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LibJS: Sprinkle [[unlikely]] on the PutBy* cache miss code paths

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These caches are gonna be hitting most of the time, so let's give the
compiler a hint about this.

1.01x speed-up on MicroBench/pic-add-own.js
This commit is contained in:
Andreas Kling 2025-10-10 12:16:15 +02:00 • committed by Andreas Kling
commit 7462c10ee2
Notes: github-actions[bot] 2025-10-11 18:10:06 +00:00
1 changed files with 14 additions and 14 deletions
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28
Libraries/LibJS/Bytecode/Interpreter.cpp
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@ -1202,12 +1202,12 @@ template<PutKind kind>
ThrowCompletionOr<void> put_by_property_key(VM& vm, Value base, Value this_value, Value value, Optional<Utf16FlyString const&> const& base_identifier, PropertyKey name, PropertyLookupCache* caches = nullptr)
{
// Better error message than to_object would give
if (vm.in_strict_mode() && base.is_nullish())
if (vm.in_strict_mode() && base.is_nullish()) [[unlikely]]
return vm.throw_completion<TypeError>(ErrorType::ReferenceNullishSetProperty, name, base.to_string_without_side_effects());
// a. Let baseObj be ? ToObject(V.[[Base]]).
auto maybe_object = base.to_object(vm);
if (maybe_object.is_error())
if (maybe_object.is_error()) [[unlikely]]
return throw_null_or_undefined_property_access(vm, base, base_identifier, name);
auto object = maybe_object.release_value();
@ -1233,27 +1233,27 @@ ThrowCompletionOr<void> put_by_property_key(VM& vm, Value base, Value this_value
case PutKind::Normal: {
auto this_value_object = MUST(this_value.to_object(vm));
auto& from_shape = this_value_object->shape();
if (caches) {
if (caches) [[likely]] {
for (auto& cache : caches->entries) {
switch (cache.type) {
case PropertyLookupCache::Entry::Type::Empty:
break;
case PropertyLookupCache::Entry::Type::ChangePropertyInPrototypeChain: {
if (!cache.prototype)
if (!cache.prototype) [[unlikely]]
break;
// OPTIMIZATION: If the prototype chain hasn't been mutated in a way that would invalidate the cache, we can use it.
bool can_use_cache = [&]() -> bool {
if (&object->shape() != cache.shape)
if (&object->shape() != cache.shape) [[unlikely]]
return false;
if (!cache.prototype_chain_validity)
if (!cache.prototype_chain_validity) [[unlikely]]
return false;
if (!cache.prototype_chain_validity->is_valid())
if (!cache.prototype_chain_validity->is_valid()) [[unlikely]]
return false;
return true;
}();
if (can_use_cache) {
auto value_in_prototype = cache.prototype->get_direct(cache.property_offset.value());
if (value_in_prototype.is_accessor()) {
if (value_in_prototype.is_accessor()) [[unlikely]] {
(void)TRY(call(vm, value_in_prototype.as_accessor().setter(), this_value, value));
return {};
}
@ -1261,10 +1261,10 @@ ThrowCompletionOr<void> put_by_property_key(VM& vm, Value base, Value this_value
break;
}
case PropertyLookupCache::Entry::Type::ChangeOwnProperty: {
if (cache.shape != &object->shape())
if (cache.shape != &object->shape()) [[unlikely]]
break;
auto value_in_object = object->get_direct(cache.property_offset.value());
if (value_in_object.is_accessor()) {
if (value_in_object.is_accessor()) [[unlikely]] {
(void)TRY(call(vm, value_in_object.as_accessor().setter(), this_value, value));
} else {
object->put_direct(*cache.property_offset, value);
@ -1274,12 +1274,12 @@ ThrowCompletionOr<void> put_by_property_key(VM& vm, Value base, Value this_value
case PropertyLookupCache::Entry::Type::AddOwnProperty: {
// OPTIMIZATION: If the object's shape is the same as the one cached before adding the new property, we can
// reuse the resulting shape from the cache.
if (cache.from_shape != &object->shape())
if (cache.from_shape != &object->shape()) [[unlikely]]
break;
if (!cache.shape)
if (!cache.shape) [[unlikely]]
break;
// The cache is invalid if the prototype chain has been mutated, since such a mutation could have added a setter for the property.
if (cache.prototype_chain_validity && !cache.prototype_chain_validity->is_valid())
if (cache.prototype_chain_validity && !cache.prototype_chain_validity->is_valid()) [[unlikely]]
break;
object->unsafe_set_shape(*cache.shape);
object->put_direct(*cache.property_offset, value);
@ -1353,7 +1353,7 @@ ThrowCompletionOr<void> put_by_property_key(VM& vm, Value base, Value this_value
object->define_direct_property(name, value, Attribute::Enumerable | Attribute::Writable | Attribute::Configurable);
break;
case PutKind::Prototype:
if (value.is_object() || value.is_null())
if (value.is_object() || value.is_null()) [[likely]]
MUST(object->internal_set_prototype_of(value.is_object() ? &value.as_object() : nullptr));
break;
}