mma.h

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// Copyright © 2024 Apple Inc.
 
#pragma once
 
#include <metal_simdgroup>
#include <metal_simdgroup_matrix>
#include <metal_stdlib>
 
#include "mlx/backend/metal/kernels/steel/attn/transforms.h"
#include "mlx/backend/metal/kernels/steel/defines.h"
#include "mlx/backend/metal/kernels/steel/utils/integral_constant.h"
 
using namespace metal;

// MMA helper
 
namespace mlx {
namespace steel {
 
template <typename RInt, typename CInt>
struct Shape2D {
  RInt r;
  CInt c;
 
  Shape2D(RInt r_, CInt c_) : r(r_), c(c_) {}
};
 
template <typename Shape, typename Layout>
struct Layout2D {
  Shape shape;
  Layout layout;
};
 
template <typename T, int kFragRows_, int kFragCols_>
struct BaseMMAFrag {
  static_assert(
      kFragRows_ == 8,
      "Only 8 x 8 fragment matrices are currently supported");
  static_assert(
      kFragCols_ == 8,
      "Only 8 x 8 fragment matrices are currently supported");
};
 
template <typename T>
struct BaseMMAFrag<T, 8, 8> {
  STEEL_CONST int kFragRows = 8;
  STEEL_CONST int kFragCols = 8;
 
  STEEL_CONST int kElemsPerFrag = (kFragRows * kFragCols) / 32;
 
  STEEL_CONST int kElemRows = 1;
  STEEL_CONST int kElemCols = 2;
 
  static_assert(
      kElemRows * kElemCols == kElemsPerFrag,
      "MMAFrag shape is not consistent with MMAFrag size");
 
  typedef metal::simdgroup_matrix<T, kFragRows, kFragCols> mat_type;
  typedef metal::vec<T, kElemsPerFrag> frag_type;
  typedef metal::vec<T, kElemRows> row_frag_type;
  typedef metal::vec<T, kElemCols> col_frag_type;
 
  template <typename U>
  using dtype_mat_t = typename metal::simdgroup_matrix<U, kFragRows, kFragCols>;
 
  template <typename U>
  using dtype_frag_t = typename metal::vec<U, kElemsPerFrag>;
 
  METAL_FUNC static constexpr short2 get_coord(ushort simd_lane_id
                                               [[thread_index_in_simdgroup]]) {
    const short qid = simd_lane_id / 4;
    const short fm = (qid & 4) + ((simd_lane_id / 2) % 4);
    const short fn = (qid & 2) * 2 + (simd_lane_id % 2) * 2;
    return short2{fn, fm};
  }
 
  template <typename SrcPtrType, typename StrX, typename StrY>
  METAL_FUNC static constexpr void
  load(thread frag_type& dst, SrcPtrType src, StrX str_x, StrY str_y) {
    STEEL_PRAGMA_UNROLL
    for (short i = 0; i < kElemRows; i++) {
      STEEL_PRAGMA_UNROLL
      for (short j = 0; j < kElemCols; j++) {
        dst[i * kElemCols + j] = static_cast<T>(src[i * str_x + j * str_y]);
      }
    }
  }
 
  template <
      typename SrcPtrType,
      typename StrX,
      typename StrY,
      typename LimX,
      typename LimY,
      typename OffX,
      typename OffY>
  METAL_FUNC static constexpr void load_safe(
      thread frag_type& dst,
      SrcPtrType src,
      StrX str_x,
      StrY str_y,
      LimX lim_x,
      LimY lim_y,
      OffX off_x = Int<0>{},
      OffY off_y = Int<0>{}) {
    STEEL_PRAGMA_UNROLL
    for (short i = 0; i < kElemRows; i++) {
      STEEL_PRAGMA_UNROLL
      for (short j = 0; j < kElemCols; j++) {
        if ((off_x + i) < lim_x && (off_y + j) < lim_y) {
          dst[i * kElemCols + j] =
              static_cast<T>(src[(off_x + i) * str_x + (off_y + j) * str_y]);
        } else {
          dst[i * kElemCols + j] = T(0);
        }
      }
    }
  }
 
  template <typename DstPtrType, typename StrX, typename StrY>
  METAL_FUNC static constexpr void
  store(const thread frag_type& src, DstPtrType dst, StrX str_x, StrY str_y) {
    using U = pointer_element_t<DstPtrType>;
 
