// Copyright (c) 2017 Google Inc.

//

// 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_OPT_DEAD_VARIABLE_ELIMINATION_H_

#define SOURCE_OPT_DEAD_VARIABLE_ELIMINATION_H_

#include <climits>

#include <unordered_map>

#include "source/opt/decoration_manager.h"

#include "source/opt/mem_pass.h"

namespace spvtools {

namespace opt {

class DeadVariableElimination : public MemPass {

 public:

  const char* name() const override { return "eliminate-dead-variables"; }

  Status Process() override;

  IRContext::Analysis GetPreservedAnalyses() override {

    return IRContext::kAnalysisDefUse | IRContext::kAnalysisConstants |

           IRContext::kAnalysisTypes;

  }

 private:

  // Deletes the OpVariable instruction who result id is |result_id|.

  void DeleteVariable(uint32_t result_id);

  // Keeps track of the number of references of an id.  Once that value is 0, it

  // is safe to remove the corresponding instruction.

  //

  // Note that the special value kMustKeep is used to indicate that the

  // instruction cannot be deleted for reasons other that is being explicitly

  // referenced.

  std::unordered_map<uint32_t, size_t> reference_count_;

  // Special value used to indicate that an id cannot be safely deleted.

  enum { kMustKeep = INT_MAX };

};

}  // namespace opt

}  // namespace spvtools

#endif  // SOURCE_OPT_DEAD_VARIABLE_ELIMINATION_H_