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LibJS: Reduce inline cache memory usage
Store bytecode property lookup caches as tiered handles instead of eagerly allocating four entries for every cache slot. Each slot starts empty, grows to one monomorphic entry after the first cacheable lookup, and promotes to the existing four-entry table when another cache key appears. Global variable caches keep one inline property entry because they usually warm up as global object property accesses. This keeps common global access allocation-free while still avoiding the inherited polymorphic cache cost. Generated asm offsets now point at the lazy property-cache storage and the inline global entry, and asm fast paths bail out for empty property cache slots.
This commit is contained in:
Andreas Kling
Andreas Kling
parent
75b2bcd7e4
commit
0a49dd1c28
Notes:
github-actions[bot]
2026-05-18 23:13:46 +00:00
Author: https://github.com/awesomekling
Commit: 0a49dd1c28
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/9479
7 changed files with 336 additions and 94 deletions
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@ -7,6 +7,7 @@
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#include <AK/BinarySearch.h>
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#include <AK/NumericLimits.h>
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#include <AK/QuickSort.h>
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#include <AK/StdLibExtras.h>
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#include <LibGC/Heap.h>
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#include <LibGC/HeapBlock.h>
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#include <LibJS/Bytecode/BasicBlock.h>
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@ -67,6 +68,152 @@ size_t InstructionStream::external_memory_size() const
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});
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}
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static_assert(alignof(PropertyLookupCache::MonomorphicData) > PropertyLookupCache::polymorphic_data_tag);
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static_assert(alignof(PropertyLookupCache::PolymorphicData) > PropertyLookupCache::polymorphic_data_tag);
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static_assert(offsetof(PropertyLookupCache::MonomorphicData, entry) == 0);
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static_assert(offsetof(PropertyLookupCache::PolymorphicData, entries) == 0);
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PropertyLookupCache::PropertyLookupCache(PropertyLookupCache&& other)
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: m_data(exchange(other.m_data, 0))
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{
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}
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PropertyLookupCache& PropertyLookupCache::operator=(PropertyLookupCache&& other)
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{
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if (this != &other) {
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clear();
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m_data = exchange(other.m_data, 0);
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}
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return *this;
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}
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PropertyLookupCache::~PropertyLookupCache()
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{
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clear();
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}
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PropertyLookupCache::MonomorphicData* PropertyLookupCache::monomorphic_data()
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{
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if (!m_data || (m_data & polymorphic_data_tag))
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return nullptr;
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return reinterpret_cast<MonomorphicData*>(m_data);
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}
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PropertyLookupCache::MonomorphicData const* PropertyLookupCache::monomorphic_data() const
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{
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if (!m_data || (m_data & polymorphic_data_tag))
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return nullptr;
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return reinterpret_cast<MonomorphicData const*>(m_data);
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}
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PropertyLookupCache::PolymorphicData* PropertyLookupCache::polymorphic_data()
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{
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if (!(m_data & polymorphic_data_tag))
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return nullptr;
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return reinterpret_cast<PolymorphicData*>(m_data & ~polymorphic_data_tag);
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}
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PropertyLookupCache::PolymorphicData const* PropertyLookupCache::polymorphic_data() const
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{
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if (!(m_data & polymorphic_data_tag))
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return nullptr;
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return reinterpret_cast<PolymorphicData const*>(m_data & ~polymorphic_data_tag);
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}
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void PropertyLookupCache::set_monomorphic_data(MonomorphicData* data)
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{
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VERIFY(data);
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VERIFY(!(reinterpret_cast<FlatPtr>(data) & polymorphic_data_tag));
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m_data = reinterpret_cast<FlatPtr>(data);
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}
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void PropertyLookupCache::set_polymorphic_data(PolymorphicData* data)
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{
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VERIFY(data);
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VERIFY(!(reinterpret_cast<FlatPtr>(data) & polymorphic_data_tag));
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m_data = reinterpret_cast<FlatPtr>(data) | polymorphic_data_tag;
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}
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PropertyLookupCache::Entry* PropertyLookupCache::first_entry()
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{
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if (auto* data = monomorphic_data())
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return &data->entry;
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if (auto* data = polymorphic_data())
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return &data->entries[0];
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return nullptr;
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}
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PropertyLookupCache::Entry const* PropertyLookupCache::first_entry() const
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{
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if (auto* data = monomorphic_data())
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return &data->entry;
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if (auto* data = polymorphic_data())
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return &data->entries[0];
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return nullptr;
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}
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Span<PropertyLookupCache::Entry> PropertyLookupCache::entries()