    STEEL_PRAGMA_UNROLL
    for (short i = 0; i < kElemRows; i++) {
      STEEL_PRAGMA_UNROLL
      for (short j = 0; j < kElemCols; j++) {
        dst[i * str_x + j * str_y] = static_cast<U>(src[i * kElemCols + j]);
      }
    }
  }
 
  template <
      typename DstPtrType,
      typename StrX,
      typename StrY,
      typename LimX,
      typename LimY,
      typename OffX,
      typename OffY>
  METAL_FUNC static constexpr void store_safe(
      const thread frag_type& src,
      DstPtrType dst,
      StrX str_x,
      StrY str_y,
      LimX lim_x,
      LimY lim_y,
      OffX off_x = Int<0>{},
      OffY off_y = Int<0>{}) {
    using U = pointer_element_t<DstPtrType>;
 
    STEEL_PRAGMA_UNROLL
    for (short i = 0; i < kElemRows; i++) {
      STEEL_PRAGMA_UNROLL
      for (short j = 0; j < kElemCols; j++) {
        if ((off_x + i) < lim_x && (off_y + j) < lim_y) {
          dst[(off_x + i) * str_x + (off_y + j) * str_y] =
              static_cast<U>(src[i * kElemCols + j]);
        }
      }
    }
  }
 
  template <typename Atype, typename Btype, typename Ctype>
  METAL_FUNC static constexpr void mma(
      thread frag_type& D,
      thread dtype_frag_t<Atype>& A,
      thread dtype_frag_t<Btype>& B,
      thread dtype_frag_t<Ctype>& C) {
    mat_type D_mat;
    dtype_mat_t<Atype> A_mat;
    dtype_mat_t<Btype> B_mat;
    dtype_mat_t<Ctype> C_mat;
 
    reinterpret_cast<thread dtype_frag_t<Atype>&>(A_mat.thread_elements()) = A;
    reinterpret_cast<thread dtype_frag_t<Btype>&>(B_mat.thread_elements()) = B;
    reinterpret_cast<thread dtype_frag_t<Ctype>&>(C_mat.thread_elements()) = C;
 
    mma(D_mat, A_mat, B_mat, C_mat);
 
    D = reinterpret_cast<thread frag_type&>(D_mat.thread_elements());
  }
 
  template <typename Atype, typename Btype, typename Ctype>
  METAL_FUNC static constexpr void mma(
      thread mat_type& D,
      thread dtype_mat_t<Atype>& A,
      thread dtype_mat_t<Btype>& B,
      thread dtype_mat_t<Ctype>& C) {
    simdgroup_multiply_accumulate(D, A, B, C);
  }
 
  template <typename Op>
  METAL_FUNC static constexpr void row_reduce(
      thread const frag_type& inp_vals,
      thread T* reduced_vals) {
    T thr_reduce = Op::apply(inp_vals.x, inp_vals.y);
 
    T qgr_reduce = simd_shuffle_xor(thr_reduce, ushort(1));
    qgr_reduce = Op::apply(thr_reduce, qgr_reduce);
 
