Fix tests for MIR loop lowering

Fixes the hash test to recognize that MirValidated can change when changing
around labels, and add a new test that makes sure we're lowering loop statements
correctly.

src/test/incremental/hashes/loop_expressions.rs

@@ -179,7 +179,7 @@ pub fn change_continue_label() {
 }
 
 #[cfg(not(cfail1))]
-#[rustc_clean(cfg="cfail2", except="HirBody, TypeckTables")]
+#[rustc_clean(cfg="cfail2", except="HirBody, MirValidated, TypeckTables")]
 #[rustc_clean(cfg="cfail3")]
 pub fn change_continue_label() {
     let mut _x = 0;

src/test/mir-opt/loop_test.rs

@@ -0,0 +1,49 @@
+// Copyright 2018 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 identify_regions -Z emit-end-regions
+
+// Tests to make sure we correctly generate falseUnwind edges in loops
+
+fn main() {
+    // Exit early at runtime. Since only care about the generated MIR
+    // and not the runtime behavior (which is exercised by other tests)
+    // we just bail early. Without this the test just loops infinitely.
+    if true {
+        return;
+    }
+    loop {
+        let x = 1;
+        continue;
+    }
+}
+
+// END RUST SOURCE
+// START rustc.main.SimplifyCfg-qualify-consts.after.mir
+//    ...
+//    bb1: { // The cleanup block
+//        resume;
+//    }
+//    ...
+//    bb3: { // Entry into the loop
+//        _1 = ();
+//        goto -> bb4;
+//    }
+//    bb4: { // The loop_block
+//        falseUnwind -> [real: bb5, cleanup: bb1];
+//    }
+//    bb5: { // The loop body (body_block)
+//        StorageLive(_5);
+//        _5 = const 1i32;
+//        StorageDead(_5);
+//        goto -> bb4;
+//    }
+//    ...
+// END rustc.main.SimplifyCfg-qualify-consts.after.mir