[GHC] #14737: Improve performance of Simplify.simplCast

[GHC]

#14737: Improve performance of Simplify.simplCast
-------------------------------------+-------------------------------------
        Reporter:  tdammers          |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #11735 #14683     |  Differential Rev(s):  Phab:D4385
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by simonpj):

 Yes, use that defn of `isReflexiveCo`; and then delete
 `isReflexiveCo_maybe` because it is not otherwise called.

 However, that may still leave `simplCast` at the top... does it? If it was
 taking 78% of 20sec before, that's 16 sec.  So reducing that to near-zero
 (which it should be) would take use to 5s, not 12s.

 What happens if you leave out the call to `isReflexiveCo` altogether?
 It'll get done in the next round anyway, by `optCoercion`.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14737#comment:8>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler