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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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78
Libraries/LibJS/Runtime/Shape.h Normal file
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/*
* Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#pragma once
#include <AK/FlyString.h>
#include <AK/HashMap.h>
#include <AK/OwnPtr.h>
#include <LibJS/Forward.h>
#include <LibJS/Runtime/Cell.h>
#include <LibJS/Runtime/Value.h>
namespace JS {
struct PropertyMetadata {
size_t offset { 0 };
u8 attributes { 0 };
};
class Shape final : public Cell {
public:
virtual ~Shape() override;
Shape();
Shape(Shape* previous_shape, const FlyString& property_name, u8 property_attributes);
Shape(Shape* previous_shape, Object* new_prototype);
Shape* create_put_transition(const FlyString& name, u8 attributes);
Shape* create_prototype_transition(Object* new_prototype);
Object* prototype() { return m_prototype; }
const Object* prototype() const { return m_prototype; }
Optional<PropertyMetadata> lookup(const FlyString&) const;
const HashMap<FlyString, PropertyMetadata>& property_table() const;
size_t property_count() const;
void set_prototype_without_transition(Object* new_prototype) { m_prototype = new_prototype; }
private:
virtual const char* class_name() const override { return "Shape"; }
virtual void visit_children(Visitor&) override;
void ensure_property_table() const;
mutable OwnPtr<HashMap<FlyString, PropertyMetadata>> m_property_table;
HashMap<FlyString, Shape*> m_forward_transitions;
Shape* m_previous { nullptr };
FlyString m_property_name;
u8 m_property_attributes { 0 };
Object* m_prototype { nullptr };
};
}