Revert "[esnext] load `iterator.next` only once at beginning of iteration"

This reverts commit bf4cc9ee.

Reason for revert: Breaks windows with msvc and linux with gcc
https://build.chromium.org/p/client.v8/builders/V8%20Win64%20-%20msvc/builds/841
https://build.chromium.org/p/client.v8/builders/V8%20Linux%20gcc%204.8/builds/17265

Original change's description:
> [esnext] load `iterator.next` only once at beginning of iteration
> 
> https://github.com/tc39/ecma262/pull/988 gained concensus during the
> september 2017 TC39 meetings. This moves the load of the "next" method
> to the very beginning of the iteration protocol, rather than during
> each iteration step.
> 
> This impacts:
> 
> - yield*
> - for-of loops
> - spread arguments
> - array spreads
> 
> In the v8 implementation, this also affects async iteration versions of
> these things (the sole exception being the Async-From-Sync iterator,
> which requires a few more changes to work with this, likely done in a
> followup patch).
> 
> This change introduces a new AST node, ResolvedProperty, which can be used
> as a callee by Call nodes to produce the same bytecode as Property calls,
> without observably re-loading the property. This is used in several
> AST-desugarings involving the iteration protocol.
> 
> BUG=v8:6861, v8:5699
> R=​rmcilroy@chromium.org, neis@chromium.org, adamk@chromium.org
> 
> Cq-Include-Trybots: luci.v8.try:v8_linux_noi18n_rel_ng
> Change-Id: Ib81106a0182687fc5efea0bc32302ad06376773b
> Reviewed-on: https://chromium-review.googlesource.com/687997
> Commit-Queue: Caitlin Potter <caitp@igalia.com>
> Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
> Reviewed-by: Adam Klein <adamk@chromium.org>
> Reviewed-by: Georg Neis <neis@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#50452}

TBR=rmcilroy@chromium.org,adamk@chromium.org,neis@chromium.org,caitp@igalia.com,caitp@chromium.org

Change-Id: I1797c0d596dfd6850d6f0f505f591a7a990dd1f1
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:6861, v8:5699
Cq-Include-Trybots: luci.v8.try:v8_linux_noi18n_rel_ng
Reviewed-on: https://chromium-review.googlesource.com/857616Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50454}

src/ast/ast-numbering.cc

@@ -195,11 +195,6 @@ void AstNumberingVisitor::VisitProperty(Property* node) {
   Visit(node->obj());
 }
 
-void AstNumberingVisitor::VisitResolvedProperty(ResolvedProperty* node) {
-  Visit(node->object());
-  Visit(node->property());
-}
-
 void AstNumberingVisitor::VisitAssignment(Assignment* node) {
   Visit(node->target());
   Visit(node->value());
@@ -256,7 +251,6 @@ void AstNumberingVisitor::VisitForInStatement(ForInStatement* node) {
 
 void AstNumberingVisitor::VisitForOfStatement(ForOfStatement* node) {
   Visit(node->assign_iterator());  // Not part of loop.
-  Visit(node->assign_next());
   node->set_first_suspend_id(suspend_count_);
   Visit(node->next_result());
   Visit(node->result_done());

src/ast/ast-traversal-visitor.h

@@ -392,14 +392,6 @@ void AstTraversalVisitor<Subclass>::VisitProperty(Property* expr) {
   RECURSE_EXPRESSION(Visit(expr->key()));
 }
 
-template <class Subclass>
-void AstTraversalVisitor<Subclass>::VisitResolvedProperty(
-    ResolvedProperty* expr) {
-  PROCESS_EXPRESSION(expr);
-  RECURSE_EXPRESSION(VisitVariableProxy(expr->object()));
-  RECURSE_EXPRESSION(VisitVariableProxy(expr->property()));
-}
-
 template <class Subclass>
 void AstTraversalVisitor<Subclass>::VisitCall(Call* expr) {
   PROCESS_EXPRESSION(expr);

src/ast/ast.cc

@@ -805,10 +805,6 @@ Call::CallType Call::GetCallType() const {
     }
   }
 
-  if (expression()->IsResolvedProperty()) {
-    return RESOLVED_PROPERTY_CALL;
-  }
-
   return OTHER_CALL;
 }
 

src/ast/ast.h

@@ -94,7 +94,6 @@ namespace internal {
   V(Literal)                    \
   V(NativeFunctionLiteral)      \
   V(Property)                   \
-  V(ResolvedProperty)           \
   V(RewritableExpression)       \
   V(Spread)                     \
   V(SuperCallReference)         \
@@ -591,13 +590,11 @@ class ForInStatement final : public ForEachStatement {
 class ForOfStatement final : public ForEachStatement {
  public:
   void Initialize(Statement* body, Variable* iterator,
-                  Expression* assign_iterator, Expression* assign_next,
-                  Expression* next_result, Expression* result_done,
-                  Expression* assign_each) {
+                  Expression* assign_iterator, Expression* next_result,
+                  Expression* result_done, Expression* assign_each) {
     ForEachStatement::Initialize(body);
     iterator_ = iterator;
     assign_iterator_ = assign_iterator;
-    assign_next_ = assign_next;
     next_result_ = next_result;
     result_done_ = result_done;
     assign_each_ = assign_each;
@@ -612,9 +609,6 @@ class ForOfStatement final : public ForEachStatement {
     return assign_iterator_;
   }
 
