Function phases 

pub fn phases(sections: &[SpatialProgram]) -> (Vec<usize>, Vec<bool>)

★ THE CHIPS RUN AT ONCE. The source writes chip 0’s slice of an op, then chip 1’s; composed in that order with a barrier after each, chip 1 would wait out chip 0’s whole slice. Two sections may share a PHASE — run with no barrier between them — when they are on disjoint chips and neither touches what the other writes. See phase_order.