Constant STATE_MIN_SIZE 

pub const STATE_MIN_SIZE: usize = _ /* 16usize */;

The smallest state object any future may have: the tag and output slots are read and written unconditionally, for every future, including one whose async fn returns unit and has no temps at all. A state object with n MIR temps is (STATE_SLOT_TEMPS + n) * 8 bytes, which is never smaller than this.