runtime/vm/intermediate_language.h

// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

#ifndef VM_INTERMEDIATE_LANGUAGE_H_
#define VM_INTERMEDIATE_LANGUAGE_H_

#include "vm/allocation.h"
#include "vm/ast.h"
#include "vm/growable_array.h"
#include "vm/handles_impl.h"
#include "vm/locations.h"
#include "vm/method_recognizer.h"
#include "vm/object.h"
#include "vm/parser.h"

namespace dart {

DECLARE_FLAG(bool, throw_on_javascript_int_overflow);

class BitVector;
class BlockEntryInstr;
class BoxIntegerInstr;
class BufferFormatter;
class CatchBlockEntryInstr;
class ComparisonInstr;
class Definition;
class Environment;
class FlowGraph;
class FlowGraphBuilder;
class FlowGraphCompiler;
class FlowGraphVisitor;
class Instruction;
class LocalVariable;
class ParsedFunction;
class Range;
class RangeAnalysis;
class RangeBoundary;
class UnboxIntegerInstr;

// CompileType describes type of the value produced by the definition.
//
// It captures the following properties:
//    - whether value can potentially be null or it is definitely not null;
//    - concrete class id of the value or kDynamicCid if unknown statically;
//    - abstract super type of the value, concrete type of the value in runtime
//      is guaranteed to be sub type of this type.
//
// Values of CompileType form a lattice with a None type as a bottom and a
// nullable Dynamic type as a top element. Method Union provides a join
// operation for the lattice.
class CompileType : public ValueObject {
 public:
  static const bool kNullable = true;
  static const bool kNonNullable = false;

  CompileType(bool is_nullable, intptr_t cid, const AbstractType* type)
      : is_nullable_(is_nullable), cid_(cid), type_(type) { }

  CompileType(const CompileType& other)
      : ValueObject(),
        is_nullable_(other.is_nullable_),
        cid_(other.cid_),
        type_(other.type_) { }

  CompileType& operator=(const CompileType& other) {
    is_nullable_ = other.is_nullable_;
    cid_ = other.cid_;
    type_ =  other.type_;
    return *this;
  }

  bool is_nullable() const { return is_nullable_; }

  // Return type such that concrete value's type in runtime is guaranteed to
  // be subtype of it.
  const AbstractType* ToAbstractType();

  // Return class id such that it is either kDynamicCid or in runtime
  // value is guaranteed to have an equal class id.
  intptr_t ToCid();

  // Return class id such that it is either kDynamicCid or in runtime
  // value is guaranteed to be either null or have an equal class id.
  intptr_t ToNullableCid();

  // Returns true if the value is guaranteed to be not-null or is known to be
  // always null.
  bool HasDecidableNullability();

  // Returns true if the value is known to be always null.
  bool IsNull();

  // Returns true if this type is more specific than given type.
  bool IsMoreSpecificThan(const AbstractType& other);

  // Returns true if value of this type is assignable to a location of the
  // given type.
  bool IsAssignableTo(const AbstractType& type) {
    bool is_instance;
    return CanComputeIsInstanceOf(type, kNullable, &is_instance) &&
           is_instance;
  }

  // Create a new CompileType representing given combination of class id and
  // abstract type. The pair is assumed to be coherent.
  static CompileType Create(intptr_t cid, const AbstractType& type);

  CompileType CopyNonNullable() const {
    return CompileType(kNonNullable, cid_, type_);
  }

  static CompileType CreateNullable(bool is_nullable, intptr_t cid) {
    return CompileType(is_nullable, cid, NULL);
  }

  // Create a new CompileType representing given abstract type. By default
  // values as assumed to be nullable.
  static CompileType FromAbstractType(const AbstractType& type,
                                      bool is_nullable = kNullable);

  // Create a new CompileType representing an value with the given class id.
  // Resulting CompileType is nullable only if cid is kDynamicCid or kNullCid.
  static CompileType FromCid(intptr_t cid);

  // Create None CompileType. It is the bottom of the lattice and is used to
  // represent type of the phi that was not yet inferred.
  static CompileType None() {
    return CompileType(kNullable, kIllegalCid, NULL);
  }

  // Create Dynamic CompileType. It is the top of the lattice and is used to
  // represent unknown type.
  static CompileType Dynamic();

  static CompileType Null();

  // Create non-nullable Bool type.
  static CompileType Bool();

  // Create non-nullable Int type.
  static CompileType Int();

  // Create non-nullable String type.
  static CompileType String();

  // Perform a join operation over the type lattice.
  void Union(CompileType* other);

  // Returns true if this and other types are the same.
  bool IsEqualTo(CompileType* other) {
    return (is_nullable_ == other->is_nullable_) &&
        (ToNullableCid() == other->ToNullableCid()) &&
        (ToAbstractType()->Equals(*other->ToAbstractType()));
  }

  bool IsNone() const {
    return (cid_ == kIllegalCid) && (type_ == NULL);
  }

  bool IsInt() {
    return !is_nullable() &&
      ((ToCid() == kSmiCid) ||
       (ToCid() == kMintCid) ||
       ((type_ != NULL) && (type_->Equals(Type::Handle(Type::IntType())))));
  }

  void PrintTo(BufferFormatter* f) const;
  const char* ToCString() const;

 private:
  bool CanComputeIsInstanceOf(const AbstractType& type,
                              bool is_nullable,
                              bool* is_instance);

  bool is_nullable_;
  intptr_t cid_;
  const AbstractType* type_;
};


// Zone allocated wrapper for the CompileType value.
class ZoneCompileType : public ZoneAllocated {
 public:
  static CompileType* Wrap(const CompileType& type) {
    ZoneCompileType* zone_type = new ZoneCompileType(type);
    return zone_type->ToCompileType();
  }

  CompileType* ToCompileType() {
    return &type_;
  }

 protected:
  explicit ZoneCompileType(const CompileType& type) : type_(type) { }

  CompileType type_;
};


// ConstrainedCompileType represents a compile type that is computed from
// another compile type.
class ConstrainedCompileType : public ZoneCompileType {
 public:
  virtual ~ConstrainedCompileType() { }

  // Recompute compile type.
  virtual void Update() = 0;

 protected:
  explicit ConstrainedCompileType(const CompileType& type)
      : ZoneCompileType(type) { }
};


// NotNullConstrainedCompileType represents not-null constraint applied to
// the source compile type. Result is non-nullable version of the incoming
// compile type. It is used to represent compile type propagated downwards
// from strict comparison with the null constant.
class NotNullConstrainedCompileType : public ConstrainedCompileType {
 public:
  explicit NotNullConstrainedCompileType(CompileType* source)
      : ConstrainedCompileType(source->CopyNonNullable()), source_(source) { }

  virtual void Update() {
    type_ = source_->CopyNonNullable();
  }

 private:
  CompileType* source_;
};


class EffectSet : public ValueObject {
 public:
  enum Effects {
    kNoEffects = 0,
    kExternalization = 1,
    kLastEffect = kExternalization
  };

  EffectSet(const EffectSet& other)
      : ValueObject(), effects_(other.effects_) {
  }

  bool IsNone() const { return effects_ == kNoEffects; }

  static EffectSet None() { return EffectSet(kNoEffects); }
  static EffectSet All() {
    ASSERT(EffectSet::kLastEffect == 1);
    return EffectSet(kExternalization);
  }

  static EffectSet Externalization() {
    return EffectSet(kExternalization);
  }

  bool ToInt() { return effects_; }

 private:
  explicit EffectSet(intptr_t effects) : effects_(effects) { }

  intptr_t effects_;
};


class Value : public ZoneAllocated {
 public:
  // A forward iterator that allows removing the current value from the
  // underlying use list during iteration.
  class Iterator {
   public:
    explicit Iterator(Value* head) : next_(head) { Advance(); }
    Value* Current() const { return current_; }
    bool Done() const { return current_ == NULL; }
    void Advance() {
      // Pre-fetch next on advance and cache it.
      current_ = next_;
      if (next_ != NULL) next_ = next_->next_use();
    }
   private:
    Value* current_;
    Value* next_;
  };

  explicit Value(Definition* definition)
      : definition_(definition),
        previous_use_(NULL),
        next_use_(NULL),
        instruction_(NULL),
        use_index_(-1),
        reaching_type_(NULL) { }

  Definition* definition() const { return definition_; }
  void set_definition(Definition* definition) { definition_ = definition; }

  Value* previous_use() const { return previous_use_; }
  void set_previous_use(Value* previous) { previous_use_ = previous; }

  Value* next_use() const { return next_use_; }
  void set_next_use(Value* next) { next_use_ = next; }

  bool IsSingleUse() const {
    return (next_use_ == NULL) && (previous_use_ == NULL);
  }

  Instruction* instruction() const { return instruction_; }
  void set_instruction(Instruction* instruction) { instruction_ = instruction; }

  intptr_t use_index() const { return use_index_; }
  void set_use_index(intptr_t index) { use_index_ = index; }

  static void AddToList(Value* value, Value** list);
  void RemoveFromUseList();

  // Change the definition after use lists have been computed.
  inline void BindTo(Definition* definition);
  inline void BindToEnvironment(Definition* definition);

  Value* Copy(Zone* zone) { return new(zone) Value(definition_); }

  // This function must only be used when the new Value is dominated by
  // the original Value.
  Value* CopyWithType() {
    Value* copy = new Value(definition_);
    copy->reaching_type_ = reaching_type_;
    return copy;
  }

  CompileType* Type();

  void SetReachingType(CompileType* type) {
    reaching_type_ = type;
  }

  void PrintTo(BufferFormatter* f) const;

  const char* ToCString() const;

  const char* DebugName() const { return "Value"; }

  bool IsSmiValue() { return Type()->ToCid() == kSmiCid; }

  // Returns true if this value binds to the constant: 0xFFFFFFFF.
  bool BindsTo32BitMaskConstant() const;

  // Return true if the value represents a constant.
  bool BindsToConstant() const;

  // Return true if the value represents the constant null.
  bool BindsToConstantNull() const;

  // Assert if BindsToConstant() is false, otherwise returns the constant value.
  const Object& BoundConstant() const;

  // Compile time constants, Bool, Smi and Nulls do not need to update
  // the store buffer.
  bool NeedsStoreBuffer();

  bool Equals(Value* other) const;

 private:
  friend class FlowGraphPrinter;

  Definition* definition_;
  Value* previous_use_;
  Value* next_use_;
  Instruction* instruction_;
  intptr_t use_index_;

  CompileType* reaching_type_;

  DISALLOW_COPY_AND_ASSIGN(Value);
};


// An embedded container with N elements of type T.  Used (with partial
// specialization for N=0) because embedded arrays cannot have size 0.
template<typename T, intptr_t N>
class EmbeddedArray {
 public:
  EmbeddedArray() : elements_() { }

  intptr_t length() const { return N; }

  const T& operator[](intptr_t i) const {
    ASSERT(i < length());
    return elements_[i];
  }

  T& operator[](intptr_t i) {
    ASSERT(i < length());
    return elements_[i];
  }

  const T& At(intptr_t i) const {
    return (*this)[i];
  }

  void SetAt(intptr_t i, const T& val) {
    (*this)[i] = val;
  }

 private:
  T elements_[N];
};


template<typename T>
class EmbeddedArray<T, 0> {
 public:
  intptr_t length() const { return 0; }
  const T& operator[](intptr_t i) const {
    UNREACHABLE();
    static T sentinel = 0;
    return sentinel;
  }
  T& operator[](intptr_t i) {
    UNREACHABLE();
    static T sentinel = 0;
    return sentinel;
  }
};


// Instructions.

