[GHC] #7499: Case-inspecting unboxed unit causes codegen crash

[GHC]

#7499: Case-inspecting unboxed unit causes codegen crash
-------------------------------+--------------------------------------------
Reporter:  rl                  |          Owner:                  
    Type:  bug                 |         Status:  new             
Priority:  normal              |      Component:  Compiler        
 Version:  7.6.1               |       Keywords:                  
      Os:  Unknown/Multiple    |   Architecture:  Unknown/Multiple
 Failure:  Compile-time crash  |      Blockedby:                  
Blocking:                      |        Related:                  
-------------------------------+--------------------------------------------
 Here is a minimal test case:

 {{{
 foo :: (() -> (# #)) -> Int
 foo f = case f () of (# #) -> 5
 }}}

 GHC crashes with:

 {{{
 ghc.exe: panic! (the 'impossible' happened)
   (GHC version 7.6.1 for i386-unknown-mingw32):
         compiler\codeGen\CgCase.lhs:572:15-61: Irrefutable pattern failed
 for pattern ((CoreSyn.DEFAULT,
                                         deflt_absC) : others)
 }}}

 Here is the actual function (simplified) that triggered the bug:

 {{{
 foo :: [a] -> Int
 foo xs = foldl' (flip seq) () xs `seq` 5
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7499>
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