Canonicalise Monoid instances in GHC

IOW, code compiles -Wnoncanonical-monoid-instances clean now

3 files changed, 6 insertions, 10 deletions

diff --git a/compiler/utils/OrdList.hs b/compiler/utils/OrdList.hs
index 1660090ba7..90fdefb908 100644
--- a/compiler/utils/OrdList.hs
+++ b/compiler/utils/OrdList.hs
@@ -41,7 +41,7 @@ instance Semigroup (OrdList a) where
 
 instance Monoid (OrdList a) where
   mempty = nilOL
-  mappend = appOL
+  mappend = (Semigroup.<>)
   mconcat = concatOL
 
 instance Functor OrdList where
diff --git a/compiler/utils/UniqMap.hs b/compiler/utils/UniqMap.hs
index 5bd609e597..c0960dd5b2 100644
--- a/compiler/utils/UniqMap.hs
+++ b/compiler/utils/UniqMap.hs
@@ -49,7 +49,7 @@ import UniqFM
 import Unique
 import Outputable
 
-import Data.Semigroup   ( Semigroup(..) )
+import Data.Semigroup as Semi ( Semigroup(..) )
 import Data.Coerce
 import Data.Maybe
 import Data.Typeable
@@ -65,7 +65,7 @@ instance Semigroup (UniqMap k a) where
 
 instance Monoid (UniqMap k a) where
     mempty = emptyUniqMap
-    mappend = plusUniqMap
+    mappend = (Semi.<>)
 
 instance (Outputable k, Outputable a) => Outputable (UniqMap k a) where
     ppr (UniqMap m) =
diff --git a/compiler/utils/UniqSet.hs b/compiler/utils/UniqSet.hs
index fcac865ea8..d09b337d12 100644
--- a/compiler/utils/UniqSet.hs
+++ b/compiler/utils/UniqSet.hs
@@ -52,7 +52,7 @@ import Data.Coerce
 import Outputable
 import Data.Foldable (foldl')
 import Data.Data
-import qualified Data.Semigroup
+import qualified Data.Semigroup as Semi
 
 -- Note [UniqSet invariant]
 -- ~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -61,7 +61,8 @@ import qualified Data.Semigroup
 -- It means that to implement mapUniqSet you have to update
 -- both the keys and the values.
 
-newtype UniqSet a = UniqSet {getUniqSet' :: UniqFM a} deriving Data
+newtype UniqSet a = UniqSet {getUniqSet' :: UniqFM a}
+                  deriving (Data, Semi.Semigroup, Monoid)
 
 emptyUniqSet :: UniqSet a
 emptyUniqSet = UniqSet emptyUFM
@@ -186,11 +187,6 @@ unsafeUFMToUniqSet = UniqSet
 
 instance Outputable a => Outputable (UniqSet a) where
     ppr = pprUniqSet ppr
-instance Data.Semigroup.Semigroup (UniqSet a) where
-  (<>) = mappend
-instance Monoid (UniqSet a) where
-  mempty = UniqSet mempty
-  UniqSet s `mappend` UniqSet t = UniqSet (s `mappend` t)
 
 pprUniqSet :: (a -> SDoc) -> UniqSet a -> SDoc
 pprUniqSet f (UniqSet s) = pprUniqFM f s