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LibJS: Stop converting between Object <-> IteratorRecord all the time

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This patch makes IteratorRecord an Object. Although it's not exposed to
author code, this does allow us to store it in a VM register.

Now that we can store it in a VM register, we don't need to convert it
back and forth between IteratorRecord and Object when accessing it from
bytecode.

The big win here is avoiding 3 [[Get]] accesses on every iteration step
of for..of loops. There are also a bunch of smaller efficiencies gained.

20% speed-up on this microbenchmark:

    function go(a) {
        for (const p of a) {
        }
    }
    const a = [];
    a.length = 1_000_000;
    go(a);
This commit is contained in:
Andreas Kling 2023-12-07 10:44:41 +01:00
parent 4966c083df
commit 4699c81fc1
23 changed files with 226 additions and 144 deletions
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95
Userland/Libraries/LibJS/Bytecode/CommonImplementations.cpp
View file

@ -654,31 +654,9 @@ ThrowCompletionOr<NonnullGCPtr<Object>> super_call_with_argument_array(VM& vm, V
return result;
}
// FIXME: Since the accumulator is a Value, we store an object there and have to convert back and forth between that an Iterator records. Not great.
// Make sure to put this into the accumulator before the iterator object disappears from the stack to prevent the members from being GC'd.
Object* iterator_to_object(VM& vm, IteratorRecord iterator)
{
auto& realm = *vm.current_realm();
auto object = Object::create(realm, nullptr);
object->define_direct_property(vm.names.iterator, iterator.iterator, 0);
object->define_direct_property(vm.names.next, iterator.next_method, 0);
object->define_direct_property(vm.names.done, Value(iterator.done), 0);
return object;
}
IteratorRecord object_to_iterator(VM& vm, Object& object)
{
return IteratorRecord {
.iterator = &MUST(object.get(vm.names.iterator)).as_object(),
.next_method = MUST(object.get(vm.names.next)),
.done = MUST(object.get(vm.names.done)).as_bool()
};
}
ThrowCompletionOr<NonnullGCPtr<Array>> iterator_to_array(VM& vm, Value iterator)
{
auto iterator_object = TRY(iterator.to_object(vm));
auto iterator_record = object_to_iterator(vm, iterator_object);
auto& iterator_record = verify_cast<IteratorRecord>(iterator.as_object());
auto array = MUST(Array::create(*vm.current_realm(), 0));
size_t index = 0;
@ -832,47 +810,42 @@ ThrowCompletionOr<Object*> get_object_property_iterator(VM& vm, Value value)
properties.set(move(property_key));
}
}
IteratorRecord iterator {
.iterator = object,
.next_method = NativeFunction::create(
*vm.current_realm(),
[items = move(properties)](VM& vm) mutable -> ThrowCompletionOr<Value> {
auto& realm = *vm.current_realm();
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);
return result_object;
}
auto key = items.take_first();
// If the property is deleted, don't include it (invariant no. 2)
if (!TRY(iterated_object.has_property(key)))
continue;
result_object->define_direct_property(vm.names.done, JS::Value(false), default_attributes);
if (key.is_number())
result_object->define_direct_property(vm.names.value, PrimitiveString::create(vm, TRY_OR_THROW_OOM(vm, String::number(key.as_number()))), default_attributes);
else if (key.is_string())
result_object->define_direct_property(vm.names.value, PrimitiveString::create(vm, key.as_string()), default_attributes);
else
VERIFY_NOT_REACHED(); // We should not have non-string/number keys.
auto& realm = *vm.current_realm();
auto callback = NativeFunction::create(
*vm.current_realm(), [items = move(properties)](VM& vm) mutable -> ThrowCompletionOr<Value> {
auto& realm = *vm.current_realm();
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);
return result_object;
}
},
1,
vm.names.next),
.done = false,
};
return iterator_to_object(vm, move(iterator));
auto key = items.take_first();
// If the property is deleted, don't include it (invariant no. 2)
if (!TRY(iterated_object.has_property(key)))
continue;
result_object->define_direct_property(vm.names.done, JS::Value(false), default_attributes);
if (key.is_number())
result_object->define_direct_property(vm.names.value, PrimitiveString::create(vm, TRY_OR_THROW_OOM(vm, String::number(key.as_number()))), default_attributes);
else if (key.is_string())
result_object->define_direct_property(vm.names.value, PrimitiveString::create(vm, key.as_string()), default_attributes);
else
VERIFY_NOT_REACHED(); // We should not have non-string/number keys.
return result_object;
}
},
1, vm.names.next);
return vm.heap().allocate<IteratorRecord>(realm, realm, object, callback, false).ptr();
}
}