// This file is part of Eigen, a lightweight C++ template library
// for linear algebra.
//
// Copyright (C) 2014 Benoit Steiner <benoit.steiner.goog@gmail.com>
//
// This Source Code Form is subject to the terms of the Mozilla
// Public License v. 2.0. If a copy of the MPL was not distributed
// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.

#ifndef EIGEN_CXX11_TENSOR_TENSOR_EXECUTOR_H
#define EIGEN_CXX11_TENSOR_TENSOR_EXECUTOR_H

namespace Eigen {

/**
 * \class TensorExecutor
 * \ingroup CXX11_Tensor_Module
 *
 * \brief The tensor executor class.
 *
 * This class is responsible for launch the evaluation of the expression on
 * the specified computing device.
 *
 * @tparam Vectorizable can use packet math (SSE/AVX/etc... registers and
 *                      instructions)
 * @tparam Tileable     can use block based tensor evaluation
 *                      (see TensorBlock.h)
 */
namespace internal {

/**
 * Default strategy: the expression is evaluated sequentially with a single cpu
 * thread, without vectorization and block evaluation.
 */
template <typename Expression, typename Device, bool Vectorizable,
          bool Tileable>
class TensorExecutor {
 public:
  typedef typename Expression::Index StorageIndex;

  EIGEN_DEVICE_FUNC
  static EIGEN_STRONG_INLINE void run(const Expression& expr,
                         const Device& device = Device()) {
    TensorEvaluator<Expression, Device> evaluator(expr, device);
    const bool needs_assign = evaluator.evalSubExprsIfNeeded(NULL);
    if (needs_assign) {
      const StorageIndex size = array_prod(evaluator.dimensions());
      for (StorageIndex i = 0; i < size; ++i) {
        evaluator.evalScalar(i);
      }
    }
    evaluator.cleanup();
  }
};

/**
 * Process all the data with a single cpu thread, using vectorized instructions.
 */
template <typename Expression>
class TensorExecutor<Expression, DefaultDevice, /*Vectorizable*/ true,
                     /*Tileable*/ false> {
 public:
  typedef typename Expression::Index StorageIndex;

  EIGEN_DEVICE_FUNC
  static EIGEN_STRONG_INLINE void run(const Expression& expr,
                         const DefaultDevice& device = DefaultDevice()) {
    TensorEvaluator<Expression, DefaultDevice> evaluator(expr, device);
    const bool needs_assign = evaluator.evalSubExprsIfNeeded(NULL);
    if (needs_assign) {
      const StorageIndex size = array_prod(evaluator.dimensions());
      const int PacketSize = unpacket_traits<typename TensorEvaluator<
          Expression, DefaultDevice>::PacketReturnType>::size;

      // Give compiler a strong possibility to unroll the loop. But don't insist
      // on unrolling, because if the function is expensive compiler should not
      // unroll the loop at the expense of inlining.
      const StorageIndex UnrolledSize =
          (size / (4 * PacketSize)) * 4 * PacketSize;
      for (StorageIndex i = 0; i < UnrolledSize; i += 4 * PacketSize) {
        for (StorageIndex j = 0; j < 4; j++) {
          evaluator.evalPacket(i + j * PacketSize);
        }
      }
      const StorageIndex VectorizedSize = (size / PacketSize) * PacketSize;
      for (StorageIndex i = UnrolledSize; i < VectorizedSize; i += PacketSize) {
        evaluator.evalPacket(i);
      }
      for (StorageIndex i = VectorizedSize; i < size; ++i) {
        evaluator.evalScalar(i);
      }
    }
    evaluator.cleanup();
  }
};

/**
 * Process all the data with a single cpu thread, using blocks of data. By
 * sizing a block to fit L1 cache we get better cache performance.
 */
template <typename Expression, bool Vectorizable>
class TensorExecutor<Expression, DefaultDevice, Vectorizable,
                     /*Tileable*/ true> {
 public:
  typedef typename traits<Expression>::Scalar Scalar;
  typedef typename remove_const<Scalar>::type ScalarNoConst;

  typedef TensorEvaluator<Expression, DefaultDevice> Evaluator;
  typedef typename traits<Expression>::Index StorageIndex;

  static const int NumDims = traits<Expression>::NumDimensions;

