[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:  mpickering
            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):  phab:D2657
       Wiki Page:                    |
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Comment (by mpickering):

 The call to `nubAvails` wasn't added, I pushed it into the branch which
 deals with an explicit export list, where we actually need to do the
 nubbing.

 It doesn't seem like too much work to make the function deal with
 duplicates correctly. I'm not sure the other places are too critical but I
 will keep it in mind if I am ever working in that area.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12754#comment:13>
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