[GHC] #13996: Non-cheap primop is duplicated

[GHC]

#13996: Non-cheap primop is duplicated
-------------------------------------+-------------------------------------
           Reporter:  simonpj        |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           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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 Conal Elliot [https://mail.haskell.org/pipermail/ghc-
 devs/2017-July/014407.html writes]: I have
 {{{
 exampleC :: Double -> Double -> Double
 exampleC = \ t -> let s = sin t in \ x -> x + s
 }}}
 But the `sin` ends up being pushed inside the lambda by the optimiser,
 like so:
 {{{
 exampleC = \ t x -> x + sin t
 }}}
 So if I do `map (exampleC v) xs` I end up computing `sin v` once for each
 element of `xs` rather than once.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13996>
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