Auto merge of #38855 - Mark-Simulacrum:immediate-fix, r=eddyb

Fix ICE on i686 when calling immediate() on OperandValue::Ref in return

Fixes #38727, and adds a test case.

r? @eddyb

src/test/run-pass/issue-38727.rs

@@ -0,0 +1,21 @@
+// Copyright 2017 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.
+
+#[repr(u64)]
+enum A {
+    A = 0u64,
+    B = !0u64,
+}
+
+fn cmp() -> A {
+    A::B
+}
+
+fn main() {}