[GHC] #11555: catch under unsafePerformIO breaks on -O1

[GHC]

#11555: catch under unsafePerformIO breaks on -O1
-------------------------------------+-------------------------------------
           Reporter:  slyfox         |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1-rc2
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Discovered on xmonad-0.12 test failure.
 Happens on today's -HEAD and ghc-8.0.1-rc1,-rc2

 Short example is (needs only base):
 {{{#!hs
 -- cat F.hs
 module F where

 import qualified Control.Exception as C
 import System.IO.Unsafe
 import qualified Data.List as L

 abort :: String -> a
 abort x = error $ "xmonad: StackSet: " ++ x

 prop_abort x = unsafePerformIO $ C.catch (abort "fail")
                                          (\(C.SomeException e) ->
                                            return $ "xmonad: StackSet:
 fail" `L.isPrefixOf` show e )
    where
      _ = x :: Int
 }}}

 Session 1 [ok]:
 {{{
 $ ghci F.hs

 GHCi, version 8.0.0.20160204: http://www.haskell.org/ghc/  :? for help
 [1 of 1] Compiling F                ( F.hs, interpreted )
 Ok, modules loaded: F.

 *F> prop_abort 1
 True
 }}}

 Session 2 [fails]:
 {{{
 $ ghci -O1 -fobject-code F.hs

 GHCi, version 8.0.0.20160204: http://www.haskell.org/ghc/  :? for help
 [1 of 1] Compiling F                ( F.hs, F.o )
 Ok, modules loaded: F.

 Prelude F> prop_abort 1
 *** Exception: xmonad: StackSet: fail
 CallStack (from HasCallStack):
   error, called at F.hs:9:11 in main:F
 }}}

 I would expect exception to be caught on both cases.
 Is it unreasonable expectation in light of unsafePerformIO?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11555>
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