llvm/Target/TargetInstrInfo.h

//===-- llvm/Target/TargetInstrInfo.h - Instruction 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 the target machine instruction set to the code generator.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_TARGET_TARGETINSTRINFO_H
#define LLVM_TARGET_TARGETINSTRINFO_H

#include "llvm/Target/TargetInstrDesc.h"
#include "llvm/CodeGen/MachineFunction.h"

namespace llvm {

class InstrItineraryData;
class LiveVariables;
class MCAsmInfo;
class MachineMemOperand;
class MachineRegisterInfo;
class MDNode;
class MCInst;
class SDNode;
class ScheduleHazardRecognizer;
class SelectionDAG;
class TargetRegisterClass;
class TargetRegisterInfo;

template<class T> class SmallVectorImpl;


//---------------------------------------------------------------------------
///
/// TargetInstrInfo - Interface to description of machine instruction set
///
class TargetInstrInfo {
  const TargetInstrDesc *Descriptors; // Raw array to allow static init'n
  unsigned NumOpcodes;                // Number of entries in the desc array

  TargetInstrInfo(const TargetInstrInfo &);  // DO NOT IMPLEMENT
  void operator=(const TargetInstrInfo &);   // DO NOT IMPLEMENT
public:
  TargetInstrInfo(const TargetInstrDesc *desc, unsigned NumOpcodes);
  virtual ~TargetInstrInfo();

  unsigned getNumOpcodes() const { return NumOpcodes; }

  /// get - Return the machine instruction descriptor that corresponds to the
  /// specified instruction opcode.
  ///
  const TargetInstrDesc &get(unsigned Opcode) const {
    assert(Opcode < NumOpcodes && "Invalid opcode!");
    return Descriptors[Opcode];
  }

  /// isTriviallyReMaterializable - Return true if the instruction is trivially
  /// rematerializable, meaning it has no side effects and requires no operands
  /// that aren't always available.
  bool isTriviallyReMaterializable(const MachineInstr *MI,
                                   AliasAnalysis *AA = 0) const {
    return MI->getOpcode() == TargetOpcode::IMPLICIT_DEF ||
           (MI->getDesc().isRematerializable() &&
            (isReallyTriviallyReMaterializable(MI, AA) ||
             isReallyTriviallyReMaterializableGeneric(MI, AA)));
  }

protected:
  /// isReallyTriviallyReMaterializable - For instructions with opcodes for
  /// which the M_REMATERIALIZABLE flag is set, this hook lets the target
  /// specify whether the instruction is actually trivially rematerializable,
  /// taking into consideration its operands. This predicate must return false
  /// if the instruction has any side effects other than producing a value, or
  /// if it requres any address registers that are not always available.
  virtual bool isReallyTriviallyReMaterializable(const MachineInstr *MI,
                                                 AliasAnalysis *AA) const {
    return false;
  }

private:
  /// isReallyTriviallyReMaterializableGeneric - For instructions with opcodes
  /// for which the M_REMATERIALIZABLE flag is set and the target hook
  /// isReallyTriviallyReMaterializable returns false, this function does
  /// target-independent tests to determine if the instruction is really
  /// trivially rematerializable.
  bool isReallyTriviallyReMaterializableGeneric(const MachineInstr *MI,
                                                AliasAnalysis *AA) const;

public:
  /// isCoalescableExtInstr - Return true if the instruction is a "coalescable"
  /// extension instruction. That is, it's like a copy where it's legal for the
  /// source to overlap the destination. e.g. X86::MOVSX64rr32. If this returns
  /// true, then it's expected the pre-extension value is available as a subreg
  /// of the result register. This also returns the sub-register index in
  /// SubIdx.
  virtual bool isCoalescableExtInstr(const MachineInstr &MI,
                                     unsigned &SrcReg, unsigned &DstReg,
                                     unsigned &SubIdx) const {
    return false;
  }

  /// isLoadFromStackSlot - If the specified machine instruction is a direct
  /// load from a stack slot, return the virtual or physical register number of
  /// the destination along with the FrameIndex of the loaded stack slot.  If
  /// not, return 0.  This predicate must return 0 if the instruction has
  /// any side effects other than loading from the stack slot.
  virtual unsigned isLoadFromStackSlot(const MachineInstr *MI,
                                       int &FrameIndex) const {
    return 0;
  }

