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ladybird/Libraries/LibJS/Bytecode/Generator.cpp
Shannon Booth f87041bf3a LibGC+Everywhere: Factor out a LibGC from LibJS 
Resulting in a massive rename across almost everywhere! Alongside the
namespace change, we now have the following names:

 * JS::NonnullGCPtr -> GC::Ref
 * JS::GCPtr -> GC::Ptr
 * JS::HeapFunction -> GC::Function
 * JS::CellImpl -> GC::Cell
 * JS::Handle -> GC::Root
2024-11-15 14:49:20 +01:00

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/*
* Copyright (c) 2021-2024, Andreas Kling <andreas@ladybird.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/QuickSort.h>
#include <AK/TemporaryChange.h>
#include <LibJS/AST.h>
#include <LibJS/Bytecode/BasicBlock.h>
#include <LibJS/Bytecode/Generator.h>
#include <LibJS/Bytecode/Instruction.h>
#include <LibJS/Bytecode/Op.h>
#include <LibJS/Bytecode/Register.h>
#include <LibJS/Runtime/ECMAScriptFunctionObject.h>
#include <LibJS/Runtime/VM.h>
namespace JS::Bytecode {
Generator::Generator(VM& vm, GC::Ptr<ECMAScriptFunctionObject const> function, MustPropagateCompletion must_propagate_completion)
: m_vm(vm)
, m_string_table(make<StringTable>())
, m_identifier_table(make<IdentifierTable>())
, m_regex_table(make<RegexTable>())
, m_constants(vm.heap())
, m_accumulator(*this, Operand(Register::accumulator()))
, m_this_value(*this, Operand(Register::this_value()))
, m_must_propagate_completion(must_propagate_completion == MustPropagateCompletion::Yes)
, m_function(function)
{
}
CodeGenerationErrorOr<void> Generator::emit_function_declaration_instantiation(ECMAScriptFunctionObject const& function)
{
if (function.m_has_parameter_expressions) {
emit<Op::CreateLexicalEnvironment>();
}
for (auto const& parameter_name : function.m_parameter_names) {
if (parameter_name.value == ECMAScriptFunctionObject::ParameterIsLocal::No) {
auto id = intern_identifier(parameter_name.key);
emit<Op::CreateVariable>(id, Op::EnvironmentMode::Lexical, false);
if (function.m_has_duplicates) {
emit<Op::InitializeLexicalBinding>(id, add_constant(js_undefined()));
}
}
}
if (function.m_arguments_object_needed) {
Optional<Operand> dst;
auto local_var_index = function.m_local_variables_names.find_first_index("arguments"sv);
if (local_var_index.has_value())
dst = local(local_var_index.value());
if (function.m_strict || !function.has_simple_parameter_list()) {
emit<Op::CreateArguments>(dst, Op::CreateArguments::Kind::Unmapped, function.m_strict);
} else {
emit<Op::CreateArguments>(dst, Op::CreateArguments::Kind::Mapped, function.m_strict);
}
}
auto const& formal_parameters = function.formal_parameters();
for (u32 param_index = 0; param_index < formal_parameters.size(); ++param_index) {
auto const& parameter = formal_parameters[param_index];
if (parameter.is_rest) {
auto argument_reg = allocate_register();
emit<Op::CreateRestParams>(argument_reg.operand(), param_index);
emit<Op::SetArgument>(param_index, argument_reg.operand());
} else if (parameter.default_value) {
auto& if_undefined_block = make_block();
auto& if_not_undefined_block = make_block();
auto argument_reg = allocate_register();
emit<Op::GetArgument>(argument_reg.operand(), param_index);
emit<Op::JumpUndefined>(
argument_reg.operand(),
Label { if_undefined_block },
Label { if_not_undefined_block });
switch_to_basic_block(if_undefined_block);
auto operand = TRY(parameter.default_value->generate_bytecode(*this));
emit<Op::SetArgument>(param_index, *operand);
emit<Op::Jump>(Label { if_not_undefined_block });
switch_to_basic_block(if_not_undefined_block);
}
if (auto const* identifier = parameter.binding.get_pointer<NonnullRefPtr<Identifier const>>(); identifier) {
if ((*identifier)->is_local()) {
auto local_variable_index = (*identifier)->local_variable_index();
emit<Op::GetArgument>(local(local_variable_index), param_index);
set_local_initialized((*identifier)->local_variable_index());
} else {
auto id = intern_identifier((*identifier)->string());
auto argument_reg = allocate_register();
emit<Op::GetArgument>(argument_reg.operand(), param_index);
if (function.m_has_duplicates) {
emit<Op::SetLexicalBinding>(id, argument_reg.operand());
} else {
emit<Op::InitializeLexicalBinding>(id, argument_reg.operand());
}
}
} else if (auto const* binding_pattern = parameter.binding.get_pointer<NonnullRefPtr<BindingPattern const>>(); binding_pattern) {
auto input_operand = allocate_register();
emit<Op::GetArgument>(input_operand.operand(), param_index);
auto init_mode = function.m_has_duplicates ? Op::BindingInitializationMode::Set : Bytecode::Op::BindingInitializationMode::Initialize;
TRY((*binding_pattern)->generate_bytecode(*this, init_mode, input_operand, false));
}
}
ScopeNode const* scope_body = nullptr;
if (is<ScopeNode>(*function.m_ecmascript_code))
scope_body = static_cast<ScopeNode const*>(function.m_ecmascript_code.ptr());
if (!function.m_has_parameter_expressions) {
if (scope_body) {
for (auto const& variable_to_initialize : function.m_var_names_to_initialize_binding) {
auto const& id = variable_to_initialize.identifier;
if (id.is_local()) {
emit<Op::Mov>(local(id.local_variable_index()), add_constant(js_undefined()));
} else {
auto intern_id = intern_identifier(id.string());
emit<Op::CreateVariable>(intern_id, Op::EnvironmentMode::Var, false);
emit<Op::InitializeVariableBinding>(intern_id, add_constant(js_undefined()));
}
}
}
} else {
emit<Op::CreateVariableEnvironment>(function.m_var_environment_bindings_count);
if (scope_body) {
for (auto const& variable_to_initialize : function.m_var_names_to_initialize_binding) {
