Using tooling from bug 186698, loading can and running "notifyutil -p com.apple.WebKit.dumpHashTableCapacity" shows: Wasted capacity: 1 998 144 bytes (used 904640 of 2902784 bytes, utilization: 31.16%) - 8209 allocations 1 0x116495945 WTF::HashTable<WTF::RefPtr<WTF::UniquedStringImpl, WTF::DumbPtrTraits<WTF::UniquedStringImpl> >, WTF::KeyValuePair<WTF::RefPtr<WTF::UniquedStringImpl, WTF::DumbPtrTraits<WTF::UniquedStringImpl> >, JSC::WriteBarrier<JSC::InferredType, WTF::DumbPtrTraits<JSC::InferredType> > >, WTF::KeyValuePairKeyExtractor<WTF::KeyValuePair<WTF::RefPtr<WTF::UniquedStringImpl, WTF::DumbPtrTraits<WTF::UniquedStringImpl> >, JSC::WriteBarrier<JSC::InferredType, WTF::DumbPtrTraits<JSC::InferredType> > > >, JSC::IdentifierRepHash, WTF::HashMap<WTF::RefPtr<WTF::UniquedStringImpl, WTF::DumbPtrTraits<WTF::UniquedStringImpl> >, JSC::WriteBarrier<JSC::InferredType, WTF::DumbPtrTraits<JSC::InferredType> >, JSC::IdentifierRepHash, WTF::HashTraits<WTF::RefPtr<WTF::UniquedStringImpl, WTF::DumbPtrTraits<WTF::UniquedStringImpl> > >, WTF::HashTraits<JSC::WriteBarrier<JSC::InferredType, WTF::DumbPtrTraits<JSC::InferredType> > > >::KeyValuePairTraits, WTF::HashTraits<WTF::RefPtr<WTF::UniquedStringImpl, WTF::DumbPtrTraits<WTF::UniquedStringImpl> > > >::HashTable() 2 0x116495925 WTF::HashMap<WTF::RefPtr<WTF::UniquedStringImpl, WTF::DumbPtrTraits<WTF::UniquedStringImpl> >, JSC::WriteBarrier<JSC::InferredType, WTF::DumbPtrTraits<JSC::InferredType> >, JSC::IdentifierRepHash, WTF::HashTraits<WTF::RefPtr<WTF::UniquedStringImpl, WTF::DumbPtrTraits<WTF::UniquedStringImpl> > >, WTF::HashTraits<JSC::WriteBarrier<JSC::InferredType, WTF::DumbPtrTraits<JSC::InferredType> > > >::HashMap() 3 0x116489b15 WTF::HashMap<WTF::RefPtr<WTF::UniquedStringImpl, WTF::DumbPtrTraits<WTF::UniquedStringImpl> >, JSC::WriteBarrier<JSC::InferredType, WTF::DumbPtrTraits<JSC::InferredType> >, JSC::IdentifierRepHash, WTF::HashTraits<WTF::RefPtr<WTF::UniquedStringImpl, WTF::DumbPtrTraits<WTF::UniquedStringImpl> > >, WTF::HashTraits<JSC::WriteBarrier<JSC::InferredType, WTF::DumbPtrTraits<JSC::InferredType> > > >::HashMap() 4 0x116489aea JSC::InferredTypeTable::InferredTypeTable(JSC::VM&) 5 0x11648894d JSC::InferredTypeTable::InferredTypeTable(JSC::VM&) 6 0x1164888d1 JSC::InferredTypeTable::create(JSC::VM&) 7 0x116675e46 JSC::Structure::willStoreValueSlow(JSC::VM&, JSC::PropertyName, JSC::JSValue, bool, JSC::InferredTypeTable::StoredPropertyAge) 8 0x11536b938 JSC::Structure::willStoreValueForNewTransition(JSC::VM&, JSC::PropertyName, JSC::JSValue, bool)
<rdar://problem/41189073>
InferredTypeTable is now removed :)