lammps/lib/kokkos/algorithms/unit_tests/TestStdAlgorithmsScalarRedVsView.cpp

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#include <gtest/gtest.h>
#include <TestStdAlgorithmsHelperFunctors.hpp>
#include <std_algorithms/Kokkos_BeginEnd.hpp>
#include <std_algorithms/Kokkos_MinMaxElementOperations.hpp>

namespace KE = Kokkos::Experimental;

namespace Test {
namespace stdalgos {

template <class ViewType>
void fill_view(ViewType dest_view) {
  using value_type = typename ViewType::value_type;
  using exe_space  = typename ViewType::execution_space;
  using aux_view_t = Kokkos::View<value_type*, exe_space>;

  const std::size_t ext = dest_view.extent(0);
  aux_view_t aux_view("aux_view", ext);
  auto v_h = create_mirror_view(Kokkos::HostSpace(), aux_view);

  for (std::size_t i = 0; i < ext; ++i) {
    v_h(i) = (value_type)i;
  }
  v_h(ext / 2) = (value_type)-101;

  Kokkos::deep_copy(aux_view, v_h);
  CopyFunctor<aux_view_t, ViewType> F1(aux_view, dest_view);
  Kokkos::parallel_for("copy", dest_view.extent(0), F1);
}

template <class ViewType, class IndexType, class ReducerType>
struct MyFunctor {
  using red_value_type = typename ReducerType::value_type;

  ViewType m_view;
  ReducerType m_reducer;

  KOKKOS_FUNCTION
  void operator()(const IndexType i, red_value_type& red_value) const {
    m_reducer.join(red_value, red_value_type{m_view(i), i});
  }

  KOKKOS_FUNCTION
  MyFunctor(ViewType view, ReducerType reducer)
      : m_view(view), m_reducer(std::move(reducer)) {}
};

TEST(scalar_vs_view_red, use_scalar) {
  using exe_space   = Kokkos::DefaultExecutionSpace;
  using index_type  = int;
  using scalar_type = int;
  using view_type   = Kokkos::View<scalar_type*, exe_space>;

  const auto ext = 10001;
  view_type view("myview", ext);
  fill_view(view);

  using reducer_type    = ::Kokkos::MinLoc<scalar_type, index_type>;
  using red_result_type = typename reducer_type::value_type;
  using func_type       = MyFunctor<view_type, index_type, reducer_type>;
  red_result_type result;
  reducer_type reducer(result);
  Kokkos::parallel_reduce("MinLocReduce",
                          Kokkos::RangePolicy<exe_space>(exe_space(), 0, ext),
                          func_type(view, reducer), reducer);
  std::cout << " use_scalar = " << result.val << '\n';
}

template <class IteratorType, class ReducerType>
struct StdMyMinFunctor {
  using index_type     = typename IteratorType::difference_type;
  using red_value_type = typename ReducerType::value_type;

  IteratorType m_first;
  ReducerType m_reducer;

  KOKKOS_FUNCTION
  void operator()(const index_type i, red_value_type& red_value) const {
    m_reducer.join(red_value, red_value_type{m_first[i], i});
  }

  KOKKOS_FUNCTION
  StdMyMinFunctor(IteratorType first, ReducerType reducer)
      : m_first(std::move(first)), m_reducer(std::move(reducer)) {}
};

template <class ViewType, class ReducerType>
struct StdMyMinFunctor2 {
  using red_value_type = typename ReducerType::value_type;

  ViewType m_view;
  ReducerType m_reducer;

  KOKKOS_FUNCTION
  void operator()(const std::size_t i, red_value_type& red_value) const {
    m_reducer.join(red_value, red_value_type{m_view(i), i});
  }

