treelite_importer.hpp

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/*
 * Copyright (c) 2023, NVIDIA CORPORATION.
 *
 * 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 <cmath>
#include <cstddef>
#include <cuml/experimental/fil/constants.hpp>
#include <cuml/experimental/fil/decision_forest.hpp>
#include <cuml/experimental/fil/detail/decision_forest_builder.hpp>
#include <cuml/experimental/fil/detail/index_type.hpp>
#include <cuml/experimental/fil/exceptions.hpp>
#include <cuml/experimental/fil/forest_model.hpp>
#include <cuml/experimental/fil/postproc_ops.hpp>
#include <cuml/experimental/fil/tree_layout.hpp>
#include <queue>
#include <stack>
#include <treelite/c_api.h>
#include <treelite/tree.h>
#include <treelite/typeinfo.h>
 
namespace ML {
namespace experimental {
namespace fil {
 
namespace detail {
template <tree_layout layout, typename T>
struct traversal_container {
  using backing_container_t =
    std::conditional_t<layout == tree_layout::depth_first, std::stack<T>, std::queue<T>>;
  void add(T const& val) { data_.push(val); }
  void add(T const& hot, T const& distant)
  {
    if constexpr (layout == tree_layout::depth_first) {
      data_.push(distant);
      data_.push(hot);
    } else {
      data_.push(hot);
      data_.push(distant);
    }
  }
  auto next()
  {
    if constexpr (std::is_same_v<backing_container_t, std::stack<T>>) {
      auto result = data_.top();
      data_.pop();
      return result;
    } else {
      auto result = data_.front();
      data_.pop();
      return result;
    }
  }
  auto peek()
  {
    if constexpr (std::is_same_v<backing_container_t, std::stack<T>>) {
      return data_.top();
    } else {
      return data_.front();
    }
  }
  [[nodiscard]] auto empty() { return data_.empty(); }
  auto size() { return data_.size(); }
 
 private:
  backing_container_t data_;
};
 
struct postproc_params_t {
  element_op element = element_op::disable;
  row_op row         = row_op::disable;
  double constant    = 1.0;
};
}  // namespace detail
 
template <tree_layout layout>
struct treelite_importer {
  template <typename tl_threshold_t, typename tl_output_t>
  struct treelite_node {
    treelite::Tree<tl_threshold_t, tl_output_t> const& tree;
    int node_id;
    index_type parent_index;
    index_type own_index;
 
    auto is_leaf() { return tree.IsLeaf(node_id); }
 
    auto get_output()
    {
      auto result = std::vector<tl_output_t>{};
      if (tree.HasLeafVector(node_id)) {
        result = tree.LeafVector(node_id);
      } else {
        result.push_back(tree.LeafValue(node_id));
      }
      return result;
    }
 
    auto get_categories() { return tree.MatchingCategories(node_id); }
 
    auto get_feature() { return tree.SplitIndex(node_id); }
 
    auto is_categorical()
    {
      return tree.SplitType(node_id) == treelite::SplitFeatureType::kCategorical;
    }
 
    auto default_distant()
    {
      auto result        = false;
      auto default_child = tree.DefaultChild(node_id);
      if (is_categorical()) {
        if (tree.CategoriesListRightChild(node_id)) {
          result = (default_child == tree.RightChild(node_id));
        } else {
          result = (default_child == tree.LeftChild(node_id));
        }
      } else {
        auto tl_operator = tree.ComparisonOp(node_id);
        if (tl_operator == treelite::Operator::kLT || tl_operator == treelite::Operator::kLE) {
          result = (default_child == tree.LeftChild(node_id));
        } else {
          result = (default_child == tree.RightChild(node_id));
        }
      }
      return result;
    }
 
    auto threshold() { return tree.Threshold(node_id); }
 
    auto categories()
    {
      auto result = decltype(tree.MatchingCategories(node_id)){};
      if (is_categorical()) { result = tree.MatchingCategories(node_id); }
      return result;
    }
 
    auto is_inclusive()
    {
      auto tl_operator = tree.ComparisonOp(node_id);
      return tl_operator == treelite::Operator::kGT || tl_operator == treelite::Operator::kLE;
    }
  };
 
  template <typename tl_threshold_t, typename tl_output_t, typename lambda_t>
  void node_for_each(treelite::Tree<tl_threshold_t, tl_output_t> const& tl_tree, lambda_t&& lambda)
  {
    using node_index_t = decltype(tl_tree.LeftChild(0));
    auto to_be_visited = detail::traversal_container<layout, node_index_t>{};
    to_be_visited.add(node_index_t{});
 
