Method SetReduceDim

paddle/phi/kernels/funcs/reduce_function.h:303–385

set reduce_dim, left_dim and update x_dim eg: x_dim = [2, 4, 6] origin_reduce_dims = [0, 1] --SetReduceDim--> x_dim = [8,6], reduce_dim = [0], left_dim = [1]

  // eg: x_dim = [2, 4, 6] origin_reduce_dims = [0, 1]
  //     --SetReduceDim--> x_dim = [8,6], reduce_dim = [0], left_dim = [1]
  void SetReduceDim() {
    std::set<int64_t> reduce_set;
    for (auto e : reduce_dims_origin) {
      auto pos = e >= 0 ? e : e + x_dim.size();
      reduce_set.insert(pos);
    }

    std::vector<int64_t> reduce_dim_temp(reduce_set.begin(), reduce_set.end());
    std::sort(reduce_dim_temp.begin(), reduce_dim_temp.end());

    // update reduce_dim and x_dim
    std::vector<int64_t> x_new_dim;

    reduce_dim.push_back(reduce_dim_temp[0]);
    x_new_dim.push_back(x_dim[0]);

    int64_t idx_reduce = 1;
    int64_t num = 0;

    if (reduce_dim_temp.size() > 1) {
      for (int64_t i = 1; i < x_dim.size(); i++) {
        if ((idx_reduce < reduce_dim_temp.size()) &&
            (i == reduce_dim_temp[idx_reduce])) {
          int64_t result =
              reduce_dim_temp[idx_reduce] - reduce_dim[reduce_dim.size() - 1];
          bool is_equal = ((result - num) == 1);
          if (is_equal) {
            x_new_dim[x_new_dim.size() - 1] *= x_dim[i];
            num++;
          } else {
            reduce_dim.push_back(reduce_dim_temp[idx_reduce] - num);
            x_new_dim.push_back(x_dim[i]);
          }
          idx_reduce++;
        } else {
          x_new_dim.push_back(x_dim[i]);
        }
      }
    } else {
      x_new_dim = x_dim;
    }

    // update x_dim
    x_dim = x_new_dim;
    std::vector<int64_t>().swap(x_new_dim);

    std::vector<int64_t> reduce_dim_new;
    int64_t is_reduced = 0;
    for (auto e : reduce_dim) {
      is_reduced |= 1 << e;
    }

    std::vector<int64_t>().swap(reduce_dim);

    for (int64_t i = 0; i < x_dim.size(); i++) {
      if ((i == 0) || (((is_reduced >> i) ^ (is_reduced >> (i - 1))) & 1)) {
        x_new_dim.push_back(x_dim[i]);
        if ((is_reduced >> i) & 1)