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/*! \file
  \brief Epilogue for threadblock scoped GEMMs using Tensor Ops.

  This assumes the shared memory tile is in a permuted layout which avoids bank conflicts on loading.
  
  When the fragment is loaded into registers, it matches the row-major thread map assumed by
  the predicated tile iterator writing to global memory.

  The epilogue rearranges the result of a matrix product through shared memory to match canonical
  tensor layouts in global memory. Epilogues support conversion and reduction operations.
*/

#pragma once

#include "cutlass/array.h"
#include "cutlass/cutlass.h"
#include "cutlass/epilogue/threadblock/output_tile_thread_map.h"
#include "cutlass/transform/pitch_linear_thread_map.h"
#include "cutlass/layout/matrix.h"
#include "cutlass/matrix_shape.h"
#include "cutlass/numeric_types.h"
#include "cutlass/tensor_ref.h"

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

namespace cutlass {
namespace epilogue {
namespace threadblock {

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

/// Tile iterator used to load output tile from shared memory in epilogue.
///
/// Satisfies: ReadableTileIterator
///
template <typename ThreadMap_,  ///< Thread map (conept: PitchLinearThreadMap)
          typename Element_,    ///< Element data type
          int MaxAlignment = ThreadMap_::kElementsPerAccess *sizeof_bits<Element_>::value / 8>
class SharedLoadIteratorPitchLinear {
 public:
  using ThreadMap = ThreadMap_;
  using Element = Element_;

  using Layout = layout::RowMajor;
  using TensorRef = TensorRef<Element, Layout>;
  using ConstTensorRef = typename TensorRef::ConstTensorRef;

  using Index = typename Layout::Index;
  using LongIndex = typename Layout::LongIndex;
  using TensorCoord = MatrixCoord;

  static int const kElementsPerAccess = ThreadMap::kElementsPerAccess;

  static int const kMinAlignment =
      ThreadMap_::kElementsPerAccess * sizeof_bits<Element_>::value / 8;

  static int const kAlignment = (MaxAlignment < kMinAlignment ? MaxAlignment : kMinAlignment);

  static int const kThreads = ThreadMap::kThreads;

  /// Fragment object
  using Fragment = Array<Element, ThreadMap::Iterations::kCount * kElementsPerAccess>;

  /// Memory access size
  using AccessType = AlignedArray<Element, kElementsPerAccess, kAlignment>;

  /// Vector type used for SMEM loads
  using LoadType =
      AlignedArray<Element,
                   const_min(128 / sizeof_bits<Element>::value, ThreadMap::kElementsPerAccess),
                   const_min(16, kAlignment)>;

  static int const kLoadsPerAccess = AccessType::kElements / LoadType::kElements;

 private:
  //
  // Data members
  //

  /// Byte-level pointer
  uint8_t *byte_pointer_;

  /// Stride along adjacent rows
  int stride_;

  /// Base address offset
  Index base_smem_address_;

 public:
  //
  // Methods
  //

  /// Constructor
  CUTLASS_DEVICE
  SharedLoadIteratorPitchLinear(TensorRef ref, int thread_idx)
      : byte_pointer_(reinterpret_cast<uint8_t *>(ref.data())),
        stride_((ref.stride(0) * sizeof_bits<Element>::value) / 8),
        base_smem_address_(0) {
    TensorCoord thread_offset = ThreadMap::initial_offset(thread_idx);

    // Initialize pointer
    // thread_offset.row() is contiguous dim
    // thread_offset.column() is stride dim
    byte_pointer_ += thread_offset.row() * sizeof(AccessType) / kElementsPerAccess+
                     thread_offset.column() * stride_ ;
  }

  /// Adds a pointer offset in units of Element
  CUTLASS_HOST_DEVICE
  void add_pointer_offset(LongIndex pointer_offset) {
    byte_pointer_ += pointer_offset * sizeof_bits<Element>::value / 8;
  }

  CUTLASS_DEVICE
  void add_tile_offset(TensorCoord const &offset) {
    byte_pointer_ +=
        offset.row() * ThreadMap::StorageShape::kContiguous * sizeof(AccessType) / kElementsPerAccess +
        offset.column() * ThreadMap::StorageShape::kStrided * stride_;
  }

  /// Loads a fragment from memory
  CUTLASS_DEVICE
  void load_with_pointer_offset(Fragment &frag, Index pointer_offset) const {
    CUTLASS_PRAGMA_UNROLL
    for (int s = 0; s < ThreadMap::Iterations::kStrided; ++s) {
      CUTLASS_PRAGMA_UNROLL
      for (int c = 0; c < ThreadMap::Iterations::kContiguous; ++c) {
        uint8_t const *byte_pointer =
            byte_pointer_ + s * ThreadMap::Delta::kStrided * stride_ +
            c * ThreadMap::Delta::kContiguous * ThreadMap::kElementsPerAccess *
                sizeof_bits<Element>::value / 8 +
            pointer_offset * sizeof_bits<Element>::value / 8 + base_smem_address_;

        int frag_base_idx = s * ThreadMap::Iterations::kContiguous + c;

        LoadType *frag_ptr = reinterpret_cast<LoadType *>(&frag);

        LoadType const *memory_pointer = reinterpret_cast<LoadType const *>(byte_pointer);

        CUTLASS_PRAGMA_UNROLL
        for (int v = 0; v < kLoadsPerAccess; ++v) {
          frag_ptr[frag_base_idx * kLoadsPerAccess + v] = memory_pointer[v];
        }
      }
    }
  }

  /// Loads a fragment from memory
  CUTLASS_DEVICE
  void set_smem_base_address(Index address) { base_smem_address_ = address; }

  /// Loads a fragment
  CUTLASS_DEVICE
  void load(Fragment &frag) const { load_with_pointer_offset(frag, 0); }
};

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

}  // namespace threadblock
}  // namespace epilogue
}  // namespace cutlass

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