Eliminate need for custom mealy, fixing laziness

The old `mealy'` was too strict in its input. By wrapping `IntMap` in a
`newtype` we can define an `NFDataX` instance for it, allowing the use of
`clash-prelude`'s `mealy`.

clash-vexriscv-sim/src/Utils/Storage.hs

@@ -2,17 +2,39 @@
 --
 -- SPDX-License-Identifier: Apache-2.0
 
-{-# LANGUAGE RecordWildCards #-}
 {-# LANGUAGE ApplicativeDo #-}
-module Utils.Storage where
+{-# LANGUAGE RecordWildCards #-}
+
+module Utils.Storage
+  ( storage
+  ) where
 
 import Clash.Prelude
 
+import Protocols.Wishbone
+import GHC.Stack (HasCallStack)
+
 import qualified Data.List as L
 import qualified Data.IntMap.Strict as I
 
-import Clash.Signal.Internal (Signal((:-)))
-import Protocols.Wishbone
+newtype MappedMemory = MappedMemory (I.IntMap (BitVector 8))
+
+unMappedMemory :: MappedMemory -> I.IntMap (BitVector 8)
+unMappedMemory (MappedMemory x) = x
+
+instance NFDataX MappedMemory where
+  -- Not a product type, so no spine
+  deepErrorX = errorX
+
+  -- Keys are 'Int's and evaluated to WHNF because this is a strict map. For 'Int's,
+  -- WHNF ~ NF, so we only need to check the values.
+  hasUndefined = any hasUndefined . I.elems . unMappedMemory
+
+  -- Not a product type, so no spine
+  ensureSpine = id
+
+  -- This is a strict map, so we dont need to do anything
+  rnfX x = seq x ()
 
 storage ::
   forall dom.
@@ -23,26 +45,34 @@ storage ::
   -- ^ contents
   Signal dom (WishboneM2S 32 4 (BitVector 32)) ->
   Signal dom (WishboneS2M (BitVector 32))
-storage contents = mealy' go (I.fromAscList $ L.zip [0..] contents)
+storage contents = mealy go (MappedMemory $ I.fromAscList $ L.zip [0..] contents)
  where
   size = L.length contents
 
-  -- Version of mealy that doesn't require NFDataX for the state.
-  -- This is needed because IntMap (Word8) does not implement NFDataX
-  mealy' fn st0 (i :- is) = o :- mealy' fn st1 is 
-    where (st1, o) = fn st0 i
-
-  go mem WishboneM2S{..}
-    | not (busCycle && strobe)        = (mem, emptyWishboneS2M)
-    | addr >= fromIntegral size       = (mem, emptyWishboneS2M { err = True })
+  go (MappedMemory mem) WishboneM2S{..}
+    | not (busCycle && strobe)        = (MappedMemory mem, emptyWishboneS2M)
+    | addr >= fromIntegral size       =
+        (MappedMemory mem, emptyWishboneS2M { err = True })
     | not writeEnable      {- read -} =
         case readDataSel mem addr busSelect of
-          Nothing -> (mem, emptyWishboneS2M { err = True })
-          Just x -> (mem, (emptyWishboneS2M @(BitVector 32)) { acknowledge = True, readData = x })
+          Nothing -> (MappedMemory mem, emptyWishboneS2M { err = True })
+          Just x -> (MappedMemory mem, (emptyWishboneS2M @(BitVector 32)) { acknowledge = True, readData = x })
     | otherwise           {- write -} =
-        (writeDataSel mem addr busSelect writeData, emptyWishboneS2M { acknowledge = True })
+        ( MappedMemory (writeDataSel mem addr busSelect writeData)
+        , emptyWishboneS2M { acknowledge = True }
+        )
 
-readDataSel :: I.IntMap (BitVector 8) -> BitVector 32 -> BitVector 4 -> Maybe (BitVector 32)
+readDataSel ::
+  HasCallStack =>
+  -- | Memory
+  I.IntMap (BitVector 8) ->
+  -- | Address
+  BitVector 32 ->
+  -- | Byte enables (@SEL@)
+  BitVector 4 ->
+  -- | Read value, or 'Nothing' if the read is invalid due to an unsupported
+  -- value of @SEL@.
+  Maybe (BitVector 32)
 readDataSel mem addr sel =
   case sel of
     0b0001 -> readByte (addr + 0)
@@ -52,8 +82,8 @@ readDataSel mem addr sel =
     0b0011 -> readWord (addr + 0)
     0b1100 -> readWord (addr + 2)
     0b1111 -> readDWord addr
-    _                    -> Nothing
-  
+    _      -> Nothing
+
   where
     readByte addr' = resize @_ @8 @32 <$> I.lookup (fromIntegral addr') mem
     readWord addr' = do
@@ -65,7 +95,18 @@ readDataSel mem addr sel =
       h <- readWord (addr' + 0)
       pure $ h `shiftL` 16 .|. l
 
-writeDataSel :: I.IntMap (BitVector 8) -> BitVector 32 -> BitVector 4 -> BitVector 32 -> I.IntMap (BitVector 8)
+writeDataSel ::
+  HasCallStack =>
+  -- | Memory
+  I.IntMap (BitVector 8) ->
+  -- | Address
+  BitVector 32 ->
+  -- | Byte enables (SEL)
+  BitVector 4 ->
+  -- | Value to write
+  BitVector 32 ->
+  -- | Updated memory
+  I.IntMap (BitVector 8)
 writeDataSel mem addr sel val =
   case sel of
     0b0001 ->
@@ -87,7 +128,7 @@ writeDataSel mem addr sel val =
       I.insert (fromIntegral $ addr + 2) lh $
       I.insert (fromIntegral $ addr + 1) hl $
       I.insert (fromIntegral $ addr + 0) hh mem
-    _ -> mem
-  
+    _ -> error $ "Got SEL = " <> show sel <> " which is unsupported"
+
   where
     (hh :: BitVector 8, hl :: BitVector 8, lh :: BitVector 8, ll :: BitVector 8) = unpack val