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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Loop vectorizer fails to maximize the use of __builtin_assume()"
href="https://llvm.org/bugs/show_bug.cgi?id=26167">26167</a>
</td>
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<th>Summary</th>
<td>Loop vectorizer fails to maximize the use of __builtin_assume()
</td>
</tr>
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<th>Product</th>
<td>tools
</td>
</tr>
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<th>Version</th>
<td>3.7
</td>
</tr>
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<th>Hardware</th>
<td>All
</td>
</tr>
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<th>OS</th>
<td>All
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>opt
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>marksl@synopsys.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>I've been able to get the loop vectorizer to understand that the number of
iterations is positive, but I can't get it to understand it's both positive and
will iterate an even number of times. A scalar loop is produced for each of the
following test cases.
void vcpy1(short* restrict d, const char* restrict l, const char* restrict r,
int N) {
__builtin_assume( (N > 1) && (N%2 == 0) );
#pragma clang loop vectorize(enable) vectorize_width(2)
for (int j=0;j<N;j++)
d[j] = l[j] + r[j];
}
void vcpy2(short* restrict d, const char* restrict l, const char* restrict r,
int N) {
__builtin_assume( (N > 1) && ((N&1) == 0) );
#pragma clang loop vectorize(enable) vectorize_width(2)
for (int j=0;j<N;j++)
d[j] = l[j] + r[j];
}
void vcpy3(short* restrict d, const char* restrict l, const char* restrict r,
int N) {
__builtin_assume(N > 1);
__builtin_assume(N%2 == 0);
#pragma clang loop vectorize(enable) vectorize_width(2)
for (int j=0;j<N;j++)
d[j] = l[j] + r[j];
}
void vcpy4(short* restrict d, const char* restrict l, const char* restrict r,
int N) {
__builtin_assume(N > 1);
__builtin_assume((N&1) == 0);
#pragma clang loop vectorize(enable) vectorize_width(2)
for (int j=0;j<N;j++)
d[j] = l[j] + r[j];
}</pre>
</div>
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