// M is a single argument macro.  It is applied to each concrete instruction
// type name.  The concrete instruction classes are the name with Instr
// concatenated.
#define FOR_EACH_INSTRUCTION(M)                                                \
  M(GraphEntry)                                                                \
  M(JoinEntry)                                                                 \
  M(TargetEntry)                                                               \
  M(IndirectEntry)                                                             \
  M(CatchBlockEntry)                                                           \
  M(Phi)                                                                       \
  M(Redefinition)                                                              \
  M(Parameter)                                                                 \
  M(ParallelMove)                                                              \
  M(PushArgument)                                                              \
  M(Return)                                                                    \
  M(Throw)                                                                     \
  M(ReThrow)                                                                   \
  M(Stop)                                                                      \
  M(Goto)                                                                      \
  M(IndirectGoto)                                                              \
  M(Branch)                                                                    \
  M(AssertAssignable)                                                          \
  M(AssertBoolean)                                                             \
  M(CurrentContext)                                                            \
  M(ClosureCall)                                                               \
  M(InstanceCall)                                                              \
  M(PolymorphicInstanceCall)                                                   \
  M(StaticCall)                                                                \
  M(LoadLocal)                                                                 \
  M(PushTemp)                                                                  \
  M(DropTemps)                                                                 \
  M(StoreLocal)                                                                \
  M(StrictCompare)                                                             \
  M(EqualityCompare)                                                           \
  M(RelationalOp)                                                              \
  M(NativeCall)                                                                \
  M(DebugStepCheck)                                                            \
  M(LoadIndexed)                                                               \
  M(LoadCodeUnits)                                                             \
  M(StoreIndexed)                                                              \
  M(StoreInstanceField)                                                        \
  M(InitStaticField)                                                           \
  M(LoadStaticField)                                                           \
  M(StoreStaticField)                                                          \
  M(BooleanNegate)                                                             \
  M(InstanceOf)                                                                \
  M(CreateArray)                                                               \
  M(AllocateObject)                                                            \
  M(LoadField)                                                                 \
  M(LoadUntagged)                                                              \
  M(LoadClassId)                                                               \
  M(InstantiateType)                                                           \
  M(InstantiateTypeArguments)                                                  \
  M(AllocateContext)                                                           \
  M(AllocateUninitializedContext)                                              \
  M(CloneContext)                                                              \
  M(BinarySmiOp)                                                               \
  M(BinaryInt32Op)                                                             \
  M(UnarySmiOp)                                                                \
  M(UnaryDoubleOp)                                                             \
  M(CheckStackOverflow)                                                        \
  M(SmiToDouble)                                                               \
  M(Int32ToDouble)                                                             \
  M(MintToDouble)                                                              \
  M(DoubleToInteger)                                                           \
  M(DoubleToSmi)                                                               \
  M(DoubleToDouble)                                                            \
  M(DoubleToFloat)                                                             \
  M(FloatToDouble)                                                             \
  M(CheckClass)                                                                \
  M(CheckClassId)                                                              \
  M(CheckSmi)                                                                  \
  M(Constant)                                                                  \
  M(UnboxedConstant)                                                           \
  M(CheckEitherNonSmi)                                                         \
  M(BinaryDoubleOp)                                                            \
  M(MathUnary)                                                                 \
  M(MathMinMax)                                                                \
  M(Box)                                                                       \
  M(Unbox)                                                                     \
  M(BoxInt64)                                                                  \
  M(UnboxInt64)                                                                \
  M(CaseInsensitiveCompareUC16)                                                \
  M(BinaryMintOp)                                                              \
  M(ShiftMintOp)                                                               \
  M(UnaryMintOp)                                                               \
  M(CheckArrayBound)                                                           \
  M(Constraint)                                                                \
  M(StringToCharCode)                                                          \
  M(StringFromCharCode)                                                        \
  M(StringInterpolate)                                                         \
  M(InvokeMathCFunction)                                                       \
  M(MergedMath)                                                                \
  M(GuardFieldClass)                                                           \
  M(GuardFieldLength)                                                          \
  M(IfThenElse)                                                                \
  M(BinaryFloat32x4Op)                                                         \
  M(Simd32x4Shuffle)                                                           \
  M(Simd32x4ShuffleMix)                                                        \
  M(Simd32x4GetSignMask)                                                       \
  M(Float32x4Constructor)                                                      \
  M(Float32x4Zero)                                                             \
  M(Float32x4Splat)                                                            \
  M(Float32x4Comparison)                                                       \
  M(Float32x4MinMax)                                                           \
  M(Float32x4Scale)                                                            \
  M(Float32x4Sqrt)                                                             \
  M(Float32x4ZeroArg)                                                          \
  M(Float32x4Clamp)                                                            \
  M(Float32x4With)                                                             \
  M(Float32x4ToInt32x4)                                                        \
  M(MaterializeObject)                                                         \
  M(Int32x4Constructor)                                                        \
  M(Int32x4BoolConstructor)                                                    \
  M(Int32x4GetFlag)                                                            \
  M(Int32x4Select)                                                             \
  M(Int32x4SetFlag)                                                            \
  M(Int32x4ToFloat32x4)                                                        \
  M(BinaryInt32x4Op)                                                           \
  M(TestSmi)                                                                   \
  M(TestCids)                                                                  \
  M(BinaryFloat64x2Op)                                                         \
  M(Float64x2Zero)                                                             \
  M(Float64x2Constructor)                                                      \
  M(Float64x2Splat)                                                            \
  M(Float32x4ToFloat64x2)                                                      \
  M(Float64x2ToFloat32x4)                                                      \
  M(Simd64x2Shuffle)                                                           \
  M(Float64x2ZeroArg)                                                          \
  M(Float64x2OneArg)                                                           \
  M(ExtractNthOutput)                                                          \
  M(BinaryUint32Op)                                                            \
  M(ShiftUint32Op)                                                             \
  M(UnaryUint32Op)                                                             \
  M(BoxUint32)                                                                 \
  M(UnboxUint32)                                                               \
  M(BoxInt32)                                                                  \
  M(UnboxInt32)                                                                \
  M(UnboxedIntConverter)                                                       \
  M(GrowRegExpStack)                                                           \
  M(Deoptimize)

#define FOR_EACH_ABSTRACT_INSTRUCTION(M)                                       \
  M(BlockEntry)                                                                \
  M(BoxInteger)                                                                \
  M(UnboxInteger)                                                              \
  M(Comparison)                                                                \
  M(UnaryIntegerOp)                                                            \
  M(BinaryIntegerOp)                                                           \

#define FORWARD_DECLARATION(type) class type##Instr;
FOR_EACH_INSTRUCTION(FORWARD_DECLARATION)
FOR_EACH_ABSTRACT_INSTRUCTION(FORWARD_DECLARATION)
#undef FORWARD_DECLARATION

#define DEFINE_INSTRUCTION_TYPE_CHECK(type)                                    \
  virtual type##Instr* As##type() { return this; }                             \
  virtual const char* DebugName() const { return #type; }                      \

// Functions required in all concrete instruction classes.
#define DECLARE_INSTRUCTION_NO_BACKEND(type)                                   \
  virtual Tag tag() const { return k##type; }                                  \
  virtual void Accept(FlowGraphVisitor* visitor);                              \
  DEFINE_INSTRUCTION_TYPE_CHECK(type)

#define DECLARE_INSTRUCTION_BACKEND()                                          \
  virtual LocationSummary* MakeLocationSummary(Zone* zone,                     \
                                               bool optimizing) const;         \
  virtual void EmitNativeCode(FlowGraphCompiler* compiler);                    \

// Functions required in all concrete instruction classes.
#define DECLARE_INSTRUCTION(type)                                              \
  DECLARE_INSTRUCTION_NO_BACKEND(type)                                         \
  DECLARE_INSTRUCTION_BACKEND()                                                \

class Instruction : public ZoneAllocated {
 public:
#define DECLARE_TAG(type) k##type,
  enum Tag {
    FOR_EACH_INSTRUCTION(DECLARE_TAG)
  };
#undef DECLARE_TAG

  explicit Instruction(intptr_t deopt_id = Thread::kNoDeoptId)
      : deopt_id_(deopt_id),
        lifetime_position_(kNoPlaceId),
        previous_(NULL),
        next_(NULL),
        env_(NULL),
        locs_(NULL),
        inlining_id_(-1) { }

  virtual ~Instruction() { }

  virtual Tag tag() const = 0;

  intptr_t deopt_id() const {
    ASSERT(CanDeoptimize() || CanBecomeDeoptimizationTarget());
    return GetDeoptId();
  }

  const ICData* GetICData(
      const ZoneGrowableArray<const ICData*>& ic_data_array) const;

  virtual intptr_t token_pos() const { return Scanner::kNoSourcePos; }

  virtual intptr_t InputCount() const = 0;
  virtual Value* InputAt(intptr_t i) const = 0;
  void SetInputAt(intptr_t i, Value* value) {
    ASSERT(value != NULL);
    value->set_instruction(this);
    value->set_use_index(i);
    RawSetInputAt(i, value);
  }

  // Remove all inputs (including in the environment) from their
  // definition's use lists.
  void UnuseAllInputs();

  // Call instructions override this function and return the number of
  // pushed arguments.
  virtual intptr_t ArgumentCount() const { return 0; }
  virtual PushArgumentInstr* PushArgumentAt(intptr_t index) const {
    UNREACHABLE();
    return NULL;
  }
  inline Definition* ArgumentAt(intptr_t index) const;

  // Returns true, if this instruction can deoptimize.
  virtual bool CanDeoptimize() const = 0;

  // Visiting support.
  virtual void Accept(FlowGraphVisitor* visitor) = 0;

  Instruction* previous() const { return previous_; }
  void set_previous(Instruction* instr) {
    ASSERT(!IsBlockEntry());
    previous_ = instr;
  }

  Instruction* next() const { return next_; }
  void set_next(Instruction* instr) {
    ASSERT(!IsGraphEntry());
    ASSERT(!IsReturn());
    ASSERT(!IsBranch() || (instr == NULL));
    ASSERT(!IsPhi());
    ASSERT(instr == NULL || !instr->IsBlockEntry());
    // TODO(fschneider): Also add Throw and ReThrow to the list of instructions
    // that do not have a successor. Currently, the graph builder will continue
    // to append instruction in case of a Throw inside an expression. This
    // condition should be handled in the graph builder
    next_ = instr;
  }

  // Link together two instruction.
  void LinkTo(Instruction* next) {
    ASSERT(this != next);
    this->set_next(next);
    next->set_previous(this);
  }

  // Removed this instruction from the graph, after use lists have been
  // computed.  If the instruction is a definition with uses, those uses are
  // unaffected (so the instruction can be reinserted, e.g., hoisting).
  Instruction* RemoveFromGraph(bool return_previous = true);

  // Normal instructions can have 0 (inside a block) or 1 (last instruction in
  // a block) successors. Branch instruction with >1 successors override this
  // function.
  virtual intptr_t SuccessorCount() const;
  virtual BlockEntryInstr* SuccessorAt(intptr_t index) const;

  void Goto(JoinEntryInstr* entry);

  virtual const char* DebugName() const = 0;

  // Printing support.
  const char* ToCString() const;
  virtual void PrintTo(BufferFormatter* f) const;
  virtual void PrintOperandsTo(BufferFormatter* f) const;

#define DECLARE_INSTRUCTION_TYPE_CHECK(Name, Type)                             \
  bool Is##Name() { return (As##Name() != NULL); }                             \
  virtual Type* As##Name() { return NULL; }
#define INSTRUCTION_TYPE_CHECK(Name)                                           \
  DECLARE_INSTRUCTION_TYPE_CHECK(Name, Name##Instr)

DECLARE_INSTRUCTION_TYPE_CHECK(Definition, Definition)
FOR_EACH_INSTRUCTION(INSTRUCTION_TYPE_CHECK)
FOR_EACH_ABSTRACT_INSTRUCTION(INSTRUCTION_TYPE_CHECK)

#undef INSTRUCTION_TYPE_CHECK
#undef DECLARE_INSTRUCTION_TYPE_CHECK

  // Returns structure describing location constraints required
  // to emit native code for this instruction.
  LocationSummary* locs() {
    ASSERT(locs_ != NULL);
    return locs_;
  }

  bool HasLocs() const { return locs_ != NULL; }

  virtual LocationSummary* MakeLocationSummary(Zone* zone,
                                               bool is_optimizing) const = 0;

  void InitializeLocationSummary(Zone* zone, bool optimizing) {
    ASSERT(locs_ == NULL);
    locs_ = MakeLocationSummary(zone, optimizing);
  }

  static LocationSummary* MakeCallSummary(Zone* zone);

  virtual void EmitNativeCode(FlowGraphCompiler* compiler) {
    UNIMPLEMENTED();
  }

  Environment* env() const { return env_; }
  void SetEnvironment(Environment* deopt_env);
  void RemoveEnvironment();

  intptr_t lifetime_position() const { return lifetime_position_; }
  void set_lifetime_position(intptr_t pos) {
    lifetime_position_ = pos;
  }

  bool HasUnmatchedInputRepresentations() const;

  // Returns representation expected for the input operand at the given index.
  virtual Representation RequiredInputRepresentation(intptr_t idx) const {
    return kTagged;
  }

  // Representation of the value produced by this computation.
  virtual Representation representation() const {
    return kTagged;
  }

  bool WasEliminated() const {
    return next() == NULL;
  }

  // Returns deoptimization id that corresponds to the deoptimization target
  // that input operands conversions inserted for this instruction can jump
  // to.
  virtual intptr_t DeoptimizationTarget() const {
    UNREACHABLE();
    return Thread::kNoDeoptId;
  }

  // Returns a replacement for the instruction or NULL if the instruction can
  // be eliminated.  By default returns the this instruction which means no
  // change.
  virtual Instruction* Canonicalize(FlowGraph* flow_graph);

  // Insert this instruction before 'next' after use lists are computed.
  // Instructions cannot be inserted before a block entry or any other
  // instruction without a previous instruction.
  void InsertBefore(Instruction* next) { InsertAfter(next->previous()); }

  // Insert this instruction after 'prev' after use lists are computed.
  void InsertAfter(Instruction* prev);

  // Append an instruction to the current one and return the tail.
  // This function updated def-use chains of the newly appended
  // instruction.
  Instruction* AppendInstruction(Instruction* tail);

  virtual bool AllowsDCE() const {
    return false;
  }

  // Returns true if CSE and LICM are allowed for this instruction.
  virtual bool AllowsCSE() const {
    return false;
  }

  // Returns set of effects created by this instruction.
  virtual EffectSet Effects() const = 0;

  // Returns set of effects that affect this instruction.
  virtual EffectSet Dependencies() const {
    UNREACHABLE();
    return EffectSet::All();
  }

  // Get the block entry for this instruction.
  virtual BlockEntryInstr* GetBlock() const;

  // Place identifiers used by the load optimization pass.
  intptr_t place_id() const { return place_id_; }
  void set_place_id(intptr_t place_id) { place_id_ = place_id; }
  bool HasPlaceId() const { return place_id_ != kNoPlaceId; }

  intptr_t inlining_id() const { return inlining_id_; }
  void set_inlining_id(intptr_t value) {
    ASSERT(value >= 0);
    inlining_id_ = value;
  }
  bool has_inlining_id() const { return inlining_id_ >= 0; }

  // Returns a hash code for use with hash maps.
  virtual intptr_t Hashcode() const;

  // Compares two instructions.  Returns true, iff:
  // 1. They have the same tag.
  // 2. All input operands are Equals.
  // 3. They satisfy AttributesEqual.
  bool Equals(Instruction* other) const;

  // Compare attributes of a instructions (except input operands and tag).
  // All instructions that participate in CSE have to override this function.
  // This function can assume that the argument has the same type as this.
  virtual bool AttributesEqual(Instruction* other) const {
    UNREACHABLE();
    return false;
  }

  virtual void InheritDeoptTarget(Zone* zone, Instruction* other);

  bool NeedsEnvironment() const {
    return CanDeoptimize() || CanBecomeDeoptimizationTarget();
  }

  virtual bool CanBecomeDeoptimizationTarget() const {
    return false;
  }

  void InheritDeoptTargetAfter(FlowGraph* flow_graph,
                               Definition* call,
                               Definition* result);

  virtual bool MayThrow() const = 0;

  bool IsDominatedBy(Instruction* dom);

  void ClearEnv() { env_ = NULL; }

 protected:
  // GetDeoptId and/or CopyDeoptIdFrom.
  friend class CallSiteInliner;
  friend class LICM;
  friend class ComparisonInstr;
  friend class Scheduler;
  friend class BlockEntryInstr;

  // Fetch deopt id without checking if this computation can deoptimize.
  intptr_t GetDeoptId() const {
    return deopt_id_;
  }

  void CopyDeoptIdFrom(const Instruction& instr) {
    deopt_id_ = instr.deopt_id_;
  }

 private:
  virtual void RawSetInputAt(intptr_t i, Value* value) = 0;

  enum {
    kNoPlaceId = -1
  };

  intptr_t deopt_id_;
  union {
    intptr_t lifetime_position_;  // Position used by register allocator.
    intptr_t place_id_;
  };
  Instruction* previous_;
  Instruction* next_;
  Environment* env_;
  LocationSummary* locs_;
  intptr_t inlining_id_;

  DISALLOW_COPY_AND_ASSIGN(Instruction);
};


class PureInstruction : public Instruction {
 public:
  explicit PureInstruction(intptr_t deopt_id)
      : Instruction(deopt_id) { }

  virtual bool AllowsCSE() const { return true; }
  virtual EffectSet Dependencies() const { return EffectSet::None(); }

  virtual EffectSet Effects() const { return EffectSet::None(); }
};


// Types to be used as ThrowsTrait for TemplateInstruction/TemplateDefinition.
struct Throws {
  static const bool kCanThrow = true;
};


struct NoThrow {
  static const bool kCanThrow = false;
};


// Types to be used as CSETrait for TemplateInstruction/TemplateDefinition.
// Pure instructions are those that allow CSE and have no effects and
// no dependencies.
template<typename DefaultBase, typename PureBase>
struct Pure {
  typedef PureBase Base;
};


template<typename DefaultBase, typename PureBase>
struct NoCSE {
  typedef DefaultBase Base;
};


template<intptr_t N,
         typename ThrowsTrait,
         template<typename Default, typename Pure> class CSETrait = NoCSE>
class TemplateInstruction: public CSETrait<Instruction, PureInstruction>::Base {
 public:
  explicit TemplateInstruction(intptr_t deopt_id = Thread::kNoDeoptId)
      : CSETrait<Instruction, PureInstruction>::Base(deopt_id), inputs_() { }

  virtual intptr_t InputCount() const { return N; }
  virtual Value* InputAt(intptr_t i) const { return inputs_[i]; }

  virtual bool MayThrow() const { return ThrowsTrait::kCanThrow; }

 protected:
  EmbeddedArray<Value*, N> inputs_;

 private:
  virtual void RawSetInputAt(intptr_t i, Value* value) {
    inputs_[i] = value;
  }
};


class MoveOperands : public ZoneAllocated {
 public:
  MoveOperands(Location dest, Location src) : dest_(dest), src_(src) { }

  Location src() const { return src_; }
  Location dest() const { return dest_; }

  Location* src_slot() { return &src_; }
  Location* dest_slot() { return &dest_; }

  void set_src(const Location& value) { src_ = value; }
  void set_dest(const Location& value) { dest_ = value; }

  // The parallel move resolver marks moves as "in-progress" by clearing the
  // destination (but not the source).
  Location MarkPending() {
    ASSERT(!IsPending());
    Location dest = dest_;
    dest_ = Location::NoLocation();
    return dest;
  }

  void ClearPending(Location dest) {
    ASSERT(IsPending());
    dest_ = dest;
  }

  bool IsPending() const {
    ASSERT(!src_.IsInvalid() || dest_.IsInvalid());
    return dest_.IsInvalid() && !src_.IsInvalid();
  }

  // True if this move a move from the given location.
  bool Blocks(Location loc) const {
    return !IsEliminated() && src_.Equals(loc);
  }

  // A move is redundant if it's been eliminated, if its source and
  // destination are the same, or if its destination is unneeded.
  bool IsRedundant() const {
    return IsEliminated() || dest_.IsInvalid() || src_.Equals(dest_);
  }

  // We clear both operands to indicate move that's been eliminated.
  void Eliminate() { src_ = dest_ = Location::NoLocation(); }
  bool IsEliminated() const {
    ASSERT(!src_.IsInvalid() || dest_.IsInvalid());
    return src_.IsInvalid();
  }

 private:
  Location dest_;
  Location src_;

  DISALLOW_COPY_AND_ASSIGN(MoveOperands);
};


class ParallelMoveInstr : public TemplateInstruction<0, NoThrow> {
 public:
  ParallelMoveInstr() : moves_(4) { }

  DECLARE_INSTRUCTION(ParallelMove)

  virtual intptr_t ArgumentCount() const { return 0; }

  virtual bool CanDeoptimize() const { return false; }

  virtual EffectSet Effects() const {
    UNREACHABLE();  // This instruction never visited by optimization passes.
    return EffectSet::None();
  }

  virtual EffectSet Dependencies() const {
    UNREACHABLE();  // This instruction never visited by optimization passes.
    return EffectSet::None();
  }

  MoveOperands* AddMove(Location dest, Location src) {
    MoveOperands* move = new MoveOperands(dest, src);
    moves_.Add(move);
    return move;
  }

  MoveOperands* MoveOperandsAt(intptr_t index) const { return moves_[index]; }

  intptr_t NumMoves() const { return moves_.length(); }

  bool IsRedundant() const;

  virtual void PrintTo(BufferFormatter* f) const;

 private:
  GrowableArray<MoveOperands*> moves_;   // Elements cannot be null.

