[GHC] #15569: Constant folding optimises 1 into 3

[GHC]

#15569: Constant folding optimises 1 into 3
-------------------------------------+-------------------------------------
        Reporter:  snowleopard       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.6.1-beta1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #9136             |  Differential Rev(s):  Phab:D5109
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by flip101):

 Since the phrases "SMT solver" and "compiler-checked way" came up.
 Wouldn't it be good for GHC to move into the direction that CakeML has
 chosen and then (at least for some parts) verify the compiler with proof?
 It could be a good addition to CI and also for local builds to run after
 the test suite. Excuse me if the question is too broad of scope, but the
 ticket seems a good example for it.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15569#comment:19>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler