[GHC] #7206: Implement cheap build

[GHC]

#7206: Implement cheap build
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        Reporter:  simonpj           |                   Owner:  simonpj
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:  ⊥
       Component:  Compiler          |                 Version:  7.4.2
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Comment (by bgamari):

 This is with `cheapBuild` being used for enumerations.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7206#comment:16>
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