From: "H.J. Lu" <hjl.tools@gmail.com>
To: Jason Merrill <jason@redhat.com>
Cc: GCC Patches <gcc-patches@gcc.gnu.org>,
Jakub Jelinek <jakub@redhat.com>,
Richard Biener <richard.guenther@gmail.com>,
Markus Trippelsdorf <markus@trippelsdorf.de>
Subject: Re: PING^1: [PATCH] Add TYPE_EMPTY_RECORD for C++ empty class
Date: Mon, 14 Dec 2015 20:39:00 -0000 [thread overview]
Message-ID: <CAMe9rOoodvn=C0NcpHiFb3nVLr2j9vXBibpSpAcE7wKcxSt3jQ@mail.gmail.com> (raw)
In-Reply-To: <566F23AE.6070604@redhat.com>
On Mon, Dec 14, 2015 at 12:16 PM, Jason Merrill <jason@redhat.com> wrote:
> On 12/12/2015 01:42 PM, Marc Glisse wrote:
>>
>> On Sat, 12 Dec 2015, Jakub Jelinek wrote:
>>
>>> On Sat, Dec 12, 2015 at 09:51:23AM -0500, Jason Merrill wrote:
>>>>
>>>> On 12/11/2015 06:52 PM, H.J. Lu wrote:
>>>>>
>>>>> On Thu, Dec 10, 2015 at 3:24 AM, Richard Biener
>>>>> <richard.guenther@gmail.com> wrote:
>>>>>>
>>>>>> On Wed, Dec 9, 2015 at 10:31 PM, Markus Trippelsdorf
>>>>>> <markus@trippelsdorf.de> wrote:
>>>>>>>
>>>>>>> On 2015.12.09 at 10:53 -0800, H.J. Lu wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>> Empty C++ class is a corner case which isn't covered in psABI nor
>>>>>>>> C++ ABI.
>>>>>>>> There is no mention of "empty record" in GCC documentation. But
>>>>>>>> there are
>>>>>>>> plenty of "empty class" in gcc/cp. This change affects all
>>>>>>>> targets. C++ ABI
>>>>>>>> should specify how it should be passed.
>>
>>
>>
>> About this patch, aren't we supposed to enable new C++ ABIs with
>> -fabi-version=42 (or whatever the next number is)?
>
>
> Yes, the patch should definitely make this conditional on
> abi_version_at_least.
>
>>>>>>> There is a C++ ABI mailinglist, where you could discuss this issue:
>>>>>>> http://sourcerytools.com/cgi-bin/mailman/listinfo/cxx-abi-dev
>>>>>>
>>>>>>
>>>>>> Yep. As long as the ABI doesn't state how to pass those I'd rather
>>>>>> _not_ change GCCs way.
>>>>>
>>>>>
>>>>> It is agreed that GCC is wrong on this:
>>>>>
>>>>>
>>>>> http://sourcerytools.com/pipermail/cxx-abi-dev/2015-December/002876.html
>>>>>
>>>>
>>>> Yes, I think this is just a (nasty) bug on some GCC targets.
>>>
>>>
>>> Well, the argument in that thread is weird, because C and C++ empty
>>> structs
>>> are different, so it isn't surprising they are passed differently.
>>> C++ makes those sizeof == 1, while C has them sizeof == 0.
>>
>>
>> Maybe it isn't surprising, but it isn't particularly helpful either. It
>> increases the number of places where the 2 are incompatible.
>> (I personally don't care about empty C structs)
>
>
> Yep. The C standard doesn't have empty structs; it's a GNU extension. But
> in any case argument passing can be compatible between C and C++, so it
> really should be.
>
>
Before I make any changes, I'd like to ask if we should make
argument passing can be compatible between C and C++ for
all targets GCC support or just x86.
--
H.J.
next prev parent reply other threads:[~2015-12-14 20:39 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-08 16:22 H.J. Lu
2015-12-09 14:05 ` Richard Biener
2015-12-09 18:53 ` H.J. Lu
2015-12-09 21:14 ` H.J. Lu
2015-12-09 21:31 ` Markus Trippelsdorf
2015-12-10 11:24 ` Richard Biener
2015-12-11 23:52 ` H.J. Lu
2015-12-12 14:51 ` Jason Merrill
2015-12-12 15:27 ` Jakub Jelinek
2015-12-12 16:45 ` H.J. Lu
2015-12-12 18:43 ` Marc Glisse
2015-12-14 20:16 ` Jason Merrill
2015-12-14 20:39 ` H.J. Lu [this message]
2015-12-14 20:44 ` Jason Merrill
2015-12-14 22:08 ` H.J. Lu
2016-01-26 19:27 ` Jason Merrill
2016-01-26 19:52 ` H.J. Lu
2016-01-26 20:23 ` Marc Glisse
2016-01-26 20:26 ` H.J. Lu
2016-01-26 20:44 ` Marc Glisse
2016-01-26 21:21 ` H.J. Lu
2016-01-26 21:40 ` Jakub Jelinek
2016-01-26 22:21 ` H.J. Lu
2016-01-27 8:10 ` Marc Glisse
2016-01-27 8:21 ` Jakub Jelinek
2016-01-27 9:03 ` Marc Glisse
2016-01-27 13:46 ` H.J. Lu
2016-01-27 15:39 ` H.J. Lu
2016-03-01 1:02 ` Jason Merrill
2016-03-01 22:44 ` H.J. Lu
2016-03-02 16:25 ` Ulrich Weigand
2016-03-02 17:34 ` H.J. Lu
2016-03-15 15:35 ` Jason Merrill
2016-03-15 16:00 ` H.J. Lu
2016-03-15 19:32 ` Jason Merrill
2016-03-16 12:38 ` H.J. Lu
2016-03-16 16:58 ` Jason Merrill
2016-03-16 17:02 ` H.J. Lu
2016-03-16 19:39 ` H.J. Lu
2016-03-16 19:43 ` Jason Merrill
2016-03-15 21:40 ` Joseph Myers
2016-03-15 22:31 ` H.J. Lu
2016-03-15 22:35 ` Joseph Myers
2016-03-16 0:23 ` H.J. Lu
2016-03-16 0:25 ` Joseph Myers
2016-03-16 2:17 ` H.J. Lu
2016-03-16 9:46 ` Bernhard Reutner-Fischer
2016-03-16 11:53 ` H.J. Lu
2016-03-16 2:51 ` Jason Merrill
2016-03-16 11:55 ` H.J. Lu
2016-03-16 14:33 ` Jason Merrill
2016-03-16 14:48 ` H.J. Lu
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