encoding/xml: make use of reflect.TypeAssert

To make the code more readable and improve performance:

goos: darwin
goarch: arm64
pkg: encoding/xml
cpu: Apple M4
                 │     old     │                 new                 │
                 │   sec/op    │   sec/op     vs base                │
Marshal-10         1.902µ ± 1%   1.496µ ± 1%  -21.37% (p=0.000 n=10)
Unmarshal-10       3.877µ ± 1%   3.418µ ± 2%  -11.84% (p=0.000 n=10)
HTMLAutoClose-10   1.314µ ± 3%   1.333µ ± 1%        ~ (p=0.270 n=10)
geomean            2.132µ        1.896µ       -11.07%

                 │     old      │                  new                  │
                 │     B/op     │     B/op      vs base                 │
Marshal-10         5.570Ki ± 0%   5.570Ki ± 0%       ~ (p=1.000 n=10) ¹
Unmarshal-10       7.586Ki ± 0%   7.555Ki ± 0%  -0.41% (p=0.000 n=10)
HTMLAutoClose-10   3.496Ki ± 0%   3.496Ki ± 0%       ~ (p=1.000 n=10) ¹
geomean            5.286Ki        5.279Ki       -0.14%
¹ all samples are equal

                 │    old     │                 new                 │
                 │ allocs/op  │ allocs/op   vs base                 │
Marshal-10         23.00 ± 0%   23.00 ± 0%       ~ (p=1.000 n=10) ¹
Unmarshal-10       185.0 ± 0%   184.0 ± 0%  -0.54% (p=0.000 n=10)
HTMLAutoClose-10   93.00 ± 0%   93.00 ± 0%       ~ (p=1.000 n=10) ¹
geomean            73.42        73.28       -0.18%
¹ all samples are equal

Updates #62121

Change-Id: Ie458e7458d4358c380374571d380ca3b65ca87bb
GitHub-Last-Rev: bb6bb3039328ca1d53ee3d56fd6597109ed76b09
GitHub-Pull-Request: golang/go#75483
Reviewed-on: https://go-review.googlesource.com/c/go/+/704215
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Carlos Amedee <carlos@golang.org>

1 files changed, 46 insertions, 31 deletions

diff --git a/src/encoding/xml/read.go b/src/encoding/xml/read.go
index af25c20f06..d3cb74b2c4 100644
--- a/src/encoding/xml/read.go
+++ b/src/encoding/xml/read.go
@@ -255,28 +255,36 @@ func (d *Decoder) unmarshalAttr(val reflect.Value, attr Attr) error {
 		}
 		val = val.Elem()
 	}
-	if val.CanInterface() && val.Type().Implements(unmarshalerAttrType) {
+	if val.CanInterface() {
 		// This is an unmarshaler with a non-pointer receiver,
 		// so it's likely to be incorrect, but we do what we're told.
-		return val.Interface().(UnmarshalerAttr).UnmarshalXMLAttr(attr)
+		if unmarshaler, ok := reflect.TypeAssert[UnmarshalerAttr](val); ok {
+			return unmarshaler.UnmarshalXMLAttr(attr)
+		}
 	}
 	if val.CanAddr() {
 		pv := val.Addr()
-		if pv.CanInterface() && pv.Type().Implements(unmarshalerAttrType) {
-			return pv.Interface().(UnmarshalerAttr).UnmarshalXMLAttr(attr)
+		if pv.CanInterface() {
+			if unmarshaler, ok := reflect.TypeAssert[UnmarshalerAttr](pv); ok {
+				return unmarshaler.UnmarshalXMLAttr(attr)
+			}
 		}
 	}
 
 	// Not an UnmarshalerAttr; try encoding.TextUnmarshaler.
-	if val.CanInterface() && val.Type().Implements(textUnmarshalerType) {
+	if val.CanInterface() {
 		// This is an unmarshaler with a non-pointer receiver,
 		// so it's likely to be incorrect, but we do what we're told.
-		return val.Interface().(encoding.TextUnmarshaler).UnmarshalText([]byte(attr.Value))
+		if textUnmarshaler, ok := reflect.TypeAssert[encoding.TextUnmarshaler](val); ok {
+			return textUnmarshaler.UnmarshalText([]byte(attr.Value))
+		}
 	}
 	if val.CanAddr() {
 		pv := val.Addr()
-		if pv.CanInterface() && pv.Type().Implements(textUnmarshalerType) {
-			return pv.Interface().(encoding.TextUnmarshaler).UnmarshalText([]byte(attr.Value))
+		if pv.CanInterface() {
+			if textUnmarshaler, ok := reflect.TypeAssert[encoding.TextUnmarshaler](pv); ok {
+				return textUnmarshaler.UnmarshalText([]byte(attr.Value))
+			}
 		}
 	}
 
