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

[GHC]

#11064: Call Arity has the trivial application case wrong
-------------------------------------+-------------------------------------
           Reporter:  nomeata        |             Owner:  nomeata
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  7.10.2
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 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.

 I just validated a patch and will push shortly.

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