BlasKernel.cpp

#define TORCH_ASSERT_NO_OPERATORS
#include <ATen/Dispatch.h>
#include <ATen/native/CPUBlas.h>
#include <c10/util/irange.h>
#include <c10/util/Unroll.h>

namespace at {
namespace native {
namespace cpublas {
namespace {

template <typename scalar_t, typename opmath_t>
void scale_(int64_t m, int64_t n, opmath_t alpha, scalar_t *a, int64_t lda) {
  if (alpha == opmath_t(1)) {
    return;  // identity
  }

  if (alpha == opmath_t(0)) {
    for (const auto j : c10::irange(n)) {
      for (const auto i : c10::irange(m)) {
        a[j * lda + i] = scalar_t(0);
      }
    }
    return;
  }

  for (const auto j : c10::irange(n)) {
    for (const auto i : c10::irange(m)) {
      a[j * lda + i] *= alpha;
    }
  }
}

template <typename Func>
auto sum(int64_t N, Func f) {
  constexpr int ilp_factor = 4;
  using acc_t = decltype(f(0));

  // Calculate independent partial sums then add together at the end
  std::array<acc_t, ilp_factor> partial_sums{};

  int64_t i = 0;
  for (; i + ilp_factor <= N; i += ilp_factor) {
    c10::ForcedUnroll<ilp_factor>{}([&](int k) {
      partial_sums[k] += f(i + k);
    });
  }
  for (; i < N; ++i) {
    partial_sums[0] += f(i);
  }
  for (int k = 1; k < ilp_factor; ++k) {
    partial_sums[0] += partial_sums[k];
  }
  return partial_sums[0];
}


template <typename scalar_t, typename opmath_t>
void gemm_notrans_(
    int64_t m, int64_t n, int64_t k,
    opmath_t alpha,
    const scalar_t *a, int64_t lda,
    const scalar_t *b, int64_t ldb,
    opmath_t beta,
    scalar_t *c, int64_t ldc) {
  // c *= beta
  scale_(m, n, beta, c, ldc);

  // c += alpha * (a @ b)
  for (const auto l : c10::irange(k)) {
    for (const auto j : c10::irange(n)) {
      opmath_t val = b[l + j * ldb] * alpha;
      int64_t i_m = m / 4;
      for (const auto i_i : c10::irange(i_m)) {
        c[j * ldc + i_i * 4 + 0] += a[i_i * 4 + 0 + l * lda] * val;
        c[j * ldc + i_i * 4 + 1] += a[i_i * 4 + 1 + l * lda] * val;
        c[j * ldc + i_i * 4 + 2] += a[i_i * 4 + 2 + l * lda] * val;
        c[j * ldc + i_i * 4 + 3] += a[i_i * 4 + 3 + l * lda] * val;
      }
      int64_t i = i_m * 4;
      for (; i < m; i++)
        c[j * ldc + i] += a[i + l * lda] * val;
    }
  }
}

template <typename scalar_t, typename opmath_t>
void gemm_transa_(
    int64_t m, int64_t n, int64_t k,
    opmath_t alpha,
    const scalar_t *a, int64_t lda,
    const scalar_t *b, int64_t ldb,
    opmath_t beta,
    scalar_t *c, int64_t ldc) {
  // c = alpha * (a.T @ b) + beta * c
  const scalar_t *a_ = a;
  for (const auto i : c10::irange(m)) {
    const scalar_t *b_ = b;
    for (const auto j : c10::irange(n)) {
      const auto dot = sum(k, [&](int64_t l) -> opmath_t {
        return static_cast<opmath_t>(a_[l]) * static_cast<opmath_t>(b_[l]);
      });
      b_ += ldb;
      if (beta == opmath_t(0)) {
        c[j*ldc+i] = alpha*dot;
      } else {
        c[j*ldc+i] = beta*c[j*ldc+i]+alpha*dot;
      }
    }
    a_ += lda;
  }
}

template <typename scalar_t, typename opmath_t>
void gemm_transb_(
    int64_t m, int64_t n, int64_t k,
    opmath_t alpha,
    const scalar_t *a, int64_t lda,
    const scalar_t *b, int64_t ldb,
    opmath_t beta,
    scalar_t *c, int64_t ldc) {
  // c *= beta
  scale_(m, n, beta, c, ldc);

