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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [OpenMP] UB when hidden helper threads is 1"
href="https://bugs.llvm.org/show_bug.cgi?id=49312">49312</a>
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<th>Summary</th>
<td>[OpenMP] UB when hidden helper threads is 1
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<th>Product</th>
<td>OpenMP
</td>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>PC
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<th>OS</th>
<td>Linux
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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>Runtime Library
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>rofirrim@gmail.com
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<p>
<div>
<pre>Hi,
while investigating another issue, we found that the macro
`KMP_GTID_TO_SHADOW_GTID` is defined in `kmp.h` as follows
#define KMP_GTID_TO_SHADOW_GTID(gtid)
((gtid) % (__kmp_hidden_helper_threads_num - 1) + 2)
When there is only one helper thread the macro attempts to compute `(gtid % 0)
- 2`. Setting the environment variable `LIBOMP_NUM_HIDDEN_HELPER_THREADS` to
`1` should be enough to trigger this.
Perhaps using only one helper thread is not valid?</pre>
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