[GHC] #1600: Optimisation: CPR the results of IO

[GHC]

#1600: Optimisation: CPR the results of IO
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        Reporter:  simonmar          |            Owner:
            Type:  task              |           Status:  new
        Priority:  lowest            |        Milestone:  7.6.2
       Component:  Compiler          |          Version:  6.6.1
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  Runtime           |       Difficulty:  Moderate (less
  performance bug                    |  than a day)
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by nomeata):

 One solution, which seems to make sense, is to make the analysis a little
 bit less precise and more careful with recursive definition. If I make
 sure that an `Id` that is a LoopBreaker never has a `DmdResult` that
 `Converges` (by lub’ing it with `Diverges`), both the example above and
 the typecheck program of nofib compiles.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/1600#comment:21>
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