Sorry for dragging this discussion out from the distant past. I'm in
the process of porting some plug-ins from the old plugin SVN branch to
the new plug-in system, and this is one of the issues blocking me. My
plug-ins maintain some tree nodes that I want to stay alive from
function to function. Managing these nodes manually isn't an option,
since they get allocated (with garbage collection) by internal GCC
functions.
Basically, my plug-in wants to sprinkle logging function calls
throughout compiled code. I generate the types and decls for these
with build_function_type_list() and build_fn_decl(), and then use them
when I need them. Now, I don't _need_ to hold on to these references,
but regenerating them every time I use them seems inefficient to me.
> We just have to add some small code [2] into the ggc_mark_roots routine of
> gcc/ggc-common.c to add the scanning using this gt_ggc_r_gt_FOO_h. This is
> not a big deal. We should simply add a routine
> ggc_register_plugin_root_tab(const struct ggc_root_tab*) that adds its
> argument to some (static variable in gcc/ggc-common.c which is a) linked
> list or vector, and have ggc_mark_root scan that list or vector by adding a
> few lines there. We require plugin initializers to call
> ggc_register_plugin_root_tab appropriatly, exactly like they do already call
> register_callback etc...
This is in fact exactly the solution I was using in the old plugin
branch (though I never submitted the code once it became clear that
the newer plug-in system was going to take over). I can send out the
patch if anyone is interested; it's as simple as it sounds.
With that extra bit of garbage collector support in place, I hacked up
a simple header file that provides macros to manually generate
ggc_add_plugin_root struct entries just like the ones gengtype would
generate (for a small set of types). So a plug-in author can declare
a vector of tree nodes like so:
static GC_ROOT_TREE_VEC (my_tree_vector);
Another macro (to be called from plugin_init()) lets the author
register that root with the garbage collector.
register_root (my_tree_vector);
This isn't an end-all solution, but it actually provides all the
support that I need for my plug-ins, and it is perhaps a useful
stepping stone.
The main reason I'm bringing this up is because I've got a handful of
plug-ins I'd like to make public. Without any support from the
garbage collector, I'll have to do some rewriting to get around the
issue. If other plug-in authors thinks this is a useful idea (would
it be sufficient to port MELT, for instance?), I'd be willing to
prepare some patches to add it in.
--Justin
