composite_backward_api.h

// Copyright (c) 2022 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 "paddle/fluid/prim/api/all.h"
#include "paddle/fluid/prim/api/generated_prim/prim_generated_api.h"
#include "paddle/phi/common/int_array.h"
#include "paddle/phi/core/ddim.h"
namespace paddle {
namespace prim {
using Tensor = paddle::experimental::Tensor;
using IntArray =
    paddle::experimental::IntArrayBase<paddle::experimental::Tensor>;
//  This function should have as same signature as phi, which defined in
//  paddle/phi/api/backward/backward_api.h
template <typename T>
void cast_grad(const Tensor& out_grad, DataType dtype, Tensor* x_grad) {
  if (x_grad) {
    auto res = cast<T>(out_grad, dtype);
    set_output<T>(res, x_grad);
  }
}
template <typename T>
void gather_grad(const Tensor& x,
                 const Tensor& index,
                 const Tensor& out_grad,
                 const Scalar& axis,
                 bool overwrite,
                 Tensor* grad_x) {
  auto zero_tensor = full<T>(phi::vectorize(x.dims()), 0.0, x.dtype());
  std::vector<int> tmp_perm;

  // change axis to rank 0
  int axis_value = axis.to<int>();
  tmp_perm.push_back(axis_value);
  // make other ranks
  for (int i = 0; i < x.dims().size(); ++i) {
    if (i != axis_value) {
      tmp_perm.push_back(i);
    }
  }
  std::vector<int> reverse_perm(tmp_perm);
  // make origin ranks
  for (int i = 0; i < static_cast<int>(tmp_perm.size()); ++i) {
    reverse_perm[tmp_perm[i]] = i;
  }

  // transpose out_grad and zero grad to target rank.
  auto tmp_zero_x_grad = transpose<T>(zero_tensor, tmp_perm);
  auto tmp_out_grad = transpose<T>(out_grad, tmp_perm);
  // scatter grad to grad_x
  auto tmp_grad_x = scatter<T>(tmp_zero_x_grad, index, tmp_out_grad, false);
  auto tmp_grad_x_tranposed = transpose<T>(tmp_grad_x, reverse_perm);
  set_output<T>(tmp_grad_x_tranposed, grad_x);
}

template <typename T>
void tanh_grad(const Tensor& out, const Tensor& grad_out, Tensor* grad_x) {
  if (!grad_x) return;
  auto grad_x_tmp = grad_out * (1 - out * out);
  set_output<T>(grad_x_tmp, grad_x);
}

template <typename T>
void reshape_grad(const Tensor& x, const Tensor& grad_out, Tensor* grad_x) {
  if (grad_x) {
    auto grad_x_tmp = reshape<T>(grad_out, phi::vectorize(x.dims()));
    set_output<T>(grad_x_tmp, grad_x);
  }
}

template <typename T>
void transpose_grad(const Tensor& grad_out,
                    const std::vector<int>& perm,
                    Tensor* grad_x) {
  if (grad_x) {
    std::vector<int> reverse_perm(perm);
    // make origin ranks
    for (int i = 0; i < static_cast<int>(perm.size()); ++i) {
      reverse_perm[perm[i]] = i;
    }
    auto grad_x_tmp = transpose<T>(grad_out, reverse_perm);
    set_output<T>(grad_x_tmp, grad_x);
  }
}

