From: "H.J. Lu" <hjl.tools@gmail.com>
To: GCC Patches <gcc-patches@gcc.gnu.org>
Cc: Jason Merrill <jason@redhat.com>,
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: Tue, 26 Jan 2016 21:21:00 -0000 [thread overview]
Message-ID: <CAMe9rOpx=-s-KZzBLWteNeY3JczmJ_p0dKN8giNkWAM92D85Rg@mail.gmail.com> (raw)
In-Reply-To: <alpine.DEB.2.20.1601262134021.8312@laptop-mg.saclay.inria.fr>
On Tue, Jan 26, 2016 at 12:44 PM, Marc Glisse <marc.glisse@inria.fr> wrote:
> On Tue, 26 Jan 2016, H.J. Lu wrote:
>
>> On Tue, Jan 26, 2016 at 12:23 PM, Marc Glisse <marc.glisse@inria.fr>
>> wrote:
>>>
>>> On Tue, 26 Jan 2016, H.J. Lu wrote:
>>>
>>>> On Tue, Jan 26, 2016 at 11:27 AM, Jason Merrill <jason@redhat.com>
>>>> wrote:
>>>>>
>>>>>
>>>>> On 12/14/2015 05:08 PM, H.J. Lu wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>> + if (abi_version_at_least (10))
>>>>>> + TYPE_EMPTY_RECORD (t) = is_really_empty_class (t);
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> This should use is_empty_class or CLASSTYPE_EMPTY_P. We don't want to
>>>>> change how classes with just a vptr are passed.
>>>>>
>>>>> Otherwise, it looks OK to me.
>>>>
>>>>
>>>>
>>>> Is true_type an empty class here? is_empty_class returns false
>>>> on this:
>>>
>>>
>>>
>>> It isn't empty in the usual C++ sense (we can't apply the empty base
>>> optimization to something that derives from it, for instance), or the one
>>> described in the itanium ABI (the relevant one here I guess). On the
>>> other
>>> hand, it is rather useless to pass it by value, so a different notion of
>>
>>
>> llvm/clang treats it as empty class and I think it should be treated
>> as "empty" class.
>
>
> Is it still empty if there are several empty members? Is there a clear
> definition somewhere of what empty means? I guess it makes sense to
> recursively allow "empty" members for this purpose.
Like this:
/* Returns true if TYPE is POD for the purpose of layout and an empty
class or an class with empty classes. */
static bool
is_empty_record (tree type)
{
if (type == error_mark_node)
return false;
if (!CLASS_TYPE_P (type))
return false;
if (CLASSTYPE_NON_LAYOUT_POD_P (type))
return false;
gcc_assert (COMPLETE_TYPE_P (type));
if (CLASSTYPE_EMPTY_P (type))
return true;
tree field;
for (field = TYPE_FIELDS (type); field; field = DECL_CHAIN (field))
if (TREE_CODE (field) == FIELD_DECL
&& !DECL_ARTIFICIAL (field)
&& !is_empty_record (TREE_TYPE (field)))
return false;
return true;
}
--
H.J.
next prev parent reply other threads:[~2016-01-26 21:21 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
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 [this message]
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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