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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - suboptimal AVX splat"
href="http://llvm.org/bugs/show_bug.cgi?id=22283">22283</a>
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<th>Summary</th>
<td>suboptimal AVX splat
</td>
</tr>
<tr>
<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>
</tr>
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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>
</tr>
<tr>
<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
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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>llvmbugs@cs.uiuc.edu
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>This is a follow-on to <a class="bz_bug_link
bz_status_NEW "
title="NEW --- - vector splats: the hard way"
href="show_bug.cgi?id=22276">bug 22276</a>, although this may be an independent bug.
In the case of a splat of a variable (such as the induction variable in a
vectorized loop), we may not be generating the optimal splat at least for an
AVX1 machine:
define <4 x i64> @splat(i64 %x) {
%scalar_to_vector = insertelement <4 x i64> undef, i64 %x, i32 0
%splat = shufflevector <4 x i64> %scalar_to_vector, <4 x i64> undef, <4 x
i32> zeroinitializer
ret <4 x i64> %splat
}
$ ./llc -mcpu=btver2 zero_vector.ll -o -
...
vmovq %rdi, %xmm0
vunpcklpd %xmm0, %xmm0, %xmm0 ## xmm0 = xmm0[0,0]
vinsertf128 $1, %xmm0, %ymm0, %ymm0
retq
I would expect this to match what we're currently generating for AVX2:
$ ./llc -mcpu=haswell zero_vector.ll -o -
...
vmovq %rdi, %xmm0
vbroadcastsd %xmm0, %ymm0
retq
If the splatted integer value is actually used in this function, then that
should be a 'vpbroadcastq' with AVX2 rather than an FP instruction.</pre>
</div>
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