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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] try harder to shuffle lower to vpermi2pd"
href="https://bugs.llvm.org/show_bug.cgi?id=40500">40500</a>
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<th>Summary</th>
<td>[x86] try harder to shuffle lower to vpermi2pd
</td>
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<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<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>
</tr>
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<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
</td>
</tr>
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<th>Reporter</th>
<td>spatel+llvm@rotateright.com
</td>
</tr>
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<th>CC</th>
<td>craig.topper@gmail.com, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk, spatel+llvm@rotateright.com
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<p>
<div>
<pre>Filing this based on a regression seen in the proposed D57336:
<a href="https://reviews.llvm.org/D57336">https://reviews.llvm.org/D57336</a>
This example is based on
"test/CodeGen/X86/avx512-shuffles/partial_permute.ll::test_8xdouble_to_4xdouble_perm_mask3()"
define <4 x double> @extract_splat(<8 x double> %x) {
%x0123 = shufflevector <8 x double> %x, <8 x double> undef, <4 x i32> <i32 0,
i32 1, i32 2, i32 3>
%x4567 = shufflevector <8 x double> %x, <8 x double> undef, <4 x i32> <i32 4,
i32 5, i32 6, i32 7>
%x45 = shufflevector <4 x double> %x4567, <4 x double> undef, <2 x i32> <i32
0, i32 1>
%x4444 = shufflevector <2 x double> %x45, <2 x double> undef, <4 x i32> <i32
0, i32 0, i32 0, i32 0>
%x0214 = shufflevector <4 x double> %x0123, <4 x double> %x4444, <4 x i32>
<i32 0, i32 2, i32 1, i32 4>
ret <4 x double> %x0214
}
$ llc -o - extractsplat.ll -mattr=avx512f
vextractf64x4 $1, %zmm0, %ymm1
vpermpd $216, %ymm0, %ymm0 # ymm0 = ymm0[0,2,1,3]
vbroadcastsd %xmm1, %ymm1
vblendps $192, %ymm1, %ymm0, %ymm0 # ymm0 =
ymm0[0,1,2,3,4,5],ymm1[6,7]
retq
If I got the shuffles right, that's the same as:
vextractf64x4 $1, %zmm0, %ymm2
vmovapd {{.*#+}} ymm1 = [0,2,1,4]
vpermi2pd %ymm2, %ymm0, %ymm1
vmovapd %ymm1, %ymm0
So the more general "vpermi2pd" with constant-loaded permute op can be used to
replace the permpd+broadcast+blend.</pre>
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