// Copyright (c) 2020 Google LLC
//
// 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.

#ifndef SOURCE_FUZZ_CALL_GRAPH_H_
#define SOURCE_FUZZ_CALL_GRAPH_H_

#include <map>
#include <set>

#include "source/opt/ir_context.h"

namespace spvtools {
namespace fuzz {

// Represents the acyclic call graph of a SPIR-V module.
// The module is assumed to be recursion-free, so there are no cycles in the
// graph. This class is immutable, so it will need to be recomputed if the
// module changes.
class CallGraph {
 public:
  // Creates a call graph corresponding to the given SPIR-V module.
  explicit CallGraph(opt::IRContext* context);

  // Returns a mapping from each function to its number of distinct callers.
  const std::map<uint32_t, uint32_t>& GetFunctionInDegree() const {
    return function_in_degree_;
  }

  // Returns the ids of the functions that |function_id| directly invokes.
  const std::set<uint32_t>& GetDirectCallees(uint32_t function_id) const {
    return call_graph_edges_.at(function_id);
  }

  // Returns the ids of the functions that |function_id| directly or indirectly
  // invokes.
  std::set<uint32_t> GetIndirectCallees(uint32_t function_id) const;

  // Returns the ids of all the functions in the graph in a topological order,
  // in relation to the function calls, which are assumed to be recursion-free.
  const std::vector<uint32_t>& GetFunctionsInTopologicalOrder() const {
    return functions_in_topological_order_;
  }

  // Returns the maximum loop nesting depth from which |function_id| can be
  // called. This is computed inter-procedurally (i.e. if main calls A from
  // depth 2 and A calls B from depth 1, the result will be 3 for A).
  // This is a static analysis, so it's not necessarily true that the depth
  // returned can actually be reached at runtime.
  uint32_t GetMaxCallNestingDepth(uint32_t function_id) const {
    return function_max_loop_nesting_depth_.at(function_id);
  }

 private:
  // Computes |call_graph_edges_| and |function_in_degree_|. For each pair (A,
  // B) of functions such that there is at least a function call from A to B,
  // adds, to |call_to_max_depth|, a mapping from (A, B) to the maximum loop
  // nesting depth (within A) of any such function call.
  void BuildGraphAndGetDepthOfFunctionCalls(
      opt::IRContext* context,
      std::map<std::pair<uint32_t, uint32_t>, uint32_t>* call_to_max_depth);

  // Computes a topological order of the functions in the graph, writing the
  // result to |functions_in_topological_order_|. Assumes that the function
  // calls are recursion-free and that |function_in_degree_| has been computed.
  void ComputeTopologicalOrderOfFunctions();

  // Computes |function_max_loop_nesting_depth_| so that each function is mapped
  // to the maximum loop nesting depth from which it can be called, as described
  // by the comment to GetMaxCallNestingDepth. Assumes that |call_graph_edges_|
  // and |functions_in_topological_order_| have been computed, and that
  // |call_to_max_depth| contains a mapping for each edge in the graph.
  void ComputeInterproceduralFunctionCallDepths(
      const std::map<std::pair<uint32_t, uint32_t>, uint32_t>&
          call_to_max_depth);

  // Pushes the direct callees of |function_id| on to |queue|.
  void PushDirectCallees(uint32_t function_id,
                         std::queue<uint32_t>* queue) const;

  // Maps each function id to the ids of its immediate callees.
  std::map<uint32_t, std::set<uint32_t>> call_graph_edges_;

  // For each function id, stores the number of distinct functions that call
  // the function.
  std::map<uint32_t, uint32_t> function_in_degree_;

  // Stores the ids of the functions in a topological order,
  // in relation to the function calls, which are assumed to be recursion-free.
  std::vector<uint32_t> functions_in_topological_order_;

  // For each function id, stores the maximum loop nesting depth that the
  // function can be called from.
  std::map<uint32_t, uint32_t> function_max_loop_nesting_depth_;
};

}  // namespace fuzz
}  // namespace spvtools

#endif  // SOURCE_FUZZ_CALL_GRAPH_H_