n }; // init IN[n] to be empty IN[n] = emptyset; // calculate IN[n] from predecessors' OUT[p] for all nodes p in predecessors(n) IN[n] = IN[n] Union OUT[p]; oldout = OUT[n]; // save old OUT[n] // update OUT[n] using transfer function f_n () OUT[n] = GEN[n] Union (IN[n] -KILL[n]); // any change to OUT[n] compared to previous value? if (OUT[n] changed) // compare oldout vs. OUT[n] { // if yes, put all successors of n into the changed set for all nodes s in successors(n) Changed = Changed U { s }; } } See also Dead-code elimination Loop-invariant code motion Reachable uses Static single assignment form Further reading Data-flow analysis Program analysis