public InstrType()
 {
     this.type   = InstrTypeEnum.INTRA;
     this.callee = null;
 }
 public InstrType(InstrTypeEnum type, string callee)
 {
     this.type   = type;
     this.callee = callee;
     Debug.Assert(type == InstrTypeEnum.INTRA || callee != null);
 }