trie/bintrie: use a sync.Pool when hashing binary tree nodes (#33989)

Binary tree hashing is quite slow, owing to many factors. One of them is
the GC pressure that is the consequence of allocating many hashers, as a
binary tree has 4x the size of an MPT. This PR introduces an
optimization that already exists for the MPT: keep a pool of hashers, in
order to reduce the amount of allocations.

trie/bintrie/hasher.go

@@ -0,0 +1,39 @@
+// Copyright 2026 go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package bintrie
+
+import (
+	"crypto/sha256"
+	"hash"
+	"sync"
+)
+
+var sha256Pool = sync.Pool{
+	New: func() any {
+		return sha256.New()
+	},
+}
+
+func newSha256() hash.Hash {
+	h := sha256Pool.Get().(hash.Hash)
+	h.Reset()
+	return h
+}
+
+func returnSha256(h hash.Hash) {
+	sha256Pool.Put(h)
+}

trie/bintrie/internal_node.go

@@ -17,7 +17,6 @@
 package bintrie
 
 import (
-	"crypto/sha256"
 	"errors"
 	"fmt"
 
@@ -125,7 +124,8 @@ func (bt *InternalNode) Hash() common.Hash {
 		return bt.hash
 	}
 
-	h := sha256.New()
+	h := newSha256()
+	defer returnSha256(h)
 	if bt.left != nil {
 		h.Write(bt.left.Hash().Bytes())
 	} else {

trie/bintrie/key_encoding.go

@@ -18,7 +18,6 @@ package bintrie
 
 import (
 	"bytes"
-	"crypto/sha256"
 
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/holiman/uint256"
@@ -51,7 +50,8 @@ func GetBinaryTreeKey(addr common.Address, key []byte) []byte {
 }
 
 func getBinaryTreeKey(addr common.Address, offset []byte, overflow bool) []byte {
-	hasher := sha256.New()
+	hasher := newSha256()
+	defer returnSha256(hasher)
 	hasher.Write(zeroHash[:12])
 	hasher.Write(addr[:])
 	var buf [32]byte

trie/bintrie/stem_node.go

@@ -18,7 +18,6 @@ package bintrie
 
 import (
 	"bytes"
-	"crypto/sha256"
 	"errors"
 	"fmt"
 	"slices"
@@ -114,14 +113,17 @@ func (bt *StemNode) Hash() common.Hash {
 	}
 
 	var data [StemNodeWidth]common.Hash
+	h := newSha256()
+	defer returnSha256(h)
 	for i, v := range bt.Values {
 		if v != nil {
-			h := sha256.Sum256(v)
-			data[i] = common.BytesToHash(h[:])
+			h.Reset()
+			h.Write(v)
+			h.Sum(data[i][:0])
 		}
 	}
+	h.Reset()
 
-	h := sha256.New()
 	for level := 1; level <= 8; level++ {
 		for i := range StemNodeWidth / (1 << level) {
 			h.Reset()