do not use executor for checking subgraph backend name

src/executor/graph_executor.cc

@@ -2061,25 +2061,26 @@ Executor *Executor::Bind(nnvm::Symbol symbol,
                          const std::vector<OpReqType> &grad_req_type,
                          const std::vector<NDArray> &aux_states,
                          Executor* shared_exec) {
-  auto exec = new exec::GraphExecutor(symbol);
+  // Verbosity level: If =1 logs the name of subgaph backend
+  //                  If >1 then additional details regarding subgraph backend is logged
   static int verbose = dmlc::GetEnv("MXNET_SUBGRAPH_VERBOSE", 1);
   std::vector<NDArray> tmp_in_args = in_args;
   std::vector<NDArray> tmp_arg_grad_store = arg_grad_store;
   std::vector<OpReqType> tmp_grad_req_type = grad_req_type;
   std::vector<NDArray> tmp_aux_states = aux_states;
 
-  if (!exec->subgraph_property().empty()) {
-    const auto& backend_name = exec->subgraph_property();
+  const auto& backend_name = dmlc::GetEnv("MXNET_SUBGRAPH_BACKEND", exec::GetDefaultSubgraphBackend());
+  if (!backend_name.empty()) {
     const auto& backend = op::SubgraphBackendRegistry::Get()->GetSubgraphBackend(backend_name);
     if (exec::SubgraphBackendCheck(backend, default_ctx, verbose)) {
       if (verbose) LOG(INFO) << "Subgraph backend " << backend_name << " is activated.";
+      // Subgraph cannot be recreated from unoptimized symbol
       symbol = exec::BuildSubgraph(symbol, backend, default_ctx, group2ctx, &tmp_in_args,
                                    &tmp_arg_grad_store, &tmp_grad_req_type, &tmp_aux_states,
                                    verbose);
-      // Subgraph cannot be recreated from unoptimized symbol
-      exec = new exec::GraphExecutor(symbol);
     }
   }
+  auto exec = new exec::GraphExecutor(symbol);
   exec->Init(symbol.Copy(), default_ctx, group2ctx, tmp_in_args, tmp_arg_grad_store,
              tmp_grad_req_type, tmp_aux_states, reinterpret_cast<Executor*>(shared_exec));
   return exec;