    auto parent_indices = detail::traversal_container<layout, index_type>{};
    auto cur_index      = index_type{};
    parent_indices.add(cur_index);
 
    while (!to_be_visited.empty()) {
      auto node_id        = to_be_visited.next();
      auto remaining_size = to_be_visited.size();
 
      auto tl_node = treelite_node<tl_threshold_t, tl_output_t>{
        tl_tree, node_id, parent_indices.next(), cur_index};
      lambda(tl_node, node_id);
 
      if (!tl_tree.IsLeaf(node_id)) {
        auto tl_left_id  = tl_tree.LeftChild(node_id);
        auto tl_right_id = tl_tree.RightChild(node_id);
        auto tl_operator = tl_tree.ComparisonOp(node_id);
        if (!tl_node.is_categorical()) {
          if (tl_operator == treelite::Operator::kLT || tl_operator == treelite::Operator::kLE) {
            to_be_visited.add(tl_right_id, tl_left_id);
          } else if (tl_operator == treelite::Operator::kGT ||
                     tl_operator == treelite::Operator::kGE) {
            to_be_visited.add(tl_left_id, tl_right_id);
          } else {
            throw model_import_error("Unrecognized Treelite operator");
          }
        } else {
          if (tl_tree.CategoriesListRightChild(node_id)) {
            to_be_visited.add(tl_left_id, tl_right_id);
          } else {
            to_be_visited.add(tl_right_id, tl_left_id);
          }
        }
        parent_indices.add(cur_index, cur_index);
      }
      ++cur_index;
    }
  }
 
  template <typename tl_threshold_t, typename tl_output_t, typename iter_t, typename lambda_t>
  void node_transform(treelite::Tree<tl_threshold_t, tl_output_t> const& tl_tree,
                      iter_t output_iter,
                      lambda_t&& lambda)
  {
    node_for_each(tl_tree, [&output_iter, &lambda](auto&& tl_node, int tl_node_id) {
      *output_iter = lambda(tl_node);
      ++output_iter;
    });
  }
 
  template <typename tl_threshold_t, typename tl_output_t, typename T, typename lambda_t>
  auto node_accumulate(treelite::Tree<tl_threshold_t, tl_output_t> const& tl_tree,
                       T init,
                       lambda_t&& lambda)
  {
    auto result = init;
    node_for_each(tl_tree, [&result, &lambda](auto&& tl_node, int tl_node_id) {
      result = lambda(result, tl_node);
    });
    return result;
  }
 
  template <typename tl_threshold_t, typename tl_output_t>
  auto get_nodes(treelite::Tree<tl_threshold_t, tl_output_t> const& tl_tree)
  {
    auto result = std::vector<treelite_node<tl_threshold_t, tl_output_t>>{};
    result.reserve(tl_tree.num_nodes);
    node_transform(tl_tree, std::back_inserter(result), [](auto&& node) { return node; });
    return result;
  }
 
  template <typename tl_threshold_t, typename tl_output_t>
  auto get_offsets(treelite::Tree<tl_threshold_t, tl_output_t> const& tl_tree)
  {
    auto result = std::vector<index_type>(tl_tree.num_nodes);
    auto nodes  = get_nodes(tl_tree);
    for (auto i = index_type{}; i < nodes.size(); ++i) {
      // Current index should always be greater than or equal to parent index.
      // Later children will overwrite values set by earlier children, ensuring
      // that most distant offset is used.
      result[nodes[i].parent_index] = index_type{i - nodes[i].parent_index};
    }
 
    return result;
  }
 
  template <typename lambda_t>
  void tree_for_each(treelite::Model const& tl_model, lambda_t&& lambda)
  {
    tl_model.Dispatch([&lambda](auto&& concrete_tl_model) {
      std::for_each(std::begin(concrete_tl_model.trees), std::end(concrete_tl_model.trees), lambda);
    });
  }
 
  template <typename iter_t, typename lambda_t>
  void tree_transform(treelite::Model const& tl_model, iter_t output_iter, lambda_t&& lambda)
  {
    tl_model.Dispatch([&output_iter, &lambda](auto&& concrete_tl_model) {
      std::transform(std::begin(concrete_tl_model.trees),
                     std::end(concrete_tl_model.trees),
                     output_iter,
                     lambda);
    });
  }
 
