code: private boolean isFirstUse(int reg) {
          LocalVariableTable lvt = getMethod().getLocalVariableTable();
          if (lvt == null) {
              return true;
          }
  
          LocalVariable lv = lvt.getLocalVariable(reg, getPC());
          return lv == null;
      }
docs: looks to see if this register has already in scope or whether is a new assignment. return true if it's a new assignment. If you can't tell, return true
  anyway. might want to change.
  
  @param reg
  the store register
  @return whether this is a new register scope assignment