Revert "Implement structural function and array types"

src/types.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_TYPES_H_
 #define V8_TYPES_H_
 
 #include "handles.h"
 
 namespace v8 {
@@ skipping 25 matching lines @@
 //
 //   Receiver = Object \/ Proxy
 //   Array < Object
 //   Function < Object
 //   RegExp < Object
 //   Undetectable < Object
 //   Detectable = Receiver \/ Number \/ Name - Undetectable
 //
 //   Class(map) < T   iff instance_type(map) < T
 //   Constant(x) < T  iff instance_type(map(x)) < T
-//   Array(T) < Array
-//   Function(R, S, T0, T1, ...) < Function
 //
-// Both structural Array and Function types are invariant in all parameters.
-// Relaxing this would make Union and Intersect operations more involved.
 // Note that Constant(x) < Class(map(x)) does _not_ hold, since x's map can
 // change! (Its instance type cannot, however.)
 // TODO(rossberg): the latter is not currently true for proxies, because of fix,
 // but will hold once we implement direct proxies.
 // However, we also define a 'temporal' variant of the subtyping relation that
 // considers the _current_ state only, i.e., Constant(x) <_now Class(map(x)).
 //
 // REPRESENTATIONAL DIMENSION
 //
 // For the representation axis, the following holds:
@@ skipping 28 matching lines @@
 //   T1->Maybe(T2)  -- tests whether T1 and T2 overlap (i.e., T1 /\ T2 =/= 0)
 //
 // Typically, the former is to be used to select representations (e.g., via
 // T->Is(SignedSmall())), and the latter to check whether a specific case needs
 // handling (e.g., via T->Maybe(Number())).
 //
 // There is no functionality to discover whether a type is a leaf in the
 // lattice. That is intentional. It should always be possible to refine the
 // lattice (e.g., splitting up number types further) without invalidating any
 // existing assumptions or tests.
-// Consequently, do not normally use Equals for type tests, always use Is!
+// Consequently, do not use pointer equality for type tests, always use Is!
 //
 // The NowIs operator implements state-sensitive subtying, as described above.
 // Any compilation decision based on such temporary properties requires runtime
 // guarding!
 //
 // PROPERTIES
 //
 // Various formal properties hold for constructors, operators, and predicates
 // over types. For example, constructors are injective, subtyping is a complete
 // partial order, union and intersection satisfy the usual algebraic properties.
@@ skipping 76 matching lines @@
                          kUndefined | kInternal)                        \
   V(Any,                 -1)
 
 #define BITSET_TYPE_LIST(V) \
   MASK_BITSET_TYPE_LIST(V) \
   REPRESENTATION_BITSET_TYPE_LIST(V) \
   SEMANTIC_BITSET_TYPE_LIST(V)
 
 
 // struct Config {
-//   typedef TypeImpl<Config> Type;
 //   typedef Base;
 //   typedef Struct;
 //   typedef Region;
 //   template<class> struct Handle { typedef type; }  // No template typedefs...
-//   template<class T> static Handle<T>::type handle(T* t);  // !is_bitset(t)
-//   template<class T> static Handle<T>::type cast(Handle<Type>::type);
+//   static Handle<Type>::type handle(Type* type);    // !is_bitset(type)
 //   static bool is_bitset(Type*);
 //   static bool is_class(Type*);
 //   static bool is_constant(Type*);
-//   static bool is_struct(Type*, int tag);
+//   static bool is_struct(Type*);
 //   static int as_bitset(Type*);
 //   static i::Handle<i::Map> as_class(Type*);
 //   static i::Handle<i::Object> as_constant(Type*);
 //   static Handle<Struct>::type as_struct(Type*);
 //   static Type* from_bitset(int bitset);
 //   static Handle<Type>::type from_bitset(int bitset, Region*);
 //   static Handle<Type>::type from_class(i::Handle<Map>, int lub, Region*);
 //   static Handle<Type>::type from_constant(i::Handle<Object>, int, Region*);
-//   static Handle<Type>::type from_struct(Handle<Struct>::type, int tag);
+//   static Handle<Type>::type from_struct(Handle<Struct>::type);
 //   static Handle<Struct>::type struct_create(int tag, int length, Region*);
 //   static void struct_shrink(Handle<Struct>::type, int length);
 //   static int struct_tag(Handle<Struct>::type);
 //   static int struct_length(Handle<Struct>::type);
 //   static Handle<Type>::type struct_get(Handle<Struct>::type, int);
 //   static void struct_set(Handle<Struct>::type, int, Handle<Type>::type);
 //   static int lub_bitset(Type*);
 // }
 template<class Config>
 class TypeImpl : public Config::Base {
  public:
-  class BitsetType;      // Internal
-  class StructuralType;  // Internal
-  class UnionType;       // Internal
-
-  class ClassType;
-  class ConstantType;
-  class ArrayType;
-  class FunctionType;
-
   typedef typename Config::template Handle<TypeImpl>::type TypeHandle;
-  typedef typename Config::template Handle<ClassType>::type ClassHandle;
-  typedef typename Config::template Handle<ConstantType>::type ConstantHandle;
-  typedef typename Config::template Handle<ArrayType>::type ArrayHandle;
-  typedef typename Config::template Handle<FunctionType>::type FunctionHandle;
-  typedef typename Config::template Handle<UnionType>::type UnionHandle;
   typedef typename Config::Region Region;
 
-  #define DEFINE_TYPE_CONSTRUCTOR(type, value)                                \
-    static TypeImpl* type() { return BitsetType::New(BitsetType::k##type); }  \
-    static TypeHandle type(Region* region) {                                  \
-      return BitsetType::New(BitsetType::k##type, region);                    \
+  #define DEFINE_TYPE_CONSTRUCTOR(type, value)                        \
+    static TypeImpl* type() { return Config::from_bitset(k##type); }  \
+    static TypeHandle type(Region* region) {                          \
+      return Config::from_bitset(k##type, region);                    \
     }
   BITSET_TYPE_LIST(DEFINE_TYPE_CONSTRUCTOR)
   #undef DEFINE_TYPE_CONSTRUCTOR
 
   static TypeHandle Class(i::Handle<i::Map> map, Region* region) {
-    return ClassType::New(map, region);
+    return Config::from_class(map, LubBitset(*map), region);
   }
   static TypeHandle Constant(i::Handle<i::Object> value, Region* region) {
-    return ConstantType::New(value, region);
-  }
-  static TypeHandle Array(TypeHandle element, Region* region) {
-    return ArrayType::New(element, region);
-  }
-  static FunctionHandle Function(
-      TypeHandle result, TypeHandle receiver, int arity, Region* region) {
-    return FunctionType::New(result, receiver, arity, region);
-  }
-  static TypeHandle Function(TypeHandle result, Region* region) {
-    return Function(result, Any(region), 0, region);
-  }
-  static TypeHandle Function(
-      TypeHandle result, TypeHandle param0, Region* region) {
-    FunctionHandle function = Function(result, Any(region), 1, region);
-    function->InitParameter(0, param0);
-    return function;
-  }
-  static TypeHandle Function(
-      TypeHandle result, TypeHandle param0, TypeHandle param1, Region* region) {
-    FunctionHandle function = Function(result, Any(region), 2, region);
-    function->InitParameter(0, param0);
-    function->InitParameter(1, param1);
-    return function;
+    return Config::from_constant(value, LubBitset(*value), region);
   }
 
   static TypeHandle Union(TypeHandle type1, TypeHandle type2, Region* reg);
   static TypeHandle Intersect(TypeHandle type1, TypeHandle type2, Region* reg);
 
   static TypeHandle Of(i::Object* value, Region* region) {
-    return Config::from_bitset(BitsetType::Lub(value), region);
+    return Config::from_bitset(LubBitset(value), region);
   }
   static TypeHandle Of(i::Handle<i::Object> value, Region* region) {
     return Of(*value, region);
   }
 
   bool IsInhabited() {
-    return !this->IsBitset() || BitsetType::IsInhabited(this->AsBitset());
+    return !this->IsBitset() || IsInhabited(this->AsBitset());
   }
 
   bool Is(TypeImpl* that) { return this == that || this->SlowIs(that); }
   template<class TypeHandle>
   bool Is(TypeHandle that) { return this->Is(*that); }
 
   bool Maybe(TypeImpl* that);
   template<class TypeHandle>
   bool Maybe(TypeHandle that) { return this->Maybe(*that); }
 