auto const& id = variable_to_initialize.identifier;
auto initial_value = allocate_register();
if (!variable_to_initialize.parameter_binding || variable_to_initialize.function_name) {
emit<Op::Mov>(initial_value, add_constant(js_undefined()));
} else {
if (id.is_local()) {
emit<Op::Mov>(initial_value, local(id.local_variable_index()));
} else {
emit<Op::GetBinding>(initial_value, intern_identifier(id.string()));
}
}
if (id.is_local()) {
emit<Op::Mov>(local(id.local_variable_index()), initial_value);
} else {
auto intern_id = intern_identifier(id.string());
emit<Op::CreateVariable>(intern_id, Op::EnvironmentMode::Var, false);
emit<Op::InitializeVariableBinding>(intern_id, initial_value);
}
}
}
}
if (!function.m_strict && scope_body) {
for (auto const& function_name : function.m_function_names_to_initialize_binding) {
auto intern_id = intern_identifier(function_name);
emit<Op::CreateVariable>(intern_id, Op::EnvironmentMode::Var, false);
emit<Op::InitializeVariableBinding>(intern_id, add_constant(js_undefined()));
}
}
if (!function.m_strict) {
bool can_elide_declarative_environment = !function.m_contains_direct_call_to_eval && (!scope_body || !scope_body->has_non_local_lexical_declarations());
if (!can_elide_declarative_environment) {
emit<Op::CreateLexicalEnvironment>(function.m_lex_environment_bindings_count);
}
}
if (scope_body) {
MUST(scope_body->for_each_lexically_scoped_declaration([&](Declaration const& declaration) {
MUST(declaration.for_each_bound_identifier([&](auto const& id) {
if (id.is_local()) {
return;
}
emit<Op::CreateVariable>(intern_identifier(id.string()),
Op::EnvironmentMode::Lexical,
declaration.is_constant_declaration(),
false,
declaration.is_constant_declaration());
}));
}));
}
for (auto const& declaration : function.m_functions_to_initialize) {
auto function = allocate_register();
emit<Op::NewFunction>(function, declaration, OptionalNone {});
if (declaration.name_identifier()->is_local()) {
emit<Op::Mov>(local(declaration.name_identifier()->local_variable_index()), function);
} else {
emit<Op::SetVariableBinding>(intern_identifier(declaration.name()), function);
}
}
return {};
}
CodeGenerationErrorOr<GC::Ref<Executable>> Generator::compile(VM& vm, ASTNode const& node, FunctionKind enclosing_function_kind, GC::Ptr<ECMAScriptFunctionObject const> function, MustPropagateCompletion must_propagate_completion, Vector<DeprecatedFlyString> local_variable_names)
{
Generator generator(vm, function, must_propagate_completion);
generator.switch_to_basic_block(generator.make_block());
SourceLocationScope scope(generator, node);
generator.m_enclosing_function_kind = enclosing_function_kind;
if (generator.is_in_async_function() && !generator.is_in_generator_function()) {
// Immediately yield with no value.
auto& start_block = generator.make_block();
generator.emit<Bytecode::Op::Yield>(Label { start_block }, generator.add_constant(js_undefined()));
generator.switch_to_basic_block(start_block);
// NOTE: This doesn't have to handle received throw/return completions, as GeneratorObject::resume_abrupt
// will not enter the generator from the SuspendedStart state and immediately completes the generator.
}
if (function)
TRY(generator.emit_function_declaration_instantiation(*function));
if (generator.is_in_generator_function()) {
// Immediately yield with no value.
auto& start_block = generator.make_block();
generator.emit<Bytecode::Op::Yield>(Label { start_block }, generator.add_constant(js_undefined()));
generator.switch_to_basic_block(start_block);
// NOTE: This doesn't have to handle received throw/return completions, as GeneratorObject::resume_abrupt
// will not enter the generator from the SuspendedStart state and immediately completes the generator.
}
auto last_value = TRY(node.generate_bytecode(generator));
if (!generator.current_block().is_terminated() && last_value.has_value()) {
generator.emit<Bytecode::Op::End>(last_value.value());
}
if (generator.is_in_generator_or_async_function()) {
// Terminate all unterminated blocks with yield return
for (auto& block : generator.m_root_basic_blocks) {
if (block->is_terminated())
continue;
generator.switch_to_basic_block(*block);
generator.emit_return<Bytecode::Op::Yield>(generator.add_constant(js_undefined()));
}
}
bool is_strict_mode = false;
if (is<Program>(node))
is_strict_mode = static_cast<Program const&>(node).is_strict_mode();
else if (is<FunctionBody>(node))
is_strict_mode = static_cast<FunctionBody const&>(node).in_strict_mode();
else if (is<FunctionDeclaration>(node))
is_strict_mode = static_cast<FunctionDeclaration const&>(node).is_strict_mode();
size_t size_needed = 0;
for (auto& block : generator.m_root_basic_blocks) {
size_needed += block->size();
}
Vector<u8> bytecode;
bytecode.ensure_capacity(size_needed);
Vector<size_t> basic_block_start_offsets;
basic_block_start_offsets.ensure_capacity(generator.m_root_basic_blocks.size());
HashMap<BasicBlock const*, size_t> block_offsets;
Vector<size_t> label_offsets;
struct UnlinkedExceptionHandlers {
size_t start_offset;
size_t end_offset;
BasicBlock const* handler;
BasicBlock const* finalizer;
};
Vector<UnlinkedExceptionHandlers> unlinked_exception_handlers;
HashMap<size_t, SourceRecord> source_map;
Optional<ScopedOperand> undefined_constant;
for (auto& block : generator.m_root_basic_blocks) {
if (!block->is_terminated()) {
// NOTE: We must ensure that the "undefined" constant, which will be used by the not yet
// emitted End instruction, is taken into account while shifting local operands by the
// number of constants.
