gc: optimize interface ==, !=
If the values being compared have different concrete types,
then they're clearly unequal without needing to invoke the
actual interface compare routine. This speeds tests for
specific values, like if err == io.EOF, by about 3x.
benchmark old ns/op new ns/op delta
BenchmarkIfaceCmp100 843 287 -65.95%
BenchmarkIfaceCmpNil100 184 182 -1.09%
Fixes #2591.
R=ken2
CC=golang-dev
https://golang.org/cl/5651073
diff --git a/src/pkg/runtime/runtime_test.go b/src/pkg/runtime/runtime_test.go
new file mode 100644
index 0000000..d68b363
--- /dev/null
+++ b/src/pkg/runtime/runtime_test.go
@@ -0,0 +1,40 @@
+// 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 runtime_test
+
+import (
+ "io"
+ "testing"
+)
+
+var errf error
+
+func errfn() error {
+ return errf
+}
+
+func errfn1() error {
+ return io.EOF
+}
+
+func BenchmarkIfaceCmp100(b *testing.B) {
+ for i := 0; i < b.N; i++ {
+ for j := 0; j < 100; j++ {
+ if errfn() == io.EOF {
+ b.Fatal("bad comparison")
+ }
+ }
+ }
+}
+
+func BenchmarkIfaceCmpNil100(b *testing.B) {
+ for i := 0; i < b.N; i++ {
+ for j := 0; j < 100; j++ {
+ if errfn1() == nil {
+ b.Fatal("bad comparison")
+ }
+ }
+ }
+}
