[GHC] #11555: catch under unsafePerformIO breaks on -O1 (was: catch _|_ breaks at -O1)

[GHC]

#11555: catch under unsafePerformIO breaks on -O1
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        Reporter:  slyfox            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  8.0.1-rc2
      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 rwbarton):

 It is fallout from #11222, but it's not a bug. There's no guarantee that
 the ''pure value'' passed to `catch` will be evaluated at any particular
 time. `catch` catches exceptions that arise from the ''execution'' of its
 IO argument action.

 Correct versions of this program would include changing `abort` to `abort
 :: Stack -> IO a; abort x = throwIO $ ...` or changing `C.catch (abort
 "fail")` to `C.catch (evaluate (abort "fail"))`. But I'm not sure that
 there is any way currently to, given an (unevaluated) IO action, evaulate
 it and execute it, catching exceptions raised by either step. A possible
 attempt would be `catch (do { a <- evaluate action; a })`, but would GHC
 see through this?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11555#comment:4>
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