Use-define chain

Within computer science, a use-definition chain (or UD chain) is a data structure that consists of a use U, of a variable, and all the definitions D of that variable that can reach that use without any other intervening definitions. A UD Chain generally means the 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.

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 optimizations, including constant propagation and common subexpression elimination.