[GHC] #2902: Example where ghc 6.10.1 fails to optimize recursive instance function calls

[GHC]

#2902: Example where ghc 6.10.1 fails to optimize recursive instance function
calls
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Reporter:  Syzygies                  |          Owner:                
    Type:  run-time performance bug  |         Status:  new           
Priority:  normal                    |      Component:  Compiler      
 Version:  6.10.1                    |       Severity:  normal        
Keywords:  class instance            |       Testcase:                
      Os:  MacOS X                   |   Architecture:  x86_64 (amd64)
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 Using ghc 6.10.1, I get over a 3x performance boost on the attached toy
 example, by moving instance function definitions out of the instance
 declaration, so that recursive calls avoid the class dictionary.

 According to SPJ, ghc 6.10.1 is supposed to perform this optimization
 automatically. I am reporting it as a bug at his request, following a
 discussion on the glasgow-haskell-users at haskell.org list.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2902>
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