  /// isLoadFromStackSlotPostFE - Check for post-frame ptr elimination
  /// stack locations as well.  This uses a heuristic so it isn't
  /// reliable for correctness.
  virtual unsigned isLoadFromStackSlotPostFE(const MachineInstr *MI,
                                             int &FrameIndex) const {
    return 0;
  }

  /// hasLoadFromStackSlot - If the specified machine instruction has
  /// a load from a stack slot, return true along with the FrameIndex
  /// of the loaded stack slot and the machine mem operand containing
  /// the reference.  If not, return false.  Unlike
  /// isLoadFromStackSlot, this returns true for any instructions that
  /// loads from the stack.  This is just a hint, as some cases may be
  /// missed.
  virtual bool hasLoadFromStackSlot(const MachineInstr *MI,
                                    const MachineMemOperand *&MMO,
                                    int &FrameIndex) const {
    return 0;
  }

  /// isStoreToStackSlot - If the specified machine instruction is a direct
  /// store to a stack slot, return the virtual or physical register number of
  /// the source reg along with the FrameIndex of the loaded stack slot.  If
  /// not, return 0.  This predicate must return 0 if the instruction has
  /// any side effects other than storing to the stack slot.
  virtual unsigned isStoreToStackSlot(const MachineInstr *MI,
                                      int &FrameIndex) const {
    return 0;
  }

  /// isStoreToStackSlotPostFE - Check for post-frame ptr elimination
  /// stack locations as well.  This uses a heuristic so it isn't
  /// reliable for correctness.
  virtual unsigned isStoreToStackSlotPostFE(const MachineInstr *MI,
                                            int &FrameIndex) const {
    return 0;
  }

  /// hasStoreToStackSlot - If the specified machine instruction has a
  /// store to a stack slot, return true along with the FrameIndex of
  /// the loaded stack slot and the machine mem operand containing the
  /// reference.  If not, return false.  Unlike isStoreToStackSlot,
  /// this returns true for any instructions that stores to the
  /// stack.  This is just a hint, as some cases may be missed.
  virtual bool hasStoreToStackSlot(const MachineInstr *MI,
                                   const MachineMemOperand *&MMO,
                                   int &FrameIndex) const {
    return 0;
  }

  /// reMaterialize - Re-issue the specified 'original' instruction at the
  /// specific location targeting a new destination register.
  /// The register in Orig->getOperand(0).getReg() will be substituted by
  /// DestReg:SubIdx. Any existing subreg index is preserved or composed with
  /// SubIdx.
  virtual void reMaterialize(MachineBasicBlock &MBB,
                             MachineBasicBlock::iterator MI,
                             unsigned DestReg, unsigned SubIdx,
                             const MachineInstr *Orig,
                             const TargetRegisterInfo &TRI) const = 0;

  /// scheduleTwoAddrSource - Schedule the copy / re-mat of the source of the
  /// two-addrss instruction inserted by two-address pass.
  virtual void scheduleTwoAddrSource(MachineInstr *SrcMI,
                                     MachineInstr *UseMI,
                                     const TargetRegisterInfo &TRI) const {
    // Do nothing.
  }

  /// duplicate - Create a duplicate of the Orig instruction in MF. This is like
  /// MachineFunction::CloneMachineInstr(), but the target may update operands
  /// that are required to be unique.
  ///
  /// The instruction must be duplicable as indicated by isNotDuplicable().
  virtual MachineInstr *duplicate(MachineInstr *Orig,
                                  MachineFunction &MF) const = 0;

  /// convertToThreeAddress - This method must be implemented by targets that
  /// set the M_CONVERTIBLE_TO_3_ADDR flag.  When this flag is set, the target
  /// may be able to convert a two-address instruction into one or more true
  /// three-address instructions on demand.  This allows the X86 target (for
  /// example) to convert ADD and SHL instructions into LEA instructions if they
  /// would require register copies due to two-addressness.
  ///
  /// This method returns a null pointer if the transformation cannot be
  /// performed, otherwise it returns the last new instruction.
  ///
  virtual MachineInstr *
  convertToThreeAddress(MachineFunction::iterator &MFI,
                   MachineBasicBlock::iterator &MBBI, LiveVariables *LV) const {
    return 0;
  }

