Editing Use-define chain (section)

{{short description|Data structure that tracks variable use and definitions}}
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Within [[computer science]], a '''use-definition chain''' (or '''UD chain''') is a [[data structure]] that consists of a use ''U'', of a [[Variable (programming)|variable]], and all the definitions ''D'' of that variable that can reach that use without any other intervening definitions.<ref name="kennedy"/><ref name="duct"/> A UD Chain generally means the [[Assignment (computer science)|assignment]] of some value to a variable.

A counterpart of a ''UD Chain'' is a '''definition-use chain''' (or '''DU chain'''), which consists of a definition ''D'' of a variable and all the uses ''U'' reachable from that definition without any other intervening definitions.<ref name="leiss"/>

Both UD and DU chains are created by using a form of [[static code analysis]] known as [[data flow analysis]]. Knowing the use-def and def-use chains for a program or subprogram is a prerequisite for many [[compiler optimization]]s, including [[constant propagation]] and [[common subexpression elimination]].