[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:  8.2.2
       Component:  Compiler          |              Version:  8.2.1-rc2
      Resolution:                    |             Keywords:  Specialise
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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Comment (by mpickering):

 Replying to [comment:4 jberryman]:
 > Thanks so much for looking into this. I maybe wasn't clear in the body
 that the reason I filed the ticket was I assumed that GHC would try to
 choose the best specialization from those in scope (since my intuition was
 specialize pragmas behave sort of like type classes in the way they leak
 via `import` statements) and from whatever specializations it might
 perform in context.
 >
 > But maybe this is expected behavior, and a manual specialization will
 always take precedence?

 The specialiser doesn't choose which specialisation to apply, it merely
 looks for specialisation opportunities and then creates a new definition
 along with a RULE which does the replacement.

 If you have conflicting specialisations then the choice about which one
 applies is left up to he rule selection mechanism which I am not as
 familiar with.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13873#comment:7>
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