[GHC] #11555: catch _|_ breaks at -O1

[GHC]

#11555: catch _|_ breaks at -O1
-------------------------------------+-------------------------------------
        Reporter:  slyfox            |                Owner:
            Type:  bug               |               Status:  patch
        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):  Phab:D1973
       Wiki Page:                    |
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"30ee9102db2f16894912e19b9d16156824611bbb/ghc"
 30ee9102/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="30ee9102db2f16894912e19b9d16156824611bbb"
 Make `catch` lazy in the action

 Previously
 ```lang=haskell
 catch (error "uh oh") (\(_ :: SomeException) -> print "it failed")
 ```
 would unexpectedly fail with "uh oh" instead of the handler being run
 due to the strictness of `catch` in its first argument. See #11555 for
 details.

 Test Plan: Validate

 Reviewers: austin, hvr, simonpj

 Reviewed By: simonpj

 Subscribers: simonpj, thomie

 Differential Revision: https://phabricator.haskell.org/D1973

 GHC Trac Issues: #11555
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11555#comment:20>
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