  /// commuteInstruction - If a target has any instructions that are
  /// commutable but require converting to different instructions or making
  /// non-trivial changes to commute them, this method can overloaded to do
  /// that.  The default implementation simply swaps the commutable operands.
  /// If NewMI is false, MI is modified in place and returned; otherwise, a
  /// new machine instruction is created and returned.  Do not call this
  /// method for a non-commutable instruction, but there may be some cases
  /// where this method fails and returns null.
  virtual MachineInstr *commuteInstruction(MachineInstr *MI,
                                           bool NewMI = false) const = 0;

  /// findCommutedOpIndices - If specified MI is commutable, return the two
  /// operand indices that would swap value. Return false if the instruction
  /// is not in a form which this routine understands.
  virtual bool findCommutedOpIndices(MachineInstr *MI, unsigned &SrcOpIdx1,
                                     unsigned &SrcOpIdx2) const = 0;

  /// produceSameValue - Return true if two machine instructions would produce
  /// identical values. By default, this is only true when the two instructions
  /// are deemed identical except for defs.
  virtual bool produceSameValue(const MachineInstr *MI0,
                                const MachineInstr *MI1) const = 0;

  /// AnalyzeBranch - Analyze the branching code at the end of MBB, returning
  /// true if it cannot be understood (e.g. it's a switch dispatch or isn't
  /// implemented for a target).  Upon success, this returns false and returns
  /// with the following information in various cases:
  ///
  /// 1. If this block ends with no branches (it just falls through to its succ)
  ///    just return false, leaving TBB/FBB null.
  /// 2. If this block ends with only an unconditional branch, it sets TBB to be
  ///    the destination block.
  /// 3. If this block ends with a conditional branch and it falls through to a
  ///    successor block, it sets TBB to be the branch destination block and a
  ///    list of operands that evaluate the condition. These operands can be
  ///    passed to other TargetInstrInfo methods to create new branches.
  /// 4. If this block ends with a conditional branch followed by an
  ///    unconditional branch, it returns the 'true' destination in TBB, the
  ///    'false' destination in FBB, and a list of operands that evaluate the
  ///    condition.  These operands can be passed to other TargetInstrInfo
  ///    methods to create new branches.
  ///
  /// Note that RemoveBranch and InsertBranch must be implemented to support
  /// cases where this method returns success.
  ///
  /// If AllowModify is true, then this routine is allowed to modify the basic
  /// block (e.g. delete instructions after the unconditional branch).
  ///
  virtual bool AnalyzeBranch(MachineBasicBlock &MBB, MachineBasicBlock *&TBB,
                             MachineBasicBlock *&FBB,
                             SmallVectorImpl<MachineOperand> &Cond,
                             bool AllowModify = false) const {
    return true;
  }

  /// RemoveBranch - Remove the branching code at the end of the specific MBB.
  /// This is only invoked in cases where AnalyzeBranch returns success. It
  /// returns the number of instructions that were removed.
  virtual unsigned RemoveBranch(MachineBasicBlock &MBB) const {
    assert(0 && "Target didn't implement TargetInstrInfo::RemoveBranch!");
    return 0;
  }

  /// InsertBranch - Insert branch code into the end of the specified
  /// MachineBasicBlock.  The operands to this method are the same as those
  /// returned by AnalyzeBranch.  This is only invoked in cases where
  /// AnalyzeBranch returns success. It returns the number of instructions
  /// inserted.
  ///
  /// It is also invoked by tail merging to add unconditional branches in
  /// cases where AnalyzeBranch doesn't apply because there was no original
  /// branch to analyze.  At least this much must be implemented, else tail
  /// merging needs to be disabled.
  virtual unsigned InsertBranch(MachineBasicBlock &MBB, MachineBasicBlock *TBB,
                                MachineBasicBlock *FBB,
                                const SmallVectorImpl<MachineOperand> &Cond,
                                DebugLoc DL) const {
    assert(0 && "Target didn't implement TargetInstrInfo::InsertBranch!");
    return 0;
  }

  /// ReplaceTailWithBranchTo - Delete the instruction OldInst and everything
  /// after it, replacing it with an unconditional branch to NewDest. This is
  /// used by the tail merging pass.
  virtual void ReplaceTailWithBranchTo(MachineBasicBlock::iterator Tail,
                                       MachineBasicBlock *NewDest) const = 0;