template <typename T>
void subtract_grad(const Tensor& x,
                   const Tensor& y,
                   const Tensor& out_grad,
                   int axis,
                   Tensor* dx,
                   Tensor* dy) {
  if (dy) {
    auto scale_out_grad = scale<T>(out_grad, -1.0, 0.0, true);
    if (x.dims() != y.dims()) {
      // Maybe need reduce here
      phi::DDim reduce_dim = get_reduce_dims(y.dims(), x.dims());
      if (!reduce_dim.size()) {
        by_pass<T>(scale_out_grad, dy);
      } else {
        auto dy_reduce_res =
            scale_out_grad.sum(phi::vectorize(reduce_dim), y.dtype(), false);
        auto dy_tmp = reshape<T>(dy_reduce_res, phi::vectorize(y.dims()));
        set_output<T>(dy_tmp, dy);
      }
    } else {
      by_pass<T>(scale_out_grad, dy);
    }
  }
  if (dx) {
    if (y.dims() != x.dims()) {
      // Maybe need reduce here
      auto reduce_dim = get_reduce_dims(x.dims(), y.dims());
      if (!reduce_dim.size()) {
        by_pass<T>(out_grad, dx);
      } else {
        auto dx_reduce_res =
            out_grad.sum(phi::vectorize(reduce_dim), x.dtype(), false);
        auto dx_tmp = reshape<T>(dx_reduce_res, phi::vectorize(x.dims()));
        set_output<T>(dx_tmp, dx);
      }
    } else {
      by_pass<T>(out_grad, dx);
    }
  }
}

template <typename T>
void add_grad(const Tensor& x,
              const Tensor& y,
              const Tensor& out_grad,
              int axis,
              Tensor* dx,
              Tensor* dy) {
  if (dy) {
    if (x.dims() != y.dims()) {
      // Maybe need reduce here
      phi::DDim reduce_dim = get_reduce_dims(y.dims(), x.dims());
      if (!reduce_dim.size()) {
        by_pass<T>(out_grad, dy);
      } else {
        auto dy_reduce_res =
            out_grad.sum(phi::vectorize(reduce_dim), y.dtype(), false);
        auto dy_tmp = reshape<T>(dy_reduce_res, phi::vectorize(y.dims()));
        set_output<T>(dy_tmp, dy);
      }

    } else {
      by_pass<T>(out_grad, dy);
    }
  }
  if (dx) {
    if (y.dims() != x.dims()) {
      // Maybe need reduce here
      auto reduce_dim = get_reduce_dims(x.dims(), y.dims());
      if (!reduce_dim.size()) {
        by_pass<T>(out_grad, dx);
      } else {
        auto dx_reduce_res =
            out_grad.sum(phi::vectorize(reduce_dim), x.dtype(), false);
        auto dx_tmp = reshape<T>(dx_reduce_res, phi::vectorize(x.dims()));
        set_output<T>(dx_tmp, dx);
      }
    } else {
      by_pass<T>(out_grad, dx);
    }
  }
}

template <typename T>
void sum_grad(const Tensor& x,
              const Tensor& out_grad,
              const IntArray& axis,
              bool keepdim,
              bool reduce_all,
              Tensor* x_grad) {
  if (!x_grad) {
    return;
  }
  std::vector<int64_t> x_dim = phi::vectorize<int64_t>(x.dims());
  int64_t axis_size = axis.size();
  int64_t x_dim_size = x_dim.size();
  reduce_all = false;
  if (reduce_all || axis_size == 0 || axis_size == x_dim_size) {
    reduce_all = true;
  } else {
    reduce_all = false;
  }
  auto x_grad_tmp = Tensor();
  if (x_dim_size == 1) {
    x_grad_tmp = out_grad.expand(IntArray(x_dim));
  } else {
    if (!keepdim) {
      auto axis_ = std::vector<int64_t>();
      if (reduce_all) {
        for (int64_t i = 1; i < x_dim_size; i++) {
          axis_.push_back(i);
        }
      } else {
        axis_ = axis.GetData();
        for (int64_t i = 0; i < axis_size; i++) {
          if (axis[i] < 0) {
            axis_[i] = axis[i] + x_dim_size;
          }
        }
      }
      auto out_grad_ = unsqueeze<T>(out_grad, axis_);
      x_grad_tmp = out_grad_.expand(IntArray(x_dim));
    } else {
      x_grad_tmp = out_grad.expand(IntArray(x_dim));
    }
  }

  set_output<T>(x_grad_tmp, x_grad);
}

template <typename T>
void divide_grad(const Tensor& x,
                 const Tensor& y,
                 const Tensor& out,
                 const Tensor& out_grad,
                 int axis,
                 Tensor* dx,
                 Tensor* dy) {
  if (dy) {
    // dy = -(x/y^2) * dout
    auto dy_res = -(x / y.pow(2.0)) * out_grad;
    if (x.dims() != y.dims()) {
      // Maybe need reduce here
      phi::DDim reduce_dim = get_reduce_dims(y.dims(), x.dims());
      if (!reduce_dim.size()) {
        set_output<T>(dy_res, dy);
      } else {
        auto dy_reduce_res =
            dy_res.sum(phi::vectorize(reduce_dim), y.dtype(), false);
        auto dy_tmp = reshape<T>(dy_reduce_res, phi::vectorize(y.dims()));
        set_output<T>(dy_tmp, dy);
      }
    } else {
      set_output<T>(dy_res, dy);
    }
  }  // indicate we will compute dy
  if (dx) {
    // dx = (1/y) * dout
    auto one_tensor = full<T>(phi::vectorize(y.dims()), 1.0, y.dtype());
    auto dx_res = one_tensor / y * out_grad;
    if (y.dims() != x.dims()) {
      // Maybe need reduce here
      auto reduce_dim = get_reduce_dims(x.dims(), y.dims());
      if (!reduce_dim.size()) {
        set_output<T>(dx_res, dx);
      } else {
        auto dx_reduce_res =
            dx_res.sum(phi::vectorize(reduce_dim), x.dtype(), false);
        auto dx_tmp = reshape<T>(dx_reduce_res, phi::vectorize(x.dims()));
        set_output<T>(dx_tmp, dx);
      }

    } else {
      set_output<T>(dx_res, dx);
    }
  }  // indicate we will compute dx
}

template <typename T>
void sqrt_grad(const Tensor& out, const Tensor& out_grad, Tensor* x_grad) {
  if (x_grad) {
    // This calculation is important for resnet.
    auto x_grad_tmp = (0.5 / out) * out_grad;
    set_output<T>(x_grad_tmp, x_grad);
  }
}

template <typename T>
void multiply_grad(const Tensor& x,
                   const Tensor& y,
                   const Tensor& out_grad,
                   int axis,
                   Tensor* x_grad,
                   Tensor* y_grad) {
  if (x_grad) {
    auto x_grad_unreduce = out_grad * y;
    if (x_grad_unreduce.dims() != x.dims()) {
      auto axes = get_reduce_dims_from_out(x_grad_unreduce.dims(), x.dims());
      if (!axes.size()) {
        set_output<T>(x_grad_unreduce, x_grad);
      } else {
        auto x_grad_reduced = x_grad_unreduce.sum(
            phi::vectorize(axes), x_grad_unreduce.dtype(), false);
        if (x_grad_reduced.dims().size() != x.dims().size()) {
          x_grad_reduced = reshape<T>(x_grad_reduced, x.shape());
        }
        set_output<T>(x_grad_reduced, x_grad);
      }
    } else {
      set_output<T>(x_grad_unreduce, x_grad);
    }
  }
  if (y_grad) {
    auto y_grad_unreduce = out_grad * x;
    if (y_grad_unreduce.dims() != y.dims()) {
      auto axes = get_reduce_dims_from_out(y_grad_unreduce.dims(), y.dims());
      if (!axes.size()) {
        set_output<T>(y_grad_unreduce, y_grad);
      } else {
        auto y_grad_reduced = y_grad_unreduce.sum(
            phi::vectorize(axes), y_grad_unreduce.dtype(), false);
        if (y_grad_reduced.dims().size() != y.dims().size()) {
          y_grad_reduced = reshape<T>(y_grad_reduced, y.shape());
        }
        set_output<T>(y_grad_reduced, y_grad);
      }
    } else {
      set_output<T>(y_grad_unreduce, y_grad);
    }
  }
}

template <typename T>
void expand_grad(const Tensor& x,
                 const Tensor& out_grad,
                 const IntArray& shape,
                 Tensor* x_grad) {
  if (x_grad) {
    auto out_dims = phi::make_ddim(shape.GetData());
    if (out_dims != x.dims()) {
      auto axes = get_reduce_dims(x.dims(), out_dims);
      if (!axes.size()) {
        by_pass<T>(out_grad, x_grad);
      } else {
        auto reduced = out_grad.sum(phi::vectorize(axes), x.dtype(), false);
        if (reduced.dims().size() != x.dims().size()) {
          reduced = reshape<T>(reduced, x.shape());
        }
        set_output<T>(reduced, x_grad);
      }
    } else {
      by_pass<T>(out_grad, x_grad);
    }
  }
}

template <typename T>
void exp_grad(const Tensor& out, const Tensor& out_grad, Tensor* x_grad) {
  if (x_grad) {
    set_output<T>(out_grad * out, x_grad);
  }
}

template <typename T>
void matmul_double_grad(const Tensor& x,
                        const Tensor& y,
                        const Tensor& grad_out,
                        const paddle::optional<Tensor>& grad_x_grad,
                        const paddle::optional<Tensor>& grad_y_grad,
                        bool transpose_x,
                        bool transpose_y,
                        Tensor* x_grad,
                        Tensor* y_grad,
                        Tensor* grad_out_grad) {
  // Get dims from the input x, y, output_grad
  std::vector<std::int64_t> x_dims = vectorize(x.dims());
  std::vector<std::int64_t> y_dims = vectorize(y.dims());
  std::vector<std::int64_t> grad_out_dims = vectorize(grad_out.dims());

  int x_ndim = x_dims.size();
  int y_ndim = y_dims.size();
  int dout_ndim = grad_out_dims.size();

  // prepare dims for x_ndim <= 1 || y_ndim <= 1
  Tensor x_help, y_help, xg_help, yg_help, out_help;

  if (x_ndim == 1 && y_ndim == 1) {
    transpose_x = false;
    transpose_y = false;
    x_help = reshape<T>(x, IntArray(std::vector<int64_t>({1, x_dims[0]})));
    y_help = reshape<T>(y, IntArray(std::vector<int64_t>({y_dims[0], 1})));
    if (grad_x_grad) {
      xg_help = reshape<T>(grad_x_grad.get(),
                           IntArray(std::vector<int64_t>({1, x_dims[0]})));
    }
    if (grad_y_grad) {
      yg_help = reshape<T>(grad_y_grad.get(),
                           IntArray(std::vector<int64_t>({y_dims[0], 1})));
    }
    out_help = reshape<T>(grad_out, IntArray(std::vector<int64_t>({1, 1})));

  } else if (x_ndim == 1) {
    transpose_x = false;
    x_help = reshape<T>(x, IntArray(std::vector<int64_t>({1, x_dims[0]})));
    y_help = y;
    if (grad_x_grad) {
      xg_help = reshape<T>(grad_x_grad.get(),
                           IntArray(std::vector<int64_t>({1, x_dims[0]})));
    }
    if (grad_y_grad) {
      yg_help = grad_y_grad.get();
    }
    auto tmp_grad_out_dims = grad_out_dims;
    tmp_grad_out_dims.insert(tmp_grad_out_dims.begin(), 1);
    out_help = reshape<T>(grad_out, IntArray(tmp_grad_out_dims));

  } else if (y_ndim == 1) {
    transpose_y = false;
    x_help = x;
    y_help = reshape<T>(y, IntArray(std::vector<int64_t>({y_dims[0], 1})));
    if (grad_x_grad) {
      xg_help = grad_x_grad.get();
    }
    if (grad_y_grad) {
      yg_help = reshape<T>(grad_y_grad.get(),
                           IntArray(std::vector<int64_t>({y_dims[0], 1})));
    }
    auto tmp_grad_out_dims = grad_out_dims;
    tmp_grad_out_dims.push_back(1);
    out_help = reshape<T>(grad_out, IntArray(tmp_grad_out_dims));

