Add a mir-opt test

Author: varkor

src/test/mir-opt/uninhabited-enum.rs

@@ -0,0 +1,37 @@
+#![feature(never_type)]
+
+pub enum Void {}
+
+#[no_mangle]
+pub fn process_never(input: *const !) {
+   let _input = unsafe { &*input };
+}
+
+#[no_mangle]
+pub fn process_void(input: *const Void) {
+   let _input = unsafe { &*input };
+   // In the future, this should end with `unreachable`, but we currently only do
+   // unreachability analysis for `!`.
+}
+
+fn main() {}
+
+// END RUST SOURCE
+//
+// START rustc.process_never.SimplifyLocals.after.mir
+// bb0: {
+//     StorageLive(_2);
+//     _2 = &(*_1);
+//     StorageDead(_2);
+//     unreachable;
+// }
+// END rustc.process_never.SimplifyLocals.after.mir
+//
+// START rustc.process_void.SimplifyLocals.after.mir
+// bb0: {
+//     StorageLive(_2);
+//     _2 = &(*_1);
+//     StorageDead(_2);
+//     return;
+// }
+// END rustc.process_void.SimplifyLocals.after.mir