always build MIR

src/librustc_mir/dump.rs

@@ -62,7 +62,7 @@ fn visit_mir<OP>(&self, attributes: &'tcx [ast::Attribute], mut walk_op: OP)
             }
         }
 
-        let always_build_mir = self.tcx.sess.opts.always_build_mir;
+        let always_build_mir = true;
         if !built_mir && always_build_mir {
             let mut closure_dump = InnerDump { tcx: self.tcx, attr: None };
             walk_op(&mut closure_dump);