[GHC] #7542: GHC doesn't optimize (strict) composition with id

[GHC]

#7542: GHC doesn't optimize (strict) composition with id
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        Reporter:  shachaf           |                Owner:  simonpj
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.6.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by dfeuer):

 That does look good. I don't know how we can determine whether the problem
 is sufficiently fixed. We have an interaction between a weird language
 feature (detectably lifted functions) and a somewhat illegitimate compiler
 transformation that tries to avoid paying too much for those. Everything
 feels a bit brittle and ill-specified.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7542#comment:28>
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