cmd/compile: rename T_old_DARRAY and update comments

Change-Id: Ifa3b1b1e5458e4f109828a476d37f1caf96fe14b
Reviewed-on: https://go-review.googlesource.com/21211
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

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

@@ -512,8 +512,8 @@ func (p *exporter) typ(t *Type) {
 		}
 		p.typ(t.Type)
 
-	case T_old_DARRAY:
-		// see p.param use of T_old_DARRAY
+	case TDDDFIELD:
+		// see p.param use of TDDDFIELD
 		p.tag(dddTag)
 		p.typ(t.Type)
 
@@ -664,9 +664,7 @@ func (p *exporter) param(q *Field, n int, numbered bool) {
 	t := q.Type
 	if q.Isddd {
 		// create a fake type to encode ... just for the p.typ call
-		// (T_old_DARRAY is not used anywhere else in the compiler,
-		// we use it here to communicate between p.param and p.typ.)
-		t = &Type{Etype: T_old_DARRAY, Type: t.Type}
+		t = &Type{Etype: TDDDFIELD, Type: t.Type}
 	}
 	p.typ(t)
 	if n > 0 {

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

@@ -284,7 +284,7 @@ func (p *importer) typ() *Type {
 		t.Type = p.typ()
 
 	case dddTag:
-		t = p.newtyp(T_old_DARRAY)
+		t = p.newtyp(TDDDFIELD)
 		t.Bound = -1
 		t.Type = p.typ()
 
@@ -447,8 +447,8 @@ func (p *importer) param(named bool) *Node {
 	typ := p.typ()
 
 	isddd := false
-	if typ.Etype == T_old_DARRAY {
-		// T_old_DARRAY indicates ... type
+	if typ.Etype == TDDDFIELD {
+		// TDDDFIELD indicates ... type
 		// TODO(mdempsky): Fix Type rekinding.
 		typ.Etype = TARRAY
 		isddd = true

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

@@ -45,7 +45,6 @@ const (
 
 	TFUNC
 	TARRAY
-	T_old_DARRAY // Doesn't seem to be used in existing code. Used now for Isddd export (see bexport.go). TODO(gri) rename.
 	TSTRUCT
 	TCHAN
 	TMAP
@@ -60,11 +59,14 @@ const (
 	TNIL
 	TBLANK
 
-	// pseudo-type for frame layout
+	// pseudo-types for frame layout
 	TFUNCARGS
 	TCHANARGS
 	TINTERMETH
 
+	// pseudo-types for import/export
+	TDDDFIELD // wrapper: contained type is a ... field
+
 	NTYPE
 )