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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Loop vectorization does not deal with a simple char reduction"
href="http://llvm.org/bugs/show_bug.cgi?id=21369">21369</a>
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<th>Summary</th>
<td>Loop vectorization does not deal with a simple char reduction
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<th>Product</th>
<td>libraries
</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>All
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Loop Optimizer
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>james.molloy@arm.com
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
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<th>Classification</th>
<td>Unclassified
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<p>
<div>
<pre>Clang currently cannot do a simple char reduction. The following program:
char arr[5000];
char f() {
char a = 0;
for (int i = 0; i < 5000; ++i)
a += arr[i];
return a;
}
Is not vectorized:
/bin/clang -O3 -o - -S test-vec.c -target arm64 -Rpass=loop-vectorize
-Rpass-analysis=loop-vectorize
test-vec.c:8:1: remark: loop not vectorized: value that could not be identified
as reduction is used outside the loop [-Rpass-analysis=loop-vectorize]
}
^
It is not immediately obvious what value has caused the vectorizer to bail out.</pre>
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