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

[GHC]

#1600: Optimisation: CPR the results of IO
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        Reporter:  simonmar          |            Owner:  nomeata
            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:  #8598
-------------------------------------+-------------------------------------

Comment (by nomeata):

 Found one possible reason for the allocation increase: boyer2 was losing a
 no-let-escape, because the insight from `Note [CPR for sum types]` was not
 applied inside a nested CPR result. Fixed that now, nofibs are running.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/1600#comment:29>
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