cmd/gc: add missing case for OCOM in defaultlit()

Fixes #3765.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/6349064

src/cmd/gc/const.c

@@ -1012,12 +1012,13 @@ defaultlit(Node **np, Type *t)
 		}
 		n->type = t;
 		return;
+	case OCOM:
 	case ONOT:
 		defaultlit(&n->left, t);
 		n->type = n->left->type;
 		return;
 	default:
-		if(n->left == N) {
+		if(n->left == N || n->right == N) {
 			dump("defaultlit", n);
 			fatal("defaultlit");
 		}

test/fixedbugs/bug445.go

@@ -0,0 +1,14 @@
+// compile
+
+// Copyright 2012 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 3765
+
+package main
+
+func f(x uint) uint {
+	m := ^(1 << x)
+	return uint(m)
+}