-  // iteratorRecord.next = iterator.next
-  Expression* assign_next() const { return assign_next_; }
-
   // result = iterator.next()  // with type check
   Expression* next_result() const {
     return next_result_;
@@ -630,12 +624,6 @@ class ForOfStatement final : public ForEachStatement {
     return assign_each_;
   }
 
-  void set_assign_iterator(Expression* e) { assign_iterator_ = e; }
-  void set_assign_next(Expression* e) { assign_next_ = e; }
-  void set_next_result(Expression* e) { next_result_ = e; }
-  void set_result_done(Expression* e) { result_done_ = e; }
-  void set_assign_each(Expression* e) { assign_each_ = e; }
-
  private:
   friend class AstNodeFactory;
 
@@ -649,7 +637,6 @@ class ForOfStatement final : public ForEachStatement {
 
   Variable* iterator_;
   Expression* assign_iterator_;
-  Expression* assign_next_;
   Expression* next_result_;
   Expression* result_done_;
   Expression* assign_each_;
@@ -1620,25 +1607,6 @@ class Property final : public Expression {
   Expression* key_;
 };
 
-// ResolvedProperty pairs a receiver field with a value field. It allows Call
-// to support arbitrary receivers while still taking advantage of TypeFeedback.
-class ResolvedProperty final : public Expression {
- public:
-  VariableProxy* object() const { return object_; }
-  VariableProxy* property() const { return property_; }
-
-  void set_object(VariableProxy* e) { object_ = e; }
-  void set_property(VariableProxy* e) { property_ = e; }
-
- private:
-  friend class AstNodeFactory;
-
-  ResolvedProperty(VariableProxy* obj, VariableProxy* property, int pos)
-      : Expression(pos, kResolvedProperty), object_(obj), property_(property) {}
-
-  VariableProxy* object_;
-  VariableProxy* property_;
-};
 
 class Call final : public Expression {
  public:
@@ -1665,7 +1633,6 @@ class Call final : public Expression {
     NAMED_SUPER_PROPERTY_CALL,
     KEYED_SUPER_PROPERTY_CALL,
     SUPER_CALL,
-    RESOLVED_PROPERTY_CALL,
     OTHER_CALL
   };
 
@@ -2137,6 +2104,7 @@ class YieldStar final : public Suspend {
   //   - One for awaiting the iterator result yielded by the delegated iterator
   //     (await_delegated_iterator_output_suspend_id)
   int await_iterator_close_suspend_id() const {
+    DCHECK_NE(-1, await_iterator_close_suspend_id_);
     return await_iterator_close_suspend_id_;
   }
   void set_await_iterator_close_suspend_id(int id) {
@@ -2144,6 +2112,7 @@ class YieldStar final : public Suspend {
   }
 
   int await_delegated_iterator_output_suspend_id() const {
+    DCHECK_NE(-1, await_delegated_iterator_output_suspend_id_);
     return await_delegated_iterator_output_suspend_id_;
   }
   void set_await_delegated_iterator_output_suspend_id(int id) {
@@ -3028,12 +2997,6 @@ class AstNodeFactory final BASE_EMBEDDED {
     return new (zone_) Property(obj, key, pos);
   }
 
-  ResolvedProperty* NewResolvedProperty(VariableProxy* obj,
-                                        VariableProxy* property,
-                                        int pos = kNoSourcePosition) {
-    return new (zone_) ResolvedProperty(obj, property, pos);
-  }
-
   Call* NewCall(Expression* expression, ZoneList<Expression*>* arguments,
                 int pos, Call::PossiblyEval possibly_eval = Call::NOT_EVAL) {
     return new (zone_) Call(expression, arguments, pos, possibly_eval);

src/ast/prettyprinter.cc

@@ -326,7 +326,6 @@ void CallPrinter::VisitProperty(Property* node) {
   }
 }
 
-void CallPrinter::VisitResolvedProperty(ResolvedProperty* node) {}
 
 void CallPrinter::VisitCall(Call* node) {
   bool was_found = false;
@@ -1250,14 +1249,6 @@ void AstPrinter::VisitProperty(Property* node) {
   }
 }
 
