// The partial derivatives are returned in `dy`. `dy` should be allocated to
// size `nx`.
// `prefix` names the scope into which all gradients operations are being added.
// `prefix` must be unique within the provided graph otherwise this operation
// will fail. If `prefix` is nullptr, the default prefixing behaviour takes
// place, see TF_AddGradients for more details.
//

  /// Requires that `*region` is not used in any concurrent or subsequent
  /// operations.
  ///
  /// This operation must be provided. See "REQUIRED OPERATIONS" above.
  void (*cleanup)(TF_ReadOnlyMemoryRegion* region);

  /// Returns a pointer to the memory region.
  ///
  /// This operation must be provided. See "REQUIRED OPERATIONS" above.
  const void* (*data)(const TF_ReadOnlyMemoryRegion* region);