cmd/gc: don't recurse infinitely when a recursive type references itself more than once

Fixes #9432

Change-Id: I08c92481afa7c7fac890aa780efc1cb2fabad528
Reviewed-on: https://go-review.googlesource.com/2115
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/gc/align.c

@@ -137,6 +137,11 @@ dowidth(Type *t)
 		return;
 	}
 
+	// break infinite recursion if the broken recursive type
+	// is referenced again
+	if(t->broke && t->width == 0)
+		return;
+
 	// defer checkwidth calls until after we're done
 	defercalc++;
 

test/fixedbugs/issue9432.go

@@ -0,0 +1,15 @@
+// errorcheck
+
+// Copyright 2014 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.
+
+// gc used to recurse infinitely when dowidth is applied
+// to a broken recursive type again.
+// See golang.org/issue/9432.
+package p
+
+type foo struct { // GCCGO_ERROR "invalid recursive type"
+	bar  foo
+	blah foo
+} // ERROR "invalid recursive type foo"