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https://github.com/SerenityOS/serenity
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LibJS: Don't evaluate computed MemberExpression LHS twice in assignments
The following snippet would cause "i" to be incremented twice(!): let a = [] let i = 0 a[++i] += 0 This patch solves the issue by remembering the base object and property name for computed MemberExpression LHS in codegen. We the store the result of the assignment to the same object and property (instead of computing the LHS again). 3 new passes on test262. :^)
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2083376618
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@ -525,7 +525,7 @@ Bytecode::CodeGenerationErrorOr<void> AssignmentExpression::generate_bytecode(By
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VERIFY(m_lhs.has<NonnullRefPtr<Expression const>>());
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auto& lhs = m_lhs.get<NonnullRefPtr<Expression const>>();
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TRY(generator.emit_load_from_reference(lhs));
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auto reference_registers = TRY(generator.emit_load_from_reference(lhs));
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Bytecode::BasicBlock* rhs_block_ptr { nullptr };
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Bytecode::BasicBlock* end_block_ptr { nullptr };
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@ -615,7 +615,10 @@ Bytecode::CodeGenerationErrorOr<void> AssignmentExpression::generate_bytecode(By
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};
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}
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TRY(generator.emit_store_to_reference(lhs));
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if (reference_registers.has_value())
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TRY(generator.emit_store_to_reference(*reference_registers));
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else
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TRY(generator.emit_store_to_reference(lhs));
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if (end_block_ptr) {
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generator.emit<Bytecode::Op::Jump>(Bytecode::Label { *end_block_ptr });
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@ -1049,7 +1052,8 @@ Bytecode::CodeGenerationErrorOr<void> ArrayExpression::generate_bytecode(Bytecod
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Bytecode::CodeGenerationErrorOr<void> MemberExpression::generate_bytecode(Bytecode::Generator& generator) const
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{
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Bytecode::Generator::SourceLocationScope scope(generator, *this);
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return generator.emit_load_from_reference(*this);
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(void)TRY(generator.emit_load_from_reference(*this));
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return {};
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}
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Bytecode::CodeGenerationErrorOr<void> FunctionDeclaration::generate_bytecode(Bytecode::Generator& generator) const
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@ -2249,7 +2253,7 @@ Bytecode::CodeGenerationErrorOr<void> TaggedTemplateLiteral::generate_bytecode(B
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Bytecode::CodeGenerationErrorOr<void> UpdateExpression::generate_bytecode(Bytecode::Generator& generator) const
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{
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Bytecode::Generator::SourceLocationScope scope(generator, *this);
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TRY(generator.emit_load_from_reference(*m_argument));
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auto reference_registers = TRY(generator.emit_load_from_reference(*m_argument));
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Optional<Bytecode::Register> previous_value_for_postfix_reg;
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if (!m_prefixed) {
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@ -2263,7 +2267,10 @@ Bytecode::CodeGenerationErrorOr<void> UpdateExpression::generate_bytecode(Byteco
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else
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generator.emit<Bytecode::Op::Decrement>();
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TRY(generator.emit_store_to_reference(*m_argument));
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if (reference_registers.has_value())
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TRY(generator.emit_store_to_reference(*reference_registers));
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else
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TRY(generator.emit_store_to_reference(*m_argument));
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if (!m_prefixed)
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generator.emit<Bytecode::Op::Load>(*previous_value_for_postfix_reg);
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@ -189,12 +189,12 @@ CodeGenerationErrorOr<Generator::ReferenceRegisters> Generator::emit_super_refer
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};
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}
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CodeGenerationErrorOr<void> Generator::emit_load_from_reference(JS::ASTNode const& node)
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CodeGenerationErrorOr<Optional<Generator::ReferenceRegisters>> Generator::emit_load_from_reference(JS::ASTNode const& node)
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{
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if (is<Identifier>(node)) {
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auto& identifier = static_cast<Identifier const&>(node);
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TRY(identifier.generate_bytecode(*this));
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return {};
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return Optional<ReferenceRegisters> {};
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}
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if (is<MemberExpression>(node)) {
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auto& expression = static_cast<MemberExpression const&>(node);
