/* Copyright 2020 The TensorFlow Authors. All Rights Reserved.

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 "llvm/ADT/DenseMap.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/FormatVariadic.h"
#include "mlir/Dialect/Func/IR/FuncOps.h"  // from @llvm-project
#include "mlir/IR/Attributes.h"  // from @llvm-project
#include "mlir/IR/Builders.h"  // from @llvm-project
#include "mlir/IR/BuiltinOps.h"  // from @llvm-project
#include "mlir/IR/BuiltinTypes.h"  // from @llvm-project
#include "mlir/IR/TypeUtilities.h"  // from @llvm-project
#include "mlir/Pass/Pass.h"  // from @llvm-project
#include "mlir/Support/LogicalResult.h"  // from @llvm-project
#include "tensorflow/compiler/mlir/tensorflow/ir/tf_device.h"
#include "tensorflow/compiler/mlir/tensorflow/ir/tf_ops.h"
#include "tensorflow/compiler/mlir/tensorflow/ir/tf_types.h"
#include "tensorflow/compiler/mlir/tensorflow/transforms/collection_ops_util.h"
#include "tensorflow/compiler/mlir/tensorflow/transforms/passes.h"
#include "tensorflow/compiler/mlir/tensorflow/utils/convert_tensor.h"
#include "tensorflow/compiler/mlir/tensorflow/utils/mangling_util.h"
#include "tensorflow/core/framework/tensor.h"
#include "tensorflow/core/framework/types.pb.h"
#include "tensorflow/core/platform/types.h"

namespace mlir {

namespace {

namespace cutil = TF::collection_ops_util;

#define GEN_PASS_DEF_TENSORLISTOPSDECOMPOSITIONPASS
#include "tensorflow/compiler/mlir/tensorflow/transforms/tf_passes.h.inc"

struct TensorListOpsDecompositionPass
    : public impl::TensorListOpsDecompositionPassBase<
          TensorListOpsDecompositionPass> {
  void runOnOperation() override;
};

// Updates func's type according to its current arguments and return values.
void UpdateFuncType(func::FuncOp func) {
  llvm::SmallVector<Type, 8> arg_types;
  for (auto arg : func.getArguments()) arg_types.push_back(arg.getType());
  func.setType(
      FunctionType::get(func.getContext(), arg_types,
                        func.front().getTerminator()->getOperandTypes()));
}

// Holds the size value of a tensor list and whether the size is statically
// known (fixed).
struct SizeInfo {
  Value size;
  bool fixed;
};

// Modifies a function's signature to rewrite tensor list arguments to buffers
// and sizes.
void ModifyFunctionSignature(
    func::FuncOp func, Type size_type,
    llvm::SmallDenseMap<Value, SizeInfo>* buffer_to_size,
    llvm::function_ref<llvm::Optional<Type>(int64_t)> arg_to_buffer_type,
    llvm::function_ref<bool(int64_t)> arg_buffer_size_is_fixed) {
  auto new_input_types = llvm::to_vector<8>(func.getFunctionType().getInputs());
  int64_t original_arg_count = new_input_types.size();
  Location loc = func.getLoc();
  for (int64_t i = 0; i < original_arg_count; ++i) {
    auto buffer_type = arg_to_buffer_type(i);
    if (!buffer_type.has_value()) continue;
    func.getArgument(i).setType(*buffer_type);
    new_input_types[i] = *buffer_type;
    auto size_arg = func.front().addArgument(size_type, loc);
    new_input_types.push_back(size_arg.getType());
    if (buffer_to_size) {
      (*buffer_to_size)[func.getArgument(i)] = {size_arg,
                                                arg_buffer_size_is_fixed(i)};
    }
  }
  UpdateFuncType(func);
}

// Holds information about a decomposed callee function for
// PartitionedCall/StatefulPartitionedCall.
struct PartitionedCallDecompositionInfo {
  bool signature_change;
  func::FuncOp decomposed_callee;
  llvm::SmallDenseMap<int64_t, int64_t> buffer_arg_to_size_arg;
  // Each element is a tuple of (buffer_return_index, size_return_index,
  // fixed_size).
  llvm::SmallVector<std::tuple<int64_t, int64_t, bool>, 8>
      buffer_ret_to_size_ret;
};

LogicalResult DecomposeTensorListOpsInternal(
    Block*, ModuleOp, llvm::SmallDenseMap<Value, SizeInfo>*,
    llvm::StringMap<PartitionedCallDecompositionInfo>*);

// Adds the corresponding sizes of tensor list buffers in block's terminator
// to the list of return values. Returns the mapping from the buffer
// indices to the added size indices, which is a list of tuples
// (buffer_return_index, size_return_index, fixed_size).
template <class TerminatorOp>
llvm::SmallVector<std::tuple<int64_t, int64_t, bool>, 8>
AddTensorListSizesToTerminator(
    Block& block, const llvm::SmallDenseMap<Value, SizeInfo>& buffer_to_size) {
  auto old_terminator = block.getTerminator();
  auto new_outputs = llvm::to_vector<8>(old_terminator->getOperands());
  llvm::SmallVector<std::tuple<int64_t, int64_t, bool>, 8>
      output_buffer_to_size;
  for (auto retval : llvm::enumerate(old_terminator->getOperands())) {
    auto it = buffer_to_size.find(retval.value());
    if (it == buffer_to_size.end()) continue;
    output_buffer_to_size.emplace_back(retval.index(), new_outputs.size(),
                                       it->getSecond().fixed);
    new_outputs.push_back(it->getSecond().size);
  }
  OpBuilder(old_terminator)
      .create<TerminatorOp>(old_terminator->getLoc(), new_outputs);
  old_terminator->erase();
  return output_buffer_to_size;
}

