[GHC] #15186: ghc 8.4.2 panic in profiling build

[GHC]

#15186: ghc 8.4.2 panic in profiling build
-------------------------------------+-------------------------------------
        Reporter:  kquick            |                Owner:  bgamari
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Profiling         |              Version:  8.4.2
      Resolution:                    |             Keywords:
Operating System:  Linux             |         Architecture:  x86_64
 Type of failure:  Compile-time      |  (amd64)
  crash or panic                     |            Test Case:  T15186
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D4755,
       Wiki Page:                    |  Phab:D4757
-------------------------------------+-------------------------------------

Comment (by Ben Gamari <ben@…>):

 In [changeset:"f0c1eb8b5640b0ec86b9fabb465ea5b841808d56/ghc" f0c1eb8/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="f0c1eb8b5640b0ec86b9fabb465ea5b841808d56"
 Conservatively estimate levity in worker/wrapper

 The worker/wrapper transform needs to determine the levity of the result
 to
 determine whether it needs to introduce a lambda to preserve laziness of
 the
 result. For this is previously used isUnliftedType. However, this may fail
 in
 the presence of levity polymorphism.

 We now instead use isLiftedType_maybe, assuming that a lambda is needed if
 the
 levity of the result cannot be determined.

 Fixes #15186.

 Test Plan: make test=T15186

 Reviewers: simonpj, goldfire, tdammers

 Reviewed By: simonpj

 Subscribers: rwbarton, thomie, carter

 GHC Trac Issues: #15186

 Differential Revision: https://phabricator.haskell.org/D4755
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15186#comment:10>
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