message: Fix up reduction to use the new poplibs API
diff: @@ -107,10 +107,10 @@ IsPoplibsPool(const HloInstruction* inst,
  window.dimensions(0).stride() != 1 ||
  window.dimensions(0).padding_low() != 0 ||
  window.dimensions(0).padding_high() != 0 ||
  - window.dimensions(3).size() != 1 ||
  - window.dimensions(3).stride() != 1 ||
  - window.dimensions(3).padding_low() != 0 ||
  - window.dimensions(3).padding_high() != 0) {
  + window.dimensions(1).size() != 1 ||
  + window.dimensions(1).stride() != 1 ||
  + window.dimensions(1).padding_low() != 0 ||
  + window.dimensions(1).padding_high() != 0) {
  return false;
  }
  @@ -419,20 +419,20 @@ CreatePoplibsWindowReduction(poplar::Graph &graph,
  const Window& window(pooling_inst->window());
  std::vector<std::size_t> kernel_shape = {
  - (std::size_t)window.dimensions(1).size(),
  - (std::size_t)window.dimensions(2).size()
  + (std::size_t)window.dimensions(2).size(),
  + (std::size_t)window.dimensions(3).size()
  };
  std::vector<unsigned> stride = {
  - (unsigned)window.dimensions(1).stride(),
  - (unsigned)window.dimensions(2).stride()
  + (unsigned)window.dimensions(2).stride(),
  + (unsigned)window.dimensions(3).stride()
  };
  std::vector<int> padding_lower = {
  - (int)window.dimensions(1).padding_low(),
  - (int)window.dimensions(2).padding_low()
  + (int)window.dimensions(2).padding_low(),
  + (int)window.dimensions(3).padding_low()
  };
  std::vector<int> padding_upper = {
  - (int)window.dimensions(1).padding_high(),
  - (int)window.dimensions(2).padding_high()
  + (int)window.dimensions(2).padding_high(),
  + (int)window.dimensions(3).padding_high()
  };
  out = popnn::pooling::pool(graph, reduction_type,
  