message: Use a more compact indexing method
diff: @@ -552,15 +552,9 @@ CreateSimpleSelectAndScatter(poplar::Graph &graph,
  start_par[dim_count] = GetOverlapLayerNum(pos, overlap);
  end_par[dim_count] = start_par[dim_count] + 1;
  - // TODO - move this into poplar
  - std::vector<std::size_t> pos_plus_one(dim_count);
  - for (unsigned d=0; d<dim_count; d++) {
  - pos_plus_one[d] = pos[d] + 1;
  - }
  -
  poplar::Tensor w_in = operand.slice(start_in, end_in).flatten();
  poplar::Tensor w_par = partial.slice(start_par, end_par).flatten();
  - poplar::Tensor s = source.slice(pos, pos_plus_one).flatten();
  + poplar::Tensor s = source.index(pos);
  // Create the vertex
  auto v = graph.addVertex(select_cs, select_vertex_name,
  