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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Handling doacross loops: dependencies"
href="https://bugs.llvm.org/show_bug.cgi?id=37582">37582</a>
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<th>Summary</th>
<td>Handling doacross loops: dependencies
</td>
</tr>
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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
</td>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Clang Compiler Support
</td>
</tr>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<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>Besides the issue of wrong scheduling as described in
<a class="bz_bug_link
bz_status_NEW "
title="NEW - Handling doacross loops: no collapse"
href="show_bug.cgi?id=37580">https://bugs.llvm.org/show_bug.cgi?id=37580</a>, the loop iterations could overlap,
based on the dendencies expresses by the depend clause:
#include <stdio.h>
#include <omp.h>
int main()
{
int i, j;
#pragma omp parallel for ordered(2) num_threads(2) schedule(static,10)
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;
}
Using schedule(static,10), I get the work distribution which I would expect for
static,1 (after fixing the other issue). The code is executed completely
sequential. While this is not wrong, the execution could do better.
-> expected behavior: thread 1 starts working on (i=1, j=0) as soon as thread 0
finished (i=0, j=0)
-> observed behavior: thread 1 starts working on (i=1, j=0) only after thread 0
finished the whole iteration i=0 and vice versa
icc using the same OpenMP runtime provides the expected behavior. So this
should be a missing feature in the compiler.</pre>
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