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ladybird/Libraries/LibJS/Bytecode/ASTCodegen.cpp
Andreas Kling 49f2f1e7cd LibJS: Skip unnecessary Mov in emit_load_from_reference for reads 
When MemberExpression::generate_bytecode calls emit_load_from_reference,
it only uses the loaded_value and discards the reference operands. For
computed member expressions (e.g. a[0]), this was generating an
unnecessary Mov to save the property register for potential store-back.

Add a ReferenceMode parameter to emit_load_from_reference. When LoadOnly
is passed, the computed property path skips the register save and Mov.
2026-02-15 23:21:46 +01:00

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/*
* Copyright (c) 2021-2025, Andreas Kling <andreas@ladybird.org>
* Copyright (c) 2021, Linus Groh <linusg@serenityos.org>
* Copyright (c) 2021, Gunnar Beutner <gbeutner@serenityos.org>
* Copyright (c) 2021, Marcin Gasperowicz <xnooga@gmail.com>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/Find.h>
#include <AK/Queue.h>
#include <LibJS/AST.h>
#include <LibJS/Bytecode/Generator.h>
#include <LibJS/Bytecode/Instruction.h>
#include <LibJS/Bytecode/Op.h>
#include <LibJS/Bytecode/Register.h>
#include <LibJS/Bytecode/StringTable.h>
#include <LibJS/Runtime/Environment.h>
#include <LibJS/Runtime/ErrorTypes.h>
#include <LibJS/Runtime/PrimitiveString.h>
#include <LibJS/Runtime/SharedFunctionInstanceData.h>
#include <LibJS/Runtime/VM.h>
#include <LibJS/Runtime/ValueInlines.h>
namespace JS {
using namespace JS::Bytecode;
static String bigint_literal_to_decimal_string(BigIntLiteral const& literal)
{
auto const& raw = literal.raw_value();
auto integer = [&] {
if (raw[0] == '0' && raw.length() >= 3) {
if (raw[1] == 'x' || raw[1] == 'X')
return MUST(Crypto::SignedBigInteger::from_base(16, raw.substring(2, raw.length() - 3)));
if (raw[1] == 'o' || raw[1] == 'O')
return MUST(Crypto::SignedBigInteger::from_base(8, raw.substring(2, raw.length() - 3)));
if (raw[1] == 'b' || raw[1] == 'B')
return MUST(Crypto::SignedBigInteger::from_base(2, raw.substring(2, raw.length() - 3)));
}
return MUST(Crypto::SignedBigInteger::from_base(10, raw.substring(0, raw.length() - 1)));
}();
return MUST(integer.to_base(10));
}
static ScopedOperand choose_dst(Bytecode::Generator& generator, Optional<ScopedOperand> const& preferred_dst)
{
if (preferred_dst.has_value())
return preferred_dst.value();
return generator.allocate_register();
}
Optional<ScopedOperand> ASTNode::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
generator.emit_todo(class_name());
return {};
}
Optional<ScopedOperand> ScopeNode::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
bool did_create_lexical_environment = false;
if (is<BlockStatement>(*this)) {
if (has_lexical_declarations()) {
did_create_lexical_environment = generator.emit_block_declaration_instantiation(*this);
}
} else if (is<Program>(*this)) {
// GlobalDeclarationInstantiation is handled by the C++ AO.
} else {
// FunctionDeclarationInstantiation is handled by the C++ AO.
}
Optional<ScopedOperand> last_result;
for (auto& child : children()) {
auto result = child->generate_bytecode(generator);
if (generator.must_propagate_completion()) {
if (result.has_value()) {
last_result = result;
if (!generator.is_current_block_terminated()) {
if (auto completion_reg = generator.current_completion_register(); completion_reg.has_value())
generator.emit_mov(*completion_reg, *result);
}
}
}
if (generator.is_current_block_terminated())
break;
}
if (did_create_lexical_environment)
generator.end_variable_scope();
return last_result;
}
Optional<ScopedOperand> EmptyStatement::generate_bytecode(Bytecode::Generator&, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
return Optional<ScopedOperand> {};
}
Optional<ScopedOperand> ExpressionStatement::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
return m_expression->generate_bytecode(generator);
}
static ThrowCompletionOr<ScopedOperand> constant_fold_unary_expression(Generator& generator, Value value, UnaryOp op)
{
switch (op) {
case UnaryOp::Minus:
return generator.add_constant(Value(-TRY(value.to_double(generator.vm()))));
case UnaryOp::Plus:
return generator.add_constant(Value(+TRY(value.to_double(generator.vm()))));
case UnaryOp::BitwiseNot:
return generator.add_constant(TRY(bitwise_not(generator.vm(), value)));
case UnaryOp::Not:
return generator.add_constant(Value(!value.to_boolean()));
default:
return throw_completion(js_null());
}
}
static Optional<ScopedOperand> try_constant_fold_unary_expression(Generator& generator, ScopedOperand& operand, UnaryOp op)
{
if (operand.operand().is_constant()) {
// OPTIMIZATION: Do some basic constant folding for unary operations on numbers.
auto value = generator.get_constant(operand);
if (auto result = constant_fold_unary_expression(generator, value, op); !result.is_error())
return result.release_value();
}
return {};
}
static ThrowCompletionOr<ScopedOperand> constant_fold_binary_expression(Generator& generator, Value lhs, Value rhs, BinaryOp m_op)
{
switch (m_op) {
case BinaryOp::Addition:
return generator.add_constant(TRY(add(generator.vm(), lhs, rhs)));
case BinaryOp::Subtraction:
return generator.add_constant(TRY(sub(generator.vm(), lhs, rhs)));
case BinaryOp::Multiplication:
return generator.add_constant(TRY(mul(generator.vm(), lhs, rhs)));
case BinaryOp::Division:
return generator.add_constant(TRY(div(generator.vm(), lhs, rhs)));
case BinaryOp::Modulo:
return generator.add_constant(TRY(mod(generator.vm(), lhs, rhs)));
case BinaryOp::Exponentiation:
return generator.add_constant(TRY(exp(generator.vm(), lhs, rhs)));
case BinaryOp::GreaterThan:
return generator.add_constant(Value { TRY(greater_than(generator.vm(), lhs, rhs)) });
case BinaryOp::GreaterThanEquals:
return generator.add_constant(Value { TRY(greater_than_equals(generator.vm(), lhs, rhs)) });
case BinaryOp::LessThan:
return generator.add_constant(Value { TRY(less_than(generator.vm(), lhs, rhs)) });
case BinaryOp::LessThanEquals:
return generator.add_constant(Value { TRY(less_than_equals(generator.vm(), lhs, rhs)) });
case BinaryOp::LooselyInequals:
return generator.add_constant(Value(!TRY(is_loosely_equal(generator.vm(), lhs, rhs))));
case BinaryOp::LooselyEquals:
return generator.add_constant(Value(TRY(is_loosely_equal(generator.vm(), lhs, rhs))));
case BinaryOp::StrictlyInequals:
return generator.add_constant(Value(!is_strictly_equal(lhs, rhs)));
case BinaryOp::StrictlyEquals:
return generator.add_constant(Value(is_strictly_equal(lhs, rhs)));
case BinaryOp::BitwiseAnd:
return generator.add_constant(TRY(bitwise_and(generator.vm(), lhs, rhs)));
case BinaryOp::BitwiseOr:
return generator.add_constant(TRY(bitwise_or(generator.vm(), lhs, rhs)));
case BinaryOp::BitwiseXor:
return generator.add_constant(TRY(bitwise_xor(generator.vm(), lhs, rhs)));
case BinaryOp::LeftShift:
return generator.add_constant(TRY(left_shift(generator.vm(), lhs, rhs)));
case BinaryOp::RightShift:
return generator.add_constant(TRY(right_shift(generator.vm(), lhs, rhs)));
case BinaryOp::UnsignedRightShift:
return generator.add_constant(TRY(unsigned_right_shift(generator.vm(), lhs, rhs)));
case BinaryOp::In:
case BinaryOp::InstanceOf:
// NOTE: We just have to throw *something* to indicate that this is not a constant foldable operation.
return throw_completion(js_null());
default:
VERIFY_NOT_REACHED();
}
}
Optional<ScopedOperand> BinaryExpression::generate_bytecode(Bytecode::Generator& generator, Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
if (m_op == BinaryOp::In && is<PrivateIdentifier>(*m_lhs)) {
auto const& private_identifier = static_cast<PrivateIdentifier const&>(*m_lhs).string();
auto base = m_rhs->generate_bytecode(generator).value();
auto dst = choose_dst(generator, preferred_dst);
generator.emit<Bytecode::Op::HasPrivateId>(dst, base, generator.intern_identifier(private_identifier));
return dst;
}
// OPTIMIZATION: If LHS and/or RHS are numeric literals, we make sure they are converted to i32/u32
// as appropriate, to avoid having to perform these conversions at runtime.
auto get_left_side = [&](Expression const& side) -> Optional<ScopedOperand> {
switch (m_op) {
case BinaryOp::BitwiseAnd:
case BinaryOp::BitwiseOr:
case BinaryOp::BitwiseXor:
case BinaryOp::LeftShift:
case BinaryOp::RightShift:
case BinaryOp::UnsignedRightShift:
// LHS will always be converted to i32 for these ops.
if (side.is_numeric_literal()) {
auto value = MUST(static_cast<NumericLiteral const&>(side).value().to_i32(generator.vm()));
return generator.add_constant(Value(value));
}
break;
default:
break;
}
return side.generate_bytecode(generator);
};
auto get_right_side = [&](Expression const& side) -> Optional<ScopedOperand> {
switch (m_op) {
case BinaryOp::BitwiseAnd:
case BinaryOp::BitwiseOr:
case BinaryOp::BitwiseXor:
// RHS will always be converted to i32 for these ops.
if (side.is_numeric_literal()) {
auto value = MUST(static_cast<NumericLiteral const&>(side).value().to_i32(generator.vm()));
return generator.add_constant(Value(value));
}
break;
case BinaryOp::LeftShift:
case BinaryOp::RightShift:
case BinaryOp::UnsignedRightShift:
// RHS will always be converted to u32 for these ops.
if (side.is_numeric_literal()) {
auto value = MUST(static_cast<NumericLiteral const&>(side).value().to_u32(generator.vm()));
return generator.add_constant(Value(value));
}
break;
default:
break;
}
return side.generate_bytecode(generator);
};
auto lhs = get_left_side(*m_lhs).value();
auto rhs = get_right_side(*m_rhs).value();
auto dst = choose_dst(generator, preferred_dst);
// OPTIMIZATION: Do some basic constant folding for binary operations.
if (lhs.operand().is_constant() && rhs.operand().is_constant()) {
if (auto result = constant_fold_binary_expression(generator, generator.get_constant(lhs), generator.get_constant(rhs), m_op); !result.is_error())
return result.release_value();
}
switch (m_op) {
case BinaryOp::Addition:
generator.emit<Bytecode::Op::Add>(dst, lhs, rhs);
break;
case BinaryOp::Subtraction:
generator.emit<Bytecode::Op::Sub>(dst, lhs, rhs);
break;
case BinaryOp::Multiplication:
generator.emit<Bytecode::Op::Mul>(dst, lhs, rhs);
break;
case BinaryOp::Division:
generator.emit<Bytecode::Op::Div>(dst, lhs, rhs);
break;
case BinaryOp::Modulo:
generator.emit<Bytecode::Op::Mod>(dst, lhs, rhs);
break;
case BinaryOp::Exponentiation:
generator.emit<Bytecode::Op::Exp>(dst, lhs, rhs);
break;
case BinaryOp::GreaterThan:
generator.emit<Bytecode::Op::GreaterThan>(dst, lhs, rhs);
break;
case BinaryOp::GreaterThanEquals:
generator.emit<Bytecode::Op::GreaterThanEquals>(dst, lhs, rhs);
break;
case BinaryOp::LessThan:
generator.emit<Bytecode::Op::LessThan>(dst, lhs, rhs);
break;
case BinaryOp::LessThanEquals:
generator.emit<Bytecode::Op::LessThanEquals>(dst, lhs, rhs);
break;
case BinaryOp::LooselyInequals:
generator.emit<Bytecode::Op::LooselyInequals>(dst, lhs, rhs);
break;
case BinaryOp::LooselyEquals:
generator.emit<Bytecode::Op::LooselyEquals>(dst, lhs, rhs);
break;
case BinaryOp::StrictlyInequals:
generator.emit<Bytecode::Op::StrictlyInequals>(dst, lhs, rhs);
break;
case BinaryOp::StrictlyEquals:
generator.emit<Bytecode::Op::StrictlyEquals>(dst, lhs, rhs);
break;
case BinaryOp::BitwiseAnd:
generator.emit<Bytecode::Op::BitwiseAnd>(dst, lhs, rhs);
break;
case BinaryOp::BitwiseOr:
if (rhs.operand().is_constant() && generator.get_constant(rhs).is_int32() && generator.get_constant(rhs).as_i32() == 0) {
// OPTIMIZATION: x | 0 == ToInt32(x)
generator.emit<Bytecode::Op::ToInt32>(dst, lhs);
break;
}
generator.emit<Bytecode::Op::BitwiseOr>(dst, lhs, rhs);
break;
case BinaryOp::BitwiseXor:
generator.emit<Bytecode::Op::BitwiseXor>(dst, lhs, rhs);
break;
case BinaryOp::LeftShift:
generator.emit<Bytecode::Op::LeftShift>(dst, lhs, rhs);
break;
case BinaryOp::RightShift:
generator.emit<Bytecode::Op::RightShift>(dst, lhs, rhs);
break;
case BinaryOp::UnsignedRightShift:
generator.emit<Bytecode::Op::UnsignedRightShift>(dst, lhs, rhs);
break;
case BinaryOp::In:
generator.emit<Bytecode::Op::In>(dst, lhs, rhs);
break;
case BinaryOp::InstanceOf:
generator.emit<Bytecode::Op::InstanceOf>(dst, lhs, rhs);
break;
default:
VERIFY_NOT_REACHED();
}
return dst;
}
static Optional<ScopedOperand> constant_fold_logical_expression(Bytecode::Generator& generator, Optional<ScopedOperand> preferred_dst, ScopedOperand& lhs, LogicalExpression const* expr)
{
auto constant = generator.get_constant(lhs);
auto return_rhs = [&] -> Optional<ScopedOperand> {
auto dst = choose_dst(generator, preferred_dst);
auto rhs = expr->rhs()->generate_bytecode(generator, dst).value();
if (rhs.operand().is_constant())
return rhs;
generator.emit_mov(dst, rhs);
return dst;
};
switch (expr->op()) {
case LogicalOp::And:
if (constant.to_boolean_slow_case())
return return_rhs();
return lhs;
case LogicalOp::Or:
if (constant.to_boolean_slow_case())
return lhs;
return return_rhs();
case LogicalOp::NullishCoalescing:
if (constant.is_nullish())
return return_rhs();
return lhs;
default:
VERIFY_NOT_REACHED();
}
return Optional<ScopedOperand> {};
}
Optional<ScopedOperand> LogicalExpression::generate_bytecode(Bytecode::Generator& generator, Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
auto lhs = m_lhs->generate_bytecode(generator, preferred_dst).value();
// OPTIMIZATION: return lhs/rhs directly if we can detect lhs as a truthy/falsey literal
if (auto constant = generator.try_get_constant(lhs); constant.has_value()) {
return constant_fold_logical_expression(generator, preferred_dst, lhs, this);
}
// lhs
// jump op (true) end (false) rhs
// rhs
// jump always (true) end
// end
auto dst = choose_dst(generator, preferred_dst);
generator.emit_mov(dst, lhs);
auto& rhs_block = generator.make_block();
auto& end_block = generator.make_block();
switch (m_op) {
case LogicalOp::And:
generator.emit_jump_if(
lhs,
Bytecode::Label { rhs_block },
Bytecode::Label { end_block });
break;
case LogicalOp::Or:
generator.emit_jump_if(
lhs,
Bytecode::Label { end_block },
Bytecode::Label { rhs_block });
break;
case LogicalOp::NullishCoalescing:
generator.emit<Bytecode::Op::JumpNullish>(
lhs,
Bytecode::Label { rhs_block },
Bytecode::Label { end_block });
break;
default:
VERIFY_NOT_REACHED();
}
generator.switch_to_basic_block(rhs_block);
auto rhs = m_rhs->generate_bytecode(generator, dst).value();
generator.emit_mov(dst, rhs);
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { end_block });
generator.switch_to_basic_block(end_block);
return dst;
}
Optional<ScopedOperand> UnaryExpression::generate_bytecode(Bytecode::Generator& generator, Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
if (m_op == UnaryOp::Delete)
return generator.emit_delete_reference(m_lhs);
Optional<ScopedOperand> src;
// Typeof needs some special handling for when the LHS is an Identifier. Namely, it shouldn't throw on unresolvable references, but instead return "undefined".
// Skip Not operator as it needs to be evaluated breadth first in order to detect `!!` optimization (otherwise the inner `!x` would eval first).
if (m_op != UnaryOp::Typeof && m_op != UnaryOp::Not)
src = m_lhs->generate_bytecode(generator).value();
auto dst = choose_dst(generator, preferred_dst);
if (src.has_value()) {
if (auto result = try_constant_fold_unary_expression(generator, *src, m_op); result.has_value())
return result.release_value();
}
switch (m_op) {
case UnaryOp::BitwiseNot:
generator.emit<Bytecode::Op::BitwiseNot>(dst, *src);
break;
case UnaryOp::Not:
if (auto nested = as_if<UnaryExpression>(*m_lhs); nested && nested->op() == UnaryOp::Not) {
auto value = nested->lhs()->generate_bytecode(generator).value();
if (value.operand().is_constant())
return generator.add_constant(Value(generator.get_constant(value).to_boolean()));
generator.emit<Bytecode::Op::ToBoolean>(dst, value);
break;
}
src = m_lhs->generate_bytecode(generator).value();
if (auto result = try_constant_fold_unary_expression(generator, *src, m_op); result.has_value())
return result.release_value();
generator.emit<Bytecode::Op::Not>(dst, *src);
break;
case UnaryOp::Plus:
generator.emit<Bytecode::Op::UnaryPlus>(dst, *src);
break;
case UnaryOp::Minus:
generator.emit<Bytecode::Op::UnaryMinus>(dst, *src);
break;
case UnaryOp::Typeof:
if (is<Identifier>(*m_lhs)) {
auto& identifier = static_cast<Identifier const&>(*m_lhs);
if (!identifier.is_local()) {
generator.emit<Bytecode::Op::TypeofBinding>(dst, generator.intern_identifier(identifier.string()));
break;
}
}
src = m_lhs->generate_bytecode(generator).value();
generator.emit<Bytecode::Op::Typeof>(dst, *src);
break;
case UnaryOp::Void:
return generator.add_constant(js_undefined());
case UnaryOp::Delete: // Delete is implemented above.
default:
VERIFY_NOT_REACHED();
}
return dst;
}
Optional<ScopedOperand> NumericLiteral::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
return generator.add_constant(Value(m_value));
}
Optional<ScopedOperand> BooleanLiteral::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
return generator.add_constant(Value(m_value));
}
Optional<ScopedOperand> NullLiteral::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
return generator.add_constant(js_null());
}
Optional<ScopedOperand> BigIntLiteral::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
// 1. Return the NumericValue of NumericLiteral as defined in 12.8.3.
auto integer = [&] {
if (m_value[0] == '0' && m_value.length() >= 3)
if (m_value[1] == 'x' || m_value[1] == 'X')
return MUST(Crypto::SignedBigInteger::from_base(16, m_value.substring(2, m_value.length() - 3)));
if (m_value[1] == 'o' || m_value[1] == 'O')
return MUST(Crypto::SignedBigInteger::from_base(8, m_value.substring(2, m_value.length() - 3)));
if (m_value[1] == 'b' || m_value[1] == 'B')
return MUST(Crypto::SignedBigInteger::from_base(2, m_value.substring(2, m_value.length() - 3)));
return MUST(Crypto::SignedBigInteger::from_base(10, m_value.substring(0, m_value.length() - 1)));
}();
return generator.add_constant(BigInt::create(generator.vm(), move(integer)));
}
Optional<ScopedOperand> StringLiteral::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
return generator.add_constant(PrimitiveString::create(generator.vm(), m_value));
}
Optional<ScopedOperand> RegExpLiteral::generate_bytecode(Bytecode::Generator& generator, Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
auto source_index = generator.intern_string(m_pattern);
auto flags_index = generator.intern_string(m_flags);
auto regex_index = generator.intern_regex(Bytecode::ParsedRegex {
.regex = m_parsed_regex,
.pattern = m_parsed_pattern,
.flags = m_parsed_flags,
});
auto dst = choose_dst(generator, preferred_dst);
generator.emit<Bytecode::Op::NewRegExp>(dst, source_index, flags_index, regex_index);
return dst;
}
Optional<ScopedOperand> Identifier::generate_bytecode(Bytecode::Generator& generator, Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
if (is_local()) {
auto local_index = this->local_index();
auto local = generator.local(local_index);
if (!generator.is_local_initialized(local_index)) {
if (local_index.is_argument()) {
// Arguments are initialized to undefined by default, so here we need to replace it with the empty value to
// trigger the TDZ check.
generator.emit<Bytecode::Op::Mov>(local, generator.add_constant(js_special_empty_value()));
}
generator.emit<Bytecode::Op::ThrowIfTDZ>(local);
}
return local;
}
if (is_global()) {
auto maybe_constant = generator.maybe_generate_builtin_constant(*this);
if (maybe_constant.has_value())
return maybe_constant.release_value();
}
auto dst = choose_dst(generator, preferred_dst);
if (is_global()) {
generator.emit<Bytecode::Op::GetGlobal>(dst, generator.intern_identifier(m_string), generator.next_global_variable_cache());
} else {
if (declaration_kind() == DeclarationKind::Var) {
generator.emit<Bytecode::Op::GetInitializedBinding>(dst, generator.intern_identifier(m_string));
} else {
generator.emit<Bytecode::Op::GetBinding>(dst, generator.intern_identifier(m_string));
}
}
return dst;
}
static Optional<ScopedOperand> arguments_to_array_for_call(Bytecode::Generator& generator, ReadonlySpan<CallExpression::Argument> arguments)
{
auto dst = generator.allocate_register();
if (arguments.is_empty()) {
generator.emit<Bytecode::Op::NewArray>(dst, ReadonlySpan<ScopedOperand> {});
return dst;
}
auto first_spread = find_if(arguments.begin(), arguments.end(), [](auto el) { return el.is_spread; });
Vector<ScopedOperand> args;
args.ensure_capacity(first_spread.index());
for (auto it = arguments.begin(); it != first_spread; ++it) {
VERIFY(!it->is_spread);
auto reg = generator.allocate_register();
auto value = it->value->generate_bytecode(generator).value();
generator.emit_mov(reg, value);
args.append(move(reg));
}
if (first_spread.index() != 0)
generator.emit_with_extra_operand_slots<Bytecode::Op::NewArray>(args.size(), dst, args.span());
else
generator.emit<Bytecode::Op::NewArray>(dst, ReadonlySpan<ScopedOperand> {});
if (first_spread != arguments.end()) {
for (auto it = first_spread; it != arguments.end(); ++it) {
auto value = it->value->generate_bytecode(generator).value();
generator.emit<Bytecode::Op::ArrayAppend>(dst, value, it->is_spread);
}
}
return dst;
}
Optional<ScopedOperand> SuperCall::generate_bytecode(Bytecode::Generator& generator, Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
Optional<ScopedOperand> arguments;
if (m_is_synthetic == IsPartOfSyntheticConstructor::Yes) {
// NOTE: This is the case where we have a fake constructor(...args) { super(...args); } which
// shouldn't call @@iterator of %Array.prototype%.
