From a2d7a2aeb1ede9c6750d7db50234dca724fa7830 Mon Sep 17 00:00:00 2001
From: Josh Bleecher Snyder <josh@tailscale.com>
Date: Mon, 17 May 2021 12:46:17 -0700
Subject: [PATCH] internal/deephash: use MapIter.Set{Key,Value}
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To get the benefit of this optimization requires help from the Go toolchain.
The changes are upstream at https://golang.org/cl/320929,
and have been pulled into the Tailscale fork at
https://github.com/tailscale/go/commit/728ecc58fd5c010c04bb7c8a56d238167e7d888f.
It also requires building with the build tag tailscale_go.

name              old time/op    new time/op    delta
Hash-8              14.0µs ± 0%    13.6µs ± 0%   -2.88%  (p=0.008 n=5+5)
HashMapAcyclic-8    24.3µs ± 1%    21.2µs ± 1%  -12.47%  (p=0.008 n=5+5)

name              old alloc/op   new alloc/op   delta
Hash-8              2.16kB ± 0%    1.58kB ± 0%  -27.01%  (p=0.008 n=5+5)
HashMapAcyclic-8    2.53kB ± 0%    0.15kB ± 0%  -93.99%  (p=0.008 n=5+5)

name              old allocs/op  new allocs/op  delta
Hash-8                77.0 ± 0%      49.0 ± 0%  -36.36%  (p=0.008 n=5+5)
HashMapAcyclic-8       202 ± 0%         4 ± 0%  -98.02%  (p=0.008 n=5+5)

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>

setkey
---
 internal/deephash/deephash.go       |  8 ++++++--
 internal/deephash/mapiter.go        | 17 +++++++++++++++++
 internal/deephash/mapiter_future.go | 19 +++++++++++++++++++
 3 files changed, 42 insertions(+), 2 deletions(-)
 create mode 100644 internal/deephash/mapiter.go
 create mode 100644 internal/deephash/mapiter_future.go

diff --git a/internal/deephash/deephash.go b/internal/deephash/deephash.go
index 8706c199f..16b89ac4e 100644
--- a/internal/deephash/deephash.go
+++ b/internal/deephash/deephash.go
@@ -240,12 +240,16 @@ func hashMapAcyclic(w *bufio.Writer, v reflect.Value, visited map[uintptr]bool)
 	defer mapHasherPool.Put(mh)
 	mh.Reset()
 	iter := v.MapRange()
+	k := reflect.New(v.Type().Key()).Elem()
+	e := reflect.New(v.Type().Elem()).Elem()
 	for iter.Next() {
+		key := iterKey(iter, k)
+		val := iterVal(iter, e)
 		mh.startEntry()
-		if !print(mh.bw, iter.Key(), visited) {
+		if !print(mh.bw, key, visited) {
 			return false
 		}
-		if !print(mh.bw, iter.Value(), visited) {
+		if !print(mh.bw, val, visited) {
 			return false
 		}
 		mh.endEntry()
diff --git a/internal/deephash/mapiter.go b/internal/deephash/mapiter.go
new file mode 100644
index 000000000..a45275dc0
--- /dev/null
+++ b/internal/deephash/mapiter.go
@@ -0,0 +1,17 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build !tailscale_go
+
+package deephash
+
+import "reflect"
+
+func iterKey(iter *reflect.MapIter, scratch reflect.Value) reflect.Value {
+	return iter.Key()
+}
+
+func iterVal(iter *reflect.MapIter, scratch reflect.Value) reflect.Value {
+	return iter.Value()
+}
diff --git a/internal/deephash/mapiter_future.go b/internal/deephash/mapiter_future.go
new file mode 100644
index 000000000..6e18dbd6a
--- /dev/null
+++ b/internal/deephash/mapiter_future.go
@@ -0,0 +1,19 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build tailscale_go
+
+package deephash
+
+import "reflect"
+
+func iterKey(iter *reflect.MapIter, scratch reflect.Value) reflect.Value {
+	iter.SetKey(scratch)
+	return scratch
+}
+
+func iterVal(iter *reflect.MapIter, scratch reflect.Value) reflect.Value {
+	iter.SetValue(scratch)
+	return scratch
+}