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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [x86, AVX] poor codegen for shufflevector with constants"
href="https://llvm.org/bugs/show_bug.cgi?id=30371">30371</a>
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<th>Summary</th>
<td>[x86, AVX] poor codegen for shufflevector with constants
</td>
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<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>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Backend: X86
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>spatel+llvm@rotateright.com
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<th>Classification</th>
<td>Unclassified
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</tr></table>
<p>
<div>
<pre>Testing with llc built from r281342:
define <4 x float> @does_it_blend(float %f) {
%a0 = insertelement <4 x float> undef, float %f, i32 0
%ret = shufflevector <4 x float> %a0, <4 x float> <float undef, float 4.0,
float 5.0, float 3.0>, <4 x i32> <i32 4, i32 5, i32 6, i32 7>
ret <4 x float> %ret
}
This should be a blendps or insertps with a vector constant, but we scalarized
the constant loads, so what could have been 2 ops (load+blend) became 6 ops:
$ ./llc blender.ll -o - -mattr=avx
vinsertps $16, LCPI0_0(%rip), %xmm0, %xmm0 ## xmm0 =
xmm0[0],mem[0],xmm0[2,3]
vinsertps $32, LCPI0_1(%rip), %xmm0, %xmm0 ## xmm0 =
xmm0[0,1],mem[0],xmm0[3]
vinsertps $48, LCPI0_2(%rip), %xmm0, %xmm0 ## xmm0 = xmm0[0,1,2],mem[0]
retq</pre>
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