net/netip: reduce allocations in Addr.String for v4-in-v6 addresses

ip.Unmap will always return an Addr with ip.z == z4 in case of an
v4-in-v6 address. Thus, Addr.string4 can be called directly without the
additional indirection.

name                      old time/op    new time/op    delta
IPString/v6_v4-4             108ns ± 3%      74ns ± 4%  -31.23%  (p=0.000 n=9+10)
IPStringExpanded/v6_v4-4    89.6ns ± 6%    77.2ns ± 3%  -13.91%  (p=0.000 n=10+10)
AddrPortString/v6_v4-4       253ns ± 8%     197ns ± 3%  -22.13%  (p=0.000 n=10+10)

name                      old alloc/op   new alloc/op   delta
IPString/v6_v4-4             40.0B ± 0%     24.0B ± 0%  -40.00%  (p=0.000 n=10+10)
IPStringExpanded/v6_v4-4     48.0B ± 0%     48.0B ± 0%     ~     (all equal)
AddrPortString/v6_v4-4       77.0B ± 0%     61.0B ± 0%  -20.78%  (p=0.000 n=10+10)

name                      old allocs/op  new allocs/op  delta
IPString/v6_v4-4              2.00 ± 0%      1.00 ± 0%  -50.00%  (p=0.000 n=10+10)
IPStringExpanded/v6_v4-4      1.00 ± 0%      1.00 ± 0%     ~     (all equal)
AddrPortString/v6_v4-4        4.00 ± 0%      3.00 ± 0%  -25.00%  (p=0.000 n=10+10)

Change-Id: Id4affaf7a493aa11579c48721294f2e5889a8bef
Reviewed-on: https://go-review.googlesource.com/c/go/+/403914
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
Auto-Submit: Tobias Klauser <tobias.klauser@gmail.com>

diff --git a/src/net/netip/netip.go b/src/net/netip/netip.go
index 2c21715af1098b147312e00bd33d11a14ad34500..5bbab951c5ce12c2f8d1cb8cc890969774ea4d03 100644 (file)
--- a/src/net/netip/netip.go
+++ b/src/net/netip/netip.go
@@ -768,11 +768,10 @@ func (ip Addr) String() string {
                return ip.string4()
        default:
                if ip.Is4In6() {
-                       // TODO(bradfitz): this could alloc less.
                        if z := ip.Zone(); z != "" {
-                               return "::ffff:" + ip.Unmap().String() + "%" + z
+                               return "::ffff:" + ip.Unmap().string4() + "%" + z
                        } else {
-                               return "::ffff:" + ip.Unmap().String()
+                               return "::ffff:" + ip.Unmap().string4()
                        }
                }
                return ip.string6()

diff --git a/src/net/netip/netip_test.go b/src/net/netip/netip_test.go
index 35f7cd69e11df01a6ecf0cbed38264f2632573fe..9fe7cae6ec6624beb6d01aac8cfdd6ffee6b3264 100644 (file)
--- a/src/net/netip/netip_test.go
+++ b/src/net/netip/netip_test.go
@@ -1894,6 +1894,31 @@ func TestNoAllocs(t *testing.T) {
        test("IPPRefix.Masked", func() { sinkPrefix = MustParsePrefix("1.2.3.4/16").Masked() })
 }
 
+func TestAddrStringAllocs(t *testing.T) {
+       tests := []struct {
+               name       string
+               ip         Addr
+               wantAllocs int
+       }{
+               {"zero", Addr{}, 0},
+               {"ipv4", MustParseAddr("192.168.1.1"), 1},
+               {"ipv6", MustParseAddr("2001:db8::1"), 1},
+               {"ipv6+zone", MustParseAddr("2001:db8::1%eth0"), 1},
+               {"ipv4-in-ipv6", MustParseAddr("::ffff:192.168.1.1"), 1},
+               {"ipv4-in-ipv6+zone", MustParseAddr("::ffff:192.168.1.1%eth0"), 1},
+       }
+       for _, tc := range tests {
+               t.Run(tc.name, func(t *testing.T) {
+                       allocs := int(testing.AllocsPerRun(1000, func() {
+                               sinkString = tc.ip.String()
+                       }))
+                       if allocs != tc.wantAllocs {
+                               t.Errorf("allocs=%d, want %d", allocs, tc.wantAllocs)
+                       }
+               })
+       }
+}
+
 func TestPrefixString(t *testing.T) {
        tests := []struct {
                ipp  Prefix