[Bug c++/80390] New: std::pair of aligned type gives bogus warning

["mail at sven-woop dot de" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80390

            Bug ID: 80390
           Summary: std::pair of aligned type gives bogus warning
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mail@sven-woop.de
  Target Milestone: ---

The following code gives a weird warning regarding using a wrong version of
::new for the aligned type. As this code does not do any allocations, and the
std::pair struct should inherit the alignment from its members this code should
be fine.

Code:
------

#include <utility>

struct alignas(32) AlignedStruct {
  int a;
};

std::pair<AlignedStruct,AlignedStruct> my_make_pair(const AlignedStruct& p0,
const AlignedStruct& p1) {
  return std::make_pair(p0,p1);
}

Command line:
--------------
g++ -Wall -o test.o -c test.cpp

Output:
--------
In file included from
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/bits/move.h:54:0,
                 from
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/bits/stl_pair.h:59,
                 from
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/utility:70,
                 from test.cpp:1:
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/type_traits: In
substitution of \u2018template<class _Tp, class _Arg, class> static
std::true_type std::__do_is_direct_constructible_impl::__test(int) [with _Tp =
AlignedStruct; _Arg = const AlignedStruct&; <template-parameter-1-3> =
<missing>]\u2019:
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/type_traits:987:41:
  required from \u2018struct std::__is_direct_constructible_impl<AlignedStruct,
const AlignedStruct&>\u2019
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/type_traits:143:12:
  required from \u2018struct std::__and_<std::is_destructible<AlignedStruct>,
std::__is_direct_constructible_impl<AlignedStruct, const AlignedStruct&>
>\u2019
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/type_traits:991:12:
  required from \u2018struct
std::__is_direct_constructible_new_safe<AlignedStruct, const
AlignedStruct&>\u2019
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/type_traits:1073:12:
  required from \u2018struct std::__is_direct_constructible_new<AlignedStruct,
const AlignedStruct&>\u2019
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/type_traits:1081:12:
  [ skipping 2 instantiation contexts, use -ftemplate-backtrace-limit=0 to
disable ]
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/type_traits:1132:12:
  required from \u2018struct std::is_constructible<AlignedStruct, const
AlignedStruct&>\u2019
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/type_traits:143:12:
  required from \u2018struct std::__and_<std::is_constructible<AlignedStruct,
const AlignedStruct&>, std::is_constructible<AlignedStruct, const
AlignedStruct&> >\u2019
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/bits/stl_pair.h:101:45:
  required from \u2018static constexpr bool std::_PCC<<anonymous>, _T1,
_T2>::_ConstructiblePair() [with _U1 = AlignedStruct; _U2 = AlignedStruct; bool
<anonymous> = true; _T1 = AlignedStruct; _T2 = AlignedStruct]\u2019
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/bits/stl_pair.h:245:35:
  required by substitution of \u2018template<class _U1, class _U2, typename
std::enable_if<(_ConstructiblePair<_U1, _U2>() &&
_ImplicitlyConvertiblePair<_U1, _U2>()), bool>::type <anonymous> > constexpr
std::pair<AlignedStruct, AlignedStruct>::pair(const AlignedStruct&, const
AlignedStruct&) [with _U1 = AlignedStruct; _U2 = AlignedStruct; typename
std::enable_if<(_ConstructiblePair<_U1, _U2>() &&
_ImplicitlyConvertiblePair<_U1, _U2>()), bool>::type <anonymous> =
<missing>]\u2019
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/bits/stl_pair.h:524:14:
  required from \u2018constexpr std::pair<typename
std::__decay_and_strip<_Tp>::__type, typename
std::__decay_and_strip<_T2>::__type> std::make_pair(_T1&&, _T2&&) [with _T1 =
const AlignedStruct&; _T2 = const AlignedStruct&; typename
std::__decay_and_strip<_T2>::__type = AlignedStruct; typename
std::__decay_and_strip<_Tp>::__type = AlignedStruct]\u2019
