net: use bytes.Equal instead of bytesEqual

bytes.Equal is written in assembly and is slightly faster than the
current Go bytesEqual from the net package.

benchcmp:
benchmark                 old ns/op     new ns/op     delta
BenchmarkIPCompare4-8     7.74          7.01          -9.43%
BenchmarkIPCompare6-8     8.47          6.86          -19.01%

Change-Id: I2a7ad35867489b46f0943aef5776a2fe1b46e2df
Reviewed-on: https://go-review.googlesource.com/36850
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/ip.go

@@ -12,6 +12,8 @@
 
 package net
 
+import _ "unsafe" // for go:linkname
+
 // IP address lengths (bytes).
 const (
 	IPv4len = 4
@@ -381,17 +383,9 @@ func (ip IP) Equal(x IP) bool {
 	return false
 }
 
-func bytesEqual(x, y []byte) bool {
-	if len(x) != len(y) {
-		return false
-	}
-	for i, b := range x {
-		if y[i] != b {
-			return false
-		}
-	}
-	return true
-}
+// bytes.Equal is implemented in runtime/asm_$goarch.s
+//go:linkname bytesEqual bytes.Equal
+func bytesEqual(x, y []byte) bool
 
 func (ip IP) matchAddrFamily(x IP) bool {
 	return ip.To4() != nil && x.To4() != nil || ip.To16() != nil && ip.To4() == nil && x.To16() != nil && x.To4() == nil

src/net/ip_test.go

@@ -6,6 +6,7 @@ package net
 
 import (
 	"bytes"
+	"math/rand"
 	"reflect"
 	"runtime"
 	"testing"
@@ -645,3 +646,32 @@ func TestIPAddrScope(t *testing.T) {
 		}
 	}
 }
+
+func BenchmarkIPEqual(b *testing.B) {
+	b.Run("IPv4", func(b *testing.B) {
+		benchmarkIPEqual(b, IPv4len)
+	})
+	b.Run("IPv6", func(b *testing.B) {
+		benchmarkIPEqual(b, IPv6len)
+	})
+}
+
+func benchmarkIPEqual(b *testing.B, size int) {
+	ips := make([]IP, 1000)
+	for i := range ips {
+		ips[i] = make(IP, size)
+		rand.Read(ips[i])
+	}
+	// Half of the N are equal.
+	for i := 0; i < b.N/2; i++ {
+		x := ips[i%len(ips)]
+		y := ips[i%len(ips)]
+		x.Equal(y)
+	}
+	// The other half are not equal.
+	for i := 0; i < b.N/2; i++ {
+		x := ips[i%len(ips)]
+		y := ips[(i+1)%len(ips)]
+		x.Equal(y)
+	}
+}