extern(C++) void flowlv();
Do live variable analysis (LVs). A variable is 'live' at some point if there is a subsequent use of it before a redefinition. Binlv = the set of variables live at the beginning of B. Boutlv = the set of variables live at the end of B. Bgen = set of variables used before any definition in B. Bkill = set of variables unambiguously defined before any use in B. Note that Bgen & Bkill = 0.