/* Copyright 2022 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 "tensorflow/core/ir/importexport/graphdef_export.h"

#include <string>
#include <utility>

#include "absl/strings/str_cat.h"
#include "llvm/ADT/PointerUnion.h"
#include "llvm/ADT/ScopeExit.h"
#include "llvm/ADT/Sequence.h"
#include "mlir/IR/Attributes.h"  // from @llvm-project
#include "mlir/IR/BuiltinAttributes.h"  // from @llvm-project
#include "mlir/IR/BuiltinOps.h"  // from @llvm-project
#include "mlir/IR/Location.h"  // from @llvm-project
#include "mlir/IR/MLIRContext.h"  // from @llvm-project
#include "mlir/IR/Operation.h"  // from @llvm-project
#include "mlir/IR/SymbolTable.h"  // from @llvm-project
#include "mlir/IR/Threading.h"  // from @llvm-project
#include "mlir/IR/Value.h"  // from @llvm-project
#include "mlir/Support/LLVM.h"  // from @llvm-project
#include "tensorflow/core/framework/attr_value.pb.h"
#include "tensorflow/core/framework/function.h"
#include "tensorflow/core/framework/function.pb.h"
#include "tensorflow/core/framework/graph.pb.h"
#include "tensorflow/core/framework/node_def.pb.h"
#include "tensorflow/core/framework/op.h"
#include "tensorflow/core/framework/op_def.pb.h"
#include "tensorflow/core/framework/op_def_builder.h"
#include "tensorflow/core/framework/types.pb.h"
#include "tensorflow/core/framework/versions.pb.h"
#include "tensorflow/core/ir/dialect.h"
#include "tensorflow/core/ir/importexport/convert_attributes.h"
#include "tensorflow/core/ir/importexport/convert_types.h"
#include "tensorflow/core/ir/importexport/functiondef_export.h"
#include "tensorflow/core/ir/ops.h"
#include "tensorflow/core/ir/types/dialect.h"
#include "tensorflow/core/platform/errors.h"
#include "tensorflow/core/platform/status.h"
#include "tensorflow/core/platform/statusor.h"

using tensorflow::AttrValue;
using tensorflow::DataType;
using tensorflow::FunctionDef;
using tensorflow::FunctionLibraryDefinition;
using tensorflow::GradientDef;
using tensorflow::GraphDef;
using tensorflow::NodeDef;
using tensorflow::OpDef;
using tensorflow::OpRegistrationData;
using tensorflow::OpRegistry;
using tensorflow::Status;
using tensorflow::StatusOr;
using tensorflow::VersionDef;
using tensorflow::errors::InvalidArgument;

namespace mlir {
namespace tfg {
namespace {
// This class implements an exporter for TFG directly to GraphDef.
class GraphDefExporter {
 public:
  GraphDefExporter(
      TFGraphDialect *dialect, const OpRegistry &registry,
      llvm::PointerUnion<SymbolTable *, const FunctionLibraryDefinition *>
          function_table)
      : ctx_(dialect->getContext()),
        dialect_(dialect),
        registry_(registry),
        function_table_(function_table) {}

  // Export a TFG module to GraphDef. The module may contain at most one GraphOp
  // and only GraphFuncOp otherwise.
  Status ExportToGraphDef(ModuleOp module, GraphDef *graph);

  // Export a TFG graph function to a FunctionDef. If the function has a
  // gradient, add it to the graph afterwards to preserve thread-safety.
  StatusOr<Optional<GradientDef>> ExportFunction(GraphFuncOp func,
                                                 FunctionDef *def);

 private:
  // Export just the input and outputs of a function signature. When
  // fully-qualifying result names, this must be done before any nodes are
  // Convert argument attributes to an ArgDef.
  StatusOr<OpDef::ArgDef> ConvertArgumentAttributes(DictionaryAttr attrs);

