[GHC] #5320: check_overlap panic (7.1 regression)

[GHC]

#5320: check_overlap panic (7.1 regression)
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    Reporter:  mikhail.vorozhtsov  |        Owner:                    
        Type:  bug                 |       Status:  new               
    Priority:  normal              |    Milestone:                    
   Component:  Compiler            |      Version:  7.1               
    Keywords:                      |     Testcase:                    
   Blockedby:                      |   Difficulty:                    
          Os:  Unknown/Multiple    |     Blocking:                    
Architecture:  Unknown/Multiple    |      Failure:  Compile-time crash
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Comment(by simonpj):

 Ian: can you merge the change to 7.2 anyway, pls?

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5320#comment:6>
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