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

  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/cutlass.h"
#include "cutlass/numeric_types.h"
#include "cutlass/array.h"
#include "cutlass/layout/matrix.h"
#include "cutlass/layout/tensor.h"
#include "cutlass/matrix_shape.h"
#include "cutlass/tensor_ref.h"
#include "cutlass/transform/pitch_linear_thread_map.h"
#include "cutlass/epilogue/threadblock/output_tile_thread_map.h"
#include "cutlass/arch/arch.h"
#include "cutlass/arch/memory.h"
#include "cutlass/conv/conv2d_problem_size.h"
#include "cutlass/epilogue/threadblock/predicated_tile_iterator_params.h"

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

namespace cutlass {

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

namespace epilogue {
namespace threadblock {

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

/// Tile iterator used to load and store output tile from global memory in epilogue.
///
/// Satisfies: ReadableTileIterator | PredicatedTileIterator | ForwardTileIterator
///
template <
  typename ThreadMap_,       ///< Thread map (conept: OutputTileThreadMap)
  typename Element_          ///< Element data type
>
class PredicatedTileIteratorStridedDgrad {
public:
  using ThreadMap = ThreadMap_;
  using Shape = typename ThreadMap::Shape;

  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 kThreads = ThreadMap::kThreads;
  static int const kIterations = ThreadMap::Count::kTile;

  static_assert( ThreadMap::Iterations::kRow > 0,"ThreadMap::Iterations::kRow must be > 0");
  static_assert( ThreadMap::Iterations::kGroup > 0,"ThreadMap::Iterations::kGroup must be > 0");
  static_assert( ThreadMap::Iterations::kCluster > 0,"ThreadMap::Iterations::kCluster must be > 0");
  static_assert( ThreadMap::Iterations::kColumn > 0,"ThreadMap::Iterations::kColumn must be > 0");

  /// Fragment object
  using Fragment = Array<
    Element, 
    ThreadMap::Iterations::kColumn * 
    ThreadMap::Iterations::kRow * 
    ThreadMap::Iterations::kGroup * 
    ThreadMap::Iterations::kCluster * ThreadMap::kElementsPerAccess>;

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

  //
  // Parameters struct
  //

  /// Uses a non-template class
  struct Params : PredicatedTileIteratorParams {

    /// Convolution problem size
    cutlass::conv::Conv2dProblemSize problem_size;
    int tiled_rows_per_filter;

    CUTLASS_HOST_DEVICE
    Params() { }

    CUTLASS_HOST_DEVICE
    Params(Layout const &layout, cutlass::conv::Conv2dProblemSize problem_size_, int threadblock_row): 
      problem_size(problem_size_), 
      PredicatedTileIteratorParams(
        layout.stride(0) * int(sizeof(AccessType)) / kElementsPerAccess,
        make_OutputTileThreadMapDesc<ThreadMap>()
      ) 
    {
  
      int tile_m_per_filter = strided_dgrad_tile_m_per_filter(problem_size, threadblock_row);

      tiled_rows_per_filter = tile_m_per_filter * threadblock_row;
    }
  };

  /// Mask object
  struct Mask {

    static int const kCount = ThreadMap::Iterations::kColumn;

    /// Predicate state
    bool predicates[kCount];

    //
    // Mask
    //
    CUTLASS_HOST_DEVICE
    Mask() {
      enable();
    }

    ///< Efficiently disables all accesses guarded by mask
    CUTLASS_HOST_DEVICE void clear() {
      CUTLASS_PRAGMA_UNROLL
      for (int i = 0; i < kCount; ++i) {
        predicates[i] = false;
      }
    }

    ///< CUTLASS_HOST_DEVICE enables all accesses guarded by mask
    CUTLASS_DEVICE void enable() {
      CUTLASS_PRAGMA_UNROLL
      for (int i = 0; i < kCount; ++i) {
        predicates[i] = true;
      }
    }
  };

private:

  //
  // Data members
  //

  /// Parameters structure containing reference and precomputed state.
  Params params_;

  /// Byte-level pointer
  uint8_t *byte_pointer_;

  /// Array of boolean values to contain steady-state predicates
  Mask mask_;

  /// Extent of the matrix tile in rows
  Index extent_row_;

  /// Starting Dx h and w dimenstion for strided dgrad mapping
  int start_h_, start_w_;

  /// Effective Dy P and Q dimenstions for strided dgrad mapping
  int p_, q_;

  /// A thread's starting row position (assuming steady-state predicates have been computed)
  Index thread_start_row_;

  /// A thread's starting column position (assuming steady-state predicates have been computed)
  Index thread_start_column_;

  /// Internal state counter
  int state_[3];
 