-void AstPrinter::VisitResolvedProperty(ResolvedProperty* node) {
-  EmbeddedVector<char, 128> buf;
-  SNPrintF(buf, "RESOLVED-PROPERTY");
-  IndentedScope indent(this, buf.start(), node->position());
-
-  PrintIndentedVisit("RECEIVER", node->object());
-  PrintIndentedVisit("PROPERTY", node->property());
-}
 
 void AstPrinter::VisitCall(Call* node) {
   EmbeddedVector<char, 128> buf;

src/builtins/builtins-collections-gen.cc

@@ -232,9 +232,10 @@ void BaseCollectionsAssembler::AddConstructorEntriesFromIterable(
 
   TNode<Object> add_func = GetAddFunction(variant, context, collection);
   IteratorBuiltinsAssembler iterator_assembler(this->state());
-  IteratorRecord iterator = iterator_assembler.GetIterator(context, iterable);
+  TNode<Object> iterator =
+      CAST(iterator_assembler.GetIterator(context, iterable));
 
-  CSA_ASSERT(this, Word32BinaryNot(IsUndefined(iterator.object)));
+  CSA_ASSERT(this, Word32BinaryNot(IsUndefined(iterator)));
 
   TNode<Object> fast_iterator_result_map =
       LoadContextElement(native_context, Context::ITERATOR_RESULT_MAP_INDEX);

src/builtins/builtins-iterator-gen.cc

@@ -11,10 +11,9 @@ namespace internal {
 
 using compiler::Node;
 
-IteratorRecord IteratorBuiltinsAssembler::GetIterator(Node* context,
-                                                      Node* object,
-                                                      Label* if_exception,
-                                                      Variable* exception) {
+Node* IteratorBuiltinsAssembler::GetIterator(Node* context, Node* object,
+                                             Label* if_exception,
+                                             Variable* exception) {
   Node* method = GetProperty(context, object, factory()->iterator_symbol());
   GotoIfException(method, if_exception, exception);
 
@@ -22,9 +21,9 @@ IteratorRecord IteratorBuiltinsAssembler::GetIterator(Node* context,
   Node* iterator = CallJS(callable, context, method, object);
   GotoIfException(iterator, if_exception, exception);
 
-  Label get_next(this), if_notobject(this, Label::kDeferred);
+  Label done(this), if_notobject(this, Label::kDeferred);
   GotoIf(TaggedIsSmi(iterator), &if_notobject);
-  Branch(IsJSReceiver(iterator), &get_next, &if_notobject);
+  Branch(IsJSReceiver(iterator), &done, &if_notobject);
 
   BIND(&if_notobject);
   {
@@ -35,21 +34,24 @@ IteratorRecord IteratorBuiltinsAssembler::GetIterator(Node* context,
     Unreachable();
   }
 
-  BIND(&get_next);
-  Node* const next = GetProperty(context, iterator, factory()->next_string());
-  GotoIfException(next, if_exception, exception);
-
-  return IteratorRecord{TNode<JSReceiver>::UncheckedCast(iterator),
-                        TNode<Object>::UncheckedCast(next)};
+  BIND(&done);
+  return iterator;
 }
 
-Node* IteratorBuiltinsAssembler::IteratorStep(
-    Node* context, const IteratorRecord& iterator, Label* if_done,
-    Node* fast_iterator_result_map, Label* if_exception, Variable* exception) {
+Node* IteratorBuiltinsAssembler::IteratorStep(Node* context, Node* iterator,
+                                              Label* if_done,
+                                              Node* fast_iterator_result_map,
+                                              Label* if_exception,
+                                              Variable* exception) {
   DCHECK_NOT_NULL(if_done);
+
+  // IteratorNext
+  Node* next_method = GetProperty(context, iterator, factory()->next_string());
+  GotoIfException(next_method, if_exception, exception);
+
   // 1. a. Let result be ? Invoke(iterator, "next", « »).
   Callable callable = CodeFactory::Call(isolate());
-  Node* result = CallJS(callable, context, iterator.next, iterator.object);
+  Node* result = CallJS(callable, context, next_method, iterator);
   GotoIfException(result, if_exception, exception);
 
   // 3. If Type(result) is not Object, throw a TypeError exception.
@@ -127,20 +129,20 @@ Node* IteratorBuiltinsAssembler::IteratorValue(Node* context, Node* result,
   return var_value.value();
 }
 