  // Convert a TFG op to a node. When converting a function, fully-qualified
  // result names must be used.
  Status ConvertOperation(Operation *op, NodeDef *node, bool is_func);

  // Get the name associated with a value.
  StatusOr<std::string> GetEdgeName(Value value, bool is_func);

  // Get the name and index of an output segment to fully qualify result names.
  // This requires querying the op registry.
  StatusOr<std::pair<StringRef, unsigned>> GetOutputSegment(OpResult result);

  // Get the name of a function argument from a function in the symbol table.
  StatusOr<StringRef> GetFunctionOutputName(unsigned result_idx,
                                            const std::string &op_name,
                                            SymbolTable &table);
  // Get the name of a function argument from a function in the library.
  static StatusOr<StringRef> GetFunctionOutputName(
      unsigned result_idx, const std::string &op_name,
      const FunctionLibraryDefinition &library);

  // The current MLIR context.
  MLIRContext *ctx_;
  // The TFG dialect instance.
  TFGraphDialect *dialect_;
  // The TF op registry to use.
  const OpRegistry &registry_;
  // A lookup table for functions.
  llvm::PointerUnion<SymbolTable *, const FunctionLibraryDefinition *>
      function_table_;
};
}  // namespace

// Returns a validated graph to export. A TFG module is valid for export if it
// contains at most one graph operation and any number of graph functions.
// Otherwise, returns an error.
static StatusOr<GraphOp> ValidateModuleForExport(ModuleOp module) {
  GraphOp graph_op;
  for (Operation &op : *module.getBody()) {
    if (isa<GraphFuncOp>(op)) continue;
    if (auto new_graph_op = dyn_cast<GraphOp>(op)) {
      if (graph_op) {
        return InvalidArgument(
            "Can't export module with two different tfg.graph");
      }
      graph_op = new_graph_op;
      continue;
    }
    return InvalidArgument(
        "Can't export module with other ops than tfg.graph or tfg.func, has: ",
        op.getName().getStringRef().str());
  }
  return graph_op;
}

// Converts a version attribute to VersionDef.
static void ExportVersionAttr(VersionAttr attr, VersionDef *version) {
  version->set_producer(attr.getProducer());
  version->set_min_consumer(attr.getMinConsumer());
  for (int32_t bad_consumer : attr.getBadConsumers())
    version->add_bad_consumers(bad_consumer);
}

Status GraphDefExporter::ExportToGraphDef(ModuleOp module, GraphDef *graph) {
  TF_ASSIGN_OR_RETURN(GraphOp graph_op, ValidateModuleForExport(module));
  if (graph_op) {
    ExportVersionAttr(graph_op.getVersion(), graph->mutable_versions());
    for (Operation &op : *graph_op.getBody()) {
      TF_RETURN_IF_ERROR(ConvertOperation(&op, graph->mutable_node()->Add(),
                                          /*is_func=*/false));
    }
  }

  const auto convert_func = [this](GraphFuncOp func, FunctionDef *def,
                                   Optional<GradientDef> &gradient) {
    // Generic functions are not on the hot path and skip the conversion to
    // Graph so just call the existing exporter.
    if (func.getGeneric()) {
      TF_ASSIGN_OR_RETURN(*def, ConvertGenericFunctionToFunctionDef(func));
    } else {
      TF_ASSIGN_OR_RETURN(gradient, ExportFunction(func, def));
    }
    return ::tensorflow::OkStatus();
  };

  // TODO(jeffniu): Don't export functions in parallel if there are too few or
  // they are too small.
  if (ctx_->isMultithreadingEnabled()) {
    ctx_->enterMultiThreadedExecution();
    auto exit =
        llvm::make_scope_exit([this] { ctx_->exitMultiThreadedExecution(); });

