[eigen] MSVC inlining - just FYI

[Hauke Heibel <hauke.heibel@xxxxxxxxxxxxxx>]

Hi all,

So, after some reading I was able to find out the following things I'ld quickly like to share.

There was a recent discussion regarding the inlining problem on comp.lang.c++.moderated

http://groups.google.com/group/comp.lang.c++.moderated/browse_thread/thread/e286bba27402a9e1/ff59c4e78f93e9ab?lnk=raot

The problem which is affecting us is that MSVC does not inline functions returning an unwindable object (an object having a non-trivial destructor or an object having members with non-trivial destructors). Here is an example where the __forceinline is ignored unless exception handling is disabled.

template <typename T>
struct UnwindableTemplate
{
  T* m_data;
  
  UnwindableTemplate() : m_data(0)
  {
  }

  ~UnwindableTemplate()
  {
    delete [] m_data;
  }
};

template <typename T>
__forceinline UnwindableTemplate<T> create_unwindable()
{
  return UnwindableTemplate<T>();
}

void main ()
{
  UnwindableTemplate<float> unwind = create_unwindable<float>();
}

Here, I choose the unwindable object to mimik our ei_matrix_storage classes for the particular case when we are dealing with dynamic sized objects. As a consequence, this leads to the fact that functions returning expressions containing matrix members by value will not be inlined. Currently it seems as if this can not be remedied. Returning a reference to a local temporary seems tempting since we are anyways trying to enforce inlining but I would refrain from such a solution and say we just live with it.

It seems as if with newer compiler versions the SSE issue mentioned in the forum is fixed and not our actual problem.

Regards,
Hauke