runtime: use unaligned loads on ppc64

benchmark                      old ns/op     new ns/op     delta
BenchmarkAlignedLoad-160       8.67          7.42          -14.42%
BenchmarkUnalignedLoad-160     8.63          7.37          -14.60%

Change-Id: Id4609d7b4038c4d2ec332efc4fe6f1adfb61b82b
Reviewed-on: https://go-review.googlesource.com/20812
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

1 files changed, 22 insertions, 0 deletions

diff --git a/src/runtime/hash_test.go b/src/runtime/hash_test.go
index 7cceab86cc..0022fd39a5 100644
--- a/src/runtime/hash_test.go
+++ b/src/runtime/hash_test.go
@@ -11,6 +11,7 @@ import (
 	. "runtime"
 	"strings"
 	"testing"
+	"unsafe"
 )
 
 // Smhasher is a torture test for hash functions.
@@ -658,3 +659,24 @@ func TestStructHash(t *testing.T) {
 		t.Errorf("too many allocs %f - hash not balanced", n)
 	}
 }
+
+var sink uint64
+
+func BenchmarkAlignedLoad(b *testing.B) {
+	var buf [16]byte
+	p := unsafe.Pointer(&buf[0])
+	var s uint64
+	for i := 0; i < b.N; i++ {
+		s += ReadUnaligned64(p)
+	}
+	sink = s
+}
+func BenchmarkUnalignedLoad(b *testing.B) {
+	var buf [16]byte
+	p := unsafe.Pointer(&buf[1])
+	var s uint64
+	for i := 0; i < b.N; i++ {
+		s += ReadUnaligned64(p)
+	}
+	sink = s
+}