    T sgr_reduce = simd_shuffle_xor(qgr_reduce, ushort(8));
    sgr_reduce = Op::apply(qgr_reduce, sgr_reduce);
 
    reduced_vals[0] = Op::apply(reduced_vals[0], sgr_reduce);
  }
 
  template <typename Op>
  METAL_FUNC static constexpr void row_bin_op(
      thread frag_type& inp_vals,
      thread T* row_vals) {
    STEEL_PRAGMA_UNROLL
    for (short i = 0; i < kElemRows; i++) {
      STEEL_PRAGMA_UNROLL
      for (short j = 0; j < kElemCols; j++) {
        inp_vals[i * kElemCols + j] =
            Op::apply(inp_vals[i * kElemCols + j], row_vals[i]);
      }
    }
  }
};
 
template <
    typename T,
    int kTileRows_,
    int kTileCols_,
    class MMAFrag_ = BaseMMAFrag<T, 8, 8>>
struct MMATile {
  using MMAFrag_t = MMAFrag_;
  using elem_type = T;
  STEEL_CONST int kFragRows = MMAFrag_t::kFragRows;
  STEEL_CONST int kFragCols = MMAFrag_t::kFragCols;
  STEEL_CONST int kElemsPerFrag = MMAFrag_t::kElemsPerFrag;
 
  STEEL_CONST int kTileRows = kTileRows_;
  STEEL_CONST int kTileCols = kTileCols_;
 
  STEEL_CONST int kRows = kTileRows * kFragRows;
  STEEL_CONST int kCols = kTileCols * kFragCols;
 
  STEEL_CONST int kNumFrags = kTileRows * kTileCols;
  STEEL_CONST int kElemsPerTile = kNumFrags * kElemsPerFrag;
 
  STEEL_CONST int kRowsPerThread = kTileRows * MMAFrag_t::kElemRows;
  STEEL_CONST int kColsPerThread = kTileCols * MMAFrag_t::kElemCols;
 
  typedef typename MMAFrag_t::mat_type mat_type;
  typedef typename MMAFrag_t::frag_type frag_type;
 
  frag_type val_frags[kNumFrags]; // = {frag_type(0)};
 
  METAL_FUNC MMATile() thread {}
 
  METAL_FUNC constexpr void clear() {
    STEEL_PRAGMA_UNROLL
    for (short i = 0; i < kNumFrags; ++i) {
      val_frags[i] = frag_type(0);
    }
  }
 
  METAL_FUNC constexpr thread frag_type& frag_at(const short i, const short j) {
    return val_frags[i * kTileCols + j];
  }
 
  METAL_FUNC constexpr const thread frag_type& frag_at(
      const short i,
      const short j) const {
    return val_frags[i * kTileCols + j];
  }
 
  METAL_FUNC mat_type mat_at(const short i, const short j) {
    mat_type val_mat;
    STEEL_PRAGMA_UNROLL
    for (short ii = 0; ii < kElemsPerFrag; ++ii) {
      val_mat.thread_elements()[ii] = frag_at(i, j)[ii];
    }
    return val_mat;
  }
 
  METAL_FUNC thread elem_type* elems() {
    return reinterpret_cast<thread elem_type*>(val_frags);
  }
 
  METAL_FUNC const thread elem_type* elems() const {
    return reinterpret_cast<const thread elem_type*>(val_frags);
  }
 
  template <typename Op>
  METAL_FUNC void row_reduce(thread T vals[kRowsPerThread]) const {
    STEEL_PRAGMA_UNROLL
    for (short i = 0; i < kTileRows; ++i) {
      STEEL_PRAGMA_UNROLL
      for (short j = 0; j < kTileCols; ++j) {
        MMAFrag_t::template row_reduce<Op>(
            frag_at(i, j), &vals[i * MMAFrag_t::kElemRows]);
      }
    }
  }
 
  template <typename Op>
  METAL_FUNC void row_bin_op(thread T vals[kRowsPerThread]) {
    STEEL_PRAGMA_UNROLL
    for (short i = 0; i < kTileRows; ++i) {
      STEEL_PRAGMA_UNROLL
      for (short j = 0; j < kTileCols; ++j) {
        MMAFrag_t::template row_bin_op<Op>(
            frag_at(i, j), &vals[i * MMAFrag_t::kElemRows]);
      }
    }
  }
 