-void IteratorBuiltinsAssembler::IteratorCloseOnException(
-    Node* context, const IteratorRecord& iterator, Label* if_exception,
-    Variable* exception) {
+void IteratorBuiltinsAssembler::IteratorCloseOnException(Node* context,
+                                                         Node* iterator,
+                                                         Label* if_exception,
+                                                         Variable* exception) {
   // Perform ES #sec-iteratorclose when an exception occurs. This simpler
   // algorithm does not include redundant steps which are never reachable from
   // the spec IteratorClose algorithm.
   DCHECK_NOT_NULL(if_exception);
   DCHECK_NOT_NULL(exception);
   CSA_ASSERT(this, IsNotTheHole(exception->value()));
-  CSA_ASSERT(this, IsJSReceiver(iterator.object));
+  CSA_ASSERT(this, IsJSReceiver(iterator));
 
   // Let return be ? GetMethod(iterator, "return").
-  Node* method =
-      GetProperty(context, iterator.object, factory()->return_string());
+  Node* method = GetProperty(context, iterator, factory()->return_string());
   GotoIfException(method, if_exception, exception);
 
   // If return is undefined, return Completion(completion).
@@ -150,7 +152,7 @@ void IteratorBuiltinsAssembler::IteratorCloseOnException(
     // Let innerResult be Call(return, iterator, « »).
     // If an exception occurs, the original exception remains bound
     Node* inner_result =
-        CallJS(CodeFactory::Call(isolate()), context, method, iterator.object);
+        CallJS(CodeFactory::Call(isolate()), context, method, iterator);
     GotoIfException(inner_result, if_exception, nullptr);
 
     // (If completion.[[Type]] is throw) return Completion(completion).
@@ -158,8 +160,9 @@ void IteratorBuiltinsAssembler::IteratorCloseOnException(
   }
 }
 
-void IteratorBuiltinsAssembler::IteratorCloseOnException(
-    Node* context, const IteratorRecord& iterator, Variable* exception) {
+void IteratorBuiltinsAssembler::IteratorCloseOnException(Node* context,
+                                                         Node* iterator,
+                                                         Variable* exception) {
   Label rethrow(this, Label::kDeferred);
   IteratorCloseOnException(context, iterator, &rethrow, exception);
 

src/builtins/builtins-iterator-gen.h

@@ -19,17 +19,16 @@ class IteratorBuiltinsAssembler : public CodeStubAssembler {
 
   // https://tc39.github.io/ecma262/#sec-getiterator --- never used for
   // @@asyncIterator.
-  IteratorRecord GetIterator(Node* context, Node* object,
-                             Label* if_exception = nullptr,
-                             Variable* exception = nullptr);
+  Node* GetIterator(Node* context, Node* object, Label* if_exception = nullptr,
+                    Variable* exception = nullptr);
 
   // https://tc39.github.io/ecma262/#sec-iteratorstep
   // Returns `false` if the iterator is done, otherwise returns an
   // iterator result.
   // `fast_iterator_result_map` refers to the map for the JSIteratorResult
   // object, loaded from the native context.
-  Node* IteratorStep(Node* context, const IteratorRecord& iterator,
-                     Label* if_done, Node* fast_iterator_result_map = nullptr,
+  Node* IteratorStep(Node* context, Node* iterator, Label* if_done,
+                     Node* fast_iterator_result_map = nullptr,
                      Label* if_exception = nullptr,
                      Variable* exception = nullptr);
 
@@ -43,9 +42,9 @@ class IteratorBuiltinsAssembler : public CodeStubAssembler {
                       Variable* exception = nullptr);
 
   // https://tc39.github.io/ecma262/#sec-iteratorclose
-  void IteratorCloseOnException(Node* context, const IteratorRecord& iterator,
+  void IteratorCloseOnException(Node* context, Node* iterator,
                                 Label* if_exception, Variable* exception);
-  void IteratorCloseOnException(Node* context, const IteratorRecord& iterator,
+  void IteratorCloseOnException(Node* context, Node* iterator,
                                 Variable* exception);
 };
 

src/builtins/builtins-promise-gen.cc

@@ -1807,9 +1807,8 @@ TF_BUILTIN(PerformNativePromiseThen, PromiseBuiltinsAssembler) {
 }
 
 Node* PromiseBuiltinsAssembler::PerformPromiseAll(
-    Node* context, Node* constructor, Node* capability,
-    const IteratorRecord& iterator, Label* if_exception,
-    Variable* var_exception) {
+    Node* context, Node* constructor, Node* capability, Node* iterator,
+    Label* if_exception, Variable* var_exception) {
   IteratorBuiltinsAssembler iter_assembler(state());
   Label close_iterator(this);
 
@@ -2015,7 +2014,7 @@ TF_BUILTIN(PromiseAll, PromiseBuiltinsAssembler) {
   // Let iterator be GetIterator(iterable).
   // IfAbruptRejectPromise(iterator, promiseCapability).
   Node* const iterable = Parameter(Descriptor::kIterable);
-  IteratorRecord iterator = iter_assembler.GetIterator(
+  Node* const iterator = iter_assembler.GetIterator(
       context, iterable, &reject_promise, &var_exception);
 
