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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - zero vector: the hard way (x86: SSE/AVX shuffles)"
href="http://llvm.org/bugs/show_bug.cgi?id=22276">22276</a>
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<th>Summary</th>
<td>zero vector: the hard way (x86: SSE/AVX shuffles)
</td>
</tr>
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<th>Product</th>
<td>libraries
</td>
</tr>
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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>
</tr>
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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>Backend: X86
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
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<th>Reporter</th>
<td>spatel+llvm@rotateright.com
</td>
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>This is an offshoot of <a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Generates a total mess of SIMD for simple array initialization"
href="show_bug.cgi?id=20225">bug 20225</a>. That bug starts off with a seemingly simple
zero vector creation:
$ cat zero_vector.ll
define <4 x i64> @zero_vector() {
%zero = insertelement <4 x i64> undef, i64 0, i32 0
%splat = shufflevector <4 x i64> %zero, <4 x i64> undef, <4 x i32>
zeroinitializer
ret <4 x i64> %splat
}
Targeting three different CPUs (SSE, AVX, AVX2) and getting three surprising
results using llc built from r226469:
$ ./llc -mcpu=core2 zero_vector.ll -o -
...
pxor %xmm0, %xmm0
pshufd $68, %xmm0, %xmm0 ## xmm0 = xmm0[0,1,0,1]
movdqa %xmm0, %xmm1
retq
$ ./llc -mcpu=sandybridge zero_vector.ll -o -
...
vxorpd %ymm0, %ymm0, %ymm0
vunpcklpd %xmm0, %xmm0, %xmm0 ## xmm0 = xmm0[0,0]
vinsertf128 $1, %xmm0, %ymm0, %ymm0
retq
$ ./llc -mcpu=haswell zero_vector.ll -o -
...
xorl %eax, %eax
vmovq %rax, %xmm0
vbroadcastsd %xmm0, %ymm0
retq</pre>
</div>
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