VERIFY(m_arguments.size() == 1);
VERIFY(m_arguments[0].is_spread);
auto const& argument = m_arguments[0];
// This generates a single argument.
arguments = argument.value->generate_bytecode(generator);
} else {
arguments = arguments_to_array_for_call(generator, m_arguments).value();
}
auto dst = choose_dst(generator, preferred_dst);
generator.emit<Bytecode::Op::SuperCallWithArgumentArray>(dst, *arguments, m_is_synthetic == IsPartOfSyntheticConstructor::Yes);
return dst;
}
Optional<ScopedOperand> AssignmentExpression::generate_bytecode(Bytecode::Generator& generator, Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
if (m_op == AssignmentOp::Assignment) {
// AssignmentExpression : LeftHandSideExpression = AssignmentExpression
return m_lhs.visit(
// 1. If LeftHandSideExpression is neither an ObjectLiteral nor an ArrayLiteral, then
[&](NonnullRefPtr<Expression const> const& lhs) -> Optional<ScopedOperand> {
// a. Let lref be the result of evaluating LeftHandSideExpression.
// b. ReturnIfAbrupt(lref).
Optional<ScopedOperand> base;
Optional<ScopedOperand> computed_property;
Optional<ScopedOperand> this_value;
bool lhs_is_super_expression = false;
if (is<MemberExpression>(*lhs)) {
auto& expression = static_cast<MemberExpression const&>(*lhs);
lhs_is_super_expression = is<SuperExpression>(expression.object());
if (!lhs_is_super_expression) {
auto generated_base = expression.object().generate_bytecode(generator).value();
base = generator.copy_if_needed_to_preserve_evaluation_order(generated_base);
} else {
// https://tc39.es/ecma262/#sec-super-keyword-runtime-semantics-evaluation
// 1. Let env be GetThisEnvironment().
// 2. Let actualThis be ? env.GetThisBinding().
this_value = generator.get_this();
// SuperProperty : super [ Expression ]
// 3. Let propertyNameReference be ? Evaluation of Expression.
// 4. Let propertyNameValue be ? GetValue(propertyNameReference).
}
if (expression.is_computed()) {
auto property = expression.property().generate_bytecode(generator).value();
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.
} else if (expression.property().is_private_identifier()) {
// Do nothing, this will be handled by PutPrivateById later.
} else {
VERIFY_NOT_REACHED();
}
if (lhs_is_super_expression) {
// 5/7. Return ? MakeSuperPropertyReference(actualThis, propertyKey, strict).
// https://tc39.es/ecma262/#sec-makesuperpropertyreference
// 1. Let env be GetThisEnvironment().
// 2. Assert: env.HasSuperBinding() is true.
// 3. Let baseValue be ? env.GetSuperBase().
// 4. Return the Reference Record { [[Base]]: baseValue, [[ReferencedName]]: propertyKey, [[Strict]]: strict, [[ThisValue]]: actualThis }.
base = generator.allocate_register();
generator.emit<Bytecode::Op::ResolveSuperBase>(*base);
}
} else if (is<Identifier>(*lhs)) {
// NOTE: For Identifiers, we cannot perform GetBinding and then write into the reference it retrieves, only SetVariable can do this.
// FIXME: However, this breaks spec as we are doing variable lookup after evaluating the RHS. This is observable in an object environment, where we visibly perform HasOwnProperty and Get(@@unscopables) on the binded object.
} else {
// Per spec 13.15.2 step 1b, we must evaluate the LHS (the call),
// then throw ReferenceError before evaluating the RHS.
(void)lhs->generate_bytecode(generator);
auto exception = generator.allocate_register();
generator.emit<Bytecode::Op::NewReferenceError>(exception, generator.intern_string(ErrorType::InvalidLeftHandAssignment.message()));
generator.perform_needed_unwinds<Bytecode::Op::Throw>();
generator.emit<Bytecode::Op::Throw>(exception);
generator.switch_to_basic_block(generator.make_block());
return generator.add_constant(js_undefined());
}
// c. If IsAnonymousFunctionDefinition(AssignmentExpression) and IsIdentifierRef of LeftHandSideExpression are both true, then
// i. Let rval be ? NamedEvaluation of AssignmentExpression with argument lref.[[ReferencedName]].
// d. Else,
// i. Let rref be the result of evaluating AssignmentExpression.
// ii. Let rval be ? GetValue(rref).
auto rval = [&]() -> ScopedOperand {
if (lhs->is_identifier()) {
return generator.emit_named_evaluation_if_anonymous_function(*m_rhs, generator.intern_identifier(static_cast<Identifier const&>(*lhs).string()));
} else {
return m_rhs->generate_bytecode(generator).value();
}
}();
// e. Perform ? PutValue(lref, rval).
if (is<Identifier>(*lhs)) {
auto& identifier = static_cast<Identifier const&>(*lhs);
if (identifier.is_local()) {
auto is_initialized = generator.is_local_initialized(identifier.local_index());
auto is_lexically_declared = generator.is_local_lexically_declared(identifier.local_index());
if (is_lexically_declared && !is_initialized) {
generator.emit<Bytecode::Op::ThrowIfTDZ>(generator.local(identifier.local_index()));
}
}
generator.emit_set_variable(identifier, rval);
} else if (is<MemberExpression>(*lhs)) {
auto& expression = static_cast<MemberExpression const&>(*lhs);
auto base_identifier = generator.intern_identifier_for_expression(expression.object());
if (expression.is_computed()) {
if (!lhs_is_super_expression)
generator.emit_put_by_value(*base, *computed_property, rval, Bytecode::PutKind::Normal, move(base_identifier));
else
generator.emit_put_by_value_with_this(*base, *computed_property, *this_value, rval, PutKind::Normal);
} else if (expression.property().is_identifier()) {
auto property_key_table_index = generator.intern_property_key(as<Identifier>(expression.property()).string());
if (!lhs_is_super_expression)
generator.emit_put_by_id(*base, property_key_table_index, rval, Bytecode::PutKind::Normal, generator.next_property_lookup_cache(), move(base_identifier));
else
generator.emit<Bytecode::Op::PutNormalByIdWithThis>(*base, *this_value, property_key_table_index, rval, generator.next_property_lookup_cache());
} else if (expression.property().is_private_identifier()) {
auto identifier_table_ref = generator.intern_identifier(as<PrivateIdentifier>(expression.property()).string());
generator.emit<Bytecode::Op::PutPrivateById>(*base, identifier_table_ref, rval);
} else {
VERIFY_NOT_REACHED();
}
} else {
VERIFY_NOT_REACHED();
}
// f. Return rval.
return rval;
},
// 2. Let assignmentPattern be the AssignmentPattern that is covered by LeftHandSideExpression.
[&](NonnullRefPtr<BindingPattern const> const& pattern) -> Optional<ScopedOperand> {
// 3. Let rref be the result of evaluating AssignmentExpression.
// 4. Let rval be ? GetValue(rref).
auto rval = m_rhs->generate_bytecode(generator).value();
// 5. Perform ? DestructuringAssignmentEvaluation of assignmentPattern with argument rval.
pattern->generate_bytecode(generator, Bytecode::Op::BindingInitializationMode::Set, rval);
// 6. Return rval.
return rval;
});
}
VERIFY(m_lhs.has<NonnullRefPtr<Expression const>>());
auto& lhs_expression = m_lhs.get<NonnullRefPtr<Expression const>>();
auto reference_operands = generator.emit_load_from_reference(lhs_expression);
auto lhs = reference_operands.loaded_value.value();
Bytecode::BasicBlock* rhs_block_ptr { nullptr };
Bytecode::BasicBlock* lhs_block_ptr { nullptr };
Bytecode::BasicBlock* end_block_ptr { nullptr };
// Logical assignments short circuit.
if (m_op == AssignmentOp::AndAssignment) { // &&=
rhs_block_ptr = &generator.make_block();
lhs_block_ptr = &generator.make_block();
end_block_ptr = &generator.make_block();
generator.emit_jump_if(
lhs,
Bytecode::Label { *rhs_block_ptr },
Bytecode::Label { *lhs_block_ptr });
} else if (m_op == AssignmentOp::OrAssignment) { // ||=
rhs_block_ptr = &generator.make_block();
lhs_block_ptr = &generator.make_block();
end_block_ptr = &generator.make_block();
generator.emit_jump_if(
lhs,
Bytecode::Label { *lhs_block_ptr },
Bytecode::Label { *rhs_block_ptr });
} else if (m_op == AssignmentOp::NullishAssignment) { // ??=
rhs_block_ptr = &generator.make_block();
lhs_block_ptr = &generator.make_block();
end_block_ptr = &generator.make_block();
generator.emit<Bytecode::Op::JumpNullish>(
lhs,
Bytecode::Label { *rhs_block_ptr },
Bytecode::Label { *lhs_block_ptr });
}
if (rhs_block_ptr)
generator.switch_to_basic_block(*rhs_block_ptr);
auto rhs = [&]() -> ScopedOperand {
if (lhs_expression->is_identifier()) {
return generator.emit_named_evaluation_if_anonymous_function(*m_rhs, generator.intern_identifier(static_cast<Identifier const&>(*lhs_expression).string()));
}
return m_rhs->generate_bytecode(generator).value();
}();
// OPTIMIZATION: If LHS is a local, we can write the result directly into it.
auto dst = [&] {
if (lhs.operand().is_local())
return lhs;
return choose_dst(generator, preferred_dst);
}();
switch (m_op) {
case AssignmentOp::AdditionAssignment:
generator.emit<Bytecode::Op::Add>(dst, lhs, rhs);
break;
case AssignmentOp::SubtractionAssignment:
generator.emit<Bytecode::Op::Sub>(dst, lhs, rhs);
break;
case AssignmentOp::MultiplicationAssignment:
generator.emit<Bytecode::Op::Mul>(dst, lhs, rhs);
break;
case AssignmentOp::DivisionAssignment:
generator.emit<Bytecode::Op::Div>(dst, lhs, rhs);
break;
case AssignmentOp::ModuloAssignment:
generator.emit<Bytecode::Op::Mod>(dst, lhs, rhs);
break;
case AssignmentOp::ExponentiationAssignment:
generator.emit<Bytecode::Op::Exp>(dst, lhs, rhs);
break;
case AssignmentOp::BitwiseAndAssignment:
generator.emit<Bytecode::Op::BitwiseAnd>(dst, lhs, rhs);
break;
case AssignmentOp::BitwiseOrAssignment:
generator.emit<Bytecode::Op::BitwiseOr>(dst, lhs, rhs);
break;
case AssignmentOp::BitwiseXorAssignment:
generator.emit<Bytecode::Op::BitwiseXor>(dst, lhs, rhs);
break;
case AssignmentOp::LeftShiftAssignment:
generator.emit<Bytecode::Op::LeftShift>(dst, lhs, rhs);
break;
case AssignmentOp::RightShiftAssignment:
generator.emit<Bytecode::Op::RightShift>(dst, lhs, rhs);
break;
case AssignmentOp::UnsignedRightShiftAssignment:
generator.emit<Bytecode::Op::UnsignedRightShift>(dst, lhs, rhs);
break;
case AssignmentOp::AndAssignment:
case AssignmentOp::OrAssignment:
case AssignmentOp::NullishAssignment:
generator.emit_mov(dst, rhs);
break;
default:
VERIFY_NOT_REACHED();
}
if (lhs_expression->is_identifier())
generator.emit_set_variable(static_cast<Identifier const&>(*lhs_expression), dst);
else
generator.emit_store_to_reference(reference_operands, dst);
if (rhs_block_ptr) {
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { *end_block_ptr });
}
if (lhs_block_ptr) {
generator.switch_to_basic_block(*lhs_block_ptr);
generator.emit_mov(dst, lhs);
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { *end_block_ptr });
}
if (end_block_ptr) {
generator.switch_to_basic_block(*end_block_ptr);
}
return dst;
}
// 14.13.3 Runtime Semantics: Evaluation, https://tc39.es/ecma262/#sec-labelled-statements-runtime-semantics-evaluation
// LabelledStatement : LabelIdentifier : LabelledItem
Optional<ScopedOperand> LabelledStatement::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
// Return ? LabelledEvaluation of this LabelledStatement with argument « ».
return generate_labelled_evaluation(generator, {});
}
// 14.13.4 Runtime Semantics: LabelledEvaluation, https://tc39.es/ecma262/#sec-runtime-semantics-labelledevaluation
// LabelledStatement : LabelIdentifier : LabelledItem
Optional<ScopedOperand> LabelledStatement::generate_labelled_evaluation(Bytecode::Generator& generator, Vector<FlyString> const& label_set, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
// Convert the m_labelled_item NNRP to a reference early so we don't have to do it every single time we want to use it.
auto const& labelled_item = *m_labelled_item;
// 1. Let label be the StringValue of LabelIdentifier.
// NOTE: Not necessary, this is m_label.
// 2. Let newLabelSet be the list-concatenation of labelSet and « label ».
// FIXME: Avoid copy here.
auto new_label_set = label_set;
new_label_set.append(m_label);
// 3. Let stmtResult be LabelledEvaluation of LabelledItem with argument newLabelSet.
Optional<ScopedOperand> stmt_result;
if (is<IterationStatement>(labelled_item)) {
auto const& iteration_statement = static_cast<IterationStatement const&>(labelled_item);
stmt_result = iteration_statement.generate_labelled_evaluation(generator, new_label_set);
} else if (is<SwitchStatement>(labelled_item)) {
auto const& switch_statement = static_cast<SwitchStatement const&>(labelled_item);
stmt_result = switch_statement.generate_labelled_evaluation(generator, new_label_set);
} else if (is<LabelledStatement>(labelled_item)) {
auto const& labelled_statement = static_cast<LabelledStatement const&>(labelled_item);
stmt_result = labelled_statement.generate_labelled_evaluation(generator, new_label_set);
} else {
auto& labelled_break_block = generator.make_block();
// NOTE: We do not need a continuable scope as `continue;` is not allowed outside of iteration statements, throwing a SyntaxError in the parser.
generator.begin_breakable_scope(Bytecode::Label { labelled_break_block }, new_label_set);
stmt_result = labelled_item.generate_bytecode(generator);
generator.end_breakable_scope();
if (!generator.is_current_block_terminated()) {
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { labelled_break_block });
}
generator.switch_to_basic_block(labelled_break_block);
}
// 4. If stmtResult.[[Type]] is break and SameValue(stmtResult.[[Target]], label) is true, then
// a. Set stmtResult to NormalCompletion(stmtResult.[[Value]]).
// NOTE: These steps are performed by making labelled break jump straight to the appropriate break block, which preserves the statement result's value in the accumulator.
// 5. Return Completion(stmtResult).
return stmt_result;
}
Optional<ScopedOperand> WhileStatement::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
return generate_labelled_evaluation(generator, {});
}
Optional<ScopedOperand> WhileStatement::generate_labelled_evaluation(Bytecode::Generator& generator, Vector<FlyString> const& label_set, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
auto& test_block = generator.make_block();
Optional<ScopedOperand> completion;
if (generator.must_propagate_completion()) {
completion = generator.allocate_register();
generator.emit_mov(*completion, generator.add_constant(js_undefined()));
}
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { test_block });
generator.switch_to_basic_block(test_block);
auto test = m_test->generate_bytecode(generator).value();
// OPTIMIZATION: If predicate is always false, ignore body and exit early
if (auto constant = generator.try_get_constant(test); constant.has_value() && !constant->to_boolean_slow_case()) {
return completion;
}
// test
// jump if_false (true) end (false) body
// body
// jump always (true) test
// end
auto& body_block = generator.make_block();
auto& end_block = generator.make_block();
generator.emit_jump_if(
test,
Bytecode::Label { body_block },
Bytecode::Label { end_block });
generator.switch_to_basic_block(body_block);
generator.begin_continuable_scope(Bytecode::Label { test_block }, label_set, completion);
generator.begin_breakable_scope(Bytecode::Label { end_block }, label_set, completion);
{
Optional<Bytecode::Generator::CompletionRegisterScope> completion_scope;
if (completion.has_value())
completion_scope.emplace(generator, *completion);
auto body = m_body->generate_bytecode(generator);
if (!generator.is_current_block_terminated() && completion.has_value() && body.has_value())
generator.emit_mov(*completion, *body);
}
generator.end_breakable_scope();
generator.end_continuable_scope();
if (!generator.is_current_block_terminated())
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { test_block });
generator.switch_to_basic_block(end_block);
return completion;
}
Optional<ScopedOperand> DoWhileStatement::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
return generate_labelled_evaluation(generator, {});
}
Optional<ScopedOperand> DoWhileStatement::generate_labelled_evaluation(Bytecode::Generator& generator, Vector<FlyString> const& label_set, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
// jump always (true) body
// test
// jump if_false (true) end (false) body
// body
// jump always (true) test
// end
auto& body_block = generator.make_block();
auto& test_block = generator.make_block();
auto& load_result_and_jump_to_end_block = generator.make_block();
auto& end_block = generator.make_block();
Optional<ScopedOperand> completion;
if (generator.must_propagate_completion()) {
completion = generator.allocate_register();
generator.emit_mov(*completion, generator.add_constant(js_undefined()));
}
// jump to the body block
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { body_block });
generator.switch_to_basic_block(test_block);
auto test = m_test->generate_bytecode(generator).value();
generator.emit_jump_if(
test,
Bytecode::Label { body_block },
Bytecode::Label { load_result_and_jump_to_end_block });
generator.switch_to_basic_block(body_block);
generator.begin_continuable_scope(Bytecode::Label { test_block }, label_set, completion);
generator.begin_breakable_scope(Bytecode::Label { end_block }, label_set, completion);
{
Optional<Bytecode::Generator::CompletionRegisterScope> completion_scope;
if (completion.has_value())
completion_scope.emplace(generator, *completion);
auto body = m_body->generate_bytecode(generator);
if (!generator.is_current_block_terminated() && completion.has_value() && body.has_value())
generator.emit_mov(*completion, *body);
}
generator.end_breakable_scope();
generator.end_continuable_scope();
if (!generator.is_current_block_terminated())
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { test_block });
generator.switch_to_basic_block(load_result_and_jump_to_end_block);
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { end_block });
generator.switch_to_basic_block(end_block);
return completion;
}
Optional<ScopedOperand> ForStatement::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
return generate_labelled_evaluation(generator, {});
}
Optional<ScopedOperand> ForStatement::generate_labelled_evaluation(Bytecode::Generator& generator, Vector<FlyString> const& label_set, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
// init
// jump always (true) test
// test
// jump if_true (true) body (false) end
// body
// jump always (true) update
// update
// jump always (true) test
// end
// If 'test' is missing, fuse the 'test' and 'body' basic blocks
// If 'update' is missing, fuse the 'body' and 'update' basic blocks
Bytecode::BasicBlock* test_block_ptr { nullptr };
Bytecode::BasicBlock* body_block_ptr { nullptr };
Bytecode::BasicBlock* update_block_ptr { nullptr };
bool has_lexical_environment = false;
Vector<IdentifierTableIndex> per_iteration_bindings;
if (m_init) {
if (m_init->is_variable_declaration()) {
auto& variable_declaration = as<VariableDeclaration>(*m_init);
auto has_non_local_variables = false;
MUST(variable_declaration.for_each_bound_identifier([&](auto const& identifier) {
if (!identifier.is_local())
has_non_local_variables = true;
}));
if (variable_declaration.is_lexical_declaration() && has_non_local_variables) {
has_lexical_environment = true;
// Setup variable scope for bound identifiers
generator.begin_variable_scope();
bool is_const = variable_declaration.is_constant_declaration();
// NOTE: Nothing in the callback throws an exception.
