[GHC] #13338: New versions of time and Cabal are causing a Core Lint error on Windows

[GHC]

#13338: New versions of time and Cabal are causing a Core Lint error on Windows
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        Reporter:  rwbarton          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by rwbarton):

 I was trying to figure out how to avoid doing the floating out when the
 result would violate the let/app invariant, or possibly how to have
 `exprOkForSpeculation` look through the binding created by floating out,
 but hang on: if the expression was originally okay for speculation, then
 can't we just float it out as an unboxed value? That would be more
 efficient too.

 If we only ever do the boxing transformation to things that were not
 originally okay for speculation, then I think we can't break the let/app
 invariant.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13338#comment:4>
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