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LibJS: Add property configuration transitions

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Object.defineProperty() can now change the attributes of a property
already on the object. Internally this becomes a shape transition with
the TransitionType::Configure. Such transitions don't expand the
property storage capacity, but rather simply keep attributes up to date
when generating a property table.
This commit is contained in:
Andreas Kling 2020-04-09 22:55:17 +02:00
parent e6d920d87d
commit 8286f8b996
5 changed files with 57 additions and 8 deletions
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24
Libraries/LibJS/Runtime/Shape.cpp
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@ -34,7 +34,17 @@ Shape* Shape::create_put_transition(const FlyString& property_name, u8 attribute
auto* new_shape = m_forward_transitions.get(property_name).value_or(nullptr);
if (new_shape && new_shape->m_attributes == attributes)
return new_shape;
new_shape = heap().allocate<Shape>(this, property_name, attributes);
new_shape = heap().allocate<Shape>(this, property_name, attributes, TransitionType::Put);
m_forward_transitions.set(property_name, new_shape);
return new_shape;
}
Shape* Shape::create_configure_transition(const FlyString& property_name, u8 attributes)
{
auto* new_shape = m_forward_transitions.get(property_name).value_or(nullptr);
if (new_shape && new_shape->m_attributes == attributes)
return new_shape;
new_shape = heap().allocate<Shape>(this, property_name, attributes, TransitionType::Configure);
m_forward_transitions.set(property_name, new_shape);
return new_shape;
}
@ -48,17 +58,19 @@ Shape::Shape()
{
}
Shape::Shape(Shape* previous_shape, const FlyString& property_name, u8 attributes)
Shape::Shape(Shape* previous_shape, const FlyString& property_name, u8 attributes, TransitionType transition_type)
: m_previous(previous_shape)
, m_property_name(property_name)
, m_attributes(attributes)
, m_prototype(previous_shape->m_prototype)
, m_transition_type(transition_type)
{
}
Shape::Shape(Shape* previous_shape, Object* new_prototype)
: m_previous(previous_shape)
, m_prototype(new_prototype)
, m_transition_type(TransitionType::Prototype)
{
}
@ -114,7 +126,13 @@ void Shape::ensure_property_table() const
// Ignore prototype transitions as they don't affect the key map.
continue;
}
m_property_table->set(shape->m_property_name, { next_offset++, shape->m_attributes });
if (shape->m_transition_type == TransitionType::Put) {
m_property_table->set(shape->m_property_name, { next_offset++, shape->m_attributes });
} else if (shape->m_transition_type == TransitionType::Configure) {
auto it = m_property_table->find(shape->m_property_name);
ASSERT(it != m_property_table->end());
it->value.attributes = shape->m_attributes;
}
}
}