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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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17
Libraries/LibJS/Runtime/Object.h
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@ -40,6 +40,9 @@ public:
Object();
virtual ~Object();
Shape& shape() { return *m_shape; }
const Shape& shape() const { return *m_shape; }
Optional<Value> get(const FlyString& property_name) const;
void put(const FlyString& property_name, Value);
@ -60,9 +63,9 @@ public:
virtual const char* class_name() const override { return "Object"; }
virtual void visit_children(Cell::Visitor&) override;
Object* prototype() { return m_prototype; }
const Object* prototype() const { return m_prototype; }
void set_prototype(Object* prototype) { m_prototype = prototype; }
Object* prototype();
const Object* prototype() const;
void set_prototype(Object*);
bool has_prototype(const Object* prototype) const;
bool has_own_property(const FlyString& property_name) const;
@ -76,11 +79,13 @@ public:
virtual Value to_primitive(PreferredType preferred_type = PreferredType::Default) const;
virtual Value to_string() const;
const HashMap<FlyString, Value>& own_properties() const { return m_properties; }
Value get_direct(size_t index) const { return m_storage[index]; }
private:
HashMap<FlyString, Value> m_properties;
Object* m_prototype { nullptr };
void set_shape(Shape&);
Shape* m_shape { nullptr };
Vector<Value> m_storage;
};
}