Reaching Definitions, Available Expressions
The data-flow framework (direction, transfer function, meet, boundary and initial values) and the round-robin iterative algorithm. Reaching definitions with gen and kill sets and a round-by-round fixed point on a four-block loop, used for use-definition chains and constant propagation. Available expressions with e_gen and e_kill, the intersection meet, why non-entry blocks start at the full set, and how the result drives global common-subexpression elimination. All sets come from a script.
