New trans codepath that builds fn body from MIR instead.

src/test/run-pass/mir_trans_spike1.rs

@@ -0,0 +1,24 @@
+// Copyright 2012 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.
+
+// A simple spike test for MIR version of trans.
+
+#![feature(rustc_attrs)]
+
+#[rustc_mir]
+fn sum(x: i32, y: i32) -> i32 {
+    x + y
+}
+
+fn main() {
+    let x = sum(22, 44);
+    assert_eq!(x, 66);
+    println!("sum()={:?}", x);
+}