//===-- llvm/CodeGen/MachineInstr.h - MachineInstr class --------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains the declaration of the MachineInstr class, which is the
// basic representation for all target dependent machine instructions used by
// the back end.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_CODEGEN_MACHINEINSTR_H
#define LLVM_CODEGEN_MACHINEINSTR_H

#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMapInfo.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/ilist.h"
#include "llvm/ADT/ilist_node.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/IR/DebugInfo.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/IR/InlineAsm.h"
#include "llvm/MC/MCInstrDesc.h"
#include "llvm/Support/ArrayRecycler.h"
#include "llvm/Target/TargetOpcodes.h"

namespace llvm {

template <typename T> class SmallVectorImpl;
class AliasAnalysis;
class TargetInstrInfo;
class TargetRegisterClass;
class TargetRegisterInfo;
class MachineFunction;
class MachineMemOperand;

//===----------------------------------------------------------------------===//
/// MachineInstr - Representation of each machine instruction.
///
/// This class isn't a POD type, but it must have a trivial destructor. When a
/// MachineFunction is deleted, all the contained MachineInstrs are deallocated
/// without having their destructor called.
///
class MachineInstr : public ilist_node<MachineInstr> {
public:
  typedef MachineMemOperand **mmo_iterator;

  /// Flags to specify different kinds of comments to output in
  /// assembly code.  These flags carry semantic information not
  /// otherwise easily derivable from the IR text.
  ///
  enum CommentFlag {
    ReloadReuse = 0x1
  };

  enum MIFlag {
    NoFlags      = 0,
    FrameSetup   = 1 << 0,              // Instruction is used as a part of
                                        // function frame setup code.
    BundledPred  = 1 << 1,              // Instruction has bundled predecessors.
    BundledSucc  = 1 << 2               // Instruction has bundled successors.
  };
private:
  const MCInstrDesc *MCID;              // Instruction descriptor.
  MachineBasicBlock *Parent;            // Pointer to the owning basic block.

  // Operands are allocated by an ArrayRecycler.
  MachineOperand *Operands;             // Pointer to the first operand.
  unsigned NumOperands;                 // Number of operands on instruction.
  typedef ArrayRecycler<MachineOperand>::Capacity OperandCapacity;
  OperandCapacity CapOperands;          // Capacity of the Operands array.

  uint8_t Flags;                        // Various bits of additional
                                        // information about machine
                                        // instruction.

  uint8_t AsmPrinterFlags;              // Various bits of information used by
                                        // the AsmPrinter to emit helpful
                                        // comments.  This is *not* semantic
                                        // information.  Do not use this for
                                        // anything other than to convey comment
                                        // information to AsmPrinter.

  uint8_t NumMemRefs;                   // Information on memory references.
  mmo_iterator MemRefs;

  DebugLoc debugLoc;                    // Source line information.

  MachineInstr(const MachineInstr&) LLVM_DELETED_FUNCTION;
  void operator=(const MachineInstr&) LLVM_DELETED_FUNCTION;
  // Use MachineFunction::DeleteMachineInstr() instead.
  ~MachineInstr() LLVM_DELETED_FUNCTION;

  // Intrusive list support
  friend struct ilist_traits<MachineInstr>;
  friend struct ilist_traits<MachineBasicBlock>;
  void setParent(MachineBasicBlock *P) { Parent = P; }

  /// MachineInstr ctor - This constructor creates a copy of the given
  /// MachineInstr in the given MachineFunction.
  MachineInstr(MachineFunction &, const MachineInstr &);

  /// MachineInstr ctor - This constructor create a MachineInstr and add the
  /// implicit operands.  It reserves space for number of operands specified by
  /// MCInstrDesc.  An explicit DebugLoc is supplied.
  MachineInstr(MachineFunction&, const MCInstrDesc &MCID,
               const DebugLoc dl, bool NoImp = false);

  // MachineInstrs are pool-allocated and owned by MachineFunction.
  friend class MachineFunction;

public:
  const MachineBasicBlock* getParent() const { return Parent; }
  MachineBasicBlock* getParent() { return Parent; }

  /// getAsmPrinterFlags - Return the asm printer flags bitvector.
  ///
  uint8_t getAsmPrinterFlags() const { return AsmPrinterFlags; }

  /// clearAsmPrinterFlags - clear the AsmPrinter bitvector
  ///
  void clearAsmPrinterFlags() { AsmPrinterFlags = 0; }

  /// getAsmPrinterFlag - Return whether an AsmPrinter flag is set.
  ///
  bool getAsmPrinterFlag(CommentFlag Flag) const {
    return AsmPrinterFlags & Flag;
  }

  /// setAsmPrinterFlag - Set a flag for the AsmPrinter.
  ///
  void setAsmPrinterFlag(CommentFlag Flag) {
    AsmPrinterFlags |= (uint8_t)Flag;
  }

  /// clearAsmPrinterFlag - clear specific AsmPrinter flags
  ///
  void clearAsmPrinterFlag(CommentFlag Flag) {
    AsmPrinterFlags &= ~Flag;
  }

  /// getFlags - Return the MI flags bitvector.
  uint8_t getFlags() const {
    return Flags;
  }

  /// getFlag - Return whether an MI flag is set.
  bool getFlag(MIFlag Flag) const {
    return Flags & Flag;
  }

  /// setFlag - Set a MI flag.
  void setFlag(MIFlag Flag) {
    Flags |= (uint8_t)Flag;
  }

  void setFlags(unsigned flags) {
    // Filter out the automatically maintained flags.
    unsigned Mask = BundledPred | BundledSucc;
    Flags = (Flags & Mask) | (flags & ~Mask);
  }

  /// clearFlag - Clear a MI flag.
  void clearFlag(MIFlag Flag) {
    Flags &= ~((uint8_t)Flag);
  }

  /// isInsideBundle - Return true if MI is in a bundle (but not the first MI
  /// in a bundle).
  ///
  /// A bundle looks like this before it's finalized:
  ///   ----------------
  ///   |      MI      |
  ///   ----------------
  ///          |
  ///   ----------------
  ///   |      MI    * |
  ///   ----------------
  ///          |
  ///   ----------------
  ///   |      MI    * |
  ///   ----------------
  /// In this case, the first MI starts a bundle but is not inside a bundle, the
  /// next 2 MIs are considered "inside" the bundle.
  ///
  /// After a bundle is finalized, it looks like this:
  ///   ----------------
  ///   |    Bundle    |
  ///   ----------------
  ///          |
  ///   ----------------
  ///   |      MI    * |
  ///   ----------------
  ///          |
  ///   ----------------
  ///   |      MI    * |
  ///   ----------------
  ///          |
  ///   ----------------
  ///   |      MI    * |
  ///   ----------------
  /// The first instruction has the special opcode "BUNDLE". It's not "inside"
  /// a bundle, but the next three MIs are.
  bool isInsideBundle() const {
    return getFlag(BundledPred);
  }

