[GHC] #11668: SPEC has a runtime cost

[GHC]

#11668: SPEC has a runtime cost
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           Reporter:  bgamari        |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  7.10.3
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Runtime
  Unknown/Multiple                   |  performance bug
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 As far as I know, `SPEC` is merely intended to help the compiler identify
 calls for which constructor specialization may be help. Yet it's not
 erased! In fact, it has a runtime representation which we need to
 construct and pass around to so-marked calls. This likely isn't killing
 the performance of anyone's programs but surely we can do better than
 this.

 Really, the whole scheme of marking functions with `SPEC` (which as far as
 I know isn't even properly documented) seems quite odd. What is stopping
 us from simply attaching pragmas to equations?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11668>
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