text: /*
   * Copyright 2018 WebAssembly Community Group participants
   *
   * 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 wasm_ir_equivalent_sets_h
  #define wasm_ir_equivalent_sets_h
  
  #include <wasm.h>
  
  namespace wasm {
  
  //
  // A map of each index to all those it is equivalent to, and some helpers.
  //
  struct EquivalentSets {
    // A set of indexes.
    typedef std::unordered_set<Index> Set;
  
    std::unordered_map<Index, std::shared_ptr<Set>> indexSets;
  
    // Clears the state completely, removing all equivalences.
    void clear() {
      indexSets.clear();
    }
  
    // Resets an index, removing any equivalences between it and others.
    void reset(Index index) {
      auto iter = indexSets.find(index);
      if (iter != indexSets.end()) {
        auto& set = iter->second;
        assert(!set->empty()); // can't be empty - we are equal to ourselves!
        if (set->size() > 1) {
          // We are not the last item, fix things up
          set->erase(index);
        }
        indexSets.erase(iter);
      }
    }
  
    // Adds a new equivalence between two indexes.
    // `justReset` is an index that was just reset, and has no
    // equivalences. `other` may have existing equivalences.
    void add(Index justReset, Index other) {
      auto iter = indexSets.find(other);
      if (iter != indexSets.end()) {
        auto& set = iter->second;
        set->insert(justReset);
        indexSets[justReset] = set;
      } else {
        auto set = std::make_shared<Set>();
        set->insert(justReset);
        set->insert(other);
        indexSets[justReset] = set;
        indexSets[other] = set;
      }
    }
  
    // Checks whether two indexes contain the same data.
    bool check(Index a, Index b) {
      if (a == b) return true;
      if (auto* set = getEquivalents(a)) {
        if (set->find(b) != set->end()) {
          return true;
        }
      }
      return false;
    }
  
    // Returns the equivalent set, or nullptr
    Set* getEquivalents(Index index) {
      auto iter = indexSets.find(index);
      if (iter != indexSets.end()) {
        return iter->second.get();
      }
      return nullptr;
    }
  };
  
  } // namespace wasm
  
  #endif // wasm_ir_equivalent_sets_h
  
  