[turbofan] Implement JSBuiltinReducer for String.prototype[Symbol.iterator].

src/compiler/js-builtin-reducer.cc

 // 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.
 
 #include "src/compiler/js-builtin-reducer.h"
 
 #include "src/compilation-dependencies.h"
 #include "src/compiler/access-builder.h"
 #include "src/compiler/js-graph.h"
 #include "src/compiler/node-matchers.h"
@@ skipping 1008 matching lines @@
 
         ReplaceWithValue(node, value, effect, control);
         return Replace(value);
       }
     }
   }
 
   return NoChange();
 }
 
+Reduction JSBuiltinReducer::ReduceStringIterator(Node* node) {
+  if (Node* receiver = GetStringWitness(node)) {
+    Node* effect = NodeProperties::GetEffectInput(node);
+    Node* control = NodeProperties::GetControlInput(node);
+    Node* context = NodeProperties::GetContextInput(node);
+
+    Node* native_context = effect = graph()->NewNode(
+        javascript()->LoadContext(0, Context::NATIVE_CONTEXT_INDEX, true),
+        context, context, effect);
+    Node* map = effect = graph()->NewNode(
+        javascript()->LoadContext(0, Context::STRING_ITERATOR_MAP_INDEX, true),
+        native_context, native_context, effect);
+
+    // allocate new iterator
+    effect = graph()->NewNode(
+        common()->BeginRegion(RegionObservability::kNotObservable), effect);
+    Node* value = effect = graph()->NewNode(
+        simplified()->Allocate(NOT_TENURED),
+        jsgraph()->Int32Constant(JSStringIterator::kSize), effect, control);
+    effect = graph()->NewNode(simplified()->StoreField(AccessBuilder::ForMap()),
+                              value, map, effect, control);
+    effect = graph()->NewNode(
+        simplified()->StoreField(AccessBuilder::ForJSObjectProperties()), value,
+        jsgraph()->EmptyFixedArrayConstant(), effect, control);
+    effect = graph()->NewNode(
+        simplified()->StoreField(AccessBuilder::ForJSObjectElements()), value,
+        jsgraph()->EmptyFixedArrayConstant(), effect, control);
+
+    // attach the iterator to this string
+    effect = graph()->NewNode(
+        simplified()->StoreField(AccessBuilder::ForJSStringIteratorString()),
+        value, receiver, effect, control);
+    effect = graph()->NewNode(
+        simplified()->StoreField(AccessBuilder::ForJSStringIteratorIndex()),
+        value, jsgraph()->SmiConstant(0), effect, control);
+
+    value = effect = graph()->NewNode(common()->FinishRegion(), value, effect);
+
+    // replace it
+    ReplaceWithValue(node, value, effect, control);
+    return Replace(value);
+  }
+  return NoChange();
+}
+
 Reduction JSBuiltinReducer::ReduceStringIteratorNext(Node* node) {
   Node* receiver = NodeProperties::GetValueInput(node, 1);
   Node* effect = NodeProperties::GetEffectInput(node);
   Node* control = NodeProperties::GetControlInput(node);
   Node* context = NodeProperties::GetContextInput(node);
   if (HasInstanceTypeWitness(receiver, effect, JS_STRING_ITERATOR_TYPE)) {
     Node* string = effect = graph()->NewNode(
         simplified()->LoadField(AccessBuilder::ForJSStringIteratorString()),
         receiver, effect, control);
     Node* index = effect = graph()->NewNode(
@@ skipping 282 matching lines @@
     case kNumberParseInt:
       reduction = ReduceNumberParseInt(node);
       break;
     case kStringFromCharCode:
       reduction = ReduceStringFromCharCode(node);
       break;
     case kStringCharAt:
       return ReduceStringCharAt(node);
     case kStringCharCodeAt:
       return ReduceStringCharCodeAt(node);
+    case kStringIterator:
+      return ReduceStringIterator(node);
     case kStringIteratorNext:
       return ReduceStringIteratorNext(node);
     case kDataViewByteLength:
       return ReduceArrayBufferViewAccessor(
           node, JS_DATA_VIEW_TYPE,
           AccessBuilder::ForJSArrayBufferViewByteLength());
     case kDataViewByteOffset:
       return ReduceArrayBufferViewAccessor(
           node, JS_DATA_VIEW_TYPE,
           AccessBuilder::ForJSArrayBufferViewByteOffset());
@@ skipping 48 matching lines @@
   return jsgraph()->simplified();
 }
 
 JSOperatorBuilder* JSBuiltinReducer::javascript() const {
   return jsgraph()->javascript();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8