[GHC] #3138: Returning a known constructor: GHC generates terrible code for cmonad

[GHC]

#3138: Returning a known constructor: GHC generates terrible code for cmonad
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    Reporter:  simonpj           |        Owner:                         
        Type:  bug               |       Status:  new                    
    Priority:  low               |    Milestone:  7.2.1                  
   Component:  Compiler          |      Version:  6.10.1                 
    Keywords:                    |     Testcase:                         
   Blockedby:                    |   Difficulty:  Unknown                
          Os:  Unknown/Multiple  |     Blocking:                         
Architecture:  Unknown/Multiple  |      Failure:  Runtime performance bug
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Comment(by batterseapower):

 See also #5075

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3138#comment:11>
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