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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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5
Libraries/LibJS/Interpreter.cpp
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@ -35,6 +35,7 @@
#include <LibJS/Runtime/NativeFunction.h>
#include <LibJS/Runtime/Object.h>
#include <LibJS/Runtime/ObjectPrototype.h>
#include <LibJS/Runtime/Shape.h>
#include <LibJS/Runtime/StringPrototype.h>
#include <LibJS/Runtime/Value.h>
@ -43,6 +44,8 @@ namespace JS {
Interpreter::Interpreter()
: m_heap(*this)
{
m_empty_object_shape = heap().allocate<Shape>();
m_object_prototype = heap().allocate<ObjectPrototype>();
m_string_prototype = heap().allocate<StringPrototype>();
m_array_prototype = heap().allocate<ArrayPrototype>();
@ -160,6 +163,8 @@ Optional<Value> Interpreter::get_variable(const FlyString& name)
void Interpreter::gather_roots(Badge<Heap>, HashTable<Cell*>& roots)
{
roots.set(m_empty_object_shape);
roots.set(m_global_object);
roots.set(m_string_prototype);
roots.set(m_object_prototype);