Use special flag (HASH_FLAG_INITIALIZED) instead of (nTableMask == 0) to indicate that HashTable is allocated.
Make nTableMask to be 0 for packed arrays.
Remove checks fo HASH_FLAG_PACKED in zend_hash_find/zend_hash_del and family (string keys are resolved through uninitialized_bucket).
Change HashTable layout for better locality.
Introduce specialized functions to compare with integer and string, to eliminate repeatable checks on each loop iteration in in_array() function.