core: only compute state root once (ethereum#30299)

This PR refactors the genesis initialization a bit, s.th. we only
compute the blockhash once instead of twice as before (during hashAlloc
and flushAlloc)

This will significantly reduce the amount of memory allocated during
genesis init

---------

Co-authored-by: Gary Rong <[email protected]>

core/genesis.go

@@ -145,13 +145,12 @@ func hashAlloc(ga *types.GenesisAlloc, isVerkle bool) (common.Hash, error) {
 	return statedb.Commit(0, false)
 }
 
-// flushAlloc is very similar with hash, but the main difference is all the generated
-// states will be persisted into the given database. Also, the genesis state
-// specification will be flushed as well.
-func flushAlloc(ga *types.GenesisAlloc, db ethdb.Database, triedb *triedb.Database, blockhash common.Hash) error {
+// flushAlloc is very similar with hash, but the main difference is all the
+// generated states will be persisted into the given database.
+func flushAlloc(ga *types.GenesisAlloc, db ethdb.Database, triedb *triedb.Database) (common.Hash, error) {
 	statedb, err := state.New(types.EmptyRootHash, state.NewDatabaseWithNodeDB(db, triedb), nil)
 	if err != nil {
-		return err
+		return common.Hash{}, err
 	}
 	for addr, account := range *ga {
 		if account.Balance != nil {
@@ -167,21 +166,15 @@ func flushAlloc(ga *types.GenesisAlloc, db ethdb.Database, triedb *triedb.Databa
 	}
 	root, err := statedb.Commit(0, false)
 	if err != nil {
-		return err
+		return common.Hash{}, err
 	}
 	// Commit newly generated states into disk if it's not empty.
 	if root != types.EmptyRootHash {
 		if err := triedb.Commit(root, true); err != nil {
-			return err
+			return common.Hash{}, err
 		}
 	}
-	// Marshal the genesis state specification and persist.
-	blob, err := json.Marshal(ga)
-	if err != nil {
-		return err
-	}
-	rawdb.WriteGenesisStateSpec(db, blockhash, blob)
-	return nil
+	return root, nil
 }
 
 func getGenesisState(db ethdb.Database, blockhash common.Hash) (alloc types.GenesisAlloc, err error) {
@@ -426,6 +419,11 @@ func (g *Genesis) ToBlock() *types.Block {
 	if err != nil {
 		panic(err)
 	}
+	return g.toBlockWithRoot(root)
+}
+
+// toBlockWithRoot constructs the genesis block with the given genesis state root.
+func (g *Genesis) toBlockWithRoot(root common.Hash) *types.Block {
 	head := &types.Header{
 		Number:     new(big.Int).SetUint64(g.Number),
 		Nonce:      types.EncodeNonce(g.Nonce),
@@ -482,8 +480,7 @@ func (g *Genesis) ToBlock() *types.Block {
 // Commit writes the block and state of a genesis specification to the database.
 // The block is committed as the canonical head block.
 func (g *Genesis) Commit(db ethdb.Database, triedb *triedb.Database) (*types.Block, error) {
-	block := g.ToBlock()
-	if block.Number().Sign() != 0 {
+	if g.Number != 0 {
 		return nil, errors.New("can't commit genesis block with number > 0")
 	}
 	config := g.Config
@@ -493,15 +490,22 @@ func (g *Genesis) Commit(db ethdb.Database, triedb *triedb.Database) (*types.Blo
 	if err := config.CheckConfigForkOrder(); err != nil {
 		return nil, err
 	}
-	if config.Clique != nil && len(block.Extra()) < 32+crypto.SignatureLength {
+	if config.Clique != nil && len(g.ExtraData) < 32+crypto.SignatureLength {
 		return nil, errors.New("can't start clique chain without signers")
 	}
-	// All the checks has passed, flushAlloc the states derived from the genesis
-	// specification as well as the specification itself into the provided
-	// database.
-	if err := flushAlloc(&g.Alloc, db, triedb, block.Hash()); err != nil {
+	// flush the data to disk and compute the state root
+	root, err := flushAlloc(&g.Alloc, db, triedb)
+	if err != nil {
+		return nil, err
+	}
+	block := g.toBlockWithRoot(root)
+
+	// Marshal the genesis state specification and persist.
+	blob, err := json.Marshal(g.Alloc)
+	if err != nil {
 		return nil, err
 	}
+	rawdb.WriteGenesisStateSpec(db, block.Hash(), blob)
 	rawdb.WriteTd(db, block.Hash(), block.NumberU64(), block.Difficulty())
 	rawdb.WriteBlock(db, block)
 	rawdb.WriteReceipts(db, block.Hash(), block.NumberU64(), nil)