  template <typename U, int w_x, int w_y, int str_x, int str_y>
  METAL_FUNC void load(const threadgroup U* src) {
    STEEL_PRAGMA_UNROLL
    for (short i = 0; i < kTileRows; ++i) {
      STEEL_PRAGMA_UNROLL
      for (short j = 0; j < kTileCols; ++j) {
        MMAFrag_t::load(
            frag_at(i, j),
            &(
                src[(i * kFragRows) * w_x * str_x +
                    (j * kFragCols) * w_y * str_y]),
            Int<str_x>{},
            Int<str_y>{});
      }
    }
  }
 
  template <typename U, int w_x, int w_y, int str_x, int str_y>
  METAL_FUNC void store(threadgroup U* dst) const {
    STEEL_PRAGMA_UNROLL
    for (short i = 0; i < kTileRows; ++i) {
      STEEL_PRAGMA_UNROLL
      for (short j = 0; j < kTileCols; ++j) {
        MMAFrag_t::store(
            frag_at(i, j),
            &(
                dst[(i * kFragRows) * w_x * str_x +
                    (j * kFragCols) * w_y * str_y]),
            Int<str_x>{},
            Int<str_y>{});
      }
    }
  }
 
  template <typename U, int w_x, int w_y>
  METAL_FUNC void load(const device U* src, const int ld) {
    STEEL_PRAGMA_UNROLL
    for (short i = 0; i < kTileRows; ++i) {
      STEEL_PRAGMA_UNROLL
      for (short j = 0; j < kTileCols; ++j) {
        MMAFrag_t::load(
            frag_at(i, j),
            &(src[(i * kFragRows) * w_x * ld + (j * kFragCols) * w_y]),
            ld,
            Int<1>{});
      }
    }
  }
 
  template <typename U, int w_x, int w_y>
  METAL_FUNC void store(device U* dst, const int ld) const {
    STEEL_PRAGMA_UNROLL
    for (short i = 0; i < kTileRows; ++i) {
      STEEL_PRAGMA_UNROLL
      for (short j = 0; j < kTileCols; ++j) {
        MMAFrag_t::store(
            frag_at(i, j),
            &(dst[(i * kFragRows) * w_x * ld + (j * kFragCols) * w_y]),
            ld,
            Int<1>{});
      }
    }
  }
 
  template <typename U, int w_x, int w_y>
  METAL_FUNC void
  load_safe(const device U* src, const int ld, const short2 src_tile_dims) {
    STEEL_PRAGMA_UNROLL
    for (int i = 0; i < kTileRows; ++i) {
      STEEL_PRAGMA_UNROLL
      for (int j = 0; j < kTileCols; ++j) {
        MMAFrag_t::load_safe(
            frag_at(i, j),
            src,
            ld,
            Int<1>{},
            src_tile_dims.y,
            src_tile_dims.x,
            (i * kFragRows) * w_x,
            (j * kFragCols) * w_y);
      }
    }
  }
 
  template <typename U, int w_x, int w_y>
  METAL_FUNC void
  store_safe(device U* dst, const int ld, const short2 dst_tile_dims) const {
    STEEL_PRAGMA_UNROLL
    for (int i = 0; i < kTileRows; ++i) {
      STEEL_PRAGMA_UNROLL
      for (int j = 0; j < kTileCols; ++j) {
        MMAFrag_t::store_safe(
            frag_at(i, j),
            dst,
            ld,
            Int<1>{},
            dst_tile_dims.y,
            dst_tile_dims.x,
            (i * kFragRows) * w_x,
            (j * kFragCols) * w_y);
      }
    }
  }
};
 
template <
    typename Dtype,
    typename Atype,
    typename Btype,
    typename Ctype,
    int M,
    int N,
    int K,
    class MMAFragD,
    class MMAFragA,
    class MMAFragB,
    class MMAFragC>
METAL_FUNC void tile_matmad(
    thread MMATile<Dtype, M, N, MMAFragD>& D,
    thread MMATile<Atype, M, K, MMAFragA>& A,
    thread MMATile<Btype, K, N, MMAFragB>& B,
    thread MMATile<Ctype, M, N, MMAFragC>& C) {
  STEEL_PRAGMA_UNROLL
  for (short m = 0; m < M; ++m) {
    STEEL_PRAGMA_UNROLL
    for (short n = 0; n < N; ++n) {
      short m_serp = m; //(n % 2) ? (M - 1 - m) : m;
      short n_serp = (m % 2) ? (N - 1 - n) : n;
 
