Add TyCon Set/Env and use them in a few places.

Firstly this improves code clarity.

But it also has performance benefits as we no longer
go through the name of the TyCon to get at it's unique.

In order to make this work the recursion check for TyCon
has been moved into it's own module in order to avoid import
cycles.

compiler/GHC/Core/Coercion.hs

@@ -135,6 +135,7 @@ import GHC.Core.TyCo.Subst
 import GHC.Core.TyCo.Tidy
 import GHC.Core.Type
 import GHC.Core.TyCon
+import GHC.Core.TyCon.RecWalk
 import GHC.Core.Coercion.Axiom
 import {-# SOURCE #-} GHC.Core.Utils ( mkFunctionType )
 import GHC.Types.Var

compiler/GHC/Core/Opt/Arity.hs

@@ -52,7 +52,8 @@ import GHC.Core.Type     as Type
 import GHC.Core.Coercion as Type
 
 import GHC.Core.DataCon
-import GHC.Core.TyCon     ( initRecTc, checkRecTc, tyConArity )
+import GHC.Core.TyCon     ( tyConArity )
+import GHC.Core.TyCon.RecWalk     ( initRecTc, checkRecTc )
 import GHC.Core.Predicate ( isDictTy )
 import GHC.Core.Multiplicity
 import GHC.Types.Var.Set

compiler/GHC/Core/Opt/SpecConstr.hs

@@ -31,7 +31,7 @@ import GHC.Core.DataCon
 import GHC.Core.Coercion hiding( substCo )
 import GHC.Core.Rules
 import GHC.Core.Type     hiding ( substTy )
-import GHC.Core.TyCon   ( tyConName )
+import GHC.Core.TyCon   ( tyConUnique )
 import GHC.Core.Multiplicity
 import GHC.Types.Id
 import GHC.Core.Ppr     ( pprParendExpr )
@@ -56,7 +56,7 @@ import GHC.Types.Unique.FM
 import GHC.Utils.Monad
 import Control.Monad    ( zipWithM )
 import Data.List
-import GHC.Builtin.Names ( specTyConName )
+import GHC.Builtin.Names ( specTyConKey )
 import GHC.Unit.Module
 import Data.Ord( comparing )
 
@@ -983,7 +983,7 @@ forceSpecArgTy env ty
 forceSpecArgTy env ty
   | Just (tycon, tys) <- splitTyConApp_maybe ty
   , tycon /= funTyCon
-      = tyConName tycon == specTyConName
+      = tyConUnique tycon == specTyConKey
         || any (forceSpecArgTy env) tys
 
 forceSpecArgTy _ _ = False

compiler/GHC/Core/Opt/WorkWrap/Utils.hs

@@ -40,6 +40,7 @@ import GHC.Core.Coercion
 import GHC.Core.FamInstEnv
 import GHC.Types.Basic       ( Boxity(..) )
 import GHC.Core.TyCon
+import GHC.Core.TyCon.RecWalk
 import GHC.Types.Unique.Supply
 import GHC.Types.Unique
 import GHC.Data.Maybe

compiler/GHC/Core/Predicate.hs

@@ -34,6 +34,7 @@ import GHC.Prelude
 import GHC.Core.Type
 import GHC.Core.Class
 import GHC.Core.TyCon
+import GHC.Core.TyCon.RecWalk
 import GHC.Types.Var
 import GHC.Core.Coercion
 import GHC.Core.Multiplicity ( scaledThing )

compiler/GHC/Core/TyCon.hs

@@ -126,10 +126,6 @@ module GHC.Core.TyCon(
         primRepsCompatible,
         primRepCompatible,
 
-        -- * Recursion breaking
-        RecTcChecker, initRecTc, defaultRecTcMaxBound,
-        setRecTcMaxBound, checkRecTc
-
 ) where
 
 #include "HsVersions.h"
@@ -2710,83 +2706,6 @@ instance Binary Injectivity where
                     _ -> do { xs <- get bh
                             ; return (Injective xs) } }
 
-{-
-************************************************************************
-*                                                                      *
-           Walking over recursive TyCons
-*                                                                      *
-************************************************************************
-
-Note [Expanding newtypes and products]
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-When expanding a type to expose a data-type constructor, we need to be
-careful about newtypes, lest we fall into an infinite loop. Here are
-the key examples:
-
-  newtype Id  x = MkId x
-  newtype Fix f = MkFix (f (Fix f))
-  newtype T     = MkT (T -> T)
-
-  Type           Expansion
- --------------------------
-  T              T -> T
-  Fix Maybe      Maybe (Fix Maybe)
-  Id (Id Int)    Int
-  Fix Id         NO NO NO
-
-Notice that
- * We can expand T, even though it's recursive.
- * We can expand Id (Id Int), even though the Id shows up
-   twice at the outer level, because Id is non-recursive
-
-So, when expanding, we keep track of when we've seen a recursive
-newtype at outermost level; and bail out if we see it again.
-
-We sometimes want to do the same for product types, so that the
-strictness analyser doesn't unbox infinitely deeply.
-
-More precisely, we keep a *count* of how many times we've seen it.
-This is to account for
-   data instance T (a,b) = MkT (T a) (T b)
-Then (#10482) if we have a type like
-        T (Int,(Int,(Int,(Int,Int))))
-we can still unbox deeply enough during strictness analysis.
-We have to treat T as potentially recursive, but it's still
-good to be able to unwrap multiple layers.
-
-The function that manages all this is checkRecTc.
--}
-
-data RecTcChecker = RC !Int (NameEnv Int)
-  -- The upper bound, and the number of times
-  -- we have encountered each TyCon
-
--- | Initialise a 'RecTcChecker' with 'defaultRecTcMaxBound'.
-initRecTc :: RecTcChecker
-initRecTc = RC defaultRecTcMaxBound emptyNameEnv
-
--- | The default upper bound (100) for the number of times a 'RecTcChecker' is
--- allowed to encounter each 'TyCon'.
-defaultRecTcMaxBound :: Int
-defaultRecTcMaxBound = 100
--- Should we have a flag for this?
-
--- | Change the upper bound for the number of times a 'RecTcChecker' is allowed
--- to encounter each 'TyCon'.
-setRecTcMaxBound :: Int -> RecTcChecker -> RecTcChecker
-setRecTcMaxBound new_bound (RC _old_bound rec_nts) = RC new_bound rec_nts
-
-checkRecTc :: RecTcChecker -> TyCon -> Maybe RecTcChecker
--- Nothing      => Recursion detected
--- Just rec_tcs => Keep going
-checkRecTc (RC bound rec_nts) tc
-  = case lookupNameEnv rec_nts tc_name of
-      Just n | n >= bound -> Nothing
-             | otherwise  -> Just (RC bound (extendNameEnv rec_nts tc_name (n+1)))
-      Nothing             -> Just (RC bound (extendNameEnv rec_nts tc_name 1))
-  where
-    tc_name = tyConName tc
-
 -- | Returns whether or not this 'TyCon' is definite, or a hole
 -- that may be filled in at some later point.  See Note [Skolem abstract data]
 tyConSkolem :: TyCon -> Bool