@@ -303,12 +311,7 @@ func (d *Decoder) unmarshalAttr(val reflect.Value, attr Attr) error {
 	return copyValue(val, []byte(attr.Value))
 }
 
-var (
-	attrType            = reflect.TypeFor[Attr]()
-	unmarshalerType     = reflect.TypeFor[Unmarshaler]()
-	unmarshalerAttrType = reflect.TypeFor[UnmarshalerAttr]()
-	textUnmarshalerType = reflect.TypeFor[encoding.TextUnmarshaler]()
-)
+var attrType = reflect.TypeFor[Attr]()
 
 const (
 	maxUnmarshalDepth     = 10000
@@ -352,27 +355,35 @@ func (d *Decoder) unmarshal(val reflect.Value, start *StartElement, depth int) e
 		val = val.Elem()
 	}
 
-	if val.CanInterface() && val.Type().Implements(unmarshalerType) {
+	if val.CanInterface() {
 		// This is an unmarshaler with a non-pointer receiver,
 		// so it's likely to be incorrect, but we do what we're told.
-		return d.unmarshalInterface(val.Interface().(Unmarshaler), start)
+		if unmarshaler, ok := reflect.TypeAssert[Unmarshaler](val); ok {
+			return d.unmarshalInterface(unmarshaler, start)
+		}
 	}
 
 	if val.CanAddr() {
 		pv := val.Addr()
-		if pv.CanInterface() && pv.Type().Implements(unmarshalerType) {
-			return d.unmarshalInterface(pv.Interface().(Unmarshaler), start)
+		if pv.CanInterface() {
+			if unmarshaler, ok := reflect.TypeAssert[Unmarshaler](pv); ok {
+				return d.unmarshalInterface(unmarshaler, start)
+			}
 		}
 	}
 
-	if val.CanInterface() && val.Type().Implements(textUnmarshalerType) {
-		return d.unmarshalTextInterface(val.Interface().(encoding.TextUnmarshaler))
+	if val.CanInterface() {
+		if textUnmarshaler, ok := reflect.TypeAssert[encoding.TextUnmarshaler](val); ok {
+			return d.unmarshalTextInterface(textUnmarshaler)
+		}
 	}
 
 	if val.CanAddr() {
 		pv := val.Addr()
-		if pv.CanInterface() && pv.Type().Implements(textUnmarshalerType) {
-			return d.unmarshalTextInterface(pv.Interface().(encoding.TextUnmarshaler))
+		if pv.CanInterface() {
+			if textUnmarshaler, ok := reflect.TypeAssert[encoding.TextUnmarshaler](pv); ok {
+				return d.unmarshalTextInterface(textUnmarshaler)
+			}
 		}
 	}
 
@@ -453,7 +464,7 @@ func (d *Decoder) unmarshal(val reflect.Value, start *StartElement, depth int) e
 				return UnmarshalError(e)
 			}
 			fv := finfo.value(sv, initNilPointers)
-			if _, ok := fv.Interface().(Name); ok {
+			if _, ok := reflect.TypeAssert[Name](fv); ok {
 				fv.Set(reflect.ValueOf(start.Name))
 			}
 		}
@@ -578,20 +589,24 @@ Loop:
 		}
 	}
 
-	if saveData.IsValid() && saveData.CanInterface() && saveData.Type().Implements(textUnmarshalerType) {
-		if err := saveData.Interface().(encoding.TextUnmarshaler).UnmarshalText(data); err != nil {
-			return err
+	if saveData.IsValid() && saveData.CanInterface() {
+		if textUnmarshaler, ok := reflect.TypeAssert[encoding.TextUnmarshaler](saveData); ok {
+			if err := textUnmarshaler.UnmarshalText(data); err != nil {
+				return err
+			}
+			saveData = reflect.Value{}
 		}
-		saveData = reflect.Value{}
 	}
 
 	if saveData.IsValid() && saveData.CanAddr() {
 		pv := saveData.Addr()
-		if pv.CanInterface() && pv.Type().Implements(textUnmarshalerType) {
-			if err := pv.Interface().(encoding.TextUnmarshaler).UnmarshalText(data); err != nil {
-				return err
+		if pv.CanInterface() {
+			if textUnmarshaler, ok := reflect.TypeAssert[encoding.TextUnmarshaler](pv); ok {
+				if err := textUnmarshaler.UnmarshalText(data); err != nil {
+					return err
+				}
+				saveData = reflect.Value{}
 			}
-			saveData = reflect.Value{}
 		}
 	}