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

#pragma once

#include "cutlass/cutlass.h"
#include "cutlass/gemm/dispatch_policy.hpp"
#include "cutlass/epilogue/collective/detail.hpp"

#include "cute/tensor.hpp"
#include "cute/numeric/numeric_types.hpp"
#include "cutlass/trace.h"

#include "cutlass/cuda_host_adapter.hpp"
/////////////////////////////////////////////////////////////////////////////////////////////////

namespace cutlass {
namespace epilogue {
namespace collective {

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

// Applies an element wise operation to all elements within the fragment
// and writes them out to destination storage.
template <
  class ElementC_,
  class StrideC_,
  class StrideD_,
  class ThreadEpilogueOp_,
  class EpilogueSchedule_
>
class DefaultEpilogueArray {
public:
  //
  // Type Aliases
  //
  using EpilogueSchedule = EpilogueSchedule_;
  using DispatchPolicy = EpilogueSchedule_;
  
  // 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 = ElementC_;
  using StrideC = StrideC_;
  using InternalStrideC = cute::remove_pointer_t<StrideC>;
  using ElementD = typename ThreadEpilogueOp::ElementD;
  using StrideD = StrideD_;
  using InternalStrideD = cute::remove_pointer_t<StrideD>;

  using GmemElementC = cute::conditional_t<cute::is_void_v<ElementC>, ElementD, ElementC>; // prevents void ref breakages

  using GmemTiledCopyC = void;
  using GmemTiledCopyD = void;

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

  static_assert(cute::is_same_v<EpilogueSchedule, PtrArrayNoSmemWarpSpecialized> || cute::is_same_v<EpilogueSchedule, PtrArrayDefault> || cute::is_same_v<EpilogueSchedule, PtrArrayNoSmemWarpSpecializedTransposed>, "Incompatible epilogue schedule.");
  static_assert(rank(InternalStrideC{}) == 3, "StrideCD must be rank-3: [M, N, L]");
  static_assert(rank(InternalStrideD{}) == 3, "StrideCD must be rank-3: [M, N, L]");

  struct SharedStorage { };

  using TensorMapStorage = SharedStorage;

  // Host side epilogue arguments
  struct Arguments {
    typename ThreadEpilogueOp::Params thread{};
    ElementC const** ptr_C = nullptr;
    StrideC dC{};
    ElementD** ptr_D = nullptr;
    StrideD dD{};
  };

  // Device side epilogue params
  using Params = Arguments;

  //
  // Methods
  //

  template <class ProblemShape>
  static constexpr Params
  to_underlying_arguments(
      ProblemShape const&,
      Arguments const& args,
      [[maybe_unused]] void* workspace) {
    return args;
  }

  template <class ProblemShape>
  static size_t
  get_workspace_size(ProblemShape const& problem_shape, Arguments const& args, int sm_count) {
    return 0;
  }

  template <class ProblemShape>
  static cutlass::Status
  initialize_workspace(ProblemShape const& problem_shape, Arguments const& args, void* workspace, cudaStream_t stream,
    CudaHostAdapter* cuda_adapter = nullptr) {
    return cutlass::Status::kSuccess;
  }

  template<class ProblemShape>
  static bool
  can_implement(
      [[maybe_unused]] ProblemShape const& problem_shape,
      [[maybe_unused]] Arguments const& args) {
    return true;
  }

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

  CUTLASS_DEVICE
  bool
  is_source_needed() {
    // For Ptr-Array or Grouped Gemm we cannot determine if source is needed based on first beta.
    return true;
  }

  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,
      [[maybe_unused]] ResidueMNK,
      int thread_idx,
      [[maybe_unused]] char*)
  {
    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");

    // 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);
    // Batches are managed by using appropriate pointers to C and D matrices
    const int32_t mock_L = 1;
    const int32_t mock_l_coord = 0;
    // Slice to get the tile this CTA is responsible for
    auto [m_coord, n_coord, k_coord, l_coord] = blk_coord_mnkl;

    // If scalar alpha/beta are provided, i.e., same alpha/beta applies to all batches/groups.
    // If pointers to alpha/beta are provided, i.e., alpha/beta can differ between batches/groups,
    // we get the correct alpha/beta values for the current batch/group using group index.
    ThreadEpilogueOp epilogue_op = ThreadEpilogueOp(params.thread, l_coord);

    if (epilogue_op.is_source_needed() && params.dC == nullptr) {
      // Beta value is non-zero while pointer to C is a nullptr
      assert(0);
    }

    auto [stride_c, stride_d] = [&, l = l_coord]() {
      if constexpr (!cute::is_same_v<InternalStrideC, StrideC>) {
        // If grouped gemm
        if (epilogue_op.is_source_needed()) {
            return make_tuple(
                detail::get_epilogue_stride<EpilogueSchedule>(params.dC[l]),
                detail::get_epilogue_stride<EpilogueSchedule>(params.dD[l])
            );
        } 
        else {
          return make_tuple(
              InternalStrideC{}, 
              detail::get_epilogue_stride<EpilogueSchedule>(params.dD[l])
          );
        }
      } 
      else {
        return make_tuple(
            detail::get_epilogue_stride<EpilogueSchedule>(params.dC),
            detail::get_epilogue_stride<EpilogueSchedule>(params.dD)
        );
      }
    }();
    
    // Represent the full output tensor
    ElementC const* ptr_C_l = nullptr;
    if (epilogue_op.is_source_needed()) {
      ptr_C_l = params.ptr_C[l_coord];
    }
    Tensor mC_mnl = make_tensor(make_gmem_ptr<GmemElementC>(ptr_C_l), make_shape(M,N,mock_L), stride_c);     // (m,n,l)
    Tensor mD_mnl = make_tensor(make_gmem_ptr(params.ptr_D[l_coord]), make_shape(M,N,mock_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)

    Tensor gC = gC_mnl(_,_,m_coord,n_coord, mock_l_coord);                                             // (BLK_M,BLK_N)
    Tensor gD = gD_mnl(_,_,m_coord,n_coord, mock_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.");

    // Absolute coordinate tensors (dynamic)
    Tensor mD_crd = make_identity_tensor(make_shape(M,N));                                                     // (M,N)
    Tensor cD_mn = local_tile(mD_crd, take<0,2>(blk_shape_MNK), make_coord(m_coord, n_coord));         // (BLK_M,BLK_N)
    Tensor tCcD = thr_mma.partition_C(cD_mn);                                                      // (VEC,THR_M,THR_N)

    // 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_shape(M,N))) {
          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_shape(M,N))) {
          tCgD(i) = epilogue_op(accumulators(i));
        }
      }
    }
  }

private:
  Params params;
};

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

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

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