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LibJS: Use a premade shape for normal function objects

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This avoids going through all the shape transitions when setting up the
most common form of ESFO.

This is extremely hot on Uber Eats, and this provides some relief.
This commit is contained in:
Andreas Kling
2025-03-25 20:08:38 +00:00
committed by Andreas Kling
parent 60fd406903
commit c037bda455
Notes: github-actions[bot] 2025-03-27 23:13:08 +00:00 
Author: https://github.com/awesomekling
Commit: https://github.com/LadybirdBrowser/ladybird/commit/c037bda455d
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/4128
Reviewed-by: https://github.com/Hendiadyoin1
5 changed files with 61 additions and 22 deletions
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55
Libraries/LibJS/Runtime/ECMAScriptFunctionObject.cpp
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@@ -76,6 +76,9 @@ ECMAScriptFunctionObject::ECMAScriptFunctionObject(FlyString name, ByteString so
, m_is_arrow_function(is_arrow_function)
, m_kind(kind)
{
if (!m_is_arrow_function && m_kind == FunctionKind::Normal)
unsafe_set_shape(m_realm->intrinsics().normal_function_shape());
// NOTE: This logic is from OrdinaryFunctionCreate, https://tc39.es/ecma262/#sec-ordinaryfunctioncreate
// 9. If thisMode is lexical-this, set F.[[ThisMode]] to lexical.
@@ -347,30 +350,38 @@ void ECMAScriptFunctionObject::initialize(Realm& realm)
m_name_string = PrimitiveString::create(vm, m_name);
MUST(define_property_or_throw(vm.names.length, { .value = Value(m_function_length), .writable = false, .enumerable = false, .configurable = true }));
MUST(define_property_or_throw(vm.names.name, { .value = m_name_string, .writable = false, .enumerable = false, .configurable = true }));
if (!m_is_arrow_function && m_kind == FunctionKind::Normal) {
put_direct(realm.intrinsics().normal_function_length_offset(), Value(m_function_length));
put_direct(realm.intrinsics().normal_function_name_offset(), m_name_string);
if (!m_is_arrow_function) {
Object* prototype = nullptr;
switch (m_kind) {
case FunctionKind::Normal:
prototype = Object::create_with_premade_shape(realm.intrinsics().normal_function_prototype_shape());
prototype->put_direct(realm.intrinsics().normal_function_prototype_constructor_offset(), this);
break;
case FunctionKind::Generator:
// prototype is "g1.prototype" in figure-2 (https://tc39.es/ecma262/img/figure-2.png)
prototype = Object::create_prototype(realm, realm.intrinsics().generator_function_prototype_prototype());
break;
case FunctionKind::Async:
break;
case FunctionKind::AsyncGenerator:
prototype = Object::create_prototype(realm, realm.intrinsics().async_generator_function_prototype_prototype());
break;
auto prototype = Object::create_with_premade_shape(realm.intrinsics().normal_function_prototype_shape());
prototype->put_direct(realm.intrinsics().normal_function_prototype_constructor_offset(), this);
put_direct(realm.intrinsics().normal_function_prototype_offset(), prototype);
} else {
MUST(define_property_or_throw(vm.names.length, { .value = Value(m_function_length), .writable = false, .enumerable = false, .configurable = true }));
MUST(define_property_or_throw(vm.names.name, { .value = m_name_string, .writable = false, .enumerable = false, .configurable = true }));
if (!m_is_arrow_function) {
Object* prototype = nullptr;
switch (m_kind) {
case FunctionKind::Normal:
VERIFY_NOT_REACHED();
break;
case FunctionKind::Generator:
// prototype is "g1.prototype" in figure-2 (https://tc39.es/ecma262/img/figure-2.png)
prototype = Object::create_prototype(realm, realm.intrinsics().generator_function_prototype_prototype());
break;
case FunctionKind::Async:
break;
case FunctionKind::AsyncGenerator:
prototype = Object::create_prototype(realm, realm.intrinsics().async_generator_function_prototype_prototype());
break;
}
// 27.7.4 AsyncFunction Instances, https://tc39.es/ecma262/#sec-async-function-instances
// AsyncFunction instances do not have a prototype property as they are not constructible.
if (m_kind != FunctionKind::Async)
define_direct_property(vm.names.prototype, prototype, Attribute::Writable);
}
// 27.7.4 AsyncFunction Instances, https://tc39.es/ecma262/#sec-async-function-instances
// AsyncFunction instances do not have a prototype property as they are not constructible.
if (m_kind != FunctionKind::Async)
define_direct_property(vm.names.prototype, prototype, Attribute::Writable);
}
}