  template <typename T, typename lambda_t>
  auto tree_accumulate(treelite::Model const& tl_model, T init, lambda_t&& lambda)
  {
    auto result = init;
    tree_for_each(tl_model, [&result, &lambda](auto&& tree) { result = lambda(result, tree); });
    return result;
  }
 
  auto num_trees(treelite::Model const& tl_model)
  {
    auto result = index_type{};
    tl_model.Dispatch(
      [&result](auto&& concrete_tl_model) { result = concrete_tl_model.trees.size(); });
    return result;
  }
 
  auto get_offsets(treelite::Model const& tl_model)
  {
    auto result = std::vector<std::vector<index_type>>{};
    result.reserve(num_trees(tl_model));
    tree_transform(
      tl_model, std::back_inserter(result), [this](auto&& tree) { return get_offsets(tree); });
    return result;
  }
 
  auto get_tree_sizes(treelite::Model const& tl_model)
  {
    auto result = std::vector<index_type>{};
    tree_transform(
      tl_model, std::back_inserter(result), [](auto&& tree) { return tree.num_nodes; });
    return result;
  }
 
  auto get_num_class(treelite::Model const& tl_model)
  {
    auto result = index_type{};
    tl_model.Dispatch(
      [&result](auto&& concrete_tl_model) { result = concrete_tl_model.task_param.num_class; });
    return result;
  }
 
  auto get_num_feature(treelite::Model const& tl_model)
  {
    auto result = index_type{};
    tl_model.Dispatch(
      [&result](auto&& concrete_tl_model) { result = concrete_tl_model.num_feature; });
    return result;
  }
 
  auto get_max_num_categories(treelite::Model const& tl_model)
  {
    return tree_accumulate(tl_model, index_type{}, [this](auto&& accum, auto&& tree) {
      return node_accumulate(tree, accum, [](auto&& cur_accum, auto&& tl_node) {
        auto result = cur_accum;
        for (auto&& cat : tl_node.categories()) {
          result = (cat + 1 > result) ? cat + 1 : result;
        }
        return result;
      });
    });
  }
 
  auto get_num_categorical_nodes(treelite::Model const& tl_model)
  {
    return tree_accumulate(tl_model, index_type{}, [this](auto&& accum, auto&& tree) {
      return node_accumulate(tree, accum, [](auto&& cur_accum, auto&& tl_node) {
        return cur_accum + tl_node.is_categorical();
      });
    });
  }
 
  auto get_num_leaf_vector_nodes(treelite::Model const& tl_model)
  {
    return tree_accumulate(tl_model, index_type{}, [this](auto&& accum, auto&& tree) {
      return node_accumulate(tree, accum, [](auto&& cur_accum, auto&& tl_node) {
        return cur_accum + (tl_node.is_leaf() && tl_node.get_output().size() > 1);
      });
    });
  }
 
  auto get_average_factor(treelite::Model const& tl_model)
  {
    auto result = double{};
    tl_model.Dispatch([&result](auto&& concrete_tl_model) {
      if (concrete_tl_model.average_tree_output) {
        if (concrete_tl_model.task_type == treelite::TaskType::kMultiClfGrovePerClass) {
          result = concrete_tl_model.trees.size() / concrete_tl_model.task_param.num_class;
        } else {
          result = concrete_tl_model.trees.size();
        }
      } else {
        result = 1.0;
      }
    });
    return result;
  }
 
  auto get_bias(treelite::Model const& tl_model)
  {
    auto result = double{};
    tl_model.Dispatch(
      [&result](auto&& concrete_tl_model) { result = concrete_tl_model.param.global_bias; });
    return result;
  }
 