// Adds the corresponding sizes of tensor list buffers in func's return values
// to the list of return values. Returns the mapping from the buffer indices to
// the added size indices, which is a list of tuples (buffer_return_index,
// size_return_index, fixed_size).
llvm::SmallVector<std::tuple<int64_t, int64_t, bool>, 8> ModifyFunctionReturn(
    func::FuncOp func,
    const llvm::SmallDenseMap<Value, SizeInfo>& buffer_to_size) {
  auto output_buffer_to_size = AddTensorListSizesToTerminator<func::ReturnOp>(
      func.front(), buffer_to_size);
  UpdateFuncType(func);
  return output_buffer_to_size;
}

LogicalResult HandleWhileOp(
    TF::WhileOp while_op, ModuleOp module,
    llvm::SmallDenseMap<Value, SizeInfo>* buffer_to_size,
    llvm::StringMap<PartitionedCallDecompositionInfo>*
        decomposed_partitioned_call_callees) {
  // Rewrite body.
  auto body = while_op.body_function();
  llvm::SmallDenseMap<Value, SizeInfo> body_map;
  auto find_arg_tensor_list_type = [&](int64_t index) -> llvm::Optional<Type> {
    auto it = buffer_to_size->find(while_op.getOperand(index));
    if (it == buffer_to_size->end()) return llvm::None;
    return it->getFirst().getType();
  };
  auto arg_buffer_size_is_fixed = [&](int64_t index) {
    return (*buffer_to_size)[while_op.getOperand(index)].fixed;
  };
  OpBuilder builder(while_op);
  ModifyFunctionSignature(body, cutil::GetSizeType(builder), &body_map,
                          find_arg_tensor_list_type, arg_buffer_size_is_fixed);
  if (failed(DecomposeTensorListOpsInternal(
          &body.front(), module, &body_map,
          decomposed_partitioned_call_callees))) {
    return failure();
  }
  auto output_buffer_to_size = ModifyFunctionReturn(body, body_map);

  // Rewrite cond.
  auto cond = while_op.cond_function();
  llvm::SmallDenseMap<Value, SizeInfo> cond_map;
  ModifyFunctionSignature(cond, cutil::GetSizeType(builder), &cond_map,
                          find_arg_tensor_list_type, arg_buffer_size_is_fixed);
  if (failed(DecomposeTensorListOpsInternal(
          &cond.front(), module, &cond_map,
          decomposed_partitioned_call_callees))) {
    return failure();
  }
  if (output_buffer_to_size.empty()) {
    return success();
  }
  // Create the new while op.
  auto new_while_operands = llvm::to_vector<8>(while_op.getOperands());
  for (int64_t i = 0; i < while_op.getNumResults(); ++i) {
    auto it = buffer_to_size->find(while_op.getOperand(i));
    if (it == buffer_to_size->end()) continue;
    new_while_operands.push_back(it->getSecond().size);
  }
  auto new_while = builder.create<TF::WhileOp>(
      while_op.getLoc(), body.getFunctionType().getInputs(), new_while_operands,
      while_op->getAttrs());
  for (const auto& entry : output_buffer_to_size) {
    (*buffer_to_size)[new_while.getResult(std::get<0>(entry))] = {
        new_while.getResult(std::get<1>(entry)), std::get<2>(entry)};
  }
  while_op.replaceAllUsesWith(
      new_while.getResults().take_front(while_op.getNumResults()));
  while_op.erase();
  return success();
}

template <class CaseOrIfOp>
LogicalResult HandleCaseOrIfOp(
    CaseOrIfOp op, ArrayRef<func::FuncOp> branches, ModuleOp module,
    llvm::SmallDenseMap<Value, SizeInfo>* buffer_to_size,
    llvm::StringMap<PartitionedCallDecompositionInfo>*
        decomposed_partitioned_call_callees) {
  // Rewrite the branches.
  SmallVector<llvm::SmallDenseMap<Value, SizeInfo>, 2> branch_maps;
  branch_maps.resize(branches.size());

  auto find_arg_buffer_type = [&](int64_t index) -> llvm::Optional<Type> {
    auto it = buffer_to_size->find(op.getOperand(index + 1));
    if (it == buffer_to_size->end()) return llvm::None;
    return it->getFirst().getType();
  };
  auto arg_buffer_size_is_fixed = [&](int64_t index) {
    return (*buffer_to_size)[op.getOperand(index + 1)].fixed;
  };
  OpBuilder builder(op);
  for (const auto& pair : llvm::zip(branches, branch_maps)) {
    func::FuncOp branch = std::get<0>(pair);
    llvm::SmallDenseMap<Value, SizeInfo>& branch_map = std::get<1>(pair);
    ModifyFunctionSignature(branch, cutil::GetSizeType(builder), &branch_map,
                            find_arg_buffer_type, arg_buffer_size_is_fixed);

    if (failed(DecomposeTensorListOpsInternal(
            &branch.front(), module, &branch_map,
            decomposed_partitioned_call_callees)))
      return failure();
  }

  const bool arg_no_changed = branch_maps.front().empty();
  auto output_buffer_to_size =
      ModifyFunctionReturn(branches.front(), branch_maps.front());
  for (const auto& pair : llvm::drop_begin(llvm::zip(branches, branch_maps), 1))
    ModifyFunctionReturn(std::get<0>(pair), std::get<1>(pair));

  if (output_buffer_to_size.empty() && arg_no_changed) return success();

