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

1 files changed, 3 insertions, 1 deletions

diff --git a/compiler/cmm/CLabel.hs b/compiler/cmm/CLabel.hs
index b262371b65..447eee8e8d 100644
--- a/compiler/cmm/CLabel.hs
+++ b/compiler/cmm/CLabel.hs
@@ -66,6 +66,7 @@ module CLabel (
         mkSMAP_DIRTY_infoLabel,
         mkEMPTY_MVAR_infoLabel,
         mkArrWords_infoLabel,
+        mkRUBBISH_ENTRY_infoLabel,
 
         mkTopTickyCtrLabel,
         mkCAFBlackHoleInfoTableLabel,
@@ -506,7 +507,7 @@ mkDirty_MUT_VAR_Label, mkSplitMarkerLabel, mkUpdInfoLabel,
     mkEMPTY_MVAR_infoLabel, mkTopTickyCtrLabel,
     mkCAFBlackHoleInfoTableLabel, mkCAFBlackHoleEntryLabel,
     mkArrWords_infoLabel, mkSMAP_FROZEN_infoLabel, mkSMAP_FROZEN0_infoLabel,
-    mkSMAP_DIRTY_infoLabel :: CLabel
+    mkSMAP_DIRTY_infoLabel, mkRUBBISH_ENTRY_infoLabel :: CLabel
 mkDirty_MUT_VAR_Label           = mkForeignLabel (fsLit "dirty_MUT_VAR") Nothing ForeignLabelInExternalPackage IsFunction
 mkSplitMarkerLabel              = CmmLabel rtsUnitId (fsLit "__stg_split_marker")    CmmCode
 mkUpdInfoLabel                  = CmmLabel rtsUnitId (fsLit "stg_upd_frame")         CmmInfo
@@ -524,6 +525,7 @@ mkArrWords_infoLabel            = CmmLabel rtsUnitId (fsLit "stg_ARR_WORDS")
 mkSMAP_FROZEN_infoLabel         = CmmLabel rtsUnitId (fsLit "stg_SMALL_MUT_ARR_PTRS_FROZEN") CmmInfo
 mkSMAP_FROZEN0_infoLabel        = CmmLabel rtsUnitId (fsLit "stg_SMALL_MUT_ARR_PTRS_FROZEN0") CmmInfo
 mkSMAP_DIRTY_infoLabel          = CmmLabel rtsUnitId (fsLit "stg_SMALL_MUT_ARR_PTRS_DIRTY") CmmInfo
+mkRUBBISH_ENTRY_infoLabel       = CmmLabel rtsUnitId (fsLit "stg_RUBBISH_ENTRY")     CmmInfo
 
 -----
 mkCmmInfoLabel,   mkCmmEntryLabel, mkCmmRetInfoLabel, mkCmmRetLabel,