  /// isBundled - Return true if this instruction part of a bundle. This is true
  /// if either itself or its following instruction is marked "InsideBundle".
  bool isBundled() const {
    return isBundledWithPred() || isBundledWithSucc();
  }

  /// Return true if this instruction is part of a bundle, and it is not the
  /// first instruction in the bundle.
  bool isBundledWithPred() const { return getFlag(BundledPred); }

  /// Return true if this instruction is part of a bundle, and it is not the
  /// last instruction in the bundle.
  bool isBundledWithSucc() const { return getFlag(BundledSucc); }

  /// Bundle this instruction with its predecessor. This can be an unbundled
  /// instruction, or it can be the first instruction in a bundle.
  void bundleWithPred();

  /// Bundle this instruction with its successor. This can be an unbundled
  /// instruction, or it can be the last instruction in a bundle.
  void bundleWithSucc();

  /// Break bundle above this instruction.
  void unbundleFromPred();

  /// Break bundle below this instruction.
  void unbundleFromSucc();

  /// getDebugLoc - Returns the debug location id of this MachineInstr.
  ///
  DebugLoc getDebugLoc() const { return debugLoc; }

  /// \brief Return the debug variable referenced by
  /// this DBG_VALUE instruction.
  DIVariable getDebugVariable() const {
    assert(isDebugValue() && "not a DBG_VALUE");
    DIVariable Var(getOperand(2).getMetadata());
    assert(Var.Verify() && "not a DIVariable");
    return Var;
  }

  /// \brief Return the complex address expression referenced by
  /// this DBG_VALUE instruction.
  DIExpression getDebugExpression() const {
    assert(isDebugValue() && "not a DBG_VALUE");
    DIExpression Expr(getOperand(3).getMetadata());
    assert(Expr.Verify() && "not a DIExpression");
    return Expr;
  }

  /// emitError - Emit an error referring to the source location of this
  /// instruction. This should only be used for inline assembly that is somehow
  /// impossible to compile. Other errors should have been handled much
  /// earlier.
  ///
  /// If this method returns, the caller should try to recover from the error.
  ///
  void emitError(StringRef Msg) const;

  /// getDesc - Returns the target instruction descriptor of this
  /// MachineInstr.
  const MCInstrDesc &getDesc() const { return *MCID; }

  /// getOpcode - Returns the opcode of this MachineInstr.
  ///
  int getOpcode() const { return MCID->Opcode; }

  /// Access to explicit operands of the instruction.
  ///
  unsigned getNumOperands() const { return NumOperands; }

  const MachineOperand& getOperand(unsigned i) const {
    assert(i < getNumOperands() && "getOperand() out of range!");
    return Operands[i];
  }
  MachineOperand& getOperand(unsigned i) {
    assert(i < getNumOperands() && "getOperand() out of range!");
    return Operands[i];
  }

  /// getNumExplicitOperands - Returns the number of non-implicit operands.
  ///
  unsigned getNumExplicitOperands() const;

  /// iterator/begin/end - Iterate over all operands of a machine instruction.
  typedef MachineOperand *mop_iterator;
  typedef const MachineOperand *const_mop_iterator;

  mop_iterator operands_begin() { return Operands; }
  mop_iterator operands_end() { return Operands + NumOperands; }

  const_mop_iterator operands_begin() const { return Operands; }
  const_mop_iterator operands_end() const { return Operands + NumOperands; }

  iterator_range<mop_iterator> operands() {
    return iterator_range<mop_iterator>(operands_begin(), operands_end());
  }
  iterator_range<const_mop_iterator> operands() const {
    return iterator_range<const_mop_iterator>(operands_begin(), operands_end());
  }
  iterator_range<mop_iterator> explicit_operands() {
    return iterator_range<mop_iterator>(
        operands_begin(), operands_begin() + getNumExplicitOperands());
  }
  iterator_range<const_mop_iterator> explicit_operands() const {
    return iterator_range<const_mop_iterator>(
        operands_begin(), operands_begin() + getNumExplicitOperands());
  }
  iterator_range<mop_iterator> implicit_operands() {
    return iterator_range<mop_iterator>(explicit_operands().end(),
                                        operands_end());
  }
  iterator_range<const_mop_iterator> implicit_operands() const {
    return iterator_range<const_mop_iterator>(explicit_operands().end(),
                                              operands_end());
  }
  iterator_range<mop_iterator> defs() {
    return iterator_range<mop_iterator>(
        operands_begin(), operands_begin() + getDesc().getNumDefs());
  }
  iterator_range<const_mop_iterator> defs() const {
    return iterator_range<const_mop_iterator>(
        operands_begin(), operands_begin() + getDesc().getNumDefs());
  }
  iterator_range<mop_iterator> uses() {
    return iterator_range<mop_iterator>(
        operands_begin() + getDesc().getNumDefs(), operands_end());
  }
  iterator_range<const_mop_iterator> uses() const {
    return iterator_range<const_mop_iterator>(
        operands_begin() + getDesc().getNumDefs(), operands_end());
  }

  /// Access to memory operands of the instruction
  mmo_iterator memoperands_begin() const { return MemRefs; }
  mmo_iterator memoperands_end() const { return MemRefs + NumMemRefs; }
  bool memoperands_empty() const { return NumMemRefs == 0; }

  iterator_range<mmo_iterator>  memoperands() {
    return iterator_range<mmo_iterator>(memoperands_begin(), memoperands_end());
  }
  iterator_range<mmo_iterator> memoperands() const {
    return iterator_range<mmo_iterator>(memoperands_begin(), memoperands_end());
  }

  /// hasOneMemOperand - Return true if this instruction has exactly one
  /// MachineMemOperand.
  bool hasOneMemOperand() const {
    return NumMemRefs == 1;
  }

  /// API for querying MachineInstr properties. They are the same as MCInstrDesc
  /// queries but they are bundle aware.