  // Recreate the op.
  auto new_operands = llvm::to_vector<8>(op.getOperands());
  for (int64_t i = 1; i < op.getNumOperands(); ++i) {
    auto it = buffer_to_size->find(op.getOperand(i));
    if (it == buffer_to_size->end()) continue;
    new_operands.push_back(it->getSecond().size);
  }
  func::FuncOp first_branch = branches.front();
  auto new_op = OpBuilder(op).create<CaseOrIfOp>(
      op.getLoc(), first_branch.getFunctionType().getResults(), new_operands,
      op->getAttrs());
  for (const auto& entry : output_buffer_to_size) {
    (*buffer_to_size)[new_op.getResult(std::get<0>(entry))] = {
        new_op.getResult(std::get<1>(entry)), std::get<2>(entry)};
  }
  op.replaceAllUsesWith(new_op.getResults().take_front(op.getNumResults()));
  op.erase();
  return success();
}

LogicalResult HandleWhileRegionOp(
    TF::WhileRegionOp while_op, ModuleOp module,
    llvm::SmallDenseMap<Value, SizeInfo>* buffer_to_size,
    llvm::StringMap<PartitionedCallDecompositionInfo>*
        decomposed_partitioned_call_callees) {
  OpBuilder builder(while_op);
  auto modify_region_arguments = [&](Region& region) {
    int64_t original_arg_count = region.getNumArguments();
    for (int64_t i = 0; i < original_arg_count; ++i) {
      auto operand = while_op.getOperand(i);
      auto it = buffer_to_size->find(operand);
      if (it == buffer_to_size->end()) continue;
      auto buffer_type = it->getFirst().getType();
      region.getArgument(i).setType(buffer_type);
      auto size_arg =
          region.addArgument(cutil::GetSizeType(builder), region.getLoc());
      (*buffer_to_size)[region.getArgument(i)] = {size_arg,
                                                  it->getSecond().fixed};
    }
  };

  // Rewrite body.
  Region& body_region = while_op.body();
  modify_region_arguments(body_region);
  if (failed(DecomposeTensorListOpsInternal(
          &body_region.front(), module, buffer_to_size,
          decomposed_partitioned_call_callees))) {
    return failure();
  }
  auto output_buffer_to_size = AddTensorListSizesToTerminator<TF::YieldOp>(
      body_region.front(), *buffer_to_size);

  // Rewrite cond.
  Region& cond_region = while_op.cond();
  modify_region_arguments(cond_region);
  if (failed(DecomposeTensorListOpsInternal(
          &cond_region.front(), module, buffer_to_size,
          decomposed_partitioned_call_callees))) {
    return failure();
  }

  if (output_buffer_to_size.empty()) return success();

  // Create the new while op.
  auto new_while_operands = llvm::to_vector<8>(while_op.getOperands());
  for (int64_t i = 0; i < while_op.getNumResults(); ++i) {
    auto it = buffer_to_size->find(while_op.getOperand(i));
    if (it == buffer_to_size->end()) continue;
    new_while_operands.push_back(it->getSecond().size);
  }
  auto new_while = builder.create<TF::WhileRegionOp>(
      while_op.getLoc(), body_region.front().getTerminator()->getOperandTypes(),
      new_while_operands, while_op->getAttrs());
  new_while.body().takeBody(body_region);
  new_while.cond().takeBody(cond_region);
  for (const auto& entry : output_buffer_to_size) {
    (*buffer_to_size)[new_while.getResult(std::get<0>(entry))] = {
        new_while.getResult(std::get<1>(entry)), std::get<2>(entry)};
  }
  while_op.replaceAllUsesWith(
      new_while.getResults().take_front(while_op.getNumResults()));
  while_op.erase();
  return success();
}

LogicalResult HandleIfRegionOp(
    TF::IfRegionOp if_op, ModuleOp module,
    llvm::SmallDenseMap<Value, SizeInfo>* buffer_to_size,
    llvm::StringMap<PartitionedCallDecompositionInfo>*
        decomposed_partitioned_call_callees) {
  // Rewrite the branches.
  Region& then_branch = if_op.then_branch();
  Region& else_branch = if_op.else_branch();
  if (failed(DecomposeTensorListOpsInternal(
          &then_branch.front(), module, buffer_to_size,
          decomposed_partitioned_call_callees)))
    return failure();
  if (failed(DecomposeTensorListOpsInternal(
          &else_branch.front(), module, buffer_to_size,
          decomposed_partitioned_call_callees)))
    return failure();

  auto output_buffer_to_size = AddTensorListSizesToTerminator<TF::YieldOp>(
      then_branch.front(), *buffer_to_size);
  AddTensorListSizesToTerminator<TF::YieldOp>(else_branch.front(),
                                              *buffer_to_size);

  if (output_buffer_to_size.empty()) return success();

  // Recreate the op.
  auto new_op = OpBuilder(if_op).create<TF::IfRegionOp>(
      if_op.getLoc(), then_branch.front().getTerminator()->getOperandTypes(),
      if_op.getOperand(), if_op->getAttrs());
  for (const auto& entry : output_buffer_to_size) {
    (*buffer_to_size)[new_op.getResult(std::get<0>(entry))] = {
        new_op.getResult(std::get<1>(entry)), std::get<2>(entry)};
  }

  new_op.then_branch().takeBody(if_op.then_branch());
  new_op.else_branch().takeBody(if_op.else_branch());

  if_op.replaceAllUsesWith(
      new_op.getResults().take_front(if_op.getNumResults()));
  if_op.erase();
  return success();
}

LogicalResult HandleCaseRegionOp(
    TF::CaseRegionOp case_op, ModuleOp module,
    llvm::SmallDenseMap<Value, SizeInfo>* buffer_to_size,
    llvm::StringMap<PartitionedCallDecompositionInfo>*
        decomposed_partitioned_call_callees) {
  // Rewrite the branches.
  RegionRange branches = case_op.getRegions();

  for (Region* branch : branches) {
    if (failed(DecomposeTensorListOpsInternal(
            &branch->front(), module, buffer_to_size,
            decomposed_partitioned_call_callees)))
      return failure();
  }

  // Get the output buffer index to size index mapping one of the branches. It
  // should be same for all the branches so we only get it for the first branch.
  Region* first_branch = branches.front();
  auto output_buffer_to_size = AddTensorListSizesToTerminator<TF::YieldOp>(
      first_branch->front(), *buffer_to_size);
  for (Region* branch : branches.drop_front()) {
    AddTensorListSizesToTerminator<TF::YieldOp>(branch->front(),
                                                *buffer_to_size);
  }

  if (output_buffer_to_size.empty()) return success();

  // Recreate the op.
  auto new_op = OpBuilder(case_op).create<TF::CaseRegionOp>(
      case_op.getLoc(),
      first_branch->front().getTerminator()->getOperandTypes(),
      case_op.getOperand(), case_op->getAttrs(), case_op.getNumRegions());
  for (const auto& entry : output_buffer_to_size) {
    (*buffer_to_size)[new_op.getResult(std::get<0>(entry))] = {
        new_op.getResult(std::get<1>(entry)), std::get<2>(entry)};
  }

  for (auto pair : llvm::zip(new_op.getRegions(), case_op.getRegions())) {
    std::get<0>(pair)->takeBody(*std::get<1>(pair));
  }
  case_op.replaceAllUsesWith(
      new_op.getResults().take_front(case_op.getNumResults()));
  case_op.erase();
  return success();
}

template <typename CallOp>
LogicalResult HandlePartitionedCallOp(
    CallOp call, func::FuncOp callee, ModuleOp module,
    llvm::SmallDenseMap<Value, SizeInfo>* buffer_to_size,
    llvm::StringMap<PartitionedCallDecompositionInfo>*
        decomposed_partitioned_call_callees) {
  auto emplace_res = decomposed_partitioned_call_callees->try_emplace(
      callee.getName(), PartitionedCallDecompositionInfo());
  auto& info = emplace_res.first->second;
  // Recreates the call op with info.
  auto recreate_caller = [&] {
    auto new_operands = llvm::to_vector<8>(call.getOperands());
    for (int64_t i = 0; i < call.getNumOperands(); ++i) {
      auto arg_it = info.buffer_arg_to_size_arg.find(i);
      if (arg_it == info.buffer_arg_to_size_arg.end()) continue;
      auto it = buffer_to_size->find(call.getOperand(i));
      if (it == buffer_to_size->end()) {
        call.emitOpError("unknown tensor list.");
        return failure();
      }
      assert(arg_it->second == new_operands.size());
      new_operands.push_back(it->getSecond().size);
    }
    OpBuilder builder(call);
    auto new_call = builder.create<CallOp>(
        call.getLoc(), info.decomposed_callee.getFunctionType().getResults(),
        new_operands, call->getAttrs());
    new_call->setAttr(
        "f", SymbolRefAttr::get(
                 builder.getContext(),
                 const_cast<func::FuncOp&>(info.decomposed_callee).getName()));
    for (const auto& entry : info.buffer_ret_to_size_ret) {
      (*buffer_to_size)[new_call.getResult(std::get<0>(entry))] = {
          new_call.getResult(std::get<1>(entry)), std::get<2>(entry)};
    }
    call.replaceAllUsesWith(
        new_call.getResults().take_front(call.getNumResults()));
    call.erase();
    return success();
  };
  if (!emplace_res.second) {
    // This callee was handled before.
    if (!info.signature_change) return success();
    return recreate_caller();
  }
  // Rewrite the callee.
  llvm::SmallDenseMap<Value, SizeInfo> callee_map;
  func::FuncOp lowered_callee = callee;
  if (!callee.isPrivate()) {
    // Clone non-private callee in case of signature change.
    lowered_callee = callee.clone();
    lowered_callee.setPrivate();
  }
  auto find_arg_buffer_type = [&](int64_t index) -> llvm::Optional<Type> {
    auto it = buffer_to_size->find(call.getOperand(index));
    if (it == buffer_to_size->end()) return llvm::None;
    return it->getFirst().getType();
  };
  auto arg_buffer_size_is_fixed = [&](int64_t index) {
    return (*buffer_to_size)[call.getOperand(index)].fixed;
  };
  ModifyFunctionSignature(lowered_callee, cutil::GetSizeType(OpBuilder(call)),
                          &callee_map, find_arg_buffer_type,
                          arg_buffer_size_is_fixed);
  const bool args_no_changed = callee_map.empty();
  if (failed(DecomposeTensorListOpsInternal(
          &lowered_callee.front(), module, &callee_map,
          decomposed_partitioned_call_callees))) {
    return failure();
  }
  info.buffer_ret_to_size_ret =
      ModifyFunctionReturn(lowered_callee, callee_map);
  info.decomposed_callee = lowered_callee;
  if (args_no_changed && info.buffer_ret_to_size_ret.empty()) {
    // Signature is not modified. We do not need to keep two copies.
    info.signature_change = false;
    if (lowered_callee != callee) {
      lowered_callee.setName(
          StringAttr::get(callee->getContext(), callee.getName()));
      callee.erase();
      SymbolTable(module).insert(lowered_callee);
    }
  } else {
    info.signature_change = true;
    for (auto& entry : callee_map) {
      auto buffer_arg = entry.getFirst().dyn_cast<BlockArgument>();
      if (!buffer_arg) continue;
      info.buffer_arg_to_size_arg[buffer_arg.getArgNumber()] =
          entry.getSecond().size.cast<BlockArgument>().getArgNumber();
    }
    if (lowered_callee != callee) {
      // Add the clone with a new name.
      lowered_callee.setName(StringAttr::get(
          callee->getContext(),
          llvm::formatv("{0}_tensorlist_decomposed", callee.getName()).str()));
      SymbolTable(module).insert(lowered_callee);
      callee = lowered_callee;
    }
  }
  if (info.signature_change) return recreate_caller();
  return success();
}