  KOKKOS_FUNCTION
  StdMyMinFunctor2(ViewType viewIn, ReducerType reducer)
      : m_view(viewIn), m_reducer(std::move(reducer)) {}
};

template <class ExecutionSpace, class IteratorType>
IteratorType my_min_1(const ExecutionSpace& ex, IteratorType first,
                      IteratorType last) {
  using index_type = typename IteratorType::difference_type;
  using value_type = typename IteratorType::value_type;
  using reducer_type =
      Kokkos::MinFirstLoc<value_type, index_type, ExecutionSpace>;
  using result_view_type = typename reducer_type::result_view_type;
  using func_t           = StdMyMinFunctor<IteratorType, reducer_type>;

  result_view_type result("min_or_max_elem_impl_result");
  reducer_type reducer(result);
  const auto num_elements = Kokkos::Experimental::distance(first, last);
  ::Kokkos::parallel_reduce(
      "label", Kokkos::RangePolicy<ExecutionSpace>(ex, 0, num_elements),
      func_t(first, reducer), reducer);
  const auto result_h =
      ::Kokkos::create_mirror_view_and_copy(::Kokkos::HostSpace(), result);
  return first + result_h().loc;
}

template <class ExecutionSpace, class IteratorType>
IteratorType my_min_2(const ExecutionSpace& ex, IteratorType first,
                      IteratorType last) {
  using index_type   = typename IteratorType::difference_type;
  using value_type   = typename IteratorType::value_type;
  using reducer_type = Kokkos::MinFirstLoc<value_type, index_type>;
  using result_type  = typename reducer_type::value_type;
  using func_t       = StdMyMinFunctor<IteratorType, reducer_type>;

  result_type result;
  reducer_type reducer(result);
  const auto num_elements = Kokkos::Experimental::distance(first, last);
  ::Kokkos::parallel_reduce(
      "label", Kokkos::RangePolicy<ExecutionSpace>(ex, 0, num_elements),
      func_t(first, reducer), reducer);
  return first + result.loc;
}

template <class ExecutionSpace, class ViewType>
std::size_t my_min_3(const ExecutionSpace& ex, ViewType view) {
  using index_type   = std::size_t;
  using value_type   = typename ViewType::value_type;
  using reducer_type = Kokkos::MinFirstLoc<value_type, index_type>;
  using result_type  = typename reducer_type::value_type;
  using func_t       = StdMyMinFunctor2<ViewType, reducer_type>;

  result_type result;
  reducer_type reducer(result);
  const auto num_elements = view.extent(0);
  ::Kokkos::parallel_reduce(
      "label", Kokkos::RangePolicy<ExecutionSpace>(ex, 0, num_elements),
      func_t(view, reducer), reducer);
  return result.loc;
}

TEST(scalar_vs_view_red, my_min_it_use_result_view) {
  using exe_space = Kokkos::DefaultExecutionSpace;
  using view_type = Kokkos::View<int*, exe_space>;
  view_type view("myview", 10001);
  fill_view(view);

  auto rit = my_min_1(exe_space(), KE::cbegin(view), KE::cend(view));
  std::cout << " my_min_el = " << KE::distance(KE::cbegin(view), rit) << '\n';
}

TEST(scalar_vs_view_red, my_min_no_it_use_result_scalar) {
  using exe_space = Kokkos::DefaultExecutionSpace;
  using view_type = Kokkos::View<int*, exe_space>;
  view_type view("myview", 10001);
  fill_view(view);

  auto ind = my_min_3(exe_space(), view);
  std::cout << " my_min_el = " << ind << '\n';
}

TEST(scalar_vs_view_red, my_min_it_use_result_scalar) {
  using exe_space = Kokkos::DefaultExecutionSpace;
  using view_type = Kokkos::View<int*, exe_space>;
  view_type view("myview", 10001);
  fill_view(view);

  auto rit = my_min_2(exe_space(), KE::cbegin(view), KE::cend(view));
  std::cout << " my_min_el = " << KE::distance(KE::cbegin(view), rit) << '\n';
}

}  // namespace stdalgos
}  // namespace Test