filter.go: Use strict patterns

Author: sjakobi

Data/HashMap/Internal.hs

@@ -1893,9 +1893,6 @@ difference = go 0
 -- TODO: This could be faster if we would keep track of which elements of ary2
 -- we've already matched. Those could be skipped when we check the following
 -- elements of ary1.
---
--- TODO: For some reason, ary2 is unboxed, but ary1 is not.
--- https://gitlab.haskell.org/ghc/ghc/-/issues/26525
 differenceCollisions :: Eq k => Hash -> A.Array (Leaf k v1) -> HashMap k v1 -> Hash -> A.Array (Leaf k v2) -> HashMap k v1
 differenceCollisions !h1 !ary1 t1 !h2 !ary2
   | h1 == h2 =

Data/HashMap/Internal/Array.hs

@@ -507,7 +507,10 @@ filter f = \ ary ->
       len <- go ary mary 0 0 n
       shrink mary len
   where
-    go ary mary iAry iMary n
+    -- Without the @!@ on @ary@ we end up reboxing the array when using
+    -- 'differenceCollisions'. See
+    -- https://gitlab.haskell.org/ghc/ghc/-/issues/26525.
+    go !ary !mary !iAry !iMary !n
       | iAry >= n = return iMary
       | otherwise = do
         x <- indexM ary iAry