4fa5748093
This gives FunctionNode a "might need arguments object" boolean flag and
sets it based on the simplest possible heuristic for this: if we
encounter an identifier called "arguments" or "eval" up to the next
(nested) function declaration or expression, we won't need an arguments
object. Otherwise, we *might* need one - the final decision is made in
the FunctionDeclarationInstantiation AO.
Now, this is obviously not perfect. Even if you avoid eval, something
like `foo.arguments` will still trigger a false positive - but it's a
start and already massively cuts down on needlessly allocated objects,
especially in real-world code that is often minified, and so a full
"arguments" identifier will be an actual arguments object more often
than not.
To illustrate the actual impact of this change, here's the number of
allocated arguments objects during a full test-js run:
Before:
- Unmapped arguments objects: 78765
- Mapped arguments objects: 2455
After:
- Unmapped arguments objects: 18
- Mapped arguments objects: 37
This results in a ~5% speedup of test-js on my Linux host machine, and
about 3.5% on i686 Serenity in QEMU (warm runs, average of 5).
The following microbenchmark (calling an empty function 1M times) runs
25% faster on Linux and 45% on Serenity:
function foo() {}
for (var i = 0; i < 1_000_000; ++i)
foo();
test262 reports no changes in either direction, apart from a speedup :^)
108 lines
4.6 KiB
C++
108 lines
4.6 KiB
C++
/*
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* Copyright (c) 2020-2021, Andreas Kling <kling@serenityos.org>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include <LibJS/AST.h>
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#include <LibJS/Bytecode/Generator.h>
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#include <LibJS/Runtime/FunctionObject.h>
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namespace JS {
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// 10.2 ECMAScript Function Objects, https://tc39.es/ecma262/#sec-ecmascript-function-objects
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class ECMAScriptFunctionObject final : public FunctionObject {
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JS_OBJECT(ECMAScriptFunctionObject, FunctionObject);
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public:
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enum class ConstructorKind : u8 {
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Base,
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Derived,
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};
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enum class ThisMode : u8 {
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Lexical,
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Strict,
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Global,
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};
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static ECMAScriptFunctionObject* create(GlobalObject&, FlyString name, Statement const& ecmascript_code, Vector<FunctionNode::Parameter> parameters, i32 m_function_length, Environment* parent_scope, FunctionKind, bool is_strict, bool might_need_arguments_object = true, bool is_arrow_function = false);
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ECMAScriptFunctionObject(FlyString name, Statement const& ecmascript_code, Vector<FunctionNode::Parameter> parameters, i32 m_function_length, Environment* parent_scope, Object& prototype, FunctionKind, bool is_strict, bool might_need_arguments_object, bool is_arrow_function);
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virtual void initialize(GlobalObject&) override;
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virtual ~ECMAScriptFunctionObject();
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Statement const& ecmascript_code() const { return m_ecmascript_code; }
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Vector<FunctionNode::Parameter> const& formal_parameters() const { return m_formal_parameters; };
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virtual Value call() override;
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virtual Value construct(FunctionObject& new_target) override;
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virtual const FlyString& name() const override { return m_name; };
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void set_name(const FlyString& name);
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void set_is_class_constructor() { m_is_class_constructor = true; };
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auto& bytecode_executable() const { return m_bytecode_executable; }
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Environment* environment() { return m_environment; }
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virtual Realm* realm() const override { return m_realm; }
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ConstructorKind constructor_kind() const { return m_constructor_kind; };
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void set_constructor_kind(ConstructorKind constructor_kind) { m_constructor_kind = constructor_kind; }
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ThisMode this_mode() const { return m_this_mode; }
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Object* home_object() const { return m_home_object; }
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void set_home_object(Object* home_object) { m_home_object = home_object; }
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struct InstanceField {
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StringOrSymbol name;
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ECMAScriptFunctionObject* initializer { nullptr };
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void define_field(VM& vm, Object& receiver) const;
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};
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Vector<InstanceField> const& fields() const { return m_fields; }
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void add_field(StringOrSymbol property_key, ECMAScriptFunctionObject* initializer) { m_fields.empend(property_key, initializer); }
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// This is for IsSimpleParameterList (static semantics)
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bool has_simple_parameter_list() const { return m_has_simple_parameter_list; }
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virtual bool has_constructor() const override { return true; }
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protected:
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virtual bool is_strict_mode() const final { return m_strict; }
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private:
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virtual bool is_ecmascript_function_object() const override { return true; }
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virtual FunctionEnvironment* new_function_environment(Object* new_target) override;
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virtual void visit_edges(Visitor&) override;
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ThrowCompletionOr<void> function_declaration_instantiation(Interpreter*);
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Value execute_function_body();
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// Internal Slots of ECMAScript Function Objects, https://tc39.es/ecma262/#table-internal-slots-of-ecmascript-function-objects
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Environment* m_environment { nullptr }; // [[Environment]]
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Vector<FunctionNode::Parameter> const m_formal_parameters; // [[FormalParameters]]
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NonnullRefPtr<Statement> m_ecmascript_code; // [[ECMAScriptCode]]
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ConstructorKind m_constructor_kind { ConstructorKind::Base }; // [[ConstructorKind]]
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Realm* m_realm { nullptr }; // [[Realm]]
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ThisMode m_this_mode { ThisMode::Global }; // [[ThisMode]]
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bool m_strict { false }; // [[Strict]]
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Object* m_home_object { nullptr }; // [[HomeObject]]
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Vector<InstanceField> m_fields; // [[Fields]]
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bool m_is_class_constructor { false }; // [[IsClassConstructor]]
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FlyString m_name;
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Optional<Bytecode::Executable> m_bytecode_executable;
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i32 m_function_length { 0 };
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FunctionKind m_kind { FunctionKind::Regular };
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bool m_might_need_arguments_object { true };
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bool m_is_arrow_function { false };
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bool m_has_simple_parameter_list { false };
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};
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}
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