// Parses an R1 value to `shape` if it is a TF::ConstOp output. Otherwise,
// returns an error.
LogicalResult GetConstShapeValue(Value shape_value,
                                 llvm::SmallVector<int64_t, 8>* shape) {
  auto shape_op = shape_value.getDefiningOp();
  if (!shape_op) return failure();
  auto shape_const_op = llvm::dyn_cast<TF::ConstOp>(shape_op);
  if (!shape_const_op) return failure();
  for (const auto& v : shape_const_op.value().getValues<APInt>()) {
    int64_t dim_size = v.getSExtValue();
    if (dim_size == ShapedType::kDynamicSize) return failure();
    shape->push_back(dim_size);
  }
  return success();
}

// Checks the result Variant type to infer the element shape if fully defined.
// If the Variant type has multiple subtypes or does not have static shape,
// return error.
LogicalResult GetElementShapeFromResultType(
    Type type, llvm::SmallVector<int64_t, 8>* shape) {
  auto variant_type = getElementTypeOrSelf(type).dyn_cast<TF::VariantType>();
  if (!variant_type || variant_type.getSubtypes().size() != 1) return failure();
  TensorType tensor_type = variant_type.getSubtypes().front();
  if (!tensor_type.hasStaticShape()) return failure();
  for (auto d : tensor_type.getShape()) shape->push_back(d);
  return success();
}

LogicalResult HandleEmptyTensorListOp(
    TF::EmptyTensorListOp list,
    llvm::SmallDenseMap<Value, SizeInfo>* buffer_to_size) {
  Value buffer;
  OpBuilder builder(list);
  llvm::SmallVector<int64_t, 8> element_shape;
  // Infer TensorList element shape from the return type first, and then from
  // the const element shape operand. We first check the return type because
  // shape inference might have successfully inferred the element shape from
  // write operations on the TensorList.
  if (failed(GetElementShapeFromResultType(list.getType(), &element_shape))) {
    if (failed(GetConstShapeValue(list.element_shape(), &element_shape))) {
      return list.emitOpError("unknown tensor list element shape");
    }
  }
  if (failed(cutil::CreateInitBufferValue(
          element_shape, list.max_num_elements(), list, list.element_dtype(),
          builder, &buffer))) {
    return failure();
  }
  Value size = cutil::GetR1Const({0LL}, builder, list.getLoc());
  list.handle().replaceAllUsesWith(buffer);
  (*buffer_to_size)[buffer] = {size, /*fixed=*/false};
  list.erase();
  return success();
}

LogicalResult HandleTensorListReserveOp(
    TF::TensorListReserveOp list,
    llvm::SmallDenseMap<Value, SizeInfo>* buffer_to_size) {
  Value buffer;
  OpBuilder builder(list);
  llvm::SmallVector<int64_t, 8> element_shape;
  // Infer TensorList element shape from the return type first, and then from
  // the const element shape operand. We first check the return type because
  // shape inference might have successfully inferred the element shape from
  // write operations on the TensorList.
  if (failed(GetElementShapeFromResultType(list.getType(), &element_shape))) {
    if (failed(GetConstShapeValue(list.element_shape(), &element_shape))) {
      return list.emitOpError("unknown tensor list element shape");
    }
  }
  if (failed(cutil::CreateInitBufferValue(element_shape, list.num_elements(),
                                          list, list.element_dtype(), builder,
                                          &buffer))) {
    return failure();
  }
  Value size = cutil::ReshapeScalarToSizeType(builder, list.num_elements(),
                                              list.getLoc());
  (*buffer_to_size)[buffer] = {size, /*fixed=*/true};
  list.handle().replaceAllUsesWith(buffer);
  list.erase();
  return success();
}

