[GHC] #12754: Adding an explicit export list halves compilation time.

[GHC]

#12754: Adding an explicit export list halves compilation time.
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        Reporter:  mpickering        |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by niteria):

 I built profiled GHC and it confirms what Matthew already said,
 `nubAvails` makes up all the extra allocations.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12754#comment:6>
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