Workaround #34427 by using memset of 0 on ARM to set the discriminant.

src/test/run-pass/issue-34427.rs

@@ -0,0 +1,26 @@
+// Copyright 2016 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.
+
+// Issue #34427: On ARM, the code in `foo` at one time was generating
+// a machine code instruction of the form: `str r0, [r0, rN]!` (for
+// some N), which is not legal because the source register and base
+// register cannot be identical in the preindexed form signalled by
+// the `!`.
+//
+// See LLVM bug: https://llvm.org/bugs/show_bug.cgi?id=28809
+
+#[inline(never)]
+fn foo(n: usize) -> Vec<Option<(*mut (), &'static ())>> {
+    (0..n).map(|_| None).collect()
+}
+
+fn main() {
+    let _ = (foo(10), foo(32));
+}