compiler/GHC/Core/TyCon/Env.hs

+{-
+(c) The University of Glasgow 2006
+(c) The GRASP/AQUA Project, Glasgow University, 1992-1998
+
+\section[TyConEnv]{@TyConEnv@: tyCon environments}
+-}
+
+{-# LANGUAGE CPP, DeriveDataTypeable #-}
+
+{-# LANGUAGE BangPatterns #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+
+
+module GHC.Core.TyCon.Env (
+        -- * TyCon environment (map)
+        TyConEnv,
+
+        -- ** Manipulating these environments
+        mkTyConEnv, mkTyConEnvWith,
+        emptyTyConEnv, isEmptyTyConEnv,
+        unitTyConEnv, nameEnvElts,
+        extendTyConEnv_C, extendTyConEnv_Acc, extendTyConEnv,
+        extendTyConEnvList, extendTyConEnvList_C,
+        filterTyConEnv, anyTyConEnv,
+        plusTyConEnv, plusTyConEnv_C, plusTyConEnv_CD, plusTyConEnv_CD2, alterTyConEnv,
+        lookupTyConEnv, lookupTyConEnv_NF, delFromTyConEnv, delListFromTyConEnv,
+        elemTyConEnv, mapTyConEnv, disjointTyConEnv,
+
+        DTyConEnv,
+
+        emptyDTyConEnv,
+        lookupDTyConEnv,
+        delFromDTyConEnv, filterDTyConEnv,
+        mapDTyConEnv,
+        adjustDTyConEnv, alterDTyConEnv, extendDTyConEnv,
+    ) where
+
+#include "HsVersions.h"
+
+import GHC.Prelude
+
+import GHC.Types.Unique.FM
+import GHC.Types.Unique.DFM
+import GHC.Core.TyCon (TyCon)
+
+import GHC.Data.Maybe
+
+{-
+************************************************************************
+*                                                                      *
+\subsection{TyCon environment}
+*                                                                      *
+************************************************************************
+-}
+
+-- | TyCon Environment
+type TyConEnv a = UniqFM TyCon a       -- Domain is TyCon
+
+emptyTyConEnv       :: TyConEnv a
+isEmptyTyConEnv     :: TyConEnv a -> Bool
+mkTyConEnv          :: [(TyCon,a)] -> TyConEnv a
+mkTyConEnvWith      :: (a -> TyCon) -> [a] -> TyConEnv a
+nameEnvElts        :: TyConEnv a -> [a]
+alterTyConEnv       :: (Maybe a-> Maybe a) -> TyConEnv a -> TyCon -> TyConEnv a
+extendTyConEnv_C    :: (a->a->a) -> TyConEnv a -> TyCon -> a -> TyConEnv a
+extendTyConEnv_Acc  :: (a->b->b) -> (a->b) -> TyConEnv b -> TyCon -> a -> TyConEnv b
+extendTyConEnv      :: TyConEnv a -> TyCon -> a -> TyConEnv a
+plusTyConEnv        :: TyConEnv a -> TyConEnv a -> TyConEnv a
+plusTyConEnv_C      :: (a->a->a) -> TyConEnv a -> TyConEnv a -> TyConEnv a
+plusTyConEnv_CD     :: (a->a->a) -> TyConEnv a -> a -> TyConEnv a -> a -> TyConEnv a
+plusTyConEnv_CD2    :: (Maybe a->Maybe a->a) -> TyConEnv a -> TyConEnv a -> TyConEnv a
+extendTyConEnvList  :: TyConEnv a -> [(TyCon,a)] -> TyConEnv a
