// 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.

#include "source/opt/local_redundancy_elimination.h"

#include "source/opt/value_number_table.h"

namespace spvtools {

namespace opt {

Pass::Status LocalRedundancyEliminationPass::Process() {

  bool modified = false;

  ValueNumberTable vnTable(context());

  for (auto& func : *get_module()) {

    for (auto& bb : func) {

      // Keeps track of all ids that contain a given value number. We keep

      // track of multiple values because they could have the same value, but

      // different decorations.

      std::map<uint32_t, uint32_t> value_to_ids;

      if (EliminateRedundanciesInBB(&bb, vnTable, &value_to_ids))

        modified = true;

    }

  }

  return (modified ? Status::SuccessWithChange : Status::SuccessWithoutChange);

}

bool LocalRedundancyEliminationPass::EliminateRedundanciesInBB(

    BasicBlock* block, const ValueNumberTable& vnTable,

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

  bool modified = false;

  auto func = [this, &vnTable, &modified, value_to_ids](Instruction* inst) {

    if (inst->result_id() == 0) {

      return;

    }

    uint32_t value = vnTable.GetValueNumber(inst);

    if (value == 0) {

      return;

    }

    auto candidate = value_to_ids->insert({value, inst->result_id()});

    if (!candidate.second) {

      context()->KillNamesAndDecorates(inst);

      context()->ReplaceAllUsesWith(inst->result_id(), candidate.first->second);

      context()->KillInst(inst);

      modified = true;

    }

  };

  block->ForEachInst(func);

  return modified;

}

}  // namespace opt

}  // namespace spvtools