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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [x86] Failure to optimize vector shuffle in conversion"
href="https://bugs.llvm.org/show_bug.cgi?id=49081">49081</a>
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<th>Summary</th>
<td>[x86] Failure to optimize vector shuffle in conversion
</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>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</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
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</tr>
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<th>Reporter</th>
<td>gabravier@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>craig.topper@gmail.com, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk, pengfei.wang@intel.com, spatel+llvm@rotateright.com
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<p>
<div>
<pre>typedef int v4si __attribute__((vector_size(16)));
typedef float v4sf __attribute__((vector_size(16)));
v4sf f(v4si f)
{
return (v4sf){(float)f[1], (float)f[1], (float)f[2], (float)f[3]};
}
With -O3, GCC outputs this:
f(int __vector(4)):
pshufd xmm0, xmm0, 229
cvtdq2ps xmm0, xmm0
ret
LLVM outputs this:
f(int __vector(4)):
pshufd xmm1, xmm0, 85 # xmm1 = xmm0[1,1,1,1]
cvtdq2ps xmm1, xmm1
pshufd xmm2, xmm0, 238 # xmm2 = xmm0[2,3,2,3]
cvtdq2ps xmm2, xmm2
pshufd xmm0, xmm0, 255 # xmm0 = xmm0[3,3,3,3]
cvtdq2ps xmm0, xmm0
unpcklps xmm2, xmm0 # xmm2 = xmm2[0],xmm0[0],xmm2[1],xmm0[1]
shufps xmm1, xmm2, 64 # xmm1 = xmm1[0,0],xmm2[0,1]
movaps xmm0, xmm1
ret</pre>
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