Add regression test for #20582. Fixes #20582.

Author: nikomatsakis

src/test/run-pass/associated-types-region-erasure-issue-20582.rs

@@ -0,0 +1,27 @@
+// Copyright 2015 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.
+
+// Regression test for #20582. This test caused an ICE related to
+// inconsistent region erasure in trans.
+
+struct Foo<'a> {
+    buf: &'a[u8]
+}
+
+impl<'a> Iterator for Foo<'a> {
+    type Item = &'a[u8];
+
+    fn next(&mut self) -> Option<<Self as Iterator>::Item> {
+        Some(self.buf)
+    }
+}
+
+fn main() {
+}