  DISALLOW_COPY_AND_ASSIGN(ParallelMoveInstr);
};


// Basic block entries are administrative nodes.  There is a distinguished
// graph entry with no predecessor.  Joins are the only nodes with multiple
// predecessors.  Targets are all other basic block entries.  The types
// enforce edge-split form---joins are forbidden as the successors of
// branches.
class BlockEntryInstr : public Instruction {
 public:
  virtual intptr_t PredecessorCount() const = 0;
  virtual BlockEntryInstr* PredecessorAt(intptr_t index) const = 0;

  intptr_t preorder_number() const { return preorder_number_; }
  void set_preorder_number(intptr_t number) { preorder_number_ = number; }

  intptr_t postorder_number() const { return postorder_number_; }
  void set_postorder_number(intptr_t number) { postorder_number_ = number; }

  intptr_t block_id() const { return block_id_; }

  void set_start_pos(intptr_t pos) { start_pos_ = pos; }
  intptr_t start_pos() const { return start_pos_; }
  void  set_end_pos(intptr_t pos) { end_pos_ = pos; }
  intptr_t end_pos() const { return end_pos_; }

  BlockEntryInstr* dominator() const { return dominator_; }
  BlockEntryInstr* ImmediateDominator() const;

  const GrowableArray<BlockEntryInstr*>& dominated_blocks() {
    return dominated_blocks_;
  }

  void AddDominatedBlock(BlockEntryInstr* block) {
    block->set_dominator(this);
    dominated_blocks_.Add(block);
  }
  void ClearDominatedBlocks() { dominated_blocks_.Clear(); }

  bool Dominates(BlockEntryInstr* other) const;

  Instruction* last_instruction() const { return last_instruction_; }
  void set_last_instruction(Instruction* instr) { last_instruction_ = instr; }

  ParallelMoveInstr* parallel_move() const {
    return parallel_move_;
  }

  bool HasParallelMove() const {
    return parallel_move_ != NULL;
  }

  bool HasNonRedundantParallelMove() const {
    return HasParallelMove() && !parallel_move()->IsRedundant();
  }

  ParallelMoveInstr* GetParallelMove() {
    if (parallel_move_ == NULL) {
      parallel_move_ = new ParallelMoveInstr();
    }
    return parallel_move_;
  }

  // Discover basic-block structure of the current block.  Must be called
  // on all graph blocks in preorder to yield valid results.  As a side effect,
  // the block entry instructions in the graph are assigned preorder numbers.
  // The array 'preorder' maps preorder block numbers to the block entry
  // instruction with that number.  The depth first spanning tree is recorded
  // in the array 'parent', which maps preorder block numbers to the preorder
  // number of the block's spanning-tree parent.  As a side effect of this
  // function, the set of basic block predecessors (e.g., block entry
  // instructions of predecessor blocks) and also the last instruction in the
  // block is recorded in each entry instruction.  Returns true when called the
  // first time on this particular block within one graph traversal, and false
  // on all successive calls.
  bool DiscoverBlock(
      BlockEntryInstr* predecessor,
      GrowableArray<BlockEntryInstr*>* preorder,
      GrowableArray<intptr_t>* parent);

  // Perform a depth first search to prune code not reachable from an OSR
  // entry point.
  bool PruneUnreachable(FlowGraphBuilder* builder,
                        GraphEntryInstr* graph_entry,
                        Instruction* parent,
                        intptr_t osr_id,
                        BitVector* block_marks);

  virtual intptr_t InputCount() const { return 0; }
  virtual Value* InputAt(intptr_t i) const {
    UNREACHABLE();
    return NULL;
  }

  virtual intptr_t ArgumentCount() const { return 0; }

  virtual bool CanBecomeDeoptimizationTarget() const {
    // BlockEntry environment is copied to Goto and Branch instructions
    // when we insert new blocks targeting this block.
    return true;
  }

  virtual bool CanDeoptimize() const { return false; }

  virtual EffectSet Effects() const { return EffectSet::None(); }
  virtual EffectSet Dependencies() const { return EffectSet::None(); }

  virtual bool MayThrow() const { return false; }

  intptr_t try_index() const { return try_index_; }
  void set_try_index(intptr_t index) {
    try_index_ = index;
  }

  // True for blocks inside a try { } region.
  bool InsideTryBlock() const {
    return try_index_ != CatchClauseNode::kInvalidTryIndex;
  }

  BitVector* loop_info() const { return loop_info_; }
  void set_loop_info(BitVector* loop_info) {
    loop_info_ = loop_info;
  }

  virtual BlockEntryInstr* GetBlock() const {
    return const_cast<BlockEntryInstr*>(this);
  }

  // Helper to mutate the graph during inlining. This block should be
  // replaced with new_block as a predecessor of all of this block's
  // successors.
  void ReplaceAsPredecessorWith(BlockEntryInstr* new_block);

  void set_block_id(intptr_t block_id) { block_id_ = block_id; }

  intptr_t offset() const { return offset_; }
  void set_offset(intptr_t offset) { offset_ = offset; }

  // For all instruction in this block: Remove all inputs (including in the
  // environment) from their definition's use lists for all instructions.
  void ClearAllInstructions();

  DEFINE_INSTRUCTION_TYPE_CHECK(BlockEntry)

 protected:
  BlockEntryInstr(intptr_t block_id, intptr_t try_index)
      : Instruction(Thread::Current()->GetNextDeoptId()),
        block_id_(block_id),
        try_index_(try_index),
        preorder_number_(-1),
        postorder_number_(-1),
        dominator_(NULL),
        dominated_blocks_(1),
        last_instruction_(NULL),
        offset_(-1),
        parallel_move_(NULL),
        loop_info_(NULL) {
  }

 private:
  virtual void RawSetInputAt(intptr_t i, Value* value) { UNREACHABLE(); }

  virtual void ClearPredecessors() = 0;
  virtual void AddPredecessor(BlockEntryInstr* predecessor) = 0;

  void set_dominator(BlockEntryInstr* instr) { dominator_ = instr; }

  intptr_t block_id_;
  intptr_t try_index_;
  intptr_t preorder_number_;
  intptr_t postorder_number_;
  // Starting and ending lifetime positions for this block.  Used by
  // the linear scan register allocator.
  intptr_t start_pos_;
  intptr_t end_pos_;
  BlockEntryInstr* dominator_;  // Immediate dominator, NULL for graph entry.
  // TODO(fschneider): Optimize the case of one child to save space.
  GrowableArray<BlockEntryInstr*> dominated_blocks_;
  Instruction* last_instruction_;

  // Offset of this block from the start of the emitted code.
  intptr_t offset_;

  // Parallel move that will be used by linear scan register allocator to
  // connect live ranges at the start of the block.
  ParallelMoveInstr* parallel_move_;

  // Bit vector containg loop blocks for a loop header indexed by block
  // preorder number.
  BitVector* loop_info_;

  DISALLOW_COPY_AND_ASSIGN(BlockEntryInstr);
};


class ForwardInstructionIterator : public ValueObject {
 public:
  explicit ForwardInstructionIterator(BlockEntryInstr* block_entry)
      : current_(block_entry) {
    Advance();
  }

  void Advance() {
    ASSERT(!Done());
    current_ = current_->next();
  }

  bool Done() const { return current_ == NULL; }

  // Removes 'current_' from graph and sets 'current_' to previous instruction.
  void RemoveCurrentFromGraph();

  Instruction* Current() const { return current_; }

 private:
  Instruction* current_;
};


class BackwardInstructionIterator : public ValueObject {
 public:
  explicit BackwardInstructionIterator(BlockEntryInstr* block_entry)
      : block_entry_(block_entry), current_(block_entry->last_instruction()) {
    ASSERT(block_entry_->previous() == NULL);
  }

  void Advance() {
    ASSERT(!Done());
    current_ = current_->previous();
  }

  bool Done() const { return current_ == block_entry_; }

  void RemoveCurrentFromGraph();

  Instruction* Current() const { return current_; }

 private:
  BlockEntryInstr* block_entry_;
  Instruction* current_;
};


class GraphEntryInstr : public BlockEntryInstr {
 public:
  GraphEntryInstr(const ParsedFunction& parsed_function,
                  TargetEntryInstr* normal_entry,
                  intptr_t osr_id);

  DECLARE_INSTRUCTION(GraphEntry)

  virtual intptr_t PredecessorCount() const { return 0; }
  virtual BlockEntryInstr* PredecessorAt(intptr_t index) const {
    UNREACHABLE();
    return NULL;
  }
  virtual intptr_t SuccessorCount() const;
  virtual BlockEntryInstr* SuccessorAt(intptr_t index) const;

  void AddCatchEntry(CatchBlockEntryInstr* entry) { catch_entries_.Add(entry); }

  CatchBlockEntryInstr* GetCatchEntry(intptr_t index);

  void AddIndirectEntry(IndirectEntryInstr* entry) {
    indirect_entries_.Add(entry);
  }

  GrowableArray<Definition*>* initial_definitions() {
    return &initial_definitions_;
  }
  ConstantInstr* constant_null();

  bool IsCompiledForOsr() const { return osr_id_ != Thread::kNoDeoptId; }

  intptr_t entry_count() const { return entry_count_; }
  void set_entry_count(intptr_t count) { entry_count_ = count; }

  intptr_t spill_slot_count() const { return spill_slot_count_; }
  void set_spill_slot_count(intptr_t count) {
    ASSERT(count >= 0);
    spill_slot_count_ = count;
  }

  // Number of stack slots reserved for compiling try-catch. For functions
  // without try-catch, this is 0. Otherwise, it is the number of local
  // variables.
  intptr_t fixed_slot_count() const { return fixed_slot_count_; }
  void set_fixed_slot_count(intptr_t count) {
    ASSERT(count >= 0);
    fixed_slot_count_ = count;
  }
  TargetEntryInstr* normal_entry() const { return normal_entry_; }

  const ParsedFunction& parsed_function() const {
    return parsed_function_;
  }

  const GrowableArray<CatchBlockEntryInstr*>& catch_entries() const {
    return catch_entries_;
  }

  const GrowableArray<IndirectEntryInstr*>& indirect_entries() const {
    return indirect_entries_;
  }

  virtual void PrintTo(BufferFormatter* f) const;

 private:
  virtual void ClearPredecessors() {}
  virtual void AddPredecessor(BlockEntryInstr* predecessor) { UNREACHABLE(); }

  const ParsedFunction& parsed_function_;
  TargetEntryInstr* normal_entry_;
  GrowableArray<CatchBlockEntryInstr*> catch_entries_;
  // Indirect targets are blocks reachable only through indirect gotos.
  GrowableArray<IndirectEntryInstr*> indirect_entries_;
  GrowableArray<Definition*> initial_definitions_;
  const intptr_t osr_id_;
  intptr_t entry_count_;
  intptr_t spill_slot_count_;
  intptr_t fixed_slot_count_;  // For try-catch in optimized code.

  DISALLOW_COPY_AND_ASSIGN(GraphEntryInstr);
};


class JoinEntryInstr : public BlockEntryInstr {
 public:
  JoinEntryInstr(intptr_t block_id, intptr_t try_index)
      : BlockEntryInstr(block_id, try_index),
        predecessors_(2),  // Two is the assumed to be the common case.
        phis_(NULL) { }

  DECLARE_INSTRUCTION(JoinEntry)

  virtual intptr_t PredecessorCount() const { return predecessors_.length(); }
  virtual BlockEntryInstr* PredecessorAt(intptr_t index) const {
    return predecessors_[index];
  }

  // Returns -1 if pred is not in the list.
  intptr_t IndexOfPredecessor(BlockEntryInstr* pred) const;

  ZoneGrowableArray<PhiInstr*>* phis() const { return phis_; }

  PhiInstr* InsertPhi(intptr_t var_index, intptr_t var_count);
  void RemoveDeadPhis(Definition* replacement);

  void InsertPhi(PhiInstr* phi);
  void RemovePhi(PhiInstr* phi);

  virtual void PrintTo(BufferFormatter* f) const;

  virtual EffectSet Effects() const { return EffectSet::None(); }
  virtual EffectSet Dependencies() const { return EffectSet::None(); }

 private:
  // Classes that have access to predecessors_ when inlining.
  friend class BlockEntryInstr;
  friend class InlineExitCollector;
  friend class PolymorphicInliner;
  friend class IndirectEntryInstr;  // Access in il_printer.cc.

