[GHC] #12364: Demand analysis for sum types

[GHC]

#12364: Demand analysis for sum types
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        Reporter:  nomeata           |                Owner:
            Type:  task              |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by nomeata):

 I was about to say “But this flag is not checked anywhere in the demand
 analyzer” (because it is) and did some git archeology, and I found commit
 changeset:3e7e5ba8333d318c38b4cfc538a97fdca0aed5b1/ghc which replaced the
 use of `isRecursiveTyCon` with one using `RecTcChecker`.

 From my rough reading is that we look one level deep ''on every
 iteration'', so we still get deeply nested result. I was able to produce
 an unsound result this way, but it belongs to #12368, so I added it there
 as a comment.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12364#comment:12>
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