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<base href="http://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - making zeros the hard way: scalar load into zero vector (AVX)"
href="http://llvm.org/bugs/show_bug.cgi?id=22685">22685</a>
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<th>Summary</th>
<td>making zeros the hard way: scalar load into zero vector (AVX)
</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>
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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: X86
</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>llvmbugs@cs.uiuc.edu
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>$ cat insert.ll
define <8 x float> @mov00(float* %ptr) {
%val = load float* %ptr
%vec = insertelement <8 x float> zeroinitializer, float %val, i32 0
ret <8 x float> %vec
}
Using llc built from r230234:
$ ./llc insert.ll -o - -mattr=avx
...
vxorps %xmm0, %xmm0, %xmm0
vinsertps $0, (%rdi), %xmm0, %xmm0 ## xmm0 = mem[0],xmm0[1,2,3]
vxorps %ymm1, %ymm1, %ymm1
vinsertf128 $0, %xmm0, %ymm1, %ymm0
retq
But if we change the vector to be undef initialized:
%vec = insertelement <8 x float> undef, float %val, i32 0
We get the expected:
vmovss (%rdi), %xmm0 ## xmm0 = mem[0],zero,zero,zero
retq
-----------------------------------------------------------------------------
This may be complicated by the fact that a non-VEX prefix 'movss' leaves the
upper 128-bit undef.
But with AVX, the Intel manual says:
VMOVSS (VEX.NDS.128.F3.0F 10 /r when the source operand is memory and the
destination is an XMM register)
DEST[31:0] <- SRC[31:0]
DEST[VLMAX-1:32] <- 0</pre>
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