allow missing FCorrectLayout (#457)

* allow missing FCorrectLayout

* misunderstood OpMap[], fix

nnvm/src/pass/correct_layout.cc

@@ -28,11 +28,11 @@ nnvm::NodePtr CreateLayoutTransformNode(const Layout& src,
 using LayoutAttrDict = std::unordered_map<const Node*, std::vector<Layout> >;
 
 /*!
- * \brief A simple layout infer pass that will
+ * \brief A simple layout infer & correct pass that will
  *        insert layout transform nodes automatically.
  */
 nnvm::Graph CorrectLayout(nnvm::Graph src) {
-  static auto& op_infer_layout =
+  static auto& op_correct_layout =
     nnvm::Op::GetAttr<FCorrectLayout>("FCorrectLayout");
 
   const IndexedGraph& idx = src.indexed_graph();
@@ -91,14 +91,13 @@ nnvm::Graph CorrectLayout(nnvm::Graph src) {
       }
     }
 
-    const auto& flayout = op_infer_layout[new_node->op()];
-    CHECK(flayout != nullptr) << "Attribute FCorrectLayout"
-                              << " is not registered by op " << inode.source->op()->name
-                              << " we are not able to complete layout transform.";
+    if (op_correct_layout.count(new_node->op())) {
+      const auto &flayout = op_correct_layout[new_node->op()];
       CHECK(flayout(new_node->attrs, &request_ilayouts, &last_request_ilayouts, &produce_olayouts))
         << "Layout infer fail";
       CHECK_EQ(request_ilayouts.size(), num_inputs);
       CHECK_EQ(produce_olayouts.size(), num_outputs);
+    }
 
     // update new layouts
     new_layouts[new_node.get()] = std::move(produce_olayouts);