That function is a bit too low level to called from multiple places. It's always used in tandem with `rb_shape_set_too_complex` and both have to know how the object is laid out to update the `iv_ptr`. So instead we can provide two higher level function: - `rb_obj_copy_ivs_to_hash_table` to prepare a `st_table` from an arbitrary oject. - `rb_obj_convert_to_too_complex` to assign the new `st_table` to the old object, and safely free the old `iv_ptr`. Unfortunately both can't be combined into one, because `rb_obj_copy_ivar` need `rb_obj_copy_ivs_to_hash_table` to copy from one object to another.