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ladybird/Userland/Libraries/LibJS/Bytecode/Generator.cpp
Andreas Kling 350e6c54d7 LibJS: Remove dedicated iterator result instructions in favor of GetById 
When iterating over an iterable, we get back a JS object with the fields
"value" and "done".

Before this change, we've had two dedicated instructions for retrieving
the two fields: IteratorResultValue and IteratorResultDone. These had no
fast path whatsoever and just did a generic [[Get]] access to fetch the
corresponding property values.

By replacing the instructions with GetById("value") and GetById("done"),
they instantly get caching and JIT fast paths for free, making iterating
over iterables much faster. :^)

26% speed-up on this microbenchmark:

    function go(a) {
        for (const p of a) {
        }
    }
    const a = [];
    a.length = 1_000_000;
    go(a);
2023-12-07 18:12:24 +01:00

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/*
* Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#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/VM.h>
namespace JS::Bytecode {
Generator::Generator()
: m_string_table(make<StringTable>())
, m_identifier_table(make<IdentifierTable>())
, m_regex_table(make<RegexTable>())
{
}
CodeGenerationErrorOr<NonnullGCPtr<Executable>> Generator::generate(VM& vm, ASTNode const& node, FunctionKind enclosing_function_kind)
{
Generator generator;
generator.switch_to_basic_block(generator.make_block());
SourceLocationScope scope(generator, node);
generator.m_enclosing_function_kind = enclosing_function_kind;
if (generator.is_in_generator_or_async_function()) {
// Immediately yield with no value.
auto& start_block = generator.make_block();
generator.emit<Bytecode::Op::Yield>(Label { start_block });
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.
}
TRY(node.generate_bytecode(generator));
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<Bytecode::Op::LoadImmediate>(js_undefined());
generator.emit<Bytecode::Op::Yield>(nullptr);
}
}
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();
else if (is<FunctionExpression>(node))
is_strict_mode = static_cast<FunctionExpression const&>(node).is_strict_mode();
auto executable = vm.heap().allocate_without_realm<Executable>(
move(generator.m_identifier_table),
move(generator.m_string_table),
move(generator.m_regex_table),
node.source_code(),
generator.m_next_property_lookup_cache,
generator.m_next_global_variable_cache,
generator.m_next_environment_variable_cache,
generator.m_next_register,
move(generator.m_root_basic_blocks),
is_strict_mode);
return executable;
}
void Generator::grow(size_t additional_size)
{
VERIFY(m_current_basic_block);
m_current_basic_block->grow(additional_size);
}
Register Generator::allocate_register()
{
VERIFY(m_next_register != NumericLimits<u32>::max());
return Register { m_next_register++ };
}
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;
}
void Generator::block_declaration_instantiation(ScopeNode const& scope_node)
{
start_boundary(BlockBoundaryType::LeaveLexicalEnvironment);
emit<Bytecode::Op::BlockDeclarationInstantiation>(scope_node);
}
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::ReferenceRegisters> 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_register = allocate_register();
emit<Bytecode::Op::ResolveThisBinding>();
emit<Bytecode::Op::Store>(actual_this_register);
Optional<Bytecode::Register> computed_property_value_register;
if (expression.is_computed()) {
// SuperProperty : super [ Expression ]
// 3. Let propertyNameReference be ? Evaluation of Expression.
// 4. Let propertyNameValue be ? GetValue(propertyNameReference).
TRY(expression.property().generate_bytecode(*this));
computed_property_value_register = allocate_register();
emit<Bytecode::Op::Store>(*computed_property_value_register);
}
// 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_register = allocate_register();
emit<Bytecode::Op::ResolveSuperBase>();
emit<Bytecode::Op::Store>(super_base_register);
