[GHC] #11396: deriving Ix with custom ifThenElse causes "Bad call to tagToEnum#"

[GHC]

#11396: deriving Ix with custom ifThenElse causes "Bad call to tagToEnum#"
-------------------------------------+-------------------------------------
        Reporter:  Lemming           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  8.0.1-rc1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by bgamari):

 This is a regression relative to 7.10.3.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11396#comment:2>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler