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LibJS: Reuse the internal iterator object across a for..in iteration

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Instead of creating a new iterator result Object for every step of
for..in iteration, we can create a single object up front and reuse it
for every step. This avoids generating a bunch of garbage that isn't
observable by author code anyway.

We can also reuse the existing premade shape for these objects.
This commit is contained in:
Andreas Kling 2025-03-19 17:13:31 -05:00 • committed by Andreas Kling
parent 37bf083536
commit fb3d1c2754
Notes: github-actions[bot] 2025-03-20 17:52:32 +00:00
1 changed files with 10 additions and 7 deletions

17
Libraries/LibJS/Bytecode/Interpreter.cpp
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@ -1771,18 +1771,21 @@ inline ThrowCompletionOr<Object*> get_object_property_iterator(VM& vm, Value val
properties.remove_all_matching([&](auto& entry) { return !entry.enumerable; });
auto& realm = *vm.current_realm();
auto result_object = Object::create_with_premade_shape(realm.intrinsics().iterator_result_object_shape());
auto value_offset = realm.intrinsics().iterator_result_object_value_offset();
auto done_offset = realm.intrinsics().iterator_result_object_done_offset();
auto callback = NativeFunction::create(
*vm.current_realm(), [items = move(properties)](VM& vm) mutable -> ThrowCompletionOr<Value> {
auto& realm = *vm.current_realm();
*vm.current_realm(), [items = move(properties), result_object, value_offset, done_offset](VM& vm) mutable -> ThrowCompletionOr<Value> {
auto iterated_object_value = vm.this_value();
if (!iterated_object_value.is_object())
return vm.throw_completion<InternalError>("Invalid state for GetObjectPropertyIterator.next"sv);
auto& iterated_object = iterated_object_value.as_object();
auto result_object = Object::create(realm, nullptr);
while (true) {
if (items.is_empty()) {
result_object->define_direct_property(vm.names.done, JS::Value(true), default_attributes);
result_object->put_direct(done_offset, JS::Value(true));
return result_object;
}
@ -1792,12 +1795,12 @@ inline ThrowCompletionOr<Object*> get_object_property_iterator(VM& vm, Value val
if (!TRY(iterated_object.has_property(key)))
continue;
result_object->define_direct_property(vm.names.done, JS::Value(false), default_attributes);
result_object->put_direct(done_offset, JS::Value(false));
if (key.is_number())
result_object->define_direct_property(vm.names.value, PrimitiveString::create(vm, String::number(key.as_number())), default_attributes);
result_object->put_direct(value_offset, PrimitiveString::create(vm, String::number(key.as_number())));
else if (key.is_string())
result_object->define_direct_property(vm.names.value, PrimitiveString::create(vm, key.as_string()), default_attributes);
result_object->put_direct(value_offset, PrimitiveString::create(vm, key.as_string()));
else
VERIFY_NOT_REACHED(); // We should not have non-string/number keys.