undefined_constant = generator.add_constant(js_undefined());
break;
}
}
auto number_of_registers = generator.m_next_register;
auto number_of_constants = generator.m_constants.size();
// Pass: Rewrite the bytecode to use the correct register and constant indices.
for (auto& block : generator.m_root_basic_blocks) {
Bytecode::InstructionStreamIterator it(block->instruction_stream());
while (!it.at_end()) {
auto& instruction = const_cast<Instruction&>(*it);
instruction.visit_operands([number_of_registers, number_of_constants](Operand& operand) {
switch (operand.type()) {
case Operand::Type::Register:
break;
case Operand::Type::Local:
operand.offset_index_by(number_of_registers + number_of_constants);
break;
case Operand::Type::Constant:
operand.offset_index_by(number_of_registers);
break;
default:
VERIFY_NOT_REACHED();
}
});
++it;
}
}
// Also rewrite the `undefined` constant if we have one for inserting End.
if (undefined_constant.has_value())
undefined_constant.value().operand().offset_index_by(number_of_registers);
for (auto& block : generator.m_root_basic_blocks) {
basic_block_start_offsets.append(bytecode.size());
if (block->handler() || block->finalizer()) {
unlinked_exception_handlers.append({
.start_offset = bytecode.size(),
.end_offset = 0,
.handler = block->handler(),
.finalizer = block->finalizer(),
});
}
block_offsets.set(block.ptr(), bytecode.size());
for (auto& [offset, source_record] : block->source_map()) {
source_map.set(bytecode.size() + offset, source_record);
}
Bytecode::InstructionStreamIterator it(block->instruction_stream());
while (!it.at_end()) {
auto& instruction = const_cast<Instruction&>(*it);
if (instruction.type() == Instruction::Type::Jump) {
auto& jump = static_cast<Bytecode::Op::Jump&>(instruction);
// OPTIMIZATION: Don't emit jumps that just jump to the next block.
if (jump.target().basic_block_index() == block->index() + 1) {
if (basic_block_start_offsets.last() == bytecode.size()) {
// This block is empty, just skip it.
basic_block_start_offsets.take_last();
}
++it;
continue;
}
// OPTIMIZATION: For jumps to a return-or-end-only block, we can emit a `Return` or `End` directly instead.
auto& target_block = *generator.m_root_basic_blocks[jump.target().basic_block_index()];
if (target_block.is_terminated()) {
auto target_instruction_iterator = InstructionStreamIterator { target_block.instruction_stream() };
auto& target_instruction = *target_instruction_iterator;
if (target_instruction.type() == Instruction::Type::Return) {
auto& return_instruction = static_cast<Bytecode::Op::Return const&>(target_instruction);
Op::Return return_op(return_instruction.value());
bytecode.append(reinterpret_cast<u8 const*>(&return_op), return_op.length());
++it;
continue;
}
if (target_instruction.type() == Instruction::Type::End) {
auto& return_instruction = static_cast<Bytecode::Op::End const&>(target_instruction);
Op::End end_op(return_instruction.value());
bytecode.append(reinterpret_cast<u8 const*>(&end_op), end_op.length());
++it;
continue;
}
}
}
// OPTIMIZATION: For `JumpIf` where one of the targets is the very next block,
// we can emit a `JumpTrue` or `JumpFalse` (to the other block) instead.
if (instruction.type() == Instruction::Type::JumpIf) {
auto& jump = static_cast<Bytecode::Op::JumpIf&>(instruction);
if (jump.true_target().basic_block_index() == block->index() + 1) {
Op::JumpFalse jump_false(jump.condition(), Label { jump.false_target() });
auto& label = jump_false.target();
size_t label_offset = bytecode.size() + (bit_cast<FlatPtr>(&label) - bit_cast<FlatPtr>(&jump_false));
label_offsets.append(label_offset);
bytecode.append(reinterpret_cast<u8 const*>(&jump_false), jump_false.length());
++it;
continue;
}
if (jump.false_target().basic_block_index() == block->index() + 1) {
Op::JumpTrue jump_true(jump.condition(), Label { jump.true_target() });
auto& label = jump_true.target();
size_t label_offset = bytecode.size() + (bit_cast<FlatPtr>(&label) - bit_cast<FlatPtr>(&jump_true));
label_offsets.append(label_offset);
bytecode.append(reinterpret_cast<u8 const*>(&jump_true), jump_true.length());
++it;
continue;
}
}
instruction.visit_labels([&](Label& label) {
size_t label_offset = bytecode.size() + (bit_cast<FlatPtr>(&label) - bit_cast<FlatPtr>(&instruction));
label_offsets.append(label_offset);
});
bytecode.append(reinterpret_cast<u8 const*>(&instruction), instruction.length());
++it;
}
if (!block->is_terminated()) {
Op::End end(*undefined_constant);
bytecode.append(reinterpret_cast<u8 const*>(&end), end.length());
}
if (block->handler() || block->finalizer()) {
unlinked_exception_handlers.last().end_offset = bytecode.size();
}
}
for (auto label_offset : label_offsets) {
auto& label = *reinterpret_cast<Label*>(bytecode.data() + label_offset);
auto* block = generator.m_root_basic_blocks[label.basic_block_index()].ptr();
label.set_address(block_offsets.get(block).value());
}
auto executable = vm.heap().allocate<Executable>(
move(bytecode),
move(generator.m_identifier_table),
move(generator.m_string_table),
move(generator.m_regex_table),
move(generator.m_constants),
node.source_code(),
generator.m_next_property_lookup_cache,
generator.m_next_global_variable_cache,
generator.m_next_register,
is_strict_mode);
Vector<Executable::ExceptionHandlers> linked_exception_handlers;
for (auto& unlinked_handler : unlinked_exception_handlers) {
auto start_offset = unlinked_handler.start_offset;
auto end_offset = unlinked_handler.end_offset;
auto handler_offset = unlinked_handler.handler ? block_offsets.get(unlinked_handler.handler).value() : Optional<size_t> {};
