core/state: perform updates before deletions when mutating tries (eth…

…ereum#29201)

This addresses an edge-case (detailed in the code comment) where the computation of the intermediate trie root would force the unnecessary resolution of a hash node. The change makes it so that when we process changes from a block, we first process trie-updates and afterwards process trie-deletions.

core/state/state_object.go

@@ -298,6 +298,18 @@ func (s *stateObject) updateTrie() (Trie, error) {
 	}
 	// Insert all the pending storage updates into the trie
 	usedStorage := make([][]byte, 0, len(s.pendingStorage))
+
+	// Perform trie updates before deletions.  This prevents resolution of unnecessary trie nodes
+	//  in circumstances similar to the following:
+	//
+	// Consider nodes `A` and `B` who share the same full node parent `P` and have no other siblings.
+	// During the execution of a block:
+	// - `A` is deleted,
+	// - `C` is created, and also shares the parent `P`.
+	// If the deletion is handled first, then `P` would be left with only one child, thus collapsed
+	// into a shortnode. This requires `B` to be resolved from disk.
+	// Whereas if the created node is handled first, then the collapse is avoided, and `B` is not resolved.
+	var deletions []common.Hash
 	for key, value := range s.pendingStorage {
 		// Skip noop changes, persist actual changes
 		if value == s.originStorage[key] {
@@ -307,13 +319,7 @@ func (s *stateObject) updateTrie() (Trie, error) {
 		s.originStorage[key] = value
 
 		var encoded []byte // rlp-encoded value to be used by the snapshot
-		if (value == common.Hash{}) {
-			if err := tr.DeleteStorage(s.address, key[:]); err != nil {
-				s.db.setError(err)
-				return nil, err
-			}
-			s.db.StorageDeleted += 1
-		} else {
+		if (value != common.Hash{}) {
 			// Encoding []byte cannot fail, ok to ignore the error.
 			trimmed := common.TrimLeftZeroes(value[:])
 			encoded, _ = rlp.EncodeToBytes(trimmed)
@@ -322,6 +328,8 @@ func (s *stateObject) updateTrie() (Trie, error) {
 				return nil, err
 			}
 			s.db.StorageUpdated += 1
+		} else {
+			deletions = append(deletions, key)
 		}
 		// Cache the mutated storage slots until commit
 		if storage == nil {
@@ -353,6 +361,13 @@ func (s *stateObject) updateTrie() (Trie, error) {
 		// Cache the items for preloading
 		usedStorage = append(usedStorage, common.CopyBytes(key[:])) // Copy needed for closure
 	}
+	for _, key := range deletions {
+		if err := tr.DeleteStorage(s.address, key[:]); err != nil {
+			s.db.setError(err)
+			return nil, err
+		}
+		s.db.StorageDeleted += 1
+	}
 	if s.db.prefetcher != nil {
 		s.db.prefetcher.used(s.addrHash, s.data.Root, usedStorage)
 	}

core/state/statedb.go

@@ -541,12 +541,11 @@ func (s *StateDB) updateStateObject(obj *stateObject) {
 }
 
 // deleteStateObject removes the given object from the state trie.
-func (s *StateDB) deleteStateObject(obj *stateObject) {
+func (s *StateDB) deleteStateObject(addr common.Address) {
 	// Track the amount of time wasted on deleting the account from the trie
 	defer func(start time.Time) { s.AccountUpdates += time.Since(start) }(time.Now())
 
 	// Delete the account from the trie
-	addr := obj.Address()
 	if err := s.trie.DeleteAccount(addr); err != nil {
 		s.setError(fmt.Errorf("deleteStateObject (%x) error: %v", addr[:], err))
 	}
@@ -917,16 +916,30 @@ func (s *StateDB) IntermediateRoot(deleteEmptyObjects bool) common.Hash {
 		}
 	}
 	usedAddrs := make([][]byte, 0, len(s.stateObjectsPending))
+	// Perform updates before deletions.  This prevents resolution of unnecessary trie nodes
+	// in circumstances similar to the following:
+	//
+	// Consider nodes `A` and `B` who share the same full node parent `P` and have no other siblings.
+	// During the execution of a block:
+	// - `A` self-destructs,
+	// - `C` is created, and also shares the parent `P`.
+	// If the self-destruct is handled first, then `P` would be left with only one child, thus collapsed
+	// into a shortnode. This requires `B` to be resolved from disk.
+	// Whereas if the created node is handled first, then the collapse is avoided, and `B` is not resolved.
+	var deletedAddrs []common.Address
 	for addr := range s.stateObjectsPending {
-		if obj := s.stateObjects[addr]; obj.deleted {
-			s.deleteStateObject(obj)
-			s.AccountDeleted += 1
-		} else {
+		if obj := s.stateObjects[addr]; !obj.deleted {
 			s.updateStateObject(obj)
 			s.AccountUpdated += 1
+		} else {
+			deletedAddrs = append(deletedAddrs, obj.address)
 		}
 		usedAddrs = append(usedAddrs, common.CopyBytes(addr[:])) // Copy needed for closure
 	}
+	for _, deletedAddr := range deletedAddrs {
+		s.deleteStateObject(deletedAddr)
+		s.AccountDeleted += 1
+	}
 	if prefetcher != nil {
 		prefetcher.used(common.Hash{}, s.originalRoot, usedAddrs)
 	}