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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - OpenMP doacross loop nest with a decreasing induction variable abends"
href="https://bugs.llvm.org/show_bug.cgi?id=45132">45132</a>
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<th>Summary</th>
<td>OpenMP doacross loop nest with a decreasing induction variable abends
</td>
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<th>Product</th>
<td>clang
</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
</td>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>OpenMP
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>t-kawashima@fujitsu.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<pre>Created <span class=""><a href="attachment.cgi?id=23210" name="attach_23210" title="doacross.1.c in OpenMP 4.5 exmaples with reverse-order modification">attachment 23210</a> <a href="attachment.cgi?id=23210&action=edit" title="doacross.1.c in OpenMP 4.5 exmaples with reverse-order modification">[details]</a></span>
doacross.1.c in OpenMP 4.5 exmaples with reverse-order modification
[Envinronment]
OS: Linux
CPU: x86_64 and AArch64
LLVM/Clang/OpenMP: latest master branch (commit cfff4851acc)
The attached program `doacross.reverse.c` is a modified version of
`doacross.1.c` in the official 'OpenMP Examples Version 4.5.0' (page 194)
<<a href="https://github.com/OpenMP/Examples/blob/v4.5.0/sources/Example_doacross.1.c">https://github.com/OpenMP/Examples/blob/v4.5.0/sources/Example_doacross.1.c</a>>.
The modified points are:
- decrease the induction variable `i` (see the diff below)
- change `depend(sink: i+1)` to depend(sink: i-1) (see the diff below)
- implement `foo`, `bar`, `baz`, and `main`
--------------------------------
#pragma omp for ordered(1)
- for (i=N-1; i>1; i--)
+ for (i=1; i<N; i++)
{
A[i] = foo(i);
- #pragma omp ordered depend(sink: i+1)
+ #pragma omp ordered depend(sink: i-1)
B[i] = bar(A[i], B[i-1]);
#pragma omp ordered depend(source)
C[i] = baz(B[i]);
}
--------------------------------
When this program is compiled with -fopenmp and executed, a segmentation fault
occurs.
--------------------------------
$ clang -fopenmp doacross.reverse.c
$ ./a.out
Segmentation fault
--------------------------------
The number of threads is irrelevant. I can reproduce it with OMP_NUM_THREADS=2.</pre>
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