[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:  osa1
            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:  #14677, #15155    |  Differential Rev(s):  Phab:D5196,
       Wiki Page:                    |  Phab:D5201, Phab:D5226
-------------------------------------+-------------------------------------

Comment (by simonpj):

 > Revert change in app_ok general case, don't give case binders
 evaldUnfolding in simplAlts (first suggestion in comment:77)

 This is my preferred option; I don't like disabling binder swapping - it's
 there for a good reason!

 It would be illuminating to know (perhaps via `-ticky`) what code is
 improved by reverting the `app_ok` general case.   If we knew, we could
 add an example to the code so that we had a concrete reason for that
 `isEvaldUnfolding` case.  But it's only curiosity.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15696#comment:83>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler