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LibJS: Don't make extra copies of every JS function's source code

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Instead, let functions have a view into the AST's SourceCode object's
underlying string data. The source string is kept alive by the AST, so
it's fine to have views into it as long as the AST exists.

Reduces memory footprint on my x.com home feed by 65 MiB.
This commit is contained in:
Andreas Kling
2025-12-20 14:23:47 -06:00
committed by Andreas Kling
parent 9c8322d1b3
commit 63eccc5640
Notes: github-actions[bot] 2025-12-21 16:07:21 +00:00 
Author: https://github.com/awesomekling
Commit: https://github.com/LadybirdBrowser/ladybird/commit/63eccc56407
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/7209
9 changed files with 120 additions and 42 deletions
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69
Libraries/LibJS/Runtime/ECMAScriptFunctionObject.cpp
View File

@@ -34,23 +34,53 @@ namespace JS {
GC_DEFINE_ALLOCATOR(ECMAScriptFunctionObject);
GC::Ref<ECMAScriptFunctionObject> ECMAScriptFunctionObject::create(Realm& realm, Utf16FlyString name, ByteString source_text, Statement const& ecmascript_code, NonnullRefPtr<FunctionParameters const> parameters, i32 function_length, Vector<LocalVariable> local_variables_names, Environment* parent_environment, PrivateEnvironment* private_environment, FunctionKind kind, bool is_strict, FunctionParsingInsights parsing_insights, bool is_arrow_function, Variant<PropertyKey, PrivateName, Empty> class_field_initializer_name)
static GC::Ref<Object> prototype_for_function_kind(Realm& realm, FunctionKind kind)
{
Object* prototype = nullptr;
switch (kind) {
case FunctionKind::Normal:
prototype = realm.intrinsics().function_prototype();
break;
return realm.intrinsics().function_prototype();
case FunctionKind::Generator:
prototype = realm.intrinsics().generator_function_prototype();
break;
return realm.intrinsics().generator_function_prototype();
case FunctionKind::Async:
prototype = realm.intrinsics().async_function_prototype();
break;
return realm.intrinsics().async_function_prototype();
case FunctionKind::AsyncGenerator:
prototype = realm.intrinsics().async_generator_function_prototype();
break;
return realm.intrinsics().async_generator_function_prototype();
}
VERIFY_NOT_REACHED();
}
GC::Ref<ECMAScriptFunctionObject> ECMAScriptFunctionObject::create(Realm& realm, Utf16FlyString name, Utf16String source_text, Statement const& ecmascript_code, NonnullRefPtr<FunctionParameters const> parameters, i32 function_length, Vector<LocalVariable> local_variables_names, Environment* parent_environment, PrivateEnvironment* private_environment, FunctionKind kind, bool is_strict, FunctionParsingInsights parsing_insights, bool is_arrow_function, Variant<PropertyKey, PrivateName, Empty> class_field_initializer_name)
{
auto prototype = prototype_for_function_kind(realm, kind);
auto shared_data = realm.heap().allocate<SharedFunctionInstanceData>(
realm.vm(),
kind,
move(name),
function_length,
*parameters,
ecmascript_code,
Utf16View {},
is_strict,
is_arrow_function,
parsing_insights,
move(local_variables_names));
shared_data->m_class_field_initializer_name = move(class_field_initializer_name);
shared_data->m_source_text_owner = move(source_text);
shared_data->m_source_text = shared_data->m_source_text_owner.utf16_view();
return realm.create<ECMAScriptFunctionObject>(
move(shared_data),
parent_environment,
private_environment,
*prototype);
}
GC::Ref<ECMAScriptFunctionObject> ECMAScriptFunctionObject::create(Realm& realm, Utf16FlyString name, Utf16View source_text, Statement const& ecmascript_code, NonnullRefPtr<FunctionParameters const> parameters, i32 function_length, Vector<LocalVariable> local_variables_names, Environment* parent_environment, PrivateEnvironment* private_environment, FunctionKind kind, bool is_strict, FunctionParsingInsights parsing_insights, bool is_arrow_function, Variant<PropertyKey, PrivateName, Empty> class_field_initializer_name)
{
auto prototype = prototype_for_function_kind(realm, kind);
auto shared_data = realm.heap().allocate<SharedFunctionInstanceData>(
realm.vm(),
@@ -74,7 +104,7 @@ GC::Ref<ECMAScriptFunctionObject> ECMAScriptFunctionObject::create(Realm& realm,
*prototype);
}
GC::Ref<ECMAScriptFunctionObject> ECMAScriptFunctionObject::create(Realm& realm, Utf16FlyString name, Object& prototype, ByteString source_text, Statement const& ecmascript_code, NonnullRefPtr<FunctionParameters const> parameters, i32 function_length, Vector<LocalVariable> local_variables_names, Environment* parent_environment, PrivateEnvironment* private_environment, FunctionKind kind, bool is_strict, FunctionParsingInsights parsing_insights, bool is_arrow_function, Variant<PropertyKey, PrivateName, Empty> class_field_initializer_name)
GC::Ref<ECMAScriptFunctionObject> ECMAScriptFunctionObject::create(Realm& realm, Utf16FlyString name, Object& prototype, Utf16View source_text, Statement const& ecmascript_code, NonnullRefPtr<FunctionParameters const> parameters, i32 function_length, Vector<LocalVariable> local_variables_names, Environment* parent_environment, PrivateEnvironment* private_environment, FunctionKind kind, bool is_strict, FunctionParsingInsights parsing_insights, bool is_arrow_function, Variant<PropertyKey, PrivateName, Empty> class_field_initializer_name)
{
auto shared_data = realm.heap().allocate<SharedFunctionInstanceData>(
realm.vm(),
@@ -96,6 +126,20 @@ GC::Ref<ECMAScriptFunctionObject> ECMAScriptFunctionObject::create(Realm& realm,
prototype);
}
GC::Ref<ECMAScriptFunctionObject> ECMAScriptFunctionObject::create_from_function_data(
GC::Ref<Realm> realm,
GC::Ref<SharedFunctionInstanceData> shared_data,
GC::Ptr<Environment> parent_environment,
GC::Ptr<PrivateEnvironment> private_environment,
Object& prototype)
{
return realm->create<ECMAScriptFunctionObject>(
*shared_data,
parent_environment,
private_environment,
prototype);
}
GC::Ref<ECMAScriptFunctionObject> ECMAScriptFunctionObject::create_from_function_node(
FunctionNode const& function_node,
Utf16FlyString name,
@@ -137,7 +181,8 @@ GC::Ref<ECMAScriptFunctionObject> ECMAScriptFunctionObject::create_from_function
function_node.set_shared_data(shared_data);
}
return realm->create<ECMAScriptFunctionObject>(
return create_from_function_data(
realm,
*shared_data,
parent_environment,
private_environment,