[GHC] #13052: unsafePerformIO duped on multithread if within the same IO thunk

[GHC]

#13052: unsafePerformIO duped on multithread if within the same IO thunk
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        Reporter:  gelisam           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.2-rc2
      Resolution:                    |             Keywords:
Operating System:  MacOS X           |         Architecture:  x86_64
 Type of failure:  Incorrect result  |  (amd64)
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by akio):

 * cc: akio (added)


Comment:

 The parallel GC may duplicate constructors and other immutable closures,
 but isn't it supposed to be careful not to duplicate thunks?

 Also I can reproduce this behavior (on Linux) with and without `+RTS -qg`,
 so the GC behavior doesn't seem to explain this completely.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13052#comment:2>
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