[GHC] #13458: Panic with unsafeCoerce and -dcore-lint

[GHC]

#13458: Panic with unsafeCoerce and -dcore-lint
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        Reporter:  dfeuer            |                Owner:  goldfire
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler (Type    |              Version:  8.1
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by rwbarton):

 If you change the type signature to `unsafeCoerce' :: Int# -> Int#` then
 the generated core is
 {{{
 unsafeCoerce'
   = (id @ Any)
     `cast` (UnsafeCo representational Any Int#
             -> UnsafeCo representational Any Int#
             :: ((Any -> Any) :: *) ~R# ((Int# -> Int#) :: *))
 }}}
 Optimizing the coercion like this seems dubious when the new coercions are
 ill-kinded.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13458#comment:7>
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