  auto get_postproc_params(treelite::Model const& tl_model)
  {
    auto result = detail::postproc_params_t{};
    tl_model.Dispatch([&result](auto&& concrete_tl_model) {
      auto tl_pred_transform = std::string{concrete_tl_model.param.pred_transform};
      if (tl_pred_transform == std::string{"identity"} ||
          tl_pred_transform == std::string{"identity_multiclass"}) {
        result.element = element_op::disable;
        result.row     = row_op::disable;
      } else if (tl_pred_transform == std::string{"signed_square"}) {
        result.element = element_op::signed_square;
      } else if (tl_pred_transform == std::string{"hinge"}) {
        result.element = element_op::hinge;
      } else if (tl_pred_transform == std::string{"sigmoid"}) {
        result.constant = concrete_tl_model.param.sigmoid_alpha;
        result.element  = element_op::sigmoid;
      } else if (tl_pred_transform == std::string{"exponential"}) {
        result.element = element_op::exponential;
      } else if (tl_pred_transform == std::string{"exponential_standard_ratio"}) {
        result.constant = -concrete_tl_model.param.ratio_c / std::log(2);
        result.element  = element_op::exponential;
      } else if (tl_pred_transform == std::string{"logarithm_one_plus_exp"}) {
        result.element = element_op::logarithm_one_plus_exp;
      } else if (tl_pred_transform == std::string{"max_index"}) {
        result.row = row_op::max_index;
      } else if (tl_pred_transform == std::string{"softmax"}) {
        result.row = row_op::softmax;
      } else if (tl_pred_transform == std::string{"multiclass_ova"}) {
        result.constant = concrete_tl_model.param.sigmoid_alpha;
        result.element  = element_op::sigmoid;
      } else {
        throw model_import_error{"Unrecognized Treelite pred_transform string"};
      }
    });
    return result;
  }
 
  auto uses_double_thresholds(treelite::Model const& tl_model)
  {
    auto result = false;
    switch (tl_model.GetThresholdType()) {
      case treelite::TypeInfo::kFloat64: result = true; break;
      case treelite::TypeInfo::kFloat32: result = false; break;
      default: throw model_import_error("Unrecognized Treelite threshold type");
    }
    return result;
  }
 
  auto uses_double_outputs(treelite::Model const& tl_model)
  {
    auto result = false;
    switch (tl_model.GetThresholdType()) {
      case treelite::TypeInfo::kFloat64: result = true; break;
      case treelite::TypeInfo::kFloat32: result = false; break;
      case treelite::TypeInfo::kUInt32: result = false; break;
      default: throw model_import_error("Unrecognized Treelite threshold type");
    }
    return result;
  }
 
  auto uses_integer_outputs(treelite::Model const& tl_model)
  {
    auto result = false;
    switch (tl_model.GetThresholdType()) {
      case treelite::TypeInfo::kFloat64: result = false; break;
      case treelite::TypeInfo::kFloat32: result = false; break;
      case treelite::TypeInfo::kUInt32: result = true; break;
      default: throw model_import_error("Unrecognized Treelite threshold type");
    }
    return result;
  }
 
  template <index_type variant_index>
  auto import_to_specific_variant(index_type target_variant_index,
                                  treelite::Model const& tl_model,
                                  index_type num_class,
                                  index_type num_feature,
                                  index_type max_num_categories,
                                  std::vector<std::vector<index_type>> const& offsets,
                                  index_type align_bytes           = index_type{},
                                  raft_proto::device_type mem_type = raft_proto::device_type::cpu,
                                  int device                       = 0,
                                  raft_proto::cuda_stream stream   = raft_proto::cuda_stream{})
  {
    auto result = decision_forest_variant{};
    if constexpr (variant_index != std::variant_size_v<decision_forest_variant>) {
      if (variant_index == target_variant_index) {
        using forest_model_t = std::variant_alternative_t<variant_index, decision_forest_variant>;
        auto builder =
          detail::decision_forest_builder<forest_model_t>(max_num_categories, align_bytes);
        auto tree_count = num_trees(tl_model);
        auto tree_index = index_type{};
        tree_for_each(tl_model, [this, &builder, &tree_index, &offsets](auto&& tree) {
          builder.start_new_tree();
          auto node_index = index_type{};
          node_for_each(
            tree, [&builder, &tree_index, &node_index, &offsets](auto&& node, int tl_node_id) {
              if (node.is_leaf()) {
                auto output = node.get_output();
                builder.set_output_size(output.size());
                if (output.size() > index_type{1}) {
                  builder.add_leaf_vector_node(std::begin(output), std::end(output), tl_node_id);
                } else {
                  builder.add_node(typename forest_model_t::io_type(output[0]), tl_node_id, true);
                }
              } else {
                if (node.is_categorical()) {
                  auto categories = node.get_categories();
                  builder.add_categorical_node(std::begin(categories),
                                               std::end(categories),
                                               tl_node_id,
                                               node.default_distant(),
                                               node.get_feature(),
                                               offsets[tree_index][node_index]);
                } else {
                  builder.add_node(typename forest_model_t::threshold_type(node.threshold()),
                                   tl_node_id,
                                   false,
                                   node.default_distant(),
                                   false,
                                   node.get_feature(),
                                   offsets[tree_index][node_index],
                                   node.is_inclusive());
                }
              }
              ++node_index;
            });
          ++tree_index;
        });
 