  // Direct access to phis_ in order to resize it due to phi elimination.
  friend class ConstantPropagator;
  friend class DeadCodeElimination;

  virtual void ClearPredecessors() { predecessors_.Clear(); }
  virtual void AddPredecessor(BlockEntryInstr* predecessor);

  GrowableArray<BlockEntryInstr*> predecessors_;
  ZoneGrowableArray<PhiInstr*>* phis_;

  DISALLOW_COPY_AND_ASSIGN(JoinEntryInstr);
};


class PhiIterator : public ValueObject {
 public:
  explicit PhiIterator(JoinEntryInstr* join)
      : phis_(join->phis()), index_(0) { }

  void Advance() {
    ASSERT(!Done());
    index_++;
  }

  bool Done() const {
    return (phis_ == NULL) || (index_ >= phis_->length());
  }

  PhiInstr* Current() const {
    return (*phis_)[index_];
  }

 private:
  ZoneGrowableArray<PhiInstr*>* phis_;
  intptr_t index_;
};


class TargetEntryInstr : public BlockEntryInstr {
 public:
  TargetEntryInstr(intptr_t block_id, intptr_t try_index)
      : BlockEntryInstr(block_id, try_index),
        predecessor_(NULL),
        edge_weight_(0.0) { }

  DECLARE_INSTRUCTION(TargetEntry)

  double edge_weight() const { return edge_weight_; }
  void set_edge_weight(double weight) { edge_weight_ = weight; }
  void adjust_edge_weight(double scale_factor) { edge_weight_ *= scale_factor; }

  virtual intptr_t PredecessorCount() const {
    return (predecessor_ == NULL) ? 0 : 1;
  }
  virtual BlockEntryInstr* PredecessorAt(intptr_t index) const {
    ASSERT((index == 0) && (predecessor_ != NULL));
    return predecessor_;
  }

  virtual void PrintTo(BufferFormatter* f) const;

 private:
  friend class BlockEntryInstr;  // Access to predecessor_ when inlining.

  virtual void ClearPredecessors() { predecessor_ = NULL; }
  virtual void AddPredecessor(BlockEntryInstr* predecessor) {
    ASSERT(predecessor_ == NULL);
    predecessor_ = predecessor;
  }

  BlockEntryInstr* predecessor_;
  double edge_weight_;

  DISALLOW_COPY_AND_ASSIGN(TargetEntryInstr);
};


class IndirectEntryInstr : public JoinEntryInstr {
 public:
  IndirectEntryInstr(intptr_t block_id,
                     intptr_t indirect_id,
                     intptr_t try_index)
      : JoinEntryInstr(block_id, try_index),
        indirect_id_(indirect_id) { }

  DECLARE_INSTRUCTION(IndirectEntry)

  virtual void PrintTo(BufferFormatter* f) const;

  intptr_t indirect_id() const { return indirect_id_; }

 private:
  const intptr_t indirect_id_;
};


class CatchBlockEntryInstr : public BlockEntryInstr {
 public:
  CatchBlockEntryInstr(intptr_t block_id,
                       intptr_t try_index,
                       const Array& handler_types,
                       intptr_t catch_try_index,
                       const LocalVariable& exception_var,
                       const LocalVariable& stacktrace_var,
                       bool needs_stacktrace)
      : BlockEntryInstr(block_id, try_index),
        predecessor_(NULL),
        catch_handler_types_(Array::ZoneHandle(handler_types.raw())),
        catch_try_index_(catch_try_index),
        exception_var_(exception_var),
        stacktrace_var_(stacktrace_var),
        needs_stacktrace_(needs_stacktrace) { }

  DECLARE_INSTRUCTION(CatchBlockEntry)

  virtual intptr_t PredecessorCount() const {
    return (predecessor_ == NULL) ? 0 : 1;
  }
  virtual BlockEntryInstr* PredecessorAt(intptr_t index) const {
    ASSERT((index == 0) && (predecessor_ != NULL));
    return predecessor_;
  }

  const LocalVariable& exception_var() const { return exception_var_; }
  const LocalVariable& stacktrace_var() const { return stacktrace_var_; }

  bool needs_stacktrace() const { return needs_stacktrace_; }

  // Returns try index for the try block to which this catch handler
  // corresponds.
  intptr_t catch_try_index() const {
    return catch_try_index_;
  }
  GrowableArray<Definition*>* initial_definitions() {
    return &initial_definitions_;
  }

  virtual void PrintTo(BufferFormatter* f) const;

 private:
  friend class BlockEntryInstr;  // Access to predecessor_ when inlining.

  virtual void ClearPredecessors() { predecessor_ = NULL; }
  virtual void AddPredecessor(BlockEntryInstr* predecessor) {
    ASSERT(predecessor_ == NULL);
    predecessor_ = predecessor;
  }

  BlockEntryInstr* predecessor_;
  const Array& catch_handler_types_;
  const intptr_t catch_try_index_;
  GrowableArray<Definition*> initial_definitions_;
  const LocalVariable& exception_var_;
  const LocalVariable& stacktrace_var_;
  const bool needs_stacktrace_;

  DISALLOW_COPY_AND_ASSIGN(CatchBlockEntryInstr);
};


// If the result of the allocation is not stored into any field, passed
// as an argument or used in a phi then it can't alias with any other
// SSA value.
class AliasIdentity : public ValueObject {
 public:
  // It is unknown if value has aliases.
  static AliasIdentity Unknown() { return AliasIdentity(kUnknown); }

  // It is known that value can have aliases.
  static AliasIdentity Aliased() { return AliasIdentity(kAliased); }

  // It is known that value has no aliases.
  static AliasIdentity NotAliased() { return AliasIdentity(kNotAliased); }

  // It is known that value has no aliases and it was selected by
  // allocation sinking pass as a candidate.
  static AliasIdentity AllocationSinkingCandidate() {
    return AliasIdentity(kAllocationSinkingCandidate);
  }

  bool IsUnknown() const { return value_ == kUnknown; }
  bool IsAliased() const { return value_ == kAliased; }
  bool IsNotAliased() const { return (value_ & kNotAliased) != 0; }
  bool IsAllocationSinkingCandidate() const {
    return value_ == kAllocationSinkingCandidate;
  }

  AliasIdentity(const AliasIdentity& other)
      : ValueObject(), value_(other.value_) {
  }

  AliasIdentity& operator=(const AliasIdentity& other) {
    value_ = other.value_;
    return *this;
  }

 private:
  explicit AliasIdentity(intptr_t value) : value_(value) { }

  enum {
    kUnknown = 0,
    kNotAliased = 1,
    kAliased = 2,
    kAllocationSinkingCandidate = 3,
  };

  COMPILE_ASSERT((kUnknown & kNotAliased) == 0);
  COMPILE_ASSERT((kAliased & kNotAliased) == 0);
  COMPILE_ASSERT((kAllocationSinkingCandidate & kNotAliased) != 0);

  intptr_t value_;
};


// Abstract super-class of all instructions that define a value (Bind, Phi).
class Definition : public Instruction {
 public:
  explicit Definition(intptr_t deopt_id = Thread::kNoDeoptId);

  // Overridden by definitions that have call counts.
  virtual intptr_t CallCount() const {
    UNREACHABLE();
    return -1;
  }

  intptr_t temp_index() const { return temp_index_; }
  void set_temp_index(intptr_t index) { temp_index_ = index; }
  void ClearTempIndex() { temp_index_ = -1; }
  bool HasTemp() const { return temp_index_ >= 0; }

  intptr_t ssa_temp_index() const { return ssa_temp_index_; }
  void set_ssa_temp_index(intptr_t index) {
    ASSERT(index >= 0);
    ssa_temp_index_ = index;
  }
  bool HasSSATemp() const { return ssa_temp_index_ >= 0; }
  void ClearSSATempIndex() { ssa_temp_index_ = -1; }
  bool HasPairRepresentation() const {
#if defined(TARGET_ARCH_X64)
    return (representation() == kPairOfTagged) ||
           (representation() == kPairOfUnboxedDouble);
#else
    return (representation() == kPairOfTagged) ||
           (representation() == kPairOfUnboxedDouble) ||
           (representation() == kUnboxedMint);
#endif
  }

  // Compile time type of the definition, which may be requested before type
  // propagation during graph building.
  CompileType* Type() {
    if (type_ == NULL) {
      type_ = ZoneCompileType::Wrap(ComputeType());
    }
    return type_;
  }

  // Does this define a mint?
  inline bool IsMintDefinition();

  bool IsInt32Definition() {
    return IsBinaryInt32Op() ||
           IsBoxInt32() ||
           IsUnboxInt32() ||
           IsUnboxedIntConverter();
  }

  // Compute compile type for this definition. It is safe to use this
  // approximation even before type propagator was run (e.g. during graph
  // building).
  virtual CompileType ComputeType() const {
    return CompileType::Dynamic();
  }

  // Update CompileType of the definition. Returns true if the type has changed.
  virtual bool RecomputeType() {
    return false;
  }

  bool UpdateType(CompileType new_type) {
    if (type_ == NULL) {
      type_ = ZoneCompileType::Wrap(new_type);
      return true;
    }

    if (type_->IsNone() || !type_->IsEqualTo(&new_type)) {
      *type_ = new_type;
      return true;
    }

    return false;
  }

  bool HasUses() const {
    return (input_use_list_ != NULL) || (env_use_list_ != NULL);
  }
  bool HasOnlyUse(Value* use) const;
  bool HasOnlyInputUse(Value* use) const;


  Value* input_use_list() const { return input_use_list_; }
  void set_input_use_list(Value* head) { input_use_list_ = head; }

  Value* env_use_list() const { return env_use_list_; }
  void set_env_use_list(Value* head) { env_use_list_ = head; }

  void AddInputUse(Value* value) { Value::AddToList(value, &input_use_list_); }
  void AddEnvUse(Value* value) { Value::AddToList(value, &env_use_list_); }

  // Replace uses of this definition with uses of other definition or value.
  // Precondition: use lists must be properly calculated.
  // Postcondition: use lists and use values are still valid.
  void ReplaceUsesWith(Definition* other);

  // Replace this definition and all uses with another definition.  If
  // replacing during iteration, pass the iterator so that the instruction
  // can be replaced without affecting iteration order, otherwise pass a
  // NULL iterator.
  void ReplaceWith(Definition* other, ForwardInstructionIterator* iterator);

  // Printing support. These functions are sometimes overridden for custom
  // formatting. Otherwise, it prints in the format "opcode(op1, op2, op3)".
  virtual void PrintTo(BufferFormatter* f) const;
  virtual void PrintOperandsTo(BufferFormatter* f) const;

  // A value in the constant propagation lattice.
  //    - non-constant sentinel
  //    - a constant (any non-sentinel value)
  //    - unknown sentinel
  Object& constant_value();

  virtual void InferRange(RangeAnalysis* analysis, Range* range);

  Range* range() const { return range_; }
  void set_range(const Range&);

  // Definitions can be canonicalized only into definitions to ensure
  // this check statically we override base Canonicalize with a Canonicalize
  // returning Definition (return type is covariant).
  virtual Definition* Canonicalize(FlowGraph* flow_graph);

  static const intptr_t kReplacementMarker = -2;

  Definition* Replacement() {
    if (ssa_temp_index_ == kReplacementMarker) {
      return reinterpret_cast<Definition*>(temp_index_);
    }
    return this;
  }

  void SetReplacement(Definition* other) {
    ASSERT(ssa_temp_index_ >= 0);
    ASSERT(WasEliminated());
    ssa_temp_index_ = kReplacementMarker;
    temp_index_ = reinterpret_cast<intptr_t>(other);
  }

  virtual AliasIdentity Identity() const {
    return AliasIdentity::Unknown();
  }

  virtual void SetIdentity(AliasIdentity identity) {
    UNREACHABLE();
  }

  Definition* OriginalDefinition();

  virtual Definition* AsDefinition() { return this; }

 protected:
  friend class RangeAnalysis;
  friend class Value;

  Range* range_;
  CompileType* type_;

 private:
  intptr_t temp_index_;
  intptr_t ssa_temp_index_;
  Value* input_use_list_;
  Value* env_use_list_;

