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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Missed loop vectorization due to the presence of switch"
href="https://bugs.llvm.org/show_bug.cgi?id=48844">48844</a>
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<tr>
<th>Summary</th>
<td>Missed loop vectorization due to the presence of switch
</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>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Loop Optimizer
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<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>#include <algorithm>
#include <vector>
#include <cstdint>
void replace_if_epi8(std::vector<int8_t>& v) {
std::replace_if(v.begin(), v.end(), [](int8_t x){return x == 13 || x ==
-12; }, 42);
}
void replace_if_epi32(std::vector<int32_t>& v) {
std::replace_if(v.begin(), v.end(), [](int8_t x){return x == 13 || x ==
-12; }, 42);
}
LLVM fails to vectorize this code - possibly due to presence of switch (OR cond
is converted to switch).
<a href="https://godbolt.org/z/sY5oT9">https://godbolt.org/z/sY5oT9</a>
Second example:
void replace_if_epi8(std::vector<int8_t>& v) {
std::replace_if(v.begin(), v.end(), [](int8_t x){return x == 13 ; }, 42);
}
void replace_if_epi32(std::vector<int32_t>& v) {
std::replace_if(v.begin(), v.end(), [](int8_t x){return x == 13; }, 42);
}
This code is nicely vectorized by LLVM.
<a href="https://godbolt.org/z/jx4dqo">https://godbolt.org/z/jx4dqo</a>
So either simplifycfg should not create switches before vectorizers (easy fix,
maybe profitable for other optimizations too?), and/or vectorizers should know
how to handle them.</pre>
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