MUST(variable_declaration.for_each_bound_identifier([&](auto const& identifier) {
if (identifier.is_local())
return;
auto index = generator.intern_identifier(identifier.string());
generator.emit<Bytecode::Op::CreateVariable>(index, Bytecode::Op::EnvironmentMode::Lexical, is_const, false, false);
if (!is_const) {
per_iteration_bindings.append(index);
}
}));
}
}
(void)m_init->generate_bytecode(generator);
}
// CreatePerIterationEnvironment (https://tc39.es/ecma262/multipage/ecmascript-language-statements-and-declarations.html#sec-createperiterationenvironment)
auto generate_per_iteration_bindings = [&per_iteration_bindings = static_cast<Vector<IdentifierTableIndex> const&>(per_iteration_bindings),
&generator]() {
if (per_iteration_bindings.is_empty()) {
return;
}
// Copy all the last values into registers for use in step 1.e.iii
// Register copies of bindings are required since the changing of the
// running execution context in the final step requires leaving the
// current variable scope before creating "thisIterationEnv"
Vector<ScopedOperand> registers;
for (auto const& binding : per_iteration_bindings) {
auto reg = generator.allocate_register();
generator.emit<Bytecode::Op::GetBinding>(reg, binding);
registers.append(reg);
}
generator.end_variable_scope();
generator.begin_variable_scope();
for (size_t i = 0; i < per_iteration_bindings.size(); ++i) {
generator.emit<Bytecode::Op::CreateVariable>(per_iteration_bindings[i], Bytecode::Op::EnvironmentMode::Lexical, false, false, false);
generator.emit<Bytecode::Op::InitializeLexicalBinding>(per_iteration_bindings[i], registers[i]);
}
};
if (m_init) {
// CreatePerIterationEnvironment where lastIterationEnv is the variable
// scope created above for bound identifiers
generate_per_iteration_bindings();
}
body_block_ptr = &generator.make_block();
if (m_update)
update_block_ptr = &generator.make_block();
else
update_block_ptr = body_block_ptr;
if (m_test)
test_block_ptr = &generator.make_block();
else
test_block_ptr = body_block_ptr;
auto& end_block = generator.make_block();
Optional<ScopedOperand> completion;
if (generator.must_propagate_completion()) {
completion = generator.allocate_register();
generator.emit_mov(*completion, generator.add_constant(js_undefined()));
}
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { *test_block_ptr });
if (m_test) {
generator.switch_to_basic_block(*test_block_ptr);
auto test = m_test->generate_bytecode(generator).value();
// OPTIMIZATION: test value is always falsey, skip body entirely
if (auto constant = generator.try_get_constant(test); constant.has_value() && !constant->to_boolean_slow_case()) {
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { end_block });
generator.switch_to_basic_block(end_block);
if (has_lexical_environment)
generator.end_variable_scope();
return completion;
}
generator.emit_jump_if(test, Bytecode::Label { *body_block_ptr }, Bytecode::Label { end_block });
}
if (m_update) {
generator.switch_to_basic_block(*update_block_ptr);
(void)m_update->generate_bytecode(generator);
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { *test_block_ptr });
}
generator.switch_to_basic_block(*body_block_ptr);
generator.begin_continuable_scope(Bytecode::Label { m_update ? *update_block_ptr : *test_block_ptr }, label_set, completion);
generator.begin_breakable_scope(Bytecode::Label { end_block }, label_set, completion);
{
Optional<Bytecode::Generator::CompletionRegisterScope> completion_scope;
if (completion.has_value())
completion_scope.emplace(generator, *completion);
auto body = m_body->generate_bytecode(generator);
if (!generator.is_current_block_terminated() && completion.has_value() && body.has_value())
generator.emit_mov(*completion, *body);
}
generator.end_breakable_scope();
generator.end_continuable_scope();
if (!generator.is_current_block_terminated()) {
// CreatePerIterationEnvironment where lastIterationEnv is the environment
// created by the previous CreatePerIterationEnvironment setup
generate_per_iteration_bindings();
if (m_update) {
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { *update_block_ptr });
} else {
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { *test_block_ptr });
}
}
generator.switch_to_basic_block(end_block);
// Leave the environment setup by CreatePerIterationEnvironment or if there
// are no perIterationBindings the variable scope created for bound
// identifiers
if (has_lexical_environment)
generator.end_variable_scope();
return completion;
}
Optional<ScopedOperand> ObjectExpression::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
auto object = choose_dst(generator, preferred_dst);
// Determine if this is a simple object literal (all KeyValue with StringLiteral keys
// that are not numeric indices). Simple literals can benefit from shape caching with
// direct property offset writes. Numeric string keys like "0" are stored in indexed
// storage rather than shape-based storage, so they can't use the fast path.
bool is_simple = !m_properties.is_empty();
for (auto& property : m_properties) {
if (property->type() != ObjectProperty::Type::KeyValue || !is<StringLiteral>(property->key())) {
is_simple = false;
break;
}
// Check if the key is a numeric index (would be stored in indexed storage)
auto const& key = static_cast<StringLiteral const&>(property->key()).value();
if (!key.is_empty() && !(key.code_unit_at(0) == '0' && key.length_in_code_units() > 1)) {
auto property_index = key.to_number<u32>(TrimWhitespace::No);
if (property_index.has_value() && property_index.value() < NumericLimits<u32>::max()) {
is_simple = false;
break;
}
}
}
Optional<u32> shape_cache_index;
if (is_simple)
shape_cache_index = generator.next_object_shape_cache();
generator.emit<Bytecode::Op::NewObject>(object, shape_cache_index.value_or(NumericLimits<u32>::max()));
if (m_properties.is_empty())
return object;
generator.push_home_object(object);
u32 property_slot = 0;
for (auto& property : m_properties) {
Bytecode::PutKind property_kind;
switch (property->type()) {
case ObjectProperty::Type::KeyValue:
property_kind = Bytecode::PutKind::Own;
break;
case ObjectProperty::Type::Getter:
property_kind = Bytecode::PutKind::Getter;
break;
case ObjectProperty::Type::Setter:
property_kind = Bytecode::PutKind::Setter;
break;
case ObjectProperty::Type::ProtoSetter:
property_kind = Bytecode::PutKind::Prototype;
break;
case ObjectProperty::Type::Spread:
generator.emit<Bytecode::Op::PutBySpread>(object, property->key().generate_bytecode(generator).value());
continue;
}
if (is<StringLiteral>(property->key())) {
auto& string_literal = static_cast<StringLiteral const&>(property->key());
Optional<ScopedOperand> value;
if (property_kind == Bytecode::PutKind::Prototype) {
value = property->value().generate_bytecode(generator).value();
} else {
auto identifier = string_literal.value();
if (property_kind == Bytecode::PutKind::Getter)
identifier = Utf16String::formatted("get {}", identifier);
else if (property_kind == Bytecode::PutKind::Setter)
identifier = Utf16String::formatted("set {}", identifier);
auto name = generator.intern_identifier(identifier);
value = generator.emit_named_evaluation_if_anonymous_function(property->value(), name, {}, property->is_method());
}
auto property_key_table_index = generator.intern_property_key(string_literal.value());
// For simple object literals, use InitObjectLiteralProperty for direct offset writes
if (is_simple) {
generator.emit<Bytecode::Op::InitObjectLiteralProperty>(object, property_key_table_index, *value, *shape_cache_index, property_slot++);
} else {
generator.emit_put_by_id(object, property_key_table_index, *value, property_kind, generator.next_property_lookup_cache());
}
} else {
auto property_name = property->key().generate_bytecode(generator).value();
// ComputedPropertyName evaluation calls ToPropertyKey, which includes ToPrimitive(hint: string).
// This must happen before the value expression is evaluated per the spec for
// PropertyDefinitionEvaluation (PropertyDefinition : PropertyName : AssignmentExpression):
// 1. Let propKey be ? Evaluation of PropertyName.
// [then] 5/6. Evaluate the AssignmentExpression.
// ToPrimitive is the only step in ToPropertyKey with user-observable side effects.
// After this, the ToPrimitive inside put_by_value's to_property_key is a no-op.
generator.emit<Bytecode::Op::ToPrimitiveWithStringHint>(property_name, property_name);
auto value = generator.emit_named_evaluation_if_anonymous_function(property->value(), {}, {}, property->is_method());
generator.emit_put_by_value(object, property_name, value, property_kind, {});
}
}
generator.pop_home_object();
if (shape_cache_index.has_value())
generator.emit<Bytecode::Op::CacheObjectShape>(object, *shape_cache_index);
return object;
}
Optional<ScopedOperand> ArrayExpression::generate_bytecode(Bytecode::Generator& generator, Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
if (m_elements.is_empty()) {
auto dst = choose_dst(generator, preferred_dst);
generator.emit<Bytecode::Op::NewArray>(dst, ReadonlySpan<ScopedOperand> {});
return dst;
}
if (all_of(m_elements, [](auto element) { return !element || is<PrimitiveLiteral>(*element); })) {
// If all elements are constant primitives, we can just emit a single instruction to initialize the array,
// instead of emitting instructions to manually evaluate them one-by-one
Vector<Value> values;
values.resize_with_default_value(m_elements.size(), js_special_empty_value());
for (auto i = 0u; i < m_elements.size(); ++i) {
if (!m_elements[i])
continue;
values[i] = static_cast<PrimitiveLiteral const&>(*m_elements[i]).value();
}
auto dst = choose_dst(generator, preferred_dst);
generator.emit_with_extra_value_slots<Bytecode::Op::NewPrimitiveArray>(values.size(), dst, values);
return dst;
}
auto first_spread = find_if(m_elements.begin(), m_elements.end(), [](auto el) { return el && is<SpreadExpression>(*el); });
Vector<ScopedOperand> args;
args.ensure_capacity(m_elements.size());
for (auto it = m_elements.begin(); it != first_spread; ++it) {
if (*it) {
auto value = (*it)->generate_bytecode(generator).value();
args.append(generator.copy_if_needed_to_preserve_evaluation_order(value));
} else {
args.append(generator.add_constant(js_special_empty_value()));
}
}
auto dst = choose_dst(generator, preferred_dst);
if (first_spread.index() != 0) {
generator.emit_with_extra_operand_slots<Bytecode::Op::NewArray>(args.size(), dst, args);
} else {
generator.emit<Bytecode::Op::NewArray>(dst, ReadonlySpan<ScopedOperand> {});
}
if (first_spread != m_elements.end()) {
for (auto it = first_spread; it != m_elements.end(); ++it) {
if (!*it) {
generator.emit<Bytecode::Op::ArrayAppend>(dst, generator.add_constant(js_special_empty_value()), false);
} else {
auto value = (*it)->generate_bytecode(generator).value();
generator.emit<Bytecode::Op::ArrayAppend>(dst, value, *it && is<SpreadExpression>(**it));
}
}
}
return dst;
}
Optional<ScopedOperand> MemberExpression::generate_bytecode(Bytecode::Generator& generator, Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
auto reference = generator.emit_load_from_reference(*this, preferred_dst, Bytecode::Generator::ReferenceMode::LoadOnly);
return reference.loaded_value;
}
Optional<ScopedOperand> FunctionDeclaration::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
if (m_is_hoisted) {
Bytecode::Generator::SourceLocationScope scope(generator, *this);
auto index = generator.intern_identifier(name());
auto value = generator.allocate_register();
generator.emit<Bytecode::Op::GetBinding>(value, index);
generator.emit<Bytecode::Op::SetVariableBinding>(index, value);
}
return Optional<ScopedOperand> {};
}
Optional<ScopedOperand> FunctionExpression::generate_bytecode_with_lhs_name(Bytecode::Generator& generator, Optional<Bytecode::IdentifierTableIndex> lhs_name, Optional<ScopedOperand> preferred_dst, bool is_method) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
bool has_name = !name().is_empty();
Optional<Bytecode::IdentifierTableIndex> name_identifier;
if (has_name) {
generator.begin_variable_scope();
name_identifier = generator.intern_identifier(name());
generator.emit<Bytecode::Op::CreateVariable>(*name_identifier, Bytecode::Op::EnvironmentMode::Lexical, true, false, false);
}
auto new_function = choose_dst(generator, preferred_dst);
generator.emit_new_function(new_function, *this, lhs_name, is_method);
if (has_name) {
generator.emit<Bytecode::Op::InitializeLexicalBinding>(*name_identifier, new_function);
generator.end_variable_scope();
}
return new_function;
}
Optional<ScopedOperand> FunctionExpression::generate_bytecode(Bytecode::Generator& generator, Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
return generate_bytecode_with_lhs_name(generator, {}, preferred_dst);
}
static void generate_object_binding_pattern_bytecode(Bytecode::Generator& generator, BindingPattern const& pattern, Bytecode::Op::BindingInitializationMode initialization_mode, ScopedOperand const& object)
{
generator.emit<Bytecode::Op::ThrowIfNullish>(object);
Vector<ScopedOperand> excluded_property_names;
auto has_rest = false;
if (pattern.entries.size() > 0)
has_rest = pattern.entries[pattern.entries.size() - 1].is_rest;
for (auto& [name, alias, initializer, is_rest] : pattern.entries) {
if (is_rest) {
VERIFY(!initializer);
if (name.has<NonnullRefPtr<Identifier const>>()) {
auto identifier = name.get<NonnullRefPtr<Identifier const>>();
auto copy = generator.allocate_register();
generator.emit_with_extra_operand_slots<Bytecode::Op::CopyObjectExcludingProperties>(
excluded_property_names.size(), copy, object, excluded_property_names);
generator.emit_set_variable(*identifier, copy, initialization_mode);
return;
}
if (alias.has<NonnullRefPtr<MemberExpression const>>()) {
auto copy = generator.allocate_register();
generator.emit_with_extra_operand_slots<Bytecode::Op::CopyObjectExcludingProperties>(
excluded_property_names.size(), copy, object, excluded_property_names);
generator.emit_store_to_reference(alias.get<NonnullRefPtr<MemberExpression const>>(), copy);
return;
}
VERIFY_NOT_REACHED();
}
auto value = generator.allocate_register();
if (name.has<NonnullRefPtr<Identifier const>>()) {
auto const& identifier = name.get<NonnullRefPtr<Identifier const>>()->string();
if (has_rest) {
excluded_property_names.append(generator.add_constant(PrimitiveString::create(generator.vm(), identifier)));
}
generator.emit_get_by_id(value, object, generator.intern_property_key(identifier));
} else {
auto expression = name.get<NonnullRefPtr<Expression const>>();
auto property_name = expression->generate_bytecode(generator).value();
if (has_rest) {
auto excluded_name = generator.copy_if_needed_to_preserve_evaluation_order(property_name);
excluded_property_names.append(excluded_name);
}
generator.emit_get_by_value(value, object, property_name);
}
if (initializer) {
auto& if_undefined_block = generator.make_block();
auto& if_not_undefined_block = generator.make_block();
generator.emit<Bytecode::Op::JumpUndefined>(
value,
Bytecode::Label { if_undefined_block },
Bytecode::Label { if_not_undefined_block });
generator.switch_to_basic_block(if_undefined_block);
Optional<ScopedOperand> default_value;
if (auto const* alias_identifier = alias.get_pointer<NonnullRefPtr<Identifier const>>()) {
default_value = generator.emit_named_evaluation_if_anonymous_function(*initializer, generator.intern_identifier((*alias_identifier)->string()));
} else if (auto const* lhs = name.get_pointer<NonnullRefPtr<Identifier const>>()) {
default_value = generator.emit_named_evaluation_if_anonymous_function(*initializer, generator.intern_identifier((*lhs)->string()));
} else {
default_value = initializer->generate_bytecode(generator).value();
}
generator.emit_mov(value, *default_value);
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { if_not_undefined_block });
generator.switch_to_basic_block(if_not_undefined_block);
}
if (alias.has<NonnullRefPtr<BindingPattern const>>()) {
auto& binding_pattern = *alias.get<NonnullRefPtr<BindingPattern const>>();
auto nested_value = generator.copy_if_needed_to_preserve_evaluation_order(value);
binding_pattern.generate_bytecode(generator, initialization_mode, nested_value);
} else if (alias.has<Empty>()) {
// NB: Computed property names always require an alias, so name can't be an Expression here.
VERIFY(!name.has<NonnullRefPtr<Expression const>>());
auto const& identifier = *name.get<NonnullRefPtr<Identifier const>>();
generator.emit_set_variable(identifier, value, initialization_mode);
} else if (alias.has<NonnullRefPtr<MemberExpression const>>()) {
generator.emit_store_to_reference(alias.get<NonnullRefPtr<MemberExpression const>>(), value);
} else {
auto const& identifier = *alias.get<NonnullRefPtr<Identifier const>>();
generator.emit_set_variable(identifier, value, initialization_mode);
}
}
}
static void generate_array_binding_pattern_bytecode(Bytecode::Generator& generator, BindingPattern const& pattern, Bytecode::Op::BindingInitializationMode initialization_mode, ScopedOperand const& input_array, [[maybe_unused]] Optional<ScopedOperand> preferred_dst = {})
{
/*
* Consider the following destructuring assignment:
*
* let [a, b, c, d, e] = o;
*
* It would be fairly trivial to just loop through this iterator, getting the value
* at each step and assigning them to the binding sequentially. However, this is not
* correct: once an iterator is exhausted, it must not be called again. This complicates
* the bytecode. In order to accomplish this, we do the following:
*
* - Reserve a special boolean register which holds 'true' if the iterator is exhausted,
* and false otherwise
* - When we are retrieving the value which should be bound, we first check this register.
* If it is 'true', we load undefined. Otherwise, we grab the next value from the iterator.
*
* Note that the is_exhausted register does not need to be loaded with false because the
* first IteratorNext bytecode is _not_ proceeded by an exhausted check, as it is
* unnecessary.
*/
auto is_iterator_exhausted = generator.allocate_register();
generator.emit_mov(is_iterator_exhausted, generator.add_constant(Value(false)));
auto iterator_object = generator.allocate_register();
auto iterator_next_method = generator.allocate_register();
auto iterator_done_property = generator.allocate_register();
generator.emit<Bytecode::Op::GetIterator>(iterator_object, iterator_next_method, iterator_done_property, input_array, IteratorHint::Sync);
bool first = true;
auto assign_value_to_alias = [&](auto& alias, ScopedOperand value) {
return alias.visit(
[&](Empty) -> void {
// This element is an elision
},
[&](NonnullRefPtr<Identifier const> const& identifier) -> void {
generator.emit_set_variable(*identifier, value, initialization_mode);
},
[&](NonnullRefPtr<BindingPattern const> const& pattern) -> void {
pattern->generate_bytecode(generator, initialization_mode, value);
},
[&](NonnullRefPtr<MemberExpression const> const& expr) -> void {
generator.emit_store_to_reference(*expr, value);
});
};
auto temp_iterator_result = generator.allocate_register();
for (auto& [name, alias, initializer, is_rest] : pattern.entries) {
VERIFY(name.has<Empty>());
if (is_rest) {
VERIFY(!initializer);
// 13.15.5.3 AssignmentRestElement : ... DestructuringAssignmentTarget
// Step 1: If DestructuringAssignmentTarget is not ObjectLiteral or ArrayLiteral,
// let lref be ? Evaluation of DestructuringAssignmentTarget.
// The reference must be evaluated BEFORE iterating the remaining elements.
Optional<Bytecode::Generator::ReferenceOperands> lref;
if (auto const* member_expr = alias.get_pointer<NonnullRefPtr<MemberExpression const>>())
lref = generator.emit_evaluate_reference(**member_expr);
auto value = generator.allocate_register();
if (first) {
// The iterator has not been called, and is thus known to be not exhausted
generator.emit<Bytecode::Op::IteratorToArray>(value, iterator_object, iterator_next_method, iterator_done_property);
} else {
auto& if_exhausted_block = generator.make_block();
auto& if_not_exhausted_block = generator.make_block();
auto& continuation_block = generator.make_block();
generator.emit_jump_if(
is_iterator_exhausted,
Bytecode::Label { if_exhausted_block },
Bytecode::Label { if_not_exhausted_block });
value = generator.allocate_register();
generator.switch_to_basic_block(if_exhausted_block);
generator.emit<Bytecode::Op::NewArray>(value, ReadonlySpan<ScopedOperand> {});
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { continuation_block });
generator.switch_to_basic_block(if_not_exhausted_block);
generator.emit<Bytecode::Op::IteratorToArray>(value, iterator_object, iterator_next_method, iterator_done_property);
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { continuation_block });
generator.switch_to_basic_block(continuation_block);
}
if (lref.has_value())
generator.emit_store_to_reference(*lref, value);
else
assign_value_to_alias(alias, value);
return;
}
// 13.15.5.5 AssignmentElement : DestructuringAssignmentTarget Initializer(opt)
// Step 1: If DestructuringAssignmentTarget is not ObjectLiteral or ArrayLiteral,
// let lref be ? Evaluation of DestructuringAssignmentTarget.
// The reference must be evaluated BEFORE calling IteratorStepValue.