  Object* constant_value_;

  DISALLOW_COPY_AND_ASSIGN(Definition);
};


// Change a value's definition after use lists have been computed.
inline void Value::BindTo(Definition* def) {
  RemoveFromUseList();
  set_definition(def);
  def->AddInputUse(this);
}


inline void Value::BindToEnvironment(Definition* def) {
  RemoveFromUseList();
  set_definition(def);
  def->AddEnvUse(this);
}


class PureDefinition : public Definition {
 public:
  explicit PureDefinition(intptr_t deopt_id)
      : Definition(deopt_id) { }

  virtual bool AllowsCSE() const { return true; }
  virtual EffectSet Dependencies() const { return EffectSet::None(); }

  virtual EffectSet Effects() const { return EffectSet::None(); }
};


template<intptr_t N,
         typename ThrowsTrait,
         template<typename Impure, typename Pure> class CSETrait = NoCSE>
class TemplateDefinition : public CSETrait<Definition, PureDefinition>::Base {
 public:
  explicit TemplateDefinition(intptr_t deopt_id = Thread::kNoDeoptId)
      : CSETrait<Definition, PureDefinition>::Base(deopt_id), inputs_() { }

  virtual intptr_t InputCount() const { return N; }
  virtual Value* InputAt(intptr_t i) const { return inputs_[i]; }

  virtual bool MayThrow() const { return ThrowsTrait::kCanThrow; }

 protected:
  EmbeddedArray<Value*, N> inputs_;

 private:
  friend class BranchInstr;
  friend class IfThenElseInstr;

  virtual void RawSetInputAt(intptr_t i, Value* value) {
    inputs_[i] = value;
  }
};


struct BranchLabels {
  Label* true_label;
  Label* false_label;
  Label* fall_through;
};


class InductionVariableInfo;


class PhiInstr : public Definition {
 public:
  PhiInstr(JoinEntryInstr* block, intptr_t num_inputs)
    : block_(block),
      inputs_(num_inputs),
      is_alive_(false),
      representation_(kTagged),
      reaching_defs_(NULL),
      loop_variable_info_(NULL) {
    for (intptr_t i = 0; i < num_inputs; ++i) {
      inputs_.Add(NULL);
    }
  }

  // Get the block entry for that instruction.
  virtual BlockEntryInstr* GetBlock() const { return block(); }
  JoinEntryInstr* block() const { return block_; }

  virtual CompileType ComputeType() const;
  virtual bool RecomputeType();

  intptr_t InputCount() const { return inputs_.length(); }

  Value* InputAt(intptr_t i) const { return inputs_[i]; }

  virtual bool CanDeoptimize() const { return false; }

  virtual EffectSet Effects() const { return EffectSet::None(); }

  // Phi is alive if it reaches a non-environment use.
  bool is_alive() const { return is_alive_; }
  void mark_alive() { is_alive_ = true; }
  void mark_dead() { is_alive_ = false; }

  virtual Representation RequiredInputRepresentation(intptr_t i) const {
    return representation_;
  }

  virtual Representation representation() const {
    return representation_;
  }

  virtual void set_representation(Representation r) {
    representation_ = r;
  }

  virtual intptr_t Hashcode() const {
    UNREACHABLE();
    return 0;
  }

  DECLARE_INSTRUCTION(Phi)

  virtual void PrintTo(BufferFormatter* f) const;

  virtual void InferRange(RangeAnalysis* analysis, Range* range);

  BitVector* reaching_defs() const {
    return reaching_defs_;
  }

  void set_reaching_defs(BitVector* reaching_defs) {
    reaching_defs_ = reaching_defs;
  }

  virtual bool MayThrow() const { return false; }

  // A phi is redundant if all input operands are the same.
  bool IsRedundant() const;

  void set_induction_variable_info(InductionVariableInfo* info) {
    loop_variable_info_ = info;
  }

  InductionVariableInfo* induction_variable_info() {
    return loop_variable_info_;
  }

 private:
  // Direct access to inputs_ in order to resize it due to unreachable
  // predecessors.
  friend class ConstantPropagator;

  void RawSetInputAt(intptr_t i, Value* value) { inputs_[i] = value; }

  JoinEntryInstr* block_;
  GrowableArray<Value*> inputs_;
  bool is_alive_;
  Representation representation_;

  BitVector* reaching_defs_;
  InductionVariableInfo* loop_variable_info_;

  DISALLOW_COPY_AND_ASSIGN(PhiInstr);
};


class ParameterInstr : public Definition {
 public:
  ParameterInstr(intptr_t index,
                 BlockEntryInstr* block,
                 Register base_reg = FPREG)
      : index_(index), base_reg_(base_reg), block_(block) { }

  DECLARE_INSTRUCTION(Parameter)

  intptr_t index() const { return index_; }
  Register base_reg() const { return base_reg_; }

  // Get the block entry for that instruction.
  virtual BlockEntryInstr* GetBlock() const { return block_; }

  intptr_t InputCount() const { return 0; }
  Value* InputAt(intptr_t i) const {
    UNREACHABLE();
    return NULL;
  }

  virtual bool CanDeoptimize() const { return false; }

  virtual EffectSet Effects() const { return EffectSet::None(); }
  virtual EffectSet Dependencies() const { return EffectSet::None(); }

  virtual intptr_t Hashcode() const {
    UNREACHABLE();
    return 0;
  }

  virtual void PrintOperandsTo(BufferFormatter* f) const;

  virtual CompileType ComputeType() const;

  virtual bool MayThrow() const { return false; }

 private:
  virtual void RawSetInputAt(intptr_t i, Value* value) { UNREACHABLE(); }

  const intptr_t index_;
  const Register base_reg_;
  BlockEntryInstr* block_;

  DISALLOW_COPY_AND_ASSIGN(ParameterInstr);
};


class PushArgumentInstr : public TemplateDefinition<1, NoThrow> {
 public:
  explicit PushArgumentInstr(Value* value) {
    SetInputAt(0, value);
  }

  DECLARE_INSTRUCTION(PushArgument)

  virtual CompileType ComputeType() const;

  Value* value() const { return InputAt(0); }

  virtual bool CanDeoptimize() const { return false; }

  virtual EffectSet Effects() const { return EffectSet::None(); }

  virtual void PrintOperandsTo(BufferFormatter* f) const;

 private:
  DISALLOW_COPY_AND_ASSIGN(PushArgumentInstr);
};


inline Definition* Instruction::ArgumentAt(intptr_t index) const {
  return PushArgumentAt(index)->value()->definition();
}


class ReturnInstr : public TemplateInstruction<1, NoThrow> {
 public:
  ReturnInstr(intptr_t token_pos, Value* value)
      : TemplateInstruction(Thread::Current()->GetNextDeoptId()),
        token_pos_(token_pos) {
    SetInputAt(0, value);
  }

  DECLARE_INSTRUCTION(Return)

  virtual intptr_t token_pos() const { return token_pos_; }
  Value* value() const { return inputs_[0]; }

  virtual bool CanBecomeDeoptimizationTarget() const {
    // Return instruction might turn into a Goto instruction after inlining.
    // Every Goto must have an environment.
    return true;
  }

  virtual bool CanDeoptimize() const { return false; }

  virtual EffectSet Effects() const { return EffectSet::None(); }

 private:
  const intptr_t token_pos_;

  DISALLOW_COPY_AND_ASSIGN(ReturnInstr);
};


class ThrowInstr : public TemplateInstruction<0, Throws> {
 public:
  explicit ThrowInstr(intptr_t token_pos)
      : TemplateInstruction(Thread::Current()->GetNextDeoptId()),
        token_pos_(token_pos) {
  }

  DECLARE_INSTRUCTION(Throw)

  virtual intptr_t ArgumentCount() const { return 1; }

  virtual intptr_t token_pos() const { return token_pos_; }

  virtual bool CanDeoptimize() const { return true; }

  virtual EffectSet Effects() const { return EffectSet::None(); }

 private:
  const intptr_t token_pos_;

  DISALLOW_COPY_AND_ASSIGN(ThrowInstr);
};


class ReThrowInstr : public TemplateInstruction<0, Throws> {
 public:
  // 'catch_try_index' can be CatchClauseNode::kInvalidTryIndex if the
  // rethrow has been artifically generated by the parser.
  ReThrowInstr(intptr_t token_pos, intptr_t catch_try_index)
      : TemplateInstruction(Thread::Current()->GetNextDeoptId()),
        token_pos_(token_pos),
        catch_try_index_(catch_try_index) {
  }

  DECLARE_INSTRUCTION(ReThrow)

  virtual intptr_t ArgumentCount() const { return 2; }

  virtual intptr_t token_pos() const { return token_pos_; }
  intptr_t catch_try_index() const { return catch_try_index_; }

  virtual bool CanDeoptimize() const { return true; }

  virtual EffectSet Effects() const { return EffectSet::None(); }

 private:
  const intptr_t token_pos_;
  const intptr_t catch_try_index_;

  DISALLOW_COPY_AND_ASSIGN(ReThrowInstr);
};


class StopInstr : public TemplateInstruction<0, NoThrow> {
 public:
  explicit StopInstr(const char* message)
      : message_(message) {
    ASSERT(message != NULL);
  }

  const char* message() const { return message_; }

  DECLARE_INSTRUCTION(Stop);

  virtual intptr_t ArgumentCount() const { return 0; }

  virtual bool CanDeoptimize() const { return false; }

  virtual EffectSet Effects() const { return EffectSet::None(); }

  virtual EffectSet Dependencies() const { return EffectSet::None(); }

 private:
  const char* message_;

  DISALLOW_COPY_AND_ASSIGN(StopInstr);
};


class GotoInstr : public TemplateInstruction<0, NoThrow> {
 public:
  explicit GotoInstr(JoinEntryInstr* entry)
    : TemplateInstruction(Thread::Current()->GetNextDeoptId()),
      block_(NULL),
      successor_(entry),
      edge_weight_(0.0),
      parallel_move_(NULL) {
  }

  DECLARE_INSTRUCTION(Goto)

  BlockEntryInstr* block() const { return block_; }
  void set_block(BlockEntryInstr* block) { block_ = block; }

  JoinEntryInstr* successor() const { return successor_; }
  void set_successor(JoinEntryInstr* successor) { successor_ = successor; }
  virtual intptr_t SuccessorCount() const;
  virtual BlockEntryInstr* SuccessorAt(intptr_t index) const;

  double edge_weight() const { return edge_weight_; }
  void set_edge_weight(double weight) { edge_weight_ = weight; }
  void adjust_edge_weight(double scale_factor) { edge_weight_ *= scale_factor; }

  virtual bool CanBecomeDeoptimizationTarget() const {
    // Goto instruction can be used as a deoptimization target when LICM
    // hoists instructions out of the loop.
    return true;
  }

  virtual bool CanDeoptimize() const { return false; }

  virtual EffectSet Effects() const { return EffectSet::None(); }

  ParallelMoveInstr* parallel_move() const {
    return parallel_move_;
  }

  bool HasParallelMove() const {
    return parallel_move_ != NULL;
  }

  bool HasNonRedundantParallelMove() const {
    return HasParallelMove() && !parallel_move()->IsRedundant();
  }

  ParallelMoveInstr* GetParallelMove() {
    if (parallel_move_ == NULL) {
      parallel_move_ = new ParallelMoveInstr();
    }
    return parallel_move_;
  }

  virtual void PrintTo(BufferFormatter* f) const;

 private:
  BlockEntryInstr* block_;
  JoinEntryInstr* successor_;
  double edge_weight_;

