请教下为啥下面的代码 返回两个false

package main

import "fmt"

func double(x *int) {
    *x += *x
    x = nil
}

func main() {
    var a = 3
    double(&a)
    fmt.Println(a, &a == nil) // 6 false
    fmt.Println("======================")
    p := &a
    double(p)
    fmt.Println(a, p == nil) //12 false
}