[GHC] #15173: Tests are failing with segfaults under CircleCI

[GHC]

#15173: Tests are failing with segfaults under CircleCI
-------------------------------------+-------------------------------------
        Reporter:  bgamari           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.2.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D4721
       Wiki Page:                    |
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Comment (by Simon Marlow <marlowsd@…>):

 In [changeset:"d424d4a46a729f8530e9273282d22b6b8f34daaa/ghc"
 d424d4a4/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="d424d4a46a729f8530e9273282d22b6b8f34daaa"
 Fix a bug in SRT generation

 Summary:
 I had good intentions, but they were not being followed. In particular,
 this comment:

 ```
 ---  - we never resolve a reference to a CAF to the contents of its SRT,
 since
 ---    the point of SRTs is to keep CAFs alive.
 ```

 was not true, because we updated the srtMap after generating the SRT
 for a CAF. Therefore it was possible for another CAF to refer to an
 earlier CAF, and the reference to the earlier CAF would be shortcutted
 to refer to its SRT instead of pointing to the CAF itself.

 The fix is just to not update the srtMap when generating the SRT for a
 CAF, but I also refactored the code and comments around this to be a bit
 better organised.

 Test Plan: Harbourmaster

 Reviewers: bgamari, michalt, simonpj, erikd

 Subscribers: rwbarton, thomie, carter

 GHC Trac Issues: #15173, #15168

 Differential Revision: https://phabricator.haskell.org/D4721
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15173#comment:7>
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