  EIGEN_DEVICE_FUNC
  static EIGEN_STRONG_INLINE void run(const Expression& expr,
                         const DefaultDevice& device = DefaultDevice()) {
    typedef TensorBlock<ScalarNoConst, StorageIndex, NumDims, Evaluator::Layout> TensorBlock;
    typedef TensorBlockMapper<ScalarNoConst, StorageIndex, NumDims, Evaluator::Layout> TensorBlockMapper;

    Evaluator evaluator(expr, device);
    Index total_size = array_prod(evaluator.dimensions());
    Index cache_size = device.firstLevelCacheSize() / sizeof(Scalar);

    if (total_size < cache_size) {
      // TODO(andydavis) Reduce block management overhead for small tensors.
      // TODO(wuke) Do not do this when evaluating TensorBroadcastingOp.
      internal::TensorExecutor<Expression, DefaultDevice, Vectorizable,
                               /*Tileable*/ false>::run(expr, device);
      return;
    }

    const bool needs_assign = evaluator.evalSubExprsIfNeeded(NULL);
    if (needs_assign) {
      // Size tensor blocks to fit in cache (or requested target block size).
      Index block_total_size = numext::mini(cache_size, total_size);
      TensorBlockShapeType block_shape = kSkewedInnerDims;
      // Query expression tree for desired block size/shape.
      std::vector<TensorOpResourceRequirements> resources;
      evaluator.getResourceRequirements(&resources);
      MergeResourceRequirements(resources, &block_shape, &block_total_size);

      TensorBlockMapper block_mapper(evaluator.dimensions(), block_shape,
                                     block_total_size);
      block_total_size = block_mapper.block_dims_total_size();

      Scalar* data = static_cast<Scalar*>(
          device.allocate(block_total_size * sizeof(Scalar)));

      const StorageIndex total_block_count = block_mapper.total_block_count();
      for (StorageIndex i = 0; i < total_block_count; ++i) {
        TensorBlock block = block_mapper.GetBlockForIndex(i, data);
        evaluator.evalBlock(&block);
      }
      device.deallocate(data);
    }
    evaluator.cleanup();
  }
};

/**
 * Multicore strategy: the index space is partitioned and each partition is
 * executed on a single core.
 */
#ifdef EIGEN_USE_THREADS
template <typename Evaluator, typename StorageIndex, bool Vectorizable>
struct EvalRange {
  static void run(Evaluator* evaluator_in, const StorageIndex first,
                  const StorageIndex last) {
    Evaluator evaluator = *evaluator_in;
    eigen_assert(last >= first);
    for (StorageIndex i = first; i < last; ++i) {
      evaluator.evalScalar(i);
    }
  }

  static StorageIndex alignBlockSize(StorageIndex size) { return size; }
};

template <typename Evaluator, typename StorageIndex>
struct EvalRange<Evaluator, StorageIndex, /*Vectorizable*/ true> {
  static const int PacketSize =
      unpacket_traits<typename Evaluator::PacketReturnType>::size;

  static void run(Evaluator* evaluator_in, const StorageIndex first,
                  const StorageIndex last) {
    Evaluator evaluator = *evaluator_in;
    eigen_assert(last >= first);
    StorageIndex i = first;
    if (last - first >= PacketSize) {
      eigen_assert(first % PacketSize == 0);
      StorageIndex last_chunk_offset = last - 4 * PacketSize;
      // Give compiler a strong possibility to unroll the loop. But don't insist
      // on unrolling, because if the function is expensive compiler should not
      // unroll the loop at the expense of inlining.
      for (; i <= last_chunk_offset; i += 4 * PacketSize) {
        for (StorageIndex j = 0; j < 4; j++) {
          evaluator.evalPacket(i + j * PacketSize);
        }
      }
      last_chunk_offset = last - PacketSize;
      for (; i <= last_chunk_offset; i += PacketSize) {
        evaluator.evalPacket(i);
      }
    }
    for (; i < last; ++i) {
      evaluator.evalScalar(i);
    }
  }

  static StorageIndex alignBlockSize(StorageIndex size) {
    // Align block size to packet size and account for unrolling in run above.
    if (size >= 16 * PacketSize) {
      return (size + 4 * PacketSize - 1) & ~(4 * PacketSize - 1);
    }
    // Aligning to 4 * PacketSize would increase block size by more than 25%.
    return (size + PacketSize - 1) & ~(PacketSize - 1);
  }
};

template <typename Expression, bool Vectorizable, bool Tileable>
class TensorExecutor<Expression, ThreadPoolDevice, Vectorizable, Tileable> {
 public:
  typedef typename Expression::Index StorageIndex;

  static EIGEN_STRONG_INLINE void run(const Expression& expr,
                         const ThreadPoolDevice& device) {
    typedef TensorEvaluator<Expression, ThreadPoolDevice> Evaluator;
    typedef EvalRange<Evaluator, StorageIndex, Vectorizable> EvalRange;

