added a bitmask to the density field; slows down from 189 ms to 302.148 ms due to atomic activation - needs ld/st-aware access lowering
added a bitmask to the density field; slows down from 189 ms to 302.148 ms due to atomic activation - needs ld/st-aware access lowering

yuanming-hu/taichi,yuanming-hu/taichi,yuanming-hu/taichi,yuanming-hu/taichi