[Bug libstdc++/67214] New: undefined behaviour in std::num_get::_M_extract_int()

["malcolm.parsons at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67214

            Bug ID: 67214
           Summary: undefined behaviour in std::num_get::_M_extract_int()
           Product: gcc
           Version: 4.8.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: malcolm.parsons at gmail dot com
  Target Milestone: ---

$ cat num_get.cpp 
#include <iostream>
#include <sstream>
#include <boost/math/special_functions/nonfinite_num_facets.hpp>

int main()
{
    std::locale loc;
    auto loc1 = std::locale{loc, new boost::math::nonfinite_num_get<char>};
    std::locale::global(loc1);

    std::string s{"-1"};
    std::istringstream is{s};

    bool v;
    is >> v;
    std::cout << v << '\n';
    return 0;
}

$ clang++-3.6 --std=c++11 -fsanitize=undefined num_get.cpp -o num_get -O2

$ ./num_get 
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/bits/locale_facets.tcc:468:6:
runtime error: negation of -9223372036854775808 cannot be represented in type
'long'; cast to an unsigned type to negate this value to itself

line 468 is the third line below:

      const __unsigned_type __max =
        (__negative && __gnu_cxx::__numeric_traits<_ValueT>::__is_signed)
        ? -__gnu_cxx::__numeric_traits<_ValueT>::__min
        : __gnu_cxx::__numeric_traits<_ValueT>::__max;

I'm reporting against libstdc++ 4.8.4, but these lines have not changed in git
master.