auto finalizer_offset = unlinked_handler.finalizer ? block_offsets.get(unlinked_handler.finalizer).value() : Optional<size_t> {};
linked_exception_handlers.append({ start_offset, end_offset, handler_offset, finalizer_offset });
}
quick_sort(linked_exception_handlers, [](auto const& a, auto const& b) {
return a.start_offset < b.start_offset;
});
executable->exception_handlers = move(linked_exception_handlers);
executable->basic_block_start_offsets = move(basic_block_start_offsets);
executable->source_map = move(source_map);
executable->local_variable_names = move(local_variable_names);
executable->local_index_base = number_of_registers + number_of_constants;
executable->length_identifier = generator.m_length_identifier;
generator.m_finished = true;
return executable;
}
CodeGenerationErrorOr<GC::Ref<Executable>> Generator::generate_from_ast_node(VM& vm, ASTNode const& node, FunctionKind enclosing_function_kind)
{
Vector<DeprecatedFlyString> local_variable_names;
if (is<ScopeNode>(node))
local_variable_names = static_cast<ScopeNode const&>(node).local_variables_names();
return compile(vm, node, enclosing_function_kind, {}, MustPropagateCompletion::Yes, move(local_variable_names));
}
CodeGenerationErrorOr<GC::Ref<Executable>> Generator::generate_from_function(VM& vm, ECMAScriptFunctionObject const& function)
{
return compile(vm, function.ecmascript_code(), function.kind(), &function, MustPropagateCompletion::No, function.local_variables_names());
}
void Generator::grow(size_t additional_size)
{
VERIFY(m_current_basic_block);
m_current_basic_block->grow(additional_size);
}
ScopedOperand Generator::allocate_register()
{
if (!m_free_registers.is_empty()) {
return ScopedOperand { *this, Operand { m_free_registers.take_last() } };
}
VERIFY(m_next_register != NumericLimits<u32>::max());
return ScopedOperand { *this, Operand { Register { m_next_register++ } } };
}
void Generator::free_register(Register reg)
{
m_free_registers.append(reg);
}
ScopedOperand Generator::local(u32 local_index)
{
return ScopedOperand { *this, Operand { Operand::Type::Local, static_cast<u32>(local_index) } };
}
Generator::SourceLocationScope::SourceLocationScope(Generator& generator, ASTNode const& node)
: m_generator(generator)
, m_previous_node(m_generator.m_current_ast_node)
{
m_generator.m_current_ast_node = &node;
}
Generator::SourceLocationScope::~SourceLocationScope()
{
m_generator.m_current_ast_node = m_previous_node;
}
Generator::UnwindContext::UnwindContext(Generator& generator, Optional<Label> finalizer)
: m_generator(generator)
, m_finalizer(finalizer)
, m_previous_context(m_generator.m_current_unwind_context)
{
m_generator.m_current_unwind_context = this;
}
Generator::UnwindContext::~UnwindContext()
{
VERIFY(m_generator.m_current_unwind_context == this);
m_generator.m_current_unwind_context = m_previous_context;
}
Label Generator::nearest_continuable_scope() const
{
return m_continuable_scopes.last().bytecode_target;
}
bool Generator::emit_block_declaration_instantiation(ScopeNode const& scope_node)
{
bool needs_block_declaration_instantiation = false;
MUST(scope_node.for_each_lexically_scoped_declaration([&](Declaration const& declaration) {
if (declaration.is_function_declaration()) {
needs_block_declaration_instantiation = true;
return;
}
MUST(declaration.for_each_bound_identifier([&](auto const& id) {
if (!id.is_local())
needs_block_declaration_instantiation = true;
}));
}));
if (!needs_block_declaration_instantiation)
return false;
// FIXME: Generate the actual bytecode for block declaration instantiation
// and get rid of the BlockDeclarationInstantiation instruction.
start_boundary(BlockBoundaryType::LeaveLexicalEnvironment);
emit<Bytecode::Op::BlockDeclarationInstantiation>(scope_node);
return true;
}
void Generator::begin_variable_scope()
{
start_boundary(BlockBoundaryType::LeaveLexicalEnvironment);
emit<Bytecode::Op::CreateLexicalEnvironment>();
}
void Generator::end_variable_scope()
{
end_boundary(BlockBoundaryType::LeaveLexicalEnvironment);
if (!m_current_basic_block->is_terminated()) {
emit<Bytecode::Op::LeaveLexicalEnvironment>();
}
}
void Generator::begin_continuable_scope(Label continue_target, Vector<DeprecatedFlyString> const& language_label_set)
{
m_continuable_scopes.append({ continue_target, language_label_set });
start_boundary(BlockBoundaryType::Continue);
}
void Generator::end_continuable_scope()
{
m_continuable_scopes.take_last();
end_boundary(BlockBoundaryType::Continue);
}
Label Generator::nearest_breakable_scope() const
{
return m_breakable_scopes.last().bytecode_target;
}
void Generator::begin_breakable_scope(Label breakable_target, Vector<DeprecatedFlyString> const& language_label_set)
{
m_breakable_scopes.append({ breakable_target, language_label_set });
start_boundary(BlockBoundaryType::Break);
}
void Generator::end_breakable_scope()
{
m_breakable_scopes.take_last();
end_boundary(BlockBoundaryType::Break);
}
CodeGenerationErrorOr<Generator::ReferenceOperands> Generator::emit_super_reference(MemberExpression const& expression)
{
VERIFY(is<SuperExpression>(expression.object()));
// https://tc39.es/ecma262/#sec-super-keyword-runtime-semantics-evaluation
// 1. Let env be GetThisEnvironment().
// 2. Let actualThis be ? env.GetThisBinding().
auto actual_this = get_this();
Optional<ScopedOperand> computed_property_value;
if (expression.is_computed()) {
// SuperProperty : super [ Expression ]
// 3. Let propertyNameReference be ? Evaluation of Expression.
// 4. Let propertyNameValue be ? GetValue(propertyNameReference).
computed_property_value = TRY(expression.property().generate_bytecode(*this)).value();
}
// 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 base_value = allocate_register();
emit<Bytecode::Op::ResolveSuperBase>(base_value);
// 4. Return the Reference Record { [[Base]]: baseValue, [[ReferencedName]]: propertyKey, [[Strict]]: strict, [[ThisValue]]: actualThis }.
return ReferenceOperands {
.base = base_value,
.referenced_name = computed_property_value,
.this_value = actual_this,
};
}
CodeGenerationErrorOr<Generator::ReferenceOperands> Generator::emit_load_from_reference(JS::ASTNode const& node, Optional<ScopedOperand> preferred_dst)
{
if (is<Identifier>(node)) {
auto& identifier = static_cast<Identifier const&>(node);
auto loaded_value = TRY(identifier.generate_bytecode(*this, preferred_dst)).value();
return ReferenceOperands {
.loaded_value = loaded_value,
};
}
if (!is<MemberExpression>(node)) {
return CodeGenerationError {
&node,
"Unimplemented/invalid node used as a reference"sv
};
}
auto& expression = static_cast<MemberExpression const&>(node);
// https://tc39.es/ecma262/#sec-super-keyword-runtime-semantics-evaluation
if (is<SuperExpression>(expression.object())) {
auto super_reference = TRY(emit_super_reference(expression));
auto dst = preferred_dst.has_value() ? preferred_dst.value() : allocate_register();
if (super_reference.referenced_name.has_value()) {
// 5. Let propertyKey be ? ToPropertyKey(propertyNameValue).
// FIXME: This does ToPropertyKey out of order, which is observable by Symbol.toPrimitive!
emit<Bytecode::Op::GetByValueWithThis>(dst, *super_reference.base, *super_reference.referenced_name, *super_reference.this_value);
} else {
// 3. Let propertyKey be StringValue of IdentifierName.
auto identifier_table_ref = intern_identifier(verify_cast<Identifier>(expression.property()).string());
emit_get_by_id_with_this(dst, *super_reference.base, identifier_table_ref, *super_reference.this_value);
}
super_reference.loaded_value = dst;
return super_reference;
}
auto base = TRY(expression.object().generate_bytecode(*this)).value();
auto base_identifier = intern_identifier_for_expression(expression.object());
if (expression.is_computed()) {
auto property = TRY(expression.property().generate_bytecode(*this)).value();
auto saved_property = allocate_register();
emit<Bytecode::Op::Mov>(saved_property, property);
auto dst = preferred_dst.has_value() ? preferred_dst.value() : allocate_register();
emit<Bytecode::Op::GetByValue>(dst, base, property, move(base_identifier));
return ReferenceOperands {
.base = base,
.referenced_name = saved_property,
.this_value = base,
.loaded_value = dst,
};
}
if (expression.property().is_identifier()) {
auto identifier_table_ref = intern_identifier(verify_cast<Identifier>(expression.property()).string());
auto dst = preferred_dst.has_value() ? preferred_dst.value() : allocate_register();
emit_get_by_id(dst, base, identifier_table_ref, move(base_identifier));
return ReferenceOperands {
.base = base,
.referenced_identifier = identifier_table_ref,
.this_value = base,
.loaded_value = dst,
};
}
if (expression.property().is_private_identifier()) {
auto identifier_table_ref = intern_identifier(verify_cast<PrivateIdentifier>(expression.property()).string());
auto dst = preferred_dst.has_value() ? preferred_dst.value() : allocate_register();
emit<Bytecode::Op::GetPrivateById>(dst, base, identifier_table_ref);
return ReferenceOperands {
.base = base,
.referenced_private_identifier = identifier_table_ref,
.this_value = base,
.loaded_value = dst,
};
}
return CodeGenerationError {
&expression,
"Unimplemented non-computed member expression"sv
};
}
CodeGenerationErrorOr<void> Generator::emit_store_to_reference(JS::ASTNode const& node, ScopedOperand value)
{
if (is<Identifier>(node)) {
auto& identifier = static_cast<Identifier const&>(node);
emit_set_variable(identifier, value);
return {};
}
if (is<MemberExpression>(node)) {
auto& expression = static_cast<MemberExpression const&>(node);
// https://tc39.es/ecma262/#sec-super-keyword-runtime-semantics-evaluation
if (is<SuperExpression>(expression.object())) {
auto super_reference = TRY(emit_super_reference(expression));
// 4. Return the Reference Record { [[Base]]: baseValue, [[ReferencedName]]: propertyKey, [[Strict]]: strict, [[ThisValue]]: actualThis }.
if (super_reference.referenced_name.has_value()) {
// 5. Let propertyKey be ? ToPropertyKey(propertyNameValue).
// FIXME: This does ToPropertyKey out of order, which is observable by Symbol.toPrimitive!
emit<Bytecode::Op::PutByValueWithThis>(*super_reference.base, *super_reference.referenced_name, *super_reference.this_value, value);
} else {
// 3. Let propertyKey be StringValue of IdentifierName.
