Optimal register coloring is NP hard, but no compiler does that; heuristics are no worse than quadratic and give near-optimal. The Mill specializer part that s

Optimal register coloring is NP hard, but no compiler does that; heuristics are no worse than quadratic and give near-optimal. The Mill specializer part that schedules ops is linear, while the part that assigns belt numbers and inserts spills is NlogN in the number of ops in an EBB because it does some sorts.