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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Handling doacross loops: no collapse"
href="https://bugs.llvm.org/show_bug.cgi?id=37580">37580</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Handling doacross loops: no collapse
</td>
</tr>
<tr>
<th>Product</th>
<td>OpenMP
</td>
</tr>
<tr>
<th>Version</th>
<td>unspecified
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Clang Compiler Support
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>protze@itc.rwth-aachen.de
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>#include <stdio.h>
#include <omp.h>
int main()
{
int i, j;
#pragma omp parallel for ordered(2) num_threads(2) schedule(static,1) \
private(i,j)
for (i = 0; i < 10; i++)
for (j = 0; j < 10; j++)
{
#pragma omp ordered depend(sink:i-1,j) depend (sink:i,j-1)
printf ("test %i i=%d j=%d\n",omp_get_thread_num(),i,j);
#pragma omp ordered depend(source)
}
return 0;
}
According to the OpenMP spec, this code should execute i=0 and i=2 on thread 0
and i=1, i=3 on thread 1. The ordered(2) clause does not change the scheduling.
The behavior of clang looks like collapse(2) is implied.
-> expected behavior: i is distributed between the threads,
-> observed behavior: j is distributed between the threads.
Since icc in combination with the same (LLVM) OpenMP runtime provides correct
behavior (besides a bug in privatization of j), this should be a compiler bug
in clang.
Also, explicitly adding collapse(1) does not help.</pre>
</div>
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