   // Let result be PerformPromiseAll(iteratorRecord, C, promiseCapability).
@@ -2152,7 +2151,7 @@ TF_BUILTIN(PromiseRace, PromiseBuiltinsAssembler) {
   // Let iterator be GetIterator(iterable).
   // IfAbruptRejectPromise(iterator, promiseCapability).
   Node* const iterable = Parameter(Descriptor::kIterable);
-  IteratorRecord iterator = iter_assembler.GetIterator(
+  Node* const iterator = iter_assembler.GetIterator(
       context, iterable, &reject_promise, &var_exception);
 
   // Let result be PerformPromiseRace(iteratorRecord, C, promiseCapability).

src/builtins/builtins-promise-gen.h

@@ -157,7 +157,7 @@ class PromiseBuiltinsAssembler : public CodeStubAssembler {
   Node* CreateThrowerFunction(Node* reason, Node* native_context);
 
   Node* PerformPromiseAll(Node* context, Node* constructor, Node* capability,
-                          const IteratorRecord& record, Label* if_exception,
+                          Node* iterator, Label* if_exception,
                           Variable* var_exception);
 
   Node* IncrementSmiCell(Node* cell, Label* if_overflow = nullptr);

src/code-stub-assembler.h

@@ -71,17 +71,6 @@ enum class PrimitiveType { kBoolean, kNumber, kString, kSymbol };
     promise_default_resolve_handler_symbol,                                   \
     PromiseDefaultResolveHandlerSymbol)
 
-// Returned from IteratorBuiltinsAssembler::GetIterator(). Struct is declared
-// here to simplify use in other generated builtins.
-struct IteratorRecord {
- public:
-  // iteratorRecord.[[Iterator]]
-  compiler::TNode<JSReceiver> object;
-
-  // iteratorRecord.[[NextMethod]]
-  compiler::TNode<Object> next;
-};
-
 // Provides JavaScript-specific "macro-assembler" functionality on top of the
 // CodeAssembler. By factoring the JavaScript-isms out of the CodeAssembler,
 // it's possible to add JavaScript-specific useful CodeAssembler "macros"

src/interpreter/bytecode-generator.h

@@ -151,24 +151,9 @@ class BytecodeGenerator final : public AstVisitor<BytecodeGenerator> {
   void BuildAwait(int suspend_id);
 
   void BuildGetIterator(Expression* iterable, IteratorType hint);
-
-  // Create an IteratorRecord with pre-allocated registers holding the next
-  // method and iterator object.
-  IteratorRecord BuildGetIteratorRecord(Expression* iterable,
-                                        Register iterator_next,
-                                        Register iterator_object,
-                                        IteratorType hint);
-
-  // Create an IteratorRecord allocating new registers to hold the next method
-  // and iterator object.
   IteratorRecord BuildGetIteratorRecord(Expression* iterable,
                                         IteratorType hint);
   void BuildIteratorNext(const IteratorRecord& iterator, Register next_result);
-  void BuildIteratorClose(const IteratorRecord& iterator, int suspend_id = -1);
-  void BuildCallIteratorMethod(Register iterator, const AstRawString* method,
-                               RegisterList receiver_and_args,
-                               BytecodeLabel* if_called,
-                               BytecodeLabels* if_notcalled);
 
   void BuildArrayLiteralSpread(Spread* spread, Register array);
 

src/parsing/parser.cc

@@ -1889,11 +1889,13 @@ void Parser::DeclareFunctionNameVar(const AstRawString* function_name,
 //     !%_IsJSReceiver(result = Await(iterator.next())) &&
 //         %ThrowIteratorResultNotAnObject(result)
 // [endif]
-Expression* Parser::BuildIteratorNextResult(VariableProxy* iterator,
-                                            VariableProxy* next,
+Expression* Parser::BuildIteratorNextResult(Expression* iterator,
                                             Variable* result, IteratorType type,
                                             int pos) {
-  Expression* next_property = factory()->NewResolvedProperty(iterator, next);
+  Expression* next_literal = factory()->NewStringLiteral(
+      ast_value_factory()->next_string(), kNoSourcePosition);
+  Expression* next_property =
+      factory()->NewProperty(iterator, next_literal, kNoSourcePosition);
   ZoneList<Expression*>* next_arguments =
       new (zone()) ZoneList<Expression*>(0, zone());
   Expression* next_call =
@@ -2096,7 +2098,6 @@ Statement* Parser::InitializeForOfStatement(
   auto avfactory = ast_value_factory();
 
   Variable* iterator = NewTemporary(avfactory->dot_iterator_string());
-  Variable* next = NewTemporary(avfactory->empty_string());
   Variable* result = NewTemporary(avfactory->dot_result_string());
   Variable* completion = NewTemporary(avfactory->empty_string());
 
