elementwise_add_op.h

/* Copyright (c) 2016 PaddlePaddle Authors. All Rights Reserved.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License. */
#pragma once

#include <algorithm>
#include <utility>
#include "paddle/fluid/operators/elementwise/elementwise_op.h"
#include "paddle/fluid/operators/elementwise/elementwise_op_function.cu.h"
#include "paddle/fluid/operators/elementwise/elementwise_op_function.h"
#include "paddle/fluid/operators/math/blas.h"
#include "paddle/fluid/operators/math/math_function.h"
#ifdef PADDLE_WITH_CUDA
#ifdef __NVCC__
#include <cuda.h>
#include <cuda_fp16.h>
#include "cub/cub.cuh"
#endif
#endif

namespace paddle {
namespace operators {

template <typename DeviceContext, typename T>
void default_elementwise_add(const framework::ExecutionContext &ctx,
                             const framework::Tensor *x,
                             const framework::Tensor *y, framework::Tensor *z) {
  int axis = ctx.Attr<int>("axis");
  auto x_dims = x->dims();
  auto y_dims = y->dims();
  if (x_dims.size() >= y_dims.size()) {
    ElementwiseComputeEx<AddFunctor<T>, DeviceContext, T>(ctx, x, y, axis,
                                                          AddFunctor<T>(), z);
  } else {
    ElementwiseComputeEx<InverseAddFunctor<T>, DeviceContext, T>(
        ctx, x, y, axis, InverseAddFunctor<T>(), z);
  }
}

template <typename DeviceContext, typename T, class Enable = void>
struct SameDimsElemwiseAdd {
  void operator()(const framework::ExecutionContext &ctx,
                  const framework::Tensor *x, const framework::Tensor *y,
                  framework::Tensor *z);
};

template <typename DeviceContext, typename T>
class ElementwiseAddKernel : public framework::OpKernel<T> {
 public:
  void Compute(const framework::ExecutionContext &ctx) const override {
    auto *x = ctx.Input<framework::LoDTensor>("X");
    auto *y = ctx.Input<framework::LoDTensor>("Y");
    auto *z = ctx.Output<framework::LoDTensor>("Out");
    z->mutable_data<T>(ctx.GetPlace());
    auto dims_equal = x->dims() == y->dims();
    if (dims_equal) {
      SameDimsElemwiseAdd<DeviceContext, T> same_dims_add;
      same_dims_add(ctx, x, y, z);
    } else {
      default_elementwise_add<DeviceContext, T>(ctx, x, y, z);
    }
  }
};

template <typename T>
struct IdentityGrad {
  HOSTDEVICE T operator()(T x, T y, T out, T dout) const { return dout; }
};

template <typename DeviceContext, typename T>
void default_elementwise_add_grad(const framework::ExecutionContext &ctx,
                                  const framework::Tensor *x,
                                  const framework::Tensor *y,
                                  const framework::Tensor *out,
                                  const framework::Tensor *dout,
                                  framework::Tensor *dx,
                                  framework::Tensor *dy) {
  int axis = ctx.Attr<int>("axis");

  ElemwiseExplicitGradCompute<DeviceContext, T, IdentityGrad<T>,
                              IdentityGrad<T>>(ctx, *x, *y, *out, *dout, axis,
                                               dx, dy, IdentityGrad<T>(),
                                               IdentityGrad<T>());
}

template <typename DeviceContext, typename T>
typename std::enable_if<
    std::is_floating_point<T>::value &&
    std::is_same<DeviceContext, platform::CPUDeviceContext>::value>::type
elementwise_add_grad(const framework::ExecutionContext &ctx,
                     const framework::Tensor *x, const framework::Tensor *y,
                     const framework::Tensor *out,
                     const framework::Tensor *dout, framework::Tensor *dx,
                     framework::Tensor *dy) {
  auto blas = math::GetBlas<DeviceContext, T>(ctx);
  if (dx) {
    blas.VCOPY(dout->numel(), dout->data<T>(),
               dx->mutable_data<T>(ctx.GetPlace()));
  }

  if (dy) {
    blas.VCOPY(dout->numel(), dout->data<T>(),
               dy->mutable_data<T>(ctx.GetPlace()));
  }
}

template <typename DeviceContext, typename T>
typename std::enable_if<
    !std::is_floating_point<T>::value &&
    std::is_same<DeviceContext, platform::CPUDeviceContext>::value>::type
elementwise_add_grad(const framework::ExecutionContext &ctx,
                     const framework::Tensor *x, const framework::Tensor *y,
                     const framework::Tensor *out,
                     const framework::Tensor *dout, framework::Tensor *dx,
                     framework::Tensor *dy) {
  default_elementwise_add_grad<DeviceContext, T>(ctx, x, y, out, dout, dx, dy);
}

