cmd/compile, etc: use tflag to optimize Name()==""

Improves JSON decoding benchmark:

	name                  old time/op    new time/op    delta
	CodeDecoder-8           41.3ms ± 6%    39.8ms ± 1%  -3.61%  (p=0.000 n=10+10)

	name                  old speed      new speed      delta
	CodeDecoder-8         47.0MB/s ± 6%  48.7MB/s ± 1%  +3.66%  (p=0.000 n=10+10)

Change-Id: I524ee05c432fad5252e79b29222ec635c1dee4b4
Reviewed-on: https://go-review.googlesource.com/24452
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/compile/internal/gc/reflect.go

@@ -799,6 +799,7 @@ func typeptrdata(t *Type) int64 {
 const (
 	tflagUncommon  = 1 << 0
 	tflagExtraStar = 1 << 1
+	tflagNamed     = 1 << 2
 )
 
 var dcommontype_algarray *Sym
@@ -852,6 +853,9 @@ func dcommontype(s *Sym, ot int, t *Type) int {
 	if uncommonSize(t) != 0 {
 		tflag |= tflagUncommon
 	}
+	if t.Sym != nil && t.Sym.Name != "" {
+		tflag |= tflagNamed
+	}
 
 	exported := false
 	p := Tconv(t, FmtLeft|FmtUnsigned)

src/reflect/type.go

@@ -268,6 +268,9 @@ const (
 	// a program, the type *T also exists and reusing the str data
 	// saves binary size.
 	tflagExtraStar tflag = 1 << 1
+
+	// tflagNamed means the type has a name.
+	tflagNamed tflag = 1 << 2
 )
 
 // rtype is the common implementation of most values.
@@ -893,34 +896,10 @@ func hasPrefix(s, prefix string) bool {
 }
 
 func (t *rtype) Name() string {
-	s := t.String()
+	if t.tflag&tflagNamed == 0 {
-	switch s[0] {
-	case 'm':
-		if hasPrefix(s, "map[") {
-			return ""
-		}
-	case 's':
-		if hasPrefix(s, "struct {") {
-			return ""
-		}
-	case 'c':
-		if hasPrefix(s, "chan ") {
-			return ""
-		}
-		if hasPrefix(s, "chan<-") {
-			return ""
-		}
-	case 'f':
-		if hasPrefix(s, "func(") {
-			return ""
-		}
-	case 'i':
-		if hasPrefix(s, "interface {") {
-			return ""
-		}
-	case '[', '*', '<':
 		return ""
 	}
+	s := t.String()
 	i := len(s) - 1
 	for i >= 0 {
 		if s[i] == '.' {

src/runtime/type.go

@@ -19,6 +19,7 @@ type tflag uint8
 const (
 	tflagUncommon  tflag = 1 << 0
 	tflagExtraStar tflag = 1 << 1
+	tflagNamed     tflag = 1 << 2
 )
 
 // Needs to be in sync with ../cmd/compile/internal/ld/decodesym.go:/^func.commonsize,
@@ -116,29 +117,10 @@ func hasPrefix(s, prefix string) bool {
 }
 
 func (t *_type) name() string {
+	if t.tflag&tflagNamed == 0 {
+		return ""
+	}
 	s := t.string()
-	if hasPrefix(s, "map[") {
-		return ""
-	}
-	if hasPrefix(s, "struct {") {
-		return ""
-	}
-	if hasPrefix(s, "chan ") {
-		return ""
-	}
-	if hasPrefix(s, "chan<-") {
-		return ""
-	}
-	if hasPrefix(s, "func(") {
-		return ""
-	}
-	if hasPrefix(s, "interface {") {
-		return ""
-	}
-	switch s[0] {
-	case '[', '*', '<':
-		return ""
-	}
 	i := len(s) - 1
 	for i >= 0 {
 		if s[i] == '.' {