text: // Copyright (c) 2018 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.
  
  #include "dominator_analysis.h"
  
  #include <unordered_set>
  
  namespace spvtools {
  namespace opt {
  
  ir::BasicBlock* DominatorAnalysisBase::CommonDominator(
      ir::BasicBlock* b1, ir::BasicBlock* b2) const {
    if (!b1 || !b2) return nullptr;
  
    std::unordered_set<ir::BasicBlock*> seen;
    ir::BasicBlock* block = b1;
    while (block && seen.insert(block).second) {
      block = ImmediateDominator(block);
    }
  
    block = b2;
    while (block && !seen.count(block)) {
      block = ImmediateDominator(block);
    }
  
    return block;
  }
  
  }  // namespace opt
  }  // namespace spvtools
  