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LibJS: Start implementing object shapes

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This patch adds JS::Shape, which implements a transition tree for our
Object class. Object property keys, prototypes and attributes are now
stored in a Shape, and each Object has a Shape.

When adding a property to an Object, we make a transition from the old
Shape to a new Shape. If we've made the same exact transition in the
past (with another Object), we reuse the same transition and both
objects may now share a Shape.

This will become the foundation of inline caching and other engine
optimizations in the future. :^)
This commit is contained in:
Andreas Kling 2020-04-02 19:32:21 +02:00
parent 3906d2b46a
commit 5e6e1fd482
10 changed files with 252 additions and 29 deletions
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70
Libraries/LibJS/Runtime/Object.cpp
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@ -31,22 +31,39 @@
#include <LibJS/Runtime/NativeFunction.h>
#include <LibJS/Runtime/NativeProperty.h>
#include <LibJS/Runtime/Object.h>
#include <LibJS/Runtime/Shape.h>
#include <LibJS/Runtime/Value.h>
namespace JS {
Object::Object()
{
set_prototype(interpreter().object_prototype());
m_shape = interpreter().empty_object_shape();
m_shape->set_prototype_without_transition(interpreter().object_prototype());
}
Object::~Object()
{
}
Object* Object::prototype()
{
return shape().prototype();
}
const Object* Object::prototype() const
{
return shape().prototype();
}
void Object::set_prototype(Object* new_prototype)
{
m_shape = m_shape->create_prototype_transition(new_prototype);
}
bool Object::has_prototype(const Object* prototype) const
{
for (auto* object = m_prototype; object; object = object->prototype()) {
for (auto* object = this->prototype(); object; object = object->prototype()) {
if (object == prototype)
return true;
}
@ -55,9 +72,13 @@ bool Object::has_prototype(const Object* prototype) const
Optional<Value> Object::get_own_property(const Object& this_object, const FlyString& property_name) const
{
auto value_here = m_properties.get(property_name);
if (value_here.has_value() && value_here.value().is_object() && value_here.value().as_object().is_native_property()) {
auto& native_property = static_cast<const NativeProperty&>(value_here.value().as_object());
auto metadata = shape().lookup(property_name);
if (!metadata.has_value())
return {};
auto value_here = m_storage[metadata.value().offset];
if (value_here.is_object() && value_here.as_object().is_native_property()) {
auto& native_property = static_cast<const NativeProperty&>(value_here.as_object());
auto& interpreter = const_cast<Object*>(this)->interpreter();
auto& call_frame = interpreter.push_call_frame();
call_frame.this_value = const_cast<Object*>(&this_object);
@ -68,19 +89,32 @@ Optional<Value> Object::get_own_property(const Object& this_object, const FlyStr
return value_here;
}
void Object::set_shape(Shape& new_shape)
{
m_storage.resize(new_shape.property_count());
m_shape = &new_shape;
}
bool Object::put_own_property(Object& this_object, const FlyString& property_name, Value value)
{
auto value_here = m_properties.get(property_name);
if (value_here.has_value() && value_here.value().is_object() && value_here.value().as_object().is_native_property()) {
auto& native_property = static_cast<NativeProperty&>(value_here.value().as_object());
auto metadata = shape().lookup(property_name);
if (!metadata.has_value()) {
auto* new_shape = m_shape->create_put_transition(property_name, 0);
set_shape(*new_shape);
metadata = shape().lookup(property_name);
ASSERT(metadata.has_value());
}
auto value_here = m_storage[metadata.value().offset];
if (value_here.is_object() && value_here.as_object().is_native_property()) {
auto& native_property = static_cast<NativeProperty&>(value_here.as_object());
auto& interpreter = const_cast<Object*>(this)->interpreter();
auto& call_frame = interpreter.push_call_frame();
call_frame.this_value = &this_object;
dbg() << "put_own_property: " << &this_object << " . " << property_name << " = " << value;
native_property.set(interpreter, value);
interpreter.pop_call_frame();
} else {
m_properties.set(property_name, value);
m_storage[metadata.value().offset] = value;
}
return true;
}
@ -101,10 +135,11 @@ void Object::put(const FlyString& property_name, Value value)
{
Object* object = this;
while (object) {
auto value_here = object->m_properties.get(property_name);
if (value_here.has_value()) {
if (value_here.value().is_object() && value_here.value().as_object().is_native_property()) {
auto& native_property = static_cast<NativeProperty&>(value_here.value().as_object());
auto metadata = object->shape().lookup(property_name);
if (metadata.has_value()) {
auto value_here = object->m_storage[metadata.value().offset];
if (value_here.is_object() && value_here.as_object().is_native_property()) {
auto& native_property = static_cast<NativeProperty&>(value_here.as_object());
auto& interpreter = const_cast<Object*>(this)->interpreter();
auto& call_frame = interpreter.push_call_frame();
call_frame.this_value = this;
@ -133,15 +168,12 @@ void Object::put_native_property(const FlyString& property_name, AK::Function<Va
void Object::visit_children(Cell::Visitor& visitor)
{
Cell::visit_children(visitor);
if (m_prototype)
visitor.visit(m_prototype);
for (auto& it : m_properties)
visitor.visit(it.value);
visitor.visit(m_shape);
}
bool Object::has_own_property(const FlyString& property_name) const
{
return m_properties.get(property_name).has_value();
return shape().lookup(property_name).has_value();
}
Value Object::to_primitive(PreferredType preferred_type) const