8336831: Optimize StringConcatHelper.simpleConcat

Reviewed-by: liach, redestad, rriggs
JinhangZhang · Jul 23, 2024 · 285c7e8 · 285c7e8
1 parent e40128d
commit 285c7e8
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Showing 2 changed files with 33 additions and 16 deletions.
diff --git a/src/java.base/share/classes/java/lang/String.java b/src/java.base/share/classes/java/lang/String.java
@@ -2987,7 +2987,7 @@ public String concat(String str) {
         if (str.isEmpty()) {
             return this;
         }
-        return StringConcatHelper.simpleConcat(this, str);
+        return StringConcatHelper.doConcat(this, str);
     }
 
     /**

diff --git a/src/java.base/share/classes/java/lang/StringConcatHelper.java b/src/java.base/share/classes/java/lang/StringConcatHelper.java
@@ -321,15 +321,24 @@ static String simpleConcat(Object first, Object second) {
             // newly created string required, see JLS 15.18.1
             return new String(s1);
         }
-        // start "mixing" in length and coder or arguments, order is not
-        // important
-        long indexCoder = mix(initialCoder(), s1);
-        indexCoder = mix(indexCoder, s2);
-        byte[] buf = newArray(indexCoder);
-        // prepend each argument in reverse order, since we prepending
-        // from the end of the byte array
-        indexCoder = prepend(indexCoder, buf, s2, s1);
-        return newString(buf, indexCoder);
+        return doConcat(s1, s2);
+    }
+
+    /**
+     * Perform a simple concatenation between two non-empty strings.
+     *
+     * @param s1         first argument
+     * @param s2         second argument
+     * @return String    resulting string
+     */
+    @ForceInline
+    static String doConcat(String s1, String s2) {
+        byte coder = (byte) (s1.coder() | s2.coder());
+        int newLength = (s1.length() + s2.length()) << coder;
+        byte[] buf = newArray(newLength);
+        s1.getBytes(buf, 0, coder);
+        s2.getBytes(buf, s1.length(), coder);
+        return new String(buf, coder);
     }
 
     /**
@@ -395,14 +404,22 @@ static byte[] newArrayWithSuffix(String suffix, long indexCoder) {
      */
     @ForceInline
     static byte[] newArray(long indexCoder) {
-        int index = (int)indexCoder;
-        if (indexCoder >= UTF16) {
-            index <<= 1;
-        }
-        if (index < 0) {
+        byte coder = (byte)(indexCoder >> 32);
+        int index = ((int)indexCoder) << coder;
+        return newArray(index);
+    }
+
+    /**
+     * Allocates an uninitialized byte array based on the length
+     * @param length
+     * @return the newly allocated byte array
+     */
+    @ForceInline
+    static byte[] newArray(int length) {
+        if (length < 0) {
             throw new OutOfMemoryError("Overflow: String length out of range");
         }
-        return (byte[]) UNSAFE.allocateUninitializedArray(byte.class, index);
+        return (byte[]) UNSAFE.allocateUninitializedArray(byte.class, length);
     }
 
     /**