uninitialized_zval appears in multiple places in the PHP kernel, but I don't know what it does. For example, in the ZEND_ASSIGN_DIM_SPEC_CV_UNUSED_OP_DATA_CONST_HANDLER handler:
variable_ptr = zend_hash_next_index_insert(Z_ARRVAL_P(object_ptr), &EG(uninitialized_zval));
Why use uninitialized_zval? And when will use uninitialized_zval?