[GHC] #3313: Uncertain bug report (panic!)

[GHC]

#3313: Uncertain bug report (panic!)
----------------------------------+-----------------------------------------
    Reporter:  semanticprecision  |        Owner:                  
        Type:  bug                |       Status:  new             
    Priority:  normal             |    Milestone:  6.12.1          
   Component:  Compiler           |      Version:  6.10.2          
    Severity:  normal             |   Resolution:                  
    Keywords:                     |   Difficulty:  Unknown         
    Testcase:                     |           Os:  Unknown/Multiple
Architecture:  x86                |  
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Changes (by igloo):

  * difficulty:  => Unknown
  * milestone:  => 6.12.1

Comment:

 Thanks for the report. It breaks the HEAD too.

 Here's a minimal testcase:
 {{{
 module Foo where

 import Data.Word

 bytesToGrayscaleImage :: Word -> Maybe ()
 bytesToGrayscaleImage 5 = Just ()
 bytesToGrayscaleImage 6 = Just ()
 bytesToGrayscaleImage _ = Nothing
 }}}

 {{{
 $ ghci Foo.hs
 GHCi, version 6.11.20090710: http://www.haskell.org/ghc/  :? for help
 Loading package ghc-prim ... linking ... done.
 Loading package integer-gmp-0.1.0.0 ... linking ... done.
 Loading package integer ... linking ... done.
 Loading package base ... linking ... done.
 Loading package ffi-1.0 ... linking ... done.
 [1 of 1] Compiling Foo              ( Foo.hs, interpreted )
 ghc-stage2: panic! (the 'impossible' happened)
   (GHC version 6.11.20090710 for x86_64-unknown-linux):
         schemeE(AnnCase).my_discr __word 5

 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

 >
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3313#comment:3>
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