[GHC] #16029: Inadequate absence analysis

[GHC]

#16029: Inadequate absence analysis
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        Reporter:  simonpj           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.6.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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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/16029#comment:2>
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