[GHC] #11064: Call Arity has the trivial application case wrong

[GHC]

#11064: Call Arity has the trivial application case wrong
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        Reporter:  nomeata           |                Owner:  nomeata
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.2
      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 Joachim Breitner <mail@…>):

 In [changeset:"a58eeb7febd67c93dab82de7049ef1dcdecd34e9/ghc" a58eeb7/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="a58eeb7febd67c93dab82de7049ef1dcdecd34e9"
 Call Arity: In "e x", the result of "x" is not shared

 in contrast to "e (f x)", where CorePrep will turn it into "let y = f x
 in e x". So in
   let f = ...
   in e (f x)
 we know that f is called at most once, but in
   let f = ...
   in e f
 we do not know that.

 Previously Call Arity would assume that in "e x", "x" is evaluated at
 most once. This rarely would make a difference (the argument "x" is
 analized with an incoming arity of 0, so no eta-expansion would be done
 anyways), but of course this should still be fixed.

 This fixes #11064.

 Note the corresponding code dmdTransformThunkDmd in DmdAnal.
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11064#comment:1>
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