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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [InstCombine] fold extractelt(trunc(bitcast X))) -> extractelt"
href="https://llvm.org/bugs/show_bug.cgi?id=31770">31770</a>
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<th>Summary</th>
<td>[InstCombine] fold extractelt(trunc(bitcast X))) -> extractelt
</td>
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<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<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>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Scalar Optimizations
</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>spatel+llvm@rotateright.com
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</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>We're missing a vector fold as Zvi noted here:
<a href="http://lists.llvm.org/pipermail/llvm-dev/2017-January/109539.html">http://lists.llvm.org/pipermail/llvm-dev/2017-January/109539.html</a>
define i32 @B(<8 x i32> %V) {
%B = bitcast <8 x i32> %V to <4 x i64>
%T = trunc <4 x i64> %B to <4 x i32>
%E = extractelement <4 x i32> %T, i32 1
ret i32 %E
}
On little-endian, this should be:
define i32 @B(<8 x i32> %V) {
%E = extractelement <8 x i32> %V, i32 2
ret i32 %E
}
There's a similar-looking fold already in InstCombine called
"foldVecTruncToExtElt()".</pre>
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