  } else {
    x_help = x;
    y_help = y;
    if (grad_x_grad) {
      xg_help = grad_x_grad.get();
    }
    if (grad_y_grad) {
      yg_help = grad_y_grad.get();
    }
    out_help = grad_out;
  }

  bool is_broadcast = true;
  if (x_ndim <= 2 && y_ndim <= 2) {
    is_broadcast = false;
  } else if (x_ndim != y_ndim) {
    is_broadcast = true;
  } else {
    is_broadcast = !std::equal(
        x_dims.cbegin(), x_dims.cbegin() + x_ndim - 2, y_dims.cbegin());
  }
  Tensor dx, dy, ddout_1, ddout_2, ddout;
  if (!grad_x_grad && !grad_y_grad) {
    x_grad = nullptr;
    y_grad = nullptr;
    grad_out_grad = nullptr;
    return;

  } else if (!grad_x_grad) {
    y_grad = nullptr;
    if (!transpose_x && !transpose_y) {
      if (x_grad) {
        dx = matmul<T>(out_help, yg_help, false, true);
      }
      if (grad_out_grad) {
        ddout = matmul<T>(x_help, yg_help, false, false);
      }
    } else if (!transpose_x && transpose_y) {
      if (x_grad) {
        dx = matmul<T>(out_help, yg_help, false, false);
      }
      if (grad_out_grad) {
        ddout = matmul<T>(x_help, yg_help, false, true);
      }
    } else if (transpose_x && !transpose_y) {
      if (x_grad) {
        dx = matmul<T>(yg_help, out_help, false, true);
      }
      if (grad_out_grad) {
        ddout = matmul<T>(x_help, yg_help, true, false);
      }
    } else {
      if (x_grad) {
        dx = matmul<T>(yg_help, out_help, true, true);
      }
      if (grad_out_grad) {
        ddout = matmul<T>(x_help, yg_help, true, true);
      }
    }

  } else if (!grad_y_grad) {
    x_grad = nullptr;
    if (!transpose_x && !transpose_y) {
      if (y_grad) {
        dy = matmul<T>(xg_help, out_help, true, false);
      }
      if (grad_out_grad) {
        ddout = matmul<T>(xg_help, y_help, false, false);
      }
    } else if (!transpose_x && transpose_y) {
      if (y_grad) {
        dy = matmul<T>(out_help, xg_help, true, false);
      }
      if (grad_out_grad) {
        ddout = matmul<T>(xg_help, y_help, false, true);
      }
    } else if (transpose_x && !transpose_y) {
      if (y_grad) {
        dy = matmul<T>(xg_help, out_help, false, false);
      }
      if (grad_out_grad) {
        ddout = matmul<T>(xg_help, y_help, true, false);
      }
    } else {
      if (y_grad) {
        dy = matmul<T>(out_help, xg_help, true, true);
      }
      if (grad_out_grad) {
        ddout = matmul<T>(xg_help, y_help, true, true);
      }
    }

  } else {
    if (!transpose_x && !transpose_y) {
      if (x_grad) {
        dx = matmul<T>(out_help, yg_help, false, true);
      }
      if (y_grad) {
        dy = matmul<T>(xg_help, out_help, true, false);
      }
      if (grad_out_grad) {
        ddout_1 = matmul<T>(x_help, yg_help, false, false);
        ddout_2 = matmul<T>(xg_help, y_help, false, false);
        ddout = add<T>(ddout_1, ddout_2);
      }
    } else if (!transpose_x && transpose_y) {
      if (x_grad) {
        dx = matmul<T>(out_help, yg_help, false, false);
      }

      if (y_grad) {
        dy = matmul<T>(out_help, xg_help, true, false);
      }
      if (grad_out_grad) {
        ddout_1 = matmul<T>(x_help, yg_help, false, true);
        ddout_2 = matmul<T>(xg_help, y_help, false, true);
        ddout = add<T>(ddout_1, ddout_2);
      }
    } else if (transpose_x && !transpose_y) {
      if (x_grad) {
        dx = matmul<T>(yg_help, out_help, false, true);
      }

      if (y_grad) {
        dy = matmul<T>(xg_help, out_help, false, false);
      }
      if (grad_out_grad) {
        ddout_1 = matmul<T>(x_help, yg_help, true, false);
        ddout_2 = matmul<T>(xg_help, y_help, true, false);
        ddout = add<T>(ddout_1, ddout_2);
      }
    } else {
      if (x_grad) {
        dx = matmul<T>(yg_help, out_help, true, true);
      }
      if (y_grad) {
        dy = matmul<T>(out_help, xg_help, true, true);
      }
      if (grad_out_grad) {
        ddout_1 = matmul<T>(x_help, yg_help, true, true);
        ddout_2 = matmul<T>(xg_help, y_help, true, true);
        ddout = add<T>(ddout_1, ddout_2);
      }
    }
  }

  if (is_broadcast) {
    // Case3: broadcast. It need cost much time to reduce sum for the
    // broadcast and wastes the memory.
    // So we should avoid the case in reality.
    VLOG(3) << "It need cost much time to reduce sum for the broadcast and "
               "wastes the memory. So we should avoid the case in reality";
    // Reduce sum to get grad by ReduceSum
    if (x_grad) {
      auto tx_dims = x_dims;
      auto tx_ndim = x_ndim;
      auto tdout_ndim = dout_ndim;
      if (x_ndim == 1) {
        tx_dims = std::vector<int64_t>({1, x_dims[0]});
        tx_ndim = x_ndim + 1;
        tdout_ndim = dout_ndim + 1;
      }

      auto x_grad_reduce_dims =
          get_reduce_dims(dx, tdout_ndim, tx_ndim, &tx_dims);

      if (!x_grad_reduce_dims.empty()) {
        dx = sum<T>(dx, IntArray(x_grad_reduce_dims), dy.dtype(), true);
      }
      reshape<T>(dx, IntArray(tx_dims));
    }

    if (y_grad) {
      auto ty_dims = y_dims;
      auto ty_ndim = y_ndim;
      auto tdout_ndim = dout_ndim;
      if (y_ndim == 1) {
        ty_dims = std::vector<int64_t>({y_dims[0], 1});
        ty_ndim = y_ndim + 1;
        tdout_ndim = dout_ndim + 1;
      }

      auto y_grad_reduce_dims =
          get_reduce_dims(dy, tdout_ndim, ty_ndim, &ty_dims);

      if (!y_grad_reduce_dims.empty()) {
        dy = sum<T>(dy, IntArray(y_grad_reduce_dims), dy.dtype(), true);
      }
      reshape<T>(dy, IntArray(ty_dims));
    }
  }

  // recover the original dim of output (delete 1)
  std::vector<int64_t> dx_dims =
      dx.initialized() ? vectorize(dx.dims()) : std::vector<int64_t>({});
  std::vector<int64_t> dy_dims =
      dy.initialized() ? vectorize(dy.dims()) : std::vector<int64_t>({});
  std::vector<int64_t> ddout_dims =
      ddout.initialized() ? vectorize(ddout.dims()) : std::vector<int64_t>({});
  if (x_ndim == 1 && y_ndim == 1) {
    if (dx.initialized() && dx_dims[0] == 1) {
      dx = reshape<T>(dx, IntArray(x_dims));
    }
    if (dy.initialized() && dy_dims.back() == 1) {
      dy = reshape<T>(dy, IntArray(y_dims));
    }
    if (ddout.initialized() && ddout_dims == std::vector<int64_t>({1, 1})) {
      ddout = reshape<T>(ddout, IntArray(std::vector<int64_t>({1})));
    }
  } else if (x_ndim == 1) {
    if (dx.initialized() && dx_dims[0] == 1) {
      dx = reshape<T>(dx, IntArray(x_dims));
    }
    if (ddout.initialized() && ddout_dims[0] == 1) {
      ddout = reshape<T>(ddout,
                         IntArray(std::vector<int64_t>(
                             {ddout_dims.cbegin() + 1, ddout_dims.cend()})));
    }
  } else if (y_ndim == 1) {
    if (dy.initialized() && dy_dims.back() == 1) {
      dy = reshape<T>(dy, IntArray(y_dims));
    }
    if (ddout.initialized() && ddout_dims.back() == 1) {
      ddout = reshape<T>(ddout,
                         IntArray(std::vector<int64_t>(
                             {ddout_dims.cbegin(),
                              ddout_dims.cbegin() + ddout_dims.size() - 1})));
    }
  }

  if (x_grad) {
    set_output<T>(dx, x_grad);
  }
  if (y_grad) {
    set_output<T>(dy, y_grad);
  }
  if (grad_out_grad) {
    set_output<T>(ddout, grad_out_grad);
  }
}

template <typename T>
void slice_grad(const Tensor& input,
                const Tensor& out_grad,
                const std::vector<int64_t>& axes,
                const IntArray& starts,
                const IntArray& ends,
                const std::vector<int64_t>& infer_flags,
                const std::vector<int64_t>& decrease_axis,
                Tensor* input_grad) {
  if (input_grad) {
    size_t rank = input.dims().size();
    auto out_dims = out_grad.dims();
    auto in_dims = input.dims();

    auto decrease_size = decrease_axis.size();
    if (decrease_size > 0) {
      if (decrease_size == static_cast<size_t>(in_dims.size())) {
        // all dims decrease
        out_dims = phi::make_ddim(std::vector<int>(decrease_size, 1));
      } else {
        std::vector<int> origin_out_shape(out_dims.size() + decrease_size, -1);
        for (size_t i = 0; i < decrease_size; ++i) {
          origin_out_shape[decrease_axis[i]] = 1;
        }

        int index = 0;
        for (size_t i = 0; i < origin_out_shape.size(); ++i) {
          if (origin_out_shape[i] == -1) {
            origin_out_shape[i] = out_dims[index];
            ++index;
          }
        }
        out_dims = phi::make_ddim(origin_out_shape);
      }
    }

    std::vector<int> offsets(rank, 0);
    std::vector<int> extents(rank, 0);
    for (size_t i = 0; i < rank; ++i) {
      offsets[i] = 0;
      extents[i] = out_dims[i];
    }

    for (size_t i = 0; i < axes.size(); ++i) {
      int axis = axes[i];
      int64_t start = starts[i] < 0 ? (starts[i] + in_dims[axis]) : starts[i];
      start = std::max(start, static_cast<int64_t>(0));
      offsets[axis] = start;
    }

    std::vector<int> paddings;
    for (size_t i = 0; i < rank; ++i) {
      paddings.push_back(offsets[i]);
      paddings.push_back((in_dims[i] - out_dims[i]) - offsets[i]);
    }

    auto out_tmp = pad<T>(out_grad, paddings, 0.0);
    set_output<T>(out_tmp, input_grad);
  }
}

template <typename T>
void cumsum_grad(const Tensor& x,
                 const Tensor& out_grad,
                 const Scalar& axis,
                 bool flatten,
                 bool exclusive,
                 bool reverse,
                 Tensor* x_grad) {
  if (x_grad) {
    auto grad = cumsum<T>(out_grad, axis, flatten, exclusive, !reverse);
    grad = reshape<T>(grad, x.shape());
    set_output<T>(grad, x_grad);
  }
}

template <typename T>
void topk_grad(const Tensor& x,
               const Tensor& indices,
               const Tensor& out_grad,
               const Scalar& k,
               const int& axis,
               const bool& largest,
               const bool& sorted,
               Tensor* x_grad) {
  if (x_grad) {
    auto zero_tensor = full<T>(phi::vectorize(x.dims()), 0.0, x.dtype());
    auto x_grad_tmp = put_along_axis<T>(zero_tensor, indices, out_grad, axis);

    set_output<T>(x_grad_tmp, x_grad);
  }
}

}  // namespace prim
}  // namespace paddle