  // Parallel move that will be used by linear scan register allocator to
  // connect live ranges at the end of the block and resolve phis.
  ParallelMoveInstr* parallel_move_;
};


// IndirectGotoInstr represents a dynamically computed jump. Only
// IndirectEntryInstr targets are valid targets of an indirect goto. The
// concrete target to jump to is given as a parameter to the indirect goto.
//
// In order to preserve split-edge form, an indirect goto does not itself point
// to its targets. Instead, for each possible target, the successors_ field
// will contain an ordinary goto instruction that jumps to the target.
// TODO(zerny): Implement direct support instead of embedding gotos.
//
// Byte offsets of all possible targets are stored in the offsets_ array. The
// desired offset is looked up while the generated code is executing, and passed
// to IndirectGoto as an input.
class IndirectGotoInstr : public TemplateInstruction<1, NoThrow> {
 public:
  IndirectGotoInstr(TypedData* offsets,
                    Value* offset_from_start)
    : offsets_(*offsets) {
    SetInputAt(0, offset_from_start);
  }

  DECLARE_INSTRUCTION(IndirectGoto)

  virtual Representation RequiredInputRepresentation(intptr_t idx) const {
    ASSERT(idx == 0);
    return kNoRepresentation;
  }

  virtual intptr_t ArgumentCount() const { return 0; }

  void AddSuccessor(TargetEntryInstr* successor) {
    ASSERT(successor->next()->IsGoto());
    ASSERT(successor->next()->AsGoto()->successor()->IsIndirectEntry());
    successors_.Add(successor);
  }

  virtual intptr_t SuccessorCount() const { return successors_.length(); }
  virtual TargetEntryInstr* SuccessorAt(intptr_t index) const {
    ASSERT(index < SuccessorCount());
    return successors_[index];
  }

  virtual bool CanDeoptimize() const { return false; }
  virtual bool CanBecomeDeoptimizationTarget() const { return false; }

  virtual EffectSet Effects() const { return EffectSet::None(); }

  virtual void PrintTo(BufferFormatter* f) const;

  Value* offset() const { return inputs_[0]; }
  void ComputeOffsetTable();

 private:
  GrowableArray<TargetEntryInstr*> successors_;
  TypedData& offsets_;
};


class ComparisonInstr : public TemplateDefinition<2, NoThrow, Pure> {
 public:
  Value* left() const { return inputs_[0]; }
  Value* right() const { return inputs_[1]; }

  virtual intptr_t token_pos() const { return token_pos_; }
  Token::Kind kind() const { return kind_; }

  virtual ComparisonInstr* CopyWithNewOperands(Value* left, Value* right) = 0;

  virtual void EmitBranchCode(FlowGraphCompiler* compiler,
                              BranchInstr* branch) = 0;

  virtual Condition EmitComparisonCode(FlowGraphCompiler* compiler,
                                       BranchLabels labels) = 0;

  void SetDeoptId(const Instruction& instr) {
    CopyDeoptIdFrom(instr);
  }

  // Operation class id is computed from collected ICData.
  void set_operation_cid(intptr_t value) { operation_cid_ = value; }
  intptr_t operation_cid() const { return operation_cid_; }

  void NegateComparison() {
    kind_ = Token::NegateComparison(kind_);
  }

  virtual bool CanBecomeDeoptimizationTarget() const { return true; }
  virtual intptr_t DeoptimizationTarget() const { return GetDeoptId(); }

  virtual bool AttributesEqual(Instruction* other) const {
    ComparisonInstr* other_comparison = other->AsComparison();
    return kind() == other_comparison->kind() &&
        (operation_cid() == other_comparison->operation_cid());
  }

  DEFINE_INSTRUCTION_TYPE_CHECK(Comparison)

 protected:
  ComparisonInstr(intptr_t token_pos,
                  Token::Kind kind,
                  Value* left,
                  Value* right,
                  intptr_t deopt_id = Thread::kNoDeoptId)
      : TemplateDefinition(deopt_id),
        token_pos_(token_pos),
        kind_(kind),
        operation_cid_(kIllegalCid) {
    SetInputAt(0, left);
    if (right != NULL) {
      SetInputAt(1, right);
    }
  }

 private:
  const intptr_t token_pos_;
  Token::Kind kind_;
  intptr_t operation_cid_;  // Set by optimizer.

  DISALLOW_COPY_AND_ASSIGN(ComparisonInstr);
};


class BranchInstr : public Instruction {
 public:
  explicit BranchInstr(ComparisonInstr* comparison)
      : Instruction(Thread::Current()->GetNextDeoptId()),
        comparison_(comparison),
        is_checked_(false),
        constrained_type_(NULL),
        constant_target_(NULL) {
    ASSERT(comparison->env() == NULL);
    for (intptr_t i = comparison->InputCount() - 1; i >= 0; --i) {
      comparison->InputAt(i)->set_instruction(this);
    }
  }

  DECLARE_INSTRUCTION(Branch)

  virtual intptr_t ArgumentCount() const {
    return comparison()->ArgumentCount();
  }

  intptr_t InputCount() const { return comparison()->InputCount(); }

  Value* InputAt(intptr_t i) const { return comparison()->InputAt(i); }

  virtual intptr_t token_pos() const { return comparison_->token_pos(); }

  virtual bool CanDeoptimize() const {
    // Branches need a deoptimization info in checked mode if they
    // can throw a type check error.
    return comparison()->CanDeoptimize() || is_checked();
  }

  virtual bool CanBecomeDeoptimizationTarget() const {
    return comparison()->CanBecomeDeoptimizationTarget();
  }

  virtual EffectSet Effects() const {
    return comparison()->Effects();
  }

  ComparisonInstr* comparison() const { return comparison_; }
  void SetComparison(ComparisonInstr* comp);

  void set_is_checked(bool value) { is_checked_ = value; }
  bool is_checked() const { return is_checked_; }

  virtual intptr_t DeoptimizationTarget() const {
    return comparison()->DeoptimizationTarget();
  }

  virtual Representation RequiredInputRepresentation(intptr_t i) const {
    return comparison()->RequiredInputRepresentation(i);
  }

  virtual Instruction* Canonicalize(FlowGraph* flow_graph);

  virtual void PrintTo(BufferFormatter* f) const;

  // Set compile type constrained by the comparison of this branch.
  // FlowGraphPropagator propagates it downwards into either true or false
  // successor.
  void set_constrained_type(ConstrainedCompileType* type) {
    constrained_type_ = type;
  }

  // Return compile type constrained by the comparison of this branch.
  ConstrainedCompileType* constrained_type() const {
    return constrained_type_;
  }

  void set_constant_target(TargetEntryInstr* target) {
    ASSERT(target == true_successor() || target == false_successor());
    constant_target_ = target;
  }
  TargetEntryInstr* constant_target() const {
    return constant_target_;
  }

  virtual void InheritDeoptTarget(Zone* zone, Instruction* other);

  virtual bool MayThrow() const {
    return comparison()->MayThrow();
  }

  TargetEntryInstr* true_successor() const { return true_successor_; }
  TargetEntryInstr* false_successor() const { return false_successor_; }

  TargetEntryInstr** true_successor_address() { return &true_successor_; }
  TargetEntryInstr** false_successor_address() { return &false_successor_; }

  virtual intptr_t SuccessorCount() const;
  virtual BlockEntryInstr* SuccessorAt(intptr_t index) const;

 private:
  virtual void RawSetInputAt(intptr_t i, Value* value) {
    comparison()->RawSetInputAt(i, value);
  }

  TargetEntryInstr* true_successor_;
  TargetEntryInstr* false_successor_;
  ComparisonInstr* comparison_;
  bool is_checked_;
  ConstrainedCompileType* constrained_type_;
  TargetEntryInstr* constant_target_;

  DISALLOW_COPY_AND_ASSIGN(BranchInstr);
};


class DeoptimizeInstr : public TemplateInstruction<0, NoThrow, Pure> {
 public:
  DeoptimizeInstr(ICData::DeoptReasonId deopt_reason, intptr_t deopt_id)
      : TemplateInstruction(deopt_id),
        deopt_reason_(deopt_reason) {
  }

  virtual bool CanDeoptimize() const { return true; }

  virtual bool AttributesEqual(Instruction* other) const {
    return true;
  }

  DECLARE_INSTRUCTION(Deoptimize)

 private:
  const ICData::DeoptReasonId deopt_reason_;

  DISALLOW_COPY_AND_ASSIGN(DeoptimizeInstr);
};


class RedefinitionInstr : public TemplateDefinition<1, NoThrow> {
 public:
  explicit RedefinitionInstr(Value* value) {
    SetInputAt(0, value);
  }

  DECLARE_INSTRUCTION(Redefinition)

  Value* value() const { return inputs_[0]; }

  virtual CompileType ComputeType() const;
  virtual bool RecomputeType();

  virtual bool CanDeoptimize() const { return false; }
  virtual EffectSet Dependencies() const { return EffectSet::None(); }
  virtual EffectSet Effects() const { return EffectSet::None(); }

 private:
  DISALLOW_COPY_AND_ASSIGN(RedefinitionInstr);
};


class ConstraintInstr : public TemplateDefinition<1, NoThrow> {
 public:
  ConstraintInstr(Value* value, Range* constraint)
      : constraint_(constraint),
        target_(NULL) {
    SetInputAt(0, value);
  }

  DECLARE_INSTRUCTION(Constraint)

  virtual CompileType ComputeType() const;

  virtual bool CanDeoptimize() const { return false; }

  virtual EffectSet Effects() const { return EffectSet::None(); }

  virtual bool AttributesEqual(Instruction* other) const {
    UNREACHABLE();
    return false;
  }

  virtual void PrintOperandsTo(BufferFormatter* f) const;

  Value* value() const { return inputs_[0]; }
  Range* constraint() const { return constraint_; }

  virtual void InferRange(RangeAnalysis* analysis, Range* range);

  // Constraints for branches have their target block stored in order
  // to find the the comparsion that generated the constraint:
  // target->predecessor->last_instruction->comparison.
  void set_target(TargetEntryInstr* target) {
    target_ = target;
  }
  TargetEntryInstr* target() const {
    return target_;
  }

 private:
  Range* constraint_;
  TargetEntryInstr* target_;

  DISALLOW_COPY_AND_ASSIGN(ConstraintInstr);
};


class ConstantInstr : public TemplateDefinition<0, NoThrow, Pure> {
 public:
  explicit ConstantInstr(const Object& value);

  DECLARE_INSTRUCTION(Constant)
  virtual CompileType ComputeType() const;

  virtual Definition* Canonicalize(FlowGraph* flow_graph);

  const Object& value() const { return value_; }

  virtual void PrintOperandsTo(BufferFormatter* f) const;

  virtual bool CanDeoptimize() const { return false; }

  virtual void InferRange(RangeAnalysis* analysis, Range* range);

  virtual bool AttributesEqual(Instruction* other) const;

 private:
  const Object& value_;

  DISALLOW_COPY_AND_ASSIGN(ConstantInstr);
};


// Merged ConstantInstr -> UnboxedXXX into UnboxedConstantInstr.
// TODO(srdjan): Implemented currently for doubles only, should implement
// for other unboxing instructions.
class UnboxedConstantInstr : public ConstantInstr {
 public:
  explicit UnboxedConstantInstr(const Object& value,
                                Representation representation);

  virtual Representation representation() const {
    return representation_;
  }

  // Either NULL or the address of the unboxed constant.
  uword constant_address() const { return constant_address_; }

  DECLARE_INSTRUCTION(UnboxedConstant)

 private:
  const Representation representation_;
  uword constant_address_;  // Either NULL or points to the untagged constant.