      STEEL_PRAGMA_UNROLL
      for (short k = 0; k < K; ++k) {
        MMAFragD::mma(
            D.frag_at(m_serp, n_serp),
            A.frag_at(m_serp, k),
            B.frag_at(k, n_serp),
            C.frag_at(m_serp, n_serp));
      }
    }
  }
}
 
template <
    typename T,
    typename U,
    int BM,
    int BN,
    int BK,
    int WM,
    int WN,
    bool transpose_a,
    bool transpose_b,
    short lda_tgp,
    short ldb_tgp,
    typename AccumType = float,
    typename Epilogue = TransformNone<U, AccumType>>
struct BlockMMA {
  // MMAFrag size
  STEEL_CONST short kFragSize = 8;
  using MMAFrag_acc_t = BaseMMAFrag<AccumType, kFragSize, kFragSize>;
 
  // Warp tile simdgroup matrix strides along M
  STEEL_CONST short TM_stride = kFragSize * WM;
  // Warp tile simdgroup matrix strides along M
  STEEL_CONST short TN_stride = kFragSize * WN;
 
  // Warp tile size along M
  STEEL_CONST short TM = BM / TM_stride;
  // Warp tile size along N
  STEEL_CONST short TN = BN / TN_stride;
 
  // Threadgroup A strides
  STEEL_CONST short A_str_m = transpose_a ? 1 : lda_tgp; // M
  STEEL_CONST short A_str_k = transpose_a ? lda_tgp : 1; // K
 
  // Threadgroup B strides
  STEEL_CONST short B_str_k = transpose_b ? 1 : ldb_tgp; // K
  STEEL_CONST short B_str_n = transpose_b ? ldb_tgp : 1; // N
 
  // Threadgroup strides along K
  STEEL_CONST short tile_stride_a = kFragSize * A_str_k;
  STEEL_CONST short tile_stride_b = kFragSize * B_str_k;
 
  // Simdgroup matrices
  MMATile<AccumType, TM, 1, MMAFrag_acc_t> Atile;
  MMATile<AccumType, 1, TN, MMAFrag_acc_t> Btile;
  MMATile<AccumType, TM, TN, MMAFrag_acc_t> Ctile;
 
  // Offsets within threadgroup
  short sm;
  short sn;
 
  short As_offset;
  short Bs_offset;
 
  /* Constructor */
  METAL_FUNC BlockMMA(
      ushort simd_group_id [[simdgroup_index_in_threadgroup]],
      ushort simd_lane_id [[thread_index_in_simdgroup]]) {
    // Determine thread position in simdgroup matrix
    short tm = kFragSize * (simd_group_id / WN);
    short tn = kFragSize * (simd_group_id % WN);
 
    short2 simd_coord = MMAFrag_acc_t::get_coord(simd_lane_id);
    sm = simd_coord.y;
    sn = simd_coord.x;
 
    // Determine thread and simdgroup offset
    As_offset = (tm + sm) * A_str_m + (sn)*A_str_k; // M, K
    Bs_offset = (sm)*B_str_k + (tn + sn) * B_str_n; // K, N
 
    sm += tm;
    sn += tn;
  }
 
  /* (BM, BK) X (BK, BN) multiply accumulate function */
  METAL_FUNC void mma(const threadgroup T* As, const threadgroup T* Bs) {
    // Adjust for simdgroup and thread location
    As += As_offset;
    Bs += Bs_offset;
 
