data flow analysis
http://cms.brookes.ac.uk/staff/HongZhu/testbookweb/ch03.html
Definition of d (of t) reaches statement u if a path of CFG edges exists from d to u that does not pass through an unambiguous definition of t.
- definition reaches statement
- path of edges exists from A to B
- path does not pass through definition of t
A definition reaches a use if value written
by definition may be read by use.
- definition and use
- written and read
