[GHC] #11549: Add -fshow-runtime-rep

[GHC]

#11549: Add -fshow-runtime-rep
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        Reporter:  goldfire          |                Owner:  goldfire
            Type:  bug               |               Status:  patch
        Priority:  highest           |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D1961
       Wiki Page:                    |
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"371608f1cdaf20c49eb6c5ec165b9eb08b745a89/ghc" 371608f/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="371608f1cdaf20c49eb6c5ec165b9eb08b745a89"
 Default RuntimeRep variables unless -fprint-explicit-runtime-reps

 Summary:
 Addresses #11549 by defaulting `RuntimeRep` variables to `PtrRepLifted`
 and adding a new compiler flag `-fprint-explicit-runtime-reps` to
 disable this behavior.

 This is just a guess at the right way to go about this. If it's
 wrong-beyond-any-hope just say so.

 Test Plan: Working on a testcase

 Reviewers: goldfire, austin

 Subscribers: simonpj, thomie

 Differential Revision: https://phabricator.haskell.org/D1961

 GHC Trac Issues: #11549
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11549#comment:8>
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