  DISALLOW_COPY_AND_ASSIGN(UnboxedConstantInstr);
};


class AssertAssignableInstr : public TemplateDefinition<3, Throws, Pure> {
 public:
  AssertAssignableInstr(intptr_t token_pos,
                        Value* value,
                        Value* instantiator,
                        Value* instantiator_type_arguments,
                        const AbstractType& dst_type,
                        const String& dst_name,
                        intptr_t deopt_id)
      : TemplateDefinition(deopt_id),
        token_pos_(token_pos),
        dst_type_(AbstractType::ZoneHandle(dst_type.raw())),
        dst_name_(dst_name) {
    ASSERT(!dst_type.IsNull());
    ASSERT(!dst_name.IsNull());
    SetInputAt(0, value);
    SetInputAt(1, instantiator);
    SetInputAt(2, instantiator_type_arguments);
  }

  DECLARE_INSTRUCTION(AssertAssignable)
  virtual CompileType ComputeType() const;
  virtual bool RecomputeType();

  Value* value() const { return inputs_[0]; }
  Value* instantiator() const { return inputs_[1]; }
  Value* instantiator_type_arguments() const { return inputs_[2]; }

  virtual intptr_t token_pos() const { return token_pos_; }
  const AbstractType& dst_type() const { return dst_type_; }
  void set_dst_type(const AbstractType& dst_type) {
    dst_type_ = dst_type.raw();
  }
  const String& dst_name() const { return dst_name_; }

  virtual void PrintOperandsTo(BufferFormatter* f) const;

  virtual bool CanDeoptimize() const { return true; }

  virtual bool CanBecomeDeoptimizationTarget() const {
    // AssertAssignable instructions that are specialized by the optimizer
    // (e.g. replaced with CheckClass) need a deoptimization descriptor before.
    return true;
  }

  virtual Definition* Canonicalize(FlowGraph* flow_graph);

  virtual bool AttributesEqual(Instruction* other) const;

 private:
  const intptr_t token_pos_;
  AbstractType& dst_type_;
  const String& dst_name_;

  DISALLOW_COPY_AND_ASSIGN(AssertAssignableInstr);
};


class AssertBooleanInstr : public TemplateDefinition<1, Throws, Pure> {
 public:
  AssertBooleanInstr(intptr_t token_pos, Value* value)
      : TemplateDefinition(Thread::Current()->GetNextDeoptId()),
        token_pos_(token_pos) {
    SetInputAt(0, value);
  }

  DECLARE_INSTRUCTION(AssertBoolean)
  virtual CompileType ComputeType() const;

  virtual intptr_t token_pos() const { return token_pos_; }
  Value* value() const { return inputs_[0]; }

  virtual void PrintOperandsTo(BufferFormatter* f) const;

  virtual bool CanDeoptimize() const { return true; }

  virtual Definition* Canonicalize(FlowGraph* flow_graph);

  virtual bool AttributesEqual(Instruction* other) const { return true; }

 private:
  const intptr_t token_pos_;

  DISALLOW_COPY_AND_ASSIGN(AssertBooleanInstr);
};


// Denotes the current context, normally held in a register.  This is
// a computation, not a value, because it's mutable.
class CurrentContextInstr : public TemplateDefinition<0, NoThrow> {
 public:
  CurrentContextInstr()
      : TemplateDefinition(Thread::Current()->GetNextDeoptId()) {
  }

  DECLARE_INSTRUCTION(CurrentContext)
  virtual CompileType ComputeType() const;

  virtual bool CanDeoptimize() const { return false; }

  virtual EffectSet Effects() const { return EffectSet::None(); }
  virtual EffectSet Dependencies() const { return EffectSet::None(); }
  virtual bool AttributesEqual(Instruction* other) const { return true; }

 private:
  DISALLOW_COPY_AND_ASSIGN(CurrentContextInstr);
};


class ClosureCallInstr : public TemplateDefinition<1, Throws> {
 public:
  ClosureCallInstr(Value* function,
                   ClosureCallNode* node,
                   ZoneGrowableArray<PushArgumentInstr*>* arguments)
      : TemplateDefinition(Thread::Current()->GetNextDeoptId()),
        ast_node_(*node),
        arguments_(arguments) {
    SetInputAt(0, function);
  }

  DECLARE_INSTRUCTION(ClosureCall)

  const Array& argument_names() const { return ast_node_.arguments()->names(); }
  virtual intptr_t token_pos() const { return ast_node_.token_pos(); }

  virtual intptr_t ArgumentCount() const { return arguments_->length(); }
  virtual PushArgumentInstr* PushArgumentAt(intptr_t index) const {
    return (*arguments_)[index];
  }

  // TODO(kmillikin): implement exact call counts for closure calls.
  virtual intptr_t CallCount() const { return 1; }

  virtual void PrintOperandsTo(BufferFormatter* f) const;

  virtual bool CanDeoptimize() const { return true; }

  virtual EffectSet Effects() const { return EffectSet::All(); }

 private:
  const ClosureCallNode& ast_node_;
  ZoneGrowableArray<PushArgumentInstr*>* arguments_;

  DISALLOW_COPY_AND_ASSIGN(ClosureCallInstr);
};


class InstanceCallInstr : public TemplateDefinition<0, Throws> {
 public:
  InstanceCallInstr(intptr_t token_pos,
                    const String& function_name,
                    Token::Kind token_kind,
                    ZoneGrowableArray<PushArgumentInstr*>* arguments,
                    const Array& argument_names,
                    intptr_t checked_argument_count,
                    const ZoneGrowableArray<const ICData*>& ic_data_array)
      : TemplateDefinition(Thread::Current()->GetNextDeoptId()),
        ic_data_(NULL),
        token_pos_(token_pos),
        function_name_(function_name),
        token_kind_(token_kind),
        arguments_(arguments),
        argument_names_(argument_names),
        checked_argument_count_(checked_argument_count) {
    ic_data_ = GetICData(ic_data_array);
    ASSERT(function_name.IsNotTemporaryScopedHandle());
    ASSERT(!arguments->is_empty());
    ASSERT(argument_names.IsZoneHandle() || argument_names.InVMHeap());
    ASSERT(Token::IsBinaryOperator(token_kind) ||
           Token::IsEqualityOperator(token_kind) ||
           Token::IsRelationalOperator(token_kind) ||
           Token::IsUnaryOperator(token_kind) ||
           Token::IsIndexOperator(token_kind) ||
           Token::IsTypeTestOperator(token_kind) ||
           Token::IsTypeCastOperator(token_kind) ||
           token_kind == Token::kGET ||
           token_kind == Token::kSET ||
           token_kind == Token::kILLEGAL);
  }

  DECLARE_INSTRUCTION(InstanceCall)

  const ICData* ic_data() const { return ic_data_; }
  bool HasICData() const {
    return (ic_data() != NULL) && !ic_data()->IsNull();
  }

  // ICData can be replaced by optimizer.
  void set_ic_data(const ICData* value) { ic_data_ = value; }

  virtual intptr_t token_pos() const { return token_pos_; }
  const String& function_name() const { return function_name_; }
  Token::Kind token_kind() const { return token_kind_; }
  virtual intptr_t ArgumentCount() const { return arguments_->length(); }
  virtual PushArgumentInstr* PushArgumentAt(intptr_t index) const {
    return (*arguments_)[index];
  }
  const Array& argument_names() const { return argument_names_; }
  intptr_t checked_argument_count() const { return checked_argument_count_; }

  virtual void PrintOperandsTo(BufferFormatter* f) const;

  virtual bool CanDeoptimize() const { return true; }

  virtual bool CanBecomeDeoptimizationTarget() const {
    // Instance calls that are specialized by the optimizer need a
    // deoptimization descriptor before the call.
    return true;
  }

  virtual EffectSet Effects() const { return EffectSet::All(); }

 protected:
  friend class FlowGraphOptimizer;
  void set_ic_data(ICData* value) { ic_data_ = value; }

 private:
  const ICData* ic_data_;
  const intptr_t token_pos_;
  const String& function_name_;
  const Token::Kind token_kind_;  // Binary op, unary op, kGET or kILLEGAL.
  ZoneGrowableArray<PushArgumentInstr*>* const arguments_;
  const Array& argument_names_;
  const intptr_t checked_argument_count_;

  DISALLOW_COPY_AND_ASSIGN(InstanceCallInstr);
};


class PolymorphicInstanceCallInstr : public TemplateDefinition<0, Throws> {
 public:
  PolymorphicInstanceCallInstr(InstanceCallInstr* instance_call,
                               const ICData& ic_data,
                               bool with_checks)
      : TemplateDefinition(instance_call->deopt_id()),
        instance_call_(instance_call),
        ic_data_(ic_data),
        with_checks_(with_checks) {
    ASSERT(instance_call_ != NULL);
    ASSERT(ic_data.NumberOfChecks() > 0);
  }

  InstanceCallInstr* instance_call() const { return instance_call_; }
  bool with_checks() const { return with_checks_; }
  virtual intptr_t token_pos() const { return instance_call_->token_pos(); }

  virtual intptr_t ArgumentCount() const {
    return instance_call()->ArgumentCount();
  }
  virtual PushArgumentInstr* PushArgumentAt(intptr_t index) const {
    return instance_call()->PushArgumentAt(index);
  }

  bool HasSingleRecognizedTarget() const;

  bool HasOnlyDispatcherTargets() const;

  virtual intptr_t CallCount() const { return ic_data().AggregateCount(); }

  DECLARE_INSTRUCTION(PolymorphicInstanceCall)

  const ICData& ic_data() const { return ic_data_; }

  virtual bool CanDeoptimize() const { return true; }

  virtual EffectSet Effects() const { return EffectSet::All(); }

  virtual void PrintOperandsTo(BufferFormatter* f) const;

 private:
  InstanceCallInstr* instance_call_;
  const ICData& ic_data_;
  const bool with_checks_;

  DISALLOW_COPY_AND_ASSIGN(PolymorphicInstanceCallInstr);
};


class StrictCompareInstr : public ComparisonInstr {
 public:
  StrictCompareInstr(intptr_t token_pos,
                     Token::Kind kind,
                     Value* left,
                     Value* right,
                     bool needs_number_check);

  DECLARE_INSTRUCTION(StrictCompare)

  virtual ComparisonInstr* CopyWithNewOperands(Value* left, Value* right);

  virtual CompileType ComputeType() const;

  virtual void PrintOperandsTo(BufferFormatter* f) const;

  virtual bool CanDeoptimize() const { return false; }

  virtual Definition* Canonicalize(FlowGraph* flow_graph);

  virtual void EmitBranchCode(FlowGraphCompiler* compiler,
                              BranchInstr* branch);

  virtual Condition EmitComparisonCode(FlowGraphCompiler* compiler,
                                       BranchLabels labels);

  bool needs_number_check() const { return needs_number_check_; }
  void set_needs_number_check(bool value) { needs_number_check_ = value; }

  bool AttributesEqual(Instruction* other) const;

 private:
  // True if the comparison must check for double, Mint or Bigint and
  // use value comparison instead.
  bool needs_number_check_;

  DISALLOW_COPY_AND_ASSIGN(StrictCompareInstr);
};


// Comparison instruction that is equivalent to the (left & right) == 0
// comparison pattern.
class TestSmiInstr : public ComparisonInstr {
 public:
  TestSmiInstr(intptr_t token_pos, Token::Kind kind, Value* left, Value* right)
      : ComparisonInstr(token_pos, kind, left, right) {
    ASSERT(kind == Token::kEQ || kind == Token::kNE);
  }

  DECLARE_INSTRUCTION(TestSmi);

  virtual ComparisonInstr* CopyWithNewOperands(Val