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LibWeb+LibJS: Skip function environment allocation if possible

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If a function has the following properties:
- uses only local variables and registers
- does not use `this`
- does not use `new.target`
- does not use `super`
- does not use direct eval() calls

then it is possible to entirely skip function environment allocation
because it will never be used

This change adds gathering of information whether a function needs to
access `this` from environment and updates `prepare_for_ordinary_call()`
to skip allocation when possible.

For now, this optimisation is too aggressively blocked; e.g. if `this`
is used in a function scope, then all functions in outer scopes have to
allocate an environment. It could be improved in the future, although
this implementation already allows skipping >80% of environment
allocations on Discord, GitHub and Twitter.
This commit is contained in:
Aliaksandr Kalenik 2024-05-03 22:54:12 +02:00 • committed by Andreas Kling
commit 4d5823a5bc
Notes: sideshowbarker 2024-07-17 06:20:50 +09:00
12 changed files with 94 additions and 46 deletions
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7
Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.h
View file

@ -38,8 +38,8 @@ public:
Global,
};
static NonnullGCPtr<ECMAScriptFunctionObject> create(Realm&, DeprecatedFlyString name, ByteString source_text, Statement const& ecmascript_code, Vector<FunctionParameter> parameters, i32 m_function_length, Vector<DeprecatedFlyString> local_variables_names, Environment* parent_environment, PrivateEnvironment* private_environment, FunctionKind, bool is_strict, bool might_need_arguments_object = true, bool contains_direct_call_to_eval = true, bool is_arrow_function = false, Variant<PropertyKey, PrivateName, Empty> class_field_initializer_name = {});
static NonnullGCPtr<ECMAScriptFunctionObject> create(Realm&, DeprecatedFlyString name, Object& prototype, ByteString source_text, Statement const& ecmascript_code, Vector<FunctionParameter> parameters, i32 m_function_length, Vector<DeprecatedFlyString> local_variables_names, Environment* parent_environment, PrivateEnvironment* private_environment, FunctionKind, bool is_strict, bool might_need_arguments_object = true, bool contains_direct_call_to_eval = true, bool is_arrow_function = false, Variant<PropertyKey, PrivateName, Empty> class_field_initializer_name = {});
static NonnullGCPtr<ECMAScriptFunctionObject> create(Realm&, DeprecatedFlyString name, ByteString source_text, Statement const& ecmascript_code, Vector<FunctionParameter> parameters, i32 m_function_length, Vector<DeprecatedFlyString> local_variables_names, Environment* parent_environment, PrivateEnvironment* private_environment, FunctionKind, bool is_strict, UsesThis uses_this, bool might_need_arguments_object = true, bool contains_direct_call_to_eval = true, bool is_arrow_function = false, Variant<PropertyKey, PrivateName, Empty> class_field_initializer_name = {});
static NonnullGCPtr<ECMAScriptFunctionObject> create(Realm&, DeprecatedFlyString name, Object& prototype, ByteString source_text, Statement const& ecmascript_code, Vector<FunctionParameter> parameters, i32 m_function_length, Vector<DeprecatedFlyString> local_variables_names, Environment* parent_environment, PrivateEnvironment* private_environment, FunctionKind, bool is_strict, UsesThis uses_this, bool might_need_arguments_object = true, bool contains_direct_call_to_eval = true, bool is_arrow_function = false, Variant<PropertyKey, PrivateName, Empty> class_field_initializer_name = {});
virtual void initialize(Realm&) override;
virtual ~ECMAScriptFunctionObject() override = default;
@ -104,7 +104,7 @@ protected:
virtual Completion ordinary_call_evaluate_body();
private:
ECMAScriptFunctionObject(DeprecatedFlyString name, ByteString source_text, Statement const& ecmascript_code, Vector<FunctionParameter> parameters, i32 m_function_length, Vector<DeprecatedFlyString> local_variables_names, Environment* parent_environment, PrivateEnvironment* private_environment, Object& prototype, FunctionKind, bool is_strict, bool might_need_arguments_object, bool contains_direct_call_to_eval, bool is_arrow_function, Variant<PropertyKey, PrivateName, Empty> class_field_initializer_name);
ECMAScriptFunctionObject(DeprecatedFlyString name, ByteString source_text, Statement const& ecmascript_code, Vector<FunctionParameter> parameters, i32 m_function_length, Vector<DeprecatedFlyString> local_variables_names, Environment* parent_environment, PrivateEnvironment* private_environment, Object& prototype, FunctionKind, bool is_strict, UsesThis uses_this, bool might_need_arguments_object, bool contains_direct_call_to_eval, bool is_arrow_function, Variant<PropertyKey, PrivateName, Empty> class_field_initializer_name);
virtual bool is_ecmascript_function_object() const override { return true; }
virtual void visit_edges(Visitor&) override;
@ -161,6 +161,7 @@ private:
Vector<FunctionDeclaration const&> m_functions_to_initialize;
bool m_arguments_object_needed { false };
bool m_is_module_wrapper { false };
bool m_function_environment_needed { false };
Vector<VariableNameToInitialize> m_var_names_to_initialize_binding;
Vector<DeprecatedFlyString> m_function_names_to_initialize_binding;