// 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_LOCAL_REDUNDANCY_ELIMINATION_H_

#define SOURCE_OPT_LOCAL_REDUNDANCY_ELIMINATION_H_

#include <map>

#include "source/opt/ir_context.h"

#include "source/opt/pass.h"

#include "source/opt/value_number_table.h"

namespace spvtools {

namespace opt {

// This pass implements local redundancy elimination. Its goal is to reduce the

// number of times the same value is computed. It works on each basic block

// independently, ie local. For each instruction in a basic block, it gets the

// value number for the result id, |id|, of the instruction. If that value

// number has already been computed in the basic block, it tries to replace the

// uses of |id| by the id that already contains the same value. Then the

// current instruction is deleted.

class LocalRedundancyEliminationPass : public Pass {

 public:

  const char* name() const override { return "local-redundancy-elimination"; }

  Status Process() override;

  IRContext::Analysis GetPreservedAnalyses() override {

    return IRContext::kAnalysisDefUse |

           IRContext::kAnalysisInstrToBlockMapping |

           IRContext::kAnalysisDecorations | IRContext::kAnalysisCombinators |

           IRContext::kAnalysisCFG | IRContext::kAnalysisDominatorAnalysis |

           IRContext::kAnalysisNameMap | IRContext::kAnalysisConstants |

           IRContext::kAnalysisTypes;

  }

 protected:

  // Deletes instructions in |block| whose value is in |value_to_ids| or is

  // computed earlier in |block|.

  //

  // |vnTable| must have computed a value number for every result id defined

  // in |bb|.

  //

  // |value_to_ids| is a map from value number to ids.  If {vn, id} is in

  // |value_to_ids| then vn is the value number of id, and the definition of id

  // dominates |bb|.

  //

  // Returns true if the module is changed.

  bool EliminateRedundanciesInBB(BasicBlock* block,

                                 const ValueNumberTable& vnTable,

                                 std::map<uint32_t, uint32_t>* value_to_ids);

};

}  // namespace opt

}  // namespace spvtools

#endif  // SOURCE_OPT_LOCAL_REDUNDANCY_ELIMINATION_H_