// 4. Return the Reference Record { [[Base]]: baseValue, [[ReferencedName]]: propertyKey, [[Strict]]: strict, [[ThisValue]]: actualThis }.
return ReferenceRegisters {
.base = super_base_register,
.referenced_name = move(computed_property_value_register),
.this_value = actual_this_register,
};
}
CodeGenerationErrorOr<Optional<Generator::ReferenceRegisters>> Generator::emit_load_from_reference(JS::ASTNode const& node, CollectRegisters collect_registers)
{
if (is<Identifier>(node)) {
auto& identifier = static_cast<Identifier const&>(node);
TRY(identifier.generate_bytecode(*this));
return Optional<ReferenceRegisters> {};
}
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));
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::Load>(*super_reference.referenced_name);
emit<Bytecode::Op::GetByValueWithThis>(super_reference.base, 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(identifier_table_ref, super_reference.this_value);
}
return super_reference;
} else {
TRY(expression.object().generate_bytecode(*this));
if (expression.is_computed()) {
auto object_reg = allocate_register();
emit<Bytecode::Op::Store>(object_reg);
TRY(expression.property().generate_bytecode(*this));
Optional<Register> property_reg {};
if (collect_registers == CollectRegisters::Yes) {
property_reg = allocate_register();
emit<Bytecode::Op::Store>(property_reg.value());
}
emit<Bytecode::Op::GetByValue>(object_reg);
if (collect_registers == CollectRegisters::Yes)
return ReferenceRegisters {
.base = object_reg,
.referenced_name = property_reg.value(),
.this_value = object_reg,
};
return Optional<ReferenceRegisters> {};
} else if (expression.property().is_identifier()) {
auto identifier_table_ref = intern_identifier(verify_cast<Identifier>(expression.property()).string());
emit_get_by_id(identifier_table_ref);
} else if (expression.property().is_private_identifier()) {
auto identifier_table_ref = intern_identifier(verify_cast<PrivateIdentifier>(expression.property()).string());
emit<Bytecode::Op::GetPrivateById>(identifier_table_ref);
} else {
return CodeGenerationError {
&expression,
"Unimplemented non-computed member expression"sv
};
}
}
return Optional<ReferenceRegisters> {};
}
VERIFY_NOT_REACHED();
}
CodeGenerationErrorOr<void> Generator::emit_store_to_reference(JS::ASTNode const& node)
{
if (is<Identifier>(node)) {
auto& identifier = static_cast<Identifier const&>(node);
emit_set_variable(identifier);
return {};
}
if (is<MemberExpression>(node)) {
// NOTE: The value is in the accumulator, so we have to store that away first.
auto value_reg = allocate_register();
emit<Bytecode::Op::Store>(value_reg);
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));
emit<Bytecode::Op::Load>(value_reg);
// 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);
} 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, Bytecode::Op::PropertyKind::KeyValue, next_property_lookup_cache());
}
} else {
TRY(expression.object().generate_bytecode(*this));
auto object_reg = allocate_register();
emit<Bytecode::Op::Store>(object_reg);
if (expression.is_computed()) {
TRY(expression.property().generate_bytecode(*this));
auto property_reg = allocate_register();
emit<Bytecode::Op::Store>(property_reg);
emit<Bytecode::Op::Load>(value_reg);
emit<Bytecode::Op::PutByValue>(object_reg, property_reg);
} else if (expression.property().is_identifier()) {
emit<Bytecode::Op::Load>(value_reg);
auto identifier_table_ref = intern_identifier(verify_cast<Identifier>(expression.property()).string());
emit<Bytecode::Op::PutById>(object_reg, identifier_table_ref, Bytecode::Op::PropertyKind::KeyValue, next_property_lookup_cache());
} else if (expression.property().is_private_identifier()) {
emit<Bytecode::Op::Load>(value_reg);
auto identifier_table_ref = intern_identifier(verify_cast<PrivateIdentifier>(expression.property()).string());
emit<Bytecode::Op::PutPrivateById>(object_reg, identifier_table_ref);
} 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(ReferenceRegisters const& reference_registers)
{
if (reference_registers.base == reference_registers.this_value)
emit<Bytecode::Op::PutByValue>(reference_registers.base, reference_registers.referenced_name.value());
else
emit<Bytecode::Op::PutByValueWithThis>(reference_registers.base, reference_registers.referenced_name.value(), reference_registers.this_value);
return {};
}
CodeGenerationErrorOr<void> Generator::emit_delete_reference(JS::ASTNode const& node)
{
if (is<Identifier>(node)) {
auto& identifier = static_cast<Identifier const&>(node);
if (identifier.is_local())
emit<Bytecode::Op::LoadImmediate>(Value(false));
else
emit<Bytecode::Op::DeleteVariable>(intern_identifier(identifier.string()));
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));
if (super_reference.referenced_name.has_value()) {
emit<Bytecode::Op::DeleteByValueWithThis>(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>(super_reference.this_value, identifier_table_ref);
}
return {};
}
TRY(expression.object().generate_bytecode(*this));
if (expression.is_computed()) {
auto object_reg = allocate_register();
emit<Bytecode::Op::Store>(object_reg);
TRY(expression.property().generate_bytecode(*this));
emit<Bytecode::Op::DeleteByValue>(object_reg);
} else if (expression.property().is_identifier()) {
auto identifier_table_ref = intern_identifier(verify_cast<Identifier>(expression.property()).string());
emit<Bytecode::Op::DeleteById>(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 {};
}
// 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).
TRY(node.generate_bytecode(*this));
// 3. If ref is not a Reference Record, return true.
emit<Bytecode::Op::LoadImmediate>(Value(true));
// NOTE: The rest of the steps are handled by Delete{Variable,ByValue,Id}.
return {};
}
void Generator::emit_set_variable(JS::Identifier const& identifier, Bytecode::Op::SetVariable::InitializationMode initialization_mode, Bytecode::Op::EnvironmentMode mode)
{
if (identifier.is_local()) {
emit<Bytecode::Op::SetLocal>(identifier.local_variable_index());
} else {
emit<Bytecode::Op::SetVariable>(intern_identifier(identifier.string()), next_environment_variable_cache(), initialization_mode, mode);
}
}
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:
VERIFY(last_was_finally || !m_current_unwind_context->finalizer().has_value());
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;
};
}
}
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) {
VERIFY(last_was_finally || !m_current_unwind_context->finalizer().has_value());
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(Register register_)
{
m_home_objects.append(register_);
}
void Generator::pop_home_object()
{
m_home_objects.take_last();
}
void Generator::emit_new_function(FunctionExpression const& function_node, Optional<IdentifierTableIndex> lhs_name)
{
if (m_home_objects.is_empty())
emit<Op::NewFunction>(function_node, lhs_name);
else
emit<Op::NewFunction>(function_node, lhs_name, m_home_objects.last());
}
CodeGenerationErrorOr<void> Generator::emit_named_evaluation_if_anonymous_function(Expression const& expression, Optional<IdentifierTableIndex> lhs_name)
{
if (is<FunctionExpression>(expression)) {
auto const& function_expression = static_cast<FunctionExpression const&>(expression);
if (!function_expression.has_name()) {
TRY(function_expression.generate_bytecode_with_lhs_name(*this, move(lhs_name)));
return {};
}
}
if (is<ClassExpression>(expression)) {
auto const& class_expression = static_cast<ClassExpression const&>(expression);
if (!class_expression.has_name()) {
TRY(class_expression.generate_bytecode_with_lhs_name(*this, move(lhs_name)));
return {};
}
}
TRY(expression.generate_bytecode(*this));
return {};
}
void Generator::emit_get_by_id(IdentifierTableIndex id)
{
emit<Op::GetById>(id, m_next_property_lookup_cache++);
}
void Generator::emit_get_by_id_with_this(IdentifierTableIndex id, Register this_reg)
{
emit<Op::GetByIdWithThis>(id, this_reg, m_next_property_lookup_cache++);
}
void Generator::emit_iterator_value()
{
emit_get_by_id(intern_identifier("value"sv));
}
void Generator::emit_iterator_complete()
{
emit_get_by_id(intern_identifier("done"sv));
}
}
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