Data dependences, which relate statements that compute data values to statements that use those values, are useful for automating a variety of program-comprehension-related activities, such as reverse engineering, impact analysis, and debugging. Unfortunat

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def={x} use={}def={y} use={}def={} use={x,y}

7

def={} use={y}

1 begin M2 read x3 read y

4 if x > y then5 read x6 print x else

8 print y endif9 end M

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def={x} use={}def={} use={x}

56

8

Figure1:Sampleprogramtoillustratede nitions,uses,anddatadependences(above);control- owgraphfortheprogramannotatedwithdefandusesets(below).

CFGcanalsobebuiltatthebasic-blocklevel;insuchaCFG,eachnoderepresentsasequenceofsingle-entry,single-exit

statements.

1A