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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Fail to compile OpenMP array reduction"
href="https://bugs.llvm.org/show_bug.cgi?id=39084">39084</a>
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<th>Summary</th>
<td>Fail to compile OpenMP array reduction
</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>All
</td>
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<th>OS</th>
<td>All
</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
</td>
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<th>Component</th>
<td>Clang Compiler Support
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>james.h.cownie@intel.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>OpenMP 4.5 includes reductions on array sections, which should allow code like
this to work
int myroutine(double *a, double *sum, int n)
{
int i;
#pragma omp for reduction(+:sum[:1])
for(i=0;i<n;i++){
sum[0] += a[i];
}
return 0;
}
However, clang objects to this because it cannot prove that *a is shared.
GCC however accepts it <a href="https://godbolt.org/z/4JwPYu">https://godbolt.org/z/4JwPYu</a> , and it is useful. (See
<a href="https://stackoverflow.com/questions/52333881/is-it-possible-to-use-a-reduction-variable-from-a-passed-by-pointer-argument-ins/">https://stackoverflow.com/questions/52333881/is-it-possible-to-use-a-reduction-variable-from-a-passed-by-pointer-argument-ins/</a>
for instance).
We should accept it as well.
(There may be a clarification in OpenMP 5.0 that this should be legal. Even if
such a clarification is not forthcoming, not allowing it sees perverse.)</pre>
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