I'll let others knowledgeable in this area to comment and provide inputs
to this proposal. I just want to say thank you for bringing up this
discussion to the mailing list first, providing the necessary context
and explanation and seeking feedback, before creating a JBS issue or a
RFR PR.
-Jaikiran
On 30/07/25 7:48 pm, wenshao wrote:
In the discussion of `8355177: Speed up StringBuilder::append(char[])
via Unsafe::copyMemory` (https://github.com/openjdk/jdk/pull/24773),
@liach (Chen Liang) suggested reusing the StringUTF16::putCharsSB
method introduced in PR #24773 instead of the Intrinsic implementation
in the StringUTF16::toBytes method.
Original:
```java
@IntrinsicCandidate
public static byte[] toBytes(char[] value, int off, int len) {
byte[] val = newBytesFor(len);
for (int i = 0; i < len; i++) {
putChar(val, i, value[off]);
off++;
}
return val;
}
```
After:
```java
public static byte[] toBytes(char[] value, int off, int len) {
byte[] val = (byte[])
Unsafe.getUnsafe().allocateUninitializedArray(byte.class,
newBytesLength(len));
putCharsSB(val, 0, value, off, off + len);
return val;
}
```
This replacement does not degrade performance. Running
StringConstructor.newStringFromCharsMixedBegin verified that
performance is consistent with the original on x64 and slightly
improved on aarch64.
The implementation after replacing the Intrinsic implementation
removed 100 lines of C++ code, leaving only Java and Unsafe code, no
Intrinsic or C++ code, which makes the code more maintainable.
I've submitted a draft PR https://github.com/openjdk/jdk/pull/26553 ,
please give me some feedback.
-
Shaojin Wen
