LibJS: Make IteratorRecord inherit from Cell, not Object

This shaves its size down from 104 bytes to 48 bytes, cutting GC
pressure caused by this type in more than half.

Libraries/LibJS/Bytecode/Interpreter.cpp

@@ -1613,7 +1613,7 @@ inline ThrowCompletionOr<GC::Ref<Object>> super_call_with_argument_array(VM& vm,
 
 inline ThrowCompletionOr<GC::Ref<Array>> iterator_to_array(VM& vm, Value iterator)
 {
-    auto& iterator_record = as<IteratorRecord>(iterator.as_object());
+    auto& iterator_record = static_cast<IteratorRecord&>(iterator.as_cell());
 
     auto array = MUST(Array::create(*vm.current_realm(), 0));
     size_t index = 0;
@@ -1719,7 +1719,7 @@ inline ThrowCompletionOr<Value> delete_by_value_with_this(Bytecode::Interpreter&
 }
 
 // 14.7.5.9 EnumerateObjectProperties ( O ), https://tc39.es/ecma262/#sec-enumerate-object-properties
-inline ThrowCompletionOr<Object*> get_object_property_iterator(VM& vm, Value value)
+inline ThrowCompletionOr<Value> get_object_property_iterator(VM& vm, Value value)
 {
     // While the spec does provide an algorithm, it allows us to implement it ourselves so long as we meet the following invariants:
     //    1- Returned property keys do not include keys that are Symbols
@@ -1804,7 +1804,7 @@ inline ThrowCompletionOr<Object*> get_object_property_iterator(VM& vm, Value val
             }
         },
         1, vm.names.next);
-    return realm.create<IteratorRecord>(realm, object, callback, false).ptr();
+    return vm.heap().allocate<IteratorRecord>(object, callback, false);
 }
 
 ByteString Instruction::to_byte_string(Bytecode::Executable const& executable) const
@@ -2915,14 +2915,14 @@ ThrowCompletionOr<void> GetIterator::execute_impl(Bytecode::Interpreter& interpr
 
 ThrowCompletionOr<void> GetObjectFromIteratorRecord::execute_impl(Bytecode::Interpreter& interpreter) const
 {
-    auto& iterator_record = as<IteratorRecord>(interpreter.get(m_iterator_record).as_object());
+    auto& iterator_record = static_cast<IteratorRecord&>(interpreter.get(m_iterator_record).as_cell());
     interpreter.set(m_object, iterator_record.iterator);
     return {};
 }
 
 ThrowCompletionOr<void> GetNextMethodFromIteratorRecord::execute_impl(Bytecode::Interpreter& interpreter) const
 {
-    auto& iterator_record = as<IteratorRecord>(interpreter.get(m_iterator_record).as_object());
+    auto& iterator_record = static_cast<IteratorRecord&>(interpreter.get(m_iterator_record).as_cell());
     interpreter.set(m_next_method, iterator_record.next_method);
     return {};
 }
@@ -2938,14 +2938,15 @@ ThrowCompletionOr<void> GetMethod::execute_impl(Bytecode::Interpreter& interpret
 
 ThrowCompletionOr<void> GetObjectPropertyIterator::execute_impl(Bytecode::Interpreter& interpreter) const
 {
-    interpreter.set(dst(), TRY(get_object_property_iterator(interpreter.vm(), interpreter.get(object()))));
+    auto iterator_record = TRY(get_object_property_iterator(interpreter.vm(), interpreter.get(object())));
+    interpreter.set(dst(), iterator_record);
     return {};
 }
 
 ThrowCompletionOr<void> IteratorClose::execute_impl(Bytecode::Interpreter& interpreter) const
 {
     auto& vm = interpreter.vm();
-    auto& iterator = as<IteratorRecord>(interpreter.get(m_iterator_record).as_object());
+    auto& iterator = static_cast<IteratorRecord&>(interpreter.get(m_iterator_record).as_cell());
 
     // FIXME: Return the value of the resulting completion. (Note that m_completion_value can be empty!)
     TRY(iterator_close(vm, iterator, Completion { m_completion_type, m_completion_value }));
@@ -2955,7 +2956,7 @@ ThrowCompletionOr<void> IteratorClose::execute_impl(Bytecode::Interpreter& inter
 ThrowCompletionOr<void> AsyncIteratorClose::execute_impl(Bytecode::Interpreter& interpreter) const
 {
     auto& vm = interpreter.vm();
-    auto& iterator = as<IteratorRecord>(interpreter.get(m_iterator_record).as_object());
+    auto& iterator = static_cast<IteratorRecord&>(interpreter.get(m_iterator_record).as_cell());
 