    // Prepare the arguments to parallel for each.
    struct Argument {
      GraphFuncOp func;
      FunctionDef *def;
      Status status;
      Optional<GradientDef> gradient;
    };
    std::vector<Argument> args;
    for (auto func : module.getOps<GraphFuncOp>())
      args.push_back(Argument{func, graph->mutable_library()->add_function()});
    const auto process_func = [&convert_func](Argument &arg) {
      arg.status = convert_func(arg.func, arg.def, arg.gradient);
      return success(arg.status.ok());
    };

    // Execute the exports in parallel.
    if (failed(failableParallelForEach(ctx_, args, process_func))) {
      Status result;
      for (const Argument &arg : args) {
        result.Update(arg.status);
      }
      return result;
    }
  } else {
    for (auto func : module.getOps<GraphFuncOp>()) {
      Optional<GradientDef> gradient;
      TF_RETURN_IF_ERROR(convert_func(
          func, graph->mutable_library()->add_function(), gradient));
      if (gradient)
        *graph->mutable_library()->add_gradient() = std::move(*gradient);
    }
  }

  return ::tensorflow::OkStatus();
}

// The only dialect attributes allowed have the "tf." prefix. This is a slightly
// faster check that an attribute is a dialect attribute.
static bool IsDialectAttr(const NamedAttribute &attr) {
  return attr.getName().getValue().startswith("tf.");
}

// Export the given attribute list.
static Status ConvertAttributes(
    tensorflow::protobuf::Map<std::string, AttrValue> *map,
    ArrayRef<NamedAttribute> attrs) {
  for (const NamedAttribute &attr : attrs) {
    if (!IsDialectAttr(attr)) continue;
    StringRef name = attr.getName().strref().drop_front(/*strlen("tf.")=*/3);
    TF_ASSIGN_OR_RETURN((*map)[name.str()], ConvertAttribute(attr.getValue()));
  }
  return ::tensorflow::OkStatus();
}

StatusOr<Optional<GradientDef>> GraphDefExporter::ExportFunction(
    GraphFuncOp func, FunctionDef *def) {
  std::string func_name = func.getSymName().str();

  // TODO(jeffniu): Exploit the sorted order of the function attributes.

  // Get a gradient, if there is one.
  Optional<GradientDef> gradient;
  if (Optional<StringRef> gradient_name = func.getGradient()) {
    gradient.emplace();
    gradient->set_gradient_func(gradient_name->str());
    gradient->set_function_name(func_name);
  }

  // Convert the first-class attributes.
  OpDef *signature = def->mutable_signature();
  signature->set_name(func_name);
  if (Optional<StringRef> description = func.getDescription())
    signature->set_description(description->str());
  signature->set_is_stateful(func.getIsStateful());

  if (DenseIntElementsAttr keys = func.getResourceArgUniqueIdsKeysAttr()) {
    DenseIntElementsAttr values = func.getResourceArgUniqueIdsValuesAttr();
    if (!values) {
      return InvalidArgument(
          "'resource_arg_unique_ids_keys' is present but "
          "'resource_arg_unique_ids_values' is missing");
    }
    if (keys.size() != values.size()) {
      return InvalidArgument(
          "'resource_arg_unique_ids_keys' is not the same size as "
          "'resource_arg_unique_ids_values'");
    }
    auto *id_map = def->mutable_resource_arg_unique_id();
    for (auto kv :
         llvm::zip(keys.getValues<int32_t>(), values.getValues<int32_t>()))
      (*id_map)[std::get<0>(kv)] = std::get<1>(kv);
  }

  // Convert other attributes with the "tf." prefix.
  TF_RETURN_IF_ERROR(ConvertAttributes(def->mutable_attr(), func->getAttrs()));

  // Convert the arguments.
  for (int i = 0, e = func.getNumArguments(); i < e; i += 2) {
    auto attrs = func.getArgAttrs().getValue()[i].cast<DictionaryAttr>();
    TF_ASSIGN_OR_RETURN(OpDef::ArgDef &arg = *signature->add_input_arg(),
                        ConvertArgumentAttributes(attrs));
    DataType dtype;
    TF_RETURN_IF_ERROR(ConvertToDataType(
        func.getArgument(i).getType().cast<TensorType>().getElementType(),
        &dtype));
    arg.set_type(dtype);
    // Convert the attributes.
    if (llvm::any_of(attrs, [](const NamedAttribute &attr) {
          return IsDialectAttr(attr);
        })) {
      auto *map = (*def->mutable_arg_attr())[i / 2].mutable_attr();
      TF_RETURN_IF_ERROR(ConvertAttributes(map, attrs.getValue()));
    }
  }

  // Convert the results.
  auto return_op = cast<ReturnOp>(func.SingleBlock::getBody()->getTerminator());
  for (auto it :
       llvm::zip(func.getResultTypes(),
                 func.getAllResultAttrs().getAsRange<DictionaryAttr>(),
                 TFOp(return_op).getNonControlOperands())) {
    TF_ASSIGN_OR_RETURN(OpDef::ArgDef &arg = *signature->add_output_arg(),
                        ConvertArgumentAttributes(std::get<1>(it)));
    DataType dtype;
    TF_RETURN_IF_ERROR(ConvertToDataType(
        std::get<0>(it).cast<TensorType>().getElementType(), &dtype));
    arg.set_type(dtype);
    // Map the result.
    TF_ASSIGN_OR_RETURN((*def->mutable_ret())[arg.name()],
                        GetEdgeName(std::get<2>(it), /*is_func=*/true));
  }

  // Convert the control results.
  for (auto it :
       llvm::zip(return_op.getControlRetAttrs().getAsRange<DictionaryAttr>(),
                 TFOp(return_op).getControlOperands())) {
    // The control result attributes contain only the name.
    DictionaryAttr attrs = std::get<0>(it);
    if (attrs.empty())
      return InvalidArgument("Control result is missing 'tfg.name'");
    assert(attrs.begin()->getName() == dialect_->getTfgNameAttrIdentifier());
    std::string name = attrs.begin()->getValue().cast<StringAttr>().str();
    signature->add_control_output(name);
    // Map the control result.
    TF_ASSIGN_OR_RETURN(std::string value_name,
                        GetEdgeName(std::get<1>(it), /*is_func=*/true));
    // Add the control result name without '^'.
    def->mutable_control_ret()->insert({std::move(name), value_name.substr(1)});
  }

  // Convert the body.
  for (Operation &op : func.SingleBlock::getBody()->without_terminator())
    TF_RETURN_IF_ERROR(
        ConvertOperation(&op, def->add_node_def(), /*is_func=*/true));

  return gradient;
}

StatusOr<OpDef::ArgDef> GraphDefExporter::ConvertArgumentAttributes(
    DictionaryAttr attrs) {
  OpDef::ArgDef arg;
  auto name = attrs.getAs<StringAttr>(dialect_->getTfgNameAttrIdentifier());
  if (!name) return InvalidArgument("argument is missing 'tfg.name'");
  arg.set_name(name.str());
  if (auto description =
          attrs.getAs<StringAttr>(dialect_->getTfgDescriptionAttrIdentifier()))
    arg.set_description(description.str());
  arg.set_is_ref(!!attrs.get(dialect_->getTfgIsRefAttrIdentifier()));
  TF_RETURN_IF_ERROR(ConvertHandleData(
      attrs.getAs<ArrayAttr>(dialect_->getTfgHandleDataAttrIdentifier()),
      &arg));
  if (auto full_type = attrs.getAs<tf_type::FullTypeAttr>(
          dialect_->getTfgFullTypeAttrIdentifier())) {
    TF_ASSIGN_OR_RETURN(*arg.mutable_experimental_full_type(),
                        ConvertAttribute(full_type));
  }
  return arg;
}

