Re: Question about code generation

[Andrea Corallo <acorallo@gnu.org>]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Helmut Eller <eller.helmut@gmail.com>
>> Cc: Eli Zaretskii <eliz@gnu.org>,  emacs-devel@gnu.org
>> Date: Fri, 10 May 2024 14:57:17 +0200
>> 
>> On Fri, May 10 2024, Gerd Möllmann wrote:
>> 
>> >> But I guess I'm misunderstanding what you are asking about.
>> >
>> > I was thinking of (making my life easier and) generating the fix_
>> > functions in igc.c, as an example, from knowledge that a C parser has
>> > which members are in a given struct, what's their type, Lisp_Object,
>> > pointer to something interesting, ...
>> >
>> > Together with meta infos passed to a code generator this could be used
>> > for all sorts of things, I guess.
>> 
>> Would be nice to write things like:
>> 
>> struct foo {
>>    void* bar [[emacs::igc_fix_obj]];
>> }
>> 
>> and then run a gcc or clang plugin over it and generate the needed code.
>> 
>> Can libgccjit be used to parse C code and could we write the plugin in
>> Emacs Lisp?  That would be fun.
>
> AFAIU, libgccjit needs GIMPL, and you drive it by calling the
> respective functions from libgccjit.  But Andrea will tell for sure.

I think in this case libgccjit goes the other way of what would be need
here.  Libgccjit allowed us to develop an Elisp front-end while here the
frontend we need is already the C one that comes with GCC.

What we want is a GCC plugin, essentially a custom pass that analyses
say lisp.h and output something (in this case some C code).

Not many people know that should be even possible to write it in python
thanks to David Malcolm work
<https://gcc-python-plugin.readthedocs.io/en/latest/>, certanly not
Elisp :/ but probably quicker than doing it in C.

Thanks

  Andrea