LogicalResult HandleTensorListFromTensorOp(
    TF::TensorListFromTensorOp list,
    llvm::SmallDenseMap<Value, SizeInfo>* buffer_to_size) {
  OpBuilder builder(list);
  Value buffer = builder.create<TF::IdentityOp>(
      list.getLoc(), ArrayRef<Type>{list.tensor().getType()},
      ArrayRef<Value>{list.tensor()});
  auto type = buffer.getType().cast<TensorType>();
  if (!type.hasStaticShape()) {
    return list.emitOpError("TensorListFromTensorOp input has unknown shape.");
  }
  Value size = cutil::GetR1Const({type.getShape()[0]}, builder, list.getLoc());
  (*buffer_to_size)[buffer] = {size, /*fixed=*/true};
  list.output_handle().replaceAllUsesWith(buffer);
  list.erase();
  return success();
}

LogicalResult HandleTensorListPushBackOp(
    TF::TensorListPushBackOp push,
    llvm::SmallDenseMap<Value, SizeInfo>* buffer_to_size) {
  auto buffer = push.input_handle();
  auto it = buffer_to_size->find(buffer);
  if (it == buffer_to_size->end()) {
    return push.emitOpError(
        "found tf.TensorListPushBack on unknown TensorList.");
  }
  if (it->getSecond().fixed) {
    return push.emitError("cannot push on a fixed-size tensor list");
  }
  auto size = it->getSecond().size;
  OpBuilder builder(push);
  auto new_buffer =
      cutil::SetElement(size, buffer, push.tensor(), builder, push.getLoc());
  auto new_size = builder.create<TF::AddV2Op>(
      push.getLoc(), ArrayRef<Type>{size.getType()},
      ArrayRef<Value>{size, cutil::GetR1Const({1LL}, builder, push.getLoc())});
  push.output_handle().replaceAllUsesWith(new_buffer);
  (*buffer_to_size)[new_buffer] = {new_size, /*fixed=*/false};
  push.erase();
  return success();
}

LogicalResult HandleTensorListPopBackOp(
    TF::TensorListPopBackOp pop,
    llvm::SmallDenseMap<Value, SizeInfo>* buffer_to_size) {
  auto buffer = pop.input_handle();
  auto it = buffer_to_size->find(buffer);
  if (it == buffer_to_size->end()) {
    pop.emitOpError("found tf.TensorListPopBack on unknown TensorList.");
    return failure();
  }
  if (it->getSecond().fixed) {
    return pop.emitError("cannot pop on a fixed-size tensor list");
  }
  auto size = it->getSecond().size;
  OpBuilder builder(pop);
  auto new_buffer = builder.create<TF::IdentityOp>(
      pop.getLoc(), ArrayRef<Type>{buffer.getType()}, ArrayRef<Value>{buffer});
  auto new_size = builder.create<TF::SubOp>(
      pop.getLoc(), ArrayRef<Type>{size.getType()},
      ArrayRef<Value>{size, cutil::GetR1Const({1LL}, builder, pop.getLoc())});
  auto element = cutil::GetElement(new_size, new_buffer, builder, pop.getLoc());
  pop.output_handle().replaceAllUsesWith(new_buffer);
  pop.tensor().replaceAllUsesWith(element);
  pop.erase();
  (*buffer_to_size)[new_buffer] = {new_size, /*fixed=*/false};
  return success();
}

LogicalResult HandleTensorListGetItemOp(
    TF::TensorListGetItemOp get_item,
    const llvm::SmallDenseMap<Value, SizeInfo>& buffer_to_size) {
  auto buffer = get_item.input_handle();
  auto it = buffer_to_size.find(buffer);
  if (it == buffer_to_size.end()) {
    get_item.emitOpError("found tf.TensorListGetItemOp on unknown TensorList.");
    return failure();
  }
  OpBuilder builder(get_item);
  auto index = cutil::ReshapeScalarToSizeType(builder, get_item.index(),
                                              get_item.getLoc());
  auto element =
      cutil::GetElement(index, buffer, OpBuilder(get_item), get_item.getLoc());
  get_item.item().replaceAllUsesWith(element);
  get_item.erase();
  return success();
}

LogicalResult HandleTensorListSetItemOp(
    TF::TensorListSetItemOp set_item,
    llvm::SmallDenseMap<Value, SizeInfo>* buffer_to_size) {
  auto buffer = set_item.input_handle();
  auto it = buffer_to_size->find(buffer);
  if (it == buffer_to_size->end()) {
    set_item.emitOpError("found tf.TensorListSetItemOp on unknown TensorList.");
    return failure();
  }
  OpBuilder builder(set_item);
  auto index = cutil::ReshapeScalarToSizeType(builder, set_item.index(),
                                              set_item.getLoc());
  auto new_buffer = cutil::SetElement(index, buffer, set_item.item(), builder,
                                      set_item.getLoc());
  set_item.output_handle().replaceAllUsesWith(new_buffer);
  auto size = it->getSecond();
  (*buffer_to_size)[new_buffer] = size;
  set_item.erase();
  return success();
}

