[GHC] #8668: SPECIALIZE silently fails to apply

[GHC]

#8668: SPECIALIZE silently fails to apply
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        Reporter:  crockeea          |            Owner:
            Type:  bug               |           Status:  new
        Priority:  normal            |        Milestone:
       Component:  Compiler          |          Version:  7.6.2
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  x86_64 (amd64)
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by crockeea):

 Replying to [comment:4 simonpj]:
 > Incidentally, if you want GHC to auto-specialise an '''imported'''
 function, to types that may not even be in scope in the defining module,
 you should mark that function as `INLINABLE`

 I have been playing around with this some more, and found something
 interesting. As I mentioned, despite the fact that I have everything
 marked `INLINABLE`, GHC was *not* auto-specializing `plusFastCyc`.
 However, if I partially apply the call to `plusFastCyc` in Main to
 `iterate (plusFastCyc y) ...` instead of `iterate (\x -> plusFastCyc y x)
 ...`, GHC *does* automatically specialize the call to `plusFastCyc`.
 However, the code is still slow because `(+)` is still not specialized. I
 might expect (+) to be specialized for two reasons

   1. It is called at the top level in Main.hs in the `foldl`.
   2. The docs say that *when* there is an explicit pragma, specialization
 is transitive. I could hope that auto-specialization is also transitive.
 Is this the case?

 Is the problem of GHC specializing the partially applied function but not
 the fully applied version related to ticket:8099?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8668#comment:19>
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