Re: Deprecating -fgnu-tm support for GCC 14 and removing it for GCC 15

[Jason Merrill <jason@redhat.com>]

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On Mon, Dec 18, 2023 at 3:04 AM Richard Biener via Gcc <gcc@gcc.gnu.org>
wrote:

> On Mon, Dec 18, 2023 at 2:35 AM Andrew Pinski via Gcc <gcc@gcc.gnu.org>
> wrote:
> >
> > On Sun, Dec 17, 2023 at 1:20 PM Eric Gallager <egall@gwmail.gwu.edu>
> wrote:
> > >
> > > On Sat, Dec 16, 2023 at 3:16 PM Andrew Pinski via Gcc <gcc@gcc.gnu.org>
> wrote:
> > > >
> > > > -fgnu-tm support has not been improved since GCC 5 or earlier. It is
> > > > not even supported with LTO. Does it make sense to deprecate the
> > > > support for GCC 14 and remove it in GCC 15?
> > > >
> > > > Thanks,
> > > > Andrew Pinski
> > >
> > > Personally, since GCC is in stage 3 now, I would push that schedule
> > > back a release and move deprecation to GCC 15, and then only remove it
> > > for GCC 16 if no one objects, but then again I don't actually use
> > > -fgnu-tm myself, so I wouldn't be too upset if the faster schedule is
> > > chosen instead.
> >
> > Considering -fgnu-tm has been broken for LTO ever since LTO was
> > introduced, and broken with -fsanitize=undefined and broken with many
> > code that might use internal functions (known since 2015), I suspect
> > nobody is using this option in production nor even trying it out. If
> > this was stage1, I might even just recommend removing the support. But
> > deprecating it during stage 3 seems like a fair compromise.
>
> Btw, I'm OK with deprecating it for GCC 14.  Can you please propose a
> patch for changes.html and add a diagnostic message when -fgnu-tm is used
> (disabled with -Wno-deprecated)?
>

Deprecation makes sense to me.

But keep in mind that transactional memory is still the subject of research
and standardization efforts, though the current proposal (wg21.link/n4923)
is significantly simpler than the earlier TS that GCC implemented.  I don't
know how much of the current implementation would carry over, but I'd be
cautious about tearing everything out just yet.

Jason