  enum QueryType {
    IgnoreBundle,    // Ignore bundles
    AnyInBundle,     // Return true if any instruction in bundle has property
    AllInBundle      // Return true if all instructions in bundle have property
  };

  /// hasProperty - Return true if the instruction (or in the case of a bundle,
  /// the instructions inside the bundle) has the specified property.
  /// The first argument is the property being queried.
  /// The second argument indicates whether the query should look inside
  /// instruction bundles.
  bool hasProperty(unsigned MCFlag, QueryType Type = AnyInBundle) const {
    // Inline the fast path for unbundled or bundle-internal instructions.
    if (Type == IgnoreBundle || !isBundled() || isBundledWithPred())
      return getDesc().getFlags() & (1 << MCFlag);

    // If this is the first instruction in a bundle, take the slow path.
    return hasPropertyInBundle(1 << MCFlag, Type);
  }

  /// isVariadic - Return true if this instruction can have a variable number of
  /// operands.  In this case, the variable operands will be after the normal
  /// operands but before the implicit definitions and uses (if any are
  /// present).
  bool isVariadic(QueryType Type = IgnoreBundle) const {
    return hasProperty(MCID::Variadic, Type);
  }

  /// hasOptionalDef - Set if this instruction has an optional definition, e.g.
  /// ARM instructions which can set condition code if 's' bit is set.
  bool hasOptionalDef(QueryType Type = IgnoreBundle) const {
    return hasProperty(MCID::HasOptionalDef, Type);
  }

  /// isPseudo - Return true if this is a pseudo instruction that doesn't
  /// correspond to a real machine instruction.
  ///
  bool isPseudo(QueryType Type = IgnoreBundle) const {
    return hasProperty(MCID::Pseudo, Type);
  }

  bool isReturn(QueryType Type = AnyInBundle) const {
    return hasProperty(MCID::Return, Type);
  }

  bool isCall(QueryType Type = AnyInBundle) const {
    return hasProperty(MCID::Call, Type);
  }

  /// isBarrier - Returns true if the specified instruction stops control flow
  /// from executing the instruction immediately following it.  Examples include
  /// unconditional branches and return instructions.
  bool isBarrier(QueryType Type = AnyInBundle) const {
    return hasProperty(MCID::Barrier, Type);
  }

  /// isTerminator - Returns true if this instruction part of the terminator for
  /// a basic block.  Typically this is things like return and branch
  /// instructions.
  ///
  /// Various passes use this to insert code into the bottom of a basic block,
  /// but before control flow occurs.
  bool isTerminator(QueryType Type = AnyInBundle) const {
    return hasProperty(MCID::Terminator, Type);
  }

  /// isBranch - Returns true if this is a conditional, unconditional, or
  /// indirect branch.  Predicates below can be used to discriminate between
  /// these cases, and the TargetInstrInfo::AnalyzeBranch method can be used to
  /// get more information.
  bool isBranch(QueryType Type = AnyInBundle) const {
    return hasProperty(MCID::Branch, Type);
  }

  /// isIndirectBranch - Return true if this is an indirect branch, such as a
  /// branch through a register.
  bool isIndirectBranch(QueryType Type = AnyInBundle) const {
    return hasProperty(MCID::IndirectBranch, Type);
  }

  /// isConditionalBranch - Return true if this is a branch which may fall
  /// through to the next instruction or may transfer control flow to some other
  /// block.  The TargetInstrInfo::AnalyzeBranch method can be used to get more
  /// information about this branch.
  bool isConditionalBranch(QueryType Type = AnyInBundle) const {
    return isBranch(Type) & !isBarrier(Type) & !isIndirectBranch(Type);
  }

  /// isUnconditionalBranch - Return true if this is a branch which always
  /// transfers control flow to some other block.  The
  /// TargetInstrInfo::AnalyzeBranch method can be used to get more information
  /// about this branch.
  bool isUnconditionalBranch(QueryType Type = AnyInBundle) const {
    return isBranch(Type) & isBarrier(Type) & !isIndirectBranch(Type);
  }

  /// Return true if this instruction has a predicate operand that
  /// controls execution.  It may be set to 'always', or may be set to other
  /// values.   There are various methods in TargetInstrInfo that can be used to
  /// control and modify the predicate in this instruction.
  bool isPredicable(QueryType Type = AllInBundle) const {
    // If it's a bundle than all bundled instructions must be predicable for this
    // to return true.
    return hasProperty(MCID::Predicable, Type);
  }

  /// isCompare - Return true if this instruction is a comparison.
  bool isCompare(QueryType Type = IgnoreBundle) const {
    return hasProperty(MCID::Compare, Type);
  }

  /// isMoveImmediate - Return true if this instruction is a move immediate
  /// (including conditional moves) instruction.
  bool isMoveImmediate(QueryType Type = IgnoreBundle) const {
    return hasProperty(MCID::MoveImm, Type);
  }

  /// isBitcast - Return true if this instruction is a bitcast instruction.
  ///
  bool isBitcast(QueryType Type = IgnoreBundle) const {
    return hasProperty(MCID::Bitcast, Type);
  }

  /// isSelect - Return true if this instruction is a select instruction.
  ///
  bool isSelect(QueryType Type = IgnoreBundle) const {
    return hasProperty(MCID::Select, Type);
  }

  /// isNotDuplicable - Return true if this instruction cannot be safely
  /// duplicated.  For example, if the instruction has a unique labels attached
  /// to it, duplicating it would cause multiple definition errors.
  bool isNotDuplicable(QueryType Type = AnyInBundle) const {
    return hasProperty(MCID::NotDuplicable, Type);
  }

  /// hasDelaySlot - Returns true if the specified instruction has a delay slot
  /// which must be filled by the code generator.
  bool hasDelaySlot(QueryType Type = AnyInBundle) const {
    return hasProperty(MCID::DelaySlot, Type);
  }

  /// canFoldAsLoad - Return true for instructions that can be folded as
  /// memory operands in other instructions. The most common use for this
  /// is instructions that are simple loads from memory that don't modify
  /// the loaded value in any way, but it can also be used for instructions
  /// that can be expressed as constant-pool loads, such as V_SETALLONES
  /// on x86, to allow them to be folded when it is beneficial.
  /// This should only be set on instructions that return a value in their
  /// only virtual register definition.
  bool canFoldAsLoad(QueryType Type = IgnoreBundle) const {
    return hasProperty(MCID::FoldableAsLoad, Type);
  }

