fix PrimUnlifted's version of copy# which was broken. This fixes correctness issue with Mergesort (only)

Author: michaelborkowski

src/Array/Mutable.hs

@@ -117,14 +117,14 @@ set (Array lo'@(GHC.I# lo) hi !arr) i'@(GHC.I# i) !a =
 
 {-# INLINE copy #-}
 copy :: HasPrim a => Array a -> Int -> Array a -> Int -> Int -> Array a
-copy s@(Array (GHC.I# lo1) _hi1 src) (GHC.I# src_offset)
-      d@(Array (GHC.I# lo2) _hi2 dst) (GHC.I# dst_offset)
-      (GHC.I# n) =
+copy s@(Array lo1'@(GHC.I# lo1) _hi1 src) (GHC.I# src_offset)
+     d@(Array      (GHC.I# lo2) _hi2 dst) (GHC.I# dst_offset)
+     (GHC.I# n) =
 #ifdef PRIM_MUTABLE_ARRAYS
-  case copy# (get s 0) src (lo1 GHC.+# src_offset) dst (lo2 GHC.+# dst_offset) n of
+  case copy# (get# src lo1) src (lo1 GHC.+# src_offset) dst (lo2 GHC.+# dst_offset) n of
     dst_arr' -> d { array = dst_arr' }
 #else
-  case copy# src (lo1 GHC.+# src_offset) dst (lo2 GHC.+# dst_offset) n of
+  case copy#                src (lo1 GHC.+# src_offset) dst (lo2 GHC.+# dst_offset) n of
     dst_arr' -> d { array = dst_arr' }
 #endif
 

src/Array/Mutable/PrimUnlifted.hs

@@ -53,11 +53,12 @@ set# (Array# !arr) i !a =
 {-# NOINLINE copy# #-}
 copy# :: P.Prim a => a -> Array# a -> GHC.Int# -> Array# a -> GHC.Int# -> GHC.Int# -> Array# a
 copy# elt (Array# !src) src_offset (Array# !dst) dst_offset n =
-  case GHC.runRW# (GHC.copyMutableByteArray# src src_offset_bytes dst dst_offset_bytes n) of
+  case GHC.runRW# (GHC.copyMutableByteArray# src src_offset_bytes dst dst_offset_bytes n_bytes) of
     _ -> Array# dst
   where
     src_offset_bytes = (P.sizeOf# elt) GHC.*# src_offset
     dst_offset_bytes = (P.sizeOf# elt) GHC.*# dst_offset
+    n_bytes          = (P.sizeOf# elt) GHC.*# n
 
 
 size# :: Array# a -> GHC.Int#