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Re: [PING PATCH, PR 57748] Set mode of structures with zero sized arrays to be BLK
- From: Richard Biener <rguenther at suse dot de>
- To: Jakub Jelinek <jakub at redhat dot com>
- Cc: GCC Patches <gcc-patches at gcc dot gnu dot org>, "Joseph S. Myers" <joseph at codesourcery dot com>
- Date: Wed, 28 Aug 2013 10:05:11 +0200 (CEST)
- Subject: Re: [PING PATCH, PR 57748] Set mode of structures with zero sized arrays to be BLK
- Authentication-results: sourceware.org; auth=none
- References: <20130802114531 dot GE2728 at virgil dot suse> <20130823151122 dot GC32344 at virgil dot suse> <20130823152923 dot GN1814 at tucnak dot redhat dot com> <20130827140342 dot GA3564 at virgil dot suse> <20130827140906 dot GI21876 at tucnak dot zalov dot cz>
On Tue, 27 Aug 2013, Jakub Jelinek wrote:
> On Tue, Aug 27, 2013 at 04:03:42PM +0200, Martin Jambor wrote:
> > On Fri, Aug 23, 2013 at 05:29:23PM +0200, Jakub Jelinek wrote:
> > > On Fri, Aug 23, 2013 at 05:11:22PM +0200, Martin Jambor wrote:
> > > > Hi Jakub and/or Joseph,
> > > >
> > > > the reporter of this bug seems to be very anxious to have it fixed in
> > > > the repository. While Richi is away, do you think you could have a
> > > > look? It is very small.
> > >
> > > Isn't this ABI incompatible change (at least potential on various targets)?
> > > If so, then it shouldn't be applied to release branches, because it would
> > > create (potential?) ABI incompatibility between 4.8. and 4.8.2.
> > >
> > I don't know. I did a few attempts to observe a change in the calling
> > convention of a function accepting a zero sized array terminated
> > structure by value (on x86_64) but I did not succeed. On the other
> > hand, I assume there are many other ways how a mode can influence ABI.
> > So I'll try to have a look whether we can hack around this situation
> > in 4.8's expr.c instead.
> All I remember that e.g. the number of regressions from PR20020 was big,
> and any kind of TYPE_MODE changes are just extremely risky.
> Perhaps x86_64 in the ABI decisions never uses mode, but we have tons of
> other targets and it would surprise me if none of those were affected.
> > Nevertheless, is this patch ok for trunk?
> I'll defer that to Richard now that he is back ;)
Eh ... :/
I'm extremely nervous about this change. I also believe the change
is unrelated to the issue in the bugreport (even if it happens to
fix the ICE).
Let me have a (short) look.