[GHC] #7392: "the impossible happened" when compiling Types.Substitutions

[GHC]

#7392: "the impossible happened" when compiling Types.Substitutions
---------------------------------+------------------------------------------
    Reporter:  martindemello     |       Owner:                    
        Type:  bug               |      Status:  new               
    Priority:  normal            |   Milestone:                    
   Component:  Compiler          |     Version:  7.6.1             
    Keywords:                    |          Os:  Linux             
Architecture:  Unknown/Multiple  |     Failure:  Compile-time crash
  Difficulty:  Unknown           |    Testcase:                    
   Blockedby:                    |    Blocking:                    
     Related:                    |  
---------------------------------+------------------------------------------
Changes (by simonpj):

  * difficulty:  => Unknown


Old description:

> Ran into this when trying to compile elm from git:
>
> $ cabal install
> Resolving dependencies...
> Configuring Elm-0.5.0.1...
> Building Elm-0.5.0.1...
> Preprocessing library Elm-0.5.0.1...
> [ 3 of 26] Compiling Types.Substitutions ( src/Types/Substitutions.hs,
> dist/build/Types/Substitutions.o )
> ghc: panic! (the 'impossible' happened)
>   (GHC version 7.6.1 for i386-unknown-linux):
>         compiler/codeGen/CgCase.lhs:572:15-61: Irrefutable pattern failed
> for pattern ((CoreSyn.DEFAULT,
>                                         deflt_absC) : others)
>

> Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
>
> Failed to install Elm-0.5.0.1

New description:

 Ran into this when trying to compile elm from git:
 {{{
 $ cabal install
 Resolving dependencies...
 Configuring Elm-0.5.0.1...
 Building Elm-0.5.0.1...
 Preprocessing library Elm-0.5.0.1...
 [ 3 of 26] Compiling Types.Substitutions ( src/Types/Substitutions.hs,
 dist/build/Types/Substitutions.o )
 ghc: panic! (the 'impossible' happened)
   (GHC version 7.6.1 for i386-unknown-linux):
         compiler/codeGen/CgCase.lhs:572:15-61: Irrefutable pattern failed
 for pattern ((CoreSyn.DEFAULT,
                                         deflt_absC) : others)
 }}}
 Failed to install Elm-0.5.0.1

--

Comment:

 Can you give explicit instructions to reproduce?  Hackage only has Elm
 0.3.6.2, and I don't know if you think that exposes the bug.

 I had a look at download from the github repo, but it was going to install
 two dozen packages with muttering about breaking some alread-installed
 ones, so I lost heart.

 Could you try with `-dcore-lint`.  If that fails, send the output.  If
 not, can you use `-ddump-simpl -ddump-stg` and send that?

 Simon

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7392#comment:1>
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