[GHC] #13423: Exception to I/O hack in demand analyzer too broad

[GHC]

#13423: Exception to I/O hack in demand analyzer too broad
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        Reporter:  dfeuer            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Other             |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by dfeuer):

 Replying to [comment:1 rwbarton]:
 > Is this really wrong in this case though? In a single-threaded context
 there is no observable difference between writing an `IORef` and then
 diverging, and diverging immediately; and in a multi-threaded context the
 ordering of `writeIORef` with respect to anything else is not guaranteed.

 That's not true. Someone could write

 {{{#!hs
 fish n ref next `catch` \(e :: E) -> readIORef ref >>= ...
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13423#comment:2>
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