[GHC] #9390: Inlining prevents evaluation of ignored parts of unboxed tuples

[GHC]

#9390: Inlining prevents evaluation of ignored parts of unboxed tuples
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              Reporter:  snoyberg    |            Owner:
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:  7.8.4
             Component:  Compiler    |          Version:  7.8.3
            Resolution:              |         Keywords:
      Operating System:  Linux       |     Architecture:  x86_64 (amd64)
       Type of failure:  Incorrect   |       Difficulty:  Unknown
  result at runtime                  |       Blocked By:
             Test Case:              |  Related Tickets:
              Blocking:              |
Differential Revisions:              |
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Comment (by snoyberg):

 I'm confused about the end of your comment, in particular:

 > `unsafeInterleaveIO` lets you ensure that it occurs after the effects
 thus far in the do-block have occurred

 But your example then implies that the `x` thunk will reliably be
 evaluated before `V.freeze vm >>= print`, which does not seem to follow
 from your comment. Can you clarify?

 I'd be happy to take a crack at writing up some documentation. For a
 while, I've wanted to have a clear set of rules for when
 `unsafePerformIO`, `unsafeDupablePerformIO`, and `inlinePerformIO` (aka
 unsafeAccursedPerformIO) are safe to use. Once I get some more clarity
 from our discussion here, I'd like to take a pass at such a Wiki page, and
 would greatly appreciate your review.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9390#comment:11>
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