    // Iterate over BK in blocks of kFragSize
    STEEL_PRAGMA_UNROLL
    for (short kk = 0; kk < BK; kk += kFragSize) {
      simdgroup_barrier(mem_flags::mem_none);
 
      Atile.template load<T, WM, 1, A_str_m, A_str_k>(As);
 
      simdgroup_barrier(mem_flags::mem_none);
 
      Btile.template load<T, 1, WN, B_str_k, B_str_n>(Bs);
 
      simdgroup_barrier(mem_flags::mem_none);
 
      tile_matmad(Ctile, Atile, Btile, Ctile);
 
      // Progress to next simdgroup tile
      As += tile_stride_a;
      Bs += tile_stride_b;
    }
  }
 
  /* Store results from simdgroup_matrix results into device memory */
  METAL_FUNC void store_result(device U* D, const int ldd) {
    // Apply epilogue
    STEEL_PRAGMA_UNROLL
    for (short i = 0; i < decltype(Ctile)::kElemsPerTile; i++) {
      Ctile.elems()[i] = Epilogue::apply(Ctile.elems()[i]);
    }
 
    // Adjust for simdgroup and thread location
    D += sm * ldd + sn;
 
    Ctile.template store<U, WM, WN>(D, ldd);
  }
 
  METAL_FUNC void
  store_result_safe(device U* D, const int ldd, short2 dst_tile_dims) {
    // Apply epilogue
    STEEL_PRAGMA_UNROLL
    for (short i = 0; i < decltype(Ctile)::kElemsPerTile; i++) {
      Ctile.elems()[i] = Epilogue::apply(Ctile.elems()[i]);
    }
 
    // Adjust for simdgroup and thread location
    D += sm * ldd + sn;
    dst_tile_dims -= short2(sn, sm);
 
    if (dst_tile_dims.x <= 0 || dst_tile_dims.y <= 0)
      return;
 
    Ctile.template store_safe<U, WM, WN>(D, ldd, dst_tile_dims);
  }
 
  /* Apply epilogue */
  template <typename UnaryEpilogue>
  METAL_FUNC void apply_epilogue(thread const UnaryEpilogue& epilogue_op) {
    // Loop over all simdgroup tiles
    STEEL_PRAGMA_UNROLL
    for (short i = 0; i < decltype(Ctile)::kElemsPerTile; i++) {
      Ctile.elems()[i] = epilogue_op.apply(Ctile.elems()[i]);
    }
  }
 
  /* Apply epilogue */
  template <typename BinaryEpilogue>
  METAL_FUNC void apply_epilogue(
      const device U* C,
      const int ldc,
      const int fdc,
      thread const BinaryEpilogue& epilogue_op) {
    // Adjust for simdgroup and thread location
    C += (sm)*ldc + (sn)*fdc;
 
    // Loop over all simdgroup tiles
    STEEL_PRAGMA_UNROLL
    for (short i = 0; i < TM; i++) {
      STEEL_PRAGMA_UNROLL
      for (short j = 0; j < TN; j++) {
        // Get accumulated result and associated offset in C
        thread auto& accum = Ctile.frag_at(i, j);
        int offset_c = (i * TM_stride) * ldc + (j * TN_stride) * fdc;
 
        // Apply epilogue
        STEEL_PRAGMA_UNROLL
        for (short k = 0; k < decltype(Ctile)::kElemsPerFrag; k++) {
          accum[k] = epilogue_op.apply(accum[k], C[offset_c + k * fdc]);
        }
      }
    }
  }
 
  /* Apply epilogue */
  template <typename BinaryEpilogue>
  METAL_FUNC void apply_epilogue_safe(
      const device U* C,
      const int ldc,
      const int fdc,
      short2 dst_tile_dims,
      thread const BinaryEpilogue& epilogue_op) {
    // Adjust for simdgroup and thread location
    C += (sm)*ldc + (sn)*fdc;
    dst_tile_dims -= short2(sn, sm);
 
    if (dst_tile_dims.x <= 0 || dst_tile_dims.y <= 0)
      return;
 
