[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:  closed
        Priority:  highest           |            Milestone:  8.6.2
       Component:  Compiler          |              Version:  8.6.1
      Resolution:  fixed             |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Incorrect result  |            Test Case:
  at runtime                         |  codeGen/should_run/T15696_1,
                                     |  T15696_2, T15696_3
      Blocked By:                    |             Blocking:
 Related Tickets:  #14677, #15155    |  Differential Rev(s):  Phab:D5196,
       Wiki Page:                    |  Phab:D5201, Phab:D5226
-------------------------------------+-------------------------------------

Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:"d77501cd5b9060e38acd50e11e0c5aae89d75b65/ghc"
 d77501cd/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="d77501cd5b9060e38acd50e11e0c5aae89d75b65"
 Improvements to demand analysis

 This patch collects a few improvements triggered by Trac #15696,
 and fixing Trac #16029

 * Stop making toCleanDmd behave specially for unlifted types.
   This special case was the cause of stupid behaviour in Trac
   #16029.  And to my joy I discovered the let/app invariant
   rendered it unnecessary.  (Maybe the special case pre-dated
   the let/app invariant.)

   Result: less special-case handling in the compiler, and
   better perf for the compiled code.

 * In WwLib.mkWWstr_one, treat seqDmd like U(AAA).  It was not
   being so treated before, which again led to stupid code.

 * Update and improve Notes

 There are .stderr test wibbles because we get slightly different
 strictness signatures for an argumment of unlifted type:
     <L,U> rather than <S,U>        for Int#
     <S,U> rather than <S(S),U(U)>  for Int
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15696#comment:92>
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