        builder.set_average_factor(get_average_factor(tl_model));
        builder.set_bias(get_bias(tl_model));
        auto postproc_params = get_postproc_params(tl_model);
        builder.set_element_postproc(postproc_params.element);
        builder.set_row_postproc(postproc_params.row);
        builder.set_postproc_constant(postproc_params.constant);
 
        result.template emplace<variant_index>(
          builder.get_decision_forest(num_feature, num_class, mem_type, device, stream));
      } else {
        result = import_to_specific_variant<variant_index + 1>(target_variant_index,
                                                               tl_model,
                                                               num_class,
                                                               num_feature,
                                                               max_num_categories,
                                                               offsets,
                                                               align_bytes,
                                                               mem_type,
                                                               device,
                                                               stream);
      }
    }
    return result;
  }
 
  auto import(treelite::Model const& tl_model,
              index_type align_bytes                   = index_type{},
              std::optional<bool> use_double_precision = std::nullopt,
              raft_proto::device_type dev_type         = raft_proto::device_type::cpu,
              int device                               = 0,
              raft_proto::cuda_stream stream           = raft_proto::cuda_stream{})
  {
    auto result                = decision_forest_variant{};
    auto num_feature           = get_num_feature(tl_model);
    auto max_num_categories    = get_max_num_categories(tl_model);
    auto num_categorical_nodes = get_num_categorical_nodes(tl_model);
    auto num_leaf_vector_nodes = get_num_leaf_vector_nodes(tl_model);
    auto use_double_thresholds = use_double_precision.value_or(uses_double_thresholds(tl_model));
 
    auto offsets    = get_offsets(tl_model);
    auto max_offset = std::accumulate(
      std::begin(offsets),
      std::end(offsets),
      index_type{},
      [&offsets](auto&& cur_max, auto&& tree_offsets) {
        return std::max(cur_max,
                        *std::max_element(std::begin(tree_offsets), std::end(tree_offsets)));
      });
    auto tree_sizes = std::vector<index_type>{};
    std::transform(std::begin(offsets),
                   std::end(offsets),
                   std::back_inserter(tree_sizes),
                   [](auto&& tree_offsets) { return tree_offsets.size(); });
 
    auto variant_index = get_forest_variant_index(use_double_thresholds,
                                                  max_offset,
                                                  num_feature,
                                                  num_categorical_nodes,
                                                  max_num_categories,
                                                  num_leaf_vector_nodes,
                                                  layout);
    auto num_class     = get_num_class(tl_model);
    return forest_model{import_to_specific_variant<index_type{}>(variant_index,
                                                                 tl_model,
                                                                 num_class,
                                                                 num_feature,
                                                                 max_num_categories,
                                                                 offsets,
                                                                 align_bytes,
                                                                 dev_type,
                                                                 device,
                                                                 stream)};
  }
};
 
auto import_from_treelite_model(treelite::Model const& tl_model,
                                tree_layout layout                       = preferred_tree_layout,
                                index_type align_bytes                   = index_type{},
                                std::optional<bool> use_double_precision = std::nullopt,
                                raft_proto::device_type dev_type = raft_proto::device_type::cpu,
                                int device                       = 0,
                                raft_proto::cuda_stream stream   = raft_proto::cuda_stream{})
{
  auto result = forest_model{};
  switch (layout) {
    case tree_layout::depth_first:
      result = treelite_importer<tree_layout::depth_first>{}.import(
        tl_model, align_bytes, use_double_precision, dev_type, device, stream);
      break;
    case tree_layout::breadth_first:
      result = treelite_importer<tree_layout::breadth_first>{}.import(
        tl_model, align_bytes, use_double_precision, dev_type, device, stream);
      break;
  }
  return result;
}
 
auto import_from_treelite_handle(ModelHandle tl_handle,
                                 tree_layout layout                       = preferred_tree_layout,
                                 index_type align_bytes                   = index_type{},
                                 std::optional<bool> use_double_precision = std::nullopt,
                                 raft_proto::device_type dev_type = raft_proto::device_type::cpu,
                                 int device                       = 0,
                                 raft_proto::cuda_stream stream   = raft_proto::cuda_stream{})
{
  return import_from_treelite_model(*static_cast<treelite::Model*>(tl_handle),
                                    layout,
                                    align_bytes,
                                    use_double_precision,
                                    dev_type,
                                    device,
                                    stream);
}
 
}  // namespace fil
}  // namespace experimental
}  // namespace ML