// Converts a location to the debug information for the node def, if we find
// supported location, that is a top-level NameLoc or any NameLoc nested inside
// a FusedLoc. Other kind of location are ignored. If a NameLoc is of the form
// "name@func" we parse it and import the two appropriately.
static void ExtractExperimentalDebugInfoFromLocation(
    Location inst_loc, NodeDef::ExperimentalDebugInfo *debug_info) {
  auto add_name_loc = [&](mlir::NameLoc name_loc) {
    StringRef node, func;
    std::tie(node, func) = name_loc.getName().strref().split('@');
    debug_info->add_original_node_names(node.str());
    if (!func.empty()) debug_info->add_original_func_names(func.str());
  };
  if (auto fused = inst_loc.dyn_cast<mlir::FusedLoc>()) {
    for (Location loc : fused.getLocations())
      if (auto name_loc = loc.dyn_cast<mlir::NameLoc>()) add_name_loc(name_loc);
    return;
  }
  if (auto name_loc = inst_loc.dyn_cast<mlir::NameLoc>())
    add_name_loc(name_loc);
}

Status ConvertToNodeDef(
    Operation *op, NodeDef *node, TFGraphDialect *dialect,
    function_ref<StatusOr<std::string>(Value)> get_value_name) {
  // Convert first-class attributes.
  if (auto name =
          op->getAttrOfType<StringAttr>(dialect->getNameAttrIdentifier()))
    node->set_name(name.str());
  if (auto device =
          op->getAttrOfType<StringAttr>(dialect->getDeviceAttrIdentifier()))
    node->set_device(device.str());
  if (auto full_type = op->getAttrOfType<tf_type::FullTypeAttr>(
          dialect->getFullTypeAttrIdentifier())) {
    TF_ASSIGN_OR_RETURN(*node->mutable_experimental_type(),
                        ConvertAttribute(full_type));
  }
  {
    if (auto assigned_device = op->getAttrOfType<StringAttr>(
            dialect->getAssignedDeviceAttrIdentifier())) {
      if (!assigned_device.getValue().empty()) {
        (*node->mutable_attr())[dialect->getAssignedDeviceAttrKey().str()]
            .set_s(assigned_device.str());
      }
    }
  }
  // Convert other attributes.
  for (const NamedAttribute &attr : op->getAttrs()) {
    if (attr.getName() == dialect->getAssignedDeviceAttrIdentifier() ||
        attr.getName() == dialect->getDeviceAttrIdentifier() ||
        attr.getName() == dialect->getFullTypeAttrIdentifier() ||
        attr.getName() == dialect->getNameAttrIdentifier())
      continue;
    TF_ASSIGN_OR_RETURN((*node->mutable_attr())[attr.getName().str()],
                        ConvertAttribute(attr.getValue()));
  }

  // Set the op name.
  node->set_op(op->getName().stripDialect().str());

  // Set the input names.
  for (Value operand : op->getOperands()) {
    TF_ASSIGN_OR_RETURN(std::string input_name, get_value_name(operand));
    node->add_input(std::move(input_name));
  }

  // Export the location as debug info.
  if (!op->getLoc().isa<UnknownLoc>()) {
    ExtractExperimentalDebugInfoFromLocation(
        op->getLoc(), node->mutable_experimental_debug_info());
    if (node->experimental_debug_info().original_node_names().empty())
      node->clear_experimental_debug_info();
  }

  return ::tensorflow::OkStatus();
}

Status GraphDefExporter::ConvertOperation(Operation *op, NodeDef *node,
                                          bool is_func) {
  return ConvertToNodeDef(op, node, dialect_, [&](Value value) {
    return GetEdgeName(value, is_func);
  });
}

