encoding/gob: change typeInfo.encoder type to atomic.Pointer[T]

Replace loading and storing an atomic.Value of type pointer with
atomic.Pointer.

Change-Id: I018ac1e18eee4f203ebca65c2833daf991075371
Reviewed-on: https://go-review.googlesource.com/c/go/+/422174
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Rob Pike <r@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Rob Pike <r@golang.org>

src/encoding/gob/encode.go

@@ -577,7 +577,7 @@ func encOpFor(rt reflect.Type, inProgress map[reflect.Type]*encOp, building map[
 			op = func(i *encInstr, state *encoderState, sv reflect.Value) {
 				state.update(i)
 				// indirect through info to delay evaluation for recursive structs
-				enc := info.encoder.Load().(*encEngine)
+				enc := info.encoder.Load()
 				state.enc.encodeStruct(state.b, enc, sv)
 			}
 		case reflect.Interface:
@@ -661,8 +661,8 @@ func getEncEngine(ut *userTypeInfo, building map[*typeInfo]bool) *encEngine {
 	if err != nil {
 		error_(err)
 	}
-	enc, ok := info.encoder.Load().(*encEngine)
-	if !ok {
+	enc := info.encoder.Load()
+	if enc == nil {
 		enc = buildEncEngine(info, ut, building)
 	}
 	return enc
@@ -675,8 +675,8 @@ func buildEncEngine(info *typeInfo, ut *userTypeInfo, building map[*typeInfo]boo
 	}
 	info.encInit.Lock()
 	defer info.encInit.Unlock()
-	enc, ok := info.encoder.Load().(*encEngine)
-	if !ok {
+	enc := info.encoder.Load()
+	if enc == nil {
 		if building == nil {
 			building = make(map[*typeInfo]bool)
 		}

src/encoding/gob/type.go

@@ -672,8 +672,8 @@ func (w *wireType) string() string {
 
 type typeInfo struct {
 	id      typeId
-	encInit sync.Mutex   // protects creation of encoder
-	encoder atomic.Value // *encEngine
+	encInit sync.Mutex // protects creation of encoder
+	encoder atomic.Pointer[encEngine]
 	wire    *wireType
 }