[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:                    |  Phab:D5201
-------------------------------------+-------------------------------------

Comment (by osa1):

 Interestingly, if I revert the Cmm bits and always introduce a case on
 dataToTag# args in CorePrep I can validate. Patch is
 [https://github.com/osa1/ghc/commit/1b9bd4769c2c70b23ef8739aba116f9d18628b00
 here]. I'll compare the differences in generated code in this branch and
 Phab:D5201.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15696#comment:56>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler