Compute very busy expressions(VBEs).
That is,expressions that are evaluated along
separate paths.
Bin = the set of VBEs at the beginning of B.
Bout = the set of VBEs at the end of B.
Bgen = set of expressions X+Y such that X+Y is
evaluated before any def of X or Y.
Bkill = set of expressions X+Y such that X or Y could
be defined before X+Y is computed.
Note that gen and kill are mutually exclusive.
Compute very busy expressions(VBEs). That is,expressions that are evaluated along separate paths. Bin = the set of VBEs at the beginning of B. Bout = the set of VBEs at the end of B. Bgen = set of expressions X+Y such that X+Y is evaluated before any def of X or Y. Bkill = set of expressions X+Y such that X or Y could be defined before X+Y is computed. Note that gen and kill are mutually exclusive.