Method of Building A use-def (or ud) Chain
- Set definitions in statement s(0)
- For each i in, find live definitions that have use in statement s(i)
- Make a link among definitions and uses
- Set the statement s(i), as definition statement
- Kill previous definitions
With this algorithm, two things are accomplished:
- A directed acyclic graph (DAG) is created on the variable uses and definitions. The DAG specifies a data dependency among assignment statements, as well as a partial order (therefore parallelism among statements).
- When statement s(i) is reached, there is a list of live variable assignments. If only one assignment is live, for example, constant propagation might be used.
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