    Evaluator evaluator(expr, device);
    const bool needs_assign = evaluator.evalSubExprsIfNeeded(NULL);
    if (needs_assign) {
      const StorageIndex size = array_prod(evaluator.dimensions());
      device.parallelFor(size, evaluator.costPerCoeff(Vectorizable),
                         EvalRange::alignBlockSize,
                         [&evaluator](StorageIndex first, StorageIndex last) {
                           EvalRange::run(&evaluator, first, last);
                         });
    }
    evaluator.cleanup();
  }
};

template <typename Expression, bool Vectorizable>
class TensorExecutor<Expression, ThreadPoolDevice, Vectorizable, /*Tileable*/ true> {
 public:
  typedef typename traits<Expression>::Scalar Scalar;
  typedef typename remove_const<Scalar>::type ScalarNoConst;

  typedef TensorEvaluator<Expression, ThreadPoolDevice> Evaluator;
  typedef typename traits<Expression>::Index StorageIndex;

  static const int NumDims = traits<Expression>::NumDimensions;

  static EIGEN_STRONG_INLINE void run(const Expression& expr,
                         const ThreadPoolDevice& device) {
    typedef TensorBlockMapper<ScalarNoConst, StorageIndex, NumDims, Evaluator::Layout> TensorBlockMapper;

    Evaluator evaluator(expr, device);
    Index total_size = array_prod(evaluator.dimensions());
    Index cache_size = device.firstLevelCacheSize() / sizeof(Scalar);
    if (total_size < cache_size) {
      // TODO(andydavis) Reduce block management overhead for small tensors.
      internal::TensorExecutor<Expression, ThreadPoolDevice, Vectorizable,
                               false>::run(expr, device);
      evaluator.cleanup();
      return;
    }

    const bool needs_assign = evaluator.evalSubExprsIfNeeded(NULL);
    if (needs_assign) {
      TensorBlockShapeType block_shape = kSkewedInnerDims;
      Index block_total_size = 0;
      // Query expression tree for desired block size/shape.
      std::vector<internal::TensorOpResourceRequirements> resources;
      evaluator.getResourceRequirements(&resources);
      MergeResourceRequirements(resources, &block_shape, &block_total_size);
      int num_threads = device.numThreads();

      // Estimate minimum block size based on cost.
      TensorOpCost cost = evaluator.costPerCoeff(Vectorizable);
      double taskSize = TensorCostModel<ThreadPoolDevice>::taskSize(1, cost);
      size_t block_size = static_cast<size_t>(1.0 / taskSize);
      TensorBlockMapper block_mapper(evaluator.dimensions(), block_shape,
                                     block_size);
      block_size = block_mapper.block_dims_total_size();
      const size_t aligned_blocksize =
          EIGEN_MAX_ALIGN_BYTES *
          divup<size_t>(block_size * sizeof(Scalar), EIGEN_MAX_ALIGN_BYTES);
      void* buf = device.allocate((num_threads + 1) * aligned_blocksize);
      device.parallelFor(
          block_mapper.total_block_count(), cost * block_size,
          [=, &device, &evaluator, &block_mapper](StorageIndex first,
                                                  StorageIndex last) {
            // currentThreadId() returns -1 if called from a thread not in the
            // thread pool, such as the main thread dispatching Eigen
            // expressions.
            const int thread_idx = device.currentThreadId();
            eigen_assert(thread_idx >= -1 && thread_idx < num_threads);
            Scalar* thread_buf = reinterpret_cast<Scalar*>(
                static_cast<char*>(buf) + aligned_blocksize * (thread_idx + 1));
            for (StorageIndex i = first; i < last; ++i) {
              auto block = block_mapper.GetBlockForIndex(i, thread_buf);
              evaluator.evalBlock(&block);
            }
          });
      device.deallocate(buf);
    }
    evaluator.cleanup();
  }
};

