Data Flow Analysis for an Interval
If the expressions that are available on entry to the head of the interval are known, the values for all blocks in the interval can be computed.
For each block b whose predecessors have had their values computed,
availentry(b) = ∏x ∈ Γ^-1 b availexit(x)
availexit(b) = availentry(b) · not( kill(b) ) + comp(b)
No expressions are available on entry to the first block of a program.