reflect: add a copy of BenchmarkMap

This is a copy of reflect_test.BenchmakMap from the Go standard library,
added in http://golang.org/cl/345486.

This is added to x/benchmarks only temporarily as a sample 'go test'
benchmark to use with benchmarking tools. This benchmark was selected in
particular because it had a significant performance improvement with a
recent upstream change (http://golang.org/cl/345486).

Change-Id: I2bff47ffbaab1d471a37ec3cba4bea88cc78d8ed
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/353649
Trust: Michael Pratt <mpratt@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>

reflect/reflect_test.go

diff --git a/reflect/reflect_test.go b/reflect/reflect_test.go
new file mode 100644
index 0000000..f02be3e
--- /dev/null
+++ b/reflect/reflect_test.go
@@ -0,0 +1,60 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package reflect_test
+
+import (
+	"fmt"
+	"reflect"
+	"testing"
+)
+
+// BenchmarkMap is a copy of reflect_test.BenchmarkMap from the Go standard
+// library, placed here for basic benchmarking testing.
+func BenchmarkMap(b *testing.B) {
+	type V *int
+	value := reflect.ValueOf((V)(nil))
+	stringKeys := []string{}
+	mapOfStrings := map[string]V{}
+	uint64Keys := []uint64{}
+	mapOfUint64s := map[uint64]V{}
+	for i := 0; i < 100; i++ {
+		stringKey := fmt.Sprintf("key%d", i)
+		stringKeys = append(stringKeys, stringKey)
+		mapOfStrings[stringKey] = nil
+
+		uint64Key := uint64(i)
+		uint64Keys = append(uint64Keys, uint64Key)
+		mapOfUint64s[uint64Key] = nil
+	}
+
+	tests := []struct {
+		label          string
+		m, keys, value reflect.Value
+	}{
+		{"StringKeys", reflect.ValueOf(mapOfStrings), reflect.ValueOf(stringKeys), value},
+		{"Uint64Keys", reflect.ValueOf(mapOfUint64s), reflect.ValueOf(uint64Keys), value},
+	}
+
+	for _, tt := range tests {
+		b.Run(tt.label, func(b *testing.B) {
+			b.Run("MapIndex", func(b *testing.B) {
+				b.ReportAllocs()
+				for i := 0; i < b.N; i++ {
+					for j := tt.keys.Len() - 1; j >= 0; j-- {
+						tt.m.MapIndex(tt.keys.Index(j))
+					}
+				}
+			})
+			b.Run("SetMapIndex", func(b *testing.B) {
+				b.ReportAllocs()
+				for i := 0; i < b.N; i++ {
+					for j := tt.keys.Len() - 1; j >= 0; j-- {
+						tt.m.SetMapIndex(tt.keys.Index(j), tt.value)
+					}
+				}
+			})
+		})
+	}
+}