reflect: parallelize benchmarks

Add a benchmark for PtrTo: it's the motivation for #17973, which is
the motivation for #18177.

Results remain comparable with the non-parallel version with -cpu=1:

benchmark                             old ns/op     new ns/op     delta
BenchmarkCall                         357           360           +0.84%
BenchmarkCall-6                       90.3          90.7          +0.44%
BenchmarkCallArgCopy/size=128         319           323           +1.25%
BenchmarkCallArgCopy/size=128-6       329           82.2          -75.02%
BenchmarkCallArgCopy/size=256         354           335           -5.37%
BenchmarkCallArgCopy/size=256-6       340           85.2          -74.94%
BenchmarkCallArgCopy/size=1024        374           703           +87.97%
BenchmarkCallArgCopy/size=1024-6      378           95.8          -74.66%
BenchmarkCallArgCopy/size=4096        627           631           +0.64%
BenchmarkCallArgCopy/size=4096-6      643           120           -81.34%
BenchmarkCallArgCopy/size=65536       10502         10169         -3.17%
BenchmarkCallArgCopy/size=65536-6     10298         2240          -78.25%
BenchmarkFieldByName1                 139           132           -5.04%
BenchmarkFieldByName1-6               144           24.9          -82.71%
BenchmarkFieldByName2                 2721          2778          +2.09%
BenchmarkFieldByName2-6               3953          578           -85.38%
BenchmarkFieldByName3                 19136         18357         -4.07%
BenchmarkFieldByName3-6               23072         3850          -83.31%
BenchmarkInterfaceBig                 12.7          15.5          +22.05%
BenchmarkInterfaceBig-6               14.2          2.48          -82.54%
BenchmarkInterfaceSmall               13.1          15.1          +15.27%
BenchmarkInterfaceSmall-6             13.0          2.54          -80.46%
BenchmarkNew                          43.8          43.0          -1.83%
BenchmarkNew-6                        40.5          6.67          -83.53%

benchmark                             old MB/s     new MB/s     speedup
BenchmarkCallArgCopy/size=128         400.24       395.15       0.99x
BenchmarkCallArgCopy/size=128-6       388.74       1557.76      4.01x
BenchmarkCallArgCopy/size=256         722.44       762.44       1.06x
BenchmarkCallArgCopy/size=256-6       751.98       3003.83      3.99x
BenchmarkCallArgCopy/size=1024        2733.22      1455.50      0.53x
BenchmarkCallArgCopy/size=1024-6      2706.40      10687.53     3.95x
BenchmarkCallArgCopy/size=4096        6523.32      6488.25      0.99x
BenchmarkCallArgCopy/size=4096-6      6363.85      34003.09     5.34x
BenchmarkCallArgCopy/size=65536       6239.88      6444.46      1.03x
BenchmarkCallArgCopy/size=65536-6     6363.83      29255.26     4.60x

benchmark           old allocs     new allocs     delta
BenchmarkCall       0              0              +0.00%
BenchmarkCall-6     0              0              +0.00%

benchmark           old bytes     new bytes     delta
BenchmarkCall       0             0             +0.00%
BenchmarkCall-6     0             0             +0.00%

updates #17973
updates #18177

Change-Id: If70c5c742e8d1b138347f4963ad7cff38fffc018
Reviewed-on: https://go-review.googlesource.com/36831
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/reflect/all_test.go

@@ -1576,9 +1576,11 @@ func BenchmarkCallArgCopy(b *testing.B) {
 			args := []Value{size.arg}
 			b.SetBytes(int64(size.arg.Len()))
 			b.ResetTimer()
-			for i := 0; i < b.N; i++ {
-				size.fv.Call(args)
-			}
+			b.RunParallel(func(pb *testing.PB) {
+				for pb.Next() {
+					size.fv.Call(args)
+				}
+			})
 		}
 		name := fmt.Sprintf("size=%v", size.arg.Len())
 		b.Run(name, bench)
@@ -2556,6 +2558,28 @@ func TestPtrToGC(t *testing.T) {
 	}
 }
 
+func BenchmarkPtrTo(b *testing.B) {
+	// Construct a type with a zero ptrToThis.
+	type T struct{ int }
+	t := SliceOf(TypeOf(T{}))
+	ptrToThis := ValueOf(t).Elem().FieldByName("ptrToThis")
+	if !ptrToThis.IsValid() {
+		b.Fatalf("%v has no ptrToThis field; was it removed from rtype?", t)
+	}
+	if ptrToThis.Int() != 0 {
+		b.Fatalf("%v.ptrToThis unexpectedly nonzero", t)
+	}
+	b.ResetTimer()
+
+	// Now benchmark calling PtrTo on it: we'll have to hit the ptrMap cache on
+	// every call.
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			PtrTo(t)
+		}
+	})
+}
+
 func TestAddr(t *testing.T) {
 	var p struct {
 		X, Y int
@@ -4909,16 +4933,20 @@ type B1 struct {
 
 func BenchmarkFieldByName1(b *testing.B) {
 	t := TypeOf(B1{})
-	for i := 0; i < b.N; i++ {
-		t.FieldByName("Z")
-	}
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			t.FieldByName("Z")
+		}
+	})
 }
 
 func BenchmarkFieldByName2(b *testing.B) {
 	t := TypeOf(S3{})
-	for i := 0; i < b.N; i++ {
-		t.FieldByName("B")
-	}
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			t.FieldByName("B")
+		}
+	})
 }
 
 type R0 struct {
@@ -5001,9 +5029,11 @@ func TestEmbed(t *testing.T) {
 
 func BenchmarkFieldByName3(b *testing.B) {
 	t := TypeOf(R0{})
-	for i := 0; i < b.N; i++ {
-		t.FieldByName("X")
-	}
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			t.FieldByName("X")
+		}
+	})
 }
 
 type S struct {
@@ -5013,9 +5043,11 @@ type S struct {
 
 func BenchmarkInterfaceBig(b *testing.B) {
 	v := ValueOf(S{})
-	for i := 0; i < b.N; i++ {
-		v.Interface()
-	}
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			v.Interface()
+		}
+	})
 	b.StopTimer()
 }
 
@@ -5031,9 +5063,11 @@ func TestAllocsInterfaceBig(t *testing.T) {
 
 func BenchmarkInterfaceSmall(b *testing.B) {
 	v := ValueOf(int64(0))
-	for i := 0; i < b.N; i++ {
-		v.Interface()
-	}
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			v.Interface()
+		}
+	})
 }
 
 func TestAllocsInterfaceSmall(t *testing.T) {
@@ -6007,9 +6041,11 @@ func TestOffsetLock(t *testing.T) {
 
 func BenchmarkNew(b *testing.B) {
 	v := TypeOf(XM{})
-	for i := 0; i < b.N; i++ {
-		New(v)
-	}
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			New(v)
+		}
+	})
 }
 
 func TestSwapper(t *testing.T) {