[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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Comment(by simonpj@…):

 commit ed54858977e98a833a5767a9c2d07b05c20e5aff
 {{{
 Author: Simon Peyton Jones <simonpj at microsoft.com>
 Date:   Fri May 3 12:00:19 2013 +0100

     Do not duplicate work in SpecConstr (fix Trac #7865)

     This is a bad bug, if a rare one.
     See Note [Work-free values only in environment].

     Thanks to Amos Robinson for finding it.

  compiler/specialise/SpecConstr.lhs |   63
 +++++++++++++++++++++++++++++++++---
  1 files changed, 58 insertions(+), 5 deletions(-)
 }}}

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7865#comment:4>
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