-  bool Equals(TypeImpl* that) { return this->Is(that) && that->Is(this); }
-  template<class TypeHandle>
-  bool Equals(TypeHandle that) { return this->Equals(*that); }
-
   // Equivalent to Constant(value)->Is(this), but avoiding allocation.
   bool Contains(i::Object* val);
   bool Contains(i::Handle<i::Object> val) { return this->Contains(*val); }
 
   // State-dependent versions of Of and Is that consider subtyping between
   // a constant and its map class.
   static TypeHandle NowOf(i::Object* value, Region* region);
   static TypeHandle NowOf(i::Handle<i::Object> value, Region* region) {
     return NowOf(*value, region);
   }
   bool NowIs(TypeImpl* that);
   template<class TypeHandle>
   bool NowIs(TypeHandle that)  { return this->NowIs(*that); }
   inline bool NowContains(i::Object* val);
   bool NowContains(i::Handle<i::Object> val) { return this->NowContains(*val); }
 
   bool IsClass() { return Config::is_class(this); }
   bool IsConstant() { return Config::is_constant(this); }
-  bool IsArray() { return Config::is_struct(this, StructuralType::kArrayTag); }
-  bool IsFunction() {
-    return Config::is_struct(this, StructuralType::kFunctionTag);
-  }
-
-  ClassType* AsClass() { return ClassType::cast(this); }
-  ConstantType* AsConstant() { return ConstantType::cast(this); }
-  ArrayType* AsArray() { return ArrayType::cast(this); }
-  FunctionType* AsFunction() { return FunctionType::cast(this); }
+  i::Handle<i::Map> AsClass() { return Config::as_class(this); }
+  i::Handle<i::Object> AsConstant() { return Config::as_constant(this); }
 
   int NumClasses();
   int NumConstants();
 
-  template<class T> class Iterator;
-  inline Iterator<i::Map> Classes();
-  inline Iterator<i::Object> Constants();
+  template<class T>
+  class Iterator {
+   public:
+    bool Done() const { return index_ < 0; }
+    i::Handle<T> Current();
+    void Advance();
 
-  static inline TypeImpl* cast(typename Config::Base* object);
+   private:
+    template<class> friend class TypeImpl;
+
+    Iterator() : index_(-1) {}
+    explicit Iterator(TypeHandle type) : type_(type), index_(-1) {
+      Advance();
+    }
+
+    inline bool matches(TypeHandle type);
+    inline TypeHandle get_type();
+
+    TypeHandle type_;
+    int index_;
+  };
+
+  Iterator<i::Map> Classes() {
+    if (this->IsBitset()) return Iterator<i::Map>();
+    return Iterator<i::Map>(Config::handle(this));
+  }
+  Iterator<i::Object> Constants() {
+    if (this->IsBitset()) return Iterator<i::Object>();
+    return Iterator<i::Object>(Config::handle(this));
+  }
+
+  static TypeImpl* cast(typename Config::Base* object) {
+    TypeImpl* t = static_cast<TypeImpl*>(object);
+    ASSERT(t->IsBitset() || t->IsClass() || t->IsConstant() || t->IsUnion());
+    return t;
+  }
 
   template<class OtherTypeImpl>
   static TypeHandle Convert(
       typename OtherTypeImpl::TypeHandle type, Region* region);
 
   enum PrintDimension { BOTH_DIMS, SEMANTIC_DIM, REPRESENTATION_DIM };
   void TypePrint(PrintDimension = BOTH_DIMS);
   void TypePrint(FILE* out, PrintDimension = BOTH_DIMS);
 
- protected:
+ private:
   template<class> friend class Iterator;
   template<class> friend class TypeImpl;
+  friend struct ZoneTypeConfig;
+  friend struct HeapTypeConfig;
 
-  template<class T>
-  static typename Config::template Handle<T>::type handle(T* type) {
-    return Config::handle(type);
-  }
+  enum Tag {
+    kClassTag,
+    kConstantTag,
+    kUnionTag
+  };
 