     // FIXME: Return the value of the resulting completion. (Note that m_completion_value can be empty!)
     TRY(async_iterator_close(vm, iterator, Completion { m_completion_type, m_completion_value }));
@@ -2965,7 +2966,7 @@ ThrowCompletionOr<void> AsyncIteratorClose::execute_impl(Bytecode::Interpreter&
 ThrowCompletionOr<void> IteratorNext::execute_impl(Bytecode::Interpreter& interpreter) const
 {
     auto& vm = interpreter.vm();
-    auto& iterator_record = as<IteratorRecord>(interpreter.get(m_iterator_record).as_object());
+    auto& iterator_record = static_cast<IteratorRecord&>(interpreter.get(m_iterator_record).as_cell());
     interpreter.set(dst(), TRY(iterator_next(vm, iterator_record)));
     return {};
 }

Libraries/LibJS/Runtime/AsyncFromSyncIteratorPrototype.cpp

@@ -211,7 +211,7 @@ GC::Ref<IteratorRecord> create_async_from_sync_iterator(VM& vm, GC::Ref<Iterator
     auto next_method = MUST(async_iterator->get(vm.names.next));
 
     // 4. Let iteratorRecord be the Iterator Record { [[Iterator]]: asyncIterator, [[NextMethod]]: nextMethod, [[Done]]: false }.
-    auto iterator_record = realm.create<IteratorRecord>(realm, async_iterator, next_method, false);
+    auto iterator_record = vm.heap().allocate<IteratorRecord>(async_iterator, next_method, false);
 
     // 5. Return iteratorRecord.
     return iterator_record;

Libraries/LibJS/Runtime/Iterator.cpp

@@ -31,7 +31,7 @@ Iterator::Iterator(Object& prototype, GC::Ref<IteratorRecord> iterated)
 }
 
 Iterator::Iterator(Object& prototype)
-    : Iterator(prototype, prototype.shape().realm().create<IteratorRecord>(prototype.shape().realm(), nullptr, js_undefined(), false))
+    : Iterator(prototype, prototype.heap().allocate<IteratorRecord>(nullptr, js_undefined(), false))
 {
 }
 
@@ -43,8 +43,7 @@ ThrowCompletionOr<GC::Ref<IteratorRecord>> get_iterator_direct(VM& vm, Object& o
 
     // 2. Let iteratorRecord be Record { [[Iterator]]: obj, [[NextMethod]]: nextMethod, [[Done]]: false }.
     // 3. Return iteratorRecord.
-    auto& realm = *vm.current_realm();
-    return realm.create<IteratorRecord>(realm, object, next_method, false);
+    return vm.heap().allocate<IteratorRecord>(object, next_method, false);
 }
 
 // 7.4.3 GetIteratorFromMethod ( obj, method ), https://tc39.es/ecma262/#sec-getiteratorfrommethod
@@ -61,8 +60,7 @@ ThrowCompletionOr<GC::Ref<IteratorRecord>> get_iterator_from_method(VM& vm, Valu
     auto next_method = TRY(iterator.get(vm, vm.names.next));
 
     // 4. Let iteratorRecord be the Iterator Record { [[Iterator]]: iterator, [[NextMethod]]: nextMethod, [[Done]]: false }.
-    auto& realm = *vm.current_realm();
-    auto iterator_record = realm.create<IteratorRecord>(realm, iterator.as_object(), next_method, false);
+    auto iterator_record = vm.heap().allocate<IteratorRecord>(iterator.as_object(), next_method, false);
 
     // 5. Return iteratorRecord.
     return iterator_record;

Libraries/LibJS/Runtime/Iterator.h

@@ -17,14 +17,13 @@
 namespace JS {
 
 // 7.4.1 Iterator Records, https://tc39.es/ecma262/#sec-iterator-records
-class IteratorRecord final : public Object {
-    JS_OBJECT(IteratorRecord, Object);
+class IteratorRecord final : public Cell {
+    GC_CELL(IteratorRecord, Cell);
     GC_DECLARE_ALLOCATOR(IteratorRecord);
 
 public:
-    IteratorRecord(Realm& realm, GC::Ptr<Object> iterator, Value next_method, bool done)
-        : Object(ConstructWithoutPrototypeTag::Tag, realm)
-        , iterator(iterator)
+    IteratorRecord(GC::Ptr<Object> iterator, Value next_method, bool done)
+        : iterator(iterator)
         , next_method(next_method)
         , done(done)
     {
@@ -36,12 +35,8 @@ public:
 
 private:
     virtual void visit_edges(Cell::Visitor&) override;
-    virtual bool is_iterator_record() const override { return true; }
 };
 
-template<>
-inline bool Object::fast_is<IteratorRecord>() const { return is_iterator_record(); }
-
 class Iterator : public Object {
     JS_OBJECT(Iterator, Object);
     GC_DECLARE_ALLOCATOR(Iterator);

Libraries/LibJS/Runtime/Object.h

@@ -195,7 +195,6 @@ public:
     virtual bool is_proxy_object() const { return false; }
     virtual bool is_native_function() const { return false; }
     virtual bool is_ecmascript_function_object() const { return false; }
-    virtual bool is_iterator_record() const { return false; }
     virtual bool is_array_iterator() const { return false; }
 
     // B.3.7 The [[IsHTMLDDA]] Internal Slot, https://tc39.es/ecma262/#sec-IsHTMLDDA-internal-slot