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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Vectorization improvement opportunity for max/min"
href="https://bugs.llvm.org/show_bug.cgi?id=35284">35284</a>
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<th>Summary</th>
<td>Vectorization improvement opportunity for max/min
</td>
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Backend: X86
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>serguei.katkov@azul.com
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<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>This is about possibly better vectorization coding for float/double max/min.
Let's consider the following c++ program (<a href="https://godbolt.org/g/yWxTCB">https://godbolt.org/g/yWxTCB</a>):
float test(float a[], int N) {
float max = -1;
for (int i = 0; i < N; i++)
max = max < a[i] ? a[i] : max;
return max;
}
clang trunk now generates a main loop with the following pattern:
movss + maxss (N times, where N might be 4 or 8).
icc 18 is able to use maxps packed instruction.
Even the code looking as:
movss 16 times (load values to xmm0-xmm15 registers)
ucommiss + ga (16 times)
and movaps in case of ga on slowpath
seems might be better.
I do not know what code would be best here but potentially there is an
opportunity here...</pre>
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