[GHC] #14777: panic when using a function defined in terms of `error`

[GHC]

#14777: panic when using a function defined in terms of `error`
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        Reporter:  zilinc            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.2
      Resolution:                    |             Keywords:
Operating System:  Linux             |         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 tdammers):

 Further, the following both get rid of the panic:

 - Moving `__impossible` into `Desugar.hs`
 - Declaring `{-#INLINE __impossible #-}`

 Both would lead to GHC inlining `__impossible`.

 This would explain how it is possible for seemingly benign changes to
 influence the appearance of the panic - changing small things would change
 the inlining heuristics, and bug may or may not be hit depending on the
 intermediate code (Core / STG) being generated.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14777#comment:20>
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