[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
-------------------------------------+-------------------------------------
        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:                    |
-------------------------------------+-------------------------------------

Comment (by simonpj):

 I don't have bandwidth to reproduce right now, but I think Matthew is
 saying we have
 {{{
 f :: forall s. State# s -> blah
 f = /\s. \(x::State# s). ....(g @s d1 d2 d3)....
 }}}
 where `g` is an overloaded function, called three dictionary arguments.
 But note that `f` is not overloaded, and so will not be auto-specialised.
 Somehow, if we specialised `f`, we could specialise `g`.

 I don't quite see how this happens.  Can you fill in a bit more detail
 about what `g` is, and what dictionaries `d1`-`d3` are?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13873#comment:5>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler