[builtins] move String.prototype[@@iterator] to C++ builtin

BUG=v8:5388
R=bmeurer@chromium.org, adamk@chromium.org
TBR=hpayer@chromium.org

Review-Url: https://codereview.chromium.org/2348493003
Cr-Commit-Position: refs/heads/master@{#39598}

BUILD.gn

@@ -392,14 +392,12 @@ action("js2c") {
     "src/js/regexp.js",
     "src/js/arraybuffer.js",
     "src/js/typedarray.js",
-    "src/js/iterator-prototype.js",
     "src/js/collection.js",
     "src/js/weak-collection.js",
     "src/js/collection-iterator.js",
     "src/js/promise.js",
     "src/js/messages.js",
     "src/js/array-iterator.js",
-    "src/js/string-iterator.js",
     "src/js/templates.js",
     "src/js/spread.js",
     "src/js/proxy.js",
@@ -927,6 +925,7 @@ v8_source_set("v8_base") {
     "src/builtins/builtins-handler.cc",
     "src/builtins/builtins-internal.cc",
     "src/builtins/builtins-interpreter.cc",
+    "src/builtins/builtins-iterator.cc",
     "src/builtins/builtins-json.cc",
     "src/builtins/builtins-math.cc",
     "src/builtins/builtins-number.cc",

src/ast/ast-types.cc

@@ -217,6 +217,7 @@ AstType::bitset AstBitsetType::Lub(i::Map* map) {
     case JS_MAP_TYPE:
     case JS_SET_ITERATOR_TYPE:
     case JS_MAP_ITERATOR_TYPE:
+    case JS_STRING_ITERATOR_TYPE:
     case JS_WEAK_MAP_TYPE:
     case JS_WEAK_SET_TYPE:
     case JS_PROMISE_TYPE:

src/bootstrapper.cc

@@ -660,6 +660,16 @@ void Genesis::CreateIteratorMaps(Handle<JSFunction> empty) {
   // Create iterator-related meta-objects.
   Handle<JSObject> iterator_prototype =
       factory()->NewJSObject(isolate()->object_function(), TENURED);
+
+  Handle<JSFunction> iterator_prototype_iterator = SimpleCreateFunction(
+      isolate(), factory()->NewStringFromAsciiChecked("[Symbol.iterator]"),
+      Builtins::kIteratorPrototypeIterator, 0, false);
+  iterator_prototype_iterator->shared()->set_native(true);
+
+  JSObject::AddProperty(iterator_prototype, factory()->iterator_symbol(),
+                        iterator_prototype_iterator, DONT_ENUM);
+  native_context()->set_initial_iterator_prototype(*iterator_prototype);
+
   Handle<JSObject> generator_object_prototype =
       factory()->NewJSObject(isolate()->object_function(), TENURED);
   native_context()->set_initial_generator_prototype(
@@ -1408,6 +1418,38 @@ void Genesis::InitializeGlobal(Handle<JSGlobalObject> global_object,
                           Builtins::kStringPrototypeTrimRight, 0, false);
     SimpleInstallFunction(prototype, "valueOf",
                           Builtins::kStringPrototypeValueOf, 0, true);
+
+    Handle<JSFunction> iterator = SimpleCreateFunction(
+        isolate, factory->NewStringFromAsciiChecked("[Symbol.iterator]"),
+        Builtins::kStringPrototypeIterator, 0, true);
+    iterator->shared()->set_native(true);
+    JSObject::AddProperty(prototype, factory->iterator_symbol(), iterator,
+                          static_cast<PropertyAttributes>(DONT_ENUM));
+  }
+
+  {  // --- S t r i n g I t e r a t o r ---
+    Handle<JSObject> iterator_prototype(
+        native_context()->initial_iterator_prototype());
+
+    Handle<JSObject> string_iterator_prototype =
+        factory->NewJSObject(isolate->object_function(), TENURED);
+    JSObject::ForceSetPrototype(string_iterator_prototype, iterator_prototype);
+
+    JSObject::AddProperty(
+        string_iterator_prototype, factory->to_string_tag_symbol(),
+        factory->NewStringFromAsciiChecked("String Iterator"),
+        static_cast<PropertyAttributes>(DONT_ENUM | READ_ONLY));
+
+    InstallFunction(string_iterator_prototype, "next", JS_OBJECT_TYPE,
+                    JSObject::kHeaderSize, MaybeHandle<JSObject>(),
+                    Builtins::kStringIteratorPrototypeNext);
+
+    Handle<JSFunction> string_iterator_function = CreateFunction(
+        isolate, factory->NewStringFromAsciiChecked("StringIterator"),
+        JS_STRING_ITERATOR_TYPE, JSStringIterator::kSize,
+        string_iterator_prototype, Builtins::kIllegal);
+    native_context()->set_string_iterator_map(
+        string_iterator_function->initial_map());
   }
 