#ifdef PADDLE_WITH_CUDA
#ifdef __NVCC__

template <typename T, int Size>
struct alignas(sizeof(T) * Size) AlignedVector {
  T val[Size];
};

template <typename T>
inline int VectorizedSize(const T *pointer) {
  uint64_t address = reinterpret_cast<uint64_t>(pointer);
  constexpr int vec4 = std::alignment_of<AlignedVector<T, 4>>::value;  // NOLINT
  if (address % vec4 == 0) {
    return 4;
  }
  return 1;
}
template <typename T, int BLOCK_W, int BLOCK_H>
__global__ void MatrixColReduce(const T *__restrict__ in, T *__restrict__ out,
                                size_t width, size_t height) {
  __shared__ T sdata[BLOCK_H][BLOCK_W + 1];
  size_t idx = threadIdx.x + blockDim.x * blockIdx.x;
  size_t width_stride = gridDim.x * blockDim.x;
  size_t full_width = (width & (~((uint64_t)(BLOCK_W - 1)))) +
                      ((width & (BLOCK_W - 1)) ? BLOCK_W : 0);
  size_t full_height = (height & (~((uint64_t)(BLOCK_H - 1)))) +
                       ((height & (BLOCK_H - 1)) ? BLOCK_H : 0);

#pragma unroll
  for (size_t w = idx; w < full_width; w += width_stride) {
    sdata[threadIdx.y][threadIdx.x] = 0;
    __syncthreads();
    size_t offset = w + threadIdx.y * width;
#pragma unroll
    for (size_t h = threadIdx.y; h < full_height;
         h += BLOCK_H) {  // block-stride loop across matrix height
      sdata[threadIdx.y][threadIdx.x] +=
          (w < width && h < height) ? in[offset] : (static_cast<T>(0));
      offset += width * BLOCK_H;
    }
    __syncthreads();

    T val = sdata[threadIdx.x][threadIdx.y];
    for (int i = warpSize >> 1; i > 0; i >>= 1)
      val += platform::CudaShuffleXorSync(0xFFFFFFFF, val, i);

    __syncthreads();
    if (threadIdx.x == 0) sdata[0][threadIdx.y] = val;
    __syncthreads();
    if ((threadIdx.y == 0) && ((w) < width)) out[w] = sdata[0][threadIdx.x];
  }
}

#if CUDA_VERSION >= 10000
template <int SIZE>
__global__ void VecFP16MatrixColReduce(const __half2 *__restrict__ in,
                                       __half2 *__restrict__ out, size_t width,
                                       size_t height) {
#if CUDA_ARCH_FP16_SUPPORTED(__CUDA_ARCH__)
  int idx = threadIdx.x + blockIdx.x * blockDim.x;
  int by = blockIdx.y;
  __half2 zero = __half2half2(static_cast<__half>(0));
  const int cols = width / 2;
  for (; idx < cols; idx += blockDim.x * gridDim.x) {
    __half2 sum = zero;
    for (int row = 0; row < SIZE; row++) {
      int index = idx + (row + by * SIZE) * cols;
      sum = __hadd2(sum, in[index]);
    }

    atomicAdd(&(out[idx]), sum);
  }
#endif
}
#endif

template <typename T>
__global__ void MatrixReduceLongWidth(const T *__restrict__ in, T *out,
                                      size_t width, size_t height) {
  int idx = threadIdx.x + blockIdx.x * blockDim.x;

  for (; idx < width; idx += blockDim.x * gridDim.x) {
    T sum = static_cast<T>(0);
    for (int row = 0; row < height; row++) {
      sum += in[idx + row * width];
    }

    out[idx] = sum;
  }
}

template <typename T, int VEC_SIZE>
__global__ void VecMatrixReduceLongWidth(const T *__restrict__ in, T *out,
                                         size_t width, size_t height) {
  using LoadT = AlignedVector<T, VEC_SIZE>;
  int idx = threadIdx.x + blockIdx.x * blockDim.x;
  int w = idx * VEC_SIZE;
  int width_stride = blockDim.x * gridDim.x * VEC_SIZE;
  for (; w < width; w += width_stride) {
    T zero = static_cast<T>(0);
    T sum[VEC_SIZE] = {zero};
    T tmp_vec[VEC_SIZE] = {zero};
    LoadT *tmp_ptr = reinterpret_cast<LoadT *>(&tmp_vec);
    for (int row = 0; row < height; row++) {
      int offset = width * row + w;
      *tmp_ptr = *reinterpret_cast<const LoadT *>(&in[offset]);
      for (int v = 0; v < VEC_SIZE; v++) {
        sum[v] += tmp_vec[v];
      }
    }

