[Bug libstdc++/34236] New: nth_element failure: infinite loop or segmentation fault

["florent dot balestrieri at ofidea dot fr" <gcc-bugzilla at gcc dot gnu dot org>]

When given certain input and certain comparator, nth_element
enters in a loop or crash the program. The problem didn't
appear when using less<double>. With the comparator:

   not2<less<double> >

it failed with an array of {1,1,1,1,2,3,4}
worked with an array of {1,1,1,1,2,3,4,5}
failed again with {1,1,1,1,2,2,2,3}

Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v
--enable-languages=c,c++,fortran,objc,obj-c++,treelang --prefix=/usr
--enable-shared --with-system-zlib --libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix --enable-nls
--program-suffix=-4.1 --enable-__cxa_atexit --enable-clocale=gnu
--enable-libstdcxx-debug --enable-mpfr --enable-checking=release i486-linux-gnu
Thread model: posix
gcc version 4.1.2 (Ubuntu 4.1.2-0ubuntu4)

command line: g++ bug_nth_element.cpp && a.out

content of bug_nth_element follows:
<<EOF
#include <vector>
#include <iterator>
#include <iostream>
int main() {
   using namespace std;
   vector<double> a;
//   fill_n (back_inserter(a), 4, 1.0); // infinite loop
   fill_n (back_inserter(a), 4, 0.0); // segmentation fault
   nth_element (a.begin(), a.begin(), a.end(), not2(less<double>()));
   copy (a.begin(), a.end(), ostream_iterator<double>(cout, "\n"));
}
EOF


-- 
           Summary: nth_element failure: infinite loop or segmentation fault
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: florent dot balestrieri at ofidea dot fr


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34236