  /// isLegalToSplitMBBAt - Return true if it's legal to split the given basic
  /// block at the specified instruction (i.e. instruction would be the start
  /// of a new basic block).
  virtual bool isLegalToSplitMBBAt(MachineBasicBlock &MBB,
                                   MachineBasicBlock::iterator MBBI) const {
    return true;
  }

  /// isProfitableToIfCvt - Return true if it's profitable to predicate
  /// instructions with accumulated instruction latency of "NumCycles"
  /// of the specified basic block, where the probability of the instructions
  /// being executed is given by Probability, and Confidence is a measure
  /// of our confidence that it will be properly predicted.
  virtual
  bool isProfitableToIfCvt(MachineBasicBlock &MBB, unsigned NumCyles,
                           unsigned ExtraPredCycles,
                           float Probability, float Confidence) const {
    return false;
  }

  /// isProfitableToIfCvt - Second variant of isProfitableToIfCvt, this one
  /// checks for the case where two basic blocks from true and false path
  /// of a if-then-else (diamond) are predicated on mutally exclusive
  /// predicates, where the probability of the true path being taken is given
  /// by Probability, and Confidence is a measure of our confidence that it
  /// will be properly predicted.
  virtual bool
  isProfitableToIfCvt(MachineBasicBlock &TMBB,
                      unsigned NumTCycles, unsigned ExtraTCycles,
                      MachineBasicBlock &FMBB,
                      unsigned NumFCycles, unsigned ExtraFCycles,
                      float Probability, float Confidence) const {
    return false;
  }

  /// isProfitableToDupForIfCvt - Return true if it's profitable for
  /// if-converter to duplicate instructions of specified accumulated
  /// instruction latencies in the specified MBB to enable if-conversion.
  /// The probability of the instructions being executed is given by
  /// Probability, and Confidence is a measure of our confidence that it
  /// will be properly predicted.
  virtual bool
  isProfitableToDupForIfCvt(MachineBasicBlock &MBB, unsigned NumCyles,
                            float Probability, float Confidence) const {
    return false;
  }

  /// copyPhysReg - Emit instructions to copy a pair of physical registers.
  virtual void copyPhysReg(MachineBasicBlock &MBB,
                           MachineBasicBlock::iterator MI, DebugLoc DL,
                           unsigned DestReg, unsigned SrcReg,
                           bool KillSrc) const {
    assert(0 && "Target didn't implement TargetInstrInfo::copyPhysReg!");
  }

  /// storeRegToStackSlot - Store the specified register of the given register
  /// class to the specified stack frame index. The store instruction is to be
  /// added to the given machine basic block before the specified machine
  /// instruction. If isKill is true, the register operand is the last use and
  /// must be marked kill.
  virtual void storeRegToStackSlot(MachineBasicBlock &MBB,
                                   MachineBasicBlock::iterator MI,
                                   unsigned SrcReg, bool isKill, int FrameIndex,
                                   const TargetRegisterClass *RC,
                                   const TargetRegisterInfo *TRI) const {
  assert(0 && "Target didn't implement TargetInstrInfo::storeRegToStackSlot!");
  }

  /// loadRegFromStackSlot - Load the specified register of the given register
  /// class from the specified stack frame index. The load instruction is to be
  /// added to the given machine basic block before the specified machine
  /// instruction.
  virtual void loadRegFromStackSlot(MachineBasicBlock &MBB,
                                    MachineBasicBlock::iterator MI,
                                    unsigned DestReg, int FrameIndex,
                                    const TargetRegisterClass *RC,
                                    const TargetRegisterInfo *TRI) const {
  assert(0 && "Target didn't implement TargetInstrInfo::loadRegFromStackSlot!");
  }

  /// emitFrameIndexDebugValue - Emit a target-dependent form of
  /// DBG_VALUE encoding the address of a frame index.  Addresses would
  /// normally be lowered the same way as other addresses on the target,
  /// e.g. in load instructions.  For targets that do not support this
  /// the debug info is simply lost.
  /// If you add this for a target you should handle this DBG_VALUE in the
  /// target-specific AsmPrinter code as well; you will probably get invalid
  /// assembly output if you don't.
  virtual MachineInstr *emitFrameIndexDebugValue(MachineFunction &MF,
                                                 int FrameIx,
                                                 uint64_t Offset,
                                                 const MDNode *MDPtr,
                                                 DebugLoc dl) const {
    return 0;
  }