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@ -213,15 +213,24 @@ CodeGenerationErrorOr<void> Generator::emit_load_from_reference(JS::ASTNode cons
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auto identifier_table_ref = intern_identifier(verify_cast<Identifier>(expression.property()).string());
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emit_get_by_id_with_this(identifier_table_ref, super_reference.this_value);
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}
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return super_reference;
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} else {
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TRY(expression.object().generate_bytecode(*this));
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if (expression.is_computed()) {
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auto object_reg = allocate_register();
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emit<Bytecode::Op::Store>(object_reg);
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TRY(expression.property().generate_bytecode(*this));
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auto property_reg = allocate_register();
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emit<Bytecode::Op::Store>(property_reg);
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emit<Bytecode::Op::GetByValue>(object_reg);
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return ReferenceRegisters {
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.base = object_reg,
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.referenced_name = property_reg,
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.this_value = object_reg,
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};
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} else if (expression.property().is_identifier()) {
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auto identifier_table_ref = intern_identifier(verify_cast<Identifier>(expression.property()).string());
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emit_get_by_id(identifier_table_ref);
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@ -235,7 +244,7 @@ CodeGenerationErrorOr<void> Generator::emit_load_from_reference(JS::ASTNode cons
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};
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}
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}
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return {};
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return Optional<ReferenceRegisters> {};
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}
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VERIFY_NOT_REACHED();
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}
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@ -306,6 +315,15 @@ CodeGenerationErrorOr<void> Generator::emit_store_to_reference(JS::ASTNode const
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};
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}
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CodeGenerationErrorOr<void> Generator::emit_store_to_reference(ReferenceRegisters const& reference_registers)
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{
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if (reference_registers.base == reference_registers.this_value)
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emit<Bytecode::Op::PutByValue>(reference_registers.base, reference_registers.referenced_name.value());
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else
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emit<Bytecode::Op::PutByValueWithThis>(reference_registers.base, reference_registers.referenced_name.value(), reference_registers.this_value);
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return {};
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}
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CodeGenerationErrorOr<void> Generator::emit_delete_reference(JS::ASTNode const& node)
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{
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if (is<Identifier>(node)) {
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@ -74,15 +74,17 @@ public:
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op->set_source_record({ m_current_ast_node->start_offset(), m_current_ast_node->end_offset() });
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}
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CodeGenerationErrorOr<void> emit_load_from_reference(JS::ASTNode const&);
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struct ReferenceRegisters {
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Register base; // [[Base]]
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Optional<Register> referenced_name; // [[ReferencedName]]
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Register this_value; // [[ThisValue]]
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};
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CodeGenerationErrorOr<Optional<ReferenceRegisters>> emit_load_from_reference(JS::ASTNode const&);
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CodeGenerationErrorOr<void> emit_store_to_reference(JS::ASTNode const&);
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CodeGenerationErrorOr<void> emit_store_to_reference(ReferenceRegisters const&);
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CodeGenerationErrorOr<void> emit_delete_reference(JS::ASTNode const&);
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struct ReferenceRegisters {
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Register base; // [[Base]]
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Optional<Bytecode::Register> referenced_name; // [[ReferencedName]]
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Register this_value; // [[ThisValue]]
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};
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CodeGenerationErrorOr<ReferenceRegisters> emit_super_reference(MemberExpression const&);
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void emit_set_variable(JS::Identifier const& identifier, Bytecode::Op::SetVariable::InitializationMode initialization_mode = Bytecode::Op::SetVariable::InitializationMode::Set, Bytecode::Op::EnvironmentMode mode = Bytecode::Op::EnvironmentMode::Lexical);
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