  // c += alpha * (a @ b.T)
  for (const auto l : c10::irange(k)) {
    for (const auto j : c10::irange(n)) {
      opmath_t val = b[j + l * ldb] * alpha;
      int64_t i_m = m / 4;
      for (const auto i_i : c10::irange(i_m)) {
        c[j * ldc + i_i * 4 + 0] += a[i_i * 4 + 0 + l * lda] * val;
        c[j * ldc + i_i * 4 + 1] += a[i_i * 4 + 1 + l * lda] * val;
        c[j * ldc + i_i * 4 + 2] += a[i_i * 4 + 2 + l * lda] * val;
        c[j * ldc + i_i * 4 + 3] += a[i_i * 4 + 3 + l * lda] * val;
      }
      int64_t i = i_m * 4;
      for (; i < m; i++)
        c[j * ldc + i] += a[i + l * lda] * val;
    }
  }
}

template <typename scalar_t, typename opmath_t>
void gemm_transab_(
    int64_t m, int64_t n, int64_t k,
    opmath_t alpha,
    const scalar_t *a, int64_t lda,
    const scalar_t *b, int64_t ldb,
    opmath_t beta,
    scalar_t *c, int64_t ldc) {
  // c = beta * c + alpha * (a.T @ b.T)
  for (const auto i : c10::irange(m)) {
    for (const auto j : c10::irange(n)) {
      const auto dot = sum(k, [&](int64_t l) -> opmath_t {
        return static_cast<opmath_t>(a[i * lda + l]) *
            static_cast<opmath_t>(b[l * ldb + j]);
      });

      if (beta == opmath_t(0)) {
        c[j * ldc + i] = alpha * dot;
      } else {
        c[j * ldc + i] = beta * c[j * ldc + i] + alpha * dot;
      }
    }
  }
}

template <typename scalar_t, typename opmath_t>
void gemm_core_(
    TransposeType transa, TransposeType transb,
    int64_t m, int64_t n, int64_t k,
    opmath_t alpha,
    const scalar_t *a, int64_t lda,
    const scalar_t *b, int64_t ldb,
    opmath_t beta,
    scalar_t *c, int64_t ldc) {
  if(transa == TransposeType::NoTranspose && transb == TransposeType::NoTranspose) {
    return gemm_notrans_(m, n, k, alpha, a, lda, b, ldb, beta, c, ldc);
  } else if(transa == TransposeType::Transpose && transb != TransposeType::Transpose) {
    gemm_transa_(m, n, k, alpha, a, lda, b, ldb, beta, c, ldc);
  } else if(transa == TransposeType::NoTranspose && transb == TransposeType::Transpose) {
    gemm_transb_(m, n, k, alpha, a, lda, b, ldb, beta, c, ldc);
  } else {  // transa == TransposeType::Transpose && transb == TransposeType::Transpose
    gemm_transab_(m, n, k, alpha, a, lda, b, ldb, beta, c, ldc);
  }
}

void cpublas_gemm_impl(
    at::ScalarType type,
    TransposeType transa, TransposeType transb,
    int64_t m, int64_t n, int64_t k,
    const Scalar& alpha,
    const void *a, int64_t lda,
    const void *b, int64_t ldb,
    const Scalar& beta,
    void *c, int64_t ldc) {
  AT_DISPATCH_ALL_TYPES_AND_COMPLEX_AND2(at::kHalf, at::kBFloat16,
    type, "cpublas_gemm_impl",
      [&]{
        using opmath_t = at::opmath_type<scalar_t>;
        gemm_core_(
            transa, transb, m, n, k,
            alpha.to<opmath_t>(),
            static_cast<const scalar_t *>(a), lda,
            static_cast<const scalar_t *>(b), ldb,
            beta.to<opmath_t>(),
            static_cast<scalar_t *>(c), ldc);
      });
}

void cpublas_axpy_impl(at::ScalarType type, int64_t n, const Scalar& _a, const void *_x, int64_t incx, void *_y, int64_t incy){
  if (type == at::kBool) {
      auto a = _a.to<bool>();
      auto x = static_cast<const bool *>(_x);
      auto y = static_cast<bool *>(_y);
      int64_t i;
      for(i = 0; i < n; i++)
        y[i*incy] |= a & x[i*incx];
  } else {
    AT_DISPATCH_ALL_TYPES_AND_COMPLEX_AND2(at::kHalf, at::kBFloat16, type, "cpublas_axpy_impl",
      [&] {
        using opmath_t = at::opmath_type<scalar_t>;
        auto a = _a.to<opmath_t>();
        auto x = static_cast<const scalar_t *>(_x);
        auto y = static_cast<scalar_t *>(_y);
        int64_t i;
        for(i = 0; i < n; i++)
          y[i*incy] += a*x[i*incx];
      });
  }
}

void cpublas_copy_impl(at::ScalarType type, int64_t n, const void *_x, int64_t incx, void *_y, int64_t incy){
  AT_DISPATCH_ALL_TYPES_AND_COMPLEX_AND4(at::kComplexHalf, at::kHalf, at::kBFloat16, at::kBool, type, "cpublas_copy_impl",
    [&] {
      auto x = static_cast<const scalar_t *>(_x);
      auto y = static_cast<scalar_t *>(_y);
      int64_t i;
      for(i = 0; i < n; i++)
        y[i*incy] = x[i*incx];
    });
}

}}  // namespace cpublas::(anonymous)


REGISTER_DISPATCH(cpublas::gemm_stub, &cpublas::cpublas_gemm_impl);
REGISTER_DISPATCH(cpublas::axpy_stub, &cpublas::cpublas_axpy_impl);
REGISTER_DISPATCH(cpublas::copy_stub, &cpublas::cpublas_copy_impl);

}}  // namespace at::native