rustc: optimize out uninhabited types and variants.

src/test/ui/print_type_sizes/uninhabited.rs

@@ -0,0 +1,18 @@
+// 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.
+
+// compile-flags: -Z print-type-sizes
+
+#![feature(never_type)]
+
+pub fn main() {
+    let _x: Option<!> = None;
+    let _y: Result<u32, !> = Ok(42);
+}

src/test/ui/print_type_sizes/uninhabited.stdout

@@ -0,0 +1,5 @@
+print-type-size type: `std::result::Result<u32, !>`: 4 bytes, alignment: 4 bytes
+print-type-size     variant `Ok`: 4 bytes
+print-type-size         field `.0`: 4 bytes
+print-type-size type: `std::option::Option<!>`: 0 bytes, alignment: 1 bytes
+print-type-size     variant `None`: 0 bytes