Handle negative axis values in Concat op. (#2252)

python/pyngraph/onnx_import/onnx_import.cpp

@@ -16,11 +16,10 @@
 
 #include <istream>
 #include <memory>
-#include <string>
-#include <vector>
-
 #include <pybind11/pybind11.h>
 #include <pybind11/stl.h>
+#include <string>
+#include <vector>
 
 #include "ngraph/frontend/onnx_import/onnx.hpp"
 #include "ngraph/function.hpp"

src/ngraph/frontend/onnx_import/op/concat.cpp

@@ -14,8 +14,12 @@
 // limitations under the License.
 //*****************************************************************************
 
+#include <cstdint>
+
 #include "concat.hpp"
+#include "exceptions.hpp"
 #include "ngraph/op/concat.hpp"
+#include "utils/common.hpp"
 
 namespace ngraph
 {
@@ -28,9 +32,15 @@ namespace ngraph
                 NodeVector concat(const Node& node)
                 {
                     NodeVector inputs{node.get_ng_inputs()};
-                    auto axis = node.get_attribute_value<int64_t>("axis");
+                    std::int64_t axis = node.get_attribute_value<std::int64_t>("axis");
+
+                    size_t valid_axis =
+                        common::convert_negative_axis(axis, inputs.at(0)->get_shape().size());
+
+                    ASSERT_VALID_ARGUMENT(node, valid_axis >= 0)
+                        << "Incorrect value of axis attribute: " << axis;
 
-                    return {std::make_shared<ngraph::op::Concat>(inputs, axis)};
+                    return {std::make_shared<ngraph::op::Concat>(inputs, valid_axis)};
                 }
 
             } // namespace set_1

src/ngraph/frontend/onnx_import/utils/common.hpp

@@ -16,7 +16,7 @@
 
 #pragma once
 
-#include <cmath>       // std::floor
+#include <cmath>       // std::floor, std::min
 #include <cstddef>     // std::size_t
 #include <iterator>    // std::begin, std::end
 #include <memory>      // std::shared_ptr, std::make_shared
@@ -135,6 +135,29 @@ namespace ngraph
                 return node;
             }
 
+            /// \brief      Handle negative axis value.
+            ///
+            /// \param[in]  axis        The requested axis value.
+            /// \param[in]  tensor_dim  The corresponding tensor dimensionality.
+            ///
+            /// \tparam     T           Provided axis value type.
+            ///
+            /// \return     If negative axis, then return sum of tensor dimension and axis.
+            ///
+            template <typename T,
+                      typename std::enable_if<std::is_integral<T>::value, int>::type = 0>
+            std::int64_t convert_negative_axis(T axis, std::size_t tensor_dim)
+            {
+                if (axis >= 0)
+                {
+                    return std::min(axis, static_cast<T>(tensor_dim));
+                }
+                else
+                {
+                    return static_cast<std::int64_t>(tensor_dim) + axis;
+                }
+            }
+
         } // namespace  common
     }     // namespace onnx_import
 } // namespace ngraph