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<base href="https://bugs.llvm.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - SLP vectorization failure"
href="https://bugs.llvm.org/show_bug.cgi?id=44286">44286</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>SLP vectorization failure
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Loop Optimizer
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>david.bolvansky@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>char src[512];
char dst[512];
#define WIDTH 32
void foo(int height, int a, int b, int c, int d, int dst_stride) {
char * ptr_src = src;
char * ptr_dst = dst;
for( int y = 0; y < height; y++ )
{
for( int x = 0; x < WIDTH; x++ )
{
char x1 = ((a + c) * ptr_src[x] ) >> 6;
char x2 = ((b + d) * ptr_src[x+1]) >> 6;
ptr_dst[x] = x1 + x2;
}
ptr_dst += dst_stride;
ptr_src += 32;
}
}
ICC and GCC can vectorize this loop, Clang does not.
<a href="https://godbolt.org/z/EsHdPg">https://godbolt.org/z/EsHdPg</a></pre>
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