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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [PPC] recognize the shufflevector equivalent of a vector select"
href="https://llvm.org/bugs/show_bug.cgi?id=28531">28531</a>
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<th>Summary</th>
<td>[PPC] recognize the shufflevector equivalent of a vector select
</td>
</tr>
<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>
</tr>
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<th>OS</th>
<td>All
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Backend: PowerPC
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>spatel+llvm@rotateright.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>$ cat shufsel.ll
define <4 x i32> @foo(<4 x i32> %a, <4 x i32> %b) {
%sel = select <4 x i1> <i1 true, i1 false, i1 false, i1 true>, <4 x i32> %a,
<4 x i32> %b
ret <4 x i32> %sel
}
define <4 x i32> @goo(<4 x i32> %a, <4 x i32> %b) {
%shuf = shufflevector <4 x i32> %a, <4 x i32> %b, <4 x i32> <i32 0, i32 5,
i32 6, i32 3>
ret <4 x i32> %shuf
}
These are functionally equivalent. Note that in <a href="http://reviews.llvm.org/D22114">http://reviews.llvm.org/D22114</a>
, there's a proposal to canonicalize to the shufflevector form of the IR.
We generate 'xxsel' and 'vperm' for a target with VSX. Is one better than the
other?
For an altivec target, the lowering to vsel is missed:
$ ./llc shufsel.ll -o - -mtriple=powerpc64 -mattr=altivec
foo: # @foo
addis 3, 2, .LCPI0_0@toc@ha
addis 4, 2, .LCPI0_1@toc@ha
addi 3, 3, .LCPI0_0@toc@l
addi 4, 4, .LCPI0_1@toc@l
lvx 4, 0, 3
lvx 5, 0, 4
vand 3, 3, 4
vand 2, 2, 5
vor 2, 2, 3
blr</pre>
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