On Oct 1, 2014, at 12:49 PM, Argyrios Kyrtzidis <[email protected]> wrote:
>>
>> On Oct 1, 2014, at 12:03 PM, Marshall Clow <[email protected]> wrote:
>>
>>
>> On Oct 1, 2014, at 10:17 AM, Bob Wilson <[email protected]> wrote:
>>
>>>>
>>>> On Oct 1, 2014, at 9:22 AM, Agustín K-ballo Bergé <[email protected]>
>>>> wrote:
>>>>
>>>> Hi Argyrios
>>>>
>>>> On 30/09/2014 10:45 p.m., Argyrios Kyrtzidis wrote:
>>>>> Hi Marshall,
>>>>>
>>>>> This seems to have caused a regression with Objective-C++, see the
>>>>> following test case:
>>>>>
>>>>> #include <type_traits>
>>>>>
>>>>> class CXXForwardClass;
>>>>> @class ObjCForwardClass;
>>>>>
>>>>> static_assert(std::is_trivially_destructible<CXXForwardClass*>::value ==
>>>>> true, "it is true"); // true
>>>>> static_assert(std::is_trivially_destructible<ObjCForwardClass*>::value ==
>>>>> true, "it is true"); // false ?
>>>>
>>>> This sounds like a pre-existing issue to me. Does the following test case
>>>> hold?
>>>>
>>>> static_assert(std::is_destructible<CXXForwardClass*>::value == true, "it
>>>> is true"); // true
>>>> static_assert(std::is_destructible<ObjCForwardClass*>::value == true, "it
>>>> is true"); // false ?
>>>
>>> No, that doesn’t work either.
>>>
>>>>
>>>>>> On Sep 2, 2014, at 9:19 AM, Marshall Clow <[email protected]> wrote:
>>>>>>
>>>>>> Author: marshall
>>>>>> Date: Tue Sep 2 11:19:38 2014
>>>>>> New Revision: 216909
>>>>>>
>>>>>> URL: http://llvm.org/viewvc/llvm-project?rev=216909&view=rev
>>>>>> Log:
>>>>>> Fix PR#20834 - 'is_trivially_destructible yeilds wrong answer for arrays
>>>>>> of unknown bound' Thanks to K-ballo for the bug report. Update a few of
>>>>>> the other tests while we're here, and fix a typo in a test name.
>>>>>>
>>>>>> --- libcxx/trunk/include/type_traits (original)
>>>>>> +++ libcxx/trunk/include/type_traits Tue Sep 2 11:19:38 2014
>>>>>> @@ -2861,7 +2861,7 @@ template <class _Tp> struct _LIBCPP_TYPE
>>>>>> #if __has_feature(has_trivial_destructor) || (_GNUC_VER >= 403)
>>>>>>
>>>>>> template <class _Tp> struct _LIBCPP_TYPE_VIS_ONLY
>>>>>> is_trivially_destructible
>>>>>> - : public integral_constant<bool, __has_trivial_destructor(_Tp)> {};
>>>>>> + : public integral_constant<bool, is_destructible<_Tp>::value &&
>>>>>> __has_trivial_destructor(_Tp)> {};
>>>>
>>>> This is the relevant change ^. Something that is not destructible cannot
>>>> be trivially destructible by definition.
>>>
>>> Right, but the issue wasn’t exposed until r216909.
>>
>> Interesting (but consistent) behavior here:
>>
>> class CXXForwardClass;
>> @class ObjCForwardClass;
>>
>> template <class U>
>> void destroy ( U& u ) { u.~U(); }
>>
>> template <class U>
>> void test () { U *p = nullptr; destroy<U*>(p); }
>>
>> int main () {
>> test<void>(); // compiles w/o error
>> test<CXXForwardClass>(); // compiles w/o error
>> test<ObjCForwardClass>(); // error.
>> }
>>
>> $ totclang11 -ObjC++ junk2.cpp
>> junk2.cpp:39:26: error: member access into incomplete type 'ObjCForwardClass'
>> void destroy ( U& u ) { u.~U(); }
>> ^
>> junk2.cpp:50:32: note: in instantiation of function template specialization
>> 'destroy<ObjCForwardClass *>' requested here
>> void test () { U *p = nullptr; destroy<U*>(p); }
>> ^
>> junk2.cpp:55:2: note: in instantiation of function template specialization
>> 'test<ObjCForwardClass>' requested here
>> test<ObjCForwardClass>();
>> ^
>> junk2.cpp:36:8: note: forward declaration of class here
>> @class ObjCForwardClass;
>> ^
>> 1 error generated.
>
> Interesting but this behavior have existed in clang forever, is libcxx
> depending on this, recently, to do the type trait ?
the bit in destroy is exactly what the standard specifies as how to test for
“is_destructible”.
Table 49:
For object types and given U equal to remove_all_extents_t<T>, if the
expression std::declval<U&>(). ̃U() is well-formed when
treated as an unevaluated operand (Clause 5), then is_destructible<T>::value is
true, otherwise it is false.
Richard Smith pointed out that destroying a pointer to an objective-C class
might require an ARC call, and so the compiler needs to see the type to figure
out if it is_destructible.
Note that is_destructible<ObjCForwardClass**>::value is true, so it’s just
pointers to objective-C objects, not pointers in general.
— Marshall_______________________________________________
cfe-commits mailing list
[email protected]
http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