Optional<Bytecode::Generator::ReferenceOperands> lref;
if (auto const* member_expr = alias.get_pointer<NonnullRefPtr<MemberExpression const>>())
lref = generator.emit_evaluate_reference(**member_expr);
auto& iterator_is_exhausted_block = generator.make_block();
if (!first) {
auto& iterator_is_not_exhausted_block = generator.make_block();
generator.emit_jump_if(
is_iterator_exhausted,
Bytecode::Label { iterator_is_exhausted_block },
Bytecode::Label { iterator_is_not_exhausted_block });
generator.switch_to_basic_block(iterator_is_not_exhausted_block);
}
auto value = generator.allocate_register();
generator.emit<Bytecode::Op::IteratorNextUnpack>(value, is_iterator_exhausted, iterator_object, iterator_next_method, iterator_done_property);
// We still have to check for exhaustion here. If the iterator is exhausted,
// we need to bail before trying to get the value
auto& no_bail_block = generator.make_block();
generator.emit_jump_if(
is_iterator_exhausted,
Bytecode::Label { iterator_is_exhausted_block },
Bytecode::Label { no_bail_block });
generator.switch_to_basic_block(no_bail_block);
auto& create_binding_block = generator.make_block();
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { create_binding_block });
// The iterator is exhausted, so we just load undefined and continue binding
generator.switch_to_basic_block(iterator_is_exhausted_block);
generator.emit_mov(value, generator.add_constant(js_undefined()));
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { create_binding_block });
generator.switch_to_basic_block(create_binding_block);
if (initializer) {
auto& value_is_undefined_block = generator.make_block();
auto& value_is_not_undefined_block = generator.make_block();
generator.emit<Bytecode::Op::JumpUndefined>(
value,
Bytecode::Label { value_is_undefined_block },
Bytecode::Label { value_is_not_undefined_block });
generator.switch_to_basic_block(value_is_undefined_block);
Optional<ScopedOperand> default_value;
if (auto const* alias_identifier = alias.get_pointer<NonnullRefPtr<Identifier const>>()) {
default_value = generator.emit_named_evaluation_if_anonymous_function(*initializer, generator.intern_identifier((*alias_identifier)->string()));
} else if (auto const* name_identifier = name.get_pointer<NonnullRefPtr<Identifier const>>()) {
default_value = generator.emit_named_evaluation_if_anonymous_function(*initializer, generator.intern_identifier((*name_identifier)->string()));
} else {
default_value = initializer->generate_bytecode(generator).value();
}
generator.emit_mov(value, *default_value);
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { value_is_not_undefined_block });
generator.switch_to_basic_block(value_is_not_undefined_block);
}
if (lref.has_value())
generator.emit_store_to_reference(*lref, value);
else
assign_value_to_alias(alias, value);
first = false;
}
auto& done_block = generator.make_block();
auto& not_done_block = generator.make_block();
generator.emit_jump_if(
is_iterator_exhausted,
Bytecode::Label { done_block },
Bytecode::Label { not_done_block });
generator.switch_to_basic_block(not_done_block);
generator.emit<Bytecode::Op::IteratorClose>(iterator_object, iterator_next_method, iterator_done_property, Completion::Type::Normal, generator.add_constant(js_undefined()));
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { done_block });
generator.switch_to_basic_block(done_block);
}
void BindingPattern::generate_bytecode(Bytecode::Generator& generator, Bytecode::Op::BindingInitializationMode initialization_mode, ScopedOperand const& input_value) const
{
if (kind == Kind::Object)
return generate_object_binding_pattern_bytecode(generator, *this, initialization_mode, input_value);
return generate_array_binding_pattern_bytecode(generator, *this, initialization_mode, input_value);
}
static void assign_value_to_variable_declarator(Bytecode::Generator& generator, VariableDeclarator const& declarator, VariableDeclaration const& declaration, ScopedOperand value)
{
auto initialization_mode = declaration.is_lexical_declaration() ? Bytecode::Op::BindingInitializationMode::Initialize : Bytecode::Op::BindingInitializationMode::Set;
declarator.target().visit(
[&](NonnullRefPtr<Identifier const> const& id) -> void {
generator.emit_set_variable(*id, value, initialization_mode);
},
[&](NonnullRefPtr<BindingPattern const> const& pattern) -> void {
pattern->generate_bytecode(generator, initialization_mode, value);
});
}
Optional<ScopedOperand> VariableDeclaration::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
for (auto& declarator : m_declarations) {
// NOTE: `var` declarations can have duplicates, but duplicate `let` or `const` bindings are a syntax error.
// Because of this, we can sink `let` and `const` directly into the preferred_dst if available.
// This is not safe for `var` since the preferred_dst may be used in the initializer.
Optional<ScopedOperand> init_dst;
if (declaration_kind() != DeclarationKind::Var) {
if (auto const* identifier = declarator->target().get_pointer<NonnullRefPtr<Identifier const>>()) {
if ((*identifier)->is_local()) {
init_dst = generator.local((*identifier)->local_index());
}
}
}
if (declarator->init()) {
auto value = [&]() -> ScopedOperand {
if (auto const* lhs = declarator->target().get_pointer<NonnullRefPtr<Identifier const>>()) {
return generator.emit_named_evaluation_if_anonymous_function(*declarator->init(), generator.intern_identifier((*lhs)->string()), init_dst);
} else {
return declarator->init()->generate_bytecode(generator, init_dst).value();
}
}();
assign_value_to_variable_declarator(generator, declarator, *this, value);
} else if (m_declaration_kind != DeclarationKind::Var) {
assign_value_to_variable_declarator(generator, declarator, *this, generator.add_constant(js_undefined()));
}
if (auto const* identifier = declarator->target().get_pointer<NonnullRefPtr<Identifier const>>()) {
if ((*identifier)->is_local()) {
generator.set_local_initialized((*identifier)->local_index());
}
}
}
// NOTE: VariableDeclaration doesn't return a completion value.
return Optional<ScopedOperand> {};
}
struct BaseAndValue {
ScopedOperand base;
ScopedOperand value;
};
static BaseAndValue get_base_and_value_from_member_expression(Bytecode::Generator& generator, MemberExpression const& member_expression)
{
// https://tc39.es/ecma262/#sec-super-keyword-runtime-semantics-evaluation
if (is<SuperExpression>(member_expression.object())) {
// 1. Let env be GetThisEnvironment().
// 2. Let actualThis be ? env.GetThisBinding().
auto this_value = generator.get_this();
Optional<ScopedOperand> computed_property;
if (member_expression.is_computed()) {
// SuperProperty : super [ Expression ]
// 3. Let propertyNameReference be ? Evaluation of Expression.
// 4. Let propertyNameValue be ? GetValue(propertyNameReference).
computed_property = member_expression.property().generate_bytecode(generator);
}
// 5/7. Return ? MakeSuperPropertyReference(actualThis, propertyKey, strict).
// https://tc39.es/ecma262/#sec-makesuperpropertyreference
// 1. Let env be GetThisEnvironment().
// 2. Assert: env.HasSuperBinding() is true.
// 3. Let baseValue be ? env.GetSuperBase().
auto super_base = generator.allocate_register();
generator.emit<Bytecode::Op::ResolveSuperBase>(super_base);
auto value = generator.allocate_register();
// 4. Return the Reference Record { [[Base]]: baseValue, [[ReferencedName]]: propertyKey, [[Strict]]: strict, [[ThisValue]]: actualThis }.
if (computed_property.has_value()) {
// 5. Let propertyKey be ? ToPropertyKey(propertyNameValue).
generator.emit_get_by_value_with_this(value, super_base, *computed_property, this_value);
} else {
// 3. Let propertyKey be StringValue of IdentifierName.
auto property_key_table_index = generator.intern_property_key(as<Identifier>(member_expression.property()).string());
generator.emit_get_by_id_with_this(value, super_base, property_key_table_index, this_value);
}
return BaseAndValue { this_value, value };
}
auto base = member_expression.object().generate_bytecode(generator).value();
auto value = generator.allocate_register();
if (member_expression.is_computed()) {
auto property = member_expression.property().generate_bytecode(generator).value();
generator.emit_get_by_value(value, base, property);
} else if (is<PrivateIdentifier>(member_expression.property())) {
generator.emit<Bytecode::Op::GetPrivateById>(
value,
base,
generator.intern_identifier(as<PrivateIdentifier>(member_expression.property()).string()));
} else {
auto base_identifier = generator.intern_identifier_for_expression(member_expression.object());
generator.emit_get_by_id(value, base, generator.intern_property_key(as<Identifier>(member_expression.property()).string()), move(base_identifier));
}
return BaseAndValue { base, value };
}
static void generate_optional_chain(Bytecode::Generator& generator, OptionalChain const& optional_chain, ScopedOperand current_value, ScopedOperand current_base, [[maybe_unused]] Optional<ScopedOperand> preferred_dst = {});
Optional<ScopedOperand> CallExpression::generate_bytecode(Bytecode::Generator& generator, Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
Optional<Bytecode::Builtin> builtin;
Optional<ScopedOperand> original_callee;
auto original_this_value = generator.add_constant(js_undefined());
auto dst = choose_dst(generator, preferred_dst);
Bytecode::Op::CallType call_type = Bytecode::Op::CallType::Call;
if (is<NewExpression>(this)) {
original_callee = m_callee->generate_bytecode(generator).value();
call_type = Bytecode::Op::CallType::Construct;
} else if (is<MemberExpression>(*m_callee)) {
auto& member_expression = static_cast<MemberExpression const&>(*m_callee);
auto base_and_value = get_base_and_value_from_member_expression(generator, member_expression);
original_callee = base_and_value.value;
original_this_value = base_and_value.base;
builtin = Bytecode::get_builtin(member_expression);
} else if (is<OptionalChain>(*m_callee)) {
auto& optional_chain = static_cast<OptionalChain const&>(*m_callee);
original_callee = generator.allocate_register();
original_this_value = generator.allocate_register();
generate_optional_chain(generator, optional_chain, *original_callee, original_this_value);
} else if (is<Identifier>(*m_callee)) {
// If the original_callee is an identifier, we may need to extract a `this` value.
// This is important when we're inside a `with` statement and calling a method on
// the environment's binding object.
// NOTE: If the identifier refers to a known "local" or "global", we know it can't be
// a `with` binding, so we can skip this.
auto& identifier = static_cast<Identifier const&>(*m_callee);
if (generator.builtin_abstract_operations_enabled() && identifier.is_global()) {
generator.generate_builtin_abstract_operation(identifier, arguments(), dst);
return dst;
}
if (identifier.string() == "eval"sv) {
call_type = Bytecode::Op::CallType::DirectEval;
}
if (identifier.is_local()) {
auto local = generator.local(identifier.local_index());
if (!generator.is_local_initialized(local.operand().index())) {
generator.emit<Bytecode::Op::ThrowIfTDZ>(local);
}
original_callee = local;
} else if (identifier.is_global()) {
original_callee = m_callee->generate_bytecode(generator).value();
} else {
original_callee = generator.allocate_register();
original_this_value = generator.allocate_register();
generator.emit<Bytecode::Op::GetCalleeAndThisFromEnvironment>(
*original_callee,
original_this_value,
generator.intern_identifier(identifier.string()));
}
} else {
// NB: For non-Reference calls, EvaluateCall sets thisValue to undefined.
// OrdinaryCallBindThis coerces undefined to the global object in sloppy mode at runtime.
original_callee = m_callee->generate_bytecode(generator).value();
}
// NOTE: If the callee/this value isn't already a temporary, we copy them to new registers
// to avoid overwriting them while evaluating arguments.
// Example: foo.bar(Object.getPrototypeOf(foo).bar = null, foo = null)
auto this_value = generator.copy_if_needed_to_preserve_evaluation_order(original_this_value);
auto callee = generator.copy_if_needed_to_preserve_evaluation_order(original_callee.value());
Optional<Bytecode::StringTableIndex> expression_string_index;
if (auto expression_string = this->expression_string(); expression_string.has_value())
expression_string_index = generator.intern_string(expression_string.release_value());
bool has_spread = any_of(arguments(), [](auto& argument) { return argument.is_spread; });
if (has_spread) {
auto arguments = arguments_to_array_for_call(generator, this->arguments()).value();
if (call_type == Op::CallType::Construct) {
generator.emit<Bytecode::Op::CallConstructWithArgumentArray>(dst, callee, this_value, arguments, expression_string_index);
} else if (call_type == Op::CallType::DirectEval) {
generator.emit<Bytecode::Op::CallDirectEvalWithArgumentArray>(dst, callee, this_value, arguments, expression_string_index);
} else {
generator.emit<Bytecode::Op::CallWithArgumentArray>(dst, callee, this_value, arguments, expression_string_index);
}
} else {
Vector<ScopedOperand> argument_operands;
argument_operands.ensure_capacity(arguments().size());
for (auto const& argument : arguments()) {
auto argument_value = argument.value->generate_bytecode(generator).value();
argument_operands.append(generator.copy_if_needed_to_preserve_evaluation_order(argument_value));
}
if (builtin.has_value() && builtin_argument_count(builtin.value()) == argument_operands.size()) {
VERIFY(call_type == Op::CallType::Call);
generator.emit_with_extra_operand_slots<Bytecode::Op::CallBuiltin>(
argument_operands.size(),
dst,
callee,
this_value,
builtin.value(),
expression_string_index,
argument_operands);
} else if (call_type == Op::CallType::Construct) {
generator.emit_with_extra_operand_slots<Bytecode::Op::CallConstruct>(
argument_operands.size(),
dst,
callee,
expression_string_index,
argument_operands);
} else if (call_type == Op::CallType::DirectEval) {
generator.emit_with_extra_operand_slots<Bytecode::Op::CallDirectEval>(
argument_operands.size(),
dst,
callee,
this_value,
expression_string_index,
argument_operands);
} else {
generator.emit_with_extra_operand_slots<Bytecode::Op::Call>(
argument_operands.size(),
dst,
callee,
this_value,
expression_string_index,
argument_operands);
}
}
return dst;
}
static ScopedOperand generate_await(
Bytecode::Generator& generator,
ScopedOperand argument,
ScopedOperand received_completion,
ScopedOperand received_completion_type,
ScopedOperand received_completion_value);
// https://tc39.es/ecma262/#sec-return-statement-runtime-semantics-evaluation
Optional<ScopedOperand> ReturnStatement::generate_bytecode(Bytecode::Generator& generator, Optional<ScopedOperand>) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
Optional<ScopedOperand> return_value;
if (m_argument) {
// ReturnStatement : return Expression ;
// 1. Let exprRef be ? Evaluation of Expression.
// 2. Let exprValue be ? GetValue(exprRef).
return_value = m_argument->generate_bytecode(generator).value();
// 3. If GetGeneratorKind() is async, set exprValue to ? Await(exprValue).
// Spec Issue?: The spec doesn't seem to do implicit await on explicit return for async functions, but does for
// async generators. However, the major engines do so, and this is observable via constructor lookups
// on Promise objects and custom thenables.
// See: https://tc39.es/ecma262/#sec-asyncblockstart
// c. Assert: If we return here, the async function either threw an exception or performed an implicit or explicit return; all awaiting is done.
if (generator.is_in_async_function()) {
auto received_completion = generator.allocate_register();
auto received_completion_type = generator.allocate_register();
auto received_completion_value = generator.allocate_register();
return_value = generate_await(generator, *return_value, received_completion, received_completion_type, received_completion_value);
}
// 4. Return Completion Record { [[Type]]: return, [[Value]]: exprValue, [[Target]]: empty }.
} else {
// ReturnStatement : return ;
// 1. Return Completion Record { [[Type]]: return, [[Value]]: undefined, [[Target]]: empty }.
return_value = generator.add_constant(js_undefined());
}
if (generator.is_in_generator_or_async_function())
generator.emit_return<Bytecode::Op::Yield>(return_value.value());
else
generator.emit_return<Bytecode::Op::Return>(return_value.value());
return return_value;
}
static void get_received_completion_type_and_value(
Bytecode::Generator& generator,
ScopedOperand received_completion,
ScopedOperand received_completion_type,
ScopedOperand received_completion_value)
{
generator.emit<Op::GetCompletionFields>(received_completion_type, received_completion_value, received_completion);
}
enum class AwaitBeforeYield {
No,
Yes,
};
static void generate_yield(Bytecode::Generator& generator,
Bytecode::Label continuation_label,
ScopedOperand argument,
ScopedOperand received_completion,
ScopedOperand received_completion_type,
ScopedOperand received_completion_value,
AwaitBeforeYield await_before_yield)
{
if (!generator.is_in_async_generator_function()) {
generator.emit<Bytecode::Op::Yield>(Bytecode::Label { continuation_label }, argument);
return;
}
if (await_before_yield == AwaitBeforeYield::Yes)
argument = generate_await(generator, argument, received_completion, received_completion_type, received_completion_value);
auto& unwrap_yield_resumption_block = generator.make_block();
generator.emit<Bytecode::Op::Yield>(Bytecode::Label { unwrap_yield_resumption_block }, argument);
generator.switch_to_basic_block(unwrap_yield_resumption_block);
generator.emit_mov(received_completion, generator.accumulator());
get_received_completion_type_and_value(generator, received_completion, received_completion_type, received_completion_value);
// 27.6.3.7 AsyncGeneratorUnwrapYieldResumption ( resumptionValue ), https://tc39.es/ecma262/#sec-asyncgeneratorunwrapyieldresumption
// 1. If resumptionValue.[[Type]] is not return, return ? resumptionValue.
auto& resumption_value_type_is_return_block = generator.make_block();
auto resumption_value_type_is_not_return_result = generator.allocate_register();
generator.emit<Bytecode::Op::StrictlyInequals>(
resumption_value_type_is_not_return_result,
received_completion_type,
generator.add_constant(Value(to_underlying(Completion::Type::Return))));
generator.emit_jump_if(
resumption_value_type_is_not_return_result,
Bytecode::Label { continuation_label },
Bytecode::Label { resumption_value_type_is_return_block });
generator.switch_to_basic_block(resumption_value_type_is_return_block);
// 2. Let awaited be Completion(Await(resumptionValue.[[Value]])).
generate_await(generator, received_completion_value, received_completion, received_completion_type, received_completion_value);
// 3. If awaited.[[Type]] is throw, return ? awaited.
auto& awaited_type_is_normal_block = generator.make_block();
auto awaited_type_is_throw_result = generator.allocate_register();
generator.emit<Bytecode::Op::StrictlyEquals>(
awaited_type_is_throw_result,
received_completion_type,
generator.add_constant(Value(to_underlying(Completion::Type::Throw))));
generator.emit_jump_if(
awaited_type_is_throw_result,
Bytecode::Label { continuation_label },
Bytecode::Label { awaited_type_is_normal_block });
// 4. Assert: awaited.[[Type]] is normal.
generator.switch_to_basic_block(awaited_type_is_normal_block);
// 5. Return Completion Record { [[Type]]: return, [[Value]]: awaited.[[Value]], [[Target]]: empty }.
generator.emit<Bytecode::Op::SetCompletionType>(received_completion, Completion::Type::Return);
generator.emit<Bytecode::Op::Jump>(continuation_label);
}
Optional<ScopedOperand> YieldExpression::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
// Note: We need to catch any scheduled exceptions and reschedule them on re-entry
// as the act of yielding would otherwise clear them out
// This only applies when we are in a finalizer
bool is_in_finalizer = generator.is_in_finalizer();
Optional<ScopedOperand> saved_exception;
Bytecode::Generator::SourceLocationScope scope(generator, *this);
VERIFY(generator.is_in_generator_function());
auto received_completion = generator.allocate_register();
auto received_completion_type = generator.allocate_register();
auto received_completion_value = generator.allocate_register();
if (m_is_yield_from) {
// 15.5.5 Runtime Semantics: Evaluation, https://tc39.es/ecma262/#sec-generator-function-definitions-runtime-semantics-evaluation
// 1. Let generatorKind be GetGeneratorKind().
// NOTE: is_in_async_generator_function differentiates the generator kind.
// 2. Let exprRef be ? Evaluation of AssignmentExpression.
// 3. Let value be ? GetValue(exprRef).
VERIFY(m_argument);
auto value = m_argument->generate_bytecode(generator).value();
// 4. Let iteratorRecord be ? GetIterator(value, generatorKind).
// 5. Let iterator be iteratorRecord.[[Iterator]].
auto iterator = generator.allocate_register();
auto next_method = generator.allocate_register();
auto iterator_done_property = generator.allocate_register();
auto iterator_hint = generator.is_in_async_generator_function() ? IteratorHint::Async : IteratorHint::Sync;
generator.emit<Bytecode::Op::GetIterator>(iterator, next_method, iterator_done_property, value, iterator_hint);
// 6. Let received be NormalCompletion(undefined).
// See get_received_completion_type_and_value above.
generator.emit_mov(received_completion_type, generator.add_constant(Value(to_underlying(Completion::Type::Normal))));
generator.emit_mov(received_completion_value, generator.add_constant(js_undefined()));
// 7. Repeat,
auto& loop_block = generator.make_block();
auto& continuation_block = generator.make_block();
auto& loop_end_block = generator.make_block();
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { loop_block });
generator.switch_to_basic_block(loop_block);
// a. If received.[[Type]] is normal, then
auto& type_is_normal_block = generator.make_block();
auto& is_type_throw_block = generator.make_block();
auto received_completion_type_register_is_normal = generator.allocate_register();
generator.emit<Bytecode::Op::StrictlyEquals>(
received_completion_type_register_is_normal,
received_completion_type,
generator.add_constant(Value(to_underlying(Completion::Type::Normal))));
generator.emit_jump_if(
received_completion_type_register_is_normal,
Bytecode::Label { type_is_normal_block },
Bytecode::Label { is_type_throw_block });
generator.switch_to_basic_block(type_is_normal_block);
// i. Let innerResult be ? Call(iteratorRecord.[[NextMethod]], iteratorRecord.[[Iterator]], « received.[[Value]] »).
auto inner_result = generator.allocate_register();
generator.emit_with_extra_operand_slots<Bytecode::Op::Call>(1, inner_result, next_method, iterator, OptionalNone {}, ReadonlySpan<ScopedOperand> { &received_completion_value, 1 });
// ii. If generatorKind is async, set innerResult to ? Await(innerResult).
if (generator.is_in_async_generator_function()) {
auto new_inner_result = generate_await(generator, inner_result, received_completion, received_completion_type, received_completion_value);
generator.emit_mov(inner_result, new_inner_result);
}
// iii. If innerResult is not an Object, throw a TypeError exception.
generator.emit<Bytecode::Op::ThrowIfNotObject>(inner_result);
// iv. Let done be ? IteratorComplete(innerResult).
auto done = generator.allocate_register();
generator.emit_iterator_complete(done, inner_result);
// v. If done is true, then
auto& type_is_normal_done_block = generator.make_block();
auto& type_is_normal_not_done_block = generator.make_block();
generator.emit_jump_if(
done,
Bytecode::Label { type_is_normal_done_block },
Bytecode::Label { type_is_normal_not_done_block });
generator.switch_to_basic_block(type_is_normal_done_block);
// 1. Return ? IteratorValue(innerResult).
auto return_value = generator.allocate_register();
generator.emit_iterator_value(return_value, inner_result);
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { loop_end_block });
generator.switch_to_basic_block(type_is_normal_not_done_block);
// vi. If generatorKind is async, set received to Completion(AsyncGeneratorYield(? IteratorValue(innerResult))).
// vii. Else, set received to Completion(GeneratorYield(innerResult)).
{
// FIXME: Yield currently only accepts a Value, not an object conforming to the IteratorResult interface, so we have to do an observable lookup of `value` here.