@@ -2109,17 +2110,6 @@ Statement* Parser::InitializeForOfStatement(
         iterable->position());
   }
 
-  Expression* assign_next;
-  {
-    assign_next = factory()->NewAssignment(
-        Token::ASSIGN, factory()->NewVariableProxy(next),
-        factory()->NewProperty(factory()->NewVariableProxy(iterator),
-                               factory()->NewStringLiteral(
-                                   avfactory->next_string(), kNoSourcePosition),
-                               kNoSourcePosition),
-        kNoSourcePosition);
-  }
-
   // [if (IteratorType == kNormal)]
   //     !%_IsJSReceiver(result = iterator.next()) &&
   //         %ThrowIteratorResultNotAnObject(result)
@@ -2129,10 +2119,9 @@ Statement* Parser::InitializeForOfStatement(
   // [endif]
   Expression* next_result;
   {
-    VariableProxy* iterator_proxy = factory()->NewVariableProxy(iterator);
-    VariableProxy* next_proxy = factory()->NewVariableProxy(next);
-    next_result = BuildIteratorNextResult(iterator_proxy, next_proxy, result,
-                                          type, next_result_pos);
+    Expression* iterator_proxy = factory()->NewVariableProxy(iterator);
+    next_result =
+        BuildIteratorNextResult(iterator_proxy, result, type, next_result_pos);
   }
 
   // result.done
@@ -2202,8 +2191,8 @@ Statement* Parser::InitializeForOfStatement(
     body = block;
   }
 
-  for_of->Initialize(body, iterator, assign_iterator, assign_next, next_result,
-                     result_done, assign_each);
+  for_of->Initialize(body, iterator, assign_iterator, next_result, result_done,
+                     assign_each);
   return finalize ? FinalizeForOfStatement(for_of, completion, type, nopos)
                   : for_of;
 }

src/parsing/parser.h

@@ -402,14 +402,13 @@ class V8_EXPORT_PRIVATE Parser : public NON_EXPORTED_BASE(ParserBase<Parser>) {
   Expression* RewriteDestructuringAssignment(Assignment* assignment);
 
   // [if (IteratorType == kAsync)]
-  //     !%_IsJSReceiver(result = Await(next.[[Call]](iterator, « »)) &&
+  //     !%_IsJSReceiver(result = Await(iterator.next()) &&
   //         %ThrowIteratorResultNotAnObject(result)
   // [else]
-  //     !%_IsJSReceiver(result = next.[[Call]](iterator, « »)) &&
+  //     !%_IsJSReceiver(result = iterator.next()) &&
   //         %ThrowIteratorResultNotAnObject(result)
   // [endif]
-  Expression* BuildIteratorNextResult(VariableProxy* iterator,
-                                      VariableProxy* next, Variable* result,
+  Expression* BuildIteratorNextResult(Expression* iterator, Variable* result,
                                       IteratorType type, int pos);
 
   // Initialize the components of a for-in / for-of statement.

src/parsing/pattern-rewriter.cc

@@ -445,11 +445,6 @@ void PatternRewriter::VisitArrayLiteral(ArrayLiteral* node,
   auto iterator = CreateTempVar(factory()->NewGetIterator(
       factory()->NewVariableProxy(temp), current_value_, IteratorType::kNormal,
       current_value_->position()));
-  auto next = CreateTempVar(factory()->NewProperty(
-      factory()->NewVariableProxy(iterator),
-      factory()->NewStringLiteral(ast_value_factory()->next_string(),
-                                  kNoSourcePosition),
-      kNoSourcePosition));
   auto done =
       CreateTempVar(factory()->NewBooleanLiteral(false, kNoSourcePosition));
   auto result = CreateTempVar();
@@ -530,8 +525,7 @@ void PatternRewriter::VisitArrayLiteral(ArrayLiteral* node,
       next_block->statements()->Add(
           factory()->NewExpressionStatement(
               parser_->BuildIteratorNextResult(
-                  factory()->NewVariableProxy(iterator),
-                  factory()->NewVariableProxy(next), result,
+                  factory()->NewVariableProxy(iterator), result,
                   IteratorType::kNormal, kNoSourcePosition),
               kNoSourcePosition),
           zone());
@@ -605,7 +599,6 @@ void PatternRewriter::VisitArrayLiteral(ArrayLiteral* node,
     // result = IteratorNext(iterator);
     Statement* get_next = factory()->NewExpressionStatement(
         parser_->BuildIteratorNextResult(factory()->NewVariableProxy(iterator),
-                                         factory()->NewVariableProxy(next),
                                          result, IteratorType::kNormal, nopos),
         nopos);
 
