source/opt/local_redundancy_elimination.h

// 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 LIBSPIRV_OPT_LOCAL_REDUNDANCY_ELIMINATION_H_
#define LIBSPIRV_OPT_LOCAL_REDUNDANCY_ELIMINATION_H_

#include "ir_context.h"
#include "pass.h"
#include "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(ir::IRContext*) override;

 private:
  // Deletes instructions in |block| whose value is in |vnTable| or is computed
  // earlier in |block|. The values computed in |block| are added to |vnTable|.
  // |value_to_ids| is a map from a value number to the result ids known to
  // contain those values. The definition of the ids in value_to_ids must
  // dominate |block|. One value needs to map to multiple ids because the ids
  // may contain the same value, but have different decorations.  Returns true
  // if the module is changed.
  bool EliminateRedundanciesInBB(
      ir::BasicBlock* block, ValueNumberTable* vnTable,
      std::vector<std::vector<uint32_t>>* value_to_ids);
};

}  // namespace opt
}  // namespace spvtools

#endif  // LIBSPIRV_OPT_LOCAL_REDUNDANCY_ELIMINATION_H_