TN_Reaching_Value_At_Op

[Jon Hsu <jonhsu@xxxxxxxxxxxxx>]

Could someone please explain what this function is supposed to do? It
seems like it is trying to find the unique instruction that defines or
uses the value of a TN from a given position by tracing through OP lists
and BB lists. However, there are questionable lines with comments like:
            if (cur_bb == bb) continue; // ignore self successor
which seem to indicate that definitions or uses inside single block
loops are skipped. Why is this done?