  /// \brief Return true if this instruction behaves
  /// the same way as the generic REG_SEQUENCE instructions.
  /// E.g., on ARM,
  /// dX VMOVDRR rY, rZ
  /// is equivalent to
  /// dX = REG_SEQUENCE rY, ssub_0, rZ, ssub_1.
  ///
  /// Note that for the optimizers to be able to take advantage of
  /// this property, TargetInstrInfo::getRegSequenceLikeInputs has to be
  /// override accordingly.
  bool isRegSequenceLike(QueryType Type = IgnoreBundle) const {
    return hasProperty(MCID::RegSequence, Type);
  }

  /// \brief Return true if this instruction behaves
  /// the same way as the generic EXTRACT_SUBREG instructions.
  /// E.g., on ARM,
  /// rX, rY VMOVRRD dZ
  /// is equivalent to two EXTRACT_SUBREG:
  /// rX = EXTRACT_SUBREG dZ, ssub_0
  /// rY = EXTRACT_SUBREG dZ, ssub_1
  ///
  /// Note that for the optimizers to be able to take advantage of
  /// this property, TargetInstrInfo::getExtractSubregLikeInputs has to be
  /// override accordingly.
  bool isExtractSubregLike(QueryType Type = IgnoreBundle) const {
    return hasProperty(MCID::ExtractSubreg, Type);
  }

  /// \brief Return true if this instruction behaves
  /// the same way as the generic INSERT_SUBREG instructions.
  /// E.g., on ARM,
  /// dX = VSETLNi32 dY, rZ, Imm
  /// is equivalent to a INSERT_SUBREG:
  /// dX = INSERT_SUBREG dY, rZ, translateImmToSubIdx(Imm)
  ///
  /// Note that for the optimizers to be able to take advantage of
  /// this property, TargetInstrInfo::getInsertSubregLikeInputs has to be
  /// override accordingly.
  bool isInsertSubregLike(QueryType Type = IgnoreBundle) const {
    return hasProperty(MCID::InsertSubreg, Type);
  }

  //===--------------------------------------------------------------------===//
  // Side Effect Analysis
  //===--------------------------------------------------------------------===//

  /// mayLoad - Return true if this instruction could possibly read memory.
  /// Instructions with this flag set are not necessarily simple load
  /// instructions, they may load a value and modify it, for example.
  bool mayLoad(QueryType Type = AnyInBundle) const {
    if (isInlineAsm()) {
      unsigned ExtraInfo = getOperand(InlineAsm::MIOp_ExtraInfo).getImm();
      if (ExtraInfo & InlineAsm::Extra_MayLoad)
        return true;
    }
    return hasProperty(MCID::MayLoad, Type);
  }


  /// mayStore - Return true if this instruction could possibly modify memory.
  /// Instructions with this flag set are not necessarily simple store
  /// instructions, they may store a modified value based on their operands, or
  /// may not actually modify anything, for example.
  bool mayStore(QueryType Type = AnyInBundle) const {
    if (isInlineAsm()) {
      unsigned ExtraInfo = getOperand(InlineAsm::MIOp_ExtraInfo).getImm();
      if (ExtraInfo & InlineAsm::Extra_MayStore)
        return true;
    }
    return hasProperty(MCID::MayStore, Type);
  }

  //===--------------------------------------------------------------------===//
  // Flags that indicate whether an instruction can be modified by a method.
  //===--------------------------------------------------------------------===//

  /// isCommutable - Return true if this may be a 2- or 3-address
  /// instruction (of the form "X = op Y, Z, ..."), which produces the same
  /// result if Y and Z are exchanged.  If this flag is set, then the
  /// TargetInstrInfo::commuteInstruction method may be used to hack on the
  /// instruction.
  ///
  /// Note that this flag may be set on instructions that are only commutable
  /// sometimes.  In these cases, the call to commuteInstruction will fail.
  /// Also note that some instructions require non-trivial modification to
  /// commute them.
  bool isCommutable(QueryType Type = IgnoreBundle) const {
    return hasProperty(MCID::Commutable, Type);
  }

  /// isConvertibleTo3Addr - Return true if this is a 2-address instruction
  /// which can be changed into a 3-address instruction if needed.  Doing this
  /// transformation can be profitable in the register allocator, because it
  /// means that the instruction can use a 2-address form if possible, but
  /// degrade into a less efficient form if the source and dest register cannot
  /// be assigned to the same register.  For example, this allows the x86
  /// backend to turn a "shl reg, 3" instruction into an LEA instruction, which
  /// is the same speed as the shift but has bigger code size.
  ///
  /// If this returns true, then the target must implement the
  /// TargetInstrInfo::convertToThreeAddress method for this instruction, which
  /// is allowed to fail if the transformation isn't valid for this specific
  /// instruction (e.g. shl reg, 4 on x86).
  ///
  bool isConvertibleTo3Addr(QueryType Type = IgnoreBundle) const {
    return hasProperty(MCID::ConvertibleTo3Addr, Type);
  }

  /// usesCustomInsertionHook - Return true if this instruction requires
  /// custom insertion support when the DAG scheduler is inserting it into a
  /// machine basic block.  If this is true for the instruction, it basically
  /// means that it is a pseudo instruction used at SelectionDAG time that is
  /// expanded out into magic code by the target when MachineInstrs are formed.
  ///
  /// If this is true, the TargetLoweringInfo::InsertAtEndOfBasicBlock method
  /// is used to insert this into the MachineBasicBlock.
  bool usesCustomInsertionHook(QueryType Type = IgnoreBundle) const {
    return hasProperty(MCID::UsesCustomInserter, Type);
  }

  /// hasPostISelHook - Return true if this instruction requires *adjustment*
  /// after instruction selection by calling a target hook. For example, this
  /// can be used to fill in ARM 's' optional operand depending on whether
  /// the conditional flag register is used.
  bool hasPostISelHook(QueryType Type = IgnoreBundle) const {
    return hasProperty(MCID::HasPostISelHook, Type);
  }

  /// isRematerializable - Returns true if this instruction is a candidate for
  /// remat.  This flag is deprecated, please don't use it anymore.  If this
  /// flag is set, the isReallyTriviallyReMaterializable() method is called to
  /// verify the instruction is really rematable.
  bool isRematerializable(QueryType Type = AllInBundle) const {
    // It's only possible to re-mat a bundle if all bundled instructions are
    // re-materializable.
    return hasProperty(MCID::Rematerializable, Type);
  }

