[GHC] #15300: Unboxed Sums Crash

[GHC]

#15300: Unboxed Sums Crash
-------------------------------------+-------------------------------------
        Reporter:  andrewthad        |                Owner:  osa1
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.5
      Resolution:                    |             Keywords:  UnboxedSums
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 osa1):

 > What about doing StgCse after unarising?

 I think this is a good idea, but it reveals another bug in StgCse.
 Basically StgCse reverts unarise by using case binders when scrutinee is a
 unboxed tuple, e.g.

 {{{
 case <unboxed_tuple> of bndr { <alts> }
 }}}

 Unarise eliminates all occurances of `bndr` in alts, but StgCse does the
 opposite, e.g. replaces `(#,#) foo bar` with `bndr`. This is caught by
 StgLint which is good.

 Patch incoming.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15300#comment:18>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler