[GHC] #14768: -O1 changes result at runtime, duplicating __DEFAULT case

[GHC]

#14768: -O1 changes result at runtime, duplicating __DEFAULT case
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        Reporter:  Bodigrim          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.4.1-alpha3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 In the test case there is no need to run it.  Core Lint picks up the error
 immediately.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14768#comment:5>
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