Cheng Shao pushed to branch wip/binary-array-no-list at Glasgow Haskell Compiler / GHC

Commits:

• 1a713d56
  by Cheng Shao at 2026-04-08T11:11:39+00:00

  compiler: improve Binary instance of Array
  
  This patch improves the `Binary` instance of `Array`:
  
  - We no longer allocate intermediate lists. When serializing an
    `Array`, we iterate over the elements directly; when deserializing
    it, we allocate the result `Array` and fill it in a loop.
  - Now we only serialize the array bounds tuple; the length field is
    not needed.
  
  Closes #27109.
  

1 changed file:

• compiler/GHC/Utils/Binary.hs

Changes:

 import Control.Monad            ( when, (<$!>), unless, forM_, void )

 import Foreign hiding (bit, setBit, clearBit, shiftL, shiftR, void)

 import Data.Array

+import Data.Array.Base (unsafeFreezeIOArray)

+import Data.Array.IArray (traverseArray_)

 import Data.Array.IO

 import Data.Array.Unsafe

 import qualified Data.Binary as Binary

 instance (Ix a, Binary a, Binary b) => Binary (Array a b) where

     put_ bh arr = do

         put_ bh $ bounds arr

-        put_ bh $ elems arr

+        traverseArray_ (put_ bh) arr

+

     get bh = do

-        bounds <- get bh

-        xs <- get bh

-        return $ listArray bounds xs

+        (l, u) <- get bh

+        marr <- newGenArray (l, u) $ \_ -> get bh

+        unsafeFreezeIOArray marr

 instance Binary a => Binary (SmallArray a) where

     put_ bh sa = do