Equations for Live Variable Analysis

Algorithm for Computing Live Variables

Data Structures for Live Variables

This time, we once again want the smallest solution -- we don't say a variable is live unless we actually find a path along which it is used before being redefined.

Thus, we start by assuming nothing is live on exit from any block. The process stops because we are only adding variables to the sets (and there are a finite number of variables).

Algorithm

Live Variable analysis

 FOR all blocks B DO
   IN(B) = Gen(B)
 ENDFOR
 WHILE there aer changes DO
   FOR each block B DO
     Out(B) =  In(S)
         S  Succ(B)
     In(B) = (Out(B) - Kill(B))  Gen(B)
   ENDFOR
 ENDWHILE
 

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