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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [instcombine] vector math/logic doesn't get the same bitwise optimizations as scalar"
href="https://llvm.org/bugs/show_bug.cgi?id=24942">24942</a>
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<th>Summary</th>
<td>[instcombine] vector math/logic doesn't get the same bitwise optimizations as scalar
</td>
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<th>Product</th>
<td>libraries
</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
</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
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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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<th>Reporter</th>
<td>spatel+llvm@rotateright.com
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</tr>
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<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>Hole in SimplifyDemandedBits, computeKnownBits, or something else?
"31" and "2" don't have any special meaning here; lots of other constant pairs
could illustrate the same point:
define i32 @lshr_and_i32(i32 %x) {
%lshr = lshr i32 %x, 31
%and = and i32 %lshr, 2
ret i32 %and
}
define <2 x i32> @lshr_and_v2i32(<2 x i32> %x) {
%lshr = lshr <2 x i32> %x, <i32 31, i32 31>
%and = and <2 x i32> %lshr, <i32 2, i32 2>
ret <2 x i32> %and
}
$ ./opt -instcombine demand.ll -S
define i32 @lshr_and_i32(i32 %x) {
ret i32 0
}
define <2 x i32> @lshr_and_v2i32(<2 x i32> %x) {
%lshr = lshr <2 x i32> %x, <i32 31, i32 31>
%and = and <2 x i32> %lshr, <i32 2, i32 2>
ret <2 x i32> %and
}</pre>
</div>
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