[GHC] #3983: -O2 makes exception disappear

[GHC]

#3983: -O2 makes exception disappear
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    Reporter:  benjamin_scarlet        |        Owner:              
        Type:  bug                     |       Status:  new         
    Priority:  normal                  |    Milestone:              
   Component:  Compiler                |      Version:  6.12.1      
    Keywords:  exception optimization  |   Difficulty:              
          Os:  Unknown/Multiple        |     Testcase:              
Architecture:  x86_64 (amd64)          |      Failure:  None/Unknown
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Comment(by simonpj):

 I suspect this is related to #3959, which I'm working on.

 Simon

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3983#comment:4>
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