  /// isAsCheapAsAMove - Returns true if this instruction has the same cost (or
  /// less) than a move instruction. This is useful during certain types of
  /// optimizations (e.g., remat during two-address conversion or machine licm)
  /// where we would like to remat or hoist the instruction, but not if it costs
  /// more than moving the instruction into the appropriate register. Note, we
  /// are not marking copies from and to the same register class with this flag.
  bool isAsCheapAsAMove(QueryType Type = AllInBundle) const {
    // Only returns true for a bundle if all bundled instructions are cheap.
    return hasProperty(MCID::CheapAsAMove, Type);
  }

  /// hasExtraSrcRegAllocReq - Returns true if this instruction source operands
  /// have special register allocation requirements that are not captured by the
  /// operand register classes. e.g. ARM::STRD's two source registers must be an
  /// even / odd pair, ARM::STM registers have to be in ascending order.
  /// Post-register allocation passes should not attempt to change allocations
  /// for sources of instructions with this flag.
  bool hasExtraSrcRegAllocReq(QueryType Type = AnyInBundle) const {
    return hasProperty(MCID::ExtraSrcRegAllocReq, Type);
  }

  /// hasExtraDefRegAllocReq - Returns true if this instruction def operands
  /// have special register allocation requirements that are not captured by the
  /// operand register classes. e.g. ARM::LDRD's two def registers must be an
  /// even / odd pair, ARM::LDM registers have to be in ascending order.
  /// Post-register allocation passes should not attempt to change allocations
  /// for definitions of instructions with this flag.
  bool hasExtraDefRegAllocReq(QueryType Type = AnyInBundle) const {
    return hasProperty(MCID::ExtraDefRegAllocReq, Type);
  }


  enum MICheckType {
    CheckDefs,      // Check all operands for equality
    CheckKillDead,  // Check all operands including kill / dead markers
    IgnoreDefs,     // Ignore all definitions
    IgnoreVRegDefs  // Ignore virtual register definitions
  };

  /// isIdenticalTo - Return true if this instruction is identical to (same
  /// opcode and same operands as) the specified instruction.
  bool isIdenticalTo(const MachineInstr *Other,
                     MICheckType Check = CheckDefs) const;

  /// Unlink 'this' from the containing basic block, and return it without
  /// deleting it.
  ///
  /// This function can not be used on bundled instructions, use
  /// removeFromBundle() to remove individual instructions from a bundle.
  MachineInstr *removeFromParent();

  /// Unlink this instruction from its basic block and return it without
  /// deleting it.
  ///
  /// If the instruction is part of a bundle, the other instructions in the
  /// bundle remain bundled.
  MachineInstr *removeFromBundle();

  /// Unlink 'this' from the containing basic block and delete it.
  ///
  /// If this instruction is the header of a bundle, the whole bundle is erased.
  /// This function can not be used for instructions inside a bundle, use
  /// eraseFromBundle() to erase individual bundled instructions.
  void eraseFromParent();

  /// Unlink 'this' from the containing basic block and delete it.
  ///
  /// For all definitions mark their uses in DBG_VALUE nodes
  /// as undefined. Otherwise like eraseFromParent().
  void eraseFromParentAndMarkDBGValuesForRemoval();

  /// Unlink 'this' form its basic block and delete it.
  ///
  /// If the instruction is part of a bundle, the other instructions in the
  /// bundle remain bundled.
  void eraseFromBundle();

  bool isEHLabel() const { return getOpcode() == TargetOpcode::EH_LABEL; }
  bool isGCLabel() const { return getOpcode() == TargetOpcode::GC_LABEL; }

  /// isLabel - Returns true if the MachineInstr represents a label.
  ///
  bool isLabel() const { return isEHLabel() || isGCLabel(); }
  bool isCFIInstruction() const {
    return getOpcode() == TargetOpcode::CFI_INSTRUCTION;
  }

  // True if the instruction represents a position in the function.
  bool isPosition() const { return isLabel() || isCFIInstruction(); }

  bool isDebugValue() const { return getOpcode() == TargetOpcode::DBG_VALUE; }
  /// A DBG_VALUE is indirect iff the first operand is a register and
  /// the second operand is an immediate.
  bool isIndirectDebugValue() const {
    return isDebugValue()
      && getOperand(0).isReg()
      && getOperand(1).isImm();
  }

  bool isPHI() const { return getOpcode() == TargetOpcode::PHI; }
  bool isKill() const { return getOpcode() == TargetOpcode::KILL; }
  bool isImplicitDef() const { return getOpcode()==TargetOpcode::IMPLICIT_DEF; }
  bool isInlineAsm() const { return getOpcode() == TargetOpcode::INLINEASM; }
  bool isMSInlineAsm() const { 
    return getOpcode() == TargetOpcode::INLINEASM && getInlineAsmDialect();
  }
  bool isStackAligningInlineAsm() const;
  InlineAsm::AsmDialect getInlineAsmDialect() const;
  bool isInsertSubreg() const {
    return getOpcode() == TargetOpcode::INSERT_SUBREG;
  }
  bool isSubregToReg() const {
    return getOpcode() == TargetOpcode::SUBREG_TO_REG;
  }
  bool isRegSequence() const {
    return getOpcode() == TargetOpcode::REG_SEQUENCE;
  }
  bool isBundle() const {
    return getOpcode() == TargetOpcode::BUNDLE;
  }
  bool isCopy() const {
    return getOpcode() == TargetOpcode::COPY;
  }
  bool isFullCopy() const {
    return isCopy() && !getOperand(0).getSubReg() && !getOperand(1).getSubReg();
  }
  bool isExtractSubreg() const {
    return getOpcode() == TargetOpcode::EXTRACT_SUBREG;
  }

  /// isCopyLike - Return true if the instruction behaves like a copy.
  /// This does not include native copy instructions.
  bool isCopyLike() const {
    return isCopy() || isSubregToReg();
  }

  /// isIdentityCopy - Return true is the instruction is an identity copy.
  bool isIdentityCopy() const {
    return isCopy() && getOperand(0).getReg() == getOperand(1).getReg() &&
      getOperand(0).getSubReg() == getOperand(1).getSubReg();
  }

