Increase type sharingwip/T20541

Fixes #20541 by making mkTyConApp do more sharing of types.
In particular, replace

* BoxedRep Lifted    ==>  LiftedRep
* BoxedRep Unlifted  ==>  UnliftedRep
* TupleRep '[]       ==>  ZeroBitRep
* TYPE ZeroBitRep    ==>  ZeroBitType

In each case, the thing on the right is a type synonym
for the thing on the left, declared in ghc-prim:GHC.Types.
See Note [Using synonyms to compress types] in GHC.Core.Type.

The synonyms for ZeroBitRep and ZeroBitType are new, but absolutely
in the same spirit as the other ones.   (These synonyms are mainly
for internal use, though the programmer can use them too.)

I also renamed GHC.Core.Ty.Rep.isVoidTy to isZeroBitTy, to be
compatible with the "zero-bit" nomenclature above.  See discussion
on !6806.

There is a tricky wrinkle: see GHC.Core.Types
  Note [Care using synonyms to compress types]

Compiler allocation decreases by up to 0.8%.

1 files changed, 12 insertions, 12 deletions

diff --git a/compiler/GHC/Core/TyCon.hs b/compiler/GHC/Core/TyCon.hs
index fd5b3df534..24807945cc 100644
--- a/compiler/GHC/Core/TyCon.hs
+++ b/compiler/GHC/Core/TyCon.hs
@@ -138,7 +138,7 @@ import GHC.Prelude
 import GHC.Platform
 
 import {-# SOURCE #-} GHC.Core.TyCo.Rep
-   ( Kind, Type, PredType, mkForAllTy, mkFunTyMany, mkTyConTy_ )
+   ( Kind, Type, PredType, mkForAllTy, mkFunTyMany, mkNakedTyConTy )
 import {-# SOURCE #-} GHC.Core.TyCo.Ppr
    ( pprType )
 import {-# SOURCE #-} GHC.Builtin.Types
@@ -1819,7 +1819,7 @@ So we compromise, and move their Kind calculation to the call site.
 -}
 
 -- | Given the name of the function type constructor and it's kind, create the
--- corresponding 'TyCon'. It is recommended to use 'GHC.Core.TyCo.Rep.funTyCon' if you want
+-- corresponding 'TyCon'. It is recommended to use 'GHC.Builtin.Types.funTyCon' if you want
 -- this functionality
 mkFunTyCon :: Name -> [TyConBinder] -> Name -> TyCon
 mkFunTyCon name binders rep_nm
@@ -1831,7 +1831,7 @@ mkFunTyCon name binders rep_nm
               tyConResKind = liftedTypeKind,
               tyConKind    = mkTyConKind binders liftedTypeKind,
               tyConArity   = length binders,
-              tyConNullaryTy = mkTyConTy_ tc,
+              tyConNullaryTy = mkNakedTyConTy tc,
               tcRepName    = rep_nm
           }
     in tc
@@ -1858,7 +1858,7 @@ mkAlgTyCon name binders res_kind roles cType stupid rhs parent gadt_syn
               tyConResKind     = res_kind,
               tyConKind        = mkTyConKind binders res_kind,
               tyConArity       = length binders,
-              tyConNullaryTy   = mkTyConTy_ tc,
+              tyConNullaryTy   = mkNakedTyConTy tc,
               tyConTyVars      = binderVars binders,
               tcRoles          = roles,
               tyConCType       = cType,
@@ -1897,7 +1897,7 @@ mkTupleTyCon name binders res_kind arity con sort parent
               tyConResKind     = res_kind,
               tyConKind        = mkTyConKind binders res_kind,
               tyConArity       = arity,
-              tyConNullaryTy   = mkTyConTy_ tc,
+              tyConNullaryTy   = mkNakedTyConTy tc,
               tcRoles          = replicate arity Representational,
               tyConCType       = Nothing,
               algTcGadtSyntax  = False,
@@ -1927,7 +1927,7 @@ mkSumTyCon name binders res_kind arity tyvars cons parent
               tyConResKind     = res_kind,
               tyConKind        = mkTyConKind binders res_kind,
               tyConArity       = arity,
-              tyConNullaryTy   = mkTyConTy_ tc,
+              tyConNullaryTy   = mkNakedTyConTy tc,
               tcRoles          = replicate arity Representational,
               tyConCType       = Nothing,
               algTcGadtSyntax  = False,
@@ -1962,7 +1962,7 @@ mkTcTyCon name binders res_kind scoped_tvs poly flav
                   , tyConResKind = res_kind
                   , tyConKind    = mkTyConKind binders res_kind
                   , tyConArity   = length binders
-                  , tyConNullaryTy = mkTyConTy_ tc
+                  , tyConNullaryTy = mkNakedTyConTy tc
                   , tcTyConScopedTyVars = scoped_tvs
                   , tcTyConIsPoly       = poly
                   , tcTyConFlavour      = flav }
@@ -2013,7 +2013,7 @@ mkPrimTyCon' name binders res_kind roles is_unlifted rep_nm
               tyConResKind = res_kind,
               tyConKind    = mkTyConKind binders res_kind,
               tyConArity   = length roles,
-              tyConNullaryTy = mkTyConTy_ tc,
+              tyConNullaryTy = mkNakedTyConTy tc,
               tcRoles      = roles,
               isUnlifted   = is_unlifted,
               primRepName  = rep_nm
@@ -2032,7 +2032,7 @@ mkSynonymTyCon name binders res_kind roles rhs is_tau is_fam_free is_forgetful
               tyConResKind   = res_kind,
               tyConKind      = mkTyConKind binders res_kind,
               tyConArity     = length binders,
-              tyConNullaryTy = mkTyConTy_ tc,
+              tyConNullaryTy = mkNakedTyConTy tc,
               tyConTyVars    = binderVars binders,
               tcRoles        = roles,
               synTcRhs       = rhs,
@@ -2055,7 +2055,7 @@ mkFamilyTyCon name binders res_kind resVar flav parent inj
             , tyConResKind = res_kind
             , tyConKind    = mkTyConKind binders res_kind
             , tyConArity   = length binders
-            , tyConNullaryTy = mkTyConTy_ tc
+            , tyConNullaryTy = mkNakedTyConTy tc
             , tyConTyVars  = binderVars binders
             , famTcResVar  = resVar
             , famTcFlav    = flav
@@ -2078,7 +2078,7 @@ mkPromotedDataCon con name rep_name binders res_kind roles rep_info
             tyConUnique   = nameUnique name,
             tyConName     = name,
             tyConArity    = length roles,
-            tyConNullaryTy = mkTyConTy_ tc,
+            tyConNullaryTy = mkNakedTyConTy tc,
             tcRoles       = roles,
             tyConBinders  = binders,
             tyConResKind  = res_kind,
@@ -2468,7 +2468,7 @@ setTcTyConKind :: TyCon -> Kind -> TyCon
 -- kind, so we don't need to update any other fields.
 -- See Note [The Purely Kinded Invariant] in GHC.Tc.Gen.HsType
 setTcTyConKind tc@(TcTyCon {}) kind = let tc' = tc { tyConKind = kind
-                                                   , tyConNullaryTy = mkTyConTy_ tc'
+                                                   , tyConNullaryTy = mkNakedTyConTy tc'
                                                        -- see Note [Sharing nullary TyCons]
                                                    }
                                       in tc'