[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            |    Milestone:                         
   Component:  Compiler          |      Version:  7.0.1                  
    Keywords:                    |     Testcase:                         
   Blockedby:                    |   Difficulty:                         
          Os:  Unknown/Multiple  |     Blocking:                         
Architecture:  Unknown/Multiple  |      Failure:  Runtime performance bug
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Comment(by batterseapower):

 I've implemented and validated a patch that does this (attached). Pretty
 straightforward, and it seems to work.

 Nofib results are:

 {{{
             Min          +0.0%     -4.1%     +0.0%     +0.5%     +0.0%
             Max          +0.1%     +0.0%     +2.3%   +274.5%     +0.0%
  Geometric Mean          +0.0%     -0.1%     +0.4%    +14.3%     -0.0%
 }}}

 So a small but solid reduction in allocations (ignore the runtime results,
 I was doing something else with the machine at the time so they can't be
 trusted).

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4962#comment:8>
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