parse_gather_elements.cpp

#include <migraphx/onnx/op_parser.hpp>
#include <migraphx/ranges.hpp>
#include <migraphx/instruction.hpp>
#include <migraphx/make_op.hpp>

namespace migraphx {
inline namespace MIGRAPHX_INLINE_NS {
namespace onnx {

struct parse_gather_elements : op_parser<parse_gather_elements>
{
    std::vector<op_desc> operators() const { return {{"GatherElements"}}; }

    instruction_ref parse(const op_desc& /*opd*/,
                          const onnx_parser& parser,
                          onnx_parser::node_info info,
                          std::vector<instruction_ref> args) const
    {
        int axis = 0;
        if(contains(info.attributes, "axis"))
        {
            axis = parser.parse_value(info.attributes.at("axis")).at<int>();
        }

        // standardize input data and index
        auto arg_data = info.make_contiguous(args[0]);
        auto arg_ind  = info.make_contiguous(args[1]);

        auto data_s = arg_data->get_shape();
        auto ind_s  = arg_ind->get_shape();

        if(data_s.lens().size() != ind_s.lens().size())
        {
            MIGRAPHX_THROW("PARSE_GATHER_ELEMENTS: input data and index must have the same rank!");
        }

        int n_rank     = static_cast<int>(data_s.lens().size());
        int tuned_axis = (axis < 0) ? (axis + n_rank) : axis;

        auto axis_stride      = data_s.strides()[tuned_axis];
        int64_t data_elem_num = static_cast<int64_t>(data_s.elements());
        // reshape the input data as one dimension and used as input data
        // to the gather operator
        arg_data = info.add_instruction(make_op("reshape", {{"dims", {data_elem_num}}}), arg_data);

        std::size_t elem_num = ind_s.elements();
        std::vector<int> ind_index(elem_num);
        std::iota(ind_index.begin(), ind_index.end(), 0);

        // convert index in input indices to that in input data
        std::vector<int> data_indices(elem_num);
        std::transform(ind_index.begin(), ind_index.end(), data_indices.begin(), [&](auto i) {
            return data_s.index(ind_s.multi(i));
        });

        std::vector<int> vec_axis_ind(elem_num);
        std::transform(ind_index.begin(), ind_index.end(), vec_axis_ind.begin(), [&](auto i) {
            return ind_s.multi(i)[tuned_axis];
        });

        auto l_shape_idx =
            info.add_literal(literal(ind_s, data_indices.begin(), data_indices.end()));
        auto l_dim_idx = info.add_literal(literal(ind_s, vec_axis_ind.begin(), vec_axis_ind.end()));
        auto l_stride  = info.add_literal(literal{{ind_s.type(), {1}}, {axis_stride}});
        l_stride = info.add_instruction(make_op("multibroadcast", {{"output_lens", ind_s.lens()}}),
                                        l_stride);
        auto dim_diff = info.add_instruction(make_op("sub"), arg_ind, l_dim_idx);
        auto delta    = info.add_instruction(make_op("mul"), dim_diff, l_stride);
        auto ind      = info.add_instruction(make_op("add"), l_shape_idx, delta);

        auto op = make_op("gather", {{"axis", 0}});
        return info.add_instruction(op, arg_data, ind);
    }
};

} // namespace onnx
} // namespace MIGRAPHX_INLINE_NS
} // namespace migraphx