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From: "ammiera at hotmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/114316] New: assert failure with _GLIBCXX_DEBUG and
 empty range of singular iterators passed std:: algorithm
Date: Tue, 12 Mar 2024 09:05:43 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114316

            Bug ID: 114316
           Summary: assert failure with _GLIBCXX_DEBUG and empty range of
                    singular iterators passed std:: algorithm
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ammiera at hotmail dot com
  Target Milestone: ---

Compiling the attached snippet with -D_GLIBCXX_DEBUG causes an assert to fi=
re:

#include <map>
#include <algorithm>
#include <iterator>

int main()
{
    std::multimap<char, int>::iterator it1{};
    std::multimap<char, int>::iterator it2{};

    (void) (it1=3D=3Dit2); // OK
    (void) std::find_if(
        it1, it2, [](const auto& el) { return el.second =3D=3D 8;});
}

The runtime error:

In function:
    constexpr _IIter std::find_if(_IIter, _IIter, _Predicate) [with _IIter =
=3D=20
    gnu_debug::_Safe_iterator<_Rb_tree_iterator<pair<const char, int> >,=20
    debug::multimap<char, int>, bidirectional_iterator_tag>; _Predicate =3D=
=20
    main()::<lambda(const auto:16&)>]

Error: function requires a valid iterator range [first, last).

Objects involved in the operation:
    iterator "first" @ 0x7ffc275311a0 {
      type =3D std::_Rb_tree_iterator<std::pair<char const, int> > (mutable
iterator);
      state =3D singular;
    }
    iterator "last" @ 0x7ffc275311d0 {
      type =3D std::_Rb_tree_iterator<std::pair<char const, int> > (mutable
iterator);
      state =3D singular;
    }
Program terminated with signal: SIGSEGV

https://godbolt.org/z/e8xa5Eoqn

Tested with C++17 and C++20 mode.

Initially discussed on the mailing list:
https://gcc.gnu.org/pipermail/libstdc++/2024-March/058461.html=