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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Codegen for shuffle (similar to vget_low_s8) can be improved"
href="https://bugs.llvm.org/show_bug.cgi?id=50436">50436</a>
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<th>Summary</th>
<td>Codegen for shuffle (similar to vget_low_s8) can be improved
</td>
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Backend: WebAssembly
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<th>Assignee</th>
<td>tlively@google.com
</td>
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<th>Reporter</th>
<td>zhin@google.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<div>
<pre>PTAL <a href="https://godbolt.org/z/bhh56TxYe">https://godbolt.org/z/bhh56TxYe</a>
The use of __builtin_shufflevector is to extract the 8 low uint8_t elements
from a uint8x16_t into a uint8x8_t. It seems like due to the way the vector
extension is used to represent Wasm's SIMD128, we are lowering to a lot of
i8x16.extract_lane and i16x8.replace_lane.
Contrast it with native x86 codegen, which is a no-op (and it is, because it is
extracting the low 64-bits of a 128-bit vector into the low 64-bits).</pre>
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</p>
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