Explicit template instantiation code is rarely called

[jorisv]

When using explicit template instantiation we heavily use Eigen::Ref as Matrix reference to avoid copy.

As an example, here the explicit template instantiation of the ABA function:

  extern template const context::VectorXs & aba<
    context::Scalar,
    context::Options,
    JointCollectionDefaultTpl,
    Eigen::Ref<const context::VectorXs>,
    Eigen::Ref<const context::VectorXs>,
    Eigen::Ref<const context::VectorXs>>(
    const context::Model &,
    context::Data &,
    const Eigen::MatrixBase<Eigen::Ref<const context::VectorXs>> &,
    const Eigen::MatrixBase<Eigen::Ref<const context::VectorXs>> &,
    const Eigen::MatrixBase<Eigen::Ref<const context::VectorXs>> &,
    const Convention);

But we rarely call this function with Eigen::Ref.
Instead, we use to write the following:

  Eigen::VectorXd q = randomConfiguration(model);
  Eigen::VectorXd v = Eigen::VectorXd::Zero(model.nv);
  Eigen::VectorXd tau = Eigen::VectorXd::Zero(model.nv);

  Eigen::VectorXd a = pinocchio::aba(model, data, q, v, tau);

This code will then rebuild the ABA function, with the following signature that mismatch the one explicitly template instantiated:

pinocchio::DataTpl<double, 0, pinocchio::JointCollectionDefaultTpl>::TangentVectorType const& pinocchio::aba<double, 0, pinocchio::JointCollectionDefaultTpl, Eigen::Matrix<double, -1, 1, 0, -1, 1>, Eigen::Matrix<double, -1, 1, 0, -1, 1>, Eigen::Matrix<double, -1, 1, 0, -1, 1> >(pinocchio::ModelTpl<double, 0, pinocchio::JointCollectionDefaultTpl> const&, pinocchio::DataTpl<double, 0, pinocchio::JointCollectionDefaultTpl>&, Eigen::MatrixBase<Eigen::Matrix<double, -1, 1, 0, -1, 1> > const&, Eigen::MatrixBase<Eigen::Matrix<double, -1, 1, 0, -1, 1> > const&, Eigen::MatrixBase<Eigen::Matrix<double, -1, 1, 0, -1, 1> > const&, pinocchio::Convention)

We can avoid this issue by forcing the use of Eigen::Ref:

  Eigen::VectorXd a = pinocchio::aba(model, data, pinocchio::make_const_ref(q), pinocchio::make_const_ref(v), pinocchio::make_const_ref(tau));

But it's really easy to call a different signature.

We should find a way to safely call an explicit template instantiation.

This will improve:

• compilation time
• binary size
  • Release
    • With ETI: 100ko
    • Without ETI: 500ko
  • Debug
    • With ETI: 5mo
    • Without ETI: 80mo

[jorisv]

Also, this do not happen when calling RNEA. The compiler call the template instantiated code.

[jorisv]

RNEA force the use of Eigen::Ref:

  template<
    typename Scalar,
    int Options,
    template<typename, int> class JointCollectionTpl,
    typename ConfigVectorType,
    typename TangentVectorType1,
    typename TangentVectorType2>
  const typename DataTpl<Scalar, Options, JointCollectionTpl>::TangentVectorType & rnea(
    const ModelTpl<Scalar, Options, JointCollectionTpl> & model,
    DataTpl<Scalar, Options, JointCollectionTpl> & data,
    const Eigen::MatrixBase<ConfigVectorType> & q,
    const Eigen::MatrixBase<TangentVectorType1> & v,
    const Eigen::MatrixBase<TangentVectorType2> & a)
  {
    return impl::rnea(model, data, make_const_ref(q), make_const_ref(v), make_const_ref(a));
  }

[jorisv]

If we find a better solution to use explicit template instantiation, we also should solve this issue: #2257