[GHC] #13873: Adding a SPECIALIZE at a callsite in Main.hs is causing a regression

[GHC]

#13873: Adding a SPECIALIZE at a callsite in Main.hs is causing a regression
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           Reporter:  jberryman      |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.2.1-rc2
           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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 Github user jmoy documents an issue with lack of specialization happening
 for INLINABLE functions in GHC 8.0 here: https://github.com/jmoy/testing-
 specialize . Testing on 8.2.1 it seems that specialization happened
 (although I didn't verify this in the core) as the result was 10x faster.
 But the odd thing to me was uncommenting the `SPECIALIZE` pragma at the
 callsite actually resulted in a significant regression:
 https://github.com/jmoy/testing-specialize/issues/1#issuecomment-310868360

 Maybe GHC is choosing the worse manual partial specialization for some
 reason. I'm sorry I can't produce a better ticket for this at the moment.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13873>
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