[GHC] #9440: Buggy binder swap in occurrence analysis

[GHC]

#9440: Buggy binder swap in occurrence analysis
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              Reporter:  afarmer     |            Owner:
                  Type:  bug         |           Status:  patch
              Priority:  normal      |        Milestone:
             Component:  Compiler    |          Version:  7.8.3
            Resolution:              |         Keywords:
      Operating System:              |     Architecture:  Unknown/Multiple
  Unknown/Multiple                   |       Difficulty:  Unknown
       Type of failure:              |       Blocked By:
  None/Unknown                       |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:  Phab:D156   |
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Comment (by Austin Seipp <austin@…>):

 In [changeset:"5d5655e9911dba10088b66421e98165c6cb8176e/ghc"]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="5d5655e9911dba10088b66421e98165c6cb8176e"
 Fix three problems with occurrence analysis on case alternatives.

 Summary:
   1. Respect condition (a) in Note [Binder swap]
   2. Respect condition (b) in Note [Binder swap]
   3. Return usage of any coercion variables in binder swap

 Fixes T9440

 Test Plan: See #9440

 Reviewers: simonpj, austin

 Reviewed By: simonpj, austin

 Subscribers: simonpj, simonmar, relrod, ezyang, carter

 Differential Revision: https://phabricator.haskell.org/D156

 GHC Trac Issues: #9440
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9440#comment:7>
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