go/parser: add benchmarks for syntax-only parsing and object resolution

Change-Id: I73d1b2d18ab4051443d66c60df493d1163d0ba3f
Reviewed-on: https://go-review.googlesource.com/c/go/+/306150
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/go/parser/performance_test.go

@@ -10,6 +10,8 @@ import (
 	"testing"
 )
 
+// TODO(rFindley): use a testdata file or file from another package here, to
+//                 avoid a moving target.
 var src = readFile("parser.go")
 
 func readFile(filename string) []byte {
@@ -28,3 +30,27 @@ func BenchmarkParse(b *testing.B) {
 		}
 	}
 }
+
+func BenchmarkParseOnly(b *testing.B) {
+	b.SetBytes(int64(len(src)))
+	for i := 0; i < b.N; i++ {
+		if _, err := ParseFile(token.NewFileSet(), "", src, ParseComments|SkipObjectResolution); err != nil {
+			b.Fatalf("benchmark failed due to parse error: %s", err)
+		}
+	}
+}
+
+func BenchmarkResolve(b *testing.B) {
+	b.SetBytes(int64(len(src)))
+	for i := 0; i < b.N; i++ {
+		b.StopTimer()
+		fset := token.NewFileSet()
+		file, err := ParseFile(fset, "", src, SkipObjectResolution)
+		if err != nil {
+			b.Fatalf("benchmark failed due to parse error: %s", err)
+		}
+		b.StartTimer()
+		handle := fset.File(file.Package)
+		resolveFile(file, handle, nil)
+	}
+}