From: Thomas Rodgers <rodgert@twrodgers.com>
To: Jakub Jelinek <jakub@redhat.com>
Cc: Jonathan Wakely <jwakely@redhat.com>,
Thomas Rodgers <trodgers@redhat.com>,
gcc Patches <gcc-patches@gcc.gnu.org>,
"libstdc++" <libstdc++@gcc.gnu.org>
Subject: Re: [PATCH] libstdc++: Clear padding bits in atomic compare_exchange
Date: Tue, 2 Nov 2021 20:06:45 -0700 [thread overview]
Message-ID: <CAAB_aXvwZJiNOZy44sQJ=yCpyXE-r9v9ja+eKuzTccnZsuaDXA@mail.gmail.com> (raw)
In-Reply-To: <20211102074951.GZ304296@tucnak>
This version of the patch specifically doesn’t deal with long double.
Mostly looking for Jonathan’s review to ensure his previous feedback is
addressed. I plan to rev the patch to handle long doubles after some
further discussion with you and Jonathan.
On Tue, Nov 2, 2021 at 12:49 AM Jakub Jelinek <jakub@redhat.com> wrote:
> On Mon, Nov 01, 2021 at 06:25:45PM -0700, Thomas Rodgers via Gcc-patches
> wrote:
> > + template<typename _Tp>
> > + constexpr bool
> > + __maybe_has_padding()
> > + {
> > +#if __has_builtin(__has_unique_object_representations)
> > + return !__has_unique_object_representations(_Tp)
> > + && !is_floating_point<_Tp>::value;
> > +#else
> > + return true;
> > +#endif
>
> I'm not sure I understand the && !is_floating_point<_Tp>::value.
> Yes, float and double will never have padding, but long double often
> will, e.g. on x86 or ia64 (but e.g. not on ppc, s390x, etc.).
> So, unless we want to play with numeric_limits, it should be either
> just return !__has_unique_object_representations(_Tp);
> or return !__has_unique_object_representations(_Tp)
> && (!is_floating_point<_Tp>::value
> || is_same<__remove_cv_t<_Tp>,long double>::value);
> or, with numeric_limits test numeric_limits<_Tp>::digits == 64
> (but I'm sure Jonathan will not want including such a header dependency
> unless it is already included).
> Or I can always provide a new __builtin_clear_padding_p ...
>
> Jakub
>
>
next prev parent reply other threads:[~2021-11-03 3:06 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-23 18:08 Thomas Rodgers
2021-09-23 19:07 ` Jakub Jelinek
2021-09-23 20:15 ` Thomas Rodgers
2021-09-23 20:15 ` Jonathan Wakely
2021-09-27 14:10 ` Thomas Rodgers
2021-09-29 12:13 ` Jonathan Wakely
2021-09-29 12:18 ` Jonathan Wakely
2021-09-29 12:28 ` Jakub Jelinek
2021-09-29 18:22 ` Thomas Rodgers
2021-09-29 18:29 ` Jakub Jelinek
2021-11-02 1:25 ` Thomas Rodgers
2021-11-02 7:49 ` Jakub Jelinek
2021-11-03 3:06 ` Thomas Rodgers [this message]
2021-11-02 8:49 ` Daniel Krügler
2022-01-18 21:48 ` Jonathan Wakely
2022-08-25 10:11 ` Patch ping (was Re: [PATCH] libstdc++: Clear padding bits in atomic compare_exchange) Jakub Jelinek
2022-09-01 22:57 ` Thomas Rodgers
2022-09-07 11:56 ` Jonathan Wakely
2022-09-07 22:06 ` Thomas Rodgers
2022-09-09 18:36 ` Rainer Orth
2022-09-09 18:46 ` Iain Sandoe
2022-09-09 19:01 ` Thomas Rodgers
2022-09-09 20:14 ` Jonathan Wakely
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