Data Flow Analysis for a Block

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

• initially, comp := &empty and kill := &empty .

• for each statement v := a b where &alpha &larr a b
  1. comp := comp &cup { &alpha }

  2. kill := kill &cup kill_v

  3. comp := (comp - kill_v) &cup { 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.

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