Warnings about vectorization

[bangerth]

Compiling ASPECT yesterday with the then-current deal.II sources yielded these warnings:

/home/bangerth/p/deal.II/1/install/include/deal.II/base/symmetric_tensor.h: In instantiation of ‘constexpr dealii::SymmetricTensor<rank_, dim, typename dealii::ProductType<Number, typename dealii::EnableIfScalar<OtherNumber>::type>::type> dealii::operator*(const dealii::SymmetricTensor<rank, dim, Number>&, const OtherNumber&) [with int rank_ = 2; int dim = 2; Number = dealii::VectorizedArray<double, 2>; OtherNumber = double; typename dealii::ProductType<Number, typename dealii::EnableIfScalar<OtherNumber>::type>::type = dealii::VectorizedArray<double, 2>]’:
/home/bangerth/p/deal.II/1/install/include/deal.II/base/symmetric_tensor.h:3582:13:   required from ‘void aspect::StokesMatrixFreeHandler<dim>::correct_stokes_rhs() [with int dim = 2]’
/home/bangerth/p/deal.II/1/projects/aspect/source/simulator/stokes_matrix_free.cc:1663:3:   required from here
/home/bangerth/p/deal.II/1/projects/aspect/source/simulator/stokes_matrix_free.cc:1055:52:   in constexpr expansion of ‘dealii::operator*<2, 2, double, dealii::VectorizedArray<double, 2> >(-1.0e+0, sym_grad_u)’
/home/bangerth/p/deal.II/1/install/include/deal.II/base/vectorization.h:2329:7: note: ‘using product_type = using type = using type = class dealii::VectorizedArray<double, 2> {aka class dealii::VectorizedArray<double, 2>}’ has no user-provided default constructor
 class VectorizedArray<double, 2>
       ^~~~~~~~~~~~~~~~~~~~~~~~~~                                                                                                         
/home/bangerth/p/deal.II/1/install/include/deal.II/base/vectorization.h:2514:11: note: and the implicitly-defined constructor does not initialize ‘__m128d dealii::VectorizedArray<double, 2>::data’                                                                                
   __m128d data;                                                                                                                          
           ^~~~                                                                                                                           
/home/bangerth/p/deal.II/1/install/include/deal.II/base/symmetric_tensor.h: In instantiation of ‘constexpr dealii::SymmetricTensor<rank_, dim, typename dealii::ProductType<Number, typename dealii::EnableIfScalar<OtherNumber>::type>::type> dealii::operator*(const dealii::SymmetricTensor<rank, dim, Number>&, const OtherNumber&) [with int rank_ = 2; int dim = 3; Number = dealii::VectorizedArray<double, 2>; OtherNumber = double; typename dealii::ProductType<Number, typename dealii::EnableIfScalar<OtherNumber>::type>::type = dealii::VectorizedArray<double, 2>]’:                                                                                                                               
/home/bangerth/p/deal.II/1/install/include/deal.II/base/symmetric_tensor.h:3582:13:   required from ‘void aspect::StokesMatrixFreeHandler<dim>::correct_stokes_rhs() [with int dim = 3]’
/home/bangerth/p/deal.II/1/projects/aspect/source/simulator/stokes_matrix_free.cc:1663:3:   required from here
/home/bangerth/p/deal.II/1/projects/aspect/source/simulator/stokes_matrix_free.cc:1055:52:   in constexpr expansion of ‘dealii::operator*<2, 3, double, dealii::VectorizedArray<double, 2> >(-1.0e+0, sym_grad_u)’
/home/bangerth/p/deal.II/1/install/include/deal.II/base/vectorization.h:2329:7: note: ‘using product_type = using type = using type = class dealii::VectorizedArray<double, 2> {aka class dealii::VectorizedArray<double, 2>}’ has no user-provided default constructor
 class VectorizedArray<double, 2>
       ^~~~~~~~~~~~~~~~~~~~~~~~~~
/home/bangerth/p/deal.II/1/install/include/deal.II/base/vectorization.h:2514:11: note: and the implicitly-defined constructor does not initialize ‘__m128d dealii::VectorizedArray<double, 2>::data’
   __m128d data;
           ^~~~

I'm not sure what to do with this -- any ideas?

[kronbichler]

This due to some constexpr Tensor changes. I've seen it as well. When I have some time I will look into it.

[masterleinad]

The code in question is

template <typename Number, int width>
inline DEAL_II_ALWAYS_INLINE VectorizedArray<Number, width>
                             operator*(const Number &u, const VectorizedArray<Number, width> &v)
{
  VectorizedArray<Number, width> tmp;
  tmp = u;
  return tmp *= v;
}

I guess we agreed to finally provide a constructor from a scalar and can then improve it.

[bangerth]

Hm. I must admit that I don't know what I need to do for this. Alternatively, could I just initialize tmp with {} here?

[masterleinad]

I have a PR in preparation for cleaning up the constexpr annotations and the related warnings/notes.

[peterrum]

@bangerth @masterleinad is this still an issue after introducing the constructor?

[masterleinad]

Should be OK after #8443, but I let @bangerth decide to close this issue.