message: For debugging purposes, it can be useful to know which ops are considered non-pure / non-constant.
diff: @@ -1997,6 +1997,9 @@ void PureFunctionalVisitor(const SessionComputation& session_computation,
  default:
  LOG(FATAL) << "Unexpected request type: " << request.request().op_case();
  }
  + if (!*is_functional) {
  + VLOG(1) << "Non-functional: " << request.request().DebugString();
  + }
  visited->insert(handle.handle());
  }
  