cmd/compile/internal/gc: introduce type for untyped constant kinds

Change-Id: Ia34b6dd099d07d5e1d4bffe775a20fa92705fdb0
Reviewed-on: https://go-review.googlesource.com/16335
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

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

@@ -963,7 +963,7 @@ var tagString = [...]string{
 // untype returns the "pseudo" untyped type for a Ctype (import/export use only).
 // (we can't use an pre-initialized array because we must be sure all types are
 // set up)
-func untype(ctype int) *Type {
+func untype(ctype Ctype) *Type {
 	switch ctype {
 	case CTINT:
 		return idealint

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

@@ -10,8 +10,6 @@ import (
 	"cmd/internal/obj"
 )
 
-// avoid <ctype.h>
-
 // The parser's maximum stack size.
 // We have to use a #define macro here since yacc
 // or bison will check for its definition and use
@@ -95,7 +93,7 @@ type Val struct {
 
 type NilVal struct{}
 
-func (v Val) Ctype() int {
+func (v Val) Ctype() Ctype {
 	switch x := v.U.(type) {
 	default:
 		Fatalf("unexpected Ctype for %T", v.U)
@@ -312,8 +310,11 @@ const (
 	NTYPE
 )
 
+// Ctype describes the constant kind of an "ideal" (untyped) constant.
+type Ctype int8
+
 const (
-	CTxxx = iota
+	CTxxx Ctype = iota
 
 	CTINT
 	CTRUNE

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

@@ -744,11 +744,11 @@ func exprcmp(c1, c2 *caseClause) int {
 	n2 := c2.node.Left
 
 	// sort by type (for switches on interface)
-	ct := int(n1.Val().Ctype())
-	if ct > int(n2.Val().Ctype()) {
+	ct := n1.Val().Ctype()
+	if ct > n2.Val().Ctype() {
 		return +1
 	}
-	if ct < int(n2.Val().Ctype()) {
+	if ct < n2.Val().Ctype() {
 		return -1
 	}
 	if !Eqtype(n1.Type, n2.Type) {