[GHC] #4012: Compilation results are not deterministic

[GHC]

#4012: Compilation results are not deterministic
-------------------------------------+-------------------------------------
        Reporter:  kili              |                Owner:  niteria
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  6.12.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Other             |            Test Case:
      Blocked By:  11362             |             Blocking:
 Related Tickets:  #10424            |  Differential Rev(s):  Phab:D910,
                                     |  Phab:D1073, Phab:D1133, Phab:D1192,
                                     |  Phab:D1268, Phab:D1360, Phab:D1373,
       Wiki Page:                    |  Phab:D1396, Phab:D1457, Phab:D1468,
  DeterministicBuilds                |  Phab:D1487, Phab:D1504, Phab:D1508
-------------------------------------+-------------------------------------

Comment (by Bartosz Nitka <niteria@…>):

 In [changeset:"348f2dbb835b1208f601bb1e8daa1d1d54507eda/ghc"
 348f2dbb/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="348f2dbb835b1208f601bb1e8daa1d1d54507eda"
 Make the Ord Module independent of Unique order (2nd try)

 The `Ord Module` instance currently uses `Unique`s for comparison.
 We don't want to use the `Unique` order because it can introduce
 nondeterminism.
 This switches `Ord ModuleName` and `Ord UnitId` to use lexicographic
 ordering making `Ord Module` deterministic transitively.

 I've run `nofib` and it doesn't make a measurable difference.

 See also Note [ModuleEnv determinism and performance].

 This fixes #12191 - the regression, that the previous version of this
 patch had.

 Test Plan:
 ./validate
 run nofib: P112

 Reviewers: simonmar, bgamari, austin

 Subscribers: thomie

 Differential Revision: https://phabricator.haskell.org/D2354

 GHC Trac Issues: #4012, #12191
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4012#comment:211>
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