Looks like MRI dropped the #size optimization in #count in 1.9.2. Comparing the 1.8 doc to the 2.0 doc also shows this is the intended behavior (interestingly, the 1.9 doc seems to be out of date)
Update to match that behavior (also fixes #922).
Don't use #size for #count in 1.9+
Starting in 1.9, #count is always computed through enumeration
Thanks! Do you think you'll be able to look into enumerator_with_size logic too?
Absolutely. Might be a couple of weeks before I can send it, but it's definitely coming.