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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [InstCombine] reduce shuffles with constants to a single shuffle"
href="https://llvm.org/bugs/show_bug.cgi?id=30264">30264</a>
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<th>Summary</th>
<td>[InstCombine] reduce shuffles with constants to a single shuffle
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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>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Scalar Optimizations
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>spatel+llvm@rotateright.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<th>Classification</th>
<td>Unclassified
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</tr></table>
<p>
<div>
<pre>I noticed this case in <a href="https://reviews.llvm.org/D24182">https://reviews.llvm.org/D24182</a> :
define <4 x float> @insertConstants(<4 x float> %x) {
%shuf1 = shufflevector <4 x float> %x, <4 x float> <float undef, float 0.0,
float undef, float undef>, <4 x i32> <i32 0, i32 5, i32 undef, i32 undef>
%shuf2 = shufflevector <4 x float> %shuf1, <4 x float> <float undef, float
undef, float 4.0, float 1.0>, <4 x i32> <i32 0, i32 1, i32 6, i32 7>
ret <4 x float> %shuf2
}
This can be combined into one shuffle instruction that we can assume is as
cheap as either of the original ones:
shufflevector <4 x float> %x, <4 x float> <float undef, float 0.0, float 4.0,
float 1.0>, <4 x i32> <i32 0, i32 5, i32 6, i32 7></pre>
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