  /// foldMemoryOperand - Attempt to fold a load or store of the specified stack
  /// slot into the specified machine instruction for the specified operand(s).
  /// If this is possible, a new instruction is returned with the specified
  /// operand folded, otherwise NULL is returned.
  /// The new instruction is inserted before MI, and the client is responsible
  /// for removing the old instruction.
  MachineInstr* foldMemoryOperand(MachineBasicBlock::iterator MI,
                                  const SmallVectorImpl<unsigned> &Ops,
                                  int FrameIndex) const;

  /// foldMemoryOperand - Same as the previous version except it allows folding
  /// of any load and store from / to any address, not just from a specific
  /// stack slot.
  MachineInstr* foldMemoryOperand(MachineBasicBlock::iterator MI,
                                  const SmallVectorImpl<unsigned> &Ops,
                                  MachineInstr* LoadMI) const;

protected:
  /// foldMemoryOperandImpl - Target-dependent implementation for
  /// foldMemoryOperand. Target-independent code in foldMemoryOperand will
  /// take care of adding a MachineMemOperand to the newly created instruction.
  virtual MachineInstr* foldMemoryOperandImpl(MachineFunction &MF,
                                          MachineInstr* MI,
                                          const SmallVectorImpl<unsigned> &Ops,
                                          int FrameIndex) const {
    return 0;
  }

  /// foldMemoryOperandImpl - Target-dependent implementation for
  /// foldMemoryOperand. Target-independent code in foldMemoryOperand will
  /// take care of adding a MachineMemOperand to the newly created instruction.
  virtual MachineInstr* foldMemoryOperandImpl(MachineFunction &MF,
                                              MachineInstr* MI,
                                          const SmallVectorImpl<unsigned> &Ops,
                                              MachineInstr* LoadMI) const {
    return 0;
  }

public:
  /// canFoldMemoryOperand - Returns true for the specified load / store if
  /// folding is possible.
  virtual
  bool canFoldMemoryOperand(const MachineInstr *MI,
                            const SmallVectorImpl<unsigned> &Ops) const =0;

  /// unfoldMemoryOperand - Separate a single instruction which folded a load or
  /// a store or a load and a store into two or more instruction. If this is
  /// possible, returns true as well as the new instructions by reference.
  virtual bool unfoldMemoryOperand(MachineFunction &MF, MachineInstr *MI,
                                unsigned Reg, bool UnfoldLoad, bool UnfoldStore,
                                 SmallVectorImpl<MachineInstr*> &NewMIs) const{
    return false;
  }

  virtual bool unfoldMemoryOperand(SelectionDAG &DAG, SDNode *N,
                                   SmallVectorImpl<SDNode*> &NewNodes) const {
    return false;
  }

  /// getOpcodeAfterMemoryUnfold - Returns the opcode of the would be new
  /// instruction after load / store are unfolded from an instruction of the
  /// specified opcode. It returns zero if the specified unfolding is not
  /// possible. If LoadRegIndex is non-null, it is filled in with the operand
  /// index of the operand which will hold the register holding the loaded
  /// value.
  virtual unsigned getOpcodeAfterMemoryUnfold(unsigned Opc,
                                      bool UnfoldLoad, bool UnfoldStore,
                                      unsigned *LoadRegIndex = 0) const {
    return 0;
  }

  /// areLoadsFromSameBasePtr - This is used by the pre-regalloc scheduler
  /// to determine if two loads are loading from the same base address. It
  /// should only return true if the base pointers are the same and the
  /// only differences between the two addresses are the offset. It also returns
  /// the offsets by reference.
  virtual bool areLoadsFromSameBasePtr(SDNode *Load1, SDNode *Load2,
                                    int64_t &Offset1, int64_t &Offset2) const {
    return false;
  }

  /// shouldScheduleLoadsNear - This is a used by the pre-regalloc scheduler to
  /// determine (in conjuction with areLoadsFromSameBasePtr) if two loads should
  /// be scheduled togther. On some targets if two loads are loading from
  /// addresses in the same cache line, it's better if they are scheduled
  /// together. This function takes two integers that represent the load offsets
  /// from the common base address. It returns true if it decides it's desirable
  /// to schedule the two loads together. "NumLoads" is the number of loads that
  /// have already been scheduled after Load1.
  virtual bool shouldScheduleLoadsNear(SDNode *Load1, SDNode *Load2,
                                       int64_t Offset1, int64_t Offset2,
                                       unsigned NumLoads) const {
    return false;
  }