    for (int v = 0; v < VEC_SIZE; v++) out[w + v] = sum[v];
  }
}
#endif
#endif
bool static RunSpecialDims(const framework::DDim &dx_dims,
                           const framework::DDim &dy_dims,
                           const framework::DDim &dout_dims, int axis) {
  auto smaller_dims = dx_dims;
  auto bigger_dims = dy_dims;
  auto smaller_dims_size = smaller_dims.size();
  auto bigger_dims_size = bigger_dims.size();
  int smaller_ignore_size = 0;
  int bigger_ignore_size = 0;
  for (int i = 0; i < smaller_dims_size; i++) {
    if (smaller_dims[i] == 1)
      smaller_ignore_size++;
    else
      break;
  }
  for (int i = 0; i < bigger_dims_size; i++) {
    if (bigger_dims[i] == 1)
      bigger_ignore_size++;
    else
      break;
  }

  int smaller_real_size = smaller_dims.size() - smaller_ignore_size;
  int bigger_real_size = bigger_dims.size() - bigger_ignore_size;

  if (smaller_real_size == bigger_real_size) return false;

  if (bigger_real_size < smaller_real_size) {
    smaller_dims = dy_dims;
    bigger_dims = dx_dims;
    std::swap(smaller_real_size, bigger_real_size);
  }
  int big_size = bigger_dims.size();
  int small_size = smaller_dims.size();
  for (int i = 1; i <= smaller_real_size; i++) {
    if (bigger_dims[big_size - i] != smaller_dims[small_size - i]) return false;
  }

  if (axis != -1 && (axis != (bigger_real_size - smaller_real_size))) {
    return false;
  }

  return true;
}

#ifdef PADDLE_WITH_CUDA
// cuda definition
template <typename DeviceContext, typename T>
typename std::enable_if<
    std::is_same<DeviceContext, platform::CUDADeviceContext>::value>::type
elementwise_add_grad(const framework::ExecutionContext &ctx,
                     const framework::Tensor *x, const framework::Tensor *y,
                     const framework::Tensor *out,
                     const framework::Tensor *dout, framework::Tensor *dx,
                     framework::Tensor *dy);
#endif

template <typename DeviceContext, typename T>
class ElementwiseAddGradKernel : public ElemwiseGradKernel<T> {
 public:
  void Compute(const framework::ExecutionContext &ctx) const override {
    ElemwiseGradKernel<T>::Compute(ctx);

    using Tensor = framework::Tensor;

    auto *x = ctx.Input<Tensor>("X");
    auto *y = ctx.Input<Tensor>("Y");
    auto *dout = ctx.Input<Tensor>(framework::GradVarName("Out"));
    auto *dx = ctx.Output<Tensor>(framework::GradVarName("X"));
    auto *dy = ctx.Output<Tensor>(framework::GradVarName("Y"));
    // skip out
    auto *out = dout;

#ifdef PADDLE_WITH_CUDA
#ifdef __NVCC__

    int axis = ctx.Attr<int>("axis");
    if (ctx.GetPlace() == platform::CUDAPlace() && dx != nullptr &&
        dy != nullptr && dout != nullptr && dx->numel() != dy->numel() &&
        RunSpecialDims(dx->dims(), dy->dims(), dout->dims(), axis)) {
      auto *dx_data = dx->mutable_data<T>(ctx.GetPlace());
      auto *dy_data = dy->mutable_data<T>(ctx.GetPlace());
      auto *dout_data = dout->data<T>();
      auto stream = ctx.cuda_device_context().stream();
      auto *out_data = dx_data;
      int width = dx->numel();
      int height = dout->numel() / width;
      if (dx->dims() == dout->dims()) {
        width = dy->numel();
        height = dout->numel() / width;
        out_data = dy_data;
        framework::TensorCopy(
            *dout, ctx.GetPlace(),
            ctx.template device_context<platform::DeviceContext>(), dx);
      } else {
        framework::TensorCopy(
            *dout, ctx.GetPlace(),
            ctx.template device_context<platform::DeviceContext>(), dy);
      }
      // special optimization using cub
      if (width == 1) {
        int nums = height;
        size_t temp_storage_bytes = 0;
        auto err = cub::DeviceReduce::Sum(nullptr, temp_storage_bytes,
                                          dout_data, out_data, nums, stream);
        PADDLE_ENFORCE_CUDA_SUCCESS(err);
        framework::Tensor tmp;
        auto *temp_storage = tmp.mutable_data<uint8_t>(
            framework::make_ddim({static_cast<int64_t>(temp_storage_bytes)}),
            ctx.GetPlace());
        err = cub::DeviceReduce::Sum(temp_storage, temp_storage_bytes,
                                     dout_data, out_data, nums, stream);
        PADDLE_ENFORCE_CUDA_SUCCESS(err);
        return;
      }

