[Bug libstdc++/58437] [4.7/4.8/4.9 Regression] Sorting value in reverse order is much slower compare to gcc44

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58437

--- Comment #25 from Marc Glisse <glisse at gcc dot gnu.org> ---
Note that naively doing what I am proposing in comment #14 (it's just an
iter_swap and a +-1) also makes reverse-sorted arrays a bad case, because of
the way we do partitioning, so it isn't an alternative to Chris's first+1
approach, more of an orthogonal optimization.