+extendTyConEnvList_C :: (a->a->a) -> TyConEnv a -> [(TyCon,a)] -> TyConEnv a
+delFromTyConEnv     :: TyConEnv a -> TyCon -> TyConEnv a
+delListFromTyConEnv :: TyConEnv a -> [TyCon] -> TyConEnv a
+elemTyConEnv        :: TyCon -> TyConEnv a -> Bool
+unitTyConEnv        :: TyCon -> a -> TyConEnv a
+lookupTyConEnv      :: TyConEnv a -> TyCon -> Maybe a
+lookupTyConEnv_NF   :: TyConEnv a -> TyCon -> a
+filterTyConEnv      :: (elt -> Bool) -> TyConEnv elt -> TyConEnv elt
+anyTyConEnv         :: (elt -> Bool) -> TyConEnv elt -> Bool
+mapTyConEnv         :: (elt1 -> elt2) -> TyConEnv elt1 -> TyConEnv elt2
+disjointTyConEnv    :: TyConEnv a -> TyConEnv a -> Bool
+
+nameEnvElts x         = eltsUFM x
+emptyTyConEnv          = emptyUFM
+isEmptyTyConEnv        = isNullUFM
+unitTyConEnv x y       = unitUFM x y
+extendTyConEnv x y z   = addToUFM x y z
+extendTyConEnvList x l = addListToUFM x l
+lookupTyConEnv x y     = lookupUFM x y
+alterTyConEnv          = alterUFM
+mkTyConEnv     l       = listToUFM l
+mkTyConEnvWith f       = mkTyConEnv . map (\a -> (f a, a))
+elemTyConEnv x y          = elemUFM x y
+plusTyConEnv x y          = plusUFM x y
+plusTyConEnv_C f x y      = plusUFM_C f x y
+plusTyConEnv_CD f x d y b = plusUFM_CD f x d y b
+plusTyConEnv_CD2 f x y    = plusUFM_CD2 f x y
+extendTyConEnv_C f x y z  = addToUFM_C f x y z
+mapTyConEnv f x           = mapUFM f x
+extendTyConEnv_Acc x y z a b  = addToUFM_Acc x y z a b
+extendTyConEnvList_C x y z = addListToUFM_C x y z
+delFromTyConEnv x y      = delFromUFM x y
+delListFromTyConEnv x y  = delListFromUFM x y
+filterTyConEnv x y       = filterUFM x y
+anyTyConEnv f x          = foldUFM ((||) . f) False x
+disjointTyConEnv x y     = disjointUFM x y
+
+lookupTyConEnv_NF env n = expectJust "lookupTyConEnv_NF" (lookupTyConEnv env n)
+
+-- | Deterministic TyCon Environment
+--
+-- See Note [Deterministic UniqFM] in "GHC.Types.Unique.DFM" for explanation why
+-- we need DTyConEnv.
+type DTyConEnv a = UniqDFM TyCon a
+
+emptyDTyConEnv :: DTyConEnv a
+emptyDTyConEnv = emptyUDFM
+
+lookupDTyConEnv :: DTyConEnv a -> TyCon -> Maybe a
+lookupDTyConEnv = lookupUDFM
+
+delFromDTyConEnv :: DTyConEnv a -> TyCon -> DTyConEnv a
+delFromDTyConEnv = delFromUDFM
+
+filterDTyConEnv :: (a -> Bool) -> DTyConEnv a -> DTyConEnv a
+filterDTyConEnv = filterUDFM
+
+mapDTyConEnv :: (a -> b) -> DTyConEnv a -> DTyConEnv b
+mapDTyConEnv = mapUDFM
+
+adjustDTyConEnv :: (a -> a) -> DTyConEnv a -> TyCon -> DTyConEnv a
+adjustDTyConEnv = adjustUDFM
+
+alterDTyConEnv :: (Maybe a -> Maybe a) -> DTyConEnv a -> TyCon -> DTyConEnv a
+alterDTyConEnv = alterUDFM
+
+extendDTyConEnv :: DTyConEnv a -> TyCon -> a -> DTyConEnv a
+extendDTyConEnv = addToUDFM

