if (OPT_IR.SANITY_CHECK) VM.assert(_firstNode == old);
if (OPT_IR.SANITY_CHECK) VM._assert(_firstNode == old);
  void insertBeforeInCodeOrder(OPT_BasicBlock old, OPT_BasicBlock toAdd) {    if (OPT_IR.SANITY_CHECK) VM.assert(toAdd.next == null);    if (OPT_IR.SANITY_CHECK) VM.assert(toAdd.prev == null);    OPT_SpaceEffGraphNode oldPrev = old.prev;    if (oldPrev == null) {      if (OPT_IR.SANITY_CHECK) VM.assert(_firstNode == old);      _firstNode = toAdd;      toAdd.append(old);    } else {      oldPrev.append(toAdd);      toAdd.append(old);    }  }