[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
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        Reporter:  mrkkrp            |                Owner:  (none)
            Type:  bug               |               Status:  new
        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):
       Wiki Page:                    |
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Comment (by RyanGlScott):

 The fact that using `dataToTag#` directly produces incorrect results is
 perhaps not terribly surprising, giving that it
 [http://git.haskell.org/ghc.git/blob/21efbc7599e39ec93b8b13b7d7b84811226e6f6f:/compiler/prelude/primops.txt.pp#l2966
 must always be applied to an evalauted argument] (see `Note
 [dataToTag#]`). The fact that the version using `getTag` breaks is more
 worrisome, since `getTag` actually forces its argument (with a bang
 pattern).

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15696#comment:16>
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