docs: private void initLiveOnEntrySets(OptFunctionNode fn, Node[] statementNodes)
      {
          int listLength = fn.getVarCount();
          itsUseBeforeDefSet = new BitSet(listLength);
          itsNotDefSet = new BitSet(listLength);
          itsLiveOnEntrySet = new BitSet(listLength);
          itsLiveOnExitSet = new BitSet(listLength);
          for (int i = itsStartNodeIndex; i <= itsEndNodeIndex; i++) {
              Node n = statementNodes[i];
              lookForVariableAccess(fn, n);
          }
          itsNotDefSet.flip(0, listLength);         // truth in advertising
      }