  /// ReverseBranchCondition - Reverses the branch condition of the specified
  /// condition list, returning false on success and true if it cannot be
  /// reversed.
  virtual
  bool ReverseBranchCondition(SmallVectorImpl<MachineOperand> &Cond) const {
    return true;
  }

  /// insertNoop - Insert a noop into the instruction stream at the specified
  /// point.
  virtual void insertNoop(MachineBasicBlock &MBB,
                          MachineBasicBlock::iterator MI) const;


  /// getNoopForMachoTarget - Return the noop instruction to use for a noop.
  virtual void getNoopForMachoTarget(MCInst &NopInst) const {
    // Default to just using 'nop' string.
  }


  /// isPredicated - Returns true if the instruction is already predicated.
  ///
  virtual bool isPredicated(const MachineInstr *MI) const {
    return false;
  }

  /// isUnpredicatedTerminator - Returns true if the instruction is a
  /// terminator instruction that has not been predicated.
  virtual bool isUnpredicatedTerminator(const MachineInstr *MI) const;

  /// PredicateInstruction - Convert the instruction into a predicated
  /// instruction. It returns true if the operation was successful.
  virtual
  bool PredicateInstruction(MachineInstr *MI,
                        const SmallVectorImpl<MachineOperand> &Pred) const = 0;

  /// SubsumesPredicate - Returns true if the first specified predicate
  /// subsumes the second, e.g. GE subsumes GT.
  virtual
  bool SubsumesPredicate(const SmallVectorImpl<MachineOperand> &Pred1,
                         const SmallVectorImpl<MachineOperand> &Pred2) const {
    return false;
  }

  /// DefinesPredicate - If the specified instruction defines any predicate
  /// or condition code register(s) used for predication, returns true as well
  /// as the definition predicate(s) by reference.
  virtual bool DefinesPredicate(MachineInstr *MI,
                                std::vector<MachineOperand> &Pred) const {
    return false;
  }

  /// isPredicable - Return true if the specified instruction can be predicated.
  /// By default, this returns true for every instruction with a
  /// PredicateOperand.
  virtual bool isPredicable(MachineInstr *MI) const {
    return MI->getDesc().isPredicable();
  }

  /// isSafeToMoveRegClassDefs - Return true if it's safe to move a machine
  /// instruction that defines the specified register class.
  virtual bool isSafeToMoveRegClassDefs(const TargetRegisterClass *RC) const {
    return true;
  }

  /// isSchedulingBoundary - Test if the given instruction should be
  /// considered a scheduling boundary. This primarily includes labels and
  /// terminators.
  virtual bool isSchedulingBoundary(const MachineInstr *MI,
                                    const MachineBasicBlock *MBB,
                                    const MachineFunction &MF) const = 0;

  /// Measure the specified inline asm to determine an approximation of its
  /// length.
  virtual unsigned getInlineAsmLength(const char *Str,
                                      const MCAsmInfo &MAI) const;

  /// CreateTargetHazardRecognizer - Allocate and return a hazard recognizer
  /// to use for this target when scheduling the machine instructions after
  /// register allocation.
  virtual ScheduleHazardRecognizer*
  CreateTargetPostRAHazardRecognizer(const InstrItineraryData*) const = 0;

  /// AnalyzeCompare - For a comparison instruction, return the source register
  /// in SrcReg and the value it compares against in CmpValue. Return true if
  /// the comparison instruction can be analyzed.
  virtual bool AnalyzeCompare(const MachineInstr *MI,
                              unsigned &SrcReg, int &Mask, int &Value) const {
    return false;
  }

  /// OptimizeCompareInstr - See if the comparison instruction can be converted
  /// into something more efficient. E.g., on ARM most instructions can set the
  /// flags register, obviating the need for a separate CMP.
  virtual bool OptimizeCompareInstr(MachineInstr *CmpInstr,
                                    unsigned SrcReg, int Mask, int Value,
                                    const MachineRegisterInfo *MRI) const {
    return false;
  }

