[GHC] #15821: Implement constant folding for Naturals

[GHC]

#15821: Implement 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
           Keywords:  newcomer       |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 #14465 has already gone a long way in improving the runtime performance of
 `Natural` numbers. However, we still lack constant folding for these
 numbers so there is money left on the table.

 To fix this you will want to implement rules similar to those for
 `Integer` in the `PrelRules` module. Additionally, you will need to
 comment back in the `CONSTANT_FOLDED` pragmas in `GHC.Natural` (see
 Phab:D5267)

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