// Copyright (c) 2018 Google LLC.

//

// 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/loop_fusion_pass.h"

#include "source/opt/loop_descriptor.h"

#include "source/opt/loop_fusion.h"

#include "source/opt/register_pressure.h"

namespace spvtools {

namespace opt {

Pass::Status LoopFusionPass::Process() {

  Status status = Status::SuccessWithoutChange;

  Module* module = context()->module();

  // Process each function in the module

  for (Function& f : *module) {

    status = CombineStatus(status, ProcessFunction(&f));

    if (status == Status::Failure) return Status::Failure;

  }

  return status;

}

Pass::Status LoopFusionPass::ProcessFunction(Function* function) {

  LoopDescriptor& ld = *context()->GetLoopDescriptor(function);

  // If a loop doesn't have a preheader needs then it needs to be created. Make

  // sure to return Status::SuccessWithChange in that case.

  bool modified = false;

  auto status = ld.CreatePreHeaderBlocksIfMissing();

  if (status == LoopDescriptor::Status::Failure) return Status::Failure;

  modified = status == LoopDescriptor::Status::SuccessWithChange;

  // TODO(tremmelg): Could the only loop that |loop| could possibly be fused be

  // picked out so don't have to check every loop

  for (auto& loop_0 : ld) {

    for (auto& loop_1 : ld) {

      LoopFusion fusion(context(), &loop_0, &loop_1);

      if (fusion.AreCompatible() && fusion.IsLegal()) {

        RegisterLiveness liveness(context(), function);

        RegisterLiveness::RegionRegisterLiveness reg_pressure{};

        liveness.SimulateFusion(loop_0, loop_1, &reg_pressure);

        if (reg_pressure.used_registers_ <= max_registers_per_loop_) {

          fusion.Fuse();

          // Recurse, as the current iterators will have been invalidated.

          ProcessFunction(function);

          return Status::SuccessWithChange;

        }

      }

    }

  }

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

}

}  // namespace opt

}  // namespace spvtools