  /// FoldImmediate - 'Reg' is known to be defined by a move immediate
  /// instruction, try to fold the immediate into the use instruction.
  virtual bool FoldImmediate(MachineInstr *UseMI, MachineInstr *DefMI,
                             unsigned Reg, MachineRegisterInfo *MRI) const {
    return false;
  }

  /// getNumMicroOps - Return the number of u-operations the given machine
  /// instruction will be decoded to on the target cpu.
  virtual unsigned getNumMicroOps(const InstrItineraryData *ItinData,
                                  const MachineInstr *MI) const;

  /// getOperandLatency - Compute and return the use operand latency of a given
  /// pair of def and use.
  /// In most cases, the static scheduling itinerary was enough to determine the
  /// operand latency. But it may not be possible for instructions with variable
  /// number of defs / uses.
  virtual int getOperandLatency(const InstrItineraryData *ItinData,
                              const MachineInstr *DefMI, unsigned DefIdx,
                              const MachineInstr *UseMI, unsigned UseIdx) const;

  virtual int getOperandLatency(const InstrItineraryData *ItinData,
                                SDNode *DefNode, unsigned DefIdx,
                                SDNode *UseNode, unsigned UseIdx) const;

  /// getInstrLatency - Compute the instruction latency of a given instruction.
  /// If the instruction has higher cost when predicated, it's returned via
  /// PredCost.
  virtual int getInstrLatency(const InstrItineraryData *ItinData,
                              const MachineInstr *MI,
                              unsigned *PredCost = 0) const;

  virtual int getInstrLatency(const InstrItineraryData *ItinData,
                              SDNode *Node) const;

  /// hasHighOperandLatency - Compute operand latency between a def of 'Reg'
  /// and an use in the current loop, return true if the target considered
  /// it 'high'. This is used by optimization passes such as machine LICM to
  /// determine whether it makes sense to hoist an instruction out even in
  /// high register pressure situation.
  virtual
  bool hasHighOperandLatency(const InstrItineraryData *ItinData,
                             const MachineRegisterInfo *MRI,
                             const MachineInstr *DefMI, unsigned DefIdx,
                             const MachineInstr *UseMI, unsigned UseIdx) const {
    return false;
  }

  /// hasLowDefLatency - Compute operand latency of a def of 'Reg', return true
  /// if the target considered it 'low'.
  virtual
  bool hasLowDefLatency(const InstrItineraryData *ItinData,
                        const MachineInstr *DefMI, unsigned DefIdx) const;
};

/// TargetInstrInfoImpl - This is the default implementation of
/// TargetInstrInfo, which just provides a couple of default implementations
/// for various methods.  This separated out because it is implemented in
/// libcodegen, not in libtarget.
class TargetInstrInfoImpl : public TargetInstrInfo {
protected:
  TargetInstrInfoImpl(const TargetInstrDesc *desc, unsigned NumOpcodes)
  : TargetInstrInfo(desc, NumOpcodes) {}
public:
  virtual void ReplaceTailWithBranchTo(MachineBasicBlock::iterator OldInst,
                                       MachineBasicBlock *NewDest) const;
  virtual MachineInstr *commuteInstruction(MachineInstr *MI,
                                           bool NewMI = false) const;
  virtual bool findCommutedOpIndices(MachineInstr *MI, unsigned &SrcOpIdx1,
                                     unsigned &SrcOpIdx2) const;
  virtual bool canFoldMemoryOperand(const MachineInstr *MI,
                                    const SmallVectorImpl<unsigned> &Ops) const;
  virtual bool PredicateInstruction(MachineInstr *MI,
                            const SmallVectorImpl<MachineOperand> &Pred) const;
  virtual void reMaterialize(MachineBasicBlock &MBB,
                             MachineBasicBlock::iterator MI,
                             unsigned DestReg, unsigned SubReg,
                             const MachineInstr *Orig,
                             const TargetRegisterInfo &TRI) const;
  virtual MachineInstr *duplicate(MachineInstr *Orig,
                                  MachineFunction &MF) const;
  virtual bool produceSameValue(const MachineInstr *MI0,
                                const MachineInstr *MI1) const;
  virtual bool isSchedulingBoundary(const MachineInstr *MI,
                                    const MachineBasicBlock *MBB,
                                    const MachineFunction &MF) const;

  virtual ScheduleHazardRecognizer *
  CreateTargetPostRAHazardRecognizer(const InstrItineraryData*) const;
};

} // End llvm namespace

#endif