  //
  // Static asserts about internal strides
  //

  static_assert(sizeof(extent_row_) == 4, "Expected 32b extents");
  static_assert(sizeof(thread_start_row_) == 4, "Expected 32b extents");
  static_assert(sizeof(PredicatedTileIteratorParams::stride) == 8, "Expected 64b strides");

private:

  //
  // Methods
  //

public:

  //
  // Methods
  //

  /// Constructor
  CUTLASS_DEVICE
  PredicatedTileIteratorStridedDgrad(
    Params const & params,
    Element *pointer,
    TensorCoord extent,
    int thread_idx,
    FastDivmod const &stride_h_divmod, FastDivmod const &stride_w_divmod,
    int start_r, int start_s,
    TensorCoord threadblock_offset = TensorCoord()
  ): 
    params_(params)
  {

    TensorCoord thread_offset = ThreadMap::initial_offset(thread_idx) + threadblock_offset;

    int r = start_r;
    int s = start_s;

    if (params_.problem_size.mode == cutlass::conv::Mode::kConvolution) {
      r = (params_.problem_size.R - 1 - r);
      s = (params_.problem_size.S - 1 - s);
    }

    // compute starting coordinates in Dx start_h_ and start_w_
    strided_dgrad_starting_coords(
      params_.problem_size, 
      stride_h_divmod, stride_w_divmod, 
      r, s, 
      start_h_, start_w_);

    p_ = (params_.problem_size.H - start_h_ + params_.problem_size.stride_h - 1) / params_.problem_size.stride_h;
    q_ = (params_.problem_size.W - start_w_ + params_.problem_size.stride_w - 1) / params_.problem_size.stride_w;

    extent_row_ = extent.row();
    thread_start_row_ = thread_offset.row();
    thread_start_column_ = thread_offset.column();

    // Initialize predicates
    CUTLASS_PRAGMA_UNROLL
    for (int c = 0; c < ThreadMap::Iterations::kColumn; ++c) {

      mask_.predicates[c] = ((thread_offset.column() 
        + ThreadMap::Delta::kColumn * c) < extent.column());
    }

    // Null pointer performs no accesses
    if (!pointer) {
      mask_.clear();
    }

    // Initialize pointer
    byte_pointer_ = reinterpret_cast<uint8_t *>(pointer);

    // Initialize internal state counter
    state_[0] = state_[1] = state_[2] = 0;
  }

  /// 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;
  }

  /// Loads a fragment from memory
  CUTLASS_DEVICE
  void load_with_byte_offset(Fragment &frag, int64_t byte_offset) {

    uint8_t *byte_pointer = byte_pointer_;
    AccessType *frag_ptr = reinterpret_cast<AccessType *>(&frag);

    CUTLASS_PRAGMA_UNROLL
    for (int cluster = 0; cluster < ThreadMap::Iterations::kCluster; ++cluster) {

      CUTLASS_PRAGMA_UNROLL
      for (int group = 0; group < ThreadMap::Iterations::kGroup; ++group) {

        CUTLASS_PRAGMA_UNROLL
        for (int row = 0; row < ThreadMap::Iterations::kRow; ++row) {

          int frag_row_idx = 
            (row + ThreadMap::Iterations::kRow * (group + ThreadMap::Iterations::kGroup * cluster));

          int row_offset = row * ThreadMap::Delta::kRow 
            + group * ThreadMap::Delta::kGroup 
            + cluster * ThreadMap::Delta::kCluster;

          // remapping rows to find the mapped_row_offset
          int npq_offset = (row_offset + thread_start_row_) % params_.tiled_rows_per_filter;

          // (STEP 4.a) [order NHW rows to be loaded and stored in output Dx NHWxC layout]
          int n = npq_offset / (p_ * q_); 
          int residual = npq_offset % (p_ * q_);
          int p = residual / q_;
          int q = residual % q_;
        
          int mapped_row_offset = n * (params_.problem_size.H * params_.problem_size.W) +
                                  (start_h_ + p * params_.problem_size.stride_h) * params_.problem_size.W +
                                  (start_w_ + q * params_.problem_size.stride_w);
          bool row_guard = mapped_row_offset < extent_row_;

          int64_t row_byte_offset = mapped_row_offset * params_.stride;

          CUTLASS_PRAGMA_UNROLL
          for (int column = 0; column < ThreadMap::Iterations::kColumn; ++column) {

            int64_t column_byte_offset = (thread_start_column_ + column * ThreadMap::Delta::kColumn) * (sizeof_bits<Element>::value / 8);

            bool guard = row_guard && mask_.predicates[column];

            cutlass::arch::global_load<
              AccessType, 
              sizeof(AccessType)
            >(
                frag_ptr[frag_row_idx * ThreadMap::Iterations::kColumn +
                         column],
                (void *)(byte_pointer + row_byte_offset + column_byte_offset + byte_offset),
                guard);
          }
        }
      }
    }
  }


