On 11 April 2017 at 08:35, Marshall Clow via Phabricator via cfe-commits <
cfe-commits@lists.llvm.org> wrote:
> mclow.lists added a comment.
>
> Complete reproducer:
>
> // Tested with with: clang++ -std=c++14 -Wunused-function
> UnusedFVassily.cpp
> //
> // UnusedFVassily.cpp:8:39: warning: unused function '__test'
> [-Wunused-function]
> // template <class _Up> static __two __test(...);
> // ^
> // UnusedFVassily.cpp:9:38: warning: unused function '__test'
> [-Wunused-function]
> // template <class _Up> static char __test(typename _Up::pointer* = 0);
> // ^
> // 2 warnings generated.
>
> #include <type_traits>
>
> namespace foo {
>
> struct __two {char __lx; char __lxx;};
> namespace __has_pointer_type_imp
> {
>
> template <class _Up> static __two __test(...);
> template <class _Up> static char __test(typename _Up::pointer* = 0);
>
> }
>
> template <class _Tp>
> struct __has_pointer_type
>
> : public std::integral_constant<bool,
> sizeof(__has_pointer_type_imp::__test<_Tp>(0))
> == 1>
>
This is a bug in libc++. If this header is included into two translation
units, they will be referencing different __test functions here (because
the template has internal linkage due to the 'static'), resulting in an ODR
violation.
> {
> };
>
> }
>
> struct S1 {};
> struct S2 { typedef void *pointer; };
>
> int main () {
> static_assert (!foo::__has_pointer_type<S1>::value, "" );
> static_assert ( foo::__has_pointer_type<S2>::value, "" );
> }
>
>
> https://reviews.llvm.org/D29877
>
>
>
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