[GHC] #10251: Bad rule generated in pathological cases

[GHC]

#10251: Bad rule generated in pathological cases
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              Reporter:  simonpj     |             Owner:
                  Type:  bug         |            Status:  new
              Priority:  normal      |         Milestone:
             Component:  Compiler    |           Version:  7.10.1
              Keywords:              |  Operating System:  Unknown/Multiple
          Architecture:              |   Type of failure:  None/Unknown
  Unknown/Multiple                   |        Blocked By:
             Test Case:              |   Related Tickets:
              Blocking:              |
Differential Revisions:              |
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 George reports: I am also seeing this on ghc 7.10.1, not sure if this is
 another instance of this bug (#9160):
 {{{
 cabal install bitmap
 [ 3 of 10] Compiling Data.Bitmap.IO ( Data/Bitmap/IO.hs,
 dist/build/Data/Bitmap/IO.o )

 Data/Bitmap/IO.hs:1248:1: Warning:

     SPECIALISE pragma for non-overloaded function ‘myPlusPtr’

 Data/Bitmap/IO.hs:1249:1: Warning:

     SPECIALISE pragma for non-overloaded function ‘myPlusPtr’

 ghc: panic! (the 'impossible' happened)

     (GHC version 7.10.1 for x86_64-apple-darwin):

         Template variable unbound in rewrite rule

     $fPixelComponentFloat3_X2Rc
     [$fPixelComponentFloat3_X2Rc]
     [$fPixelComponentFloat3_X2Rc]
     []
     []
 }}}
 But it's ''not'' #9160 at all.  So I'm making a new ticket.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10251>
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