Re: plugin hooks

[Basile STARYNKEVITCH <basile at starynkevitch dot net>]

Hello All

Rafael Espindola wrote:
> > I have a concrete example here: plugin-specific pragmas (see
> > PLUGIN_REGISTER_PRAGMA on http://gcc.gnu.org/wiki/plugin%20hook for
> > details)
> >
> > I have two imaginary use cases here.

There are not so imaginary. I am sure I will need plugin specific 
pragmas in 2010. I explained why. But I also told that it is more than 
one man-year effort to exhibit a realistic plugin needing 
PLUGIN_REGISTER_PRAGMA


> > People won't even bother to make plugins if they
> > > feel the set of hooks is blantly unsufficient. [They will either
> > > experiment on their own GCC branch, or avoid GCC entirely, for instance
> > > using LLVM instead]. But working on one's branch is much more painful
> > > than coding a plugin!
>
> I don't see a chicken and egg problem. Your work on making the GC
> accessible to plugins is a good example why it is not  :-) 

Honestly, the [enormous in my view] effort I did make to push that GGC 
related features into the trunk have been disproportionately important 
w.r.t. the result. My work on GGC plugin events is precisely a good 
example of why I need to anticipate my plugin needs.


> Sorry, the point is precisely that they should be concrete :-)
>
> If you are actually coding a plugin and get to the stage "ok, now I
> need a new hook", please send a patch adding the hook and a
> description of what the plugin is trying to do.


You are forgetting an important point in GCC.

The majority of GCC users won't compile GCC. Actually, I have concrete 
experience that most GCC users are not even able (that is willing to 
make the effort) to compile it. They will use a GCC in some distributed 
*binary* form (e.g. the gcc-4.5 package of some future Ubuntu, Debian, 
... distribution, released in mid 2010).

So in christmas 2010, a recently released Ubuntu contains the gcc-4.5 
package (the compiler) and the gcc-dev-4.5 package (enough to compile a 
gcc 4.5 plugin).

Now I (Basile) have developed a plugin by that time which will use a 
PLUGIN_REGISTER_PRAGMA. If I requires its users to compile a gcc-trunk 
(since only after mid 2010 will I be able to really demonstrate a valid 
use of PLUGIN_REGISTER_PRAGMA), nobody -I really think not a single 
person- will use my plugin. If my plugin runs on a standard 4.5 binary 
distribution of gcc, I might have a few users!


I really think we should add more plugin hooks *now* for gcc-4.5. They 
really cannot wait the future 4.6 release (in 2011, 2012?), especially 
since the patches adding them are so short. And by definition, these 
patches can't break anything [provided they don't hurt performance 
measurably on compilation not using plugins, this is why I wrote about 
plugin events whose invoke_plugin_callbacks is not called a million 
times but only a few dozen times... or perhaps a few hundred times on a 
big compilation. I mean that one additional invoke_plugin_callbacks at 
each pass execution is probably acceptable]. So adding new events should 
be done now. The PLUGIN_REGISTER_PRAGMA should not hurt performance of 
GCC, since its invoke_plugin_callbacks is called once for a whole cc1 
process!

And in a couple of years, indeed we might want to obsolete some plugin 
events (like we do obsolete some other features of GCC). Only time can 
tell which events are really useful.

Mind you, the buying point for plugins is to avoid asking users to 
compile the entire GCC compiler but still have some extension ability. 
Nobody likes to do that, except we GCC hackers, and Linux distribution 
makers.

Sometimes I have the intuition that several GCC people are afraid of 
plugins. I cannot understand why. When the Adobe Flash plugin crash in 
my Mozilla, I don't curse the Mozilla team, but Adobe (and of course the 
many sites using too much that proprietary technology). The main concern 
of the GCC community should not be abuse of plugins, it should be the 
survival of GCC in the long term.

I really think we should help as much as possible plugins to be a 
success! And in my opinion, that means provide the necessary hooks in 
4.5 [especially those for which the patch is tiny, like 
PLUGIN_REGISTER_PRAGMA] not in the trunk in a couple of years. This 
takes into account that GCC releases are quite a rare event (there is no 
major GCC release every 3 months).


Regards


PS. Are we absolutely sure that GCC will still be dominant in the 
compiler landscape five or ten years from now? I am not!

PPS. I think that most north-american GCC hackers grossly underestimate 
the effort needed to push even a minor patch for e.g. european hackers. 
There are lot of issues (English language, timezone, lack of near 
collegues working on GCC and which I could meet in a few minutes, major 
cultural differences, market differences [most processor makers are not 
European]...) to consider

--
Basile STARYNKEVITCH         http://starynkevitch.net/Basile/
email: basile<at>starynkevitch<dot>net mobile: +33 6 8501 2359
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*** opinions {are only mines, sont seulement les miennes} ***