[GHC] #15696: Derived Ord instance for enumerations with more than 8 elements seems to be incorrect

[GHC]

#15696: Derived Ord instance for enumerations with more than 8 elements seems to be
incorrect
-------------------------------------+-------------------------------------
        Reporter:  mrkkrp            |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  highest           |            Milestone:  8.6.2
       Component:  Compiler          |              Version:  8.6.1
      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):  Phab:D5196
       Wiki Page:                    |
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Changes (by osa1):

 * status:  new => patch
 * differential:   => Phab:D5196


Comment:

 Simon, please review. There are a few ways to fix this and I probably did
 the most conservative thing by always introducing a case around
 `dataToTag#`. Perhaps we want to change how we record evaluated-ness of
 CAFs in their Ids instead.

 We may also want to pay more attention to #14677 if we rely on strictness
 annotations of data constructor fields to decide on evaluatedness of
 values elsewhere.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15696#comment:21>
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