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{
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if (auto* data = monomorphic_data())
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return { &data->entry, 1 };
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if (auto* data = polymorphic_data())
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return data->entries.span();
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return {};
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}
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ReadonlySpan<PropertyLookupCache::Entry> PropertyLookupCache::entries() const
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{
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if (auto* data = monomorphic_data())
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return { &data->entry, 1 };
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if (auto* data = polymorphic_data())
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return data->entries.span();
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return {};
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}
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size_t PropertyLookupCache::external_memory_size() const
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{
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if (monomorphic_data())
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return sizeof(MonomorphicData);
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if (polymorphic_data())
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return sizeof(PolymorphicData);
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return 0;
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}
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void PropertyLookupCache::clear()
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{
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if (auto* data = monomorphic_data()) {
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delete data;
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m_data = 0;
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return;
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}
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if (auto* data = polymorphic_data()) {
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delete data;
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m_data = 0;
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}
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}
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bool PropertyLookupCache::entries_have_same_cache_key(Entry const& a, Entry const& b)
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{
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if (a.type == Entry::Type::Empty || b.type == Entry::Type::Empty)
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return false;
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if (a.type != b.type)
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return false;
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switch (a.type) {
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case Entry::Type::AddOwnProperty:
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return a.from_shape == b.from_shape && a.shape == b.shape;
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case Entry::Type::ChangeOwnProperty:
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case Entry::Type::GetOwnProperty:
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return a.shape == b.shape;
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case Entry::Type::ChangePropertyInPrototypeChain:
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case Entry::Type::GetPropertyInPrototypeChain:
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return a.shape == b.shape && a.prototype == b.prototype;
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case Entry::Type::Empty:
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VERIFY_NOT_REACHED();
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}
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VERIFY_NOT_REACHED();
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}
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ObjectPropertyIteratorCacheData::ObjectPropertyIteratorCacheData(VM& vm, Vector<PropertyKey> properties, ObjectPropertyIteratorFastPath fast_path, u32 indexed_property_count, bool receiver_has_magical_length_property, GC::Ref<Shape> shape, GC::Ptr<PrototypeChainValidity> prototype_chain_validity)
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: m_properties(move(properties))
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, m_shape(shape)
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@ -413,6 +560,8 @@ size_t Executable::external_memory_size() const
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{
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size_t size = bytecode.external_memory_size();
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size = saturating_add_external_memory_size(size, vector_external_memory_size(property_lookup_caches));
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for (auto const& cache : property_lookup_caches)
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size = saturating_add_external_memory_size(size, cache.external_memory_size());
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size = saturating_add_external_memory_size(size, vector_external_memory_size(global_variable_caches));
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size = saturating_add_external_memory_size(size, vector_external_memory_size(template_object_caches));
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size = saturating_add_external_memory_size(size, vector_external_memory_size(object_shape_caches));
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@ -469,7 +618,7 @@ static void clear_cache_entry_if_dead(PropertyLookupCache::Entry& entry)
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void StaticPropertyLookupCache::sweep_all()
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{
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for (auto* cache : static_property_lookup_caches()) {
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for (auto& entry : cache->entries)
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for (auto& entry : cache->entries())
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clear_cache_entry_if_dead(entry);
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}
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}
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@ -477,13 +626,11 @@ void StaticPropertyLookupCache::sweep_all()
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void Executable::remove_dead_cells(Badge<GC::Heap>)
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{
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for (auto& cache : property_lookup_caches) {
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for (auto& entry : cache.entries)
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clear_cache_entry_if_dead(entry);
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}
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for (auto& cache : global_variable_caches) {
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for (auto& entry : cache.entries)
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for (auto& entry : cache.entries())
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clear_cache_entry_if_dead(entry);
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}
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for (auto& cache : global_variable_caches)
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clear_cache_entry_if_dead(cache.entry);
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for (auto& cache : object_shape_caches) {
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auto* shape = cache.shape.ptr();
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if (shape && cell_is_dead(shape))
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