[GHC] #10906: `SPECIALIZE instance` could be better

[GHC]

#10906: `SPECIALIZE instance` could be better
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        Reporter:  goldfire          |                   Owner:
            Type:  feature request   |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.10.2
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Comment (by simonpj):

 I'm out of bandwidth at the moment, but

 * There is no reason not to allow `{-# SPECIALISE instance ... #-}` in an
 importing module.  As you say, to make sure that the methods got
 specialised (which is the whole point) you'd have to decorate each of them
 with `{-# INLINEABLE #-}`, but that's fair enough.

 * I don't understand why "one specialisation doesn't use another".

 * I don't understand the type-family restriction.  Maybe it's accidental.

 Happy to advise.

 Simon

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10906#comment:2>
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