#endif  // EIGEN_USE_THREADS


// GPU: the evaluation of the expression is offloaded to a GPU.
#if defined(EIGEN_USE_GPU)

template <typename Expression, bool Vectorizable, bool Tileable>
class TensorExecutor<Expression, GpuDevice, Vectorizable, Tileable> {
 public:
  typedef typename Expression::Index StorageIndex;
  static void run(const Expression& expr, const GpuDevice& device);
};


#if defined(EIGEN_GPUCC)
template <typename Evaluator, typename StorageIndex, bool Vectorizable>
struct EigenMetaKernelEval {
  static __device__ EIGEN_ALWAYS_INLINE
  void run(Evaluator& eval, StorageIndex first, StorageIndex last, StorageIndex step_size) {
    for (StorageIndex i = first; i < last; i += step_size) {
      eval.evalScalar(i);
    }
  }
};

template <typename Evaluator, typename StorageIndex>
struct EigenMetaKernelEval<Evaluator, StorageIndex, true> {
  static __device__ EIGEN_ALWAYS_INLINE
  void run(Evaluator& eval, StorageIndex first, StorageIndex last, StorageIndex step_size) {
    const StorageIndex PacketSize = unpacket_traits<typename Evaluator::PacketReturnType>::size;
    const StorageIndex vectorized_size = (last / PacketSize) * PacketSize;
    const StorageIndex vectorized_step_size = step_size * PacketSize;

    // Use the vector path
    for (StorageIndex i = first * PacketSize; i < vectorized_size;
         i += vectorized_step_size) {
      eval.evalPacket(i);
    }
    for (StorageIndex i = vectorized_size + first; i < last; i += step_size) {
      eval.evalScalar(i);
    }
  }
};

template <typename Evaluator, typename StorageIndex>
__global__ void
__launch_bounds__(1024)
EigenMetaKernel(Evaluator eval, StorageIndex size) {

  const StorageIndex first_index = blockIdx.x * blockDim.x + threadIdx.x;
  const StorageIndex step_size = blockDim.x * gridDim.x;

  const bool vectorizable = Evaluator::PacketAccess & Evaluator::IsAligned;
  EigenMetaKernelEval<Evaluator, StorageIndex, vectorizable>::run(eval, first_index, size, step_size);
}

/*static*/
template <typename Expression, bool Vectorizable, bool Tileable>
EIGEN_STRONG_INLINE void TensorExecutor<Expression, GpuDevice, Vectorizable, Tileable>::run(
    const Expression& expr, const GpuDevice& device) {
  TensorEvaluator<Expression, GpuDevice> evaluator(expr, device);
  const bool needs_assign = evaluator.evalSubExprsIfNeeded(NULL);
  if (needs_assign) {

    const int block_size = device.maxGpuThreadsPerBlock();
    const int max_blocks = device.getNumGpuMultiProcessors() *
                           device.maxGpuThreadsPerMultiProcessor() / block_size;
    const StorageIndex size = array_prod(evaluator.dimensions());
    // Create a least one block to ensure we won't crash when tensorflow calls with tensors of size 0.
    const int num_blocks = numext::maxi<int>(numext::mini<int>(max_blocks, divup<int>(size, block_size)), 1);

    LAUNCH_GPU_KERNEL(
        (EigenMetaKernel<TensorEvaluator<Expression, GpuDevice>, StorageIndex>),
        num_blocks, block_size, 0, device, evaluator, size);
  }
  evaluator.cleanup();
}

#endif  // EIGEN_GPUCC
#endif  // EIGEN_USE_GPU

// SYCL Executor policy
#ifdef EIGEN_USE_SYCL

template <typename Expression, bool Vectorizable>
class TensorExecutor<Expression, SyclDevice, Vectorizable> {
public:
  static EIGEN_STRONG_INLINE void run(const Expression &expr, const SyclDevice &device) {
    // call TensorSYCL module
    TensorSycl::run(expr, device);
  }
};

#endif

} // end namespace internal

} // end namespace Eigen

#endif // EIGEN_CXX11_TENSOR_TENSOR_EXECUTOR_H
