Re: Compiling Elisp to a native code with a GCC plugin

[Tom Tromey <tromey@redhat.com>]

>>>>> "Wojciech" == Wojciech Meyer <wojciech.meyer@googlemail.com> writes:

Tom> It could be done.  It just requires someone willing to do the work.

Wojciech> I know. I could get my old sources of generational garbage
Wojciech> collector, to work. However it is a daunting job (the worse I
Wojciech> could imagine, garbage collectors are nasty), plugging and
Wojciech> debugging a new garbage collector to such huge and esoteric (I
Wojciech> am sure people that who've been working on Emacs for years
Wojciech> will not take this words badly and understand straight away
Wojciech> what I am (a newbie) talking about) project like
Wojciech> Emacs. However I might try to experiment with it (however
Wojciech> unfortunately I am not that self confident about it ;) ).

It is always ok to ask for help.

The current collector is very simple to understand.  If you read
alloc.c, and look through the data structures representing lisp objects
(in lisp.h), you will have a pretty good idea of what is going on.


FWIW, I looked at writing an incremental collector for Emacs.  I was
primarily interested in using software write barriers... this turns out
to be hard because there is a lot of code in Emacs of the form:

   FIELD_ACCESSOR (object) = value;

... which for a software barrier has to be converted to:

   SET_FIELD_ACCESSOR (object, value);

(There are other bad things, too, like passing around a Lisp_Object*
that points to the contents of a vector.)

So, lots of grunge work, just to get the point where you could start
actually working on the GC.  I would look at automated rewriting to
make this work -- that worked out great on the concurrent branch.


There was a more real attempt based on the Boehm GC.  I think the bits
from that are still on a branch.  This GC has a generational mode that,
IIRC, is based on memory protection bits.

Tom