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LibJS: Use a premade shape when creating iterator result objects

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Instead of going through the steps of creating an empty new object,
and adding two properties ("value" and "done") to it, we can pre-bake
a shape object and cache the property offsets.

This makes creating iterator result objects in the runtime much faster.

47% speedup 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 22:30:53 +01:00
parent 706710fa13
commit f47a14b9d6
5 changed files with 28 additions and 3 deletions
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11
Userland/Libraries/LibJS/Runtime/Intrinsics.cpp
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@ -190,6 +190,16 @@ ThrowCompletionOr<void> Intrinsics::initialize_intrinsics(Realm& realm)
m_new_ordinary_function_prototype_object_shape->set_prototype_without_transition(m_object_prototype);
m_new_ordinary_function_prototype_object_shape->add_property_without_transition(vm.names.constructor, Attribute::Writable | Attribute::Configurable);
// OPTIMIZATION: A lot of runtime algorithms create an "iterator result" object.
// We pre-bake a shape for these objects and remember the property offsets.
// This allows us to construct them very quickly.
m_iterator_result_object_shape = heap().allocate_without_realm<Shape>(realm);
m_iterator_result_object_shape->set_prototype_without_transition(m_object_prototype);
m_iterator_result_object_shape->add_property_without_transition(vm.names.value, Attribute::Writable | Attribute::Configurable | Attribute::Enumerable);
m_iterator_result_object_shape->add_property_without_transition(vm.names.done, Attribute::Writable | Attribute::Configurable | Attribute::Enumerable);
m_iterator_result_object_value_offset = m_iterator_result_object_shape->lookup(vm.names.value.to_string_or_symbol()).value().offset;
m_iterator_result_object_done_offset = m_iterator_result_object_shape->lookup(vm.names.done.to_string_or_symbol()).value().offset;
// Normally Heap::allocate() takes care of this, but these are allocated via allocate_without_realm().
m_function_prototype->initialize(realm);
m_object_prototype->initialize(realm);
@ -358,6 +368,7 @@ void Intrinsics::visit_edges(Visitor& visitor)
visitor.visit(m_empty_object_shape);
visitor.visit(m_new_object_shape);
visitor.visit(m_new_ordinary_function_prototype_object_shape);
visitor.visit(m_iterator_result_object_shape);
visitor.visit(m_proxy_constructor);
visitor.visit(m_async_from_sync_iterator_prototype);
visitor.visit(m_async_generator_prototype);