auto identifier_table_ref = intern_identifier(verify_cast<Identifier>(expression.property()).string());
emit<Bytecode::Op::PutByIdWithThis>(*super_reference.base, *super_reference.this_value, identifier_table_ref, value, Bytecode::Op::PropertyKind::KeyValue, next_property_lookup_cache());
}
} else {
auto object = TRY(expression.object().generate_bytecode(*this)).value();
if (expression.is_computed()) {
auto property = TRY(expression.property().generate_bytecode(*this)).value();
emit<Bytecode::Op::PutByValue>(object, property, value);
} else if (expression.property().is_identifier()) {
auto identifier_table_ref = intern_identifier(verify_cast<Identifier>(expression.property()).string());
emit<Bytecode::Op::PutById>(object, identifier_table_ref, value, Bytecode::Op::PropertyKind::KeyValue, next_property_lookup_cache());
} else if (expression.property().is_private_identifier()) {
auto identifier_table_ref = intern_identifier(verify_cast<PrivateIdentifier>(expression.property()).string());
emit<Bytecode::Op::PutPrivateById>(object, identifier_table_ref, value);
} else {
return CodeGenerationError {
&expression,
"Unimplemented non-computed member expression"sv
};
}
}
return {};
}
return CodeGenerationError {
&node,
"Unimplemented/invalid node used a reference"sv
};
}
CodeGenerationErrorOr<void> Generator::emit_store_to_reference(ReferenceOperands const& reference, ScopedOperand value)
{
if (reference.referenced_private_identifier.has_value()) {
emit<Bytecode::Op::PutPrivateById>(*reference.base, *reference.referenced_private_identifier, value);
return {};
}
if (reference.referenced_identifier.has_value()) {
if (reference.base == reference.this_value)
emit<Bytecode::Op::PutById>(*reference.base, *reference.referenced_identifier, value, Bytecode::Op::PropertyKind::KeyValue, next_property_lookup_cache());
else
emit<Bytecode::Op::PutByIdWithThis>(*reference.base, *reference.this_value, *reference.referenced_identifier, value, Bytecode::Op::PropertyKind::KeyValue, next_property_lookup_cache());
return {};
}
if (reference.base == reference.this_value)
emit<Bytecode::Op::PutByValue>(*reference.base, *reference.referenced_name, value);
else
emit<Bytecode::Op::PutByValueWithThis>(*reference.base, *reference.referenced_name, *reference.this_value, value);
return {};
}
CodeGenerationErrorOr<Optional<ScopedOperand>> Generator::emit_delete_reference(JS::ASTNode const& node)
{
if (is<Identifier>(node)) {
auto& identifier = static_cast<Identifier const&>(node);
if (identifier.is_local()) {
return add_constant(Value(false));
}
auto dst = allocate_register();
emit<Bytecode::Op::DeleteVariable>(dst, intern_identifier(identifier.string()));
return dst;
}
if (is<MemberExpression>(node)) {
auto& expression = static_cast<MemberExpression const&>(node);
// https://tc39.es/ecma262/#sec-super-keyword-runtime-semantics-evaluation
if (is<SuperExpression>(expression.object())) {
auto super_reference = TRY(emit_super_reference(expression));
auto dst = allocate_register();
if (super_reference.referenced_name.has_value()) {
emit<Bytecode::Op::DeleteByValueWithThis>(dst, *super_reference.base, *super_reference.this_value, *super_reference.referenced_name);
} else {
auto identifier_table_ref = intern_identifier(verify_cast<Identifier>(expression.property()).string());
emit<Bytecode::Op::DeleteByIdWithThis>(dst, *super_reference.base, *super_reference.this_value, identifier_table_ref);
}
return Optional<ScopedOperand> {};
}
auto object = TRY(expression.object().generate_bytecode(*this)).value();
auto dst = allocate_register();
if (expression.is_computed()) {
auto property = TRY(expression.property().generate_bytecode(*this)).value();
emit<Bytecode::Op::DeleteByValue>(dst, object, property);
} else if (expression.property().is_identifier()) {
auto identifier_table_ref = intern_identifier(verify_cast<Identifier>(expression.property()).string());
emit<Bytecode::Op::DeleteById>(dst, object, identifier_table_ref);
} else {
// NOTE: Trying to delete a private field generates a SyntaxError in the parser.
return CodeGenerationError {
&expression,
"Unimplemented non-computed member expression"sv
};
}
return dst;
}
// Though this will have no deletion effect, we still have to evaluate the node as it can have side effects.
// For example: delete a(); delete ++c.b; etc.
// 13.5.1.2 Runtime Semantics: Evaluation, https://tc39.es/ecma262/#sec-delete-operator-runtime-semantics-evaluation
// 1. Let ref be the result of evaluating UnaryExpression.
// 2. ReturnIfAbrupt(ref).
(void)TRY(node.generate_bytecode(*this));
// 3. If ref is not a Reference Record, return true.
// NOTE: The rest of the steps are handled by Delete{Variable,ByValue,Id}.
return add_constant(Value(true));
}
void Generator::emit_set_variable(JS::Identifier const& identifier, ScopedOperand value, Bytecode::Op::BindingInitializationMode initialization_mode, Bytecode::Op::EnvironmentMode environment_mode)
{
if (identifier.is_local()) {
if (value.operand().is_local() && value.operand().index() == identifier.local_variable_index()) {
// Moving a local to itself is a no-op.