  /// isTransient - Return true if this is a transient instruction that is
  /// either very likely to be eliminated during register allocation (such as
  /// copy-like instructions), or if this instruction doesn't have an
  /// execution-time cost.
  bool isTransient() const {
    switch(getOpcode()) {
    default: return false;
    // Copy-like instructions are usually eliminated during register allocation.
    case TargetOpcode::PHI:
    case TargetOpcode::COPY:
    case TargetOpcode::INSERT_SUBREG:
    case TargetOpcode::SUBREG_TO_REG:
    case TargetOpcode::REG_SEQUENCE:
    // Pseudo-instructions that don't produce any real output.
    case TargetOpcode::IMPLICIT_DEF:
    case TargetOpcode::KILL:
    case TargetOpcode::CFI_INSTRUCTION:
    case TargetOpcode::EH_LABEL:
    case TargetOpcode::GC_LABEL:
    case TargetOpcode::DBG_VALUE:
      return true;
    }
  }

  /// Return the number of instructions inside the MI bundle, excluding the
  /// bundle header.
  ///
  /// This is the number of instructions that MachineBasicBlock::iterator
  /// skips, 0 for unbundled instructions.
  unsigned getBundleSize() const;

  /// readsRegister - Return true if the MachineInstr reads the specified
  /// register. If TargetRegisterInfo is passed, then it also checks if there
  /// is a read of a super-register.
  /// This does not count partial redefines of virtual registers as reads:
  ///   %reg1024:6 = OP.
  bool readsRegister(unsigned Reg,
                     const TargetRegisterInfo *TRI = nullptr) const {
    return findRegisterUseOperandIdx(Reg, false, TRI) != -1;
  }

  /// readsVirtualRegister - Return true if the MachineInstr reads the specified
  /// virtual register. Take into account that a partial define is a
  /// read-modify-write operation.
  bool readsVirtualRegister(unsigned Reg) const {
    return readsWritesVirtualRegister(Reg).first;
  }

  /// readsWritesVirtualRegister - Return a pair of bools (reads, writes)
  /// indicating if this instruction reads or writes Reg. This also considers
  /// partial defines.
  /// If Ops is not null, all operand indices for Reg are added.
  std::pair<bool,bool> readsWritesVirtualRegister(unsigned Reg,
                                SmallVectorImpl<unsigned> *Ops = nullptr) const;

  /// killsRegister - Return true if the MachineInstr kills the specified
  /// register. If TargetRegisterInfo is passed, then it also checks if there is
  /// a kill of a super-register.
  bool killsRegister(unsigned Reg,
                     const TargetRegisterInfo *TRI = nullptr) const {
    return findRegisterUseOperandIdx(Reg, true, TRI) != -1;
  }

  /// definesRegister - Return true if the MachineInstr fully defines the
  /// specified register. If TargetRegisterInfo is passed, then it also checks
  /// if there is a def of a super-register.
  /// NOTE: It's ignoring subreg indices on virtual registers.
  bool definesRegister(unsigned Reg,
                       const TargetRegisterInfo *TRI = nullptr) const {
    return findRegisterDefOperandIdx(Reg, false, false, TRI) != -1;
  }

  /// modifiesRegister - Return true if the MachineInstr modifies (fully define
  /// or partially define) the specified register.
  /// NOTE: It's ignoring subreg indices on virtual registers.
  bool modifiesRegister(unsigned Reg, const TargetRegisterInfo *TRI) const {
    return findRegisterDefOperandIdx(Reg, false, true, TRI) != -1;
  }

  /// registerDefIsDead - Returns true if the register is dead in this machine
  /// instruction. If TargetRegisterInfo is passed, then it also checks
  /// if there is a dead def of a super-register.
  bool registerDefIsDead(unsigned Reg,
                         const TargetRegisterInfo *TRI = nullptr) const {
    return findRegisterDefOperandIdx(Reg, true, false, TRI) != -1;
  }

  /// findRegisterUseOperandIdx() - Returns the operand index that is a use of
  /// the specific register or -1 if it is not found. It further tightens
  /// the search criteria to a use that kills the register if isKill is true.
  int findRegisterUseOperandIdx(unsigned Reg, bool isKill = false,
                                const TargetRegisterInfo *TRI = nullptr) const;

  /// findRegisterUseOperand - Wrapper for findRegisterUseOperandIdx, it returns
  /// a pointer to the MachineOperand rather than an index.
  MachineOperand *findRegisterUseOperand(unsigned Reg, bool isKill = false,
                                      const TargetRegisterInfo *TRI = nullptr) {
    int Idx = findRegisterUseOperandIdx(Reg, isKill, TRI);
    return (Idx == -1) ? nullptr : &getOperand(Idx);
  }

  /// findRegisterDefOperandIdx() - Returns the operand index that is a def of
  /// the specified register or -1 if it is not found. If isDead is true, defs
  /// that are not dead are skipped. If Overlap is true, then it also looks for
  /// defs that merely overlap the specified register. If TargetRegisterInfo is
  /// non-null, then it also checks if there is a def of a super-register.
  /// This may also return a register mask operand when Overlap is true.
  int findRegisterDefOperandIdx(unsigned Reg,
                                bool isDead = false, bool Overlap = false,
                                const TargetRegisterInfo *TRI = nullptr) const;

  /// findRegisterDefOperand - Wrapper for findRegisterDefOperandIdx, it returns
  /// a pointer to the MachineOperand rather than an index.
  MachineOperand *findRegisterDefOperand(unsigned Reg, bool isDead = false,
                                      const TargetRegisterInfo *TRI = nullptr) {
    int Idx = findRegisterDefOperandIdx(Reg, isDead, false, TRI);
    return (Idx == -1) ? nullptr : &getOperand(Idx);
  }

  /// findFirstPredOperandIdx() - Find the index of the first operand in the
  /// operand list that is used to represent the predicate. It returns -1 if
  /// none is found.
  int findFirstPredOperandIdx() const;

  /// findInlineAsmFlagIdx() - Find the index of the flag word operand that
  /// corresponds to operand OpIdx on an inline asm instruction.  Returns -1 if
  /// getOperand(OpIdx) does not belong to an inline asm operand group.
  ///
  /// If GroupNo is not NULL, it will receive the number of the operand group
  /// containing OpIdx.
  ///
  /// The flag operand is an immediate that can be decoded with methods like
  /// InlineAsm::hasRegClassConstraint().
  ///
  int findInlineAsmFlagIdx(unsigned OpIdx, unsigned *GroupNo = nullptr) const;

