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/*! \file
  \brief Functor performing elementwise operations used by epilogues.
*/

#pragma once

#include "cutlass/cutlass.h"

#include "cute/tensor.hpp"
#include "cute/numeric/int.hpp"

/////////////////////////////////////////////////////////////////////////////////////////////////

namespace cutlass {
namespace epilogue {
namespace collective {

/////////////////////////////////////////////////////////////////////////////////////////////////

using namespace cute;

/////////////////////////////////////////////////////////////////////////////////////////////////

/// Applies an element wise operation to all elements within the fragment
/// and writes them out to destination storage.
template <
  class StrideC_,
  class StrideD_,
  class ThreadEpilogueOp_
>
class DefaultTransposedEpilogue {

public:
  //
  // Type Aliases
  //
  // derived types of output thread level operator
  using ThreadEpilogueOp = ThreadEpilogueOp_;
  using ElementOutput = typename ThreadEpilogueOp::ElementOutput;
  using ElementAccumulator = typename ThreadEpilogueOp::ElementAccumulator;
  using ElementCompute = typename ThreadEpilogueOp::ElementCompute;
  using ElementScalar = ElementCompute;
  using ElementC = typename ThreadEpilogueOp::ElementC;
  using StrideC = StrideC_;
  using ElementD = typename ThreadEpilogueOp::ElementD;
  using StrideD = StrideD_;

  static const int kOutputAlignment = ThreadEpilogueOp::kCount;
  using AlignmentType = typename cute::uint_bit<sizeof_bits<ElementOutput>::value * kOutputAlignment>::type;

  static_assert(rank(StrideC{}) == 3, "StrideCD must be rank-3: [M, N, L]");
  static_assert(rank(StrideD{}) == 3, "StrideCD must be rank-3: [M, N, L]");

  struct SharedStorage { };

  // Params of epilogue::collective contain the epilogue::thread params
  struct Params {
    ElementC const* ptr_C = nullptr;
    StrideC dC{};
    ElementD* ptr_D = nullptr;
    StrideD dD{};
    typename ThreadEpilogueOp::Params thread_params{};
  };

  //
  // Methods
  //

  template <class Args>
  static constexpr Params
  to_underlying_arguments(Args const& args, void* workspace) {
    (void) workspace;
    return {args.epilogue_params};
  }

  CUTLASS_HOST_DEVICE
  DefaultTransposedEpilogue(Params const& params_) : params(params_) { }

  template<
    class ProblemShapeMNKL,
    class BlockShapeMNK,
    class BlockCoordMNKL,
    class FrgEngine, class FrgLayout,
    class TiledMma,
    class ResidueMNK
  >
  CUTLASS_HOST_DEVICE void
  operator()(
      ProblemShapeMNKL problem_shape_mnkl,
      BlockShapeMNK blk_shape_MNK,
      BlockCoordMNKL blk_coord_mnkl,
      cute::Tensor<FrgEngine, FrgLayout> const& accumulators,
      TiledMma tiled_mma,
      ResidueMNK residue_mnk,
      int thread_idx,
      char* smem_buf)
  {
    using namespace cute;
    using X = Underscore;

    static_assert(rank(ProblemShapeMNKL{}) == 4, "ProblemShapeMNKL must be rank 4");
    static_assert(is_static<BlockShapeMNK>::value, "ThreadBlock tile shape must be static");
    static_assert(rank(BlockShapeMNK{}) == 3, "BlockShapeMNK must be rank 3");
    static_assert(rank(BlockCoordMNKL{}) == 4, "BlockCoordMNKL must be rank 3");

    (void) smem_buf;
    ThreadEpilogueOp epilogue_op{params.thread_params};

    // Separate out problem shape for convenience
    auto M = get<0>(problem_shape_mnkl);
    auto N = get<1>(problem_shape_mnkl);
    auto L = get<3>(problem_shape_mnkl);

    // Tranpose stride C/D.
    auto stride_c = make_stride(get<1>(params.dC), get<0>(params.dC), get<2>(params.dC));
    auto stride_d = make_stride(get<1>(params.dD), get<0>(params.dD), get<2>(params.dD));

    // Represent the full output tensor
    Tensor mC_mnl = make_tensor(make_gmem_ptr(params.ptr_C), make_shape(M,N,L), stride_c);                  // (m,n,l)
    Tensor mD_mnl = make_tensor(make_gmem_ptr(params.ptr_D), make_shape(M,N,L), stride_d);                  // (m,n,l)
    Tensor gC_mnl = local_tile(mC_mnl, blk_shape_MNK, make_coord(_,_,_), Step<_1,_1, X>{});      // (BLK_M,BLK_N,m,n,l)
    Tensor gD_mnl = local_tile(mD_mnl, blk_shape_MNK, make_coord(_,_,_), Step<_1,_1, X>{});      // (BLK_M,BLK_N,m,n,l)

    // Slice to get the tile this CTA is responsible for
    auto [m_coord, n_coord, k_coord, l_coord] = blk_coord_mnkl;
    Tensor gC = gC_mnl(_,_,m_coord,n_coord,l_coord);                                                   // (BLK_M,BLK_N)
    Tensor gD = gD_mnl(_,_,m_coord,n_coord,l_coord);                                                   // (BLK_M,BLK_N)

    // Partition source and destination tiles to match the accumulator partitioning
    auto thr_mma = tiled_mma.get_thread_slice(thread_idx);
    Tensor tCgD = thr_mma.partition_C(gD);                                                         // (VEC,THR_M,THR_N)
    Tensor tCgC = thr_mma.partition_C(gC);                                                         // (VEC,THR_M,THR_N)

    static_assert(is_static<FrgLayout>::value, "Accumulator layout must be static");
    CUTE_STATIC_ASSERT_V(size(tCgC) == size(tCgD),
        "Source and destination must have the same number of elements.");
    CUTE_STATIC_ASSERT_V(size(tCgD) == size(accumulators),
        "Accumulator count must have the same destination element count.");

    auto cD   = make_identity_tensor(make_shape(unwrap(shape<0>(gD)), unwrap(shape<1>(gD))));
    Tensor tCcD = thr_mma.partition_C(cD);

    // source is needed
    if (epilogue_op.is_source_needed()) {
      CUTLASS_PRAGMA_UNROLL
      for (int i = 0; i < size(accumulators); ++i) {
        if (elem_less(tCcD(i), make_coord(get<0>(residue_mnk), get<1>(residue_mnk)))) {
          tCgD(i) = epilogue_op(accumulators(i), tCgC(i));
        }
      }
    }
    // source is not needed, avoid load
    else {
      CUTLASS_PRAGMA_UNROLL
      for (int i = 0; i < size(accumulators); ++i) {
        if (elem_less(tCcD(i), make_coord(get<0>(residue_mnk), get<1>(residue_mnk)))) {
          tCgD(i) = epilogue_op(accumulators(i));
        }
      }
    }
  }

private:
  Params params;
};

/////////////////////////////////////////////////////////////////////////////////////////////////

} // namespace collective
} // namespace epilogue
} // namespace cutlass

/////////////////////////////////////////////////////////////////////////////////////////////////