<div class="__aliyun_email_body_block"><div style="font-family: Tahoma, Arial, STHeitiSC-Light, SimSun"><div style="clear: both; font-family: Tahoma, Arial, STHeitiSC-Light, SimSun;"><span style="font-family: Tahoma, Arial, STHeitiSC-Light, SimSun;"><span >Thanks to Roger Riggs for suggesting that the code should not be called with Unsafe.uninitializedArray.</span></span></div><div style="clear: both; font-family: Tahoma, Arial, STHeitiSC-Light, SimSun;"><span style="font-family: Tahoma, Arial, STHeitiSC-Light, SimSun;"><span ><br ></span></span></div><div style="clear: both; font-family: Tahoma, Arial, STHeitiSC-Light, SimSun;"><span style="font-family: Tahoma, Arial, STHeitiSC-Light, SimSun;"><span >After replacing it with `new byte[]` and running `StringConstructor.newStringFromCharsMixedBegin`, I verified that performance remained consistent on x64. On aarch64, performance improved by 8% for size = 7, but decreased by 7% for size = 64.</span></span></div><div style="clear: both; font-family: Tahoma, Arial, STHeitiSC-Light, SimSun;"><span style="font-family: Tahoma, Arial, STHeitiSC-Light, SimSun;"><span ><br ></span></span></div><div style="clear: both; font-family: Tahoma, Arial, STHeitiSC-Light, SimSun;"><span style="font-family: Tahoma, Arial, STHeitiSC-Light, SimSun;"><span ><span >For detailed performance data, see the Markdown data in the draft pull request I submitted.</span><span ><a href="https://github.com/openjdk/jdk/pull/26553#issuecomment-3138357748" target="_blank">https://github.com/openjdk/jdk/pull/26553#issuecomment-3138357748</a></span></span></span></div><div style="clear: both; font-family: Tahoma, Arial, STHeitiSC-Light, SimSun;"><span style="font-family: Tahoma, Arial, STHeitiSC-Light, SimSun;"><span ><br ></span></span></div><div style="clear: both; font-family: Tahoma, Arial, STHeitiSC-Light, SimSun;"><span style="font-family: Tahoma, Arial, STHeitiSC-Light, SimSun;"><span >-</span></span></div><div style="clear: both; font-family: Tahoma, Arial, STHeitiSC-Light, SimSun;"><span style="font-family: Tahoma, Arial, STHeitiSC-Light, SimSun;"><span >Shaojin Wen</span></span></div><div style="clear: both; font-family: Tahoma, Arial, STHeitiSC-Light, SimSun;"><span style="font-family: Tahoma, Arial, STHeitiSC-Light, SimSun;"><br ></span></div><blockquote _quote="1" style="margin-right: 0px; margin-top: 0px; margin-bottom: 0px; font-family: Tahoma, Arial, STHeiti, SimSun; font-size: 14px; color: rgb(0, 0, 0);"><div class="alimail-quote"><div style="clear: both;">------------------------------------------------------------------</div><div style="clear: both;">发件人：Roger Riggs <roger.riggs@oracle.com></div><div style="clear: both;">发送时间：2025年7月31日(周四) 03:17</div><div style="clear: both;">收件人："core-libs-dev"<core-libs-dev@openjdk.org></div><div style="clear: both;">主 题：Re: Reuse the StringUTF16::putCharsSB method instead of the Intrinsic in the StringUTF16::toBytes</div><div style="clear: both;"><br ></div>Hi,<br >
<br >
Unsafe.uninitializedArray and StringConcatHelper.newArray was
created for the exclusive use of StringConcatHelper and by HotSpot
optimizations. Unsafe.uninitializedArray and
StringConcatHelper.newArray area very sensitive APIs and should NOT
be used anywhere except in StringConcatHelper and HotSpot.<br >
<br >
Regards, Roger<br >
<br >
<br >
<div class="moz-cite-prefix">On 7/30/25 11:40 AM,
<a class="moz-txt-link-abbreviated" href="mailto:jaikiran.pai@oracle.com" target="_blank">jaikiran.pai@oracle.com</a> wrote:<br >
</div>
<div style="margin: 14px 0px;">
<p style="margin-top: 14px; margin-bottom: 14px;">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.</p>
<p style="margin-top: 14px; margin-bottom: 14px;">-Jaikiran<br >
</p>
<div class="moz-cite-prefix">On 30/07/25 7:48 pm, wenshao wrote:<br >
</div>
<div style="font-family: Tahoma, Arial, STHeitiSC-Light, SimSun;">
<div style="clear: both;"><span >In the discussion of
`8355177: Speed up StringBuilder::append(char[]) via
Unsafe::copyMemory` (<a class="moz-txt-link-freetext" href="https://github.com/openjdk/jdk/pull/24773" target="_blank">https://github.com/openjdk/jdk/pull/24773</a>),
@liach (<span >Chen Liang)</span> suggested reusing the
StringUTF16::putCharsSB method introduced in PR #24773
instead of the Intrinsic implementation in the
StringUTF16::toBytes method.</span>
<div style="clear: both;"><br >
</div>
<div style="clear: both;"><span >Original:</span>
<div style="clear: both;">```java</div>
<div style="clear: both;"> @IntrinsicCandidate</div>
<div style="clear: both;"> public static byte[]
toBytes(char[] value, int off, int len) {</div>
<div style="clear: both;"> byte[] val =
newBytesFor(len);</div>
<div style="clear: both;"> for (int i = 0; i <
len; i++) {</div>
<div style="clear: both;"> putChar(val, i,
value[off]);</div>
<div style="clear: both;"> off++;</div>
<div style="clear: both;"> }</div>
<div style="clear: both;"> return val;</div>
<div style="clear: both;"> }</div>
<div style="clear: both;">```</div>
<div style="clear: both;"><br >
</div>
<div style="clear: both;">After:</div>
<div style="clear: both;">```java</div>
<div style="clear: both;"> public static byte[]
toBytes(char[] value, int off, int len) {</div>
<div style="clear: both;"> byte[] val = (byte[])
Unsafe.getUnsafe().allocateUninitializedArray(byte.class,
newBytesLength(len));</div>
<div style="clear: both;"> putCharsSB(val, 0,
value, off, off + len);</div>
<div style="clear: both;"> return val;</div>
<div style="clear: both;"> }</div>
<span >```</span></div>
<div style="clear: both;"><br >
</div>
<div style="clear: both;">This replacement does not
degrade performance. Running
StringConstructor.newStringFromCharsMixedBegin verified
that performance is consistent with the original on x64
and slightly improved on aarch64.</div>
<div style="clear: both;"><br >
</div>
<span >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.</span></div>
<div style="clear: both;"><span ><br >
</span></div>
<div style="clear: both;"><span ><span >I've submitted a draft
PR </span><span ><a class="moz-txt-link-freetext" href="https://github.com/openjdk/jdk/pull/26553" target="_blank">https://github.com/openjdk/jdk/pull/26553</a>
, please give me some feedback.</span></span></div>
<div style="clear: both;"><span >-</span></div>
<div style="clear: both;"><span >Shaojin Wen</span></div>
</div>
</div>
<br >
</div></blockquote><div style="line-height: 20px; clear: both;"><br ></div></div></div>