Add benchmarks for Data.Set.powerSet (#897)

Fixes #896

Author: jwaldmann

containers-tests/benchmarks/Set.hs

@@ -45,8 +45,12 @@ main = do
         , bench "alterF:four:strings" $ whnf (alterF_four strings) strings_s
         , bench "alterF_naive:four" $ whnf (alterF_naive_four elems) s
         , bench "alterF_naive:four:strings" $ whnf (alterF_naive_four strings) strings_s
-        , bench "powerSet" $ whnf S.powerSet (S.fromList[1..20])
-        , bench "member.powerSet" $ whnf (\ s -> all (flip S.member s) s) (S.powerSet (S.fromList [1..20]))
+        , bench "powerSet (19)" $ whnf S.powerSet (S.fromList[1..19])
+        , bench "powerSet (20)" $ whnf S.powerSet (S.fromList[1..20])
+        , bench "powerSet (21)" $ whnf S.powerSet (S.fromList[1..21])
+        , bench "member.powerSet (16)" $ whnf (\ s -> all (flip S.member s) s) (S.powerSet (S.fromList [1..16]))
+        , bench "member.powerSet (17)" $ whnf (\ s -> all (flip S.member s) s) (S.powerSet (S.fromList [1..17]))
+        , bench "member.powerSet (18)" $ whnf (\ s -> all (flip S.member s) s) (S.powerSet (S.fromList [1..18]))
         ]
   where
     elems = [1..2^12]