[GHC] #9969: panic in T7562

[GHC]

#9969: panic in T7562
-------------------------------------+-------------------------------------
              Reporter:  nomeata     |             Owner:  simonpj
                  Type:  bug         |            Status:  new
              Priority:  normal      |         Milestone:
             Component:  Compiler    |           Version:  7.8.4
              Keywords:              |  Operating System:  Unknown/Multiple
          Architecture:              |   Type of failure:  Compile-time
  Unknown/Multiple                   |  crash
             Test Case:  T7562       |        Blocked By:
              Blocking:              |   Related Tickets:  #7562
Differential Revisions:              |
-------------------------------------+-------------------------------------
 Various people observe this test failure:

 {{{
 =====> T7562(normal) 869 of 4389 [0, 0, 0]
 cd ./typecheck/should_compile && '/home/jojo/build/haskell/ghc-
 validate/inplace/bin/ghc-stage2' -fforce-recomp -dcore-lint -dcmm-lint
 -dno-debug-output -no-user-package-db -rtsopts -fno-warn-tabs -fno-ghci-
 history -c T7562.hs   -fno-warn-incomplete-patterns >T7562.comp.stderr
 2>&1
 Compile failed (status 256) errors were:

 T7562.hs:3:14: Warning:
     UNPACK pragma lacks '!' on the first argument of ‘Pair2’
     In the definition of data constructor ‘Pair2’
     In the data declaration for ‘Pair2’
 ghc-stage2: panic! (the 'impossible' happened)
   (GHC version 7.11.20150108 for x86_64-unknown-linux):
         toIfaceBang

 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
 }}}

 According to my logs, this was caused by
 changeset:9564bb8c84cbc0397a414e946cc8c28801f0fbe7/ghc

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9969>
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