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

[GHC]

#11555: catch _|_ breaks at -O1
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        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 Simon Peyton Jones <simonpj@…>):

 In [changeset:"4c3a0a4a7b999251cbbee00befbfe32b86e556e2/ghc"
 4c3a0a4a/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="4c3a0a4a7b999251cbbee00befbfe32b86e556e2"
 Fix the implementation of lazyId

 'lazy' was doing part of its job, but not all!  In particular,
 an application
   f (lazy e)
 where f is strict, was still being compiled using call-by-value in
 CorePrep.  This defeated the purpose of defining catch as
    catch a b = catch# (lazy a) b
 See Trac #11555, and Neil Mitchell's test case in comment:14

 This patch makes 'lazy' behave properly. I updated Note [lazyId magic]
 in MkId, but all the action is in CorePrep.

 I can't say I really like this, but it does the job.
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11555#comment:17>
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