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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - WebAssembly doesn't always generate f64x2.convert_low_i32x4_s/u as expected"
href="https://bugs.llvm.org/show_bug.cgi?id=51098">51098</a>
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<th>Summary</th>
<td>WebAssembly doesn't always generate f64x2.convert_low_i32x4_s/u as expected
</td>
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<th>Product</th>
<td>new-bugs
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
</td>
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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>new bugs
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>srj@google.com
</td>
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<th>CC</th>
<td>htmldeveloper@gmail.com, llvm-bugs@lists.llvm.org
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<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=25027" name="attach_25027" title="Sample .ll file to show the problem">attachment 25027</a> <a href="attachment.cgi?id=25027&action=edit" title="Sample .ll file to show the problem">[details]</a></span>
Sample .ll file to show the problem
When generating wasm code with simd128 enabled, the LLVM backend only seems to
generate the f64x2.convert_low_i32x4_s (or _u) instructions if the input vector
is *exactly* 4 wide; if the input vector is a multiple of 4 (e.g. 8), the
generated code isn't a sequence of f64x2.convert_low_i32x4_s/u instructions,
but a sequence of scalarized calls to extract_lane+convert_i64_s+replace_lane.
To see this behavior:
```
llc -march=wasm32 test_op_f64x2_convert_low_i32x4_s_0.ll -o - -O3
-mattr=+sign-ext,+simd128,+nontrapping-fptoint
```</pre>
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