runtime: exclude allocation(s) from memmove/memclr benchmarking

The overhead for allocation is not significant but it should be excluded
from the memmove/memclr benchmarking anyway.

Change-Id: I7ea86d1b85b13352ccbff16f7510caa250654dab
Reviewed-on: https://go-review.googlesource.com/c/go/+/645576
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>

Author: Dmitrii Martynov

src/runtime/memmove_test.go

@@ -292,6 +292,7 @@ func BenchmarkMemmove(b *testing.B) {
 	benchmarkSizes(b, bufSizes, func(b *testing.B, n int) {
 		x := make([]byte, n)
 		y := make([]byte, n)
+		b.ResetTimer()
 		for i := 0; i < b.N; i++ {
 			copy(x, y)
 		}
@@ -301,6 +302,7 @@ func BenchmarkMemmove(b *testing.B) {
 func BenchmarkMemmoveOverlap(b *testing.B) {
 	benchmarkSizes(b, bufSizesOverlap, func(b *testing.B, n int) {
 		x := make([]byte, n+16)
+		b.ResetTimer()
 		for i := 0; i < b.N; i++ {
 			copy(x[16:n+16], x[:n])
 		}
@@ -311,6 +313,7 @@ func BenchmarkMemmoveUnalignedDst(b *testing.B) {
 	benchmarkSizes(b, bufSizes, func(b *testing.B, n int) {
 		x := make([]byte, n+1)
 		y := make([]byte, n)
+		b.ResetTimer()
 		for i := 0; i < b.N; i++ {
 			copy(x[1:], y)
 		}
@@ -320,6 +323,7 @@ func BenchmarkMemmoveUnalignedDst(b *testing.B) {
 func BenchmarkMemmoveUnalignedDstOverlap(b *testing.B) {
 	benchmarkSizes(b, bufSizesOverlap, func(b *testing.B, n int) {
 		x := make([]byte, n+16)
+		b.ResetTimer()
 		for i := 0; i < b.N; i++ {
 			copy(x[16:n+16], x[1:n+1])
 		}
@@ -330,6 +334,7 @@ func BenchmarkMemmoveUnalignedSrc(b *testing.B) {
 	benchmarkSizes(b, bufSizes, func(b *testing.B, n int) {
 		x := make([]byte, n)
 		y := make([]byte, n+1)
+		b.ResetTimer()
 		for i := 0; i < b.N; i++ {
 			copy(x, y[1:])
 		}
@@ -362,6 +367,7 @@ func BenchmarkMemmoveUnalignedSrcDst(b *testing.B) {
 func BenchmarkMemmoveUnalignedSrcOverlap(b *testing.B) {
 	benchmarkSizes(b, bufSizesOverlap, func(b *testing.B, n int) {
 		x := make([]byte, n+1)
+		b.ResetTimer()
 		for i := 0; i < b.N; i++ {
 			copy(x[1:n+1], x[:n])
 		}
@@ -450,6 +456,7 @@ func BenchmarkMemclrUnaligned(b *testing.B) {
 func BenchmarkGoMemclr(b *testing.B) {
 	benchmarkSizes(b, []int{5, 16, 64, 256}, func(b *testing.B, n int) {
 		x := make([]byte, n)
+		b.ResetTimer()
 		for i := 0; i < b.N; i++ {
 			clear(x)
 		}