return;
}
emit<Bytecode::Op::Mov>(local(identifier.local_variable_index()), value);
} else {
auto identifier_index = intern_identifier(identifier.string());
if (environment_mode == Bytecode::Op::EnvironmentMode::Lexical) {
if (initialization_mode == Bytecode::Op::BindingInitializationMode::Initialize) {
emit<Bytecode::Op::InitializeLexicalBinding>(identifier_index, value);
} else if (initialization_mode == Bytecode::Op::BindingInitializationMode::Set) {
emit<Bytecode::Op::SetLexicalBinding>(identifier_index, value);
}
} else if (environment_mode == Bytecode::Op::EnvironmentMode::Var) {
if (initialization_mode == Bytecode::Op::BindingInitializationMode::Initialize) {
emit<Bytecode::Op::InitializeVariableBinding>(identifier_index, value);
} else if (initialization_mode == Bytecode::Op::BindingInitializationMode::Set) {
emit<Bytecode::Op::SetVariableBinding>(identifier_index, value);
}
} else {
VERIFY_NOT_REACHED();
}
}
}
static Optional<ByteString> expression_identifier(Expression const& expression)
{
if (expression.is_identifier()) {
auto const& identifier = static_cast<Identifier const&>(expression);
return identifier.string();
}
if (expression.is_numeric_literal()) {
auto const& literal = static_cast<NumericLiteral const&>(expression);
return literal.value().to_string_without_side_effects().to_byte_string();
}
if (expression.is_string_literal()) {
auto const& literal = static_cast<StringLiteral const&>(expression);
return ByteString::formatted("'{}'", literal.value());
}
if (expression.is_member_expression()) {
auto const& member_expression = static_cast<MemberExpression const&>(expression);
StringBuilder builder;
if (auto identifer = expression_identifier(member_expression.object()); identifer.has_value())
builder.append(*identifer);
if (auto identifer = expression_identifier(member_expression.property()); identifer.has_value()) {
if (member_expression.is_computed())
builder.appendff("[{}]", *identifer);
else
builder.appendff(".{}", *identifer);
}
return builder.to_byte_string();
}
return {};
}
Optional<IdentifierTableIndex> Generator::intern_identifier_for_expression(Expression const& expression)
{
if (auto identifer = expression_identifier(expression); identifer.has_value())
return intern_identifier(identifer.release_value());
return {};
}
void Generator::generate_scoped_jump(JumpType type)
{
TemporaryChange temp { m_current_unwind_context, m_current_unwind_context };
bool last_was_finally = false;
for (size_t i = m_boundaries.size(); i > 0; --i) {
auto boundary = m_boundaries[i - 1];
using enum BlockBoundaryType;
switch (boundary) {
case Break:
if (type == JumpType::Break) {
emit<Op::Jump>(nearest_breakable_scope());
return;
}
break;
case Continue:
if (type == JumpType::Continue) {
emit<Op::Jump>(nearest_continuable_scope());
return;
}
break;
case Unwind:
if (!last_was_finally) {
VERIFY(m_current_unwind_context && m_current_unwind_context->handler().has_value());
emit<Bytecode::Op::LeaveUnwindContext>();
m_current_unwind_context = m_current_unwind_context->previous();
}
last_was_finally = false;
break;
case LeaveLexicalEnvironment:
emit<Bytecode::Op::LeaveLexicalEnvironment>();
break;
case ReturnToFinally: {
VERIFY(m_current_unwind_context->finalizer().has_value());
m_current_unwind_context = m_current_unwind_context->previous();
auto jump_type_name = type == JumpType::Break ? "break"sv : "continue"sv;
auto block_name = MUST(String::formatted("{}.{}", current_block().name(), jump_type_name));
auto& block = make_block(block_name);
emit<Op::ScheduleJump>(Label { block });
switch_to_basic_block(block);
last_was_finally = true;
break;
}
case LeaveFinally:
emit<Op::LeaveFinally>();
break;
}
}
VERIFY_NOT_REACHED();
}
void Generator::generate_labelled_jump(JumpType type, DeprecatedFlyString const& label)
{
TemporaryChange temp { m_current_unwind_context, m_current_unwind_context };
size_t current_boundary = m_boundaries.size();
bool last_was_finally = false;
auto const& jumpable_scopes = type == JumpType::Continue ? m_continuable_scopes : m_breakable_scopes;
for (auto const& jumpable_scope : jumpable_scopes.in_reverse()) {
for (; current_boundary > 0; --current_boundary) {
auto boundary = m_boundaries[current_boundary - 1];
if (boundary == BlockBoundaryType::Unwind) {
if (!last_was_finally) {
VERIFY(m_current_unwind_context && m_current_unwind_context->handler().has_value());
emit<Bytecode::Op::LeaveUnwindContext>();
m_current_unwind_context = m_current_unwind_context->previous();
}
last_was_finally = false;
} else if (boundary == BlockBoundaryType::LeaveLexicalEnvironment) {
emit<Bytecode::Op::LeaveLexicalEnvironment>();
} else if (boundary == BlockBoundaryType::ReturnToFinally) {
VERIFY(m_current_unwind_context->finalizer().has_value());
m_current_unwind_context = m_current_unwind_context->previous();
auto jump_type_name = type == JumpType::Break ? "break"sv : "continue"sv;
auto block_name = MUST(String::formatted("{}.{}", current_block().name(), jump_type_name));
auto& block = make_block(block_name);
emit<Op::ScheduleJump>(Label { block });
switch_to_basic_block(block);
last_was_finally = true;
} else if ((type == JumpType::Continue && boundary == BlockBoundaryType::Continue) || (type == JumpType::Break && boundary == BlockBoundaryType::Break)) {
// Make sure we don't process this boundary twice if the current jumpable scope doesn't contain the target label.
--current_boundary;
break;
}
}
if (jumpable_scope.language_label_set.contains_slow(label)) {
emit<Op::Jump>(jumpable_scope.bytecode_target);
return;
}
}
// We must have a jumpable scope available that contains the label, as this should be enforced by the parser.