  /// getRegClassConstraint - Compute the static register class constraint for
  /// operand OpIdx.  For normal instructions, this is derived from the
  /// MCInstrDesc.  For inline assembly it is derived from the flag words.
  ///
  /// Returns NULL if the static register classs constraint cannot be
  /// determined.
  ///
  const TargetRegisterClass*
  getRegClassConstraint(unsigned OpIdx,
                        const TargetInstrInfo *TII,
                        const TargetRegisterInfo *TRI) const;

  /// \brief Applies the constraints (def/use) implied by this MI on \p Reg to
  /// the given \p CurRC.
  /// If \p ExploreBundle is set and MI is part of a bundle, all the
  /// instructions inside the bundle will be taken into account. In other words,
  /// this method accumulates all the constrains of the operand of this MI and
  /// the related bundle if MI is a bundle or inside a bundle.
  ///
  /// Returns the register class that statisfies both \p CurRC and the
  /// constraints set by MI. Returns NULL if such a register class does not
  /// exist.
  ///
  /// \pre CurRC must not be NULL.
  const TargetRegisterClass *getRegClassConstraintEffectForVReg(
      unsigned Reg, const TargetRegisterClass *CurRC,
      const TargetInstrInfo *TII, const TargetRegisterInfo *TRI,
      bool ExploreBundle = false) const;

  /// \brief Applies the constraints (def/use) implied by the \p OpIdx operand
  /// to the given \p CurRC.
  ///
  /// Returns the register class that statisfies both \p CurRC and the
  /// constraints set by \p OpIdx MI. Returns NULL if such a register class
  /// does not exist.
  ///
  /// \pre CurRC must not be NULL.
  /// \pre The operand at \p OpIdx must be a register.
  const TargetRegisterClass *
  getRegClassConstraintEffect(unsigned OpIdx, const TargetRegisterClass *CurRC,
                              const TargetInstrInfo *TII,
                              const TargetRegisterInfo *TRI) const;

  /// tieOperands - Add a tie between the register operands at DefIdx and
  /// UseIdx. The tie will cause the register allocator to ensure that the two
  /// operands are assigned the same physical register.
  ///
  /// Tied operands are managed automatically for explicit operands in the
  /// MCInstrDesc. This method is for exceptional cases like inline asm.
  void tieOperands(unsigned DefIdx, unsigned UseIdx);

  /// findTiedOperandIdx - Given the index of a tied register operand, find the
  /// operand it is tied to. Defs are tied to uses and vice versa. Returns the
  /// index of the tied operand which must exist.
  unsigned findTiedOperandIdx(unsigned OpIdx) const;

  /// isRegTiedToUseOperand - Given the index of a register def operand,
  /// check if the register def is tied to a source operand, due to either
  /// two-address elimination or inline assembly constraints. Returns the
  /// first tied use operand index by reference if UseOpIdx is not null.
  bool isRegTiedToUseOperand(unsigned DefOpIdx,
                             unsigned *UseOpIdx = nullptr) const {
    const MachineOperand &MO = getOperand(DefOpIdx);
    if (!MO.isReg() || !MO.isDef() || !MO.isTied())
      return false;
    if (UseOpIdx)
      *UseOpIdx = findTiedOperandIdx(DefOpIdx);
    return true;
  }

  /// isRegTiedToDefOperand - Return true if the use operand of the specified
  /// index is tied to a def operand. It also returns the def operand index by
  /// reference if DefOpIdx is not null.
  bool isRegTiedToDefOperand(unsigned UseOpIdx,
                             unsigned *DefOpIdx = nullptr) const {
    const MachineOperand &MO = getOperand(UseOpIdx);
    if (!MO.isReg() || !MO.isUse() || !MO.isTied())
      return false;
    if (DefOpIdx)
      *DefOpIdx = findTiedOperandIdx(UseOpIdx);
    return true;
  }

  /// clearKillInfo - Clears kill flags on all operands.
  ///
  void clearKillInfo();

  /// substituteRegister - Replace all occurrences of FromReg with ToReg:SubIdx,
  /// properly composing subreg indices where necessary.
  void substituteRegister(unsigned FromReg, unsigned ToReg, unsigned SubIdx,
                          const TargetRegisterInfo &RegInfo);

  /// addRegisterKilled - We have determined MI kills a register. Look for the
  /// operand that uses it and mark it as IsKill. If AddIfNotFound is true,
  /// add a implicit operand if it's not found. Returns true if the operand
  /// exists / is added.
  bool addRegisterKilled(unsigned IncomingReg,
                         const TargetRegisterInfo *RegInfo,
                         bool AddIfNotFound = false);

  /// clearRegisterKills - Clear all kill flags affecting Reg.  If RegInfo is
  /// provided, this includes super-register kills.
  void clearRegisterKills(unsigned Reg, const TargetRegisterInfo *RegInfo);

  /// addRegisterDead - We have determined MI defined a register without a use.
  /// Look for the operand that defines it and mark it as IsDead. If
  /// AddIfNotFound is true, add a implicit operand if it's not found. Returns
  /// true if the operand exists / is added.
  bool addRegisterDead(unsigned Reg, const TargetRegisterInfo *RegInfo,
                       bool AddIfNotFound = false);

  /// addRegisterDefined - We have determined MI defines a register. Make sure
  /// there is an operand defining Reg.
  void addRegisterDefined(unsigned Reg,
                          const TargetRegisterInfo *RegInfo = nullptr);

  /// setPhysRegsDeadExcept - Mark every physreg used by this instruction as
  /// dead except those in the UsedRegs list.
  ///
  /// On instructions with register mask operands, also add implicit-def
  /// operands for all registers in UsedRegs.
  void setPhysRegsDeadExcept(ArrayRef<unsigned> UsedRegs,
                             const TargetRegisterInfo &TRI);

  /// isSafeToMove - Return true if it is safe to move this instruction. If
  /// SawStore is set to true, it means that there is a store (or call) between
  /// the instruction's location and its intended destination.
  bool isSafeToMove(const TargetInstrInfo *TII, AliasAnalysis *AA,
                    bool &SawStore) const;

  /// hasOrderedMemoryRef - Return true if this instruction may have an ordered
  /// or volatile memory reference, or if the information describing the memory
  /// reference is not available. Return false if it is known to have no
  /// ordered or volatile memory references.
  bool hasOrderedMemoryRef() const;

  /// isInvariantLoad - Return true if this instruction is loading from a
  /// location whose value is invariant across the function.  For example,
  /// loading a value from the constant pool or from the argument area of
  /// a function if it does not change.  This should only return true of *all*
  /// loads the instruction does are invariant (if it does multiple loads).
  bool isInvariantLoad(AliasAnalysis *AA) const;

