[dev.regabi] cmd/compile: move setUnderlying to package types

Now that setUnderlying is decoupled from Nodes, it can be moved into
package types, where it really belongs.

[git-generate]
cd src/cmd/compile/internal/gc
rf '
mv setUnderlying SetUnderlying
mv SetUnderlying typex.go
mv typex.go cmd/compile/internal/types
'

cd ../types
rf '
mv typex.go type.go
'

Change-Id: I76e2d4d8a6df599f24a731c4d8e5774ec83a119c
Reviewed-on: https://go-review.googlesource.com/c/go/+/274433
Trust: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>

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

@@ -316,7 +316,7 @@ func (r *importReader) doDecl(n ir.Node) {
 		// after the underlying type has been assigned.
 		defercheckwidth()
 		underlying := r.typ()
-		setUnderlying(t, underlying)
+		types.SetUnderlying(t, underlying)
 		resumecheckwidth()
 
 		if underlying.IsInterface() {

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

@@ -3427,50 +3427,6 @@ func checkMapKeys() {
 	mapqueue = nil
 }
 
-func setUnderlying(t, underlying *types.Type) {
-	if underlying.Etype == types.TFORW {
-		// This type isn't computed yet; when it is, update n.
-		underlying.ForwardType().Copyto = append(underlying.ForwardType().Copyto, t)
-		return
-	}
-
-	ft := t.ForwardType()
-
-	// TODO(mdempsky): Fix Type rekinding.
-	t.Etype = underlying.Etype
-	t.Extra = underlying.Extra
-	t.Width = underlying.Width
-	t.Align = underlying.Align
-	t.Orig = underlying.Orig
-
-	if underlying.NotInHeap() {
-		t.SetNotInHeap(true)
-	}
-	if underlying.Broke() {
-		t.SetBroke(true)
-	}
-
-	// spec: "The declared type does not inherit any methods bound
-	// to the existing type, but the method set of an interface
-	// type [...] remains unchanged."
-	if t.IsInterface() {
-		*t.Methods() = *underlying.Methods()
-		*t.AllMethods() = *underlying.AllMethods()
-	}
-
-	// Update types waiting on this type.
-	for _, w := range ft.Copyto {
-		setUnderlying(w, t)
-	}
-
-	// Double-check use of type as embedded type.
-	if ft.Embedlineno.IsKnown() {
-		if t.IsPtr() || t.IsUnsafePtr() {
-			base.ErrorfAt(ft.Embedlineno, "embedded type cannot be a pointer")
-		}
-	}
-}
-
 func typecheckdeftype(n *ir.Name) {
 	if enableTrace && base.Flag.LowerT {
 		defer tracePrint("typecheckdeftype", n)(nil)
@@ -3492,7 +3448,7 @@ func typecheckdeftype(n *ir.Name) {
 	errorsBefore := base.Errors()
 	n.Ntype = typecheckNtype(n.Ntype)
 	if underlying := n.Ntype.Type(); underlying != nil {
-		setUnderlying(t, underlying)
+		types.SetUnderlying(t, underlying)
 	} else {
 		n.SetDiag(true)
 		n.SetType(nil)

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

@@ -5,6 +5,7 @@
 package types
 
 import (
+	"cmd/compile/internal/base"
 	"cmd/internal/obj"
 	"cmd/internal/src"
 	"fmt"
@@ -1517,3 +1518,47 @@ var (
 	TypeVoid    = newSSA("void")
 	TypeInt128  = newSSA("int128")
 )
+
+func SetUnderlying(t, underlying *Type) {
+	if underlying.Etype == TFORW {
+		// This type isn't computed yet; when it is, update n.
+		underlying.ForwardType().Copyto = append(underlying.ForwardType().Copyto, t)
+		return
+	}
+
+	ft := t.ForwardType()
+
+	// TODO(mdempsky): Fix Type rekinding.
+	t.Etype = underlying.Etype
+	t.Extra = underlying.Extra
+	t.Width = underlying.Width
+	t.Align = underlying.Align
+	t.Orig = underlying.Orig
+
+	if underlying.NotInHeap() {
+		t.SetNotInHeap(true)
+	}
+	if underlying.Broke() {
+		t.SetBroke(true)
+	}
+
+	// spec: "The declared type does not inherit any methods bound
+	// to the existing type, but the method set of an interface
+	// type [...] remains unchanged."
+	if t.IsInterface() {
+		*t.Methods() = *underlying.Methods()
+		*t.AllMethods() = *underlying.AllMethods()
+	}
+
+	// Update types waiting on this type.
+	for _, w := range ft.Copyto {
+		SetUnderlying(w, t)
+	}
+
+	// Double-check use of type as embedded type.
+	if ft.Embedlineno.IsKnown() {
+		if t.IsPtr() || t.IsUnsafePtr() {
+			base.ErrorfAt(ft.Embedlineno, "embedded type cannot be a pointer")
+		}
+	}
+}