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LibJS: Avoid redundant GC::Weak checks in hot inline cache code paths

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By copying out pointees to a temporary, we can avoid some redundant
pointer chasing inside GC::Weak when hitting our inline caches.
This commit is contained in:
Andreas Kling 2025-10-16 11:17:39 +02:00 • committed by Andreas Kling
parent dfa796a4e4
commit 7ee8645b9c
Notes: github-actions[bot] 2025-10-17 15:25:02 +00:00
2 changed files with 18 additions and 12 deletions
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20
Libraries/LibJS/Bytecode/Interpreter.cpp
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@ -1133,20 +1133,22 @@ ThrowCompletionOr<void> put_by_property_key(VM& vm, Value base, Value this_value
case PropertyLookupCache::Entry::Type::Empty:
break;
case PropertyLookupCache::Entry::Type::ChangePropertyInPrototypeChain: {
if (!cache.prototype) [[unlikely]]
auto cached_prototype = cache.prototype.ptr();
if (!cached_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) [[unlikely]]
return false;
if (!cache.prototype_chain_validity) [[unlikely]]
auto cached_prototype_chain_validity = cache.prototype_chain_validity.ptr();
if (!cached_prototype_chain_validity) [[unlikely]]
return false;
if (!cache.prototype_chain_validity->is_valid()) [[unlikely]]
if (!cached_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 (can_use_cache) [[likely]] {
auto value_in_prototype = cached_prototype->get_direct(cache.property_offset.value());
if (value_in_prototype.is_accessor()) [[unlikely]] {
(void)TRY(call(vm, value_in_prototype.as_accessor().setter(), this_value, value));
return {};
@ -1170,12 +1172,14 @@ ThrowCompletionOr<void> put_by_property_key(VM& vm, Value base, Value this_value
// reuse the resulting shape from the cache.
if (cache.from_shape != &object->shape()) [[unlikely]]
break;
if (!cache.shape) [[unlikely]]
auto cached_shape = cache.shape.ptr();
if (!cached_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()) [[unlikely]]
auto cached_prototype_chain_validity = cache.prototype_chain_validity.ptr();
if (cached_prototype_chain_validity && !cached_prototype_chain_validity->is_valid()) [[unlikely]]
break;
object->unsafe_set_shape(*cache.shape);
object->unsafe_set_shape(*cached_shape);
object->put_direct(*cache.property_offset, value);
return {};
}