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LibJS: Add optimized GetGlobal instruction to access global variables

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Using a special instruction to access global variables allows skipping
the environment chain traversal for them and going directly to the
module/global environment. Currently, this instruction only caches the
offset for bindings that belong to the global object environment.
However, there is also an opportunity to cache the offset in the global
declarative record.

This change results in a 57% increase in speed for
imaging-gaussian-blur.js in Kraken.
This commit is contained in:
Aliaksandr Kalenik 2023-07-12 04:06:59 +02:00 • committed by Andreas Kling
parent a27c4cf63c
commit 3661d674ae
7 changed files with 95 additions and 1 deletions
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60
Userland/Libraries/LibJS/Bytecode/Op.cpp
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@ -417,6 +417,61 @@ ThrowCompletionOr<void> GetVariable::execute_impl(Bytecode::Interpreter& interpr
return {};
}
ThrowCompletionOr<void> GetGlobal::execute_impl(Bytecode::Interpreter& interpreter) const
{
auto& vm = interpreter.vm();
auto& realm = *vm.current_realm();
auto const& name = interpreter.current_executable().get_identifier(m_identifier);
auto& cache = interpreter.current_executable().global_variable_caches[m_cache_index];
auto& binding_object = realm.global_environment().object_record().binding_object();
auto& declarative_record = realm.global_environment().declarative_record();
// OPTIMIZATION: If the shape of the object hasn't changed, we can use the cached property offset.
// NOTE: Unique shapes don't change identity, so we compare their serial numbers instead.
auto& shape = binding_object.shape();
if (cache.environment_serial_number == declarative_record.environment_serial_number()
&& &shape == cache.shape
&& (!shape.is_unique() || shape.unique_shape_serial_number() == cache.unique_shape_serial_number)) {
interpreter.accumulator() = binding_object.get_direct(cache.property_offset.value());
return {};
}
cache.environment_serial_number = declarative_record.environment_serial_number();
if (vm.running_execution_context().script_or_module.has<NonnullGCPtr<Module>>()) {
// NOTE: GetGlobal is used to access variables stored in the module environment and global environment.
// The module environment is checked first since it precedes the global environment in the environment chain.
auto& module_environment = *vm.running_execution_context().script_or_module.get<NonnullGCPtr<Module>>()->environment();
if (TRY(module_environment.has_binding(name))) {
// TODO: Cache offset of binding value
interpreter.accumulator() = TRY(module_environment.get_binding_value(vm, name, vm.in_strict_mode()));
return {};
}
}
if (TRY(declarative_record.has_binding(name))) {
// TODO: Cache offset of binding value
interpreter.accumulator() = TRY(declarative_record.get_binding_value(vm, name, vm.in_strict_mode()));
return {};
}
if (TRY(binding_object.has_property(name))) {
CacheablePropertyMetadata cacheable_metadata;
interpreter.accumulator() = js_undefined();
interpreter.accumulator() = TRY(binding_object.internal_get(name, interpreter.accumulator(), &cacheable_metadata));
if (cacheable_metadata.type == CacheablePropertyMetadata::Type::OwnProperty) {
cache.shape = shape;
cache.property_offset = cacheable_metadata.property_offset.value();
cache.unique_shape_serial_number = shape.unique_shape_serial_number();
}
return {};
}
return vm.throw_completion<ReferenceError>(ErrorType::UnknownIdentifier, name);
}
ThrowCompletionOr<void> GetLocal::execute_impl(Bytecode::Interpreter& interpreter) const
{
auto& vm = interpreter.vm();
@ -1463,6 +1518,11 @@ DeprecatedString GetVariable::to_deprecated_string_impl(Bytecode::Executable con
return DeprecatedString::formatted("GetVariable {} ({})", m_identifier, executable.identifier_table->get(m_identifier));
}
DeprecatedString GetGlobal::to_deprecated_string_impl(Bytecode::Executable const& executable) const
{
return DeprecatedString::formatted("GetGlobal {} ({})", m_identifier, executable.identifier_table->get(m_identifier));
}
DeprecatedString GetLocal::to_deprecated_string_impl(Bytecode::Executable const&) const
{
return DeprecatedString::formatted("GetLocal {}", m_index);