   {
@@ -2468,17 +2510,12 @@ void Bootstrapper::ExportFromRuntime(Isolate* isolate,
     native_context->set_object_to_string(*to_string);
   }
 
-  Handle<JSObject> iterator_prototype;
-
-  {
-    PrototypeIterator iter(native_context->generator_object_prototype_map());
-    iter.Advance();  // Advance to the prototype of generator_object_prototype.
-    iterator_prototype = Handle<JSObject>(iter.GetCurrent<JSObject>());
+  Handle<JSObject> iterator_prototype(
+      native_context->initial_iterator_prototype());
 
-    JSObject::AddProperty(container,
-                          factory->InternalizeUtf8String("IteratorPrototype"),
-                          iterator_prototype, NONE);
-  }
+  JSObject::AddProperty(container,
+                        factory->InternalizeUtf8String("IteratorPrototype"),
+                        iterator_prototype, NONE);
 
   {
     PrototypeIterator iter(native_context->sloppy_generator_function_map());

src/builtins/builtins-iterator.cc

+// Copyright 2016 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.
+
+#include "src/builtins/builtins.h"
+#include "src/builtins/builtins-utils.h"
+
+namespace v8 {
+namespace internal {
+
+void Builtins::Generate_IteratorPrototypeIterator(
+    CodeStubAssembler* assembler) {
+  assembler->Return(assembler->Parameter(0));
+}
+
+}  // namespace internal
+}  // namespace v8

src/builtins/builtins-string.cc

@@ -616,5 +616,59 @@ void Builtins::Generate_StringPrototypeValueOf(CodeStubAssembler* assembler) {
   assembler->Return(result);
 }
 
+BUILTIN(StringPrototypeIterator) {
+  HandleScope scope(isolate);
+  TO_THIS_STRING(object, "String.prototype[Symbol.iterator]");
+
+  Handle<String> string;
+  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, string,
+                                     Object::ToString(isolate, object));
+
+  return *isolate->factory()->NewJSStringIterator(string);
+}
+
+BUILTIN(StringIteratorPrototypeNext) {
+  HandleScope scope(isolate);
+
+  if (!args.receiver()->IsJSStringIterator()) {
+    Handle<String> reason = isolate->factory()->NewStringFromAsciiChecked(
+        "String Iterator.prototype.next");
+    THROW_NEW_ERROR_RETURN_FAILURE(
+        isolate,
+        NewTypeError(MessageTemplate::kIncompatibleMethodReceiver, reason));
+  }
+  Handle<JSStringIterator> iterator =
+      Handle<JSStringIterator>::cast(args.receiver());
+  Handle<String> string(iterator->string());
+
+  int position = iterator->index();
+  int length = string->length();
+
+  if (position < length) {
+    uint16_t lead = string->Get(position);
+    if (lead >= 0xD800 && lead <= 0xDBFF && position + 1 < length) {
+      uint16_t trail = string->Get(position + 1);
+      if (V8_LIKELY(trail >= 0xDC00 && trail <= 0xDFFF)) {
+        // Return surrogate pair code units
+        iterator->set_index(position + 2);
+        Handle<String> value =
+            isolate->factory()->NewSurrogatePairString(lead, trail);
+        return *isolate->factory()->NewJSIteratorResult(value, false);
+      }
+    }
+
+    // Return single code unit
+    iterator->set_index(position + 1);
+    Handle<String> value =
+        isolate->factory()->LookupSingleCharacterStringFromCode(lead);
+    return *isolate->factory()->NewJSIteratorResult(value, false);
+  }
+
+  iterator->set_string(isolate->heap()->empty_string());
+
+  return *isolate->factory()->NewJSIteratorResult(
+      isolate->factory()->undefined_value(), true);
+}
+
 }  // namespace internal
 }  // namespace v8

src/builtins/builtins.h

@@ -376,6 +376,9 @@ namespace internal {
   /* ES6 section 18.2.3 isNaN ( number ) */                                   \
   TFJ(GlobalIsNaN, 2)                                                         \
                                                                               \
+  /* ES6 #sec-%iteratorprototype%-@@iterator */                               \
+  TFJ(IteratorPrototypeIterator, 1)                                           \
+                                                                              \
   /* JSON */                                                                  \
   CPP(JsonParse)                                                              \
   CPP(JsonStringify)                                                          \
@@ -549,6 +552,11 @@ namespace internal {
   CPP(StringPrototypeTrimRight)                                               \
   /* ES6 section 21.1.3.28 String.prototype.valueOf () */                     \
   TFJ(StringPrototypeValueOf, 1)                                              \
+  /* ES6 #sec-string.prototype-@@iterator */                                  \
+  CPP(StringPrototypeIterator)                                                \
+                                                                              \
+  /* StringIterator */                                                        \
+  CPP(StringIteratorPrototypeNext)                                            \
                                                                               \
   /* Symbol */                                                                \
   CPP(SymbolConstructor)                                                      \

src/compiler/types.cc

@@ -214,6 +214,7 @@ Type::bitset BitsetType::Lub(i::Map* map) {
     case JS_MAP_TYPE:
     case JS_SET_ITERATOR_TYPE:
     case JS_MAP_ITERATOR_TYPE:
+    case JS_STRING_ITERATOR_TYPE:
     case JS_WEAK_MAP_TYPE:
     case JS_WEAK_SET_TYPE:
     case JS_PROMISE_TYPE:

src/contexts.h

@@ -148,6 +148,7 @@ enum ContextLookupFlags {
   V(GENERATOR_OBJECT_PROTOTYPE_MAP_INDEX, Map, generator_object_prototype_map) \
   V(INITIAL_ARRAY_PROTOTYPE_INDEX, JSObject, initial_array_prototype)          \
   V(INITIAL_GENERATOR_PROTOTYPE_INDEX, JSObject, initial_generator_prototype)  \
+  V(INITIAL_ITERATOR_PROTOTYPE_INDEX, JSObject, initial_iterator_prototype)    \
   V(INITIAL_OBJECT_PROTOTYPE_INDEX, JSObject, initial_object_prototype)        \
   V(INT16_ARRAY_FUN_INDEX, JSFunction, int16_array_fun)                        \
   V(INT16X8_FUNCTION_INDEX, JSFunction, int16x8_function)                      \

src/factory.cc

@@ -599,6 +599,19 @@ MaybeHandle<String> Factory::NewConsString(Handle<String> left,
   return result;
 }
 
+Handle<String> Factory::NewSurrogatePairString(uint16_t lead, uint16_t trail) {
+  DCHECK_GE(lead, 0xD800);
+  DCHECK_LE(lead, 0xDBFF);
+  DCHECK_GE(trail, 0xDC00);
+  DCHECK_LE(trail, 0xDFFF);
+
+  Handle<SeqTwoByteString> str =
+      isolate()->factory()->NewRawTwoByteString(2).ToHandleChecked();
+  uc16* dest = str->GetChars();
+  dest[0] = lead;
+  dest[1] = trail;
+  return str;
+}
 
 Handle<String> Factory::NewProperSubString(Handle<String> str,
                                            int begin,
@@ -733,6 +746,17 @@ Handle<ExternalOneByteString> Factory::NewNativeSourceString(
   return external_string;
 }
 
+Handle<JSStringIterator> Factory::NewJSStringIterator(Handle<String> string) {
+  Handle<Map> map(isolate()->native_context()->string_iterator_map(),
+                  isolate());
+  Handle<String> flat_string = String::Flatten(string);
+  Handle<JSStringIterator> iterator =
+      Handle<JSStringIterator>::cast(NewJSObjectFromMap(map));
+  iterator->set_string(*flat_string);
+  iterator->set_index(0);
+
+  return iterator;
+}
 
 Handle<Symbol> Factory::NewSymbol() {
   CALL_HEAP_FUNCTION(
@@ -1764,6 +1788,15 @@ Handle<JSDataView> Factory::NewJSDataView() {
       JSDataView);
 }
 
+Handle<JSIteratorResult> Factory::NewJSIteratorResult(Handle<Object> value,
+                                                      bool done) {
+  Handle<Map> map(isolate()->native_context()->iterator_result_map());
+  Handle<JSIteratorResult> js_iter_result =
+      Handle<JSIteratorResult>::cast(NewJSObjectFromMap(map));
+  js_iter_result->set_value(*value);
+  js_iter_result->set_done(*ToBoolean(done));
+  return js_iter_result;
+}
 
 Handle<JSMap> Factory::NewJSMap() {
   Handle<Map> map(isolate()->native_context()->js_map_map());

src/factory.h

@@ -180,6 +180,8 @@ class Factory final {
   MUST_USE_RESULT MaybeHandle<String> NewStringFromTwoByte(
       const ZoneVector<uc16>* str, PretenureFlag pretenure = NOT_TENURED);
 
+  Handle<JSStringIterator> NewJSStringIterator(Handle<String> string);
+
   // Allocates an internalized string in old space based on the character
   // stream.
   Handle<String> NewInternalizedStringFromUtf8(Vector<const char> str,
@@ -221,6 +223,10 @@ class Factory final {
   MUST_USE_RESULT MaybeHandle<String> NewConsString(Handle<String> left,
                                                     Handle<String> right);
 
+  // Create or lookup a single characters tring made up of a utf16 surrogate
+  // pair.
+  Handle<String> NewSurrogatePairString(uint16_t lead, uint16_t trail);
+
   // Create a new string object which holds a proper substring of a string.
   Handle<String> NewProperSubString(Handle<String> str,
                                     int begin,
@@ -508,6 +514,8 @@ class Factory final {
   Handle<JSDataView> NewJSDataView(Handle<JSArrayBuffer> buffer,
                                    size_t byte_offset, size_t byte_length);
 
+  Handle<JSIteratorResult> NewJSIteratorResult(Handle<Object> value, bool done);
+
   Handle<JSMap> NewJSMap();
   Handle<JSSet> NewJSSet();
 

src/heap/objects-visiting.cc

@@ -119,6 +119,7 @@ StaticVisitorBase::VisitorId StaticVisitorBase::GetVisitorId(
     case JS_MAP_TYPE:
     case JS_SET_ITERATOR_TYPE:
     case JS_MAP_ITERATOR_TYPE:
+    case JS_STRING_ITERATOR_TYPE:
     case JS_PROMISE_TYPE:
     case JS_BOUND_FUNCTION_TYPE:
       return GetVisitorIdForSize(kVisitJSObject, kVisitJSObjectGeneric,

src/js/iterator-prototype.js

-// Copyright 2015 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.
-
-(function(global, utils) {
-  "use strict";
-  %CheckIsBootstrapping();
-
-  var GlobalObject = global.Object;
-  var IteratorPrototype = utils.ImportNow("IteratorPrototype");
-  var iteratorSymbol = utils.ImportNow("iterator_symbol");
-
-  // 25.1.2.1 %IteratorPrototype% [ @@iterator ] ( )
-  function IteratorPrototypeIterator() {
-    return this;
-  }
-
-  utils.SetFunctionName(IteratorPrototypeIterator, iteratorSymbol);
-  %AddNamedProperty(IteratorPrototype, iteratorSymbol,
-      IteratorPrototypeIterator, DONT_ENUM);
-})

src/js/string-iterator.js

-// 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.
-
-(function(global, utils) {
-
-"use strict";
-
-%CheckIsBootstrapping();
-
-// -------------------------------------------------------------------
-// Imports
-
-var GlobalString = global.String;
-var IteratorPrototype = utils.ImportNow("IteratorPrototype");
-var iteratorSymbol = utils.ImportNow("iterator_symbol");
-var stringIteratorIteratedStringSymbol =
-    utils.ImportNow("string_iterator_iterated_string_symbol");
-var stringIteratorNextIndexSymbol =
-    utils.ImportNow("string_iterator_next_index_symbol");
-var toStringTagSymbol = utils.ImportNow("to_string_tag_symbol");
-
-// -------------------------------------------------------------------
-
-function StringIterator() {}
-
-
-// 21.1.5.1 CreateStringIterator Abstract Operation
-function CreateStringIterator(string) {
-  CHECK_OBJECT_COERCIBLE(string, 'String.prototype[Symbol.iterator]');
-  var s = TO_STRING(string);
-  var iterator = new StringIterator;
-  SET_PRIVATE(iterator, stringIteratorIteratedStringSymbol, s);
-  SET_PRIVATE(iterator, stringIteratorNextIndexSymbol, 0);
-  return iterator;
-}
-
-
-// ES6 section 21.1.5.2.1 %StringIteratorPrototype%.next ( )
-function StringIteratorNext() {
-  var iterator = this;
-  var value = UNDEFINED;
-  var done = true;
-
-  if (!IS_RECEIVER(iterator) ||
-      !HAS_DEFINED_PRIVATE(iterator, stringIteratorNextIndexSymbol)) {
-    throw %make_type_error(kIncompatibleMethodReceiver,
-                        'String Iterator.prototype.next');
-  }
-
-  var s = GET_PRIVATE(iterator, stringIteratorIteratedStringSymbol);
-  if (!IS_UNDEFINED(s)) {
-    var position = GET_PRIVATE(iterator, stringIteratorNextIndexSymbol);
-    var length = TO_UINT32(s.length);
-    if (position >= length) {
-      SET_PRIVATE(iterator, stringIteratorIteratedStringSymbol, UNDEFINED);
-    } else {
-      var first = %_StringCharCodeAt(s, position);
-      value = %_StringCharFromCode(first);
-      done = false;
-      position++;
-
-      if (first >= 0xD800 && first <= 0xDBFF && position < length) {
-        var second = %_StringCharCodeAt(s, position);
-        if (second >= 0xDC00 && second <= 0xDFFF) {
-          value += %_StringCharFromCode(second);
-          position++;
-        }
-      }
-
-      SET_PRIVATE(iterator, stringIteratorNextIndexSymbol, position);
-    }
-  }
-  return %_CreateIterResultObject(value, done);
-}
-
-
-// 21.1.3.27 String.prototype [ @@iterator ]( )
-function StringPrototypeIterator() {
-  return CreateStringIterator(this);
-}
-
-//-------------------------------------------------------------------
-
-%FunctionSetPrototype(StringIterator, {__proto__: IteratorPrototype});
-%FunctionSetInstanceClassName(StringIterator, 'String Iterator');
-
-utils.InstallFunctions(StringIterator.prototype, DONT_ENUM, [
-  'next', StringIteratorNext
-]);
-%AddNamedProperty(StringIterator.prototype, toStringTagSymbol,
-                  "String Iterator", READ_ONLY | DONT_ENUM);
-
-utils.SetFunctionName(StringPrototypeIterator, iteratorSymbol);
-%AddNamedProperty(GlobalString.prototype, iteratorSymbol,
-                  StringPrototypeIterator, DONT_ENUM);
-
-})

src/objects-body-descriptors-inl.h

@@ -474,6 +474,7 @@ ReturnType BodyDescriptorApply(InstanceType type, T1 p1, T2 p2, T3 p3) {
     case JS_MAP_TYPE:
     case JS_SET_ITERATOR_TYPE:
     case JS_MAP_ITERATOR_TYPE:
+    case JS_STRING_ITERATOR_TYPE:
     case JS_REGEXP_TYPE:
     case JS_GLOBAL_PROXY_TYPE:
     case JS_GLOBAL_OBJECT_TYPE:

src/objects-debug.cc

@@ -152,6 +152,9 @@ void HeapObject::HeapObjectVerify() {
     case JS_MAP_ITERATOR_TYPE:
       JSMapIterator::cast(this)->JSMapIteratorVerify();
       break;
+    case JS_STRING_ITERATOR_TYPE:
+      JSStringIterator::cast(this)->JSStringIteratorVerify();
+      break;
     case JS_WEAK_MAP_TYPE:
       JSWeakMap::cast(this)->JSWeakMapVerify();
       break;
@@ -779,6 +782,13 @@ void JSWeakMap::JSWeakMapVerify() {
   CHECK(table()->IsHashTable() || table()->IsUndefined(GetIsolate()));
 }
 
+void JSStringIterator::JSStringIteratorVerify() {
+  CHECK(IsJSStringIterator());
+  JSObjectVerify();
+  CHECK(string()->IsString());
+  CHECK_GE(index(), 0);
+  CHECK_LE(index(), String::kMaxLength);
+}
 
 void JSWeakSet::JSWeakSetVerify() {
   CHECK(IsJSWeakSet());

src/objects-inl.h

@@ -701,6 +701,7 @@ TYPE_CHECKER(Map, MAP_TYPE)
 TYPE_CHECKER(FixedDoubleArray, FIXED_DOUBLE_ARRAY_TYPE)
 TYPE_CHECKER(WeakFixedArray, FIXED_ARRAY_TYPE)
 TYPE_CHECKER(TransitionArray, TRANSITION_ARRAY_TYPE)
+TYPE_CHECKER(JSStringIterator, JS_STRING_ITERATOR_TYPE)
 
 bool HeapObject::IsJSWeakCollection() const {
   return IsJSWeakMap() || IsJSWeakSet();
@@ -2113,6 +2114,8 @@ int JSObject::GetHeaderSize(InstanceType type) {
       return JSArgumentsObject::kHeaderSize;
     case JS_ERROR_TYPE:
       return JSObject::kHeaderSize;
+    case JS_STRING_ITERATOR_TYPE:
+      return JSStringIterator::kSize;
     default:
       UNREACHABLE();
       return 0;
@@ -3282,6 +3285,7 @@ CAST_ACCESSOR(JSReceiver)
 CAST_ACCESSOR(JSRegExp)
 CAST_ACCESSOR(JSSet)
 CAST_ACCESSOR(JSSetIterator)
+CAST_ACCESSOR(JSStringIterator)
 CAST_ACCESSOR(JSTypedArray)
 CAST_ACCESSOR(JSValue)
 CAST_ACCESSOR(JSWeakCollection)
@@ -8270,6 +8274,12 @@ static inline Handle<Object> MakeEntryPair(Isolate* isolate, Handle<Name> key,
                                                     FAST_ELEMENTS, 2);
 }
 
+ACCESSORS(JSIteratorResult, value, Object, kValueOffset)
+ACCESSORS(JSIteratorResult, done, Object, kDoneOffset)
+
+ACCESSORS(JSStringIterator, string, String, kStringOffset)
+SMI_ACCESSORS(JSStringIterator, index, kNextIndexOffset)
+
 #undef TYPE_CHECKER
 #undef CAST_ACCESSOR
 #undef INT_ACCESSORS