-  bool IsNone() { return this == None(); }
-  bool IsAny() { return this == Any(); }
-  bool IsBitset() { return Config::is_bitset(this); }
-  bool IsUnion() { return Config::is_struct(this, StructuralType::kUnionTag); }
-
-  int AsBitset() {
-    ASSERT(this->IsBitset());
-    return static_cast<BitsetType*>(this)->Bitset();
-  }
-  UnionType* AsUnion() { return UnionType::cast(this); }
-
-  bool SlowIs(TypeImpl* that);
-
-  bool InUnion(UnionHandle unioned, int current_size);
-  static int ExtendUnion(
-      UnionHandle unioned, TypeHandle t, int current_size);
-  static int ExtendIntersection(
-      UnionHandle unioned, TypeHandle t, TypeHandle other, int current_size);
-
-  int BitsetGlb() { return BitsetType::Glb(this); }
-  int BitsetLub() { return BitsetType::Lub(this); }
-};
-
-
-template<class Config>
-class TypeImpl<Config>::BitsetType : public TypeImpl<Config> {
- private:
-  friend class TypeImpl<Config>;
+  // A structured type contains a tag an a variable number of type fields.
+  // A union is a structured type with the following invariants:
+  // - its length is at least 2
+  // - at most one field is a bitset, and it must go into index 0
+  // - no field is a union
+  typedef typename Config::Struct Struct;
+  typedef typename Config::template Handle<Struct>::type StructHandle;
 
   enum {
     #define DECLARE_TYPE(type, value) k##type = (value),
     BITSET_TYPE_LIST(DECLARE_TYPE)
     #undef DECLARE_TYPE
     kUnusedEOL = 0
   };
 
-  int Bitset() { return Config::as_bitset(this); }
+  bool IsNone() { return this == None(); }
+  bool IsAny() { return this == Any(); }
+  bool IsBitset() { return Config::is_bitset(this); }
+  bool IsStruct(Tag tag) {
+    return Config::is_struct(this)
+        && Config::struct_tag(Config::as_struct(this)) == tag;
+  }
+  bool IsUnion() { return IsStruct(kUnionTag); }
 
-  static BitsetType* New(int bitset) {
-    return static_cast<BitsetType*>(Config::from_bitset(bitset));
+  int AsBitset() { return Config::as_bitset(this); }
+  StructHandle AsStruct(Tag tag) {
+    ASSERT(IsStruct(tag));
+    return Config::as_struct(this);
   }
-  static TypeHandle New(int bitset, Region* region) {
-    return Config::from_bitset(bitset, region);
+  StructHandle AsUnion() { return AsStruct(kUnionTag); }
+
+  static int StructLength(StructHandle structured) {
+    return Config::struct_length(structured);
   }
+  static TypeHandle StructGet(StructHandle structured, int i) {
+    return Config::struct_get(structured, i);
+  }
+
+  bool SlowIs(TypeImpl* that);
 
   static bool IsInhabited(int bitset) {
     return (bitset & kRepresentation) && (bitset & kSemantic);
   }
 
-  static int Glb(TypeImpl* type);  // greatest lower bound that's a bitset
-  static int Lub(TypeImpl* type);  // least upper bound that's a bitset
-  static int Lub(i::Object* value);
-  static int Lub(i::Map* map);
+  int LubBitset();  // least upper bound that's a bitset
+  int GlbBitset();  // greatest lower bound that's a bitset
 
-  static const char* Name(int bitset);
+  static int LubBitset(i::Object* value);
+  static int LubBitset(i::Map* map);
+
+  bool InUnion(StructHandle unioned, int current_size);
+  static int ExtendUnion(
+      StructHandle unioned, TypeHandle t, int current_size);
+  static int ExtendIntersection(
+      StructHandle unioned, TypeHandle t, TypeHandle other, int current_size);
+
+  static const char* bitset_name(int bitset);
   static void BitsetTypePrint(FILE* out, int bitset);
 };
 
 
-// Internal
-// A structured type contains a tag and a variable number of type fields.
-template<class Config>
-class TypeImpl<Config>::StructuralType : public TypeImpl<Config> {
- protected:
-  template<class> friend class TypeImpl;
-  friend struct ZoneTypeConfig;  // For tags.
-  friend struct HeapTypeConfig;
-
-  enum Tag {
-    kClassTag,
-    kConstantTag,
-    kArrayTag,
-    kFunctionTag,
-    kUnionTag
-  };
-
-  int Length() {
-    return Config::struct_length(Config::as_struct(this));
-  }
-  TypeHandle Get(int i) {
-    return Config::struct_get(Config::as_struct(this), i);
-  }
-  void Set(int i, TypeHandle type) {
-    Config::struct_set(Config::as_struct(this), i, type);
-  }
-  void Shrink(int length) {
-    Config::struct_shrink(Config::as_struct(this), length);
-  }
-
-  static TypeHandle New(Tag tag, int length, Region* region) {
-    return Config::from_struct(Config::struct_create(tag, length, region));
-  }
-};
-
-
-template<class Config>
-class TypeImpl<Config>::ClassType : public TypeImpl<Config> {
- public:
-  i::Handle<i::Map> Map() { return Config::as_class(this); }
-
-  static ClassHandle New(i::Handle<i::Map> map, Region* region) {
-    return Config::template cast<ClassType>(
-        Config::from_class(map, BitsetType::Lub(*map), region));
-  }
-
-  static ClassType* cast(TypeImpl* type) {
-    ASSERT(type->IsClass());
-    return static_cast<ClassType*>(type);
-  }
-};
-
-
-template<class Config>
-class TypeImpl<Config>::ConstantType : public TypeImpl<Config> {
- public:
-  i::Handle<i::Object> Value() { return Config::as_constant(this); }
-
-  static ConstantHandle New(i::Handle<i::Object> value, Region* region) {
-    return Config::template cast<ConstantType>(
-        Config::from_constant(value, BitsetType::Lub(*value), region));
-  }
-
-  static ConstantType* cast(TypeImpl* type) {
-    ASSERT(type->IsConstant());
-    return static_cast<ConstantType*>(type);
-  }
-};
-
-
-// Internal
-// A union is a structured type with the following invariants:
-// - its length is at least 2
-// - at most one field is a bitset, and it must go into index 0
-// - no field is a union
-template<class Config>
-class TypeImpl<Config>::UnionType : public StructuralType {
- public:
-  static UnionHandle New(int length, Region* region) {
-    return Config::template cast<UnionType>(
-        StructuralType::New(StructuralType::kUnionTag, length, region));
-  }
-
-  static UnionType* cast(TypeImpl* type) {
-    ASSERT(type->IsUnion());
-    return static_cast<UnionType*>(type);
-  }
-};
-
-
-template<class Config>
-class TypeImpl<Config>::ArrayType : public StructuralType {
- public:
-  TypeHandle Element() { return this->Get(0); }
-
-  static ArrayHandle New(TypeHandle element, Region* region) {
-    ArrayHandle type = Config::template cast<ArrayType>(
-        StructuralType::New(StructuralType::kArrayTag, 1, region));
-    type->Set(0, element);
-    return type;
-  }
-
-  static ArrayType* cast(TypeImpl* type) {
-    ASSERT(type->IsArray());
-    return static_cast<ArrayType*>(type);
-  }
-};
-
-
-template<class Config>
-class TypeImpl<Config>::FunctionType : public StructuralType {
- public:
-  int Arity() { return this->Length() - 2; }
-  TypeHandle Result() { return this->Get(0); }
-  TypeHandle Receiver() { return this->Get(1); }
-  TypeHandle Parameter(int i) { return this->Get(2 + i); }
-
-  void InitParameter(int i, TypeHandle type) { this->Set(2 + i, type); }
-
-  static FunctionHandle New(
-      TypeHandle result, TypeHandle receiver, int arity, Region* region) {
-    FunctionHandle type = Config::template cast<FunctionType>(
-        StructuralType::New(StructuralType::kFunctionTag, 2 + arity, region));
-    type->Set(0, result);
-    type->Set(1, receiver);
-    return type;
-  }
-
-  static FunctionType* cast(TypeImpl* type) {
-    ASSERT(type->IsFunction());
-    return static_cast<FunctionType*>(type);
-  }
-};
-
-
-template<class Config> template<class T>
-class TypeImpl<Config>::Iterator {
- public:
-  bool Done() const { return index_ < 0; }
-  i::Handle<T> Current();
-  void Advance();
-
- private:
-  template<class> friend class TypeImpl;
-
-  Iterator() : index_(-1) {}
-  explicit Iterator(TypeHandle type) : type_(type), index_(-1) {
-    Advance();
-  }
-
-  inline bool matches(TypeHandle type);
-  inline TypeHandle get_type();
-
-  TypeHandle type_;
-  int index_;
-};
-
-
 // Zone-allocated types are either (odd) integers to represent bitsets, or
 // (even) pointers to structures for everything else.
 struct ZoneTypeConfig {
   typedef TypeImpl<ZoneTypeConfig> Type;
   class Base {};
   typedef void* Struct;
   typedef i::Zone Region;
   template<class T> struct Handle { typedef T* type; };
 
-  template<class T> static inline T* handle(T* type);
-  template<class T> static inline T* cast(Type* type);
-
+  static inline Type* handle(Type* type);
   static inline bool is_bitset(Type* type);
   static inline bool is_class(Type* type);
   static inline bool is_constant(Type* type);
-  static inline bool is_struct(Type* type, int tag);
-
+  static inline bool is_struct(Type* type);
   static inline int as_bitset(Type* type);
   static inline Struct* as_struct(Type* type);
   static inline i::Handle<i::Map> as_class(Type* type);
   static inline i::Handle<i::Object> as_constant(Type* type);
-
   static inline Type* from_bitset(int bitset);
   static inline Type* from_bitset(int bitset, Zone* zone);
   static inline Type* from_struct(Struct* structured);
   static inline Type* from_class(i::Handle<i::Map> map, int lub, Zone* zone);
   static inline Type* from_constant(
       i::Handle<i::Object> value, int lub, Zone* zone);
-
   static inline Struct* struct_create(int tag, int length, Zone* zone);
   static inline void struct_shrink(Struct* structured, int length);
   static inline int struct_tag(Struct* structured);
   static inline int struct_length(Struct* structured);
   static inline Type* struct_get(Struct* structured, int i);
   static inline void struct_set(Struct* structured, int i, Type* type);
-
   static inline int lub_bitset(Type* type);
 };
 
 typedef TypeImpl<ZoneTypeConfig> Type;
 
 
 // Heap-allocated types are either smis for bitsets, maps for classes, boxes for
 // constants, or fixed arrays for unions.
 struct HeapTypeConfig {
   typedef TypeImpl<HeapTypeConfig> Type;
   typedef i::Object Base;
   typedef i::FixedArray Struct;
   typedef i::Isolate Region;
   template<class T> struct Handle { typedef i::Handle<T> type; };
 
-  template<class T> static inline i::Handle<T> handle(T* type);
-  template<class T> static inline i::Handle<T> cast(i::Handle<Type> type);
-
+  static inline i::Handle<Type> handle(Type* type);
   static inline bool is_bitset(Type* type);
   static inline bool is_class(Type* type);
   static inline bool is_constant(Type* type);
-  static inline bool is_struct(Type* type, int tag);
-
+  static inline bool is_struct(Type* type);
   static inline int as_bitset(Type* type);
   static inline i::Handle<i::Map> as_class(Type* type);
   static inline i::Handle<i::Object> as_constant(Type* type);
   static inline i::Handle<Struct> as_struct(Type* type);
-
   static inline Type* from_bitset(int bitset);
   static inline i::Handle<Type> from_bitset(int bitset, Isolate* isolate);
   static inline i::Handle<Type> from_class(
       i::Handle<i::Map> map, int lub, Isolate* isolate);
   static inline i::Handle<Type> from_constant(
       i::Handle<i::Object> value, int lub, Isolate* isolate);
   static inline i::Handle<Type> from_struct(i::Handle<Struct> structured);
-
   static inline i::Handle<Struct> struct_create(
       int tag, int length, Isolate* isolate);
   static inline void struct_shrink(i::Handle<Struct> structured, int length);
   static inline int struct_tag(i::Handle<Struct> structured);
   static inline int struct_length(i::Handle<Struct> structured);
   static inline i::Handle<Type> struct_get(i::Handle<Struct> structured, int i);
   static inline void struct_set(
       i::Handle<Struct> structured, int i, i::Handle<Type> type);
-
   static inline int lub_bitset(Type* type);
 };
 
 typedef TypeImpl<HeapTypeConfig> HeapType;
 
 
 // A simple struct to represent a pair of lower/upper type bounds.
 template<class Config>
 struct BoundsImpl {
   typedef TypeImpl<Config> Type;
@@ skipping 45 matching lines @@
   bool Narrows(BoundsImpl that) {
     return that.lower->Is(this->lower) && this->upper->Is(that.upper);
   }
 };
 
 typedef BoundsImpl<ZoneTypeConfig> Bounds;
 
 } }  // namespace v8::internal
 
 #endif  // V8_TYPES_H_