[GHC] #11735: Optimize coercionKind

[GHC]

#11735: Optimize coercionKind
-------------------------------------+-------------------------------------
        Reporter:  goldfire          |                Owner:  (none)
            Type:  task              |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by simonpj):

 Fine. In undoing, could you also add the invariants for all Role
 annotations to the data type itself?

 * The comment on the constructor NthCo should state the invariant. Given
 (NthCo r n co) we require that lteRole r (nthRole (coercionRole co) n)) or
 something like that.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11735#comment:64>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler