Add a test for enum discriminant range overflow.

It causes an LLVM assertion for every host/target word-size combination
on incoming at the time of this writing.

src/librustc/middle/trans/adt.rs

@@ -139,7 +139,6 @@ fn generic_fields_of(cx: @CrateContext, r: &Repr, sizing: bool)
 fn load_discr(bcx: block, scrutinee: ValueRef, min: int, max: int)
     -> ValueRef {
     let ptr = GEPi(bcx, scrutinee, [0, 0]);
-    // XXX: write tests for the edge cases here
     if max + 1 == min {
         // i.e., if the range is everything.  The lo==hi case would be
         // rejected by the LLVM verifier (it would mean either an

src/test/run-pass/enum-discrim-range-overflow.rs

@@ -0,0 +1,31 @@
+// 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.
+
+pub enum E64 {
+	H64 = 0x7FFF_FFFF_FFFF_FFFF,
+	L64 = 0x8000_0000_0000_0000
+}
+pub enum E32 {
+	H32 = 0x7FFF_FFFF,
+	L32 = 0x8000_0000
+}
+
+pub fn f(e64: E64, e32: E32) -> (bool,bool) {
+	(match e64 {
+		H64 => true,
+		L64 => false
+	},
+	 match e32 {
+		H32 => true,
+		L32 => false
+	})
+}
+
+pub fn main() { }