8355177: Speed up StringBuilder::append(char[]) via UTF16::compress & Unsafe::copyMemory

src/java.base/share/classes/java/lang/AbstractStringBuilder.java

@@ -1,5 +1,6 @@
 /*
- * Copyright (c) 2003, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2003, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2025, Alibaba Group Holding Limited. All Rights Reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -1767,6 +1768,9 @@ private final void appendChars(char[] s, int off, int end) {
         int count = this.count;
         if (isLatin1()) {
             byte[] val = this.value;
+            int compressed = StringUTF16.compress(s, off, val, count, end - off);
+            count += compressed;
+            off += compressed;
             for (int i = off, j = count; i < end; i++) {
                 char c = s[i];
                 if (StringLatin1.canEncode(c)) {

src/java.base/share/classes/java/lang/StringUTF16.java

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2015, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2025, Alibaba Group Holding Limited. All Rights Reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -1312,10 +1313,13 @@ static Stream<String> lines(byte[] value) {
         return StreamSupport.stream(LinesSpliterator.spliterator(value), false);
     }
 
-    private static void putChars(byte[] val, int index, char[] str, int off, int end) {
-        while (off < end) {
-            putChar(val, index++, str[off++]);
-        }
+    private static void putCharsUnchecked(byte[] val, int index, char[] str, int off, int end) {
+        Unsafe.getUnsafe().copyMemory(
+                str,
+                Unsafe.ARRAY_CHAR_BASE_OFFSET + ((long) off << 1),
+                val,
+                Unsafe.ARRAY_BYTE_BASE_OFFSET + ((long) index << 1),
+                ((long) (end - off)) << 1);
     }
 
     public static String newString(byte[] val, int index, int len) {
@@ -1490,7 +1494,8 @@ public static void putCharSB(byte[] val, int index, int c) {
 
     public static void putCharsSB(byte[] val, int index, char[] ca, int off, int end) {
         checkBoundsBeginEnd(index, index + end - off, val);
-        putChars(val, index, ca, off, end);
+        checkBoundsBeginEnd(off, end, ca);
+        putCharsUnchecked(val, index, ca, off, end);
     }
 
     public static void putCharsSB(byte[] val, int index, CharSequence s, int off, int end) {
@@ -1666,6 +1671,10 @@ public static void checkBoundsBeginEnd(int begin, int end, byte[] val) {
         String.checkBoundsBeginEnd(begin, end, length(val));
     }
 
+    private static void checkBoundsBeginEnd(int begin, int end, char[] val) {
+        String.checkBoundsBeginEnd(begin, end, val.length);
+    }
+
     public static void checkBoundsOffCount(int offset, int count, byte[] val) {
         String.checkBoundsOffCount(offset, count, length(val));
     }

test/micro/org/openjdk/bench/java/lang/StringBuilders.java

@@ -1,5 +1,6 @@
 /*
- * Copyright (c) 2014, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2014, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2025, Alibaba Group Holding Limited. All Rights Reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -50,6 +51,7 @@ public class StringBuilders {
     private String[] str16p8p7;
     private String[] str3p9p8;
     private String[] str22p40p31;
+    private char[][] charArray22p40p31;
     private StringBuilder sbLatin1;
     private StringBuilder sbLatin2;
     private StringBuilder sbUtf16;
@@ -63,10 +65,15 @@ public void setup() {
                 "advise", "you", "to", "drive", "at", "top", "speed", "it'll",
                 "be", "a", "god", "damn", "miracle", "if", "we", "can", "get",
                 "there", "before", "you", "turn", "into", "a", "wild", "animal."};
+
         str3p4p2 = new String[]{"123", "1234", "12"};
         str16p8p7 = new String[]{"1234567890123456", "12345678", "1234567"};
         str3p9p8 = new String[]{"123", "123456789", "12345678"};
         str22p40p31 = new String[]{"1234567890123456789012", "1234567890123456789012345678901234567890", "1234567890123456789012345678901"};
+        charArray22p40p31 = new char[str22p40p31.length][];
+        for (int i = 0; i < str22p40p31.length; i++) {
+            charArray22p40p31[i] = str22p40p31[i].toCharArray();
+        }
         sbLatin1 = new StringBuilder("Latin1 string");
         sbLatin2 = new StringBuilder("Latin1 string");
         sbUtf16 = new StringBuilder("UTF-\uFF11\uFF16 string");
@@ -273,6 +280,26 @@ public int appendWithLongUtf16() {
         return buf.length();
     }
 
+    @Benchmark
+    public int appendWithCharArrayLatin1() {
+        StringBuilder buf = sbLatin1;
+        buf.delete(0, buf.length());
+        for (char[] charArray : charArray22p40p31) {
+            buf.append(charArray);
+        }
+        return buf.length();
+    }
+
+    @Benchmark
+    public int appendWithCharArrayUTF16() {
+        StringBuilder buf = sbUtf16;
+        buf.delete(0, buf.length());
+        for (char[] charArray : charArray22p40p31) {
+            buf.append(charArray);
+        }
+        return buf.length();
+    }
+
     @Benchmark
     public String toStringCharWithBool8() {
         StringBuilder result = new StringBuilder();