[go-nuts] Why copy is much slower than append when clone a slice?

[T L]

package main

import (
    "testing"
)

const N = 1024 * 1024 // number of elements
type Element int64
var x = make([]Element, N)
var y []Element


func Benchmark_CloneWithAppend(b *testing.B) {
    for i := 0; i < b.N; i++ {
        y = append([]Element(nil), x...)
    }
}

func Benchmark_CloneWithCopy(b *testing.B) {
    b.ResetTimer()
    for i := 0; i < b.N; i++ {
        t := make([]Element, N)
        copy(t, x)
        y = t
    }
}

/*
$ go test -bench=.
Benchmark_CloneWithAppend-4           2000        738281 ns/op
Benchmark_CloneWithCopy-4             1000       1822462 ns/op
*/

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