[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
-------------------------------------+-------------------------------------

Comment (by Ömer Sinan Ağacan <omeragacan@…>):

 In [changeset:"ac977688523e5d77eb6f041f043552410b0c21da/ghc"
 ac977688/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="ac977688523e5d77eb6f041f043552410b0c21da"
 Fix dataToTag# argument evaluation

 See #15696 for more details. We now always enter dataToTag# argument (done
 in
 generated Cmm, in StgCmmExpr). Any high-level optimisations on dataToTag#
 applications are done by the simplifier. Looking at tag bits (instead of
 reading the info table) for small types is left to another diff.

 Incorrect test T14626 is removed. We no longer do this optimisation (see
 comment:44, comment:45, comment:60).

 Comments and notes about special cases around dataToTag# are removed. We
 no
 longer have any special cases around it in Core.

 Other changes related to evaluating primops (seq# and dataToTag#) will be
 pursued in follow-up diffs.

 Test Plan: Validates with three regression tests

 Reviewers: simonpj, simonmar, hvr, bgamari, dfeuer

 Reviewed By: simonmar

 Subscribers: rwbarton, carter

 GHC Trac Issues: #15696

 Differential Revision: https://phabricator.haskell.org/D5201
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15696#comment:66>
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