// This only matters for non-async generators.
auto current_value = generator.allocate_register();
generator.emit_iterator_value(current_value, inner_result);
if (is_in_finalizer) {
saved_exception = generator.allocate_register();
generator.emit_mov(Bytecode::Operand(*saved_exception), Bytecode::Operand(Bytecode::Register::exception()));
}
generate_yield(generator,
Bytecode::Label { continuation_block },
current_value,
received_completion,
received_completion_type,
received_completion_value,
AwaitBeforeYield::No);
}
// b. Else if received.[[Type]] is throw, then
generator.switch_to_basic_block(is_type_throw_block);
auto& type_is_throw_block = generator.make_block();
auto& type_is_return_block = generator.make_block();
auto received_completion_type_register_is_throw = generator.allocate_register();
generator.emit<Bytecode::Op::StrictlyEquals>(
received_completion_type_register_is_throw,
received_completion_type,
generator.add_constant(Value(to_underlying(Completion::Type::Throw))));
generator.emit_jump_if(
received_completion_type_register_is_throw,
Bytecode::Label { type_is_throw_block },
Bytecode::Label { type_is_return_block });
generator.switch_to_basic_block(type_is_throw_block);
// i. Let throw be ? GetMethod(iterator, "throw").
auto throw_method = generator.allocate_register();
generator.emit<Bytecode::Op::GetMethod>(throw_method, iterator, generator.intern_property_key("throw"_utf16_fly_string));
// ii. If throw is not undefined, then
auto& throw_method_is_defined_block = generator.make_block();
auto& throw_method_is_undefined_block = generator.make_block();
generator.emit<Bytecode::Op::JumpUndefined>(
throw_method,
Bytecode::Label { throw_method_is_undefined_block },
Bytecode::Label { throw_method_is_defined_block });
generator.switch_to_basic_block(throw_method_is_defined_block);
// 1. Let innerResult be ? Call(throw, iterator, « received.[[Value]] »).
generator.emit_with_extra_operand_slots<Bytecode::Op::Call>(1, inner_result, throw_method, iterator, OptionalNone {}, ReadonlySpan<ScopedOperand> { &received_completion_value, 1 });
// 2. If generatorKind is async, set innerResult to ? Await(innerResult).
if (generator.is_in_async_generator_function()) {
auto new_result = generate_await(generator, inner_result, received_completion, received_completion_type, received_completion_value);
generator.emit_mov(inner_result, new_result);
}
// 3. NOTE: Exceptions from the inner iterator throw method are propagated. Normal completions from an inner throw method are processed similarly to an inner next.
// 4. If innerResult is not an Object, throw a TypeError exception.
generator.emit<Bytecode::Op::ThrowIfNotObject>(inner_result);
// 5. Let done be ? IteratorComplete(innerResult).
generator.emit_iterator_complete(done, inner_result);
// 6. If done is true, then
auto& type_is_throw_done_block = generator.make_block();
auto& type_is_throw_not_done_block = generator.make_block();
generator.emit_jump_if(
done,
Bytecode::Label { type_is_throw_done_block },
Bytecode::Label { type_is_throw_not_done_block });
generator.switch_to_basic_block(type_is_throw_done_block);
// a. Return ? IteratorValue(innerResult).
generator.emit_iterator_value(return_value, inner_result);
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { loop_end_block });
generator.switch_to_basic_block(type_is_throw_not_done_block);
{
// 7. If generatorKind is async, set received to Completion(AsyncGeneratorYield(? IteratorValue(innerResult))).
// 8. Else, set received to Completion(GeneratorYield(innerResult)).
// FIXME: Yield currently only accepts a Value, not an object conforming to the IteratorResult interface, so we have to do an observable lookup of `value` here.
// This only matters for non-async generators.
auto yield_value = generator.allocate_register();
generator.emit_iterator_value(yield_value, inner_result);
generate_yield(generator, Bytecode::Label { continuation_block }, yield_value, received_completion, received_completion_type, received_completion_value, AwaitBeforeYield::No);
}
generator.switch_to_basic_block(throw_method_is_undefined_block);
// 1. NOTE: If iterator does not have a throw method, this throw is going to terminate the yield* loop. But first we need to give iterator a chance to clean up.
// 2. Let closeCompletion be Completion Record { [[Type]]: normal, [[Value]]: empty, [[Target]]: empty }.
// 3. If generatorKind is async, perform ? AsyncIteratorClose(iteratorRecord, closeCompletion).
if (generator.is_in_async_generator_function()) {
// Inline AsyncIteratorClose with proper Await op to avoid
// spinning the event loop synchronously.
auto return_method = generator.allocate_register();
generator.emit<Bytecode::Op::GetMethod>(return_method, iterator, generator.intern_property_key("return"_utf16_fly_string));
auto& call_return_block = generator.make_block();
auto& after_close = generator.make_block();
generator.emit<Bytecode::Op::JumpUndefined>(return_method, Bytecode::Label { after_close }, Bytecode::Label { call_return_block });
generator.switch_to_basic_block(call_return_block);
auto inner_result = generator.allocate_register();
generator.emit_with_extra_operand_slots<Bytecode::Op::Call>(0, inner_result, return_method, iterator, OptionalNone {}, ReadonlySpan<ScopedOperand> {});
auto awaited = generate_await(generator, inner_result, received_completion, received_completion_type, received_completion_value);
generator.emit<Bytecode::Op::ThrowIfNotObject>(awaited);
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { after_close });
generator.switch_to_basic_block(after_close);
}
// 4. Else, perform ? IteratorClose(iteratorRecord, closeCompletion).
else {
generator.emit<Bytecode::Op::IteratorClose>(iterator, next_method, done, Completion::Type::Normal, generator.add_constant(js_undefined()));
}
// 5. NOTE: The next step throws a TypeError to indicate that there was a yield* protocol violation: iterator does not have a throw method.
// 6. Throw a TypeError exception.
auto exception = generator.allocate_register();
generator.emit<Bytecode::Op::NewTypeError>(exception, generator.intern_string(ErrorType::YieldFromIteratorMissingThrowMethod.message()));
generator.perform_needed_unwinds<Bytecode::Op::Throw>();
generator.emit<Bytecode::Op::Throw>(exception);
// c. Else,
// i. Assert: received.[[Type]] is return.
generator.switch_to_basic_block(type_is_return_block);
// ii. Let return be ? GetMethod(iterator, "return").
auto return_method = generator.allocate_register();
generator.emit<Bytecode::Op::GetMethod>(return_method, iterator, generator.intern_property_key("return"_utf16_fly_string));
// iii. If return is undefined, then
auto& return_is_undefined_block = generator.make_block();
auto& return_is_defined_block = generator.make_block();
generator.emit<Bytecode::Op::JumpUndefined>(
return_method,
Bytecode::Label { return_is_undefined_block },
Bytecode::Label { return_is_defined_block });
generator.switch_to_basic_block(return_is_undefined_block);
// 1. If generatorKind is async, set received.[[Value]] to ? Await(received.[[Value]]).
if (generator.is_in_async_generator_function()) {
generate_await(generator, received_completion_value, received_completion, received_completion_type, received_completion_value);
}
// 2. Return ? received.
// NOTE: This will always be a return completion.
generator.emit_return<Bytecode::Op::Yield>(received_completion_value);
generator.switch_to_basic_block(return_is_defined_block);
// iv. Let innerReturnResult be ? Call(return, iterator, « received.[[Value]] »).
auto inner_return_result = generator.allocate_register();
generator.emit_with_extra_operand_slots<Bytecode::Op::Call>(1, inner_return_result, return_method, iterator, OptionalNone {}, ReadonlySpan<ScopedOperand> { &received_completion_value, 1 });
// v. If generatorKind is async, set innerReturnResult to ? Await(innerReturnResult).
if (generator.is_in_async_generator_function()) {
auto new_value = generate_await(generator, inner_return_result, received_completion, received_completion_type, received_completion_value);
generator.emit_mov(inner_return_result, new_value);
}
// vi. If innerReturnResult is not an Object, throw a TypeError exception.
generator.emit<Bytecode::Op::ThrowIfNotObject>(inner_return_result);
// vii. Let done be ? IteratorComplete(innerReturnResult).
generator.emit_iterator_complete(done, inner_return_result);
// viii. If done is true, then
auto& type_is_return_done_block = generator.make_block();
auto& type_is_return_not_done_block = generator.make_block();
generator.emit_jump_if(
done,
Bytecode::Label { type_is_return_done_block },
Bytecode::Label { type_is_return_not_done_block });
generator.switch_to_basic_block(type_is_return_done_block);
// 1. Let value be ? IteratorValue(innerReturnResult).
auto inner_return_result_value = generator.allocate_register();
generator.emit_iterator_value(inner_return_result_value, inner_return_result);
// 2. Return Completion Record { [[Type]]: return, [[Value]]: value, [[Target]]: empty }.
generator.emit_return<Bytecode::Op::Yield>(inner_return_result_value);
generator.switch_to_basic_block(type_is_return_not_done_block);
// ix. If generatorKind is async, set received to Completion(AsyncGeneratorYield(? IteratorValue(innerReturnResult))).
// x. Else, set received to Completion(GeneratorYield(innerReturnResult)).
// FIXME: Yield currently only accepts a Value, not an object conforming to the IteratorResult interface, so we have to do an observable lookup of `value` here.
// This only matters for non-async generators.
auto received = generator.allocate_register();
generator.emit_iterator_value(received, inner_return_result);
generate_yield(generator, Bytecode::Label { continuation_block }, received, received_completion, received_completion_type, received_completion_value, AwaitBeforeYield::No);
generator.switch_to_basic_block(continuation_block);
if (is_in_finalizer)
generator.emit_mov(Bytecode::Operand(Bytecode::Register::exception()), Bytecode::Operand(*saved_exception));
generator.emit_mov(received_completion, generator.accumulator());
get_received_completion_type_and_value(generator, received_completion, received_completion_type, received_completion_value);
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { loop_block });
generator.switch_to_basic_block(loop_end_block);
return return_value;
}
Optional<ScopedOperand> argument;
if (m_argument)
argument = m_argument->generate_bytecode(generator).value();
else
argument = generator.add_constant(js_undefined());
auto& continuation_block = generator.make_block();
if (is_in_finalizer) {
saved_exception = generator.allocate_register();
generator.emit_mov(Bytecode::Operand(*saved_exception), Bytecode::Operand(Bytecode::Register::exception()));
}
generate_yield(generator, Bytecode::Label { continuation_block }, *argument, received_completion, received_completion_type, received_completion_value, AwaitBeforeYield::Yes);
generator.switch_to_basic_block(continuation_block);
if (is_in_finalizer)
generator.emit_mov(Bytecode::Operand(Bytecode::Register::exception()), Bytecode::Operand(*saved_exception));
generator.emit_mov(received_completion, generator.accumulator());
get_received_completion_type_and_value(generator, received_completion, received_completion_type, received_completion_value);
auto& normal_completion_continuation_block = generator.make_block();
auto& throw_completion_continuation_block = generator.make_block();
auto received_completion_type_is_normal = generator.allocate_register();
generator.emit<Bytecode::Op::StrictlyEquals>(
received_completion_type_is_normal,
received_completion_type,
generator.add_constant(Value(to_underlying(Completion::Type::Normal))));
generator.emit_jump_if(
received_completion_type_is_normal,
Bytecode::Label { normal_completion_continuation_block },
Bytecode::Label { throw_completion_continuation_block });
auto& throw_value_block = generator.make_block();
auto& return_value_block = generator.make_block();
generator.switch_to_basic_block(throw_completion_continuation_block);
auto received_completion_type_is_throw = generator.allocate_register();
generator.emit<Bytecode::Op::StrictlyEquals>(
received_completion_type_is_throw,
received_completion_type,
generator.add_constant(Value(to_underlying(Completion::Type::Throw))));
// If type is not equal to "throw" or "normal", assume it's "return".
generator.emit_jump_if(
received_completion_type_is_throw,
Bytecode::Label { throw_value_block },
Bytecode::Label { return_value_block });
generator.switch_to_basic_block(throw_value_block);
generator.perform_needed_unwinds<Bytecode::Op::Throw>();
generator.emit<Bytecode::Op::Throw>(received_completion_value);
generator.switch_to_basic_block(return_value_block);
generator.emit_return<Bytecode::Op::Yield>(received_completion_value);
generator.switch_to_basic_block(normal_completion_continuation_block);
return received_completion_value;
}
Optional<ScopedOperand> IfStatement::generate_bytecode(Bytecode::Generator& generator, Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
// test
// jump if_true (true) true (false) false
// true
// jump always (true) end
// false
// jump always (true) end
// end
auto predicate = m_predicate->generate_bytecode(generator).value();
Optional<ScopedOperand> completion;
if (generator.must_propagate_completion()) {
completion = choose_dst(generator, preferred_dst);
generator.emit_mov(*completion, generator.add_constant(js_undefined()));
}
auto build_block = [&](auto node, Optional<BasicBlock&> end_block = {}) -> Optional<ScopedOperand> {
Optional<Bytecode::Generator::CompletionRegisterScope> completion_scope;
if (completion.has_value())
completion_scope.emplace(generator, *completion);
auto value = node->generate_bytecode(generator, completion);
if (!generator.is_current_block_terminated()) {
if (generator.must_propagate_completion() && value.has_value())
generator.emit_mov(*completion, *value);
if (end_block.has_value())
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { *end_block });
}
return Optional<ScopedOperand> {};
};
// OPTIMIZATION: if the predicate is always true/false, only build the consequent/alternate blocks, respectively.
if (auto constant = generator.try_get_constant(predicate); constant.has_value()) {
if (constant->to_boolean_slow_case()) {
(void)build_block(m_consequent);
} else if (m_alternate) {
(void)build_block(m_alternate);
}
return completion;
}
auto& true_block = generator.make_block();
auto& false_block = generator.make_block();
// NOTE: if there is no 'else' block the end block is the same as the false block
auto& end_block = m_alternate ? generator.make_block() : false_block;
generator.emit_jump_if(
predicate,
Bytecode::Label { true_block },
Bytecode::Label { false_block });
generator.switch_to_basic_block(true_block);
(void)build_block(m_consequent, { end_block });
if (m_alternate) {
generator.switch_to_basic_block(false_block);
(void)build_block(m_alternate, { end_block });
}
generator.switch_to_basic_block(end_block);
return completion;
}
Optional<ScopedOperand> ContinueStatement::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
if (!m_target_label.has_value()) {
generator.generate_continue();
return Optional<ScopedOperand> {};
}
generator.generate_continue(m_target_label.value());
return Optional<ScopedOperand> {};
}
Optional<ScopedOperand> DebuggerStatement::generate_bytecode(Bytecode::Generator&, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
return Optional<ScopedOperand> {};
}
Optional<ScopedOperand> ConditionalExpression::generate_bytecode(Bytecode::Generator& generator, Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
auto test = m_test->generate_bytecode(generator).value();
// OPTIMIZATION: if the predicate is always true/false, only build the consequent/alternate blocks, respectively.
if (auto constant = generator.try_get_constant(test); constant.has_value()) {
auto is_always_true = constant->to_boolean_slow_case();
if (is_always_true)
return m_consequent->generate_bytecode(generator).value();
return m_alternate->generate_bytecode(generator).value();
}
// test
// jump if_true (true) true (false) false
// true
// jump always (true) end
// false
// jump always (true) end
// end
auto& true_block = generator.make_block();
auto& false_block = generator.make_block();
auto& end_block = generator.make_block();
generator.emit_jump_if(
test,
Bytecode::Label { true_block },
Bytecode::Label { false_block });
auto dst = choose_dst(generator, preferred_dst);
generator.switch_to_basic_block(true_block);
auto consequent = m_consequent->generate_bytecode(generator).value();
generator.emit_mov(dst, consequent);
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { end_block });
generator.switch_to_basic_block(false_block);
auto alternate = m_alternate->generate_bytecode(generator).value();
generator.emit_mov(dst, alternate);
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { end_block });
generator.switch_to_basic_block(end_block);
return dst;
}
Optional<ScopedOperand> SequenceExpression::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
Optional<ScopedOperand> last_value;
for (auto& expression : m_expressions) {
last_value = expression->generate_bytecode(generator);
}
return last_value;
}
Optional<ScopedOperand> TemplateLiteral::generate_bytecode(Bytecode::Generator& generator, Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
auto dst = choose_dst(generator, preferred_dst);
Vector segments(m_expressions);
segments.remove_all_matching([&](auto expr) {
return expr->is_string_literal() && static_cast<StringLiteral const&>(*expr).value().is_empty();
});
// OPTIMIZATION: Empty template literal (``) can be turned into empty string literal ("")
if (segments.size() == 0)
return generator.add_constant(Value { GC::Ref { generator.vm().empty_string() } });
if (segments.size() == 1) {
auto value = segments[0]->generate_bytecode(generator).value();
// OPTIMIZATION: String literal template (`xyz`) can be returned directly
if (value.operand().is_constant())
return value;
// OPTIMIZATION: `${x}` can be turned into ToString(x) op
generator.emit<Bytecode::Op::ToString>(dst, value);
return dst;
}
for (size_t i = 0; i < segments.size(); i++) {
auto expr = segments[i];
auto value = expr->generate_bytecode(generator).value();
if (i == 0) {
if (expr->is_string_literal()) {
generator.emit_mov(dst, value);
} else {
generator.emit<Bytecode::Op::ToString>(dst, value);
}
} else {
generator.emit<Bytecode::Op::ConcatString>(dst, value);
}
}
return dst;
}
struct TagAndThisValue {
ScopedOperand tag;
ScopedOperand this_value;
};
Optional<ScopedOperand> TaggedTemplateLiteral::generate_bytecode(Bytecode::Generator& generator, Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
auto [tag, this_value] = [&]() -> TagAndThisValue {
if (is<MemberExpression>(*m_tag)) {
auto& member_expression = static_cast<MemberExpression const&>(*m_tag);
auto base_and_value = get_base_and_value_from_member_expression(generator, member_expression);
return TagAndThisValue { .tag = base_and_value.value, .this_value = base_and_value.base };
}
if (is<Identifier>(*m_tag)) {
auto& identifier = static_cast<Identifier const&>(*m_tag);
if (identifier.is_local() || identifier.is_global()) {
// Keep the normal Identifier path so local/global tags preserve
// TDZ behavior; only non-local identifiers need with-aware
// callee/this extraction.
auto tag = m_tag->generate_bytecode(generator).value();
return TagAndThisValue { .tag = tag, .this_value = generator.add_constant(js_undefined()) };
}
auto tag = generator.allocate_register();
auto this_value = generator.allocate_register();
generator.emit<Bytecode::Op::GetCalleeAndThisFromEnvironment>(
tag,
this_value,
generator.intern_identifier(identifier.string()));
return TagAndThisValue { .tag = tag, .this_value = this_value };
}
auto tag = m_tag->generate_bytecode(generator).value();
return TagAndThisValue { .tag = tag, .this_value = generator.add_constant(js_undefined()) };
}();
// 13.2.8.4 GetTemplateObject ( templateLiteral ), https://tc39.es/ecma262/#sec-gettemplateobject
Vector<ScopedOperand> string_regs;
auto& expressions = m_template_literal->expressions();
for (size_t i = 0; i < expressions.size(); i += 2) {
// NOTE: If the string contains invalid escapes we get a null expression here,
// which we then convert to the expected `undefined` TV. See
// 12.9.6.1 Static Semantics: TV, https://tc39.es/ecma262/#sec-static-semantics-tv
if (is<NullLiteral>(expressions[i])) {
string_regs.append(generator.add_constant(js_undefined()));
} else {
auto value = expressions[i]->generate_bytecode(generator).value();
string_regs.append(move(value));
}
}
auto& raw_strings = m_template_literal->raw_strings();
for (auto const& raw_string : raw_strings) {
auto value = raw_string->generate_bytecode(generator).value();
string_regs.append(move(value));
}
auto strings_array = generator.allocate_register();
generator.emit_with_extra_operand_slots<Bytecode::Op::GetTemplateObject>(
string_regs.size(),
strings_array,
generator.next_template_object_cache(),
string_regs);
Vector<ScopedOperand> argument_regs;
argument_regs.append(strings_array);
for (size_t i = 1; i < expressions.size(); i += 2) {
auto argument = expressions[i]->generate_bytecode(generator).value();
argument_regs.append(move(argument));
}
auto dst = choose_dst(generator, preferred_dst);
generator.emit_with_extra_operand_slots<Bytecode::Op::Call>(argument_regs.size(), dst, tag, this_value, OptionalNone {}, argument_regs);
return dst;
}
Optional<ScopedOperand> UpdateExpression::generate_bytecode(Bytecode::Generator& generator, Optional<ScopedOperand>) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
auto reference = generator.emit_load_from_reference(*m_argument);
Optional<ScopedOperand> previous_value_for_postfix;
if (m_op == UpdateOp::Increment) {
if (m_prefixed) {
generator.emit<Bytecode::Op::Increment>(*reference.loaded_value);
} else {
previous_value_for_postfix = generator.allocate_register();
generator.emit<Bytecode::Op::PostfixIncrement>(*previous_value_for_postfix, *reference.loaded_value);
}
} else {
if (m_prefixed) {
generator.emit<Bytecode::Op::Decrement>(*reference.loaded_value);
} else {
previous_value_for_postfix = generator.allocate_register();
generator.emit<Bytecode::Op::PostfixDecrement>(*previous_value_for_postfix, *reference.loaded_value);
}
}
if (is<Identifier>(*m_argument))
generator.emit_store_to_reference(static_cast<Identifier const&>(*m_argument), *reference.loaded_value);
else
generator.emit_store_to_reference(reference, *reference.loaded_value);
if (!m_prefixed)
return *previous_value_for_postfix;
return *reference.loaded_value;
}
Optional<ScopedOperand> ThrowStatement::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
auto argument = m_argument->generate_bytecode(generator).value();
generator.perform_needed_unwinds<Bytecode::Op::Throw>();
generator.emit<Bytecode::Op::Throw>(argument);
return Optional<ScopedOperand> {};
}
Optional<ScopedOperand> BreakStatement::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
// FIXME: Handle finally blocks in a graceful manner
// We need to execute the finally block, but tell it to resume
// execution at the designated block
if (!m_target_label.has_value()) {
generator.generate_break();
return Optional<ScopedOperand> {};
}
generator.generate_break(m_target_label.value());
return Optional<ScopedOperand> {};
}
// Try/finally uses an explicit completion record protocol:
//
// 1. Allocate two registers: completion_type and completion_value
// 2. Every path into the finally body sets these before jumping:
// - Normal exit: completion_type = NORMAL
// - Exception: completion_type = THROW, completion_value = exception
// - Return: completion_type = RETURN, completion_value = return value
// - Break/continue: completion_type = FIRST_JUMP_INDEX + n
// 3. After the finally body, a dispatch chain checks completion_type
// and routes to the correct continuation (next block, jump target,
// return, or rethrow).
//
// For exceptions, the handler table points to an "exception preamble" block
// that catches the exception into completion_value, sets completion_type to
// THROW, and jumps to the finally body.
//
// For nested finally (e.g. break through two finally blocks), trampoline
// blocks chain through each finally layer, with each inner finally dispatching
// to a trampoline that sets up the outer finally's completion record.
Optional<ScopedOperand> TryStatement::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
auto& saved_block = generator.current_block();
Optional<Bytecode::Label> handler_target;
Optional<Bytecode::Generator::UnwindContext> unwind_context;
Bytecode::BasicBlock* next_block { nullptr };
Optional<ScopedOperand> completion;
Optional<Bytecode::Generator::FinallyContext> finally_context;
Bytecode::BasicBlock* finally_body_block_ptr { nullptr };
// Capture the lexical environment at try entry for restoration on catch/exception.
Optional<ScopedOperand> lexical_environment_at_entry;
lexical_environment_at_entry = generator.current_lexical_environment_register();
if (m_finalizer) {
// Allocate completion record registers.
auto completion_type = generator.allocate_register();
auto completion_value = generator.allocate_register();
// Create the exception preamble block (handler table points here for exceptions).
auto& exception_preamble_block = generator.make_block();
// Create the finally body block (all paths converge here).
auto& finally_body_block = generator.make_block();
finally_body_block_ptr = &finally_body_block;
// Set up FinallyContext.
finally_context.emplace(Bytecode::Generator::FinallyContext {
.completion_type = completion_type,
.completion_value = completion_value,
.finally_body = Bytecode::Label { finally_body_block },
.exception_preamble = Bytecode::Label { exception_preamble_block },
.parent = generator.current_finally_context(),
.registered_jumps = {},
.next_jump_index = Bytecode::Generator::FinallyContext::FIRST_JUMP_INDEX,
.lexical_environment_at_entry = lexical_environment_at_entry,
});
generator.set_current_finally_context(&*finally_context);
// Generate exception preamble:
// Catch completion_value
// SetLexicalEnvironment (restore to try entry)
// Mov completion_type, 1 (Throw)
// Jump finally_body
generator.switch_to_basic_block(exception_preamble_block);
generator.emit<Bytecode::Op::Catch>(completion_value);
generator.emit<Bytecode::Op::SetLexicalEnvironment>(*lexical_environment_at_entry);
generator.emit_mov(completion_type, generator.add_constant(Value(Bytecode::Generator::FinallyContext::THROW)));
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { finally_body_block });
// Set up unwind context with exception_preamble as finalizer.
generator.start_boundary(Bytecode::Generator::BlockBoundaryType::ReturnToFinally);
unwind_context.emplace(generator, Bytecode::Label { exception_preamble_block });
}
if (m_handler) {
auto& handler_block = generator.make_block();
generator.switch_to_basic_block(handler_block);
auto caught_value = generator.allocate_register();
generator.emit<Bytecode::Op::Catch>(caught_value);
generator.emit<Bytecode::Op::SetLexicalEnvironment>(*lexical_environment_at_entry);
// OPTIMIZATION: We avoid creating a lexical environment if the catch clause has no parameter.
bool did_create_variable_scope_for_catch_clause = false;
m_handler->parameter().visit(
[&](NonnullRefPtr<Identifier const> const& parameter) -> void {
if (parameter->is_local()) {
auto local = generator.local(parameter->local_index());
generator.emit_mov(local, caught_value);
generator.set_local_initialized(parameter->local_index());
} else {
generator.begin_variable_scope();
did_create_variable_scope_for_catch_clause = true;
auto parameter_identifier = generator.intern_identifier(parameter->string());
generator.emit<Bytecode::Op::CreateVariable>(parameter_identifier, Bytecode::Op::EnvironmentMode::Lexical, false, false, false);
generator.emit<Bytecode::Op::InitializeLexicalBinding>(parameter_identifier, caught_value);
}
},
[&](NonnullRefPtr<BindingPattern const> const& binding_pattern) -> void {
MUST(binding_pattern->for_each_bound_identifier([&](auto const& identifier) {
if (!identifier.is_local())
did_create_variable_scope_for_catch_clause = true;
}));
if (did_create_variable_scope_for_catch_clause)
generator.begin_variable_scope();
MUST(binding_pattern->for_each_bound_identifier([&](auto const& identifier) {
if (identifier.is_local())
return;
auto parameter_identifier = generator.intern_identifier(identifier.string());
generator.emit<Bytecode::Op::CreateVariable>(parameter_identifier, Bytecode::Op::EnvironmentMode::Lexical, false, false, false);
}));
binding_pattern->generate_bytecode(generator, Bytecode::Op::BindingInitializationMode::Initialize, caught_value);
},
[](Empty) -> void {
});
Optional<ScopedOperand> catch_completion;
{
// NB: The catch body needs its own completion register so that
// break/continue inside the catch block carries the catch's
// own completion value rather than leaking a value from an
// enclosing statement.
Optional<Bytecode::Generator::CompletionRegisterScope> completion_scope;
if (generator.must_propagate_completion()) {
catch_completion = generator.allocate_register();
generator.emit_mov(*catch_completion, generator.add_constant(js_undefined()));
completion_scope.emplace(generator, *catch_completion);
}
(void)m_handler->body().generate_bytecode(generator);
}
if (generator.must_propagate_completion()) {
if (catch_completion.has_value() && !generator.is_current_block_terminated()) {
completion = generator.allocate_register();
generator.emit_mov(*completion, *catch_completion);
}
}
handler_target = Bytecode::Label { handler_block };
if (did_create_variable_scope_for_catch_clause)
generator.end_variable_scope();
if (!generator.is_current_block_terminated()) {
if (m_finalizer) {
// Normal exit from catch → set completion_type=Normal, jump to finally.
generator.emit_mov(finally_context->completion_type, generator.add_constant(Value(Bytecode::Generator::FinallyContext::NORMAL)));
generator.emit<Bytecode::Op::Jump>(finally_context->finally_body);
} else {
VERIFY(!next_block);
VERIFY(!unwind_context.has_value());
next_block = &generator.make_block();
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { *next_block });
}
}
}
if (m_finalizer)
generator.end_boundary(Bytecode::Generator::BlockBoundaryType::ReturnToFinally);
if (m_handler) {
if (!m_finalizer) {
auto const* parent_unwind_context = generator.current_unwind_context();
if (parent_unwind_context)
unwind_context.emplace(generator, parent_unwind_context->handler());
else
unwind_context.emplace(generator, OptionalNone());
}
unwind_context->set_handler(handler_target.value());
}
auto& target_block = generator.make_block();
generator.switch_to_basic_block(saved_block);
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { target_block });
if (m_finalizer)
generator.start_boundary(Bytecode::Generator::BlockBoundaryType::ReturnToFinally);
generator.switch_to_basic_block(target_block);
Optional<ScopedOperand> try_completion;
{
// NB: The try body needs its own completion register so that
// break/continue inside the try block carries the try's own
// completion value rather than leaking a value from an enclosing
// statement.
Optional<Bytecode::Generator::CompletionRegisterScope> completion_scope;
if (generator.must_propagate_completion()) {
try_completion = generator.allocate_register();
generator.emit_mov(*try_completion, generator.add_constant(js_undefined()));
completion_scope.emplace(generator, *try_completion);
}
(void)m_block->generate_bytecode(generator);
}
if (!generator.is_current_block_terminated()) {
if (generator.must_propagate_completion()) {
if (try_completion.has_value()) {
completion = generator.allocate_register();
generator.emit_mov(*completion, *try_completion);
}
}
if (m_finalizer) {
// Normal exit from try → set completion_type=Normal, jump to finally.
generator.emit_mov(finally_context->completion_type, generator.add_constant(Value(Bytecode::Generator::FinallyContext::NORMAL)));
generator.emit<Bytecode::Op::Jump>(finally_context->finally_body);
} else {
VERIFY(unwind_context.has_value());
unwind_context.clear();
if (!next_block)
next_block = &generator.make_block();
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { *next_block });
}
}
if (m_finalizer)
generator.end_boundary(Bytecode::Generator::BlockBoundaryType::ReturnToFinally);
// Now generate the finally body and after-finally dispatch.
// We deferred this so that registered_jumps from break/continue in the try body are available.
if (m_finalizer && finally_context.has_value()) {
generator.set_current_finally_context(finally_context->parent);
// Clear the unwind context so that blocks created during finally body generation
// don't inherit the inner handler/finalizer (the inner unwind context is already
// popped at runtime by the time the finally body runs).
unwind_context.clear();
generator.switch_to_basic_block(*finally_body_block_ptr);
generator.start_boundary(Bytecode::Generator::BlockBoundaryType::LeaveFinally);
{
// NB: The finally body needs its own completion register so that
// break/continue inside the finally block carries the finally's
// own completion value (initialized to undefined) rather than
// leaking the try/catch block's completion value through.
Optional<ScopedOperand> finally_completion;
Optional<Bytecode::Generator::CompletionRegisterScope> completion_scope;
if (generator.must_propagate_completion()) {
finally_completion = generator.allocate_register();
generator.emit_mov(*finally_completion, generator.add_constant(js_undefined()));
completion_scope.emplace(generator, *finally_completion);
}
(void)m_finalizer->generate_bytecode(generator);
}
generator.end_boundary(Bytecode::Generator::BlockBoundaryType::LeaveFinally);
if (!generator.is_current_block_terminated()) {
if (!next_block)
next_block = &generator.make_block();
auto const& completion_type = finally_context->completion_type;
auto const& completion_value = finally_context->completion_value;
// After-finally dispatch chain: a series of JumpStrictlyEquals that check
// completion_type and route to the right continuation. Order:
// 1. NORMAL → fall through to next block
// 2. Each registered break/continue target
// 3. RETURN → return/yield the completion_value
// 4. Default → rethrow completion_value (must be THROW)
auto& after_normal_check = generator.make_block();
generator.emit<Bytecode::Op::JumpStrictlyEquals>(
completion_type, generator.add_constant(Value(Bytecode::Generator::FinallyContext::NORMAL)),
Bytecode::Label { *next_block }, Bytecode::Label { after_normal_check });
generator.switch_to_basic_block(after_normal_check);
// Registered break/continue jumps (indices 3+)
for (auto const& jump : finally_context->registered_jumps) {
auto& after_jump_check = generator.make_block();
generator.emit<Bytecode::Op::JumpStrictlyEquals>(
completion_type, generator.add_constant(Value(jump.index)),
jump.target, Bytecode::Label { after_jump_check });
generator.switch_to_basic_block(after_jump_check);
}
auto& return_block = generator.make_block();
auto& rethrow_block = generator.make_block();
generator.emit<Bytecode::Op::JumpStrictlyEquals>(
completion_type, generator.add_constant(Value(Bytecode::Generator::FinallyContext::RETURN)),
Bytecode::Label { return_block }, Bytecode::Label { rethrow_block });
// Generate return block.
generator.switch_to_basic_block(return_block);
if (finally_context->parent) {
// Nested finally: copy completion record to outer and jump to outer finally body.
auto& outer = *finally_context->parent;
generator.emit_mov(outer.completion_type, completion_type);
generator.emit_mov(outer.completion_value, completion_value);
generator.emit<Bytecode::Op::Jump>(outer.finally_body);
} else {
if (generator.is_in_generator_function()) {
generator.emit<Bytecode::Op::Yield>(OptionalNone {}, completion_value);
} else {
generator.emit<Bytecode::Op::Return>(completion_value);
}
}
// Default: rethrow the exception.
generator.switch_to_basic_block(rethrow_block);
generator.emit<Bytecode::Op::Throw>(completion_value);
}
}
generator.switch_to_basic_block(next_block ? *next_block : saved_block);
if (generator.must_propagate_completion()) {
if (!completion.has_value())
return generator.add_constant(js_undefined());
}
return completion;
}
Optional<ScopedOperand> SwitchStatement::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
return generate_labelled_evaluation(generator, {});
}
Optional<ScopedOperand> SwitchStatement::generate_labelled_evaluation(Bytecode::Generator& generator, Vector<FlyString> const& label_set, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
Optional<ScopedOperand> completion;
if (generator.must_propagate_completion()) {
completion = generator.allocate_register();
generator.emit_mov(*completion, generator.add_constant(js_undefined()));
}
auto discriminant = m_discriminant->generate_bytecode(generator).value();
Vector<Bytecode::BasicBlock&> case_blocks;
Bytecode::BasicBlock* entry_block_for_default { nullptr };
Bytecode::BasicBlock* next_test_block = &generator.make_block();
bool did_create_lexical_environment = false;
if (has_lexical_declarations())
did_create_lexical_environment = generator.emit_block_declaration_instantiation(*this);
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { *next_test_block });
Queue<Bytecode::BasicBlock*> test_blocks;
for (auto& switch_case : m_cases) {
if (switch_case->test())
test_blocks.enqueue(&generator.make_block());
}
for (auto& switch_case : m_cases) {
auto& case_block = generator.make_block();
if (switch_case->test()) {
generator.switch_to_basic_block(*next_test_block);
auto test_value = switch_case->test()->generate_bytecode(generator).value();
auto result = generator.allocate_register();
generator.emit<Bytecode::Op::StrictlyEquals>(result, test_value, discriminant);
next_test_block = test_blocks.dequeue();
generator.emit_jump_if(
result,
Bytecode::Label { case_block },
Bytecode::Label { *next_test_block });
} else {
entry_block_for_default = &case_block;
}
case_blocks.append(case_block);
}
generator.switch_to_basic_block(*next_test_block);
auto& end_block = generator.make_block();
if (entry_block_for_default != nullptr) {
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { *entry_block_for_default });
} else {
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { end_block });
}
auto current_block = case_blocks.begin();
generator.begin_breakable_scope(Bytecode::Label { end_block }, label_set, completion);
for (auto& switch_case : m_cases) {
generator.switch_to_basic_block(*current_block);
{
Optional<Bytecode::Generator::CompletionRegisterScope> completion_scope;
if (completion.has_value())
completion_scope.emplace(generator, *completion);
for (auto& statement : switch_case->children()) {
auto result = statement->generate_bytecode(generator);
if (generator.is_current_block_terminated())
break;
if (generator.must_propagate_completion()) {
if (result.has_value())
generator.emit_mov(*completion, *result);
else
generator.emit_mov(*completion, generator.add_constant(js_undefined()));
}
}
}
if (!generator.is_current_block_terminated()) {
auto next_block = current_block;
next_block++;
if (next_block.is_end()) {
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { end_block });
} else {
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { *next_block });
}
}
current_block++;
}
generator.end_breakable_scope();
generator.switch_to_basic_block(end_block);
if (did_create_lexical_environment)
generator.end_variable_scope();
return completion;
}
Optional<ScopedOperand> SuperExpression::generate_bytecode(Bytecode::Generator&, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
// The semantics for SuperExpression are handled in CallExpression and SuperCall.
VERIFY_NOT_REACHED();
}
Optional<ScopedOperand> ClassDeclaration::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
auto value = m_class_expression->generate_bytecode(generator).value();
generator.emit_set_variable(*m_class_expression.ptr()->m_name, value, Bytecode::Op::BindingInitializationMode::Initialize);
// NOTE: ClassDeclaration does not produce a value.
return Optional<ScopedOperand> {};
}
// 15.7.14 Runtime Semantics: ClassDefinitionEvaluation, https://tc39.es/ecma262/#sec-runtime-semantics-classdefinitionevaluation
Optional<ScopedOperand> ClassExpression::generate_bytecode_with_lhs_name(Bytecode::Generator& generator, Optional<Bytecode::IdentifierTableIndex> lhs_name, Optional<ScopedOperand> preferred_dst) const
{
// NOTE: Step 2 is not a part of NewClass instruction because it is assumed to be done before super class expression evaluation
auto parent_environment = generator.current_lexical_environment_register();
auto class_environment = generator.allocate_register();
generator.emit<Bytecode::Op::CreateLexicalEnvironment>(class_environment, parent_environment, 0);
generator.push_lexical_environment_register(class_environment);
if (has_name() || !lhs_name.has_value()) {
// NOTE: Step 3.a is not a part of NewClass instruction because it is assumed to be done before super class expression evaluation
auto interned_index = generator.intern_identifier(name());
generator.emit<Bytecode::Op::CreateVariable>(interned_index, Bytecode::Op::EnvironmentMode::Lexical, true, false, false);
}
Optional<ScopedOperand> super_class;
if (m_super_class)
super_class = m_super_class->generate_bytecode(generator).value();
bool did_emit_private_environment_allocation = false;
for (auto const& element : m_elements) {
auto opt_private_name = element->private_bound_identifier();
if (opt_private_name.has_value()) {
if (!did_emit_private_environment_allocation) {
generator.emit<Op::CreatePrivateEnvironment>();
did_emit_private_environment_allocation = true;
}
generator.emit<Op::AddPrivateName>(generator.intern_identifier(*opt_private_name));
}
}
Vector<Optional<ScopedOperand>> elements;
for (auto const& element : m_elements) {
Optional<ScopedOperand> key;
if (is<ClassMethod>(*element)) {
auto const& class_method = static_cast<ClassMethod const&>(*element);
if (!is<PrivateIdentifier>(class_method.key()))
key = class_method.key().generate_bytecode(generator);
} else if (is<ClassField>(*element)) {
auto const& class_field = static_cast<ClassField const&>(*element);
if (!is<PrivateIdentifier>(class_field.key()))
key = class_field.key().generate_bytecode(generator);
}
elements.append({ key });
}
// Build a ClassBlueprint that captures all class element metadata at codegen time.
auto& vm = generator.vm();
ClassBlueprint blueprint;
blueprint.has_super_class = !m_super_class.is_null();
blueprint.has_name = has_name();
blueprint.name = name();
blueprint.source_text = source_text();
// Register shared function data for the constructor.
auto constructor_shared_data = SharedFunctionInstanceData::create_for_function_node(vm, *m_constructor);
blueprint.constructor_shared_function_data_index = generator.register_shared_function_data(constructor_shared_data);
for (auto const& element : m_elements) {
if (is<ClassMethod>(*element)) {
auto const& class_method = static_cast<ClassMethod const&>(*element);
bool is_private = is<PrivateIdentifier>(class_method.key());
ClassElementDescriptor::Kind descriptor_kind;
switch (class_method.kind()) {
case ClassMethod::Kind::Method:
descriptor_kind = ClassElementDescriptor::Kind::Method;
break;
case ClassMethod::Kind::Getter:
descriptor_kind = ClassElementDescriptor::Kind::Getter;
break;
case ClassMethod::Kind::Setter:
descriptor_kind = ClassElementDescriptor::Kind::Setter;
break;
}
auto shared_data = SharedFunctionInstanceData::create_for_function_node(vm, class_method.function());
auto data_index = generator.register_shared_function_data(shared_data);
blueprint.elements.append({
.kind = descriptor_kind,
.is_static = element->is_static(),
.is_private = is_private,
.private_identifier = is_private ? Optional<Utf16FlyString>(static_cast<PrivateIdentifier const&>(class_method.key()).string()) : Optional<Utf16FlyString>(),
.shared_function_data_index = data_index,
.has_initializer = false,
.literal_value = {},
});
} else if (is<ClassField>(*element)) {
auto const& class_field = static_cast<ClassField const&>(*element);
bool is_private = is<PrivateIdentifier>(class_field.key());
Optional<u32> data_index;
bool has_initializer = class_field.initializer() != nullptr;
Optional<Value> literal_value;
if (has_initializer) {
auto const& initializer = *class_field.initializer();
// Detect literal initializers and store the value directly,
// avoiding function creation and calls for simple cases like x = 0.
if (is<NumericLiteral>(initializer)) {
literal_value = static_cast<NumericLiteral const&>(initializer).value();
} else if (is<BooleanLiteral>(initializer)) {
literal_value = static_cast<BooleanLiteral const&>(initializer).value();
} else if (is<NullLiteral>(initializer)) {
literal_value = js_null();
} else if (is<StringLiteral>(initializer)) {
literal_value = Value(PrimitiveString::create(vm, static_cast<StringLiteral const&>(initializer).value()));
} else if (is<UnaryExpression>(initializer)) {
auto const& unary = static_cast<UnaryExpression const&>(initializer);
if (unary.op() == UnaryOp::Minus && is<NumericLiteral>(*unary.lhs()))
literal_value = Value(-static_cast<NumericLiteral const&>(*unary.lhs()).value().as_double());
}
if (!literal_value.has_value()) {
// FIXME: For computed-key fields, the field name for anonymous function
// naming is only known at runtime. We use "" here, which means
// e.g. (new (class { [sym] = function(){} }))[sym].name would be
// "" instead of "[sym]". Non-computed keys are handled correctly.
Utf16FlyString field_name;
if (is_private) {
field_name = static_cast<PrivateIdentifier const&>(class_field.key()).string();
} else if (is<Identifier>(class_field.key())) {
field_name = static_cast<Identifier const&>(class_field.key()).string();
} else if (is<StringLiteral>(class_field.key())) {
field_name = Utf16FlyString(static_cast<StringLiteral const&>(class_field.key()).value());
} else if (is<NumericLiteral>(class_field.key())) {
field_name = Utf16FlyString(number_to_utf16_string(static_cast<NumericLiteral const&>(class_field.key()).value().as_double()));
} else if (is<BigIntLiteral>(class_field.key())) {
field_name = Utf16FlyString::from_utf8(bigint_literal_to_decimal_string(static_cast<BigIntLiteral const&>(class_field.key())));
}
auto copy_initializer = class_field.initializer();
auto function_code = create_ast_node<ClassFieldInitializerStatement>(
class_field.initializer()->source_range(),
copy_initializer.release_nonnull(),
move(field_name));
FunctionParsingInsights parsing_insights;
parsing_insights.uses_this_from_environment = true;
parsing_insights.uses_this = true;
auto shared_data = vm.heap().allocate<SharedFunctionInstanceData>(
vm,
FunctionKind::Normal,
"field"_utf16_fly_string,
0,
FunctionParameters::empty(),
*function_code,
Utf16View {},
true,
false,
parsing_insights,
Vector<LocalVariable> {});
// Set class_field_initializer_name for keys known at codegen time.
// This is needed so eval("arguments") inside field initializers
// correctly throws a SyntaxError.
if (is_private) {
auto private_name = static_cast<PrivateIdentifier const&>(class_field.key()).string();
shared_data->m_class_field_initializer_name = PrivateName(0, private_name);
} else if (is<Identifier>(class_field.key())) {
auto name = static_cast<Identifier const&>(class_field.key()).string();
shared_data->m_class_field_initializer_name = PropertyKey(name.to_utf16_string());
} else if (is<StringLiteral>(class_field.key())) {
auto name = static_cast<StringLiteral const&>(class_field.key()).value();
shared_data->m_class_field_initializer_name = PropertyKey(name);
} else if (is<NumericLiteral>(class_field.key())) {
auto name = number_to_utf16_string(static_cast<NumericLiteral const&>(class_field.key()).value().as_double());
shared_data->m_class_field_initializer_name = PropertyKey(name);
} else if (is<BigIntLiteral>(class_field.key())) {
auto name = bigint_literal_to_decimal_string(static_cast<BigIntLiteral const&>(class_field.key()));
shared_data->m_class_field_initializer_name = PropertyKey(Utf16String::from_utf8(name));
}
// For computed keys, class_field_initializer_name is set at runtime
// in construct_class().
data_index = generator.register_shared_function_data(shared_data);
}
}
blueprint.elements.append({
.kind = ClassElementDescriptor::Kind::Field,
.is_static = element->is_static(),
.is_private = is_private,
.private_identifier = is_private ? Optional<Utf16FlyString>(static_cast<PrivateIdentifier const&>(class_field.key()).string()) : Optional<Utf16FlyString>(),
.shared_function_data_index = data_index,
.has_initializer = has_initializer,
.literal_value = literal_value,
});
} else if (is<StaticInitializer>(*element)) {
auto const& static_init = static_cast<StaticInitializer const&>(*element);
FunctionParsingInsights parsing_insights;
parsing_insights.uses_this_from_environment = true;
parsing_insights.uses_this = true;
auto shared_data = vm.heap().allocate<SharedFunctionInstanceData>(
vm,
FunctionKind::Normal,
Utf16FlyString {},
0,
FunctionParameters::empty(),
static_init.function_body(),
Utf16View {},
true,
false,
parsing_insights,
static_init.function_body().local_variables_names());
auto data_index = generator.register_shared_function_data(shared_data);
blueprint.elements.append({
.kind = ClassElementDescriptor::Kind::StaticInitializer,
.is_static = true,
.is_private = false,
.private_identifier = {},
.shared_function_data_index = data_index,
.has_initializer = false,
.literal_value = {},
});
}
}
auto blueprint_index = generator.register_class_blueprint(move(blueprint));
// Restore parent environment before emitting NewClass.
generator.emit<Bytecode::Op::SetLexicalEnvironment>(parent_environment);
generator.pop_lexical_environment_register();
auto dst = choose_dst(generator, preferred_dst);
generator.emit_with_extra_slots<Op::NewClass, Optional<Operand>>(elements.size(), dst, super_class.has_value() ? super_class->operand() : Optional<Operand> {}, class_environment, blueprint_index, lhs_name, elements);
if (did_emit_private_environment_allocation) {
generator.emit<Op::LeavePrivateEnvironment>();
}
return dst;
}
Optional<ScopedOperand> ClassExpression::generate_bytecode(Bytecode::Generator& generator, Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
return generate_bytecode_with_lhs_name(generator, {}, preferred_dst);
}
Optional<ScopedOperand> SpreadExpression::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
// NOTE: All users of this should handle the behaviour of this on their own,
// assuming it returns an Array-like object
return m_target->generate_bytecode(generator);
}
Optional<ScopedOperand> ThisExpression::generate_bytecode(Bytecode::Generator& generator, Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
return generator.get_this(preferred_dst);
}
static ScopedOperand generate_await(
Bytecode::Generator& generator,
ScopedOperand argument,
ScopedOperand received_completion,
ScopedOperand received_completion_type,
ScopedOperand received_completion_value)
{
VERIFY(generator.is_in_async_function());
auto& continuation_block = generator.make_block();
generator.emit<Bytecode::Op::Await>(Bytecode::Label { continuation_block }, argument);
generator.switch_to_basic_block(continuation_block);
// FIXME: It's really magical that we can just assume that the completion value is in register 0.
// It ends up there because we "return" from the Await instruction above via the synthetic
// generator function that actually drives async execution.
generator.emit_mov(received_completion, generator.accumulator());
get_received_completion_type_and_value(generator, received_completion, received_completion_type, received_completion_value);
auto& normal_completion_continuation_block = generator.make_block();
auto& throw_value_block = generator.make_block();
auto received_completion_type_is_normal = generator.allocate_register();
generator.emit<Bytecode::Op::StrictlyEquals>(
received_completion_type_is_normal,
received_completion_type,
generator.add_constant(Value(to_underlying(Completion::Type::Normal))));
generator.emit_jump_if(
received_completion_type_is_normal,
Bytecode::Label { normal_completion_continuation_block },
Bytecode::Label { throw_value_block });
// Simplification: The only abrupt completion we receive from AsyncFunctionDriverWrapper or AsyncGenerator is Type::Throw
// So we do not need to account for the Type::Return path
generator.switch_to_basic_block(throw_value_block);
generator.perform_needed_unwinds<Bytecode::Op::Throw>();
generator.emit<Bytecode::Op::Throw>(received_completion_value);
generator.switch_to_basic_block(normal_completion_continuation_block);
return received_completion_value;
}
Optional<ScopedOperand> AwaitExpression::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
auto argument = m_argument->generate_bytecode(generator).value();
auto received_completion = generator.allocate_register();
auto received_completion_type = generator.allocate_register();
auto received_completion_value = generator.allocate_register();
generator.emit_mov(received_completion, generator.accumulator());
return generate_await(generator, argument, received_completion, received_completion_type, received_completion_value);
}
Optional<ScopedOperand> WithStatement::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
auto object = m_object->generate_bytecode(generator).value();
auto object_environment = generator.allocate_register();
generator.emit<Bytecode::Op::EnterObjectEnvironment>(object_environment, object);
generator.push_lexical_environment_register(object_environment);
// EnterObjectEnvironment sets the running execution context's lexical_environment to a new Object Environment.
generator.start_boundary(Bytecode::Generator::BlockBoundaryType::LeaveLexicalEnvironment);
auto body_result = m_body->generate_bytecode(generator);
if (!body_result.has_value())
body_result = generator.add_constant(js_undefined());
generator.end_boundary(Bytecode::Generator::BlockBoundaryType::LeaveLexicalEnvironment);
generator.pop_lexical_environment_register();
if (!generator.is_current_block_terminated())
generator.emit<Bytecode::Op::SetLexicalEnvironment>(generator.current_lexical_environment_register());
return body_result;
}
enum class LHSKind {
Assignment,
VarBinding,
LexicalBinding,
};
enum class IterationKind {
Enumerate,
Iterate,
AsyncIterate,
};
// 14.7.5.6 ForIn/OfHeadEvaluation ( uninitializedBoundNames, expr, iterationKind ), https://tc39.es/ecma262/#sec-runtime-semantics-forinofheadevaluation
struct ForInOfHeadEvaluationResult {
bool is_destructuring { false };
LHSKind lhs_kind { LHSKind::Assignment };
Optional<ScopedOperand> iterator_object;
Optional<ScopedOperand> iterator_next_method;
Optional<ScopedOperand> iterator_done_property;
};
static ForInOfHeadEvaluationResult for_in_of_head_evaluation(Bytecode::Generator& generator, IterationKind iteration_kind, Variant<NonnullRefPtr<ASTNode const>, NonnullRefPtr<BindingPattern const>> const& lhs, NonnullRefPtr<ASTNode const> const& rhs)
{
ForInOfHeadEvaluationResult result {};
bool entered_lexical_scope = false;
if (auto* ast_ptr = lhs.get_pointer<NonnullRefPtr<ASTNode const>>(); ast_ptr && is<VariableDeclaration>(**ast_ptr)) {
// Runtime Semantics: ForInOfLoopEvaluation, for any of:
// ForInOfStatement : for ( var ForBinding in Expression ) Statement
// ForInOfStatement : for ( ForDeclaration in Expression ) Statement
// ForInOfStatement : for ( var ForBinding of AssignmentExpression ) Statement
// ForInOfStatement : for ( ForDeclaration of AssignmentExpression ) Statement
auto& variable_declaration = static_cast<VariableDeclaration const&>(**ast_ptr);
result.is_destructuring = variable_declaration.declarations().first()->target().has<NonnullRefPtr<BindingPattern const>>();
result.lhs_kind = variable_declaration.is_lexical_declaration() ? LHSKind::LexicalBinding : LHSKind::VarBinding;
if (variable_declaration.declaration_kind() == DeclarationKind::Var) {
// B.3.5 Initializers in ForIn Statement Heads, https://tc39.es/ecma262/#sec-initializers-in-forin-statement-heads
auto& variable = variable_declaration.declarations().first();
if (variable->init()) {
VERIFY(variable->target().has<NonnullRefPtr<Identifier const>>());
auto identifier = variable->target().get<NonnullRefPtr<Identifier const>>();
auto identifier_table_ref = generator.intern_identifier(identifier->string());
auto value = generator.emit_named_evaluation_if_anonymous_function(*variable->init(), identifier_table_ref);
generator.emit_set_variable(*identifier, value);
}
} else {
auto has_non_local_variables = false;
MUST(variable_declaration.for_each_bound_identifier([&](auto const& identifier) {
if (!identifier.is_local())
has_non_local_variables = true;
}));
if (has_non_local_variables) {
// 1. Let oldEnv be the running execution context's LexicalEnvironment.
// NOTE: 'uninitializedBoundNames' refers to the lexical bindings (i.e. Const/Let) present in the second and last form.
// 2. If uninitializedBoundNames is not an empty List, then
entered_lexical_scope = true;
// a. Assert: uninitializedBoundNames has no duplicate entries.
// b. Let newEnv be NewDeclarativeEnvironment(oldEnv).
generator.begin_variable_scope();
// c. For each String name of uninitializedBoundNames, do
// NOTE: Nothing in the callback throws an exception.
MUST(variable_declaration.for_each_bound_identifier([&](auto const& identifier) {
if (identifier.is_local())
return;
// i. Perform ! newEnv.CreateMutableBinding(name, false).
auto interned_identifier = generator.intern_identifier(identifier.string());
generator.emit<Bytecode::Op::CreateVariable>(interned_identifier, Bytecode::Op::EnvironmentMode::Lexical, false, false, false);
}));
// d. Set the running execution context's LexicalEnvironment to newEnv.
// NOTE: Done by CreateLexicalEnvironment.
}
}
} else {
// Runtime Semantics: ForInOfLoopEvaluation, for any of:
// ForInOfStatement : for ( LeftHandSideExpression in Expression ) Statement
// ForInOfStatement : for ( LeftHandSideExpression of AssignmentExpression ) Statement
result.lhs_kind = LHSKind::Assignment;
}
// 3. Let exprRef be the result of evaluating expr.
auto object = rhs->generate_bytecode(generator).value();
// 4. Set the running execution context's LexicalEnvironment to oldEnv.
if (entered_lexical_scope)
generator.end_variable_scope();
// 5. Let exprValue be ? GetValue(exprRef).
// NOTE: No need to store this anywhere.
auto iterator_object = generator.allocate_register();
auto iterator_next_method = generator.allocate_register();
auto iterator_done_property = generator.allocate_register();
// 6. If iterationKind is enumerate, then
if (iteration_kind == IterationKind::Enumerate) {
// a. If exprValue is undefined or null, then
auto& nullish_block = generator.make_block();
auto& continuation_block = generator.make_block();
generator.emit<Bytecode::Op::JumpNullish>(
object,
Bytecode::Label { nullish_block },
Bytecode::Label { continuation_block });
// i. Return Completion Record { [[Type]]: break, [[Value]]: empty, [[Target]]: empty }.
generator.switch_to_basic_block(nullish_block);
generator.generate_break();
generator.switch_to_basic_block(continuation_block);
// b. Let obj be ! ToObject(exprValue).
// NOTE: GetObjectPropertyIterator does this.
// c. Let iterator be EnumerateObjectProperties(obj).
// d. Let nextMethod be ! GetV(iterator, "next").
// e. Return the Iterator Record { [[Iterator]]: iterator, [[NextMethod]]: nextMethod, [[Done]]: false }.
generator.emit<Bytecode::Op::GetObjectPropertyIterator>(iterator_object, iterator_next_method, iterator_done_property, object);
}
// 7. Else,
else {
// a. Assert: iterationKind is iterate or async-iterate.
// b. If iterationKind is async-iterate, let iteratorKind be async.
// c. Else, let iteratorKind be sync.
auto iterator_kind = iteration_kind == IterationKind::AsyncIterate ? IteratorHint::Async : IteratorHint::Sync;
// d. Return ? GetIterator(exprValue, iteratorKind).
generator.emit<Bytecode::Op::GetIterator>(iterator_object, iterator_next_method, iterator_done_property, object, iterator_kind);
}
result.iterator_object = iterator_object;
result.iterator_next_method = iterator_next_method;
result.iterator_done_property = iterator_done_property;
return result;
}
// 14.7.5.7 ForIn/OfBodyEvaluation ( lhs, stmt, iteratorRecord, iterationKind, lhsKind, labelSet [ , iteratorKind ] ), https://tc39.es/ecma262/#sec-runtime-semantics-forin-div-ofbodyevaluation-lhs-stmt-iterator-lhskind-labelset
static Optional<ScopedOperand> for_in_of_body_evaluation(Bytecode::Generator& generator, Variant<NonnullRefPtr<ASTNode const>, NonnullRefPtr<BindingPattern const>> const& lhs, ASTNode const& body, ForInOfHeadEvaluationResult const& head_result, IterationKind iteration_kind, Vector<FlyString> const& label_set, Bytecode::BasicBlock& loop_end, Bytecode::BasicBlock& loop_update, IteratorHint iterator_kind = IteratorHint::Sync, [[maybe_unused]] Optional<ScopedOperand> preferred_dst = {})
{
// 1. If iteratorKind is not present, set iteratorKind to sync.
// 2. Let oldEnv be the running execution context's LexicalEnvironment.
bool has_lexical_binding = false;
// 3. Let V be undefined.
Optional<ScopedOperand> completion;
if (generator.must_propagate_completion()) {
completion = generator.allocate_register();
generator.emit_mov(*completion, generator.add_constant(js_undefined()));
}
// 4. Let destructuring be IsDestructuring of lhs.
auto destructuring = head_result.is_destructuring;
// 5. If destructuring is true and if lhsKind is assignment, then
// NB: is_destructuring is only set for VariableDeclaration lhs (which always has lhs_kind
// VarBinding or LexicalBinding), so this combination is unreachable.
VERIFY(!(destructuring && head_result.lhs_kind == LHSKind::Assignment));
if (completion.has_value())
generator.set_current_breakable_scope_completion_register(*completion);
// For for-of and for-await-of, set up a synthetic FinallyContext so that
// IteratorClose/AsyncIteratorClose is called on abrupt completion (break,
// return, throw, or continue-to-outer-loop). for-in (enumerate) does not
// need iterator close per spec.
bool needs_iterator_close = (iteration_kind != IterationKind::Enumerate);
Optional<Bytecode::Generator::FinallyContext> iterator_close_finally_context;
Optional<Bytecode::Generator::UnwindContext> iterator_close_unwind_context;
Optional<ScopedOperand> close_completion_type;
Optional<ScopedOperand> close_completion_value;
Bytecode::BasicBlock* exception_preamble_block { nullptr };
Bytecode::BasicBlock* iterator_close_body_block { nullptr };
Optional<ScopedOperand> lexical_environment_at_entry;
if (needs_iterator_close) {
lexical_environment_at_entry = generator.current_lexical_environment_register();
close_completion_type = generator.allocate_register();
close_completion_value = generator.allocate_register();
exception_preamble_block = &generator.make_block();
iterator_close_body_block = &generator.make_block();
iterator_close_finally_context.emplace(Bytecode::Generator::FinallyContext {
.completion_type = *close_completion_type,
.completion_value = *close_completion_value,
.finally_body = Bytecode::Label { *iterator_close_body_block },
.exception_preamble = Bytecode::Label { *exception_preamble_block },
.parent = generator.current_finally_context(),
.registered_jumps = {},
.next_jump_index = Bytecode::Generator::FinallyContext::FIRST_JUMP_INDEX,
.lexical_environment_at_entry = lexical_environment_at_entry,
});
generator.set_current_finally_context(&*iterator_close_finally_context);
// Place ReturnToFinally between Break (pushed by caller) and Continue
// (pushed by begin_continuable_scope below). This ensures:
// - continue to this loop: hits Continue first -> direct jump (no close)
// - break/return/throw/continue-to-outer: hits ReturnToFinally -> close
generator.start_boundary(Bytecode::Generator::BlockBoundaryType::ReturnToFinally);
// NB: The UnwindContext (exception handler) is set up later, after
// the iterator-next section. Per spec, exceptions from steps a-f
// (IteratorNext, Await, IteratorComplete, IteratorValue) propagate
// directly without calling IteratorClose. Only exceptions from
// LHS assignment (steps g-j) and the loop body (step l) should
// trigger iterator close.
}
// 6. Repeat,
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { loop_update });
generator.switch_to_basic_block(loop_update);
generator.begin_continuable_scope(Bytecode::Label { loop_update }, label_set, completion);
// a. Let nextResult be ? Call(iteratorRecord.[[NextMethod]], iteratorRecord.[[Iterator]]).
auto next_value = generator.allocate_register();
auto done = generator.allocate_register();
if (iterator_kind == IteratorHint::Sync) {
generator.emit<Bytecode::Op::IteratorNextUnpack>(next_value, done, *head_result.iterator_object, *head_result.iterator_next_method, *head_result.iterator_done_property);
auto& loop_continue = generator.make_block();
generator.emit_jump_if(
done,
Bytecode::Label { loop_end },
Bytecode::Label { loop_continue });
generator.switch_to_basic_block(loop_continue);
} else {
auto next_result = generator.allocate_register();
generator.emit<Bytecode::Op::IteratorNext>(next_result, *head_result.iterator_object, *head_result.iterator_next_method, *head_result.iterator_done_property);
// b. If iteratorKind is async, set nextResult to ? Await(nextResult).
auto received_completion = generator.allocate_register();
auto received_completion_type = generator.allocate_register();
auto received_completion_value = generator.allocate_register();
generator.emit_mov(received_completion, generator.accumulator());
auto new_result = generate_await(generator, next_result, received_completion, received_completion_type, received_completion_value);
generator.emit_mov(next_result, new_result);
// c. If Type(nextResult) is not Object, throw a TypeError exception.
generator.emit<Bytecode::Op::ThrowIfNotObject>(next_result);
// d. Let done be ? IteratorComplete(nextResult).
generator.emit_iterator_complete(done, next_result);
// e. If done is true, return V.
auto& loop_continue = generator.make_block();
generator.emit_jump_if(
done,
Bytecode::Label { loop_end },
Bytecode::Label { loop_continue });
generator.switch_to_basic_block(loop_continue);
// f. Let nextValue be ? IteratorValue(nextResult).
generator.emit_iterator_value(next_value, next_result);
}
// Set up the exception handler now, after the iterator-next section.
// This ensures only LHS assignment and body exceptions trigger close.
// We must also switch to a fresh block so that subsequent code gets the
// new handler (make_block sets the handler at creation time).
if (needs_iterator_close) {
iterator_close_unwind_context.emplace(generator, Bytecode::Label { *exception_preamble_block });
auto& loop_body = generator.make_block();
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { loop_body });
generator.switch_to_basic_block(loop_body);
}
// g. If lhsKind is either assignment or varBinding, then
if (head_result.lhs_kind != LHSKind::LexicalBinding) {
// i. If destructuring is false, then
if (!destructuring) {
// 1. Let lhsRef be the result of evaluating lhs. (It may be evaluated repeatedly.)
// NOTE: We're skipping all the completion stuff that the spec does, as the unwinding mechanism will take case of doing that.
if (head_result.lhs_kind == LHSKind::VarBinding) {
auto& declaration = static_cast<VariableDeclaration const&>(*lhs.get<NonnullRefPtr<ASTNode const>>());
VERIFY(declaration.declarations().size() == 1);
assign_value_to_variable_declarator(generator, declaration.declarations().first(), declaration, next_value);
} else {
if (auto ptr = lhs.get_pointer<NonnullRefPtr<ASTNode const>>()) {
generator.emit_store_to_reference(**ptr, next_value);
} else {
auto& binding_pattern = lhs.get<NonnullRefPtr<BindingPattern const>>();
binding_pattern->generate_bytecode(generator, Bytecode::Op::BindingInitializationMode::Set, next_value);
}
}
}
}
// h. Else,
else {
// i. Assert: lhsKind is lexicalBinding.