@@ -763,7 +756,6 @@ NOT_A_PATTERN(ImportCallExpression)
 NOT_A_PATTERN(Literal)
 NOT_A_PATTERN(NativeFunctionLiteral)
 NOT_A_PATTERN(RegExpLiteral)
-NOT_A_PATTERN(ResolvedProperty)
 NOT_A_PATTERN(ReturnStatement)
 NOT_A_PATTERN(SloppyBlockFunctionStatement)
 NOT_A_PATTERN(Spread)

test/inspector/debugger/for-of-loops-expected.txt

@@ -9,10 +9,10 @@ function testFunction() {
   var arr = |_|[1];
   var all = |_|[];
   for (var |_|k in |_|arr) { all.|C|push(k); }
-  for (var |C|k of |_|arr) { all.|C|push(k); }
+  for (var |_|k of |_|arr) { all.|C|push(k); }
   for (var |_|k in |_|obj) { all.|C|push(k); }
   for (let |_|k in |_|arr) { all.|C|push(k); }
-  for (let |C|k of |_|arr) { all.|C|push(k); }
+  for (let |_|k of |_|arr) { all.|C|push(k); }
   for (let |_|k in |_|obj) { all.|C|push(k); }
 
   var iterable = |_|{
@@ -28,9 +28,9 @@ function testFunction() {
       };|R|
     }
   };
-  for (var |C|k of |_|iterable) { all.|C|push(k); }
+  for (var |_|k of |_|iterable) { all.|C|push(k); }
   |_|iterable.i = 0;
-  for (let |C|k of |_|iterable) { all.|C|push(k); }
+  for (let |_|k of |_|iterable) { all.|C|push(k); }
 |R|}
 
 (anonymous) (expr.js:0:0)

test/inspector/debugger/get-possible-breakpoints-master-expected.txt

@@ -95,10 +95,10 @@ function testForLoop() {
 |R|}
 
 function testForOfLoop() {
-  for (var |C|k of |_|[]) {}
-  for (var |C|k of |_|[1]) |_|k;
+  for (var |_|k of |_|[]) {}
+  for (var |_|k of |_|[1]) |_|k;
   var a = |_|[];
-  for (var |C|k of |_|a) {}
+  for (var |_|k of |_|a) {}
 |R|}
 
 function testForInLoop() {

test/mjsunit/es6/call-with-spread-modify-next.js

@@ -37,8 +37,6 @@
 
   var r2 = testMax(1, 2);
 
-  // .next() is only loaded once during the iteration prologue (see
-  // https://github.com/tc39/ecma262/pull/988/ and v8:6861)
-  assertEquals(1, called);
+  assertEquals(3, called);
   assertEquals(2, r2);
 })();

test/mjsunit/es6/iteration-semantics.js

@@ -220,11 +220,13 @@ assertThrows('fold(sum, 0, unreachable({}))', TypeError);
 assertThrows('fold(sum, 0, unreachable(false))', TypeError);
 assertThrows('fold(sum, 0, unreachable(37))', TypeError);
 
-// "next" is looked up only once during the iteration prologue (see
-// https://github.com/tc39/ecma262/pull/988)
-assertEquals(45, fold(sum, 0, remove_next_after(integers_until(10), 5)));
+// "next" is looked up each time.
+assertThrows('fold(sum, 0, remove_next_after(integers_until(10), 5))',
+             TypeError);
+// It is not called at any other time.
 assertEquals(45,
              fold(sum, 0, remove_next_after(integers_until(10), 10)));
+// It is not looked up too many times.
 assertEquals(45,
              fold(sum, 0, poison_next_after(integers_until(10), 10)));
 

test/mjsunit/es6/spread-call.js

@@ -376,11 +376,6 @@ testSpreadCallsStrict();
   a[3] = 4;
   var called = 0;
 
-  // .next method is only accessed during iteration prologue (see
-  // https://github.com/tc39/ecma262/pull/988)
-  let ArrayIteratorPrototype = Array.prototype[Symbol.iterator]().__proto__;
-  let ArrayIteratorPrototypeNextDescriptor =
-      Object.getOwnPropertyDescriptor(ArrayIteratorPrototype, 'next');
   Object.defineProperty(Array.prototype, 2, {
     get: function() {
       var ai = a[Symbol.iterator]();
@@ -389,8 +384,7 @@ testSpreadCallsStrict();
         get: function() {
           called++;
           return original_next;
-        },
-        configurable: true
+        }
       });
       return 3;
     },
@@ -398,10 +392,8 @@ testSpreadCallsStrict();
   });
 
   assertEquals(10, sum(...a));
-  assertEquals(0, called);
+  assertEquals(2, called);
 
