A.2 Varieties of Data Dependence

The following describes three kinds of data dependence. The notation S1, S2, and SN is used to denote statement 1, statement 2, and statement N, respectively. In each example, S2 is dependent on S1 , due to variable x .

1. Data dependence from an assignment to a use of a variable is called flow dependence or true dependence.

   (S1): x = 3;
   (S2): y = x;
   

2. Data dependence from use of a variable to a later reassignment of that variable is called antidependence.

   (S1): y = x;
   (S2): x = 3;
   

3. Data dependence from an assignment of a variable to a later reassignment of that variable is called output dependence.

   (S1): x = 3;
         :
   (SN): x = 4;