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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.
This commit is contained in:
Linus Groh 2021-08-28 17:12:14 +01:00
parent d6de0613f5
commit 222e518a53
4 changed files with 40 additions and 29 deletions

View file

@ -6,6 +6,7 @@
#pragma once
#include <AK/Badge.h>
#include <AK/HashTable.h>
#include <AK/IntrusiveList.h>
#include <AK/Noncopyable.h>
@ -49,8 +50,10 @@ public:
if constexpr (is_object)
static_cast<Object*>(cell)->disable_transitions();
cell->initialize(global_object);
if constexpr (is_object)
if constexpr (is_object) {
static_cast<Object*>(cell)->enable_transitions();
static_cast<Object*>(cell)->set_initialized(Badge<Heap> {});
}
return cell;
}

View file

@ -132,8 +132,13 @@ void GlobalObject::initialize_global_object()
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);
// Normally Heap::allocate() takes care of this, but these are allocated via allocate_without_global_object().
static_cast<FunctionPrototype*>(m_function_prototype)->initialize(*this);
m_function_prototype->set_initialized(Badge<GlobalObject> {});
static_cast<ObjectPrototype*>(m_object_prototype)->initialize(*this);
m_object_prototype->set_initialized(Badge<GlobalObject> {});
auto success = Object::internal_set_prototype_of(m_object_prototype);
VERIFY(success);
@ -265,6 +270,8 @@ void GlobalObject::initialize_global_object()
m_array_prototype_values_function = &m_array_prototype->get_without_side_effects(vm.names.values).as_function();
m_eval_function = &get_without_side_effects(vm.names.eval).as_function();
m_temporal_time_zone_prototype_get_offset_nanoseconds_for_function = &m_temporal_time_zone_prototype->get_without_side_effects(vm.names.getOffsetNanosecondsFor).as_function();
set_initialized(Badge<GlobalObject> {});
}
GlobalObject::~GlobalObject()

View file

@ -943,16 +943,21 @@ void Object::storage_set(PropertyName const& property_name, ValueAndAttributes c
return;
}
// NOTE: We disable transitions during initialize(), this makes building common runtime objects significantly faster.
// Transitions are primarily interesting when scripts add properties to objects.
if (!m_transitions_enabled && !m_shape->is_unique()) {
m_shape->add_property_without_transition(property_name, attributes);
m_storage.resize(m_shape->property_count());
m_storage[m_shape->property_count() - 1] = value;
auto property_name_string_or_symbol = property_name.to_string_or_symbol();
// NOTE: We don't do transitions or check for attribute changes during object initialization,
// which makes building common runtime objects significantly faster. Transitions are primarily
// interesting when scripts add properties to objects.
if (!m_initialized) {
if (m_shape->is_unique())
m_shape->add_property_to_unique_shape(property_name_string_or_symbol, attributes);
else
m_shape->add_property_without_transition(property_name_string_or_symbol, attributes);
m_storage.append(value);
return;
}
auto property_name_string_or_symbol = property_name.to_string_or_symbol();
auto metadata = shape().lookup(property_name_string_or_symbol);
if (!metadata.has_value()) {
@ -962,27 +967,24 @@ void Object::storage_set(PropertyName const& property_name, ValueAndAttributes c
ensure_shape_is_unique();
}
if (m_shape->is_unique()) {
if (m_shape->is_unique())
m_shape->add_property_to_unique_shape(property_name_string_or_symbol, attributes);
m_storage.resize(m_shape->property_count());
} else if (m_transitions_enabled) {
else if (!m_transitions_enabled)
m_shape->add_property_without_transition(property_name_string_or_symbol, attributes);
else
set_shape(*m_shape->create_put_transition(property_name_string_or_symbol, attributes));
} else {
m_shape->add_property_without_transition(property_name, attributes);
m_storage.resize(m_shape->property_count());
}
metadata = shape().lookup(property_name_string_or_symbol);
VERIFY(metadata.has_value());
m_storage.append(value);
return;
}
if (attributes != metadata->attributes) {
if (m_shape->is_unique()) {
if (m_shape->is_unique())
m_shape->reconfigure_property_in_unique_shape(property_name_string_or_symbol, attributes);
} else {
else if (!m_transitions_enabled)
VERIFY_NOT_REACHED(); // We currently don't have a way of doing this, and it's not used anywhere either.
else
set_shape(*m_shape->create_configure_transition(property_name_string_or_symbol, attributes));
}
metadata = shape().lookup(property_name_string_or_symbol);
VERIFY(metadata.has_value());
}
m_storage[metadata->offset] = value;
@ -1005,12 +1007,6 @@ void Object::storage_delete(PropertyName const& property_name)
m_storage.remove(metadata->offset);
}
void Object::set_shape(Shape& new_shape)
{
m_storage.resize(new_shape.property_count());
m_shape = &new_shape;
}
void Object::define_native_accessor(PropertyName const& property_name, Function<Value(VM&, GlobalObject&)> getter, Function<Value(VM&, GlobalObject&)> setter, PropertyAttributes attribute)
{
auto& vm = this->vm();

View file

@ -7,6 +7,7 @@
#pragma once
#include <AK/Badge.h>
#include <AK/HashMap.h>
#include <AK/String.h>
#include <LibJS/Forward.h>
@ -160,6 +161,9 @@ public:
void enable_transitions() { m_transitions_enabled = true; }
void disable_transitions() { m_transitions_enabled = false; }
void set_initialized(Badge<Heap>) { m_initialized = true; }
void set_initialized(Badge<GlobalObject>) { m_initialized = true; }
template<typename T>
bool fast_is() const = delete;
@ -176,12 +180,13 @@ protected:
bool m_has_parameter_map { false };
private:
void set_shape(Shape&);
void set_shape(Shape& shape) { m_shape = &shape; }
Object* prototype() { return shape().prototype(); }
Object const* prototype() const { return shape().prototype(); }
bool m_transitions_enabled { true };
bool m_initialized { false };
Shape* m_shape { nullptr };
Vector<Value> m_storage;
IndexedProperties m_indexed_properties;