  /// Loads a fragment from memory
  CUTLASS_DEVICE
  void load(Fragment &frag) {

    load_with_byte_offset(frag, 0);
  }

  /// Stores a fragment to memory
  CUTLASS_DEVICE
  void store_with_byte_offset(Fragment const &frag, int64_t byte_offset) {
    uint8_t *byte_pointer = byte_pointer_;
    AccessType const *frag_ptr = reinterpret_cast<AccessType const *>(&frag);

    CUTLASS_PRAGMA_UNROLL
    for (int cluster = 0; cluster < ThreadMap::Iterations::kCluster; ++cluster) {

      CUTLASS_PRAGMA_UNROLL
      for (int group = 0; group < ThreadMap::Iterations::kGroup; ++group) {

        CUTLASS_PRAGMA_UNROLL
        for (int row = 0; row < ThreadMap::Iterations::kRow; ++row) {

          int frag_row_idx = 
            (row + ThreadMap::Iterations::kRow * (group + ThreadMap::Iterations::kGroup * cluster));

          int row_offset = row * ThreadMap::Delta::kRow 
            + group * ThreadMap::Delta::kGroup 
            + cluster * ThreadMap::Delta::kCluster;

          // remapping rows to find the mapped_row_offset
          int npq_offset = (row_offset + thread_start_row_) % params_.tiled_rows_per_filter;

          // (STEP 4.a) [order NHW rows to be loaded and stored in output Dx NHWxC layout]
          int n = npq_offset / (p_ * q_); 
          int residual = npq_offset % (p_ * q_);
          int p = residual / q_;
          int q = residual % q_;
        
          int mapped_row_offset = n * (params_.problem_size.H * params_.problem_size.W) +
                                  (start_h_ + p * params_.problem_size.stride_h) * params_.problem_size.W +
                                  (start_w_ + q * params_.problem_size.stride_w);
          bool row_guard = mapped_row_offset < extent_row_;

          int64_t row_byte_offset = mapped_row_offset * params_.stride;
          
          CUTLASS_PRAGMA_UNROLL
          for (int column = 0; column < ThreadMap::Iterations::kColumn; ++column) {

            int64_t column_byte_offset = (thread_start_column_ + column * ThreadMap::Delta::kColumn) * (sizeof_bits<Element>::value / 8);

            bool guard = row_guard && mask_.predicates[column];

            cutlass::arch::global_store<AccessType, sizeof(AccessType) >(
                frag_ptr[frag_row_idx * ThreadMap::Iterations::kColumn + column],
                (void *)(byte_pointer + row_byte_offset + column_byte_offset + byte_offset),
                guard);            
          }
        }
      }
    }
  }


  /// Stores a fragment to memory
  CUTLASS_DEVICE
  void store(Fragment const &frag) {

    store_with_byte_offset(frag, 0);
  }

  /// Advances to the next position to load or store
  CUTLASS_HOST_DEVICE
  PredicatedTileIteratorStridedDgrad &operator++() {

    ++state_[0];

    thread_start_row_ += ThreadMap::Shape::kRow;
    
    if (state_[0] == ThreadMap::Count::kRow) {

      state_[0] = 0;
      ++state_[1];

      thread_start_row_ += (ThreadMap::Shape::kGroup - 1) * 
        ThreadMap::Shape::kRow * ThreadMap::Count::kRow;

      if (state_[1] == ThreadMap::Count::kGroup) {

        state_[1] = 0;
        ++state_[2];

        thread_start_row_ += ThreadMap::Count::kGroup * 
          ThreadMap::Shape::kGroup * ThreadMap::Count::kRow * ThreadMap::Shape::kRow;

        if (state_[2] == ThreadMap::Count::kCluster) {
          state_[2] = 0;
        }
      }
    }

    return *this;
  }

  ///< Efficiently disables all accesses guarded by mask
  CUTLASS_DEVICE void clear_mask() {
    mask_.clear();
  }

  ///< Efficiently enables all accesses guarded by mask
  CUTLASS_DEVICE void enable_mask() {
    mask_.enable();
  }

  ///< Sets the mask
  CUTLASS_DEVICE void get_mask(Mask &mask) {
    mask = mask_;
  }

  ///< Sets the mask
  CUTLASS_DEVICE void set_mask(Mask const &mask) {
    mask_ = mask;
  }
};

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

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

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