Re: gengtype: conditional GTY ? (to add before GCC 6 release)

[Richard Biener <richard dot guenther at gmail dot com>]

On Fri, Feb 12, 2016 at 1:23 PM, Basile Starynkevitch
<basile@starynkevitch.net> wrote:
> Hello All,
>
> This is motivated by MELT, but I believe it would be useful to every GCC
> plugin which tries to be
> compilable both for GCC 5 & GCC 6.
>
> The technical issue described in
> https://gcc.gnu.org/ml/gcc/2016-02/msg00149.html is that the gimple
> identifier in plugins has changed from pointer (in GCC 5 and earlier) to
> class.
>
> I feel that is a very major change w.r.t. plugins. Most (and probably all)
> GCC plugins will be affected.
> (A cosmetic patch might be to name gimpleinstance what is today gimple)
>
> A tempting way might be
>
> #if GCCPLUGIN_VERSION >= 6000
> typedef gimple* melt_gimpleptr_t;
> #else
> typedef gimple melt_gimpleptr_t;
> #endif /* GCC 6 */
>
> unfortunately, that does not work today, because gengtype does not get
> preprocessed input (and does not invoke the preprocessor).
>
> Perhaps we should consider patching gengtype to enable conditional GTY-s at
> least for typedefs.
>
> I am tempted to try implementing a conditional GTY, perhaps
>
>    typedef GTY((when(WANTPOINTER)) gimple* melt_gimpleptr_t;
>
> and
>
>    typedef GTY((unless(WANTPOINTER)) gimple melt_gimpleptr_t;
>
> then, add a condition argument to gengtype processor, perhaps invoking it as
>
>     gengtype -CWANTPOINTER ....
>
> or
>
>    gengtype --condition WANTPOINTER
>
> but this makes sense only if such a gengtype patch would go both into GCC 6
> and into the next microrelease of GCC 5, i.e. GCC 5.4
>
> I'm afraid that the current stage rules forbid that. Or, could such a patch
> be considered as a bug fix?

Sorry, no.  The plugin API was never considered stable and thus plugins have to
deal with incompatibilites as they arise.

Help with picking up the partially completed work on a stable plugin
(introspection) API
is of course welcome.

Richard.

> Opinions are welcome!
>
> Regards.
>
> PS. The very dirty alternative would be to feed gengtype with different
> variants of inputs. That is ugly.
>
>
>
> --
> Basile STARYNKEVITCH         http://starynkevitch.net/Basile/
> email: basile<at>starynkevitch<dot>net mobile: +33 6 8501 2359
> 8, rue de la Faiencerie, 92340 Bourg La Reine, France
> *** opinions {are only mine, sont seulement les miennes} ***
>