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LibJS: Introduce "dictionary" mode for object shapes

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This is similar to "unique" shapes, which were removed in commit
3d92c26445.

The key difference is that dictionary shapes don't have a serial number,
but instead have a "cacheable" flag.

Shapes become dictionaries after 64 transitions have occurred, at which
point no further transitions occur.

As long as properties are only added to a dictionary shape, it remains
cacheable. (Since if we've cached the shape pointer in an IC somewhere,
we know the IC is still valid.)

Deleting a property from a dictionary shape causes it to become an
uncacheable dictionary.

Note that deleting a property from a non-dictionary shape still performs
a delete transition.

This fixes an issue on Discord where Object.freeze() would eventually
OOM us, since they add more than 16000 properties to a single object
before freezing it.

It also yields a 15% speedup on Octane/pdfjs.js :^)
This commit is contained in:
Andreas Kling 2023-12-16 11:34:01 +01:00
parent 8255a1a5ee
commit 1e90379008
4 changed files with 94 additions and 4 deletions
Download patch file Download diff file Expand all files Collapse all files

15
Userland/Libraries/LibJS/Runtime/Shape.h
View file

@ -49,16 +49,28 @@ public:
Configure,
Prototype,
Delete,
CacheableDictionary,
UncacheableDictionary,
};
Shape* create_put_transition(StringOrSymbol const&, PropertyAttributes attributes);
Shape* create_configure_transition(StringOrSymbol const&, PropertyAttributes attributes);
Shape* create_prototype_transition(Object* new_prototype);
[[nodiscard]] NonnullGCPtr<Shape> create_delete_transition(StringOrSymbol const&);
[[nodiscard]] NonnullGCPtr<Shape> create_cacheable_dictionary_transition();
[[nodiscard]] NonnullGCPtr<Shape> create_uncacheable_dictionary_transition();
void add_property_without_transition(StringOrSymbol const&, PropertyAttributes);
void add_property_without_transition(PropertyKey const&, PropertyAttributes);
void remove_property_without_transition(StringOrSymbol const&, u32 offset);
void set_property_attributes_without_transition(StringOrSymbol const&, PropertyAttributes);
[[nodiscard]] bool is_cacheable() const { return m_cacheable; }
[[nodiscard]] bool is_dictionary() const { return m_dictionary; }
[[nodiscard]] bool is_cacheable_dictionary() const { return m_dictionary && m_cacheable; }
[[nodiscard]] bool is_uncacheable_dictionary() const { return m_dictionary && !m_cacheable; }
Realm& realm() const { return m_realm; }
Object* prototype() { return m_prototype; }
@ -103,6 +115,9 @@ private:
PropertyAttributes m_attributes { 0 };
TransitionType m_transition_type { TransitionType::Invalid };
bool m_dictionary { false };
bool m_cacheable { true };
};
}