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https://github.com/RGBCube/serenity
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LibJS: Avoid pointless transitions and metadata lookups in storage_set()
- Replace the misleading abuse of the m_transitions_enabled flag for the fast path without lookup with a new m_initialized boolean that's set either by Heap::allocate() after calling the Object's initialize(), or by the GlobalObject in its special initialize_global_object(). This makes it work regardless of the shape's uniqueness. - When we're adding a new property past the initialization phase, there's no need to do a second metadata lookup to retrieve the storage value offset - it's known to always be the shape's property count minus one. Also, instead of doing manual storage resizing and assignment via indexing, just use Vector::append(). - When we didn't add a new property but are overwriting an existing one, the property count and therefore storage value offset doesn't change, so we don't have to retrieve it either. As a result, Object::set_shape() is now solely responsible for updating the m_shape pointer and is not resizing storage anymore, so I moved it into the header.
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4 changed files with 40 additions and 29 deletions
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@ -6,6 +6,7 @@
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#pragma once
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#include <AK/Badge.h>
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#include <AK/HashTable.h>
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#include <AK/IntrusiveList.h>
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#include <AK/Noncopyable.h>
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@ -49,8 +50,10 @@ public:
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if constexpr (is_object)
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static_cast<Object*>(cell)->disable_transitions();
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cell->initialize(global_object);
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if constexpr (is_object)
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if constexpr (is_object) {
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static_cast<Object*>(cell)->enable_transitions();
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static_cast<Object*>(cell)->set_initialized(Badge<Heap> {});
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}
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return cell;
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}
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@ -132,8 +132,13 @@ void GlobalObject::initialize_global_object()
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m_new_ordinary_function_prototype_object_shape->set_prototype_without_transition(m_object_prototype);
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m_new_ordinary_function_prototype_object_shape->add_property_without_transition(vm.names.constructor, Attribute::Writable | Attribute::Configurable);
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// Normally Heap::allocate() takes care of this, but these are allocated via allocate_without_global_object().
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static_cast<FunctionPrototype*>(m_function_prototype)->initialize(*this);
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m_function_prototype->set_initialized(Badge<GlobalObject> {});
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static_cast<ObjectPrototype*>(m_object_prototype)->initialize(*this);
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m_object_prototype->set_initialized(Badge<GlobalObject> {});
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auto success = Object::internal_set_prototype_of(m_object_prototype);
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VERIFY(success);
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@ -265,6 +270,8 @@ void GlobalObject::initialize_global_object()
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m_array_prototype_values_function = &m_array_prototype->get_without_side_effects(vm.names.values).as_function();
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m_eval_function = &get_without_side_effects(vm.names.eval).as_function();
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m_temporal_time_zone_prototype_get_offset_nanoseconds_for_function = &m_temporal_time_zone_prototype->get_without_side_effects(vm.names.getOffsetNanosecondsFor).as_function();
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set_initialized(Badge<GlobalObject> {});
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}
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GlobalObject::~GlobalObject()
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@ -943,16 +943,21 @@ void Object::storage_set(PropertyName const& property_name, ValueAndAttributes c
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return;
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}
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// NOTE: We disable transitions during initialize(), this makes building common runtime objects significantly faster.
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// Transitions are primarily interesting when scripts add properties to objects.
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if (!m_transitions_enabled && !m_shape->is_unique()) {
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m_shape->add_property_without_transition(property_name, attributes);
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m_storage.resize(m_shape->property_count());
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m_storage[m_shape->property_count() - 1] = value;
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auto property_name_string_or_symbol = property_name.to_string_or_symbol();
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// NOTE: We don't do transitions or check for attribute changes during object initialization,
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// which makes building common runtime objects significantly faster. Transitions are primarily
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// interesting when scripts add properties to objects.
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if (!m_initialized) {
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if (m_shape->is_unique())
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m_shape->add_property_to_unique_shape(property_name_string_or_symbol, attributes);
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else
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m_shape->add_property_without_transition(property_name_string_or_symbol, attributes);
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m_storage.append(value);
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return;
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}
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auto property_name_string_or_symbol = property_name.to_string_or_symbol();
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auto metadata = shape().lookup(property_name_string_or_symbol);
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if (!metadata.has_value()) {
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@ -962,27 +967,24 @@ void Object::storage_set(PropertyName const& property_name, ValueAndAttributes c
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ensure_shape_is_unique();
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}
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if (m_shape->is_unique()) {
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if (m_shape->is_unique())
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m_shape->add_property_to_unique_shape(property_name_string_or_symbol, attributes);
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m_storage.resize(m_shape->property_count());
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} else if (m_transitions_enabled) {
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else if (!m_transitions_enabled)
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m_shape->add_property_without_transition(property_name_string_or_symbol, attributes);
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else
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set_shape(*m_shape->create_put_transition(property_name_string_or_symbol, attributes));
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} else {
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m_shape->add_property_without_transition(property_name, attributes);
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m_storage.resize(m_shape->property_count());
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}
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metadata = shape().lookup(property_name_string_or_symbol);
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VERIFY(metadata.has_value());
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m_storage.append(value);
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return;
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}
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if (attributes != metadata->attributes) {
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if (m_shape->is_unique()) {
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if (m_shape->is_unique())
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m_shape->reconfigure_property_in_unique_shape(property_name_string_or_symbol, attributes);
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} else {
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else if (!m_transitions_enabled)
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VERIFY_NOT_REACHED(); // We currently don't have a way of doing this, and it's not used anywhere either.
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else
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set_shape(*m_shape->create_configure_transition(property_name_string_or_symbol, attributes));
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}
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metadata = shape().lookup(property_name_string_or_symbol);
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VERIFY(metadata.has_value());
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}
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m_storage[metadata->offset] = value;
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@ -1005,12 +1007,6 @@ void Object::storage_delete(PropertyName const& property_name)
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m_storage.remove(metadata->offset);
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}
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void Object::set_shape(Shape& new_shape)
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{
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m_storage.resize(new_shape.property_count());
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m_shape = &new_shape;
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}
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void Object::define_native_accessor(PropertyName const& property_name, Function<Value(VM&, GlobalObject&)> getter, Function<Value(VM&, GlobalObject&)> setter, PropertyAttributes attribute)
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{
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auto& vm = this->vm();
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@ -7,6 +7,7 @@
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#pragma once
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#include <AK/Badge.h>
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#include <AK/HashMap.h>
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#include <AK/String.h>
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#include <LibJS/Forward.h>
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@ -160,6 +161,9 @@ public:
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void enable_transitions() { m_transitions_enabled = true; }
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void disable_transitions() { m_transitions_enabled = false; }
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void set_initialized(Badge<Heap>) { m_initialized = true; }
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void set_initialized(Badge<GlobalObject>) { m_initialized = true; }
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template<typename T>
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bool fast_is() const = delete;
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@ -176,12 +180,13 @@ protected:
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bool m_has_parameter_map { false };
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private:
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void set_shape(Shape&);
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void set_shape(Shape& shape) { m_shape = &shape; }
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Object* prototype() { return shape().prototype(); }
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Object const* prototype() const { return shape().prototype(); }
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bool m_transitions_enabled { true };
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bool m_initialized { false };
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Shape* m_shape { nullptr };
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Vector<Value> m_storage;
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IndexedProperties m_indexed_properties;
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