  /// isConstantValuePHI - If the specified instruction is a PHI that always
  /// merges together the same virtual register, return the register, otherwise
  /// return 0.
  unsigned isConstantValuePHI() const;

  /// hasUnmodeledSideEffects - Return true if this instruction has side
  /// effects that are not modeled by mayLoad / mayStore, etc.
  /// For all instructions, the property is encoded in MCInstrDesc::Flags
  /// (see MCInstrDesc::hasUnmodeledSideEffects(). The only exception is
  /// INLINEASM instruction, in which case the side effect property is encoded
  /// in one of its operands (see InlineAsm::Extra_HasSideEffect).
  ///
  bool hasUnmodeledSideEffects() const;

  /// allDefsAreDead - Return true if all the defs of this instruction are dead.
  ///
  bool allDefsAreDead() const;

  /// copyImplicitOps - Copy implicit register operands from specified
  /// instruction to this instruction.
  void copyImplicitOps(MachineFunction &MF, const MachineInstr *MI);

  //
  // Debugging support
  //
  void print(raw_ostream &OS, const TargetMachine *TM = nullptr,
             bool SkipOpers = false) const;
  void dump() const;

  //===--------------------------------------------------------------------===//
  // Accessors used to build up machine instructions.

  /// Add the specified operand to the instruction.  If it is an implicit
  /// operand, it is added to the end of the operand list.  If it is an
  /// explicit operand it is added at the end of the explicit operand list
  /// (before the first implicit operand).
  ///
  /// MF must be the machine function that was used to allocate this
  /// instruction.
  ///
  /// MachineInstrBuilder provides a more convenient interface for creating
  /// instructions and adding operands.
  void addOperand(MachineFunction &MF, const MachineOperand &Op);

  /// Add an operand without providing an MF reference. This only works for
  /// instructions that are inserted in a basic block.
  ///
  /// MachineInstrBuilder and the two-argument addOperand(MF, MO) should be
  /// preferred.
  void addOperand(const MachineOperand &Op);

  /// setDesc - Replace the instruction descriptor (thus opcode) of
  /// the current instruction with a new one.
  ///
  void setDesc(const MCInstrDesc &tid) { MCID = &tid; }

  /// setDebugLoc - Replace current source information with new such.
  /// Avoid using this, the constructor argument is preferable.
  ///
  void setDebugLoc(const DebugLoc dl) { debugLoc = dl; }

  /// RemoveOperand - Erase an operand  from an instruction, leaving it with one
  /// fewer operand than it started with.
  ///
  void RemoveOperand(unsigned i);

  /// addMemOperand - Add a MachineMemOperand to the machine instruction.
  /// This function should be used only occasionally. The setMemRefs function
  /// is the primary method for setting up a MachineInstr's MemRefs list.
  void addMemOperand(MachineFunction &MF, MachineMemOperand *MO);

  /// setMemRefs - Assign this MachineInstr's memory reference descriptor
  /// list. This does not transfer ownership.
  void setMemRefs(mmo_iterator NewMemRefs, mmo_iterator NewMemRefsEnd) {
    MemRefs = NewMemRefs;
    NumMemRefs = uint8_t(NewMemRefsEnd - NewMemRefs);
    assert(NumMemRefs == NewMemRefsEnd - NewMemRefs && "Too many memrefs");
  }

private:
  /// getRegInfo - If this instruction is embedded into a MachineFunction,
  /// return the MachineRegisterInfo object for the current function, otherwise
  /// return null.
  MachineRegisterInfo *getRegInfo();

  /// untieRegOperand - Break any tie involving OpIdx.
  void untieRegOperand(unsigned OpIdx) {
    MachineOperand &MO = getOperand(OpIdx);
    if (MO.isReg() && MO.isTied()) {
      getOperand(findTiedOperandIdx(OpIdx)).TiedTo = 0;
      MO.TiedTo = 0;
    }
  }

  /// addImplicitDefUseOperands - Add all implicit def and use operands to
  /// this instruction.
  void addImplicitDefUseOperands(MachineFunction &MF);

  /// RemoveRegOperandsFromUseLists - Unlink all of the register operands in
  /// this instruction from their respective use lists.  This requires that the
  /// operands already be on their use lists.
  void RemoveRegOperandsFromUseLists(MachineRegisterInfo&);

  /// AddRegOperandsToUseLists - Add all of the register operands in
  /// this instruction from their respective use lists.  This requires that the
  /// operands not be on their use lists yet.
  void AddRegOperandsToUseLists(MachineRegisterInfo&);

  /// hasPropertyInBundle - Slow path for hasProperty when we're dealing with a
  /// bundle.
  bool hasPropertyInBundle(unsigned Mask, QueryType Type) const;

  /// \brief Implements the logic of getRegClassConstraintEffectForVReg for the
  /// this MI and the given operand index \p OpIdx.
  /// If the related operand does not constrained Reg, this returns CurRC.
  const TargetRegisterClass *getRegClassConstraintEffectForVRegImpl(
      unsigned OpIdx, unsigned Reg, const TargetRegisterClass *CurRC,
      const TargetInstrInfo *TII, const TargetRegisterInfo *TRI) const;
};

/// MachineInstrExpressionTrait - Special DenseMapInfo traits to compare
/// MachineInstr* by *value* of the instruction rather than by pointer value.
/// The hashing and equality testing functions ignore definitions so this is
/// useful for CSE, etc.
struct MachineInstrExpressionTrait : DenseMapInfo<MachineInstr*> {
  static inline MachineInstr *getEmptyKey() {
    return nullptr;
  }

  static inline MachineInstr *getTombstoneKey() {
    return reinterpret_cast<MachineInstr*>(-1);
  }

  static unsigned getHashValue(const MachineInstr* const &MI);

  static bool isEqual(const MachineInstr* const &LHS,
                      const MachineInstr* const &RHS) {
    if (RHS == getEmptyKey() || RHS == getTombstoneKey() ||
        LHS == getEmptyKey() || LHS == getTombstoneKey())
      return LHS == RHS;
    return LHS->isIdenticalTo(RHS, MachineInstr::IgnoreVRegDefs);
  }
};

//===----------------------------------------------------------------------===//
// Debugging Support

inline raw_ostream& operator<<(raw_ostream &OS, const MachineInstr &MI) {
  MI.print(OS);
  return OS;
}

} // End llvm namespace

#endif