为什么我的:search-input.sync函数被调用了两次？

<!-- 父组件 -->
<template>
  <div>
    <child-component :search-input.sync="searchValue"></child-component>
  </div>
</template>

<script>
import ChildComponent from './ChildComponent.vue';

export default {
  components: {
    ChildComponent
  },
  data() {
    return {
      searchValue: ''
    };
  }
};
</script>

<!-- 子组件 -->
<template>
  <input :value="searchInput" @input="updateSearchInput">
</template>

<script>
export default {
  props: ['searchInput'],
  methods: {
    updateSearchInput(event) {
      this.$emit('update:searchInput', event.target.value);
    }
  }
};
</script>