Tpetra_Details_MatrixApplyHelper.hpp

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#ifndef TPETRA_MATRIX_APPLY_HELPER_HPP
#define TPETRA_MATRIX_APPLY_HELPER_HPP

#include "Kokkos_Core.hpp"
#include "KokkosSparse_spmv_handle.hpp"

#if KOKKOSKERNELS_VERSION < 40299
#error "Tpetra::Details::MatrixApplyHelper can only be included with KokkosKernels 4.3+"
#endif

namespace Tpetra {
namespace Details {

template<typename LocalMatrix, typename IntLocalMatrix, typename MultiVectorLocalView>
struct MatrixApplyHelper
{
  using Rowptrs = typename LocalMatrix::row_map_type;
  using IntRowptrs = typename IntLocalMatrix::row_map_type;
  using XVectorType = typename MultiVectorLocalView::const_type;
  using YVectorType = MultiVectorLocalView;
  using SPMVHandle = KokkosSparse::SPMVHandle<typename LocalMatrix::device_type, LocalMatrix, XVectorType, YVectorType>;
  using SPMVHandleInt = KokkosSparse::SPMVHandle<typename LocalMatrix::device_type, IntLocalMatrix, XVectorType, YVectorType>;

  MatrixApplyHelper(size_t nnz_, const typename LocalMatrix::row_map_type& rowptrs, KokkosSparse::SPMVAlgorithm algo = KokkosSparse::SPMV_DEFAULT)
    : nnz(nnz_), handle(algo), handle_int(algo)
  {
    if(shouldUseIntRowptrs())
      fillRowptrsInt(rowptrs);
    // otherwise, leave rowptrs_int empty
  }

  bool shouldUseIntRowptrs() const
  {
    // Use int-valued rowptrs if:
    // - number of entries doesn't overflow int
    // - LocalMatrix's rowptrs is not already int-typed
    return nnz <= size_t(INT_MAX) && !std::is_same_v<int, typename Rowptrs::non_const_value_type>;
  }

  // Given the local matrix, return a version with int-typed rowptrs
  IntLocalMatrix getIntRowptrMatrix(const LocalMatrix& A)
  {
    if constexpr(KokkosSparse::is_crs_matrix_v<LocalMatrix>)
    {
      return IntLocalMatrix("", A.numRows(), A.numCols(), A.nnz(),
          A.values, rowptrs_int, A.graph.entries);
    }
    else
    {
      return IntLocalMatrix("", A.numRows(), A.numCols(), A.nnz(),
          A.values, rowptrs_int, A.graph.entries, A.blockDim());
    }
  }

  void fillRowptrsInt(const Rowptrs& rowptrs)
  {
    // Populate rowptrs_int as a deep copy of rowptrs, converted to int.
    // This needs to be in its own public function because KOKKOS_LAMBDA cannot be used inside constructor or protected/private
    typename IntRowptrs::non_const_type rowptrs_temp(
        Kokkos::view_alloc(Kokkos::WithoutInitializing, "rowptrs_int"), rowptrs.extent(0));
    Kokkos::parallel_for(Kokkos::RangePolicy<typename LocalMatrix::execution_space>(0, rowptrs.extent(0)),
      KOKKOS_LAMBDA(int i)
      {
        rowptrs_temp(i) = int(rowptrs(i));
      });
    rowptrs_int = rowptrs_temp;
  }

  size_t nnz;
  // SPMVHandles are lazily initialized by actual spmv calls.
  // We declare both here because we don't know until runtime (based on nnz) which should be used.
  SPMVHandle handle;
  SPMVHandleInt handle_int;
  IntRowptrs rowptrs_int;
};
}
}

#endif // TPETRA_MATRIX_APPLY_HELPER_HPP