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<base href="https://bugs.llvm.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - vectorization differences"
href="https://bugs.llvm.org/show_bug.cgi?id=39597">39597</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>vectorization differences
</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>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>
<tr>
<th>Component</th>
<td>Loop Optimizer
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>trass3r@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>void foo(unsigned* x)
{
for (int i = 0; i < 8; ++i)
x[i] = (x[i] % 3 == 0) ? 0 : x[i];
}
void bar(unsigned* x)
{
for (int i = 0; i < 8; ++i)
if (x[i] % 3 == 0)
x[i] = 0;
}
$ clang -O3 -march=haswell -Rpass="loop|vect" -Rpass-missed="loop|vect"
-Rpass-analysis="loop|vect"
<source>:3:5: remark: completely unrolled loop with 8 iterations
[-Rpass=loop-unroll]
<source>:9:5: remark: completely unrolled loop with 8 iterations
[-Rpass=loop-unroll]
<source>:4:18: remark: Stores SLP vectorized with cost -17 and with tree size 8
[-Rpass=slp-vectorizer]
$ clang -O3 -fno-unroll-loops -march=haswell -Rpass="loop|vect"
-Rpass-missed="loop|vect" -Rpass-analysis="loop|vect"
<source>:3:5: remark: vectorized loop (vectorization width: 8, interleaved
count: 1) [-Rpass=loop-vectorize]
<source>:9:5: remark: vectorized loop (vectorization width: 8, interleaved
count: 1) [-Rpass=loop-vectorize]
The generated code is different in all 4 cases:
<a href="https://godbolt.org/z/7EaJfc">https://godbolt.org/z/7EaJfc</a></pre>
</div>
</p>
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