[GHC] #15821: Implement more constant folding for Naturals

[GHC]

#15821: Implement more constant folding for Naturals
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        Reporter:  bgamari           |                Owner:  (none)
            Type:  task              |               Status:  new
        Priority:  normal            |            Milestone:  8.8.1
       Component:  Compiler          |              Version:  8.6.1
      Resolution:                    |             Keywords:  newcomer
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 bgamari):

 Additionally, working out why we fail to reduce the case in
 [T14465](https://phabricator.haskell.org/D5267#inline-41421) would be
 great.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15821#comment:2>
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