source/reduce/operand_to_dominating_id_reduction_opportunity_finder.h

// Copyright (c) 2018 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_REDUCE_OPERAND_TO_DOMINATING_ID_REDUCTION_OPPORTUNITY_FINDER_H_
#define SOURCE_REDUCE_OPERAND_TO_DOMINATING_ID_REDUCTION_OPPORTUNITY_FINDER_H_

#include "source/reduce/reduction_opportunity_finder.h"

namespace spvtools {
namespace reduce {

// A finder that aims to bring to SPIR-V (and generalize) the idea from
// human-readable languages of e.g. finding opportunities to replace an
// expression with one of its arguments, (x + y) -> x, or with a reference to an
// identifier that was assigned to higher up in the program.  The generalization
// of this is to replace an id with a different id of the same type defined in
// some dominating instruction.
//
// If id x is defined and then used several times, changing each use of x to
// some dominating definition may eventually allow the statement defining x
// to be eliminated by another pass.
class OperandToDominatingIdReductionOpportunityFinder
    : public ReductionOpportunityFinder {
 public:
  OperandToDominatingIdReductionOpportunityFinder() = default;

  ~OperandToDominatingIdReductionOpportunityFinder() override = default;

  std::string GetName() const final;

  std::vector<std::unique_ptr<ReductionOpportunity>> GetAvailableOpportunities(
      opt::IRContext* context) const final;

 private:
  void GetOpportunitiesForDominatingInst(
      std::vector<std::unique_ptr<ReductionOpportunity>>* opportunities,
      opt::Instruction* dominating_instruction,
      opt::Function::iterator candidate_dominator_block,
      opt::Function* function, opt::IRContext* context) const;
};

}  // namespace reduce
}  // namespace spvtools

#endif  // SOURCE_REDUCE_OPERAND_TO_DOMINATING_ID_REDUCTION_OPPORTUNITY_FINDER_H_