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LibJS: Stop converting between Object <-> IteratorRecord all the time

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This patch makes IteratorRecord an Object. Although it's not exposed to
author code, this does allow us to store it in a VM register.

Now that we can store it in a VM register, we don't need to convert it
back and forth between IteratorRecord and Object when accessing it from
bytecode.

The big win here is avoiding 3 [[Get]] accesses on every iteration step
of for..of loops. There are also a bunch of smaller efficiencies gained.

20% speed-up on this microbenchmark:

    function go(a) {
        for (const p of a) {
        }
    }
    const a = [];
    a.length = 1_000_000;
    go(a);
This commit is contained in:
Andreas Kling 2023-12-07 10:44:41 +01:00
parent 4966c083df
commit 4699c81fc1
23 changed files with 226 additions and 144 deletions
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9
Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp
View file

@ -1749,16 +1749,11 @@ Bytecode::CodeGenerationErrorOr<void> YieldExpression::generate_bytecode(Bytecod
// 5. Let iterator be iteratorRecord.[[Iterator]].
auto iterator_register = generator.allocate_register();
auto iterator_identifier = generator.intern_identifier("iterator");
generator.emit_get_by_id(iterator_identifier);
generator.emit<Bytecode::Op::Store>(iterator_register);
generator.emit<Bytecode::Op::GetObjectFromIteratorRecord>(iterator_register, iterator_record_register);
// Cache iteratorRecord.[[NextMethod]] for use in step 7.a.i.
auto next_method_register = generator.allocate_register();
auto next_method_identifier = generator.intern_identifier("next");
generator.emit<Bytecode::Op::Load>(iterator_record_register);
generator.emit_get_by_id(next_method_identifier);
generator.emit<Bytecode::Op::Store>(next_method_register);
generator.emit<Bytecode::Op::GetNextMethodFromIteratorRecord>(next_method_register, iterator_record_register);
// 6. Let received be NormalCompletion(undefined).
// See get_received_completion_type_and_value above.

95
Userland/Libraries/LibJS/Bytecode/CommonImplementations.cpp
View file

@ -654,31 +654,9 @@ ThrowCompletionOr<NonnullGCPtr<Object>> super_call_with_argument_array(VM& vm, V
return result;
}
// FIXME: Since the accumulator is a Value, we store an object there and have to convert back and forth between that an Iterator records. Not great.
// Make sure to put this into the accumulator before the iterator object disappears from the stack to prevent the members from being GC'd.
Object* iterator_to_object(VM& vm, IteratorRecord iterator)
{
auto& realm = *vm.current_realm();
auto object = Object::create(realm, nullptr);
object->define_direct_property(vm.names.iterator, iterator.iterator, 0);
object->define_direct_property(vm.names.next, iterator.next_method, 0);
object->define_direct_property(vm.names.done, Value(iterator.done), 0);
return object;
}
IteratorRecord object_to_iterator(VM& vm, Object& object)
{
return IteratorRecord {
.iterator = &MUST(object.get(vm.names.iterator)).as_object(),
.next_method = MUST(object.get(vm.names.next)),
.done = MUST(object.get(vm.names.done)).as_bool()
};
}
ThrowCompletionOr<NonnullGCPtr<Array>> iterator_to_array(VM& vm, Value iterator)
{
auto iterator_object = TRY(iterator.to_object(vm));
auto iterator_record = object_to_iterator(vm, iterator_object);
auto& iterator_record = verify_cast<IteratorRecord>(iterator.as_object());
auto array = MUST(Array::create(*vm.current_realm(), 0));
size_t index = 0;
@ -832,47 +810,42 @@ ThrowCompletionOr<Object*> get_object_property_iterator(VM& vm, Value value)
properties.set(move(property_key));
}
}
IteratorRecord iterator {
.iterator = object,
.next_method = NativeFunction::create(
*vm.current_realm(),
[items = move(properties)](VM& vm) mutable -> ThrowCompletionOr<Value> {
auto& realm = *vm.current_realm();
auto iterated_object_value = vm.this_value();
if (!iterated_object_value.is_object())
return vm.throw_completion<InternalError>("Invalid state for GetObjectPropertyIterator.next"sv);
auto& iterated_object = iterated_object_value.as_object();
auto result_object = Object::create(realm, nullptr);
while (true) {
if (items.is_empty()) {
result_object->define_direct_property(vm.names.done, JS::Value(true), default_attributes);
return result_object;
}
auto key = items.take_first();
// If the property is deleted, don't include it (invariant no. 2)
if (!TRY(iterated_object.has_property(key)))
continue;
result_object->define_direct_property(vm.names.done, JS::Value(false), default_attributes);
if (key.is_number())
result_object->define_direct_property(vm.names.value, PrimitiveString::create(vm, TRY_OR_THROW_OOM(vm, String::number(key.as_number()))), default_attributes);
else if (key.is_string())
result_object->define_direct_property(vm.names.value, PrimitiveString::create(vm, key.as_string()), default_attributes);
else
VERIFY_NOT_REACHED(); // We should not have non-string/number keys.
auto& realm = *vm.current_realm();
auto callback = NativeFunction::create(
*vm.current_realm(), [items = move(properties)](VM& vm) mutable -> ThrowCompletionOr<Value> {
auto& realm = *vm.current_realm();
auto iterated_object_value = vm.this_value();
if (!iterated_object_value.is_object())
return vm.throw_completion<InternalError>("Invalid state for GetObjectPropertyIterator.next"sv);
auto& iterated_object = iterated_object_value.as_object();
auto result_object = Object::create(realm, nullptr);
while (true) {
if (items.is_empty()) {
result_object->define_direct_property(vm.names.done, JS::Value(true), default_attributes);
return result_object;
}
},
1,
vm.names.next),
.done = false,
};
return iterator_to_object(vm, move(iterator));
auto key = items.take_first();
// If the property is deleted, don't include it (invariant no. 2)
if (!TRY(iterated_object.has_property(key)))
continue;
result_object->define_direct_property(vm.names.done, JS::Value(false), default_attributes);
if (key.is_number())
result_object->define_direct_property(vm.names.value, PrimitiveString::create(vm, TRY_OR_THROW_OOM(vm, String::number(key.as_number()))), default_attributes);
else if (key.is_string())
result_object->define_direct_property(vm.names.value, PrimitiveString::create(vm, key.as_string()), default_attributes);
else
VERIFY_NOT_REACHED(); // We should not have non-string/number keys.
return result_object;
}
},
1, vm.names.next);
return vm.heap().allocate<IteratorRecord>(realm, realm, object, callback, false).ptr();
}
}

2
Userland/Libraries/LibJS/Bytecode/CommonImplementations.h
View file

@ -35,8 +35,6 @@ MarkedVector<Value> argument_list_evaluation(VM&, Value arguments);
ThrowCompletionOr<void> create_variable(VM&, DeprecatedFlyString const& name, Op::EnvironmentMode, bool is_global, bool is_immutable, bool is_strict);
ThrowCompletionOr<ECMAScriptFunctionObject*> new_class(VM&, Value super_class, ClassExpression const&, Optional<IdentifierTableIndex> const& lhs_name);
ThrowCompletionOr<NonnullGCPtr<Object>> super_call_with_argument_array(VM&, Value argument_array, bool is_synthetic);
Object* iterator_to_object(VM&, IteratorRecord);
IteratorRecord object_to_iterator(VM&, Object&);
ThrowCompletionOr<NonnullGCPtr<Array>> iterator_to_array(VM&, Value iterator);
ThrowCompletionOr<void> append(VM& vm, Value lhs, Value rhs, bool is_spread);
ThrowCompletionOr<Value> delete_by_id(Bytecode::Interpreter&, Value base, IdentifierTableIndex identifier);

2
Userland/Libraries/LibJS/Bytecode/Instruction.h
View file

@ -46,8 +46,10 @@
O(GetByValueWithThis) \
O(GetCalleeAndThisFromEnvironment) \
O(GetIterator) \
O(GetObjectFromIteratorRecord) \
O(GetMethod) \
O(GetNewTarget) \
O(GetNextMethodFromIteratorRecord) \
O(GetImportMeta) \
O(GetObjectPropertyIterator) \
O(GetPrivateById) \

