add some debugging statements

src/librustc_mir/dataflow/impls/borrows.rs

@@ -66,10 +66,13 @@ fn precompute_borrows_out_of_scope<'a, 'tcx>(
     let mut visited = FxHashSet();
     visited.insert(location);
 
+    debug!("borrow {:?} starts at {:?}", borrow_index, location);
+
     while let Some(location) = stack.pop() {
         // If region does not contain a point at the location, then add to list and skip
         // successor locations.
         if !regioncx.region_contains_point(borrow_region, location) {
+            debug!("borrow {:?} gets killed at {:?}", borrow_index, location);
             borrows_out_of_scope_at_location
                 .entry(location)
                 .or_insert(vec![])