[GHC] #12944: ghc master (8.1.20161206) panics with assertion failure with devel2 flavor and -O

[GHC]

#12944: ghc master (8.1.20161206) panics with assertion failure with devel2 flavor
and -O
-------------------------------------+-------------------------------------
        Reporter:  pacak             |                Owner:
            Type:  bug               |               Status:  closed
        Priority:  highest           |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.1
  (CodeGen)                          |
      Resolution:  fixed             |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D2844
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by simonpj):

 Also relevant (the commit message should say #12944 not #12444):
 {{{
 revision="c48595eef2bca6d91ec0a649839f8066f269e6a4"
 Never apply worker/wrapper to DFuns

 While fixing Trac #12444 I found an occasion on which we applied
 worker/wrapper to a DFunId.  This is bad: it destroys the magic
 DFunUnfolding.

 This patch is a minor refactoring that stops this corner case
 happening, and tidies up the code a bit too.
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12944#comment:14>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler