Port StringPrototypeIterator to Torque

Bug: v8:8996
Change-Id: I7930d98a9ff3b341611b2833b6847615b0ac467d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1593856
Commit-Queue: Z Nguyen-Huu <duongn@microsoft.com>
Reviewed-by: Simon Zünd <szuend@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61220}

BUILD.gn

@@ -951,6 +951,7 @@ torque_files = [
   "src/builtins/regexp-replace.tq",
   "src/builtins/string-endswith.tq",
   "src/builtins/string-html.tq",
+  "src/builtins/string-iterator.tq",
   "src/builtins/string-repeat.tq",
   "src/builtins/string-startswith.tq",
   "src/builtins/typed-array.tq",
@@ -1005,6 +1006,7 @@ torque_namespaces = [
   "regexp-replace",
   "string",
   "string-html",
+  "string-iterator",
   "string-repeat",
   "test",
   "typed-array",

src/builtins/base.tq

@@ -443,6 +443,8 @@ const REFLECT_APPLY_INDEX: constexpr NativeContextSlot
     generates 'Context::REFLECT_APPLY_INDEX';
 const REGEXP_LAST_MATCH_INFO_INDEX: constexpr NativeContextSlot
     generates 'Context::REGEXP_LAST_MATCH_INFO_INDEX';
+const INITIAL_STRING_ITERATOR_MAP_INDEX: constexpr NativeContextSlot
+    generates 'Context::INITIAL_STRING_ITERATOR_MAP_INDEX';
 extern operator '[]' macro LoadContextElement(
     NativeContext, NativeContextSlot): Object;
 extern operator '[]=' macro StoreContextElement(
@@ -2181,6 +2183,10 @@ macro GetProxyRevocableResultMap(implicit context: Context)(): Map {
   return UnsafeCast<Map>(
       LoadNativeContext(context)[PROXY_REVOCABLE_RESULT_MAP_INDEX]);
 }
+macro GetInitialStringIteratorMap(implicit context: Context)(): Map {
+  return UnsafeCast<Map>(
+      LoadNativeContext(context)[INITIAL_STRING_ITERATOR_MAP_INDEX]);
+}
 macro GetReflectApply(implicit context: Context)(): Callable {
   return UnsafeCast<Callable>(LoadNativeContext(context)[REFLECT_APPLY_INDEX]);
 }

src/builtins/builtins-definitions.h

@@ -1002,8 +1002,6 @@ namespace internal {
   TFJ(StringPrototypeValueOf, 0, kReceiver)                                    \
   /* ES6 #sec-string.raw */                                                    \
   CPP(StringRaw)                                                               \
-  /* ES6 #sec-string.prototype-@@iterator */                                   \
-  TFJ(StringPrototypeIterator, 0, kReceiver)                                   \
                                                                                \
   /* StringIterator */                                                         \
   /* ES6 #sec-%stringiteratorprototype%.next */                                \

src/builtins/builtins-string-gen.cc

@@ -2223,30 +2223,6 @@ TF_BUILTIN(StringPrototypeValueOf, CodeStubAssembler) {
   Return(result);
 }
 
-TF_BUILTIN(StringPrototypeIterator, CodeStubAssembler) {
-  TNode<Context> context = CAST(Parameter(Descriptor::kContext));
-  TNode<Object> receiver = CAST(Parameter(Descriptor::kReceiver));
-
-  Node* string =
-      ToThisString(context, receiver, "String.prototype[Symbol.iterator]");
-
-  Node* native_context = LoadNativeContext(context);
-  Node* map = LoadContextElement(native_context,
-                                 Context::INITIAL_STRING_ITERATOR_MAP_INDEX);
-  Node* iterator = Allocate(JSStringIterator::kSize);
-  StoreMapNoWriteBarrier(iterator, map);
-  StoreObjectFieldRoot(iterator, JSValue::kPropertiesOrHashOffset,
-                       RootIndex::kEmptyFixedArray);
-  StoreObjectFieldRoot(iterator, JSObject::kElementsOffset,
-                       RootIndex::kEmptyFixedArray);
-  StoreObjectFieldNoWriteBarrier(iterator, JSStringIterator::kStringOffset,
-                                 string);
-  Node* index = SmiConstant(0);
-  StoreObjectFieldNoWriteBarrier(iterator, JSStringIterator::kNextIndexOffset,
-                                 index);
-  Return(iterator);
-}
-
 // Return the |word32| codepoint at {index}. Supports SeqStrings and
 // ExternalStrings.
 TNode<Int32T> StringBuiltinsAssembler::LoadSurrogatePairAt(

src/builtins/string-iterator.tq

+// Copyright 2019 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.
+
+namespace string_iterator {
+
+  macro NewJSStringIterator(implicit context: Context)(
+      string: String, nextIndex: Smi): JSStringIterator {
+    return new JSStringIterator{
+      map: GetInitialStringIteratorMap(),
+      properties_or_hash: kEmptyFixedArray,
+      elements: kEmptyFixedArray,
+      string: string,
+      next_index: nextIndex
+    };
+  }
+
+  // ES6 #sec-string.prototype-@@iterator
+  transitioning javascript builtin StringPrototypeIterator(
+      implicit context: Context)(receiver: Object): JSStringIterator {
+    const name: String =
+        ToThisString(receiver, 'String.prototype[Symbol.iterator]');
+    const index: Smi = 0;
+    return NewJSStringIterator(name, index);
+  }
+}