[GHC] #7865: SpecConstr duplicating computations

[GHC]

#7865: SpecConstr duplicating computations
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    Reporter:  amosrobinson      |       Owner:                         
        Type:  bug               |      Status:  new                    
    Priority:  normal            |   Milestone:                         
   Component:  Compiler          |     Version:                         
    Keywords:  SpecConstr        |          Os:  Unknown/Multiple       
Architecture:  Unknown/Multiple  |     Failure:  Runtime performance bug
  Difficulty:  Unknown           |    Testcase:                         
   Blockedby:                    |    Blocking:                         
     Related:                    |  
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Changes (by simonpj):

  * difficulty:  => Unknown


Comment:

 Excellent point.  `SpecConstr` is (and I'm afraid must) do some on-the-fly
 simplification, but here is is going too far by duplicating an expensive
 sub-computation.

 I've made the on-the-fly inlining less aggressive; and written a long
 comment about it `Note [Work-free values only in environment]`. Pushing
 shortly.

 Thanks for identifying this so clearly.

 Simon

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7865#comment:3>
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