// Get the edge name of a value. If `get_output_segment` is specified, it means
// the name should be fully qualified if it is an operation result for exporting
// a function.
static StatusOr<std::string> GetValueName(
    Value value, TFGraphDialect *dialect,
    function_ref<StatusOr<std::pair<StringRef, unsigned>>(OpResult)>
        get_output_segment) {
  std::string name;
  bool is_control = value.getType() == dialect->getControlType();

  if (auto arg = value.dyn_cast<BlockArgument>()) {
    auto func = dyn_cast<GraphFuncOp>(arg.getOwner()->getParentOp());
    if (!func)
      return InvalidArgument("Expected block argument owner to be tfg.func");
    // If the block argument is a control token, use the attributes of the
    // associated data argument (which preceeds it).
    auto attrs = func.getArgAttrs()
                     .getValue()[arg.getArgNumber() - is_control]
                     .cast<DictionaryAttr>();
    auto name_attr =
        attrs.getAs<StringAttr>(dialect->getTfgNameAttrIdentifier());
    if (!name_attr) {
      return InvalidArgument(
          "Can't export graph with missing op-name for function parameter #",
          arg.getArgNumber());
    }
    name.reserve(name_attr.size() + 1);
    if (is_control) name.push_back('^');
    name.append(name_attr.data(), name_attr.size());
    return name;
  }

  auto result = value.cast<OpResult>();
  auto name_attr = result.getOwner()->getAttrOfType<StringAttr>(
      dialect->getNameAttrIdentifier());
  if (!name_attr)
    return InvalidArgument("Can't export graph with missing op-name");

  if (is_control) {
    name.reserve(1 + name_attr.size());
    name.push_back('^');
    name.append(name_attr.data(), name_attr.size());
    return name;
  }

  if (!get_output_segment) {
    name.reserve(name_attr.size() + 3);
    name.append(name_attr.data(), name_attr.size());
    if (result.getResultNumber()) {
      name.push_back(':');
      absl::StrAppend(&name, result.getResultNumber());
    }
    return name;
  }

  TF_ASSIGN_OR_RETURN(auto segment, get_output_segment(result));
  name.reserve(name_attr.size() + segment.first.size() + 4);
  name.append(name_attr.data(), name_attr.size());
  name.push_back(':');
  name.append(segment.first.data(), segment.first.size());
  name.push_back(':');
  absl::StrAppend(&name, segment.second);
  return name;
}

StatusOr<std::string> GetValueName(Value value, TFGraphDialect *dialect) {
  return GetValueName(value, dialect, /*get_output_segment=*/nullptr);
}

StatusOr<std::string> GraphDefExporter::GetEdgeName(Value value, bool is_func) {
  if (!is_func) return GetValueName(value, dialect_);
  return GetValueName(value, dialect_, [&](OpResult result) {
    return GetOutputSegment(result);
  });
}

// Get the segment size of an op's output.
static StatusOr<unsigned> GetOutputSegmentSize(Operation *op,
                                               const OpDef::ArgDef &arg) {
  if (!arg.type_list_attr().empty()) {
    if (auto v = op->getAttr(arg.type_list_attr()).dyn_cast<ArrayAttr>())
      return v.size();
    return InvalidArgument("Type attr not found: ", arg.type_list_attr());
  }
  if (arg.number_attr().empty()) return 1;
  if (auto v = op->getAttr(arg.number_attr()).dyn_cast<IntegerAttr>())
    return v.getValue().getZExtValue();
  return InvalidArgument("Type attr not found: ", arg.number_attr());
}

StatusOr<StringRef> GraphDefExporter::GetFunctionOutputName(
    unsigned result_idx, const std::string &op_name, SymbolTable &table) {
  if (auto func = table.lookup<GraphFuncOp>(op_name)) {
    if (result_idx >= func.getNumResults()) {
      return InvalidArgument("Result #", result_idx, " of function '", op_name,
                             "' is out of range");
    }
    if (auto name = func.getResultAttrOfType<StringAttr>(
            result_idx, dialect_->getTfgNameAttrIdentifier())) {
      return name.getValue();
    }
    return InvalidArgument("Function '", op_name, "' result #", result_idx,
                           "' is missing 'tfg.name'");
  }
  return InvalidArgument("Op '", op_name,
                         "' is neither registered nor a function");
}

