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<base href="https://llvm.org/bugs/" />
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [AArch64] recognize the shufflevector equivalent of a vector select"
href="https://llvm.org/bugs/show_bug.cgi?id=28530">28530</a>
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<th>Summary</th>
<td>[AArch64] 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>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>All
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Backend: AArch64
</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>
<tr>
<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
}
I'm guessing that one of these is generally better than the other (and there
may be a better way than either of these?):
$ ./llc shufsel.ll -o - -mtriple=aarch64
.LCPI0_0:
.word 4294967295 // 0xffffffff
.word 0 // 0x0
.word 0 // 0x0
.word 4294967295 // 0xffffffff
foo:
adrp x8, .LCPI0_0
ldr q2, [x8, :lo12:.LCPI0_0]
bsl v2.16b, v0.16b, v1.16b
mov v0.16b, v2.16b
ret
goo: // @goo
ext v1.16b, v0.16b, v1.16b, #12
ext v0.16b, v1.16b, v0.16b, #4
ext v1.16b, v1.16b, v1.16b, #8
ext v0.16b, v0.16b, v1.16b, #12
ret
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.</pre>
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