trie: reduce allocs in recHash (#27770)

trie/encoding.go

@@ -51,9 +51,8 @@ func hexToCompact(hex []byte) []byte {
 	return buf
 }
 
-// hexToCompactInPlace places the compact key in input buffer, returning the length
+// hexToCompactInPlace places the compact key in input buffer, returning the compacted key.
-// needed for the representation
+func hexToCompactInPlace(hex []byte) []byte {
-func hexToCompactInPlace(hex []byte) int {
 	var (
 		hexLen    = len(hex) // length of the hex input
 		firstByte = byte(0)
@@ -77,7 +76,7 @@ func hexToCompactInPlace(hex []byte) int {
 		hex[bi] = hex[ni]<<4 | hex[ni+1]
 	}
 	hex[0] = firstByte
-	return binLen
+	return hex[:binLen]
 }
 
 func compactToHex(compact []byte) []byte {

trie/encoding_test.go

@@ -86,8 +86,7 @@ func TestHexToCompactInPlace(t *testing.T) {
 	} {
 		hexBytes, _ := hex.DecodeString(key)
 		exp := hexToCompact(hexBytes)
-		sz := hexToCompactInPlace(hexBytes)
+		got := hexToCompactInPlace(hexBytes)
-		got := hexBytes[:sz]
 		if !bytes.Equal(exp, got) {
 			t.Fatalf("test %d: encoding err\ninp %v\ngot %x\nexp %x\n", i, key, got, exp)
 		}
@@ -102,8 +101,7 @@ func TestHexToCompactInPlaceRandom(t *testing.T) {
 		hexBytes := keybytesToHex(key)
 		hexOrig := []byte(string(hexBytes))
 		exp := hexToCompact(hexBytes)
-		sz := hexToCompactInPlace(hexBytes)
+		got := hexToCompactInPlace(hexBytes)
-		got := hexBytes[:sz]
 
 		if !bytes.Equal(exp, got) {
 			t.Fatalf("encoding err \ncpt %x\nhex %x\ngot %x\nexp %x\n",
@@ -119,6 +117,13 @@ func BenchmarkHexToCompact(b *testing.B) {
 	}
 }
 
+func BenchmarkHexToCompactInPlace(b *testing.B) {
+	testBytes := []byte{0, 15, 1, 12, 11, 8, 16 /*term*/}
+	for i := 0; i < b.N; i++ {
+		hexToCompactInPlace(testBytes)
+	}
+}
+
 func BenchmarkCompactToHex(b *testing.B) {
 	testBytes := []byte{0, 15, 1, 12, 11, 8, 16 /*term*/}
 	for i := 0; i < b.N; i++ {

trie/stacktrie.go

@@ -444,7 +444,7 @@ func (st *StackTrie) hashRec(hasher *hasher, path []byte) {
 	case extNode:
 		st.children[0].hashRec(hasher, append(path, st.key...))
 
-		n := shortNode{Key: hexToCompact(st.key)}
+		n := shortNode{Key: hexToCompactInPlace(st.key)}
 		if len(st.children[0].val) < 32 {
 			n.Val = rawNode(st.children[0].val)
 		} else {
@@ -460,7 +460,7 @@ func (st *StackTrie) hashRec(hasher *hasher, path []byte) {
 
 	case leafNode:
 		st.key = append(st.key, byte(16))
-		n := shortNode{Key: hexToCompact(st.key), Val: valueNode(st.val)}
+		n := shortNode{Key: hexToCompactInPlace(st.key), Val: valueNode(st.val)}
 
 		n.encode(hasher.encbuf)
 		encodedNode = hasher.encodedBytes()