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LibJS: Cache the shape for normal ECMAScriptFunctionObject prototypes

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Instead of creating a unique new prototype shape every time a function
object is instantiated, we now keep one cached with the intrinsics.

This avoids a whole lot of shape allocations, reducing GC pressure.
This commit is contained in:
Andreas Kling 2024-09-26 17:05:56 +02:00 committed by Andreas Kling
parent 795471ce31
commit 749cf2d1b5
Notes: github-actions[bot] 2024-09-26 18:24:37 +00:00 
Author: https://github.com/awesomekling
Commit: https://github.com/LadybirdBrowser/ladybird/commit/749cf2d1b54
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/1541
3 changed files with 15 additions and 2 deletions
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4
Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.cpp
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@ -354,8 +354,8 @@ void ECMAScriptFunctionObject::initialize(Realm& realm)
Object* prototype = nullptr;
switch (m_kind) {
case FunctionKind::Normal:
prototype = Object::create_prototype(realm, realm.intrinsics().object_prototype());
MUST(prototype->define_property_or_throw(vm.names.constructor, { .value = this, .writable = true, .enumerable = false, .configurable = true }));
prototype = Object::create_with_premade_shape(realm.intrinsics().new_function_object_prototype_shape());
prototype->put_direct(realm.intrinsics().new_function_object_prototype_constructor_offset(), this);
break;
case FunctionKind::Generator:
// prototype is "g1.prototype" in figure-2 (https://tc39.es/ecma262/img/figure-2.png)

7
Userland/Libraries/LibJS/Runtime/Intrinsics.cpp
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@ -188,6 +188,12 @@ ThrowCompletionOr<void> Intrinsics::initialize_intrinsics(Realm& realm)
m_new_object_shape = heap().allocate_without_realm<Shape>(realm);
m_new_object_shape->set_prototype_without_transition(m_object_prototype);
m_new_function_object_prototype_shape = heap().allocate_without_realm<Shape>(realm);
m_new_function_object_prototype_shape->set_prototype_shape();
m_new_function_object_prototype_shape->set_prototype_without_transition(m_object_prototype);
m_new_function_object_prototype_shape->add_property_without_transition(vm.names.constructor, Attribute::Writable | Attribute::Configurable | Attribute::Enumerable);
m_new_function_object_prototype_constructor_offset = m_new_function_object_prototype_shape->lookup(vm.names.constructor.to_string_or_symbol()).value().offset;
// OPTIMIZATION: A lot of runtime algorithms create an "iterator result" object.
// We pre-bake a shape for these objects and remember the property offsets.
// This allows us to construct them very quickly.
@ -367,6 +373,7 @@ void Intrinsics::visit_edges(Visitor& visitor)
visitor.visit(m_realm);
visitor.visit(m_empty_object_shape);
visitor.visit(m_new_object_shape);
visitor.visit(m_new_function_object_prototype_shape);
visitor.visit(m_iterator_result_object_shape);
visitor.visit(m_proxy_constructor);
visitor.visit(m_async_from_sync_iterator_prototype);

6
Userland/Libraries/LibJS/Runtime/Intrinsics.h
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@ -22,6 +22,9 @@ public:
NonnullGCPtr<Shape> new_object_shape() { return *m_new_object_shape; }
[[nodiscard]] NonnullGCPtr<Shape> new_function_object_prototype_shape() { return *m_new_function_object_prototype_shape; }
[[nodiscard]] u32 new_function_object_prototype_constructor_offset() { return m_new_function_object_prototype_constructor_offset; }
[[nodiscard]] NonnullGCPtr<Shape> iterator_result_object_shape() { return *m_iterator_result_object_shape; }
[[nodiscard]] u32 iterator_result_object_value_offset() { return m_iterator_result_object_value_offset; }
[[nodiscard]] u32 iterator_result_object_done_offset() { return m_iterator_result_object_done_offset; }
@ -125,6 +128,9 @@ private:
GCPtr<Shape> m_empty_object_shape;
GCPtr<Shape> m_new_object_shape;
GCPtr<Shape> m_new_function_object_prototype_shape;
u32 m_new_function_object_prototype_constructor_offset { 0 };
GCPtr<Shape> m_iterator_result_object_shape;
u32 m_iterator_result_object_value_offset { 0 };
u32 m_iterator_result_object_done_offset { 0 };