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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - slow code for absolute value of int8 x 16 vector on POWER9 at -O3"
href="https://bugs.llvm.org/show_bug.cgi?id=50905">50905</a>
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<th>Summary</th>
<td>slow code for absolute value of int8 x 16 vector on POWER9 at -O3
</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>Windows NT
</td>
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<th>Status</th>
<td>NEW
</td>
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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: PowerPC
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>clang@evan.coeusgroup.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org, nemanja.i.ibm@gmail.com
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<p>
<div>
<pre>On POWER8 and below, this code generates the same code as vec_abs, but on
POWER9 the generate code is quite terrible. Compile with -mcpu=power9 -O3.
Example (or on Compiler Explorer: <a href="https://godbolt.org/z/avnTxh9M6">https://godbolt.org/z/avnTxh9M6</a>):
#include <stdint.h>
typedef int8_t i8x16 __attribute__((__vector_size__(16)));
i8x16
i8x16_abs(i8x16 a) {
i8x16 r;
for (int i = 0 ; i < 16 ; i++) {
r[i] = (a[i] < 0) ? -a[i] : a[i];
}
return r;
}
LLVM-MCA says RThroughput is 8, vs 1.5 for the POWER8 version.</pre>
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