LogicalResult HandleTensorListLengthOp(
    TF::TensorListLengthOp length,
    const llvm::SmallDenseMap<Value, SizeInfo>& buffer_to_size) {
  auto it = buffer_to_size.find(length.input_handle());
  if (it == buffer_to_size.end()) {
    length.emitOpError("found tf.TensorListLength on unknown TensorList.");
    return failure();
  }
  OpBuilder builder(length);
  if (it->getSecond().fixed) {
    auto dim = cutil::CreateScalarConst(
        length.input_handle().getType().cast<RankedTensorType>().getDimSize(0),
        builder, length.getLoc());
    length.length().replaceAllUsesWith(dim);
  } else {
    auto current_size = it->getSecond().size;
    // Reshapes the R1 length to a scalar.
    auto reshape = builder.create<TF::ReshapeOp>(
        length.getLoc(),
        ArrayRef<Type>{RankedTensorType::get(
            {}, getElementTypeOrSelf(current_size.getType()))},
        ArrayRef<Value>{current_size,
                        cutil::GetR1Const({}, builder, length.getLoc())});
    length.length().replaceAllUsesWith(reshape);
  }
  length.erase();
  return success();
}

LogicalResult HandleTensorListElementShapeOp(
    TF::TensorListElementShapeOp elem_shape,
    const llvm::SmallDenseMap<Value, SizeInfo>& buffer_to_size) {
  if (buffer_to_size.count(elem_shape.input_handle()) == 0) {
    return elem_shape.emitOpError("unknown tensor list");
  }
  auto buffer = elem_shape.input_handle();
  auto result = cutil::GetR1Const(
      buffer.getType().cast<RankedTensorType>().getShape().drop_front(),
      OpBuilder(elem_shape), elem_shape.getLoc(),
      elem_shape.shape_type().getIntOrFloatBitWidth());
  elem_shape.element_shape().replaceAllUsesWith(result);
  elem_shape.erase();
  return success();
}

LogicalResult HandleTensorListGatherOp(
    TF::TensorListGatherOp gather,
    const llvm::SmallDenseMap<Value, SizeInfo>& buffer_to_size) {
  auto it = buffer_to_size.find(gather.input_handle());
  if (it == buffer_to_size.end()) {
    return gather.emitOpError("unknown tensor list");
  }
  auto buffer = gather.input_handle();
  auto result = cutil::GatherElements(gather.indices(), buffer,
                                      OpBuilder(gather), gather.getLoc());
  gather.values().replaceAllUsesWith(result);
  gather.erase();
  return success();
}

LogicalResult HandleTensorListScatterIntoExistingListOp(
    TF::TensorListScatterIntoExistingListOp scatter,
    llvm::SmallDenseMap<Value, SizeInfo>* buffer_to_size) {
  auto it = buffer_to_size->find(scatter.input_handle());
  if (it == buffer_to_size->end()) {
    return scatter.emitOpError("unknown tensor list");
  }
  auto buffer = scatter.input_handle();
  OpBuilder builder(scatter);
  auto indices_type = scatter.indices().getType().cast<RankedTensorType>();
  if (!indices_type) return scatter.emitOpError("unranked indices shape");
  auto shape_type = RankedTensorType::get({2}, builder.getIntegerType(32));
  auto shape = builder.create<TF::ConstOp>(
      scatter.getLoc(),
      DenseElementsAttr::get(
          shape_type, {static_cast<int>(indices_type.getDimSize(0)), 1}));
  auto indices =
      builder.create<TF::ReshapeOp>(scatter.getLoc(), scatter.indices(), shape);
  Value tensor_scatter_update = builder.create<TF::TensorScatterUpdateOp>(
      scatter.getLoc(), buffer, indices, scatter.tensor());
  scatter.output_handle().replaceAllUsesWith(tensor_scatter_update);
  scatter.erase();
  auto size = it->getSecond();
  (*buffer_to_size)[tensor_scatter_update] = size;
  return success();
}

