code: func (enh *EvalNodeHelper) dropMetricName(l labels.Labels) labels.Labels {
  	if enh.dmn == nil {
  		enh.dmn = make(map[uint64]labels.Labels, len(enh.out))
  	}
  	h := l.Hash()
  	ret, ok := enh.dmn[h]
  	if ok {
  		return ret
  	}
  	ret = dropMetricName(l)
  	enh.dmn[h] = ret
  	return ret
  }
docs: // dropMetricName is a cached version of dropMetricName.