flash-attention/csrc/cutlass/include/cute/arch/copy.hpp

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#pragma once

#include <cute/config.hpp>

#include <cute/arch/util.hpp>
#include <cute/numeric/numeric_types.hpp>

namespace cute
{

//
// Direct Copy for any type
//

template <class S, class D = S>
struct UniversalCopy
{
  using SRegisters = S[1];
  using DRegisters = D[1];

  template <class S_, class D_>
  CUTE_HOST_DEVICE static constexpr void
  copy(S_ const& src,
       D_      & dst)
  {
    dst = static_cast<D>(static_cast<S>(src));
  }

  // Accept mutable temporaries
  template <class S_, class D_>
  CUTE_HOST_DEVICE static constexpr void
  copy(S_ const& src,
       D_     && dst)
  {
    UniversalCopy<S,D>::copy(src, dst);
  }
};

//
// Placeholder for the copy algorithm's stronger auto-vectorizing behavior
//   that assumes alignment of dynamic layouts up to MaxVecBits
//

template <int MaxVecBits = 128>
struct AutoVectorizingCopyWithAssumedAlignment
     : UniversalCopy<uint_bit_t<MaxVecBits>>
{
  static_assert(MaxVecBits == 8 || MaxVecBits == 16 || MaxVecBits == 32 || MaxVecBits == 64 || MaxVecBits == 128,
                "Expected MaxVecBits to be 8 or 16 or 32 or 64 or 128 for alignment and performance.");
};

//
// Placeholder for the copy algorithm's default auto-vectorizing behavior
//   that does not assume alignment of dynamic layouts
//

using AutoVectorizingCopy = AutoVectorizingCopyWithAssumedAlignment<8>;

// Alias
using DefaultCopy = AutoVectorizingCopy;


//
// Global memory prefetch into L2
//

CUTE_HOST_DEVICE static void
prefetch(void const* gmem_ptr)
{
#if defined(__CUDA_ARCH__)
  asm volatile("prefetch.global.L2 [%0];\n" : : "l"(gmem_ptr) : "memory");
#endif
}

} // end namespace cute