// ii. Assert: lhs is a ForDeclaration.
// iii. Let iterationEnv be NewDeclarativeEnvironment(oldEnv).
// iv. Perform ForDeclarationBindingInstantiation of lhs with argument iterationEnv.
// v. Set the running execution context's LexicalEnvironment to iterationEnv.
// 14.7.5.4 Runtime Semantics: ForDeclarationBindingInstantiation, https://tc39.es/ecma262/#sec-runtime-semantics-fordeclarationbindinginstantiation
// 1. Assert: environment is a declarative Environment Record.
// NOTE: We just made it.
auto& variable_declaration = static_cast<VariableDeclaration const&>(*lhs.get<NonnullRefPtr<ASTNode const>>());
// 2. For each element name of the BoundNames of ForBinding, do
// NOTE: Nothing in the callback throws an exception.
auto has_non_local_variables = false;
MUST(variable_declaration.for_each_bound_identifier([&](auto const& identifier) {
if (!identifier.is_local())
has_non_local_variables = true;
}));
if (has_non_local_variables) {
generator.begin_variable_scope();
has_lexical_binding = true;
MUST(variable_declaration.for_each_bound_identifier([&](auto const& identifier) {
if (identifier.is_local())
return;
auto interned_identifier = generator.intern_identifier(identifier.string());
// a. If IsConstantDeclaration of LetOrConst is true, then
if (variable_declaration.is_constant_declaration()) {
// i. Perform ! environment.CreateImmutableBinding(name, true).
generator.emit<Bytecode::Op::CreateVariable>(interned_identifier, Bytecode::Op::EnvironmentMode::Lexical, true, false, true);
}
// b. Else,
else {
// i. Perform ! environment.CreateMutableBinding(name, false).
generator.emit<Bytecode::Op::CreateVariable>(interned_identifier, Bytecode::Op::EnvironmentMode::Lexical, false, false, false);
}
}));
// 3. Return unused.
// NOTE: No need to do that as we've inlined this.
}
// vi. If destructuring is false, then
if (!destructuring) {
// 1. Assert: lhs binds a single name.
// 2. Let lhsName be the sole element of BoundNames of lhs.
auto lhs_name = variable_declaration.declarations().first()->target().get<NonnullRefPtr<Identifier const>>();
// 3. Let lhsRef be ! ResolveBinding(lhsName).
// NOTE: We're skipping all the completion stuff that the spec does, as the unwinding mechanism will take case of doing that.
generator.emit_set_variable(*lhs_name, next_value, Bytecode::Op::BindingInitializationMode::Initialize, Bytecode::Op::EnvironmentMode::Lexical);
}
}
// i. If destructuring is false, then
if (!destructuring) {
// i. If lhsRef is an abrupt completion, then
// 1. Let status be lhsRef.
// ii. Else if lhsKind is lexicalBinding, then
// 1. Let status be Completion(InitializeReferencedBinding(lhsRef, nextValue)).
// iii. Else,
// 1. Let status be Completion(PutValue(lhsRef, nextValue)).
// NOTE: This is performed above.
}
// j. Else,
else {
// FIXME: i. If lhsKind is assignment, then
// 1. Let status be Completion(DestructuringAssignmentEvaluation of assignmentPattern with argument nextValue).
// ii. Else if lhsKind is varBinding, then
// 1. Assert: lhs is a ForBinding.
// 2. Let status be Completion(BindingInitialization of lhs with arguments nextValue and undefined).
// iii. Else,
// 1. Assert: lhsKind is lexicalBinding.
// 2. Assert: lhs is a ForDeclaration.
// 3. Let status be Completion(ForDeclarationBindingInitialization of lhs with arguments nextValue and iterationEnv).
if (head_result.lhs_kind == LHSKind::VarBinding || head_result.lhs_kind == LHSKind::LexicalBinding) {
auto& declaration = static_cast<VariableDeclaration const&>(*lhs.get<NonnullRefPtr<ASTNode const>>());
VERIFY(declaration.declarations().size() == 1);
auto& binding_pattern = declaration.declarations().first()->target().get<NonnullRefPtr<BindingPattern const>>();
binding_pattern->generate_bytecode(
generator,
head_result.lhs_kind == LHSKind::VarBinding ? Bytecode::Op::BindingInitializationMode::Set : Bytecode::Op::BindingInitializationMode::Initialize,
next_value);
} else {
// NB: lhs_kind is Assignment only when is_destructuring is false, so this is unreachable.
VERIFY_NOT_REACHED();
}
}
// k. If status is an abrupt completion, then
// i. Set the running execution context's LexicalEnvironment to oldEnv.
// ii. If iteratorKind is async, return ? AsyncIteratorClose(iteratorRecord, status).
// iii. If iterationKind is enumerate, then
// 1. Return ? status.
// iv. Else,
// 1. Assert: iterationKind is iterate.
// 2. Return ? IteratorClose(iteratorRecord, status).
// NB: Abrupt completions from LHS assignment and the loop body are handled
// by the synthetic FinallyContext set up above (for iterate/async-iterate).
// l. Let result be the result of evaluating stmt.
{
Optional<Bytecode::Generator::CompletionRegisterScope> completion_scope;
if (completion.has_value())
completion_scope.emplace(generator, *completion);
auto result = body.generate_bytecode(generator);
if (!generator.is_current_block_terminated() && completion.has_value() && result.has_value())
generator.emit_mov(*completion, *result);
}
// m. Set the running execution context's LexicalEnvironment to oldEnv.
if (has_lexical_binding)
generator.end_variable_scope();
generator.end_continuable_scope();
if (needs_iterator_close) {
generator.end_boundary(Bytecode::Generator::BlockBoundaryType::ReturnToFinally);
generator.set_current_finally_context(iterator_close_finally_context->parent);
iterator_close_unwind_context.clear();
}
generator.end_breakable_scope();
// The body can contain an unconditional block terminator (e.g. return, throw), so we have to check for that before generating the Jump.
if (!generator.is_current_block_terminated())
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { loop_update });
// Generate iterator close blocks for for-of/for-await-of.
if (needs_iterator_close) {
auto undefined_value = generator.add_constant(js_undefined());
// Exception preamble: catches thrown exceptions and routes to iterator close.
generator.switch_to_basic_block(*exception_preamble_block);
generator.emit<Bytecode::Op::Catch>(*close_completion_value);
generator.emit<Bytecode::Op::SetLexicalEnvironment>(*lexical_environment_at_entry);
generator.emit_mov(*close_completion_type, generator.add_constant(Value(Bytecode::Generator::FinallyContext::THROW)));
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { *iterator_close_body_block });
// Iterator close body: dispatch chain based on completion type.
generator.switch_to_basic_block(*iterator_close_body_block);
// THROW path: IteratorClose with Throw completion (original throw always wins).
auto& throw_close_block = generator.make_block();
auto& non_throw_close_block = generator.make_block();
generator.emit<Bytecode::Op::JumpStrictlyEquals>(
*close_completion_type, generator.add_constant(Value(Bytecode::Generator::FinallyContext::THROW)),
Bytecode::Label { throw_close_block }, Bytecode::Label { non_throw_close_block });
// Non-throw abrupt path (break/return/continue-to-outer): close with Normal completion.
generator.switch_to_basic_block(non_throw_close_block);
if (iterator_kind == IteratorHint::Async) {
// For async iterators, we inline the AsyncIteratorClose steps
// using a proper Await op instead of the synchronous await()
// that the AsyncIteratorClose C++ op uses. The synchronous await
// spins the event loop inside bytecode execution, which violates
// the microtask checkpoint assertion.
auto& after_close = generator.make_block();
// Spec: 7.4.13 AsyncIteratorClose ( iteratorRecord, completion )
// 3. Let innerResult be Completion(GetMethod(iterator, "return")).
auto return_method = generator.allocate_register();
generator.emit<Bytecode::Op::GetMethod>(return_method, *head_result.iterator_object, generator.intern_property_key("return"_utf16_fly_string));
// 4a/b. If return is undefined, skip close.
auto& call_return_block = generator.make_block();
generator.emit<Bytecode::Op::JumpUndefined>(return_method, Bytecode::Label { after_close }, Bytecode::Label { call_return_block });
generator.switch_to_basic_block(call_return_block);
// 4c. Set innerResult to Completion(Call(return, iterator)).
auto inner_result = generator.allocate_register();
generator.emit_with_extra_operand_slots<Bytecode::Op::Call>(0, inner_result, return_method, *head_result.iterator_object, OptionalNone {}, ReadonlySpan<ScopedOperand> {});
// 4d. Set innerResult to Completion(Await(innerResult.[[Value]])).
auto received_completion = generator.allocate_register();
auto received_completion_type = generator.allocate_register();
auto received_completion_value = generator.allocate_register();
auto awaited = generate_await(generator, inner_result, received_completion, received_completion_type, received_completion_value);
// 7. If Type(innerResult.[[Value]]) is not Object, throw a TypeError exception.
generator.emit<Bytecode::Op::ThrowIfNotObject>(awaited);
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { after_close });
generator.switch_to_basic_block(after_close);
} else {
generator.emit<Bytecode::Op::IteratorClose>(*head_result.iterator_object, *head_result.iterator_next_method, *head_result.iterator_done_property, Completion::Type::Normal, undefined_value);
}
// Dispatch registered jumps (break/continue targets, indices 3+).
for (auto const& jump : iterator_close_finally_context->registered_jumps) {
auto& after_jump_check = generator.make_block();
generator.emit<Bytecode::Op::JumpStrictlyEquals>(
*close_completion_type, generator.add_constant(Value(jump.index)),
jump.target, Bytecode::Label { after_jump_check });
generator.switch_to_basic_block(after_jump_check);
}
// RETURN path.
auto& return_block = generator.make_block();
auto& unreachable_block = generator.make_block();
generator.emit<Bytecode::Op::JumpStrictlyEquals>(
*close_completion_type, generator.add_constant(Value(Bytecode::Generator::FinallyContext::RETURN)),
Bytecode::Label { return_block }, Bytecode::Label { unreachable_block });
generator.switch_to_basic_block(return_block);
if (iterator_close_finally_context->parent) {
// Nested finally: copy completion record to outer and jump to outer finally body.
auto& outer = *iterator_close_finally_context->parent;
generator.emit_mov(outer.completion_type, *close_completion_type);
generator.emit_mov(outer.completion_value, *close_completion_value);
generator.emit<Bytecode::Op::Jump>(outer.finally_body);
} else {
if (generator.is_in_generator_function())
generator.emit<Bytecode::Op::Yield>(OptionalNone {}, *close_completion_value);
else
generator.emit<Bytecode::Op::Return>(*close_completion_value);
}
// Default: unreachable (all completion types have been dispatched).
generator.switch_to_basic_block(unreachable_block);
generator.emit<Bytecode::Op::Throw>(*close_completion_value);
// Throw close block: IteratorClose with Throw completion, then rethrow.
// Per spec step 5, the original throw always takes precedence.
generator.switch_to_basic_block(throw_close_block);
if (iterator_kind == IteratorHint::Async) {
// Inline AsyncIteratorClose with exception handler: any error from
// the close steps is discarded and the original exception is rethrown.
auto& rethrow_block = generator.make_block();
auto& close_catch_block = generator.make_block();
{
Bytecode::Generator::UnwindContext close_unwind(generator, Bytecode::Label { close_catch_block });
// Jump to a block created inside the UnwindContext so that
// GetMethod/Call/Await all have the exception handler set.
// throw_close_block was created before the UnwindContext and
// doesn't have the handler.
auto& close_try_block = generator.make_block();
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { close_try_block });
generator.switch_to_basic_block(close_try_block);
auto return_method = generator.allocate_register();
generator.emit<Bytecode::Op::GetMethod>(return_method, *head_result.iterator_object, generator.intern_property_key("return"_utf16_fly_string));
auto& call_return_block = generator.make_block();
generator.emit<Bytecode::Op::JumpUndefined>(return_method, Bytecode::Label { rethrow_block }, Bytecode::Label { call_return_block });
generator.switch_to_basic_block(call_return_block);
auto inner_result = generator.allocate_register();
generator.emit_with_extra_operand_slots<Bytecode::Op::Call>(0, inner_result, return_method, *head_result.iterator_object, OptionalNone {}, ReadonlySpan<ScopedOperand> {});
auto received_completion = generator.allocate_register();
auto received_completion_type = generator.allocate_register();
auto received_completion_value = generator.allocate_register();
generate_await(generator, inner_result, received_completion, received_completion_type, received_completion_value);
// Even if close succeeded, rethrow original (spec step 5).
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { rethrow_block });
}
// Exception handler: discard close error, rethrow original.
generator.switch_to_basic_block(close_catch_block);
auto discarded = generator.allocate_register();
generator.emit<Bytecode::Op::Catch>(discarded);
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { rethrow_block });
generator.switch_to_basic_block(rethrow_block);
generator.emit<Bytecode::Op::Throw>(*close_completion_value);
} else {
generator.emit<Bytecode::Op::IteratorClose>(*head_result.iterator_object, *head_result.iterator_next_method, *head_result.iterator_done_property, Completion::Type::Throw, *close_completion_value);
// iterator_close with Throw completion always re-throws, but if it
// somehow returns normally, rethrow the original exception.
if (!generator.is_current_block_terminated())
generator.emit<Bytecode::Op::Throw>(*close_completion_value);
}
}
generator.switch_to_basic_block(loop_end);
return completion;
}
Optional<ScopedOperand> ForInStatement::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
return generate_labelled_evaluation(generator, {});
}
// 14.7.5.5 Runtime Semantics: ForInOfLoopEvaluation, https://tc39.es/ecma262/#sec-runtime-semantics-forinofloopevaluation
Optional<ScopedOperand> ForInStatement::generate_labelled_evaluation(Bytecode::Generator& generator, Vector<FlyString> const& label_set, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
auto& loop_end = generator.make_block();
auto& loop_update = generator.make_block();
generator.begin_breakable_scope(Bytecode::Label { loop_end }, label_set);
auto head_result = for_in_of_head_evaluation(generator, IterationKind::Enumerate, m_lhs, m_rhs);
return for_in_of_body_evaluation(generator, m_lhs, body(), head_result, IterationKind::Enumerate, label_set, loop_end, loop_update);
}
Optional<ScopedOperand> ForOfStatement::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
return generate_labelled_evaluation(generator, {});
}
Optional<ScopedOperand> ForOfStatement::generate_labelled_evaluation(Bytecode::Generator& generator, Vector<FlyString> const& label_set, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
auto& loop_end = generator.make_block();
auto& loop_update = generator.make_block();
generator.begin_breakable_scope(Bytecode::Label { loop_end }, label_set);
auto head_result = for_in_of_head_evaluation(generator, IterationKind::Iterate, m_lhs, m_rhs);
return for_in_of_body_evaluation(generator, m_lhs, body(), head_result, IterationKind::Iterate, label_set, loop_end, loop_update);
}
Optional<ScopedOperand> ForAwaitOfStatement::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
return generate_labelled_evaluation(generator, {});
}
Optional<ScopedOperand> ForAwaitOfStatement::generate_labelled_evaluation(Bytecode::Generator& generator, Vector<FlyString> const& label_set, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
auto& loop_end = generator.make_block();
auto& loop_update = generator.make_block();
generator.begin_breakable_scope(Bytecode::Label { loop_end }, label_set);
auto head_result = for_in_of_head_evaluation(generator, IterationKind::AsyncIterate, m_lhs, m_rhs);
return for_in_of_body_evaluation(generator, m_lhs, m_body, head_result, IterationKind::AsyncIterate, label_set, loop_end, loop_update, IteratorHint::Async);
}
// 13.3.12.1 Runtime Semantics: Evaluation, https://tc39.es/ecma262/#sec-meta-properties-runtime-semantics-evaluation
Optional<ScopedOperand> MetaProperty::generate_bytecode(Bytecode::Generator& generator, Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
// NewTarget : new . target
if (m_type == MetaProperty::Type::NewTarget) {
// 1. Return GetNewTarget().
auto dst = choose_dst(generator, preferred_dst);
generator.emit<Bytecode::Op::GetNewTarget>(dst);
return dst;
}
// ImportMeta : import . meta
if (m_type == MetaProperty::Type::ImportMeta) {
auto dst = choose_dst(generator, preferred_dst);
generator.emit<Bytecode::Op::GetImportMeta>(dst);
return dst;
}
VERIFY_NOT_REACHED();
}
Optional<ScopedOperand> ClassFieldInitializerStatement::generate_bytecode(Bytecode::Generator& generator, Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
auto value = generator.emit_named_evaluation_if_anonymous_function(*m_expression, generator.intern_identifier(m_class_field_identifier_name), preferred_dst);
generator.perform_needed_unwinds<Bytecode::Op::Return>();
generator.emit<Bytecode::Op::Return>(value.operand());
return value;
}
static void generate_optional_chain(Bytecode::Generator& generator, OptionalChain const& optional_chain, ScopedOperand current_value, ScopedOperand current_base, [[maybe_unused]] Optional<ScopedOperand> preferred_dst)
{
Optional<ScopedOperand> new_current_value;
if (is<MemberExpression>(optional_chain.base())) {
auto& member_expression = static_cast<MemberExpression const&>(optional_chain.base());
auto base_and_value = get_base_and_value_from_member_expression(generator, member_expression);
new_current_value = base_and_value.value;
generator.emit_mov(current_base, base_and_value.base);
} else if (is<OptionalChain>(optional_chain.base())) {
auto& sub_optional_chain = static_cast<OptionalChain const&>(optional_chain.base());
generate_optional_chain(generator, sub_optional_chain, current_value, current_base);
new_current_value = current_value;
} else {
new_current_value = optional_chain.base().generate_bytecode(generator).value();
}
generator.emit_mov(current_value, *new_current_value);
auto& load_undefined_and_jump_to_end_block = generator.make_block();
auto& end_block = generator.make_block();
for (auto& reference : optional_chain.references()) {
auto is_optional = reference.visit([](auto& ref) { return ref.mode; }) == OptionalChain::Mode::Optional;
if (is_optional) {
auto& not_nullish_block = generator.make_block();
generator.emit<Bytecode::Op::JumpNullish>(
current_value,
Bytecode::Label { load_undefined_and_jump_to_end_block },
Bytecode::Label { not_nullish_block });
generator.switch_to_basic_block(not_nullish_block);
}
reference.visit(
[&](OptionalChain::Call const& call) -> void {
auto arguments = arguments_to_array_for_call(generator, call.arguments).value();
generator.emit<Bytecode::Op::CallWithArgumentArray>(current_value, current_value, current_base, arguments, OptionalNone {});
generator.emit_mov(current_base, generator.add_constant(js_undefined()));
},
[&](OptionalChain::ComputedReference const& ref) -> void {
generator.emit_mov(current_base, current_value);
auto property = ref.expression->generate_bytecode(generator).value();
generator.emit_get_by_value(current_value, current_value, property);
},
[&](OptionalChain::MemberReference const& ref) -> void {
generator.emit_mov(current_base, current_value);
generator.emit_get_by_id(current_value, current_value, generator.intern_property_key(ref.identifier->string()));
},
[&](OptionalChain::PrivateMemberReference const& ref) -> void {
generator.emit_mov(current_base, current_value);
generator.emit<Bytecode::Op::GetPrivateById>(current_value, current_value, generator.intern_identifier(ref.private_identifier->string()));
});
}
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { end_block });
generator.switch_to_basic_block(load_undefined_and_jump_to_end_block);
generator.emit_mov(current_value, generator.add_constant(js_undefined()));
generator.emit<Bytecode::Op::Jump>(Bytecode::Label { end_block });
generator.switch_to_basic_block(end_block);
}
Optional<ScopedOperand> OptionalChain::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
auto current_base = generator.allocate_register();
auto current_value = choose_dst(generator, preferred_dst);
generator.emit_mov(current_base, generator.add_constant(js_undefined()));
generate_optional_chain(generator, *this, current_value, current_base);
return current_value;
}
Optional<ScopedOperand> ImportCall::generate_bytecode(Bytecode::Generator& generator, Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
auto specifier = m_specifier->generate_bytecode(generator).value();
Optional<ScopedOperand> options;
if (m_options) {
options = m_options->generate_bytecode(generator).value();
} else {
options = generator.add_constant(js_undefined());
}
auto dst = choose_dst(generator, preferred_dst);
generator.emit<Bytecode::Op::ImportCall>(dst, specifier, *options);
return dst;
}
Optional<ScopedOperand> ExportStatement::generate_bytecode(Bytecode::Generator& generator, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
Bytecode::Generator::SourceLocationScope scope(generator, *this);
if (!is_default_export()) {
if (m_statement) {
return m_statement->generate_bytecode(generator);
}
return Optional<ScopedOperand> {};
}
VERIFY(m_statement);
if (is<FunctionDeclaration>(*m_statement) || is<ClassDeclaration>(*m_statement)) {
return m_statement->generate_bytecode(generator);
}
if (is<ClassExpression>(*m_statement)) {
auto value = generator.emit_named_evaluation_if_anonymous_function(static_cast<ClassExpression const&>(*m_statement), generator.intern_identifier("default"_utf16_fly_string));
if (!static_cast<ClassExpression const&>(*m_statement).has_name()) {
generator.emit<Bytecode::Op::InitializeLexicalBinding>(
generator.intern_identifier(ExportStatement::local_name_for_default),
value);
}
return value;
}
// ExportDeclaration : export default AssignmentExpression ;
VERIFY(is<Expression>(*m_statement));
auto value = generator.emit_named_evaluation_if_anonymous_function(static_cast<Expression const&>(*m_statement), generator.intern_identifier("default"_utf16_fly_string));
generator.emit<Bytecode::Op::InitializeLexicalBinding>(
generator.intern_identifier(ExportStatement::local_name_for_default),
value);
return value;
}
Optional<ScopedOperand> ImportStatement::generate_bytecode(Bytecode::Generator&, [[maybe_unused]] Optional<ScopedOperand> preferred_dst) const
{
return Optional<ScopedOperand> {};
}
}
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