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From: "unlvsur at live dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/107367] New: All standard library algorithms should
 detect whether they are contiguous iterators after C++20
Date: Mon, 24 Oct 2022 02:28:12 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: libstdc++
X-Bugzilla-Version: 13.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: unlvsur at live dot com
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107367

            Bug ID: 107367
           Summary: All standard library algorithms should detect whether
                    they are contiguous iterators after C++20
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: unlvsur at live dot com
  Target Milestone: ---

https://github.com/gcc-mirror/gcc/blob/00716b776200c2de6813ce706d2757eec4cb=
2735/libstdc%2B%2B-v3/include/bits/stl_algo.h#L3229

Take is_sorted for example:

  template<typename _ForwardIterator>
    _GLIBCXX20_CONSTEXPR
    inline bool
    is_sorted(_ForwardIterator __first, _ForwardIterator __last)
    { return std::is_sorted_until(__first, __last) =3D=3D __last; }

It should be optimized to

  template<typename _ForwardIterator>
    _GLIBCXX20_CONSTEXPR
    inline bool
    is_sorted(_ForwardIterator __first, _ForwardIterator __last)
    {=20
       if
constexpr(contiguous_iterator<_ForwardIterator>&&!is_pointer_v<_ForwardIter=
ator>)
{
       return is_sorted(to_address(__first),to_address(__last));
}
else
{
 return std::is_sorted_until(__first, __last) =3D=3D __last;=20
}
 }=