Re: Updated Sourceware infrastructure plans

[Janne Blomqvist <blomqvist.janne@gmail.com>]

On Thu, Apr 18, 2024 at 11:15 AM FX Coudert <fxcoudert@gmail.com> wrote:
>
> > I regenerate auto* files from time to time for libgfortran. Regenerating
> > them has always been very fragile (using --enable-maintainer-mode),
> > and difficult to get right.
>
> I have never found them difficult to regenerate, but if you have only a non maintainer build, it is a pain to have to make a new maintainer build for a minor change.
>
> Moreover, our m4 code is particularly painful to use and unreadable. I have been wondering for some time: should we switch to simpler Python scripts? It would also mean that we would have fewer files in the generated/ folder: right now, every time we add new combinations of types, we have a combinatorial explosion of files.
>
> $ ls generated/sum_*
> generated/sum_c10.c generated/sum_c17.c generated/sum_c8.c  generated/sum_i16.c generated/sum_i4.c  generated/sum_r10.c generated/sum_r17.c generated/sum_r8.c
> generated/sum_c16.c generated/sum_c4.c  generated/sum_i1.c  generated/sum_i2.c  generated/sum_i8.c  generated/sum_r16.c generated/sum_r4.c
>
> We could imagine having a single file for all sum intrinsics.
>
> How do Fortran maintainers feel about that?

For the time being I'm not an active maintainer, so my opinion doesn't
per se have weight, but back when I was active I did think about this
issue. IMHO the best of my ideas was to convert these into C++
templates. What we're essentially doing with the M4 stuff and the
proposed in-house Python reimplementation is to make up for lack of
monomorphization in plain old C. Rather than doing some DIY templates,
switch the implementation language to something which has that feature
built-in, in this case C++.  No need to convert the entire libgfortran
to C++ if you don't want to, just those objects that are generated
from the M4 templates. Something like

template<typename T>
void matmul(T* a, T* b, T* c, ...)
{
   // actual matmul code here
}

extern "C" {
  // Instantiate template for every type and export the symbol
  void matmul_r4(gfc_array_r4* a, gfc_array_r4* b, gfc_array_r4* c, ...)
  {
    matmul(a, b, c, ...);
  }
  // And so on for other types
}


-- 
Janne Blomqvist