mir: don't attempt to promote Unpromotable constant temps.

src/test/run-pass/issue-33537.rs

@@ -0,0 +1,24 @@
+// 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.
+
+#![feature(const_fn)]
+
+const fn foo() -> *const i8 {
+    b"foo" as *const _ as *const i8
+}
+
+const fn bar() -> i32 {
+    *&{(1, 2, 3).1}
+}
+
+fn main() {
+    assert_eq!(foo(), b"foo" as *const _ as *const i8);
+    assert_eq!(bar(), 2);
+}