LibJS: Add a bunch of fast_is<T> to avoid slow RTTI in hot code

Userland/Libraries/LibJS/AST.h

@@ -50,6 +50,17 @@ public:
 
     String class_name() const;
 
+    template<typename T>
+    bool fast_is() const = delete;
+
+    virtual bool is_new_expression() const { return false; }
+    virtual bool is_member_expression() const { return false; }
+    virtual bool is_super_expression() const { return false; }
+    virtual bool is_expression_statement() const { return false; }
+    virtual bool is_identifier() const { return false; }
+    virtual bool is_scope_node() const { return false; }
+    virtual bool is_program() const { return false; }
+
 protected:
     ASTNode(SourceRange source_range)
         : m_source_range(move(source_range))
@@ -108,6 +119,8 @@ public:
     Expression const& expression() const { return m_expression; };
 
 private:
+    virtual bool is_expression_statement() const override { return true; }
+
     NonnullRefPtr<Expression> m_expression;
 };
 
@@ -142,6 +155,8 @@ protected:
     }
 
 private:
+    virtual bool is_scope_node() const final { return true; }
+
     NonnullRefPtrVector<Statement> m_children;
     NonnullRefPtrVector<VariableDeclaration> m_variables;
     NonnullRefPtrVector<FunctionDeclaration> m_functions;
@@ -160,6 +175,8 @@ public:
     void set_strict_mode() { m_is_strict_mode = true; }
 
 private:
+    virtual bool is_program() const override { return true; }
+
     bool m_is_strict_mode { false };
 };
 
@@ -765,6 +782,8 @@ public:
     virtual void generate_bytecode(Bytecode::Generator&) const override;
 
 private:
+    virtual bool is_identifier() const override { return true; }
+
     FlyString m_string;
 };
 
@@ -808,6 +827,8 @@ public:
 
     virtual Value execute(Interpreter&, GlobalObject&) const override;
     virtual void dump(int indent) const override;
+
+    virtual bool is_super_expression() const override { return true; }
 };
 
 class ClassExpression final : public Expression {
@@ -908,6 +929,8 @@ public:
         : CallExpression(move(source_range), move(callee), move(arguments))
     {
     }
+
+    virtual bool is_new_expression() const override { return true; }
 };
 
 enum class AssignmentOp {
@@ -1176,6 +1199,8 @@ public:
     String to_string_approximation() const;
 
 private:
+    virtual bool is_member_expression() const override { return true; }
+
     NonnullRefPtr<Expression> m_object;
     NonnullRefPtr<Expression> m_property;
     bool m_computed { false };
@@ -1378,4 +1403,25 @@ void BindingPattern::for_each_assigned_name(C&& callback) const
     }
 }
 
+template<>
+inline bool ASTNode::fast_is<NewExpression>() const { return is_new_expression(); }
+
+template<>
+inline bool ASTNode::fast_is<MemberExpression>() const { return is_member_expression(); }
+
+template<>
+inline bool ASTNode::fast_is<SuperExpression>() const { return is_super_expression(); }
+
+template<>
+inline bool ASTNode::fast_is<Identifier>() const { return is_identifier(); }
+
+template<>
+inline bool ASTNode::fast_is<ExpressionStatement>() const { return is_expression_statement(); }
+
+template<>
+inline bool ASTNode::fast_is<ScopeNode>() const { return is_scope_node(); }
+
+template<>
+inline bool ASTNode::fast_is<Program>() const { return is_program(); }
+
 }

Userland/Libraries/LibJS/Runtime/LexicalEnvironment.h

@@ -66,6 +66,7 @@ public:
     EnvironmentRecordType type() const { return m_environment_record_type; }
 
 private:
+    virtual bool is_lexical_environment() const override { return true; }
     virtual void visit_edges(Visitor&) override;
 
     EnvironmentRecordType m_environment_record_type : 8 { EnvironmentRecordType::Declarative };
@@ -78,4 +79,7 @@ private:
     Function* m_current_function { nullptr };
 };
 
+template<>
+inline bool Object::fast_is<LexicalEnvironment>() const { return is_lexical_environment(); }
+
 }

Userland/Libraries/LibJS/Runtime/NativeFunction.h

@@ -35,9 +35,13 @@ protected:
 
 private:
     virtual LexicalEnvironment* create_environment() override final;
+    virtual bool is_native_function() const final { return true; }
 
     FlyString m_name;
     AK::Function<Value(VM&, GlobalObject&)> m_native_function;
 };
 
+template<>
+inline bool Object::fast_is<NativeFunction>() const { return is_native_function(); }
+
 }

Userland/Libraries/LibJS/Runtime/Object.h

@@ -106,6 +106,9 @@ public:
     virtual bool is_typed_array() const { return false; }
     virtual bool is_string_object() const { return false; }
     virtual bool is_global_object() const { return false; }
+    virtual bool is_proxy_object() const { return false; }
+    virtual bool is_native_function() const { return false; }
+    virtual bool is_lexical_environment() const { return false; }
 
     virtual const char* class_name() const override { return "Object"; }
     virtual void visit_edges(Cell::Visitor&) override;

Userland/Libraries/LibJS/Runtime/ProxyObject.h

@@ -46,10 +46,14 @@ private:
     virtual void visit_edges(Visitor&) override;
 
     virtual bool is_function() const override { return m_target.is_function(); }
+    virtual bool is_proxy_object() const final { return true; }
 
     Object& m_target;
     Object& m_handler;
     bool m_is_revoked { false };
 };
 
+template<>
+inline bool Object::fast_is<ProxyObject>() const { return is_proxy_object(); }
+
 }