[GHC] #13424: readMutVar# is marked can_fail

[GHC]

#13424: readMutVar# is marked can_fail
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        Reporter:  dfeuer            |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Other             |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D3340
       Wiki Page:                    |
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Comment (by David Feuer <David.Feuer@…>):

 In [changeset:"2ac13c132d039438382baef6ce52c79b29725145/ghc" 2ac13c1/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="2ac13c132d039438382baef6ce52c79b29725145"
 Let GHC know MutVar# ops can't fail

 The only way `readMutVar#` or `writeMutVar#` can fail is if its
 argument is not a valid pointer. I believe we ensure this by
 construction, and never test for pointer validity. So I think it
 should be safe to say that it can't fail.

 Fixes #13424

 Reviewers: austin, bgamari

 Reviewed By: bgamari

 Subscribers: rwbarton, thomie

 Differential Revision: https://phabricator.haskell.org/D3340
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13424#comment:2>
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