Function build_dependency_graph 

pub fn build_dependency_graph(
    reads: &[Vec<u8>],
    writes: &[Vec<u8>],
    is_barrier: &[bool],
) -> DepGraph

Build the dependency DAG from per-instruction (reads, writes, is_barrier) triples. Barriers (BAR/BSYNC/ control) force a total order across themselves: nothing moves past a barrier in either direction.