go/format: add simple benchmark framework and basic benchmark

For now, this CL adds as a first benchmark the formatting of
a 10,000 element array literal. It is easy to add additional
test cases as we see fit.

	name                   time/op
	Format/array1-10000-4    26.7ms ± 7%

	name                   speed
	Format/array1-10000-4  2.43MB/s ± 6%

	name                   alloc/op
	Format/array1-10000-4    5.52MB ± 0%

	name                   allocs/op
	Format/array1-10000-4      119k ± 0%

Updates #26528.

Change-Id: Ic8ec8f70160d122b877740412d4d4406f5f4b345
Reviewed-on: https://go-review.googlesource.com/c/153642
Reviewed-by: Ian Lance Taylor <iant@golang.org>

diff --git a/src/go/format/benchmark_test.go b/src/go/format/benchmark_test.go
new file mode 100644 (file)
index 0000000..7bd45c0
--- /dev/null
+++ b/src/go/format/benchmark_test.go
@@ -0,0 +1,91 @@
+// Copyright 2018 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.
+
+// This file provides a simple framework to add benchmarks
+// based on generated input (source) files.
+
+package format_test
+
+import (
+       "bytes"
+       "flag"
+       "fmt"
+       "go/format"
+       "io/ioutil"
+       "testing"
+)
+
+var debug = flag.Bool("debug", false, "write .src files containing formatting input; for debugging")
+
+// array1 generates an array literal with n elements of the form:
+//
+// var _ = [...]byte{
+//     // 0
+//     0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
+//     0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
+//     0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
+//     0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
+//     0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
+//     // 40
+//     0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f,
+//     0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37,
+//     ...
+//
+func array1(buf *bytes.Buffer, n int) {
+       buf.WriteString("var _ = [...]byte{\n")
+       for i := 0; i < n; {
+               if i%10 == 0 {
+                       fmt.Fprintf(buf, "\t// %d\n", i)
+               }
+               buf.WriteByte('\t')
+               for j := 0; j < 8; j++ {
+                       fmt.Fprintf(buf, "0x%02x, ", byte(i))
+                       i++
+               }
+               buf.WriteString("\n")
+       }
+       buf.WriteString("}\n")
+}
+
+var tests = []struct {
+       name string
+       gen  func(*bytes.Buffer, int)
+       n    int
+}{
+       {"array1", array1, 10000},
+       // add new test cases here as needed
+}
+
+func BenchmarkFormat(b *testing.B) {
+       var src bytes.Buffer
+       for _, t := range tests {
+               src.Reset()
+               src.WriteString("package p\n")
+               t.gen(&src, t.n)
+               data := src.Bytes()
+
+               if *debug {
+                       filename := t.name + ".src"
+                       err := ioutil.WriteFile(filename, data, 0660)
+                       if err != nil {
+                               b.Fatalf("couldn't write %s: %v", filename, err)
+                       }
+               }
+
+               b.Run(fmt.Sprintf("%s-%d", t.name, t.n), func(b *testing.B) {
+                       b.SetBytes(int64(len(data)))
+                       b.ReportAllocs()
+                       b.ResetTimer()
+                       for i := 0; i < b.N; i++ {
+                               var err error
+                               sink, err = format.Source(data)
+                               if err != nil {
+                                       b.Fatal(err)
+                               }
+                       }
+               })
+       }
+}
+
+var sink []byte