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From: Jakub Jelinek <jakub@redhat.com>
To: Thomas Rodgers <trodgers@redhat.com>
Cc: Jonathan Wakely <jwakely@redhat.com>,
	gcc Patches <gcc-patches@gcc.gnu.org>,
	libstdc++ <libstdc++@gcc.gnu.org>,
	Thomas Rodgers <rodgert@twrodgers.com>
Subject: Re: [PATCH] libstdc++: Clear padding bits in atomic compare_exchange
Date: Wed, 29 Sep 2021 20:29:47 +0200	[thread overview]
Message-ID: <20210929182947.GQ304296@tucnak> (raw)
In-Reply-To: <CAMmuTO-3s8B_geZ_Ux5DA-yeVXzt9qzZMQ3tUMra103t_LopJQ@mail.gmail.com>

On Wed, Sep 29, 2021 at 11:22:29AM -0700, Thomas Rodgers via Gcc-patches wrote:
> > The MSVC implementation uses !__has_unique_object_representations(_Tp)
> > && !is_floating_point<_Tp>::value here, which is better than mine
> > above (FP types don't have unique object reps, but also don't have
> > padding bits).

Except the 80-bit long double, that one has padding bits (similarly
_Complex long double).
As I said earlier, if you want a builtin using the __builtin_clear_padding
infrastructure that will return bool if __builtin_clear_padding expands to
something or not, it can be easily added.  GCC already uses something like
that internally.

	Jakub


  reply	other threads:[~2021-09-29 18:29 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 [this message]
2021-11-02  1:25     ` Thomas Rodgers
2021-11-02  7:49       ` Jakub Jelinek
2021-11-03  3:06         ` Thomas Rodgers
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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