// the tape, so no gradient needs to be computed from it unless this
        // target is also a source.
        auto source_tensor = sources_that_are_targets.find(id);
        if (source_tensor != sources_that_are_targets.end()) {
          Gradient* ones_like = nullptr;
          TF_RETURN_IF_ERROR(
              vspace.BuildOnesLike(source_tensor->second, &ones_like));