-  Object.defineProperty(ArrayIteratorPrototype, 'next',
-                        ArrayIteratorPrototypeNextDescriptor);
   Object.defineProperty(Array.prototype, 2, {});
 })();
 
@@ -438,9 +430,9 @@ testSpreadCallsStrict();
 
   countArgs(...a);
 
-  // .next method is only accessed during iteration prologue (see
-  // https://github.com/tc39/ecma262/pull/988)
-  assertEquals(1, called);
+  // should be called 4 times; 3 for the values, 1 for the final
+  // {value: undefined, done: true} pair
+  assertEquals(4, called);
 })();
 
 (function testArrayIteratorPrototypeModified() {

test/mjsunit/es6/super-with-spread-modify-next.js

@@ -48,9 +48,7 @@
 
   var r2 = testArgumentsPoint(1, 2);
 
-  // .next() is only loaded once during the iteration prologue (see
-  // https://github.com/tc39/ecma262/pull/988/ and v8:6861)
-  assertEquals(1, called);
+  assertEquals(3, called);
   assertInstanceof(r2, ArgumentsPoint);
   assertInstanceof(r2, Point);
   assertEquals(r2.x, 1);

test/mjsunit/es6/typedarray.js

@@ -341,30 +341,16 @@ function TestTypedArray(constr, elementSize, typicalElement) {
 
   // Modified %ArrayIteratorPrototype%.next() method is honoured (v8:5699)
   const ArrayIteratorPrototype = Object.getPrototypeOf([][Symbol.iterator]());
-  const ArrayIteratorPrototypeNextDescriptor =
-      Object.getOwnPropertyDescriptor(ArrayIteratorPrototype, 'next');
   const ArrayIteratorPrototypeNext = ArrayIteratorPrototype.next;
   ArrayIteratorPrototype.next = function() {
     return { done: true };
   };
   genArr = new constr([1, 2, 3]);
   assertEquals(0, genArr.length);
-
   ArrayIteratorPrototype.next = ArrayIteratorPrototypeNext;
 
-  // Modified %ArrayIteratorPrototype%.next() is only loaded during the iterator
-  // prologue.
-  let nextMethod = ArrayIteratorPrototypeNext;
-  let getNextCount = 0;
-  Object.defineProperty(ArrayIteratorPrototype, 'next', {
-    get() {
-      getNextCount++;
-      return nextMethod;
-    },
-    set(v) { nextMethod = v; },
-    configurable: true
-  });
-
+  // Modified %ArrayIteratorPrototype%.next() during iteration is honoured as
+  // well.
   genArr = new constr(Object.defineProperty([1, , 3], 1, {
     get() {
       ArrayIteratorPrototype.next = function() {
@@ -373,13 +359,9 @@ function TestTypedArray(constr, elementSize, typicalElement) {
       return 2;
     }
   }));
-  Object.defineProperty(ArrayIteratorPrototype, 'next',
-                        ArrayIteratorPrototypeNextDescriptor);
-  assertEquals(1, getNextCount);
-  assertEquals(3, genArr.length);
+  assertEquals(2, genArr.length);
   assertEquals(1, genArr[0]);
   assertEquals(2, genArr[1]);
-  assertEquals(3, genArr[2]);
   ArrayIteratorPrototype.next = ArrayIteratorPrototypeNext;
 }
 

test/test262/test262.status

@@ -423,8 +423,19 @@
   'built-ins/Proxy/ownKeys/return-duplicate-symbol-entries-throws': [FAIL],
 
   # https://bugs.chromium.org/p/v8/issues/detail?id=6861
+  'language/statements/for-of/iterator-next-reference': [FAIL],
+  'language/expressions/async-generator/named-yield-star-async-next': [FAIL],
+  'language/expressions/async-generator/yield-star-async-next': [FAIL],
+  'language/expressions/class/async-gen-method-yield-star-async-next': [FAIL],
+  'language/expressions/class/async-gen-method-static-yield-star-async-next': [FAIL],
+  'language/expressions/object/method-definition/async-gen-yield-star-async-next': [FAIL],
+  'language/statements/async-generator/yield-star-async-next': [FAIL],
+  'language/statements/class/async-gen-method-yield-star-async-next': [FAIL],
+  'language/statements/class/async-gen-method-static-yield-star-async-next': [FAIL],
   'language/expressions/object/method-definition/async-gen-yield-star-sync-next': [FAIL],
   'language/expressions/class/async-gen-method-static-yield-star-sync-next': [FAIL],
+
+  # https://bugs.chromium.org/p/v8/issues/detail?id=6861
   'language/expressions/async-generator/yield-star-sync-next': [FAIL],
   'language/statements/class/async-gen-method-static-yield-star-sync-next': [FAIL],
   'language/expressions/async-generator/named-yield-star-sync-next': [FAIL],