test.cpp:8:30:   required from here
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/type_traits:976:18:
note: uses \u2018void* operator new(long unsigned int)\u2019, which does not
have an alignment parameter
       = decltype(::new _Tp(declval<_Arg>()))>
                  ^~~~~~~~~~~~~~~~~~~~~~~~~~
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/type_traits:976:18:
note: use \u2018-faligned-new\u2019 to enable C++17 over-aligned new support
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/type_traits: In
substitution of \u2018template<class _Tp, class _Arg, class> static
std::true_type std::__do_is_direct_constructible_impl::__test(int) [with _Tp =
AlignedStruct; _Arg = const AlignedStruct&&; <template-parameter-1-3> =
<missing>]\u2019:
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/type_traits:987:41:
  required from \u2018struct std::__is_direct_constructible_impl<AlignedStruct,
const AlignedStruct&&>\u2019
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/type_traits:143:12:
  required from \u2018struct std::__and_<std::is_destructible<AlignedStruct>,
std::__is_direct_constructible_impl<AlignedStruct, const AlignedStruct&&>
>\u2019
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/type_traits:991:12:
  required from \u2018struct
std::__is_direct_constructible_new_safe<AlignedStruct, const
AlignedStruct&&>\u2019
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/type_traits:1073:12:
  required from \u2018struct std::__is_direct_constructible_new<AlignedStruct,
const AlignedStruct&&>\u2019
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/type_traits:1081:12:
  required from \u2018struct std::__is_direct_constructible<AlignedStruct,
const AlignedStruct&&>\u2019
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/type_traits:1121:12:
  [ skipping 2 instantiation contexts, use -ftemplate-backtrace-limit=0 to
disable ]
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/type_traits:143:12:
  required from \u2018struct std::__and_<std::is_constructible<AlignedStruct,
const AlignedStruct&&>, std::__and_<std::is_convertible<const AlignedStruct&,
AlignedStruct>, std::is_convertible<const AlignedStruct&, AlignedStruct> >
>\u2019
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/type_traits:148:12:
  required from \u2018struct std::__and_<std::is_constructible<AlignedStruct,
const AlignedStruct&>, std::is_constructible<AlignedStruct, const
AlignedStruct&&>, std::__and_<std::is_convertible<const AlignedStruct&,
AlignedStruct>, std::is_convertible<const AlignedStruct&, AlignedStruct> >
>\u2019
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/bits/stl_pair.h:150:12:
  required from \u2018static constexpr bool std::_PCC<<anonymous>, _T1,
_T2>::_MoveCopyPair() [with bool __implicit = true; _U1 = const AlignedStruct&;
_U2 = AlignedStruct; bool <anonymous> = true; _T1 = AlignedStruct; _T2 =
AlignedStruct]\u2019
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/bits/stl_pair.h:298:36:
  required by substitution of \u2018template<class _U1, typename
std::enable_if<_MoveCopyPair<true, _U1, AlignedStruct>(), bool>::type
<anonymous> > constexpr std::pair<AlignedStruct, AlignedStruct>::pair(_U1&&,
const AlignedStruct&) [with _U1 = const AlignedStruct&; typename
std::enable_if<_MoveCopyPair<true, _U1, AlignedStruct>(), bool>::type
<anonymous> = <missing>]\u2019
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/bits/stl_pair.h:524:14:
  required from \u2018constexpr std::pair<typename
std::__decay_and_strip<_Tp>::__type, typename
std::__decay_and_strip<_T2>::__type> std::make_pair(_T1&&, _T2&&) [with _T1 =
const AlignedStruct&; _T2 = const AlignedStruct&; typename
std::__decay_and_strip<_T2>::__type = AlignedStruct; typename
std::__decay_and_strip<_Tp>::__type = AlignedStruct]\u2019
test.cpp:8:30:   required from here
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/type_traits:976:18:
note: uses \u2018void* operator new(long unsigned int)\u2019, which does not
have an alignment parameter
/home/swoop/projects/gcc/latest/usr/local/include/c++/7.0.1/type_traits:976:18:
note: use \u2018-faligned-new\u2019 to enable C++17 over-aligned new support