[GHC] #12189: sigof01m broken after D2030

[GHC]

#12189: sigof01m broken after D2030
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           Reporter:  niteria        |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:  sigof01m       |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 With [https://phabricator.haskell.org/D2030 D2030] I've changed the
 implementation of `Ord UnitId` to go from being `Unique` defined to being
 lexicographic. That somehow broke `sigof01m`.

 {{{
 <ezyang> I think I know what the problem is (ghc --make isn't specifying a
 dependency from B to A)
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12189>
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