[Bug libstdc++/49559] stable_sort calls self-move-assignment operator

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49559

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011.06.28 08:41:06
     Ever Confirmed|0                           |1

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-06-28 08:41:06 UTC ---
confirmed, __copy_move_b in stl_algobase.h performs the redundant self-move

this untested change fixes the testcase but I haven't checked if it's correct
or passes the testsuite:

Index: include/bits/stl_algobase.h
===================================================================
--- include/bits/stl_algobase.h (revision 175389)
+++ include/bits/stl_algobase.h (working copy)
@@ -541,8 +541,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
         static _BI2
         __copy_move_b(_BI1 __first, _BI1 __last, _BI2 __result)
         {
-         typename iterator_traits<_BI1>::difference_type __n;
-         for (__n = __last - __first; __n > 0; --__n)
+         typename iterator_traits<_BI1>::difference_type __n
+           = __last - __first;
+         if (__n <= 1)
+           return __first;
+         for (; __n > 0; --__n)
            *--__result = std::move(*--__last);
          return __result;
        }