go/parser: ~15% faster parsing

- only compute current line position if needed
  (i.e., if a comment is present)

- added benchmark

benchmark         old ns/op    new ns/op    delta
BenchmarkParse     10902990      9313330  -14.58%

benchmark          old MB/s     new MB/s  speedup
BenchmarkParse         5.31         6.22    1.17x

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/6270043

diff --git a/src/pkg/go/parser/parser.go b/src/pkg/go/parser/parser.go
index aeeda5f3d9929c42cfc8db75018e5cdd163d004f..e0c5341d4de9858d424064b499df67bb39ea3542 100644 (file)
--- a/src/pkg/go/parser/parser.go
+++ b/src/pkg/go/parser/parser.go
@@ -296,14 +296,14 @@ func (p *parser) consumeCommentGroup(n int) (comments *ast.CommentGroup, endline
 func (p *parser) next() {
        p.leadComment = nil
        p.lineComment = nil
-       line := p.file.Line(p.pos) // current line
+       prev := p.pos
        p.next0()
 
        if p.tok == token.COMMENT {
                var comment *ast.CommentGroup
                var endline int
 
-               if p.file.Line(p.pos) == line {
+               if p.file.Line(p.pos) == p.file.Line(prev) {
                        // The comment is on same line as the previous token; it
                        // cannot be a lead comment but may be a line comment.
                        comment, endline = p.consumeCommentGroup(0)

diff --git a/src/pkg/go/parser/performance_test.go b/src/pkg/go/parser/performance_test.go
new file mode 100644 (file)
index 0000000..f2732c0
--- /dev/null
+++ b/src/pkg/go/parser/performance_test.go
@@ -0,0 +1,30 @@
+// Copyright 2012 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 parser
+
+import (
+       "go/token"
+       "io/ioutil"
+       "testing"
+)
+
+var src = readFile("parser.go")
+
+func readFile(filename string) []byte {
+       data, err := ioutil.ReadFile(filename)
+       if err != nil {
+               panic(err)
+       }
+       return data
+}
+
+func BenchmarkParse(b *testing.B) {
+       b.SetBytes(int64(len(src)))
+       for i := 0; i < b.N; i++ {
+               if _, err := ParseFile(token.NewFileSet(), "", src, ParseComments); err != nil {
+                       b.Fatalf("benchmark failed due to parse error: %s", err)
+               }
+       }
+}