    // Loop over all simdgroup tiles
    STEEL_PRAGMA_UNROLL
    for (short i = 0; i < TM; i++) {
      STEEL_PRAGMA_UNROLL
      for (short j = 0; j < TN; j++) {
        // Get accumulated result and associated offset in C
        thread auto& accum = Ctile.frag_at(i, j);
        int offset_c = (i * TM_stride) * ldc + (j * TN_stride) * fdc;
 
        constexpr short kelems = decltype(Ctile)::kElemsPerFrag;
 
        // Read C
        U c_elems[kelems] = {0};
 
        STEEL_PRAGMA_UNROLL
        for (short k = 0; k < kelems; k++) {
          if ((j * TN_stride + k) < dst_tile_dims.x) {
            c_elems[k] = C[offset_c + k * fdc];
          }
        }
 
        // Apply epilogue
        STEEL_PRAGMA_UNROLL
        for (short k = 0; k < kelems; k++) {
          accum[k] = epilogue_op.apply(accum[k], c_elems[k]);
        }
      }
    }
  }
 
  /* Store results from simdgroup_matrix results into device memory */
  METAL_FUNC void store_result(
      device U* D,
      const int ldd,
      const device U* C,
      const int ldc,
      const int fdc,
      thread const Epilogue& epilogue_op) const {
    // Adjust for simdgroup and thread location
    C += (sm)*ldc + (sn)*fdc;
    D += (sm)*ldd + sn;
 
    constexpr short kelems = decltype(Ctile)::kElemsPerFrag;
 
    // Loop over all simdgroup tiles
    STEEL_PRAGMA_UNROLL
    for (short i = 0; i < TM; i++) {
      STEEL_PRAGMA_UNROLL
      for (short j = 0; j < TN; j++) {
        // Get accumulated result and associated offset in C
        thread const auto& accum = Ctile.frag_at(i, j);
        int offset_c = (i * TM_stride) * ldc + (j * TN_stride) * fdc;
        int offset_d = (i * TM_stride) * ldd + (j * TN_stride);
 
        // Apply epilogue
        STEEL_PRAGMA_UNROLL
        for (short k = 0; k < kelems; k++) {
          D[offset_d + k] = epilogue_op.apply(accum[k], C[offset_c + k * fdc]);
        }
      }
    }
  }
 
  METAL_FUNC void store_result_safe(
      device U* D,
      const int ldd,
      const device U* C,
      const int ldc,
      const int fdc,
      short2 dst_tile_dims,
      thread const Epilogue& epilogue_op) const {
    // Adjust for simdgroup and thread location
    C += (sm)*ldc + (sn)*fdc;
    D += (sm)*ldd + sn;
    dst_tile_dims -= short2(sn, sm);
 
    if (dst_tile_dims.x <= 0 || dst_tile_dims.y <= 0)
      return;
 
    constexpr short kelems = decltype(Ctile)::kElemsPerFrag;
 
    STEEL_PRAGMA_UNROLL
    for (int i = 0; i < TM; i++) {
      if (i * TM_stride < dst_tile_dims.y) {
        STEEL_PRAGMA_UNROLL
        for (int j = 0; j < TN; j++) {
          // Get accumulated result and associated offset in C
          thread const auto& accum = Ctile.frag_at(i, j);
          int offset_c = (i * TM_stride) * ldc + (j * TN_stride) * fdc;
          int offset_d = (i * TM_stride) * ldd + (j * TN_stride);
 
          // Apply epilogue
          STEEL_PRAGMA_UNROLL
          for (short k = 0; k < kelems; k++) {
            if ((j * TN_stride + k) < dst_tile_dims.x) {
              D[offset_d + k] =
                  epilogue_op.apply(accum[k], C[offset_c + k * fdc]);
            }
          }
        }
      }
    }
  }
};
 
} // namespace steel
} // namespace mlx