[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Tinycc-devel] Add gcc cleanup attribute support
From: |
uso ewin |
Subject: |
Re: [Tinycc-devel] Add gcc cleanup attribute support |
Date: |
Thu, 3 Jan 2019 11:04:45 +0100 |
On Wed, Jan 2, 2019 at 7:48 PM Michael Matz <address@hidden> wrote:
>
> Hi,
>
> On Wed, 2 Jan 2019, uso ewin wrote:
>
> > I've try to add support to cleanup attribute to TCC:
> > https://github.com/cosmo-ray/tcc/tree/cleanup
> >
> > Are you interested in having this feature merge in mob ?
> > If yes it would be nice if someone could review my code
>
> As you found out the one-pass nature of TCC makes implementing this
> somewhat awkward. Though you found some inventive solution to this I
> don't particularly like it, specifically:
>
> * your use of tokens instead of a symbol ID in the cleanup attribute seems
> wasteful: in principle a cleanup is an association of a function
> (representable as its name, as ID) with a decl (a Sym), so that should
> be the only necessary thing, not the token string representing
> "func(&foo)" (when the cleanup is function "func" on decl "foo").
Your right, I've use Token, because I have a better knowledge
of Token handling in TCC than function generation,
and it was easier to make the first version using Token, but I should have
change that before sending my mail here,
I'm presently working on making this change.
> * your way of dealing with the "goto forward" problem is to read and
> remember all tokens after the goto until you find the label (and if so
> do the cleanups), rereading all these tokens afterwards.
>
> This feels ugly and against the one-pass nature (and is quadratic if you
> have very many gotos); several alternatives come to mind, though I
> haven't tried any of them to see if they result in less ugly code: e.g.
> you could remember all potentially scope-exiting gotos and check them at
> scope exit (redirecting them to the cleanup and then further to the real
> destination).
Well, the problem with checking this at scope exit or at the label declaration
is that as TCC do single pass generation, I can't go back and
regenerate the goto.
A way to solve this would be either to create a switch case after each label
that might need cleanup, or a dummy function for each goto in need.
Either way, the code needed to handle that would be a lot more complex
that current implementation which is ~30line for handling the forward goto case
and that is call only in scope that contain cleanup variable.
> I'm somewhat sympathetic to having that GCC extension, though it is one of
> the more arcane ones that isn't trivial to support and isn't used very
> often in the wild (did you have any software in mind that made you
> implement the extension?).
I've implement this extension for a project of mine that have an entity system,
where every entity have a refcont, so I want to add a macro that would
automatically decref my entities at scope exit (NEW_INT_ENTITY(my_int)).
The only big project I know that use cleanup is Libvirt:
https://libvirt.org/git/?p=libvirt.git;a=search;h=HEAD;s=Sukrit+Bhatnagar;st=author
but I don't know if TCC can compile it.
They did this as a 2018 google summer of code project.
> So the advantage of having that extensions
> needs to be weighed fairly lightly against the disadvantage of
> complicating TCCs sources. IMHO your current implementation leans more on
> the disadvantage side. But maybe you can rework it somewhat along the
> remarks above and it turns out more elegant?
>
If I use Sym but keep the dual parsing that would happen only
when we have a goto forward and a scope containing cleanup,
would the balance switch to the advantage side ?
Thanks for the review !
Matthias,
>
> Ciao,
> Michael.
>
> _______________________________________________
> Tinycc-devel mailing list
> address@hidden
> https://lists.nongnu.org/mailman/listinfo/tinycc-devel
- [Tinycc-devel] Add gcc cleanup attribute support, uso ewin, 2019/01/02
- Re: [Tinycc-devel] Add gcc cleanup attribute support, Christian Jullien, 2019/01/02
- Re: [Tinycc-devel] Add gcc cleanup attribute support, Michael Matz, 2019/01/02
- Re: [Tinycc-devel] Add gcc cleanup attribute support,
uso ewin <=
- Re: [Tinycc-devel] Add gcc cleanup attribute support, uso ewin, 2019/01/03
- Re: [Tinycc-devel] Add gcc cleanup attribute support, Michael Matz, 2019/01/03
- Re: [Tinycc-devel] Add gcc cleanup attribute support, uso ewin, 2019/01/04
- Re: [Tinycc-devel] Add gcc cleanup attribute support, uso ewin, 2019/01/06
- Re: [Tinycc-devel] Add gcc cleanup attribute support, uso ewin, 2019/01/08
- Re: [Tinycc-devel] Add gcc cleanup attribute support, uso ewin, 2019/01/11
- Re: [Tinycc-devel] Add gcc cleanup attribute support, uso ewin, 2019/01/15
- Re: [Tinycc-devel] Add gcc cleanup attribute support, uso ewin, 2019/01/19
- Re: [Tinycc-devel] Add gcc cleanup attribute support, Christian Jullien, 2019/01/20
- Re: [Tinycc-devel] Add gcc cleanup attribute support, uso ewin, 2019/01/21