I bet a lot of the "other" will already be iterators. It may be worth adding a stat at the end, before "other", for types wheretp->tp_iter == PyObject_SelfIter. At least for that case we can specialize it and do nothing.

(I wish we could also "unwrap" list, tuple, and range iterators, similar in spirit to our method call optimization. Basically, ifGET_ITER encounters alist_iterator,range_iterator, ortuple_iterator we just put the container itself and the current index on the stack. But that's not safe to do if its refcount is greater than one, unfortunately.)