auto merge of #6136 : jld/rust/simplifycfg-unrevert, r=thestinger

Also add the clearly marked test case that should have been there all along, and un-xfail the not-so-obvious doc test that was affected.

src/test/run-pass/enum-nullable-simplifycfg-misopt.rs

@@ -0,0 +1,24 @@
+// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+/*!
+ * This is a regression test for a bug in LLVM, fixed in upstream r179587,
+ * where the switch instructions generated for destructuring enums
+ * represented with nullable pointers could be misoptimized in some cases.
+ */
+
+enum List<X> { Nil, Cons(X, @List<X>) }
+pub fn main() {
+    match Cons(10, @Nil) {
+	Cons(10, _) => {}
+	Nil => {}
+	_ => fail!()
+    }
+}