36
Userland/Libraries/LibJS/Bytecode/Interpreter.cpp
View file

@ -1225,8 +1225,21 @@ ThrowCompletionOr<void> DeleteByValueWithThis::execute_impl(Bytecode::Interprete
ThrowCompletionOr<void> GetIterator::execute_impl(Bytecode::Interpreter& interpreter) const
{
auto& vm = interpreter.vm();
auto iterator = TRY(get_iterator(vm, interpreter.accumulator(), m_hint));
interpreter.accumulator() = iterator_to_object(vm, iterator);
interpreter.accumulator() = TRY(get_iterator(vm, interpreter.accumulator(), m_hint));
return {};
}
ThrowCompletionOr<void> GetObjectFromIteratorRecord::execute_impl(Bytecode::Interpreter& interpreter) const
{
auto& iterator_record = verify_cast<IteratorRecord>(interpreter.reg(m_iterator_record).as_object());
interpreter.reg(m_object) = iterator_record.iterator;
return {};
}
ThrowCompletionOr<void> GetNextMethodFromIteratorRecord::execute_impl(Bytecode::Interpreter& interpreter) const
{
auto& iterator_record = verify_cast<IteratorRecord>(interpreter.reg(m_iterator_record).as_object());
interpreter.reg(m_next_method) = iterator_record.next_method;
return {};
}
@ -1248,8 +1261,7 @@ ThrowCompletionOr<void> GetObjectPropertyIterator::execute_impl(Bytecode::Interp
ThrowCompletionOr<void> IteratorClose::execute_impl(Bytecode::Interpreter& interpreter) const
{
auto& vm = interpreter.vm();
auto iterator_object = TRY(interpreter.accumulator().to_object(vm));
auto iterator = object_to_iterator(vm, iterator_object);
auto& iterator = verify_cast<IteratorRecord>(interpreter.accumulator().as_object());
// FIXME: Return the value of the resulting completion. (Note that m_completion_value can be empty!)
TRY(iterator_close(vm, iterator, Completion { m_completion_type, m_completion_value, {} }));
@ -1259,8 +1271,7 @@ ThrowCompletionOr<void> IteratorClose::execute_impl(Bytecode::Interpreter& inter
ThrowCompletionOr<void> AsyncIteratorClose::execute_impl(Bytecode::Interpreter& interpreter) const
{
auto& vm = interpreter.vm();
auto iterator_object = TRY(interpreter.accumulator().to_object(vm));
auto iterator = object_to_iterator(vm, iterator_object);
auto& iterator = verify_cast<IteratorRecord>(interpreter.accumulator().as_object());
// FIXME: Return the value of the resulting completion. (Note that m_completion_value can be empty!)
TRY(async_iterator_close(vm, iterator, Completion { m_completion_type, m_completion_value, {} }));
@ -1270,8 +1281,7 @@ ThrowCompletionOr<void> AsyncIteratorClose::execute_impl(Bytecode::Interpreter&
ThrowCompletionOr<void> IteratorNext::execute_impl(Bytecode::Interpreter& interpreter) const
{
auto& vm = interpreter.vm();
auto iterator_object = TRY(interpreter.accumulator().to_object(vm));
auto iterator = object_to_iterator(vm, iterator_object);
auto& iterator = verify_cast<IteratorRecord>(interpreter.accumulator().as_object());
interpreter.accumulator() = TRY(iterator_next(vm, iterator));
return {};
@ -1818,4 +1828,14 @@ DeprecatedString Catch::to_deprecated_string_impl(Bytecode::Executable const&) c
return "Catch"sv;
}
DeprecatedString GetObjectFromIteratorRecord::to_deprecated_string_impl(Bytecode::Executable const&) const
{
return DeprecatedString::formatted("GetObjectFromIteratorRecord object:{} <- iterator_record:{}", m_object, m_iterator_record);
}
DeprecatedString GetNextMethodFromIteratorRecord::to_deprecated_string_impl(Bytecode::Executable const&) const
{
return DeprecatedString::formatted("GetNextMethodFromIteratorRecord next_method:{} <- iterator_record:{}", m_next_method, m_iterator_record);
}
}

41
Userland/Libraries/LibJS/Bytecode/Op.h
View file

@ -1373,6 +1373,46 @@ private:
IteratorHint m_hint { IteratorHint::Sync };
};
class GetObjectFromIteratorRecord final : public Instruction {
public:
GetObjectFromIteratorRecord(Register object, Register iterator_record)
: Instruction(Type::GetObjectFromIteratorRecord, sizeof(*this))
, m_object(object)
, m_iterator_record(iterator_record)
{
}
ThrowCompletionOr<void> execute_impl(Bytecode::Interpreter&) const;
DeprecatedString to_deprecated_string_impl(Bytecode::Executable const&) const;
Register object() const { return m_object; }
Register iterator_record() const { return m_iterator_record; }
private:
Register m_object;
Register m_iterator_record;
};
class GetNextMethodFromIteratorRecord final : public Instruction {
public:
GetNextMethodFromIteratorRecord(Register next_method, Register iterator_record)
: Instruction(Type::GetNextMethodFromIteratorRecord, sizeof(*this))
, m_next_method(next_method)
, m_iterator_record(iterator_record)
{
}
ThrowCompletionOr<void> execute_impl(Bytecode::Interpreter&) const;
DeprecatedString to_deprecated_string_impl(Bytecode::Executable const&) const;
Register next_method() const { return m_next_method; }
Register iterator_record() const { return m_iterator_record; }
private:
Register m_next_method;
Register m_iterator_record;
};
class GetMethod final : public Instruction {
public:
GetMethod(IdentifierTableIndex property)
@ -1551,7 +1591,6 @@ public:
private:
size_t m_index;
};
}
namespace JS::Bytecode {