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Hi Archie!<br>
<br>
The C2 compiler can use <i>automatic vectorization</i> [1] to speed up such operations. You can watch my explanation of the concept in some of my recent presentations, e.g, [2]<br>
<br>
Best, Per</div>
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Automatic vectorization, in parallel computing, is a special case of automatic parallelization, where a computer program is converted from a scalar implementation, which processes a single pair of operands at a time, to a vector implementation, which processes
one operation on multiple pairs of operands at once. For example, modern conventional computers, including specialized supercomputers ...</div>
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[1] <a href="https://en.wikipedia.org/wiki/Automatic_vectorization" id="LPlnk162055">
https://en.wikipedia.org/wiki/Automatic_vectorization</a></div>
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[2] <a href="https://youtu.be/rXv2-lN5Xgk?t=1518" id="LPlnk773235">https://youtu.be/rXv2-lN5Xgk?t=1518</a></div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> core-libs-dev <core-libs-dev-retn@openjdk.org> on behalf of Archie Cobbs <archie.cobbs@gmail.com><br>
<b>Sent:</b> Thursday, May 22, 2025 10:58 PM<br>
<b>To:</b> John R Rose <jrose@openjdk.org><br>
<b>Cc:</b> core-libs-dev@openjdk.org <core-libs-dev@openjdk.org><br>
<b>Subject:</b> Re: RFR: 8357531: The `SegmentBulkOperations::fill` method can be improved using overlaps [v5]</font>
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<div dir="ltr">On Thu, May 22, 2025 at 3:31 PM John R Rose <<a href="mailto:jrose@openjdk.org">jrose@openjdk.org</a>> wrote:</div>
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<blockquote class="x_gmail_quote" style="margin:0px 0px 0px 0.8ex; border-left:1px solid rgb(204,204,204); padding-left:1ex">
> Update benchmark to reflect new fill method<br>
<br>
Related discussion at the hardware level:<br>
<br>
<a href="https://github.com/openjdk/jdk/pull/25147#issuecomment-2902463076" rel="noreferrer" target="_blank">https://github.com/openjdk/jdk/pull/25147#issuecomment-2902463076</a>
<br>
</blockquote>
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<div>This discussion spurred me to ask a dumb question. Apologies in advance, just trying to learn here...
<div><br>
</div>
<div>If I do this:</div>
<div><br>
</div>
<div style="margin-left:40px"><span style="font-family:monospace">import java.util.Arrays;<br>
public class ArrayFiller {<br>
public static void main(String[] args) {<br>
while (true) {<br>
final byte[] array = new byte[1000000];<br>
Arrays.fill(array, (byte)0x42);<br>
}<br>
}<br>
}<br>
</span></div>
<div><br>
</div>
<div>Will C2 compile <span style="font-family:monospace"><a href="https://github.com/openjdk/jdk/blob/139a05d05959a84541a29dfae6151f92ce579ae6/src/java.base/share/classes/java/util/Arrays.java#L3275-L3308">Arrays.fill()</a></span> into something that is more
efficient than a byte-at-a-time loop like what appears in the source code?</div>
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<div>Thanks,</div>
<div>-Archie</div>
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<span class="x_gmail_signature_prefix">-- </span><br>
<div dir="ltr" class="x_gmail_signature">Archie L. Cobbs<br>
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