LogicalResult DecomposeTensorListOpsInternal(
    Block* block, ModuleOp module,
    llvm::SmallDenseMap<Value, SizeInfo>* buffer_to_size,
    llvm::StringMap<PartitionedCallDecompositionInfo>*
        decomposed_partitioned_call_callees) {
  for (auto& op : llvm::make_early_inc_range(block->getOperations())) {
    // TODO(yuanzx): Add a pass to remove identities in device computation.
    if (llvm::isa<TF::IdentityOp, TF::IdentityNOp, TF::StopGradientOp>(&op)) {
      op.replaceAllUsesWith(op.getOperands());
      op.erase();
    } else if (auto list = llvm::dyn_cast<TF::EmptyTensorListOp>(&op)) {
      if (failed(HandleEmptyTensorListOp(list, buffer_to_size))) {
        return failure();
      }
    } else if (auto list = llvm::dyn_cast<TF::TensorListReserveOp>(&op)) {
      if (failed(HandleTensorListReserveOp(list, buffer_to_size))) {
        return failure();
      }
    } else if (auto list = llvm::dyn_cast<TF::TensorListFromTensorOp>(&op)) {
      if (failed(HandleTensorListFromTensorOp(list, buffer_to_size))) {
        return failure();
      }
    } else if (auto push = llvm::dyn_cast<TF::TensorListPushBackOp>(&op)) {
      if (failed(HandleTensorListPushBackOp(push, buffer_to_size))) {
        return failure();
      }
    } else if (auto pop = llvm::dyn_cast<TF::TensorListPopBackOp>(&op)) {
      if (failed(HandleTensorListPopBackOp(pop, buffer_to_size))) {
        return failure();
      }
    } else if (auto get_item = llvm::dyn_cast<TF::TensorListGetItemOp>(&op)) {
      if (failed(HandleTensorListGetItemOp(get_item, *buffer_to_size))) {
        return failure();
      }
    } else if (auto set_item = llvm::dyn_cast<TF::TensorListSetItemOp>(&op)) {
      if (failed(HandleTensorListSetItemOp(set_item, buffer_to_size))) {
        return failure();
      }
    } else if (auto length = llvm::dyn_cast<TF::TensorListLengthOp>(&op)) {
      if (failed(HandleTensorListLengthOp(length, *buffer_to_size))) {
        return failure();
      }
    } else if (auto stack = llvm::dyn_cast<TF::TensorListStackOp>(&op)) {
      stack.tensor().replaceAllUsesWith(stack.input_handle());
      stack.erase();
    } else if (auto elem_shape =
                   llvm::dyn_cast<TF::TensorListElementShapeOp>(&op)) {
      if (failed(HandleTensorListElementShapeOp(elem_shape, *buffer_to_size))) {
        return failure();
      }
    } else if (auto gather = llvm::dyn_cast<TF::TensorListGatherOp>(&op)) {
      if (failed(HandleTensorListGatherOp(gather, *buffer_to_size))) {
        return failure();
      }
    } else if (auto scatter =
                   llvm::dyn_cast<TF::TensorListScatterIntoExistingListOp>(
                       &op)) {
      if (failed(HandleTensorListScatterIntoExistingListOp(scatter,
                                                           buffer_to_size))) {
        return failure();
      }
    } else if (auto addn = llvm::dyn_cast<TF::AddNOp>(&op)) {
      auto it = buffer_to_size->find(addn.getOperand(0));
      if (it != buffer_to_size->end()) {
        addn.sum().setType(addn.getOperand(0).getType());
        auto size = it->getSecond();
        (*buffer_to_size)[addn.sum()] = size;
      }
    } else if (auto zeros = llvm::dyn_cast<TF::ZerosLikeOp>(&op)) {
      if (buffer_to_size->count(zeros.x()) > 0) {
        zeros.y().setType(zeros.x().getType());
        auto size = (*buffer_to_size)[zeros.x()];
        (*buffer_to_size)[zeros.y()] = size;
      }
    } else if (auto while_op = llvm::dyn_cast<TF::WhileOp>(&op)) {
      if (failed(HandleWhileOp(while_op, module, buffer_to_size,
                               decomposed_partitioned_call_callees))) {
        return failure();
      }
    } else if (auto if_op = llvm::dyn_cast<TF::IfOp>(&op)) {
      if (failed(HandleCaseOrIfOp(
              if_op, {if_op.then_function(), if_op.else_function()}, module,
              buffer_to_size, decomposed_partitioned_call_callees))) {
        return failure();
      }
    } else if (auto case_op = llvm::dyn_cast<TF::CaseOp>(&op)) {
      SmallVector<func::FuncOp, 2> branches;
      case_op.get_branch_functions(branches);
      if (failed(HandleCaseOrIfOp(case_op, branches, module, buffer_to_size,
                                  decomposed_partitioned_call_callees))) {
        return failure();
      }
    } else if (auto pcall = llvm::dyn_cast<TF::PartitionedCallOp>(&op)) {
      if (!pcall.func())
        return pcall.emitOpError(
            "TensorList decomposition does not support call with nested "
            "references.");

      if (failed(HandlePartitionedCallOp(
              pcall, pcall.func(), module, buffer_to_size,
              decomposed_partitioned_call_callees))) {
        return failure();
      }
    } else if (auto spcall =
                   llvm::dyn_cast<TF::StatefulPartitionedCallOp>(&op)) {
      if (failed(HandlePartitionedCallOp(
              spcall, spcall.func(), module, buffer_to_size,
              decomposed_partitioned_call_callees))) {
        return failure();
      }
    } else if (auto while_op = llvm::dyn_cast<TF::WhileRegionOp>(&op)) {
      if (failed(HandleWhileRegionOp(while_op, module, buffer_to_size,
                                     decomposed_partitioned_call_callees))) {
        return failure();
      }
    } else if (auto if_op = llvm::dyn_cast<TF::IfRegionOp>(&op)) {
      if (failed(HandleIfRegionOp(if_op, module, buffer_to_size,
                                  decomposed_partitioned_call_callees))) {
        return failure();
      }
    } else if (auto case_op = llvm::dyn_cast<TF::CaseRegionOp>(&op)) {
      if (failed(HandleCaseRegionOp(case_op, module, buffer_to_size,
                                    decomposed_partitioned_call_callees))) {
        return failure();
      }
    }
  }
  return success();
}

LogicalResult DecomposeTensorListOps(Block* block, ModuleOp module) {
  llvm::SmallDenseMap<Value, SizeInfo> buffer_to_size;
  llvm::StringMap<PartitionedCallDecompositionInfo>
      decomposed_partitioned_call_callees;
  return DecomposeTensorListOpsInternal(block, module, &buffer_to_size,
                                        &decomposed_partitioned_call_callees);
}

void TensorListOpsDecompositionPass::runOnOperation() {
  auto module = getOperation();
  auto main = module.lookupSymbol<func::FuncOp>("main");
  if (!main) return;
  if (failed(DecomposeTensorListOps(&main.front(), module))) {
    signalPassFailure();
  }
}

}  // namespace

namespace TF {
std::unique_ptr<OperationPass<ModuleOp>>
CreateTensorListOpsDecompositionPass() {
  return std::make_unique<TensorListOpsDecompositionPass>();
}
}  // namespace TF
}  // namespace mlir
