Data Flow Analysis for a Block

Computed and killed vectors for a basic block can be found as follows:

• initially, comp := ∅ and kill := ∅ .

• for each statement v := a ° b where α ← a ° b
  1. comp := comp ∪ { α }

  2. kill := kill ∪ kill_v

  3. comp := (comp - kill_v) ∪ { v }
  where kill_v is the set of all expressions involving v directly or indirectly and (comp - kill_v) is set difference.

Example: I := I + 1
This statement first computes the expression I + 1, but then it kills it because it redefines I.