compiler/GHC/Core/TyCon/RecWalk.hs

+{-
+(c) The University of Glasgow 2006
+(c) The GRASP/AQUA Project, Glasgow University, 1992-1998
+
+Check for recursive type constructors.
+
+-}
+
+{-# LANGUAGE CPP, DeriveDataTypeable #-}
+
+module GHC.Core.TyCon.RecWalk (
+
+        -- * Recursion breaking
+        RecTcChecker, initRecTc, defaultRecTcMaxBound,
+        setRecTcMaxBound, checkRecTc
+
+    ) where
+
+#include "HsVersions.h"
+
+import GHC.Prelude
+
+import GHC.Core.TyCon
+import GHC.Core.TyCon.Env
+
+{-
+************************************************************************
+*                                                                      *
+           Walking over recursive TyCons
+*                                                                      *
+************************************************************************
+
+Note [Expanding newtypes and products]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+When expanding a type to expose a data-type constructor, we need to be
+careful about newtypes, lest we fall into an infinite loop. Here are
+the key examples:
+
+  newtype Id  x = MkId x
+  newtype Fix f = MkFix (f (Fix f))
+  newtype T     = MkT (T -> T)
+
+  Type           Expansion
+ --------------------------
+  T              T -> T
+  Fix Maybe      Maybe (Fix Maybe)
+  Id (Id Int)    Int
+  Fix Id         NO NO NO
+
+Notice that
+ * We can expand T, even though it's recursive.
+ * We can expand Id (Id Int), even though the Id shows up
+   twice at the outer level, because Id is non-recursive
+
+So, when expanding, we keep track of when we've seen a recursive
+newtype at outermost level; and bail out if we see it again.
+
+We sometimes want to do the same for product types, so that the
+strictness analyser doesn't unbox infinitely deeply.
+
+More precisely, we keep a *count* of how many times we've seen it.
+This is to account for
+   data instance T (a,b) = MkT (T a) (T b)
+Then (#10482) if we have a type like
+        T (Int,(Int,(Int,(Int,Int))))
+we can still unbox deeply enough during strictness analysis.
+We have to treat T as potentially recursive, but it's still
+good to be able to unwrap multiple layers.
+
+The function that manages all this is checkRecTc.
+-}
+
+data RecTcChecker = RC !Int (TyConEnv Int)
+  -- The upper bound, and the number of times
+  -- we have encountered each TyCon
+
+-- | Initialise a 'RecTcChecker' with 'defaultRecTcMaxBound'.
+initRecTc :: RecTcChecker
+initRecTc = RC defaultRecTcMaxBound emptyTyConEnv
+
+-- | The default upper bound (100) for the number of times a 'RecTcChecker' is
+-- allowed to encounter each 'TyCon'.
+defaultRecTcMaxBound :: Int
+defaultRecTcMaxBound = 100
+-- Should we have a flag for this?
+
+-- | Change the upper bound for the number of times a 'RecTcChecker' is allowed
+-- to encounter each 'TyCon'.
+setRecTcMaxBound :: Int -> RecTcChecker -> RecTcChecker
+setRecTcMaxBound new_bound (RC _old_bound rec_nts) = RC new_bound rec_nts
+
+checkRecTc :: RecTcChecker -> TyCon -> Maybe RecTcChecker
+-- Nothing      => Recursion detected
+-- Just rec_tcs => Keep going
+checkRecTc (RC bound rec_nts) tc
+  = case lookupTyConEnv rec_nts tc of
+      Just n | n >= bound -> Nothing
+             | otherwise  -> Just (RC bound (extendTyConEnv rec_nts tc (n+1)))
+      Nothing             -> Just (RC bound (extendTyConEnv rec_nts tc 1))

compiler/GHC/Core/TyCon/Set.hs

+{-
+(c) The University of Glasgow 2006
+(c) The GRASP/AQUA Project, Glasgow University, 1992-1998
+
+-}
+
+{-# LANGUAGE CPP, DeriveDataTypeable #-}
+
+module GHC.Core.TyCon.Set (
+        -- * TyCons set type
+        TyConSet,
+
+        -- ** Manipulating these sets
+        emptyTyConSet, unitTyConSet, mkTyConSet, unionTyConSet, unionTyConSets,
+        minusTyConSet, elemTyConSet, extendTyConSet, extendTyConSetList,
+        delFromTyConSet, delListFromTyConSet, isEmptyTyConSet, filterTyConSet,
+        intersectsTyConSet, disjointTyConSet, intersectTyConSet,
+        nameSetAny, nameSetAll
+    ) where
+
+#include "HsVersions.h"
+
+import GHC.Prelude
+
+import GHC.Types.Unique.Set
+import GHC.Core.TyCon (TyCon)
+
+type TyConSet = UniqSet TyCon
+
+emptyTyConSet       :: TyConSet
+unitTyConSet        :: TyCon -> TyConSet
+extendTyConSetList   :: TyConSet -> [TyCon] -> TyConSet
+extendTyConSet    :: TyConSet -> TyCon -> TyConSet
+mkTyConSet          :: [TyCon] -> TyConSet
+unionTyConSet      :: TyConSet -> TyConSet -> TyConSet
+unionTyConSets  :: [TyConSet] -> TyConSet
+minusTyConSet       :: TyConSet -> TyConSet -> TyConSet
+elemTyConSet        :: TyCon -> TyConSet -> Bool
+isEmptyTyConSet     :: TyConSet -> Bool
+delFromTyConSet     :: TyConSet -> TyCon -> TyConSet
+delListFromTyConSet :: TyConSet -> [TyCon] -> TyConSet
+filterTyConSet      :: (TyCon -> Bool) -> TyConSet -> TyConSet
+intersectTyConSet   :: TyConSet -> TyConSet -> TyConSet
+intersectsTyConSet  :: TyConSet -> TyConSet -> Bool
+-- ^ True if there is a non-empty intersection.
+-- @s1 `intersectsTyConSet` s2@ doesn't compute @s2@ if @s1@ is empty
+disjointTyConSet    :: TyConSet -> TyConSet -> Bool
+
+isEmptyTyConSet    = isEmptyUniqSet
+emptyTyConSet      = emptyUniqSet
+unitTyConSet       = unitUniqSet
+mkTyConSet         = mkUniqSet
+extendTyConSetList = addListToUniqSet
+extendTyConSet     = addOneToUniqSet
+unionTyConSet      = unionUniqSets
+unionTyConSets     = unionManyUniqSets
+minusTyConSet      = minusUniqSet
+elemTyConSet       = elementOfUniqSet
+delFromTyConSet    = delOneFromUniqSet
+filterTyConSet     = filterUniqSet
+intersectTyConSet  = intersectUniqSets
+disjointTyConSet   = disjointUniqSets
+
+
+delListFromTyConSet set ns = foldl' delFromTyConSet set ns
+
+intersectsTyConSet s1 s2 = not (isEmptyTyConSet (s1 `intersectTyConSet` s2))
+
+nameSetAny :: (TyCon -> Bool) -> TyConSet -> Bool
+nameSetAny = uniqSetAny
+
+nameSetAll :: (TyCon -> Bool) -> TyConSet -> Bool
+nameSetAll = uniqSetAll

compiler/GHC/HsToCore/Pmc/Solver.hs

@@ -67,6 +67,7 @@ import GHC.Core.ConLike
 import GHC.Core.DataCon
 import GHC.Core.PatSyn
 import GHC.Core.TyCon
+import GHC.Core.TyCon.RecWalk
 import GHC.Builtin.Types
 import GHC.Builtin.Types.Prim (tYPETyCon)
 import GHC.Core.TyCo.Rep

compiler/GHC/Tc/Gen/Foreign.hs

@@ -58,6 +58,7 @@ import GHC.Types.Name
 import GHC.Types.Name.Reader
 import GHC.Core.DataCon
 import GHC.Core.TyCon
+import GHC.Core.TyCon.RecWalk
 import GHC.Tc.Utils.TcType
 import GHC.Builtin.Names
 import GHC.Driver.Session

compiler/GHC/Tc/Solver/Monad.hs

@@ -174,6 +174,7 @@ import GHC.Core.Predicate
 import GHC.Types.Unique
 import GHC.Types.Unique.FM
 import GHC.Types.Unique.DFM
+import GHC.Core.TyCon.Env
 import GHC.Data.Maybe
 
 import GHC.Core.Map
@@ -2640,7 +2641,7 @@ delFunEq :: FunEqMap a -> TyCon -> [Type] -> FunEqMap a
 delFunEq m tc tys = delTcApp m (getUnique tc) tys
 
 ------------------------------
-type ExactFunEqMap a = UniqFM TyCon (ListMap TypeMap a)
+type ExactFunEqMap a = TyConEnv (ListMap TypeMap a)
 
 emptyExactFunEqs :: ExactFunEqMap a
 emptyExactFunEqs = emptyUFM

compiler/GHC/Tc/TyCl/Utils.hs

@@ -50,12 +50,13 @@ import GHC.Core.ConLike
 import GHC.Core.DataCon
 import GHC.Types.Name
 import GHC.Types.Name.Env
-import GHC.Types.Name.Set hiding (unitFV)
 import GHC.Types.Name.Reader ( mkVarUnqual )
 import GHC.Types.Id
 import GHC.Types.Id.Info
 import GHC.Types.Var.Env
 import GHC.Types.Var.Set
+import GHC.Types.Unique.Set
+import GHC.Core.TyCon.Set
 import GHC.Core.Coercion ( ltRole )
 import GHC.Types.Basic
 import GHC.Types.SrcLoc
@@ -156,7 +157,11 @@ newtype SynCycleM a = SynCycleM {
     runSynCycleM :: SynCycleState -> Either (SrcSpan, SDoc) (a, SynCycleState) }
     deriving (Functor)
 
-type SynCycleState = NameSet
+-- TODO: TyConSet is implemented as IntMap over uniques.
+-- But we could get away with something based on IntSet
+-- since we only check membershib, but never extract the
+-- elements.
+type SynCycleState = TyConSet
 
 instance Applicative SynCycleM where
     pure x = SynCycleM $ \state -> Right (x, state)
@@ -174,12 +179,12 @@ failSynCycleM loc err = SynCycleM $ \_ -> Left (loc, err)
 
 -- | Test if a 'Name' is acyclic, short-circuiting if we've
 -- seen it already.
-checkNameIsAcyclic :: Name -> SynCycleM () -> SynCycleM ()
-checkNameIsAcyclic n m = SynCycleM $ \s ->
-    if n `elemNameSet` s
+checkTyConIsAcyclic :: TyCon -> SynCycleM () -> SynCycleM ()
+checkTyConIsAcyclic tc m = SynCycleM $ \s ->
+    if tc `elemTyConSet` s
         then Right ((), s) -- short circuit
         else case runSynCycleM m s of
-                Right ((), s') -> Right ((), extendNameSet s' n)
+                Right ((), s') -> Right ((), extendTyConSet s' tc)
                 Left err -> Left err
 
 -- | Checks if any of the passed in 'TyCon's have cycles.
@@ -189,7 +194,7 @@ checkNameIsAcyclic n m = SynCycleM $ \s ->
 -- can give better error messages.
 checkSynCycles :: Unit -> [TyCon] -> [LTyClDecl GhcRn] -> TcM ()
 checkSynCycles this_uid tcs tyclds = do
-    case runSynCycleM (mapM_ (go emptyNameSet []) tcs) emptyNameSet of
+    case runSynCycleM (mapM_ (go emptyTyConSet []) tcs) emptyTyConSet of
         Left (loc, err) -> setSrcSpan loc $ failWithTc err
         Right _  -> return ()
   where
@@ -198,15 +203,15 @@ checkSynCycles this_uid tcs tyclds = do
 
     -- Short circuit if we've already seen this Name and concluded
     -- it was acyclic.
-    go :: NameSet -> [TyCon] -> TyCon -> SynCycleM ()
+    go :: TyConSet -> [TyCon] -> TyCon -> SynCycleM ()
     go so_far seen_tcs tc =
-        checkNameIsAcyclic (tyConName tc) $ go' so_far seen_tcs tc
+        checkTyConIsAcyclic tc $ go' so_far seen_tcs tc
 
     -- Expand type synonyms, complaining if you find the same
     -- type synonym a second time.
-    go' :: NameSet -> [TyCon] -> TyCon -> SynCycleM ()
+    go' :: TyConSet -> [TyCon] -> TyCon -> SynCycleM ()
     go' so_far seen_tcs tc
-        | n `elemNameSet` so_far
+        | tc `elemTyConSet` so_far
             = failSynCycleM (getSrcSpan (head seen_tcs)) $
                   sep [ text "Cycle in type synonym declarations:"
                       , nest 2 (vcat (map ppr_decl seen_tcs)) ]
@@ -221,7 +226,7 @@ checkSynCycles this_uid tcs tyclds = do
                isInteractiveModule mod)
             = return ()
         | Just ty <- synTyConRhs_maybe tc =
-            go_ty (extendNameSet so_far (tyConName tc)) (tc:seen_tcs) ty
+            go_ty (extendTyConSet so_far tc) (tc:seen_tcs) ty
         | otherwise = return ()
       where
         n = tyConName tc
@@ -234,7 +239,7 @@ checkSynCycles this_uid tcs tyclds = do
          where
           n = tyConName tc
 
-    go_ty :: NameSet -> [TyCon] -> Type -> SynCycleM ()
+    go_ty :: TyConSet -> [TyCon] -> Type -> SynCycleM ()
     go_ty so_far seen_tcs ty =
         mapM_ (go so_far seen_tcs) (synonymTyConsOfType ty)
 
@@ -284,11 +289,13 @@ and now expand superclasses for constraint (C Id):
 Each step expands superclasses one layer, and clearly does not terminate.
 -}
 
+type ClassSet = UniqSet Class
+
 checkClassCycles :: Class -> Maybe SDoc
 -- Nothing  <=> ok
 -- Just err <=> possible cycle error
 checkClassCycles cls
-  = do { (definite_cycle, err) <- go (unitNameSet (getName cls))
+  = do { (definite_cycle, err) <- go (unitUniqSet cls)