-- | Compute the predecessors of each /reachable/ block
zipPreds :: LastNode l => LGraph m l -> BlockEnv BlockSet
zipPreds g = foldl add emptyBlockEnv (postorder_dfs g)
-- | Compute the predecessors of each /reachable/ block
zipPreds :: LastNode l => LGraph m l -> BlockEnv BlockSet
zipPreds g = foldl add emptyBlockEnv (postorder_dfs g)