[GHC] #4962: Dead code fed to CorePrep because RULEs keep it alive spuriously

[GHC]

#4962: Dead code fed to CorePrep because RULEs keep it alive spuriously
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    Reporter:  batterseapower    |       Owner:                         
        Type:  bug               |      Status:  new                    
    Priority:  normal            |   Component:  Compiler               
     Version:  7.0.1             |    Keywords:                         
    Testcase:                    |   Blockedby:                         
          Os:  Unknown/Multiple  |    Blocking:                         
Architecture:  Unknown/Multiple  |     Failure:  Runtime performance bug
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Comment(by rl):

 Where is `go` used in your example? If it isn't, should it be dropped
 together with the rule?

 Simon, didn't we discuss a similar problem a while ago? I vaguely remember
 that the conclusion was to drop all local rules in CoreTidy or CorePrep
 because they can't possibly be used anywhere but they keep things alive
 which would be dead otherwise. Max, wouldn't that solve this problem?

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4962#comment:2>
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