[Bug libstdc++/83938] Speed up inplace_merge() algorithm & fix inefficient logic

[fdumont at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83938

François Dumont <fdumont at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2018-07-24
                 CC|                            |fdumont at gcc dot gnu.org
           Assignee|unassigned at gcc dot gnu.org      |fdumont at gcc dot gnu.org
   Target Milestone|---                         |9.0
     Ever confirmed|0                           |1