[GHC] #14170: 8.2.1 regression: GHC fails to simplify `natVal`

[GHC]

#14170: 8.2.1 regression: GHC fails to simplify `natVal`
-------------------------------------+-------------------------------------
        Reporter:  vagarenko         |                Owner:  Bodigrim
            Type:  bug               |               Status:  patch
        Priority:  high              |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D4212
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by Ben Gamari <ben@…>):

 In [changeset:"fe770c211631e7b4c9b0b1e88ef9b6046c6585ef/ghc"
 fe770c21/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="fe770c211631e7b4c9b0b1e88ef9b6046c6585ef"
 Built-in Natural literals in Core

 Add support for built-in Natural literals in Core.

 - Replace MachInt,MachWord, LitInteger, etc. with a single LitNumber
   constructor with a LitNumType field
 - Support built-in Natural literals
 - Add desugar warning for negative literals
 - Move Maybe(..) from GHC.Base to GHC.Maybe for module dependency
   reasons

 This patch introduces only a few rules for Natural literals (compared
 to Integer's rules). Factorization of the built-in rules for numeric
 literals will be done in another patch as this one is already big to
 review.

 Test Plan:
   validate
   test build with integer-simple

 Reviewers: hvr, bgamari, goldfire, Bodigrim, simonmar

 Reviewed By: bgamari

 Subscribers: phadej, simonpj, RyanGlScott, carter, hsyl20, rwbarton,
 thomie

 GHC Trac Issues: #14170, #14465

 Differential Revision: https://phabricator.haskell.org/D4212
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14170#comment:19>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler