[GHC] #5161: Poor performance of division; unnecessary branching

[GHC]

#5161: Poor performance of division; unnecessary branching
---------------------------------+------------------------------------------
    Reporter:  rtvd              |       Owner:                                             
        Type:  bug               |      Status:  new                                        
    Priority:  normal            |   Component:  libraries/base                             
     Version:  7.0.3             |    Keywords:  div quot rem mod performance slow branching
    Testcase:                    |   Blockedby:                                             
          Os:  Unknown/Multiple  |    Blocking:                                             
Architecture:  Unknown/Multiple  |     Failure:  Runtime performance bug                    
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 In case an Int* is divided by a constant the compiled code contains
 unnecessary checks whether the value being divided is minBound. This check
 is necessary only if a value is being divided by -1 so that an exception
 would be thrown.

 The branch can be removed by the GHC's optimiser after a small change: the
 two parts of the corresponding condition have to be flipped. This provides
 an opportunity to short-circuit this condition to 'false' without knowing
 the first argument (patch is attached).

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5161>
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