four 2-byte stores and one 1-byte
  /// store.  This only applies to setting a constant array of a constant size.
  /// @brief Specify maximum number of store instructions per memset call.
  unsigned maxStoresPerMemset;

  /// When lowering @llvm.memcpy this field specifies the maximum number of
  /// store operations that may be substituted for a call to memcpy. Targets
  /// must set this value based on the cost threshold for that target. Targets
  /// should assume that the memcpy will be done using as many of the largest
  /// store operations first, followed by smaller ones, if necessary, per
  /// alignment restrictions. For example, storing 7 bytes on a 32-bit machine
  /// with 32-bit alignment would result in one 4-byte store, a one 2-byte store
  /// and one 1-byte store. This only applies to copying a constant array of
  /// constant size.
  /// @brief Specify maximum bytes of store instructions per memcpy call.
  unsigned maxStoresPerMemcpy;

  /// When lowering @llvm.memmove this field specifies the maximum number of
  /// store instructions that may be substituted for a call to memmove. Targets
  /// must set this value based on the cost threshold for that target. Targets
  /// should assume that the memmove will be done using as many of the largest
  /// store operations first, followed by smaller ones, if necessary, per
  /// alignment restrictions. For example, moving 9 bytes on a 32-bit machine
  /// with 8-bit alignment would result in nine 1-byte stores.  This only
  /// applies to copying a constant array of constant size.
  /// @brief Specify maximum bytes of store instructions per memmove call.
  unsigned maxStoresPerMemmove;

  /// This field specifies whether the target machine permits unaligned memory
  /// accesses.  This is used, for example, to determine the size of store 
  /// operations when copying small arrays and other similar tasks.
  /// @brief Indicate whether the target permits unaligned memory accesses.
  bool allowUnalignedMemoryAccesses;
};
} // end llvm namespace

#endif