[GHC] #11106: Turning on optimizer changes behavior in 7.10.3

[GHC]

#11106: Turning on optimizer changes behavior in 7.10.3
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        Reporter:  dsf               |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by nomeata):

 Changing
 {{{
 -class Ord k => OrderKey k where
 +class OrderKey k where
 }}}
 in `Order.hs` and adding `Ord k` instances to methods and functions as
 required also makes the problem go away.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11106#comment:13>
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