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
.
- Data dependence from an assignment to a use of a variable
is called flow dependence or true dependence. For example:
(S1): x = 3;
(S2): y = x;
- Data dependence from use of a variable to a later
reassignment of that variable is called antidependence. For
example:
(S1): y = x;
(S2): x = 3;
- Data dependence from an assignment of a variable to a
later reassignment of that variable is called output dependence.
For example:
(S1): x = 3;
:
(SN): x = 4;
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Command-Line Qualifiers
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