cmd/compile: use types.IdealFoo directly in predecl

Instead of using untype(Ctype) to get corresponding untyped type.

Passes toolstash-check.

Change-Id: I311fe6c94b1f8eb2e1615101a379cd06dcab835b
Reviewed-on: https://go-review.googlesource.com/c/go/+/260698
Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

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

@@ -126,30 +126,6 @@ const (
 	aliasTag
 )
 
-// untype returns the "pseudo" untyped type for a Ctype (import/export use only).
-// (we can't use a pre-initialized array because we must be sure all types are
-// set up)
-func untype(ctype Ctype) *types.Type {
-	switch ctype {
-	case CTINT:
-		return types.Idealint
-	case CTRUNE:
-		return types.Idealrune
-	case CTFLT:
-		return types.Idealfloat
-	case CTCPLX:
-		return types.Idealcomplex
-	case CTSTR:
-		return types.Idealstring
-	case CTBOOL:
-		return types.Idealbool
-	case CTNIL:
-		return types.Types[TNIL]
-	}
-	Fatalf("exporter: unknown Ctype")
-	return nil
-}
-
 var predecl []*types.Type // initialized lazily
 
 func predeclared() []*types.Type {
@@ -184,13 +160,13 @@ func predeclared() []*types.Type {
 			types.Errortype,
 
 			// untyped types
-			untype(CTBOOL),
-			untype(CTINT),
-			untype(CTRUNE),
-			untype(CTFLT),
-			untype(CTCPLX),
-			untype(CTSTR),
-			untype(CTNIL),
+			types.Idealbool,
+			types.Idealint,
+			types.Idealrune,
+			types.Idealfloat,
+			types.Idealcomplex,
+			types.Idealstring,
+			types.Types[TNIL],
 
 			// package unsafe
 			types.Types[TUNSAFEPTR],

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

@@ -780,8 +780,8 @@ func constTypeOf(typ *types.Type) Ctype {
 }
 
 func (w *exportWriter) value(typ *types.Type, v Val) {
-	if typ.IsUntyped() {
-		typ = untype(v.Ctype())
+	if vt := idealType(v.Ctype()); typ.IsUntyped() && typ != vt {
+		Fatalf("exporter: untyped type mismatch, have: %v, want: %v", typ, vt)
 	}
 	w.typ(typ)