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<p>If I use the same example but with negative stride:</p>
<p><br>
</p>
<p>```</p>
<p><span style="font-size:12pt">for (int i = iters - 1; i >= 0; --i) {</span></p>
<p><span style="font-size:12pt"> blackhole(data[i]);</span></p>
<p></p>
<div>}</div>
<div>```</div>
<div><br>
</div>
<div>We still generate these two checks:</div>
```
<p></p>
<p></p>
<div>if (data.length <= 0) { trap() }</div>
<div><span style="font-size:12pt">if (data.length <= iters - 1) { trap() }</span></div>
<p></p>
<p>```</p>
<p><br>
</p>
<p>So even with negative stride, the upper bounds check is sufficient by itself.</p>
<p><br>
</p>
<p>I am playing around with stride/scale/offset and I cannot come up with an </p>
<p>example where the lower bounds check is important.</p>
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<div id="x_divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> hotspot-compiler-dev <hotspot-compiler-dev-retn@openjdk.org> on behalf of Vladimir Kozlov <vladimir.kozlov@oracle.com><br>
<b>Sent:</b> Thursday, February 1, 2024 11:44:29 AM<br>
<b>To:</b> hotspot-compiler-dev@openjdk.org<br>
<b>Subject:</b> RE: [EXTERNAL] What is the purpose of loop predication lower bounds check</font>
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<br>
<br>
<br>
Initial index value is variable.<br>
<br>
Reverse (negative stride) processing of array?<br>
<br>
On 2/1/24 11:31 AM, Cao, Joshua wrote:<br>
> Can I get some help with <a href="https://bugs.openjdk.org/browse/JDK-8325146?">
https://bugs.openjdk.org/browse/JDK-8325146?</a><br>
> What is<br>
> the purpose of the lower bounds check for loop predication? It seems like an<br>
> unnecessary if-check for any example I can come up with.<br>
><br>
> Whatever the reason might be, I think there are cases in which we can ellide<br>
> the lower bounds check, like in the example in the JBS issue.<br>
><br>
><br>
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