1 files changed, 137 insertions, 0 deletions
diff --git a/src/cmd/compile/internal/test/switch_test.go b/src/cmd/compile/internal/test/switch_test.go
new file mode 100644
index 0000000..30dee62
--- /dev/null
+++ b/src/cmd/compile/internal/test/switch_test.go
@@ -0,0 +1,137 @@
+// Copyright 2021 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 test
+
+import (
+	"math/bits"
+	"testing"
+)
+
+func BenchmarkSwitch8Predictable(b *testing.B) {
+	benchmarkSwitch8(b, true)
+}
+func BenchmarkSwitch8Unpredictable(b *testing.B) {
+	benchmarkSwitch8(b, false)
+}
+func benchmarkSwitch8(b *testing.B, predictable bool) {
+	n := 0
+	rng := newRNG()
+	for i := 0; i < b.N; i++ {
+		rng = rng.next(predictable)
+		switch rng.value() & 7 {
+		case 0:
+			n += 1
+		case 1:
+			n += 2
+		case 2:
+			n += 3
+		case 3:
+			n += 4
+		case 4:
+			n += 5
+		case 5:
+			n += 6
+		case 6:
+			n += 7
+		case 7:
+			n += 8
+		}
+	}
+	sink = n
+}
+
+func BenchmarkSwitch32Predictable(b *testing.B) {
+	benchmarkSwitch32(b, true)
+}
+func BenchmarkSwitch32Unpredictable(b *testing.B) {
+	benchmarkSwitch32(b, false)
+}
+func benchmarkSwitch32(b *testing.B, predictable bool) {
+	n := 0
+	rng := newRNG()
+	for i := 0; i < b.N; i++ {
+		rng = rng.next(predictable)
+		switch rng.value() & 31 {
+		case 0, 1, 2:
+			n += 1
+		case 4, 5, 6:
+			n += 2
+		case 8, 9, 10:
+			n += 3
+		case 12, 13, 14:
+			n += 4
+		case 16, 17, 18:
+			n += 5
+		case 20, 21, 22:
+			n += 6
+		case 24, 25, 26:
+			n += 7
+		case 28, 29, 30:
+			n += 8
+		default:
+			n += 9
+		}
+	}
+	sink = n
+}
+
+func BenchmarkSwitchStringPredictable(b *testing.B) {
+	benchmarkSwitchString(b, true)
+}
+func BenchmarkSwitchStringUnpredictable(b *testing.B) {
+	benchmarkSwitchString(b, false)
+}
+func benchmarkSwitchString(b *testing.B, predictable bool) {
+	a := []string{
+		"foo",
+		"foo1",
+		"foo22",
+		"foo333",
+		"foo4444",
+		"foo55555",
+		"foo666666",
+		"foo7777777",
+	}
+	n := 0
+	rng := newRNG()
+	for i := 0; i < b.N; i++ {
+		rng = rng.next(predictable)
+		switch a[rng.value()&7] {
+		case "foo":
+			n += 1
+		case "foo1":
+			n += 2
+		case "foo22":
+			n += 3
+		case "foo333":
+			n += 4
+		case "foo4444":
+			n += 5
+		case "foo55555":
+			n += 6
+		case "foo666666":
+			n += 7
+		case "foo7777777":
+			n += 8
+		}
+	}
+	sink = n
+}
+
+// A simple random number generator used to make switches conditionally predictable.
+type rng uint64
+
+func newRNG() rng {
+	return 1
+}
+func (r rng) next(predictable bool) rng {
+	if predictable {
+		return r + 1
+	}
+	return rng(bits.RotateLeft64(uint64(r), 13) * 0x3c374d)
+}
+func (r rng) value() uint64 {
+	return uint64(r)
+}