cmd/compile: fix infinite recursion in isdirectiface

Fixes #22904.

Change-Id: Id504504eda7275c10d3c665add8b7ccd23f65820
Reviewed-on: https://go-review.googlesource.com/80301
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

@@ -2022,6 +2022,10 @@ func checknil(x *Node, init *Nodes) {
 // Can this type be stored directly in an interface word?
 // Yes, if the representation is a single pointer.
 func isdirectiface(t *types.Type) bool {
+	if t.Broke() {
+		return false
+	}
+
 	switch t.Etype {
 	case TPTR32,
 		TPTR64,

test/fixedbugs/issue22904.go

@@ -0,0 +1,19 @@
+// errorcheck
+
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Issue 22904: Make sure the compiler emits a proper error message about
+// invalid recursive types rather than crashing.
+
+package p
+
+type a struct{ b }
+type b struct{ a } // ERROR "invalid recursive type"
+
+var x interface{}
+
+func f() {
+	x = a{}
+}