Instrument statement_effect_on_borrows for the lhs = &place case.

Author: pnkfelix

src/librustc_mir/dataflow/impls/borrows.rs

@@ -179,8 +179,14 @@ impl<'a, 'gcx, 'tcx> BitDenotation for Borrows<'a, 'gcx, 'tcx> {
                     if let RegionKind::ReEmpty = region {
                         // If the borrowed value dies before the borrow is used, the region for
                         // the borrow can be empty. Don't track the borrow in that case.
+                        debug!("Borrows::statement_effect_on_borrows \
+                                location: {:?} stmt: {:?} has empty region, killing {:?}",
+                               location, stmt.kind, index);
                         sets.kill(&index);
                         return
+                    } else {
+                        debug!("Borrows::statement_effect_on_borrows location: {:?} stmt: {:?}",
+                               location, stmt.kind);
                     }
 
                     assert!(self.borrow_set.region_map.get(region).unwrap_or_else(|| {