Editing Use-define chain (section)

==Method of building a ''use-def'' (or ''ud'') chain ==
# Set definitions in statement {{tmath|s(0)}}
# For each {{mvar|i}} in {{tmath|[1,n]}}, find live definitions that have use in statement {{tmath|s(i)}}
# Make a link among definitions and uses
# Set the statement {{tmath|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 {{tmath|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.