Refactored in-mem backed to use the actual trie (#5730)

substrate/client/src/in_mem.rs

@@ -464,7 +464,7 @@ pub struct BlockImportOperation<Block: BlockT> {
 	pending_block: Option<PendingBlock<Block>>,
 	pending_cache: HashMap<CacheKeyId, Vec<u8>>,
 	old_state: InMemoryBackend<HashFor<Block>>,
-	new_state: Option<InMemoryBackend<HashFor<Block>>>,
+	new_state: Option<<InMemoryBackend<HashFor<Block>> as StateBackend<HashFor<Block>>>::Transaction>,
 	aux: Vec<(Vec<u8>, Option<Vec<u8>>)>,
 	finalized_blocks: Vec<(BlockId<Block>, Option<Justification>)>,
 	set_head: Option<BlockId<Block>>,
@@ -502,7 +502,7 @@ impl<Block: BlockT> backend::BlockImportOperation<Block> for BlockImportOperatio
 		&mut self,
 		update: <InMemoryBackend<HashFor<Block>> as StateBackend<HashFor<Block>>>::Transaction,
 	) -> sp_blockchain::Result<()> {
-		self.new_state = Some(self.old_state.update(update));
+		self.new_state = Some(update);
 		Ok(())
 	}
 
@@ -525,7 +525,7 @@ impl<Block: BlockT> backend::BlockImportOperation<Block> for BlockImportOperatio
 			child_delta
 		);
 
-		self.new_state = Some(InMemoryBackend::from(transaction));
+		self.new_state = Some(transaction);
 		Ok(root)
 	}
 
@@ -638,7 +638,12 @@ impl<Block: BlockT> backend::Backend<Block> for Backend<Block> where Block::Hash
 
 			let hash = header.hash();
 
-			self.states.write().insert(hash, operation.new_state.unwrap_or_else(|| old_state.clone()));
+			let new_state = match operation.new_state {
+				Some(state) => old_state.update_backend(*header.state_root(), state),
+				None => old_state.clone(),
+			};
+
+			self.states.write().insert(hash, new_state);
 
 			self.blockchain.insert(hash, header, justification, body, pending_block.state)?;
 		}