[GHC] #12375: type synonym to unboxed tuple causes crash

[GHC]

#12375: type synonym to unboxed tuple causes crash
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        Reporter:  osa1              |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Ömer Sinan Ağacan <omeragacan@…>):

 In [changeset:"714bebff44076061d0a719c4eda2cfd213b7ac3d/ghc" 714bebf/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="714bebff44076061d0a719c4eda2cfd213b7ac3d"
 Implement unboxed sum primitive type

 Summary:
 This patch implements primitive unboxed sum types, as described in
 https://ghc.haskell.org/trac/ghc/wiki/UnpackedSumTypes.

 Main changes are:

 - Add new syntax for unboxed sums types, terms and patterns. Hidden
   behind `-XUnboxedSums`.

 - Add unlifted unboxed sum type constructors and data constructors,
   extend type and pattern checkers and desugarer.

 - Add new RuntimeRep for unboxed sums.

 - Extend unarise pass to translate unboxed sums to unboxed tuples right
   before code generation.

 - Add `StgRubbishArg` to `StgArg`, and a new type `CmmArg` for better
   code generation when sum values are involved.

 - Add user manual section for unboxed sums.

 Some other changes:

 - Generalize `UbxTupleRep` to `MultiRep` and `UbxTupAlt` to
   `MultiValAlt` to be able to use those with both sums and tuples.

 - Don't use `tyConPrimRep` in `isVoidTy`: `tyConPrimRep` is really
   wrong, given an `Any` `TyCon`, there's no way to tell what its kind
   is, but `kindPrimRep` and in turn `tyConPrimRep` returns `PtrRep`.

 - Fix some bugs on the way: #12375.

 Not included in this patch:

 - Update Haddock for new the new unboxed sum syntax.

 - `TemplateHaskell` support is left as future work.

 For reviewers:

 - Front-end code is mostly trivial and adapted from unboxed tuple code
   for type checking, pattern checking, renaming, desugaring etc.

 - Main translation routines are in `RepType` and `UnariseStg`.
   Documentation in `UnariseStg` should be enough for understanding
   what's going on.

 Credits:

 - Johan Tibell wrote the initial front-end and interface file
   extensions.

 - Simon Peyton Jones reviewed this patch many times, wrote some code,
   and helped with debugging.

 Reviewers: bgamari, alanz, goldfire, RyanGlScott, simonpj, austin,
            simonmar, hvr, erikd

 Reviewed By: simonpj

 Subscribers: Iceland_jack, ggreif, ezyang, RyanGlScott, goldfire,
              thomie, mpickering

 Differential Revision: https://phabricator.haskell.org/D2259
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12375#comment:2>
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