Refactoring module dependencies

* Make mkDependencies pure
* Use Sets instead of sorted lists

Notable perf changes:

      MultiLayerModules(normal) ghc/alloc  4130851520.0  2981473072.0 -27.8%
                 T13719(normal) ghc/alloc  4313296052.0  4151647512.0  -3.7%

Metric Decrease:
    MultiLayerModules
    T13719

1 files changed, 6 insertions, 0 deletions

diff --git a/compiler/GHC/Utils/Binary.hs b/compiler/GHC/Utils/Binary.hs
index 17fa675986..08e54acbd5 100644
--- a/compiler/GHC/Utils/Binary.hs
+++ b/compiler/GHC/Utils/Binary.hs
@@ -96,6 +96,8 @@ import Data.IORef
 import Data.Char                ( ord, chr )
 import Data.Time
 import Data.List (unfoldr)
+import Data.Set (Set)
+import qualified Data.Set as Set
 import Control.Monad            ( when, (<$!>), unless, forM_ )
 import System.IO as IO
 import System.IO.Unsafe         ( unsafeInterleaveIO )
@@ -637,6 +639,10 @@ instance Binary a => Binary [a] where
             loop n = do a <- get bh; as <- loop (n-1); return (a:as)
         loop len
 
+instance Binary a => Binary (Set a) where
+    put_ bh a = put_ bh (Set.toAscList a)
+    get bh    = Set.fromDistinctAscList <$> get bh
+
 instance (Ix a, Binary a, Binary b) => Binary (Array a b) where
     put_ bh arr = do
         put_ bh $ bounds arr