src/objects.h

@@ -57,6 +57,7 @@
 //         - JSCollection
 //           - JSSet
 //           - JSMap
+//         - JSStringIterator
 //         - JSSetIterator
 //         - JSMapIterator
 //         - JSWeakCollection
@@ -433,6 +434,7 @@ const int kStubMinorKeyBits = kSmiValueSize - kStubMajorKeyBits - 1;
   V(JS_PROMISE_TYPE)                                            \
   V(JS_REGEXP_TYPE)                                             \
   V(JS_ERROR_TYPE)                                              \
+  V(JS_STRING_ITERATOR_TYPE)                                    \
                                                                 \
   V(JS_BOUND_FUNCTION_TYPE)                                     \
   V(JS_FUNCTION_TYPE)                                           \
@@ -728,6 +730,7 @@ enum InstanceType {
   JS_PROMISE_TYPE,
   JS_REGEXP_TYPE,
   JS_ERROR_TYPE,
+  JS_STRING_ITERATOR_TYPE,
   JS_BOUND_FUNCTION_TYPE,
   JS_FUNCTION_TYPE,  // LAST_JS_OBJECT_TYPE, LAST_JS_RECEIVER_TYPE
 
@@ -1009,6 +1012,7 @@ template <class C> inline bool Is(Object* obj);
   V(JSProxy)                     \
   V(JSError)                     \
   V(JSPromise)                   \
+  V(JSStringIterator)            \
   V(JSSet)                       \
   V(JSMap)                       \
   V(JSSetIterator)               \
@@ -2615,6 +2619,10 @@ class JSDataPropertyDescriptor: public JSObject {
 // as specified by ES6 section 25.1.1.3 The IteratorResult Interface
 class JSIteratorResult: public JSObject {
  public:
+  DECL_ACCESSORS(value, Object)
+
+  DECL_ACCESSORS(done, Object)
+
   // Offsets of object fields.
   static const int kValueOffset = JSObject::kHeaderSize;
   static const int kDoneOffset = kValueOffset + kPointerSize;
@@ -10325,6 +10333,28 @@ class JSMap : public JSCollection {
   DISALLOW_IMPLICIT_CONSTRUCTORS(JSMap);
 };
 
+class JSStringIterator : public JSObject {
+ public:
+  // Dispatched behavior.
+  DECLARE_PRINTER(JSStringIterator)
+  DECLARE_VERIFIER(JSStringIterator)
+
+  DECLARE_CAST(JSStringIterator)
+
+  // [string]: the [[IteratedString]] internal field.
+  DECL_ACCESSORS(string, String)
+
+  // [index]: The [[StringIteratorNextIndex]] internal field.
+  inline int index() const;
+  inline void set_index(int value);
+
+  static const int kStringOffset = JSObject::kHeaderSize;
+  static const int kNextIndexOffset = kStringOffset + kPointerSize;
+  static const int kSize = kNextIndexOffset + kPointerSize;
+
+ private:
+  DISALLOW_IMPLICIT_CONSTRUCTORS(JSStringIterator);
+};
 
 // OrderedHashTableIterator is an iterator that iterates over the keys and
 // values of an OrderedHashTable.

src/v8.gyp

@@ -495,6 +495,7 @@
         'builtins/builtins-handler.cc',
         'builtins/builtins-internal.cc',
         'builtins/builtins-interpreter.cc',
+        'builtins/builtins-iterator.cc',
         'builtins/builtins-json.cc',
         'builtins/builtins-math.cc',
         'builtins/builtins-number.cc',
@@ -2204,14 +2205,12 @@
           'js/regexp.js',
           'js/arraybuffer.js',
           'js/typedarray.js',
-          'js/iterator-prototype.js',
           'js/collection.js',
           'js/weak-collection.js',
           'js/collection-iterator.js',
           'js/promise.js',
           'js/messages.js',
           'js/array-iterator.js',
-          'js/string-iterator.js',
           'js/templates.js',
           'js/spread.js',
           'js/proxy.js',

test/cctest/interpreter/bytecode_expectations/CallRuntime.golden

@@ -79,7 +79,7 @@ bytecodes: [
   /*   15 S> */ B(LdrUndefined), R(0),
                 B(CreateArrayLiteral), U8(0), U8(0), U8(9),
                 B(Star), R(1),
-                B(CallJSRuntime), U8(139), R(0), U8(2),
+                B(CallJSRuntime), U8(140), R(0), U8(2),
   /*   44 S> */ B(Return),
 ]
 constant pool: [