cmd/compile: add typWrapper and Type.Wrapped

Passes toolstash -cmp.

Change-Id: I7dffd9bc5bab323590df6fb591bf1e73edf2e465
Reviewed-on: https://go-review.googlesource.com/21305Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

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

@@ -198,14 +198,12 @@ func dowidth(t *Type) {
 
 		// make fake type to check later to
 		// trigger channel argument check.
-		t1 := typ(TCHANARGS)
-
-		t1.Type = t
+		t1 := typWrapper(TCHANARGS, t)
 		checkwidth(t1)
 
 	case TCHANARGS:
-		t1 := t.Type
-		dowidth(t.Type) // just in case
+		t1 := t.Wrapped()
+		dowidth(t1) // just in case
 		if t1.Type.Width >= 1<<16 {
 			Yyerror("channel element type too large (>64kB)")
 		}
@@ -273,22 +271,17 @@ func dowidth(t *Type) {
 	// make fake type to check later to
 	// trigger function argument computation.
 	case TFUNC:
-		t1 := typ(TFUNCARGS)
-
-		t1.Type = t
+		t1 := typWrapper(TFUNCARGS, t)
 		checkwidth(t1)
-
-		// width of func type is pointer
-		w = int64(Widthptr)
+		w = int64(Widthptr) // width of func type is pointer
 
 	// function is 3 cated structures;
 	// compute their widths as side-effect.
 	case TFUNCARGS:
-		t1 := t.Type
-
-		w = widstruct(t.Type, t1.Recvs(), 0, 0)
-		w = widstruct(t.Type, t1.Params(), w, Widthreg)
-		w = widstruct(t.Type, t1.Results(), w, Widthreg)
+		t1 := t.Wrapped()
+		w = widstruct(t1, t1.Recvs(), 0, 0)
+		w = widstruct(t1, t1.Params(), w, Widthreg)
+		w = widstruct(t1, t1.Results(), w, Widthreg)
 		t1.Argwid = w
 		if w%int64(Widthreg) != 0 {
 			Warn("bad type %v %d\n", t1, w)

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

@@ -517,7 +517,7 @@ func (p *exporter) typ(t *Type) {
 	case TDDDFIELD:
 		// see p.param use of TDDDFIELD
 		p.tag(dddTag)
-		p.typ(t.Type)
+		p.typ(t.Wrapped())
 
 	case TSTRUCT:
 		p.tag(structTag)
@@ -666,7 +666,7 @@ 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 = &Type{Etype: TDDDFIELD, Type: t.Type}
+		t = typWrapper(TDDDFIELD, t.Type)
 	}
 	p.typ(t)
 	if n > 0 {

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

@@ -267,6 +267,18 @@ func typeChan(elem *Type, dir uint8) *Type {
 	return t
 }
 
+// typWrapper returns a new wrapper psuedo-type.
+func typWrapper(et EType, wrapped *Type) *Type {
+	switch et {
+	case TCHANARGS, TFUNCARGS, TDDDFIELD:
+	default:
+		Fatalf("typWrapper bad etype %s", et)
+	}
+	t := typ(et)
+	t.Type = wrapped
+	return t
+}
+
 func newField() *Field {
 	return &Field{
 		Offset: BADWIDTH,
@@ -474,6 +486,16 @@ func (t *Type) Val() *Type {
 	return t.Type
 }
 
+// Wrapped returns the type that pseudo-type t wraps.
+func (t *Type) Wrapped() *Type {
+	switch t.Etype {
+	case TCHANARGS, TFUNCARGS, TDDDFIELD:
+	default:
+		Fatalf("Type.Wrapped %s", t.Etype)
+	}
+	return t.Type
+}
+
 func (t *Type) Methods() *Fields {
 	// TODO(mdempsky): Validate t?
 	return &t.methods