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LibJS: Optimize reading known-to-be-initialized var bindings

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`var` bindings are never in the temporal dead zone (TDZ), and so we
know accessing them will not throw.

We now take advantage of this by having a specialized environment
binding value getter that doesn't check for exceptional cases.

1.08x speedup on JetStream.
This commit is contained in:
Andreas Kling 2025-05-04 01:41:49 +02:00 • committed by Andreas Kling
parent ad7c1e147f
commit bf1b754e91
Notes: github-actions[bot] 2025-05-04 00:32:11 +00:00
8 changed files with 90 additions and 15 deletions
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46
Libraries/LibJS/Bytecode/Interpreter.cpp
View file

@ -631,6 +631,7 @@ FLATTEN_ON_CLANG void Interpreter::run_bytecode(size_t entry_point)
HANDLE_INSTRUCTION(GetObjectPropertyIterator);
HANDLE_INSTRUCTION(GetPrivateById);
HANDLE_INSTRUCTION(GetBinding);
HANDLE_INSTRUCTION(GetInitializedBinding);
HANDLE_INSTRUCTION(GreaterThan);
HANDLE_INSTRUCTION(GreaterThanEquals);
HANDLE_INSTRUCTION(HasPrivateId);
@ -2239,29 +2240,51 @@ ThrowCompletionOr<void> ConcatString::execute_impl(Bytecode::Interpreter& interp
return {};
}
ThrowCompletionOr<void> GetBinding::execute_impl(Bytecode::Interpreter& interpreter) const
enum class BindingIsKnownToBeInitialized {
No,
Yes,
};
template<BindingIsKnownToBeInitialized binding_is_known_to_be_initialized>
static ThrowCompletionOr<void> get_binding(Interpreter& interpreter, Operand dst, IdentifierTableIndex identifier, EnvironmentCoordinate& cache)
{
auto& vm = interpreter.vm();
auto& executable = interpreter.current_executable();
if (m_cache.is_valid()) {
if (cache.is_valid()) {
auto const* environment = interpreter.running_execution_context().lexical_environment.ptr();
for (size_t i = 0; i < m_cache.hops; ++i)
for (size_t i = 0; i < cache.hops; ++i)
environment = environment->outer_environment();
if (!environment->is_permanently_screwed_by_eval()) {
interpreter.set(dst(), TRY(static_cast<DeclarativeEnvironment const&>(*environment).get_binding_value_direct(vm, m_cache.index)));
Value value;
if constexpr (binding_is_known_to_be_initialized == BindingIsKnownToBeInitialized::No) {
value = TRY(static_cast<DeclarativeEnvironment const&>(*environment).get_binding_value_direct(vm, cache.index));
} else {
value = static_cast<DeclarativeEnvironment const&>(*environment).get_initialized_binding_value_direct(cache.index);
}
interpreter.set(dst, value);
return {};
}
m_cache = {};
cache = {};
}
auto reference = TRY(vm.resolve_binding(executable.get_identifier(m_identifier)));
auto reference = TRY(vm.resolve_binding(executable.get_identifier(identifier)));
if (reference.environment_coordinate().has_value())
m_cache = reference.environment_coordinate().value();
interpreter.set(dst(), TRY(reference.get_value(vm)));
cache = reference.environment_coordinate().value();
interpreter.set(dst, TRY(reference.get_value(vm)));
return {};
}
ThrowCompletionOr<void> GetBinding::execute_impl(Bytecode::Interpreter& interpreter) const
{
return get_binding<BindingIsKnownToBeInitialized::No>(interpreter, m_dst, m_identifier, m_cache);
}
ThrowCompletionOr<void> GetInitializedBinding::execute_impl(Bytecode::Interpreter& interpreter) const
{
return get_binding<BindingIsKnownToBeInitialized::Yes>(interpreter, m_dst, m_identifier, m_cache);
}
ThrowCompletionOr<void> GetCalleeAndThisFromEnvironment::execute_impl(Bytecode::Interpreter& interpreter) const
{
auto callee_and_this = TRY(get_callee_and_this_from_environment(
@ -3285,6 +3308,13 @@ ByteString GetBinding::to_byte_string_impl(Bytecode::Executable const& executabl
executable.identifier_table->get(m_identifier));
}
ByteString GetInitializedBinding::to_byte_string_impl(Bytecode::Executable const& executable) const
{
return ByteString::formatted("GetInitializedBinding {}, {}",
format_operand("dst"sv, dst(), executable),
executable.identifier_table->get(m_identifier));
}
ByteString GetGlobal::to_byte_string_impl(Bytecode::Executable const& executable) const
{
return ByteString::formatted("GetGlobal {}, {}", format_operand("dst"sv, dst(), executable),