// Get the name of a function argument from a function in the library.
StatusOr<StringRef> GraphDefExporter::GetFunctionOutputName(
    unsigned result_idx, const std::string &op_name,
    const FunctionLibraryDefinition &library) {
  if (const FunctionDef *function = library.Find(op_name)) {
    if (result_idx >= function->signature().output_arg_size()) {
      return InvalidArgument("Result #", result_idx, " of function '", op_name,
                             "' is out of range");
    }
    return {function->signature().output_arg(result_idx).name()};
  }
  return InvalidArgument("Op '", op_name,
                         "' is neither registered nor a function");
}

StatusOr<std::pair<StringRef, unsigned>> GraphDefExporter::GetOutputSegment(
    OpResult result) {
  // TODO(jeffniu): OpRegistry::LookUp should accept `string_view`.
  Operation *op = result.getOwner();
  std::string op_name = op->getName().stripDialect().str();
  unsigned result_idx = result.getResultNumber();
  // Only edges in functions need to have fully-qualified names. Get the segment
  // name using the op definition.
  if (const OpRegistrationData *op_reg_data = registry_.LookUp(op_name)) {
    const OpDef &op_def = op_reg_data->op_def;

    for (const OpDef::ArgDef &arg : op_def.output_arg()) {
      TF_ASSIGN_OR_RETURN(unsigned size, GetOutputSegmentSize(op, arg));
      if (size > result_idx)
        return std::pair<StringRef, unsigned>(arg.name(), result_idx);
      result_idx -= size;
    }
    return InvalidArgument("Result #", result_idx, " of op '", op_name,
                           "' is out of range");
  }
  // Try to find a function for a legacy call. Function output segments have
  // exactly one element each.
  StringRef arg_name;
  if (auto *table = function_table_.dyn_cast<SymbolTable *>()) {
    TF_ASSIGN_OR_RETURN(arg_name,
                        GetFunctionOutputName(result_idx, op_name, *table));
  } else {
    TF_ASSIGN_OR_RETURN(
        arg_name,
        GetFunctionOutputName(
            result_idx, op_name,
            *function_table_.get<const FunctionLibraryDefinition *>()));
  }
  return std::pair<StringRef, unsigned>(arg_name, 0);
}

// Convert a TFG graph directly to GraphDef.
Status ConvertToGraphDef(ModuleOp module, tensorflow::GraphDef *graph) {
  SymbolTable table(module);
  GraphDefExporter exporter(
      module.getContext()->getOrLoadDialect<TFGraphDialect>(),
      *OpRegistry::Global(), &table);
  return exporter.ExportToGraphDef(module, graph);
}

// Convert a single TFG function to a FunctionDef and add it to the function
// library. If a function with the same name already exists, replace it.
Status ConvertToFunctionDef(GraphFuncOp func,
                            FunctionLibraryDefinition &library) {
  GraphDefExporter exporter(func.getDialect(), *OpRegistry::Global(), &library);
  FunctionDef def;
  TF_ASSIGN_OR_RETURN(Optional<GradientDef> gradient,
                      exporter.ExportFunction(func, &def));
  const std::string &name = def.signature().name();
  if (library.Contains(name)) {
    TF_RETURN_IF_ERROR(library.ReplaceFunction(name, def));
  } else {
    TF_RETURN_IF_ERROR(library.AddFunctionDef(def));
  }
  if (gradient) {
    if (library.FindGradient(name).empty()) {
      TF_RETURN_IF_ERROR(library.AddGradientDef(*gradient));
    } else {
      TF_RETURN_IF_ERROR(library.ReplaceGradient(*gradient));
    }
  }
  return ::tensorflow::OkStatus();
}

}  // namespace tfg
}  // namespace mlir