VERIFY_NOT_REACHED();
}
void Generator::generate_break()
{
generate_scoped_jump(JumpType::Break);
}
void Generator::generate_break(DeprecatedFlyString const& break_label)
{
generate_labelled_jump(JumpType::Break, break_label);
}
void Generator::generate_continue()
{
generate_scoped_jump(JumpType::Continue);
}
void Generator::generate_continue(DeprecatedFlyString const& continue_label)
{
generate_labelled_jump(JumpType::Continue, continue_label);
}
void Generator::push_home_object(ScopedOperand object)
{
m_home_objects.append(object);
}
void Generator::pop_home_object()
{
m_home_objects.take_last();
}
void Generator::emit_new_function(ScopedOperand dst, FunctionExpression const& function_node, Optional<IdentifierTableIndex> lhs_name)
{
if (m_home_objects.is_empty()) {
emit<Op::NewFunction>(dst, function_node, lhs_name);
} else {
emit<Op::NewFunction>(dst, function_node, lhs_name, m_home_objects.last());
}
}
CodeGenerationErrorOr<Optional<ScopedOperand>> Generator::emit_named_evaluation_if_anonymous_function(Expression const& expression, Optional<IdentifierTableIndex> lhs_name, Optional<ScopedOperand> preferred_dst)
{
if (is<FunctionExpression>(expression)) {
auto const& function_expression = static_cast<FunctionExpression const&>(expression);
if (!function_expression.has_name()) {
return TRY(function_expression.generate_bytecode_with_lhs_name(*this, move(lhs_name), preferred_dst)).value();
}
}
if (is<ClassExpression>(expression)) {
auto const& class_expression = static_cast<ClassExpression const&>(expression);
if (!class_expression.has_name()) {
return TRY(class_expression.generate_bytecode_with_lhs_name(*this, move(lhs_name), preferred_dst)).value();
}
}
return expression.generate_bytecode(*this, preferred_dst);
}
void Generator::emit_get_by_id(ScopedOperand dst, ScopedOperand base, IdentifierTableIndex property_identifier, Optional<IdentifierTableIndex> base_identifier)
{
if (m_identifier_table->get(property_identifier) == "length"sv) {
m_length_identifier = property_identifier;
emit<Op::GetLength>(dst, base, move(base_identifier), m_next_property_lookup_cache++);
return;
}
emit<Op::GetById>(dst, base, property_identifier, move(base_identifier), m_next_property_lookup_cache++);
}
void Generator::emit_get_by_id_with_this(ScopedOperand dst, ScopedOperand base, IdentifierTableIndex id, ScopedOperand this_value)
{
if (m_identifier_table->get(id) == "length"sv) {
emit<Op::GetLengthWithThis>(dst, base, this_value, m_next_property_lookup_cache++);
return;
}
emit<Op::GetByIdWithThis>(dst, base, id, this_value, m_next_property_lookup_cache++);
}
void Generator::emit_iterator_value(ScopedOperand dst, ScopedOperand result)
{
emit_get_by_id(dst, result, intern_identifier("value"sv));
}
void Generator::emit_iterator_complete(ScopedOperand dst, ScopedOperand result)
{
emit_get_by_id(dst, result, intern_identifier("done"sv));
}
bool Generator::is_local_initialized(u32 local_index) const
{
return m_initialized_locals.find(local_index) != m_initialized_locals.end();
}
void Generator::set_local_initialized(u32 local_index)
{
m_initialized_locals.set(local_index);
}
ScopedOperand Generator::get_this(Optional<ScopedOperand> preferred_dst)
{
if (m_current_basic_block->has_resolved_this())
return this_value();
if (m_root_basic_blocks[0]->has_resolved_this()) {
m_current_basic_block->set_has_resolved_this();
return this_value();
}
// OPTIMIZATION: If we're compiling a function that doesn't allocate a FunctionEnvironment,
// it will always have the same `this` value as the outer function,
// and so the `this` value is already in the `this` register!
if (m_function && !m_function->allocates_function_environment())
return this_value();
auto dst = preferred_dst.has_value() ? preferred_dst.value() : allocate_register();
emit<Bytecode::Op::ResolveThisBinding>();
m_current_basic_block->set_has_resolved_this();
return this_value();
}
ScopedOperand Generator::accumulator()
{
return m_accumulator;
}
ScopedOperand Generator::this_value()
{
return m_this_value;
}
bool Generator::fuse_compare_and_jump(ScopedOperand const& condition, Label true_target, Label false_target)
{
auto& last_instruction = *reinterpret_cast<Instruction const*>(m_current_basic_block->data() + m_current_basic_block->last_instruction_start_offset());
#define HANDLE_COMPARISON_OP(op_TitleCase, op_snake_case, numeric_operator) \
if (last_instruction.type() == Instruction::Type::op_TitleCase) { \
auto& comparison = static_cast<Op::op_TitleCase const&>(last_instruction); \
VERIFY(comparison.dst() == condition); \
auto lhs = comparison.lhs(); \
auto rhs = comparison.rhs(); \
m_current_basic_block->rewind(); \
emit<Op::Jump##op_TitleCase>(lhs, rhs, true_target, false_target); \
return true; \
}
JS_ENUMERATE_COMPARISON_OPS(HANDLE_COMPARISON_OP);
#undef HANDLE_COMPARISON_OP
return false;
}
void Generator::emit_jump_if(ScopedOperand const& condition, Label true_target, Label false_target)
{
if (condition.operand().is_constant()) {
auto value = m_constants[condition.operand().index()];
if (value.is_boolean()) {
if (value.as_bool()) {
emit<Op::Jump>(true_target);
} else {
emit<Op::Jump>(false_target);
}
return;
}
}
// NOTE: It's only safe to fuse compare-and-jump if the condition is a temporary with no other dependents.
if (condition.operand().is_register()
&& condition.ref_count() == 1
&& m_current_basic_block->size() > 0) {
if (fuse_compare_and_jump(condition, true_target, false_target))
return;
}
emit<Op::JumpIf>(condition, true_target, false_target);
}
ScopedOperand Generator::copy_if_needed_to_preserve_evaluation_order(ScopedOperand const& operand)
{
if (!operand.operand().is_local())
return operand;
auto new_register = allocate_register();
emit<Bytecode::Op::Mov>(new_register, operand);
return new_register;
}
ScopedOperand Generator::add_constant(Value value)
{
auto append_new_constant = [&] {
m_constants.append(value);
return ScopedOperand { *this, Operand(Operand::Type::Constant, m_constants.size() - 1) };
};
if (value.is_boolean()) {
if (value.as_bool()) {
if (!m_true_constant.has_value())
m_true_constant = append_new_constant();
return m_true_constant.value();
} else {
if (!m_false_constant.has_value())
m_false_constant = append_new_constant();
return m_false_constant.value();
}
}
if (value.is_undefined()) {
if (!m_undefined_constant.has_value())
m_undefined_constant = append_new_constant();
return m_undefined_constant.value();
}
if (value.is_null()) {
if (!m_null_constant.has_value())
m_null_constant = append_new_constant();
return m_null_constant.value();
}
if (value.is_empty()) {
if (!m_empty_constant.has_value())
m_empty_constant = append_new_constant();
return m_empty_constant.value();
}
if (value.is_int32()) {
auto as_int32 = value.as_i32();
return m_int32_constants.ensure(as_int32, [&] {
return append_new_constant();
});
}
return append_new_constant();
}
}
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