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LibJS/Bytecode: Add and use copy_if_needed_to_preserve_evaluation_order

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This is a new Bytecode::Generator helper that takes an operand and
returns the same operand, or a copy of it, in case a copy is required
to preserve correct evaluation order.

This can be used in a bunch of places where we're worried about
clobbering some value after obtaining it.

Practically, locals are always copied, and temporary registers as well
as constants are returned as-is.
This commit is contained in:
Andreas Kling 2024-06-01 10:00:32 +02:00
parent 0acf89234c
commit c372a084a2
Notes: sideshowbarker 2024-07-17 23:02:37 +09:00 
Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/c372a084a2
Pull-request: https://github.com/SerenityOS/serenity/pull/24524
3 changed files with 18 additions and 34 deletions
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41
Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp
View File

@ -493,9 +493,7 @@ Bytecode::CodeGenerationErrorOr<Optional<ScopedOperand>> AssignmentExpression::g
if (expression.is_computed()) {
auto property = TRY(expression.property().generate_bytecode(generator)).value();
computed_property = generator.allocate_register();
generator.emit<Bytecode::Op::Mov>(*computed_property, property);
computed_property = generator.copy_if_needed_to_preserve_evaluation_order(property);
// To be continued later with PutByValue.
} else if (expression.property().is_identifier()) {
// Do nothing, this will be handled by PutById later.
@ -1108,14 +1106,7 @@ Bytecode::CodeGenerationErrorOr<Optional<ScopedOperand>> ArrayExpression::genera
for (auto it = m_elements.begin(); it != first_spread; ++it) {
if (*it) {
auto value = TRY((*it)->generate_bytecode(generator)).value();
// NOTE: We don't need to protect temporary registers or constants from being clobbered.
if (value.operand().is_register() || value.operand().is_constant()) {
args.append(move(value));
} else {
auto reg = generator.allocate_register();
generator.emit<Bytecode::Op::Mov>(Bytecode::Operand(reg), value);
args.append(move(reg));
}
args.append(generator.copy_if_needed_to_preserve_evaluation_order(value));
} else {
args.append(generator.add_constant(Value()));
}
@ -1241,9 +1232,8 @@ static Bytecode::CodeGenerationErrorOr<void> generate_object_binding_pattern_byt
auto property_name = TRY(expression->generate_bytecode(generator)).value();
if (has_rest) {
auto excluded_name = generator.allocate_register();
auto excluded_name = generator.copy_if_needed_to_preserve_evaluation_order(property_name);
excluded_property_names.append(excluded_name);
generator.emit<Bytecode::Op::Mov>(excluded_name, property_name);
}
generator.emit<Bytecode::Op::GetByValue>(value, object, property_name);
@ -1275,8 +1265,7 @@ static Bytecode::CodeGenerationErrorOr<void> generate_object_binding_pattern_byt
if (alias.has<NonnullRefPtr<BindingPattern const>>()) {
auto& binding_pattern = *alias.get<NonnullRefPtr<BindingPattern const>>();
auto nested_value = generator.allocate_register();
generator.emit<Bytecode::Op::Mov>(nested_value, value);
auto nested_value = generator.copy_if_needed_to_preserve_evaluation_order(value);
TRY(binding_pattern.generate_bytecode(generator, initialization_mode, nested_value, create_variables));
} else if (alias.has<Empty>()) {
if (name.has<NonnullRefPtr<Expression const>>()) {
@ -1665,14 +1654,7 @@ Bytecode::CodeGenerationErrorOr<Optional<ScopedOperand>> CallExpression::generat
// NOTE: If the callee isn't already a temporary, we copy it to a new register
// to avoid overwriting it while evaluating arguments.
auto callee = [&]() -> ScopedOperand {
if (!original_callee->operand().is_register()) {
auto callee = generator.allocate_register();
generator.emit<Bytecode::Op::Mov>(callee, *original_callee);
return callee;
}
return *original_callee;
}();
auto callee = generator.copy_if_needed_to_preserve_evaluation_order(original_callee.value());
Bytecode::Op::CallType call_type;
if (is<NewExpression>(*this)) {
@ -1698,14 +1680,7 @@ Bytecode::CodeGenerationErrorOr<Optional<ScopedOperand>> CallExpression::generat
argument_operands.ensure_capacity(arguments().size());
for (auto const& argument : arguments()) {
auto argument_value = TRY(argument.value->generate_bytecode(generator)).value();
// NOTE: We don't need to protect temporary registers or constants from being clobbered.
if (argument_value.operand().is_register() || argument_value.operand().is_constant()) {
argument_operands.append(argument_value);
} else {
auto temporary = generator.allocate_register();
generator.emit<Bytecode::Op::Mov>(temporary, argument_value);
argument_operands.append(temporary);
}
argument_operands.append(generator.copy_if_needed_to_preserve_evaluation_order(argument_value));
}
generator.emit_with_extra_operand_slots<Bytecode::Op::Call>(
argument_operands.size(),
@ -2431,9 +2406,7 @@ Bytecode::CodeGenerationErrorOr<Optional<ScopedOperand>> TaggedTemplateLiteral::
raw_string_regs.ensure_capacity(m_template_literal->raw_strings().size());
for (auto& raw_string : m_template_literal->raw_strings()) {
auto value = TRY(raw_string->generate_bytecode(generator)).value();
auto raw_string_reg = generator.allocate_register();
generator.emit<Bytecode::Op::Mov>(raw_string_reg, value);
raw_string_regs.append(move(raw_string_reg));
raw_string_regs.append(generator.copy_if_needed_to_preserve_evaluation_order(value));
}
auto raw_strings_array = generator.allocate_register();

9
Userland/Libraries/LibJS/Bytecode/Generator.cpp
View File

@ -1156,4 +1156,13 @@ void Generator::emit_jump_if(ScopedOperand const& condition, Label true_target,
emit<Op::JumpIf>(condition, true_target, false_target);
}
ScopedOperand Generator::copy_if_needed_to_preserve_evaluation_order(ScopedOperand const& operand)
{
if (!operand.operand().is_local())
return operand;
auto new_register = allocate_register();
emit<Bytecode::Op::Mov>(new_register, operand);
return new_register;
}
}

2
Userland/Libraries/LibJS/Bytecode/Generator.h
View File

@ -308,6 +308,8 @@ public:
m_boundaries.take_last();
}
[[nodiscard]] ScopedOperand copy_if_needed_to_preserve_evaluation_order(ScopedOperand const&);
[[nodiscard]] ScopedOperand get_this(Optional<ScopedOperand> preferred_dst = {});
void emit_get_by_id(ScopedOperand dst, ScopedOperand base, IdentifierTableIndex property_identifier, Optional<IdentifierTableIndex> base_identifier = {});