      constexpr int block_x = 32;
      constexpr int block_y = 32;
      dim3 blocks(block_x, block_y);

      int max_physical_threads =
          ctx.cuda_device_context().GetMaxPhysicalThreadCount();
      int max_blocks = std::max(max_physical_threads / (block_x * block_y), 1);
      int theory_block = (width + blocks.x - 1) / blocks.x;
      dim3 grids(std::min(theory_block, max_blocks));
#if CUDA_VERSION >= 10000
      if (std::is_same<T, paddle::platform::float16>::value && width < 2048 &&
          width % 2 == 0 && height % 64 == 0) {
        auto &dev_ctx =
            ctx.template device_context<platform::CUDADeviceContext>();
        math::SetConstant<platform::CUDADeviceContext, T> functor;
        if (dout->dims() == dx->dims())
          functor(dev_ctx, dy, static_cast<T>(0));
        else
          functor(dev_ctx, dx, static_cast<T>(0));
        const __half2 *ptr1 = reinterpret_cast<const __half2 *>(dout_data);
        __half2 *ptr2 = reinterpret_cast<__half2 *>(out_data);
        const int threads = 128;
        dim3 grid(1, (height + 64 - 1) / 64);
        VecFP16MatrixColReduce<64><<<grid, threads, 0, stream>>>(ptr1, ptr2,
                                                                 width, height);
        return;
      }
#endif

      if (width / height < 32) {
        MatrixColReduce<T, block_x, block_y><<<grids, blocks, 0, stream>>>(
            dout_data, out_data, width, height);
      } else {
        size_t thread_nums = 1024;
        size_t block_nums = (width + thread_nums - 1) / thread_nums;
        int vec_size = VectorizedSize<T>(dout_data);
        if (vec_size == 4 && width % 4 == 0) {
          block_nums = (width / vec_size + thread_nums - 1) / thread_nums;
          VecMatrixReduceLongWidth<T,
                                   4><<<block_nums, thread_nums, 0, stream>>>(
              dout_data, out_data, width, height);
        } else {
          MatrixReduceLongWidth<T><<<block_nums, thread_nums, 0, stream>>>(
              dout_data, out_data, width, height);
        }
      }
      return;
    }

#endif
#endif
    // Special case when dy is not needed and dx doesn't reduce
    if (dx != nullptr && dy == nullptr && dx->dims() == dout->dims()) {
      VLOG(4) << "Special case when dy is not needed and dx doesn't "
                 "reduce";
      framework::TensorCopy(
          *dout, ctx.GetPlace(),
          ctx.template device_context<platform::DeviceContext>(), dx);
    } else if (dx == nullptr && dy != nullptr && dy->dims() == dout->dims()) {
      VLOG(4) << "Special case when dx is not needed and dy doesn't "
                 "reduce";
      framework::TensorCopy(
          *dout, ctx.GetPlace(),
          ctx.template device_context<platform::DeviceContext>(), dy);
    } else if (dx != nullptr && dy != nullptr && (dx->dims() == dy->dims())) {
      elementwise_add_grad<DeviceContext, T>(ctx, x, y, out, dout, dx, dy);
    } else {
      default_elementwise_add_grad<DeviceContext, T>(ctx, x, y, out, dout, dx,
                                                     dy);
    }
  }
};

template <typename DeviceContext, typename T>
class ElementwiseAddDoubleGradKernel : public framework::OpKernel<T> {
 public:
  void Compute(const framework::ExecutionContext &ctx) const override {
    using Tensor = framework::Tensor;

    auto *y = ctx.Input<Tensor>("Y");
    auto *dout = ctx.Input<Tensor>("DOut");
    auto *ddx = ctx.Input<Tensor>("DDX");
    auto *ddy = ctx.Input<Tensor>("DDY");

    auto *ddout = ctx.Output<Tensor>("DDOut");

    // ddOut = ddx + ddy
    if (ddout) {
      Tensor ddx_safe, ddy_safe;
      GetDoubleGradSafeTensor<DeviceContext, T>(ctx, dout, ddx, &ddx_safe);
      GetDoubleGradSafeTensor<DeviceContext, T>(ctx, y, ddy, &ddy_safe);

      ddout->mutable_data<T>(ctx.GetPlace());
      default_elementwise_add<DeviceContext, T>(ctx, &ddx_safe, &ddy_safe,
                                                ddout);
    }
  }
};

}  // namespace operators
}  // namespace paddle