[GHC] #12656: ghc floats out constant despite -fno-cse

[GHC]

#12656: ghc floats out constant despite -fno-cse
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        Reporter:  nh2               |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by nh2):

 Note that `{-# OPTIONS_GHC -fno-full-laziness #-}` also doesn't help here;
 how could I prevent the floating-out so that the use of `unsafeThaw` is
 safe?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12656#comment:3>
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