cmd/compile: more Isfoo Type cleanups

Replace isideal(t) with t.IsUntyped().
Replace Istype(t, k) with t.IsKind(k).
Replace isnilinter(t) with t.IsEmptyInterface().

Also replace a lot of t.IsKind(TFOO) with t.IsFoo().

Replacements prepared mechanically with gofmt -w -r.

Passes toolstash -cmp.

Change-Id: Iba48058f3cc863e15af14277b5ff5e729e67e043
Reviewed-on: https://go-review.googlesource.com/21424
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
diff --git a/src/cmd/compile/internal/gc/ssa.go b/src/cmd/compile/internal/gc/ssa.go
index 193ee07..0f696c2 100644
--- a/src/cmd/compile/internal/gc/ssa.go
+++ b/src/cmd/compile/internal/gc/ssa.go
@@ -3475,7 +3475,7 @@
 func (s *state) ifaceType(n *Node, v *ssa.Value) *ssa.Value {
 	byteptr := Ptrto(Types[TUINT8]) // type used in runtime prototypes for runtime type (*byte)
 
-	if isnilinter(n.Type) {
+	if n.Type.IsEmptyInterface() {
 		// Have *eface. The type is the first word in the struct.
 		return s.newValue1(ssa.OpITab, byteptr, v)
 	}
@@ -4189,7 +4189,7 @@
 	if n.Class == PAUTO && !n.Addrtaken {
 		// Split this interface up into two separate variables.
 		f := ".itab"
-		if isnilinter(n.Type) {
+		if n.Type.IsEmptyInterface() {
 			f = ".type"
 		}
 		c := e.namedAuto(n.Sym.Name+f, t)