Use v1::Gather in ONNX Importer (#4037)

src/ngraph/frontend/onnx_import/op/gather.hpp

@@ -20,7 +20,7 @@
 
 #include "core/node.hpp"
 #include "ngraph/node.hpp"
-#include "ngraph/op/gather.hpp"
+#include "ngraph/opsets/opset1.hpp"
 #include "utils/common.hpp"
 
 namespace ngraph
@@ -39,7 +39,10 @@ namespace ngraph
                     auto axis = node.get_attribute_value<int64_t>("axis", 0);
                     auto valid_axis = common::validate_axis(node, axis, data->get_shape().size());
 
-                    return {std::make_shared<ngraph::op::Gather>(data, indices, valid_axis)};
+                    return {std::make_shared<opset1::Gather>(
+                        data,
+                        indices,
+                        opset1::Constant::create(element::i64, Shape{}, {valid_axis}))};
                 }
 
             } // namespace set_1

src/ngraph/pass/opset0_downgrade.cpp

@@ -231,6 +231,27 @@ namespace
         return true;
     }
 
+    bool op_cast(shared_ptr<op::v1::Gather> node)
+    {
+        auto axis_node = as_type_ptr<op::Constant>(node->input_value(2).get_node_shared_ptr());
+
+        NGRAPH_CHECK(axis_node,
+                     "Unable to convert Gather:v1 to Gather:v0 if axis is not constant. Node: ",
+                     *node);
+
+        NGRAPH_CHECK(
+            axis_node->get_element_type() == element::i64,
+            "Unable to convert Gather:v1 to Gather:v0 with axis other type than int64. Node: ",
+            *node);
+
+        int64_t axis = axis_node->get_vector<int64_t>()[0];
+
+        auto replacement_node =
+            make_shared<op::v0::Gather>(node->input_value(0), node->input_value(1), axis);
+        replace_node(node, replacement_node);
+        return true;
+    }
+
     bool op_cast(shared_ptr<op::v1::GenerateMask> node)
     {
         NGRAPH_CHECK(node->input_value(1).get_node_shared_ptr()->is_constant());
@@ -707,7 +728,7 @@ namespace
         };
         return dispatch_map;
     }
-}
+} // namespace
 
 bool pass::Opset0Downgrade::run_on_node(shared_ptr<Node> node)
 {