[GHC] #13128: Refactor AvailInfo to be more sensible

[GHC]

#13128: Refactor AvailInfo to be more sensible
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        Reporter:  mpickering        |                Owner:  mpickering
            Type:  task              |               Status:  new
        Priority:  low               |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:  12662
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by mpickering):

 I think (2) is significant and want to refactor to see. In another ticket
 pacak reported that the size of the build log was over 100mb because of
 warnings emitted from `ListSetOps`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13128#comment:3>
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