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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [X86] VPSHUFD and VPERMQ with immediates combined into VPERMD with variable mask"
href="https://bugs.llvm.org/show_bug.cgi?id=46249">46249</a>
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<th>Summary</th>
<td>[X86] VPSHUFD and VPERMQ with immediates combined into VPERMD with variable mask
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<th>Product</th>
<td>libraries
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<th>Version</th>
<td>trunk
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<th>Hardware</th>
<td>PC
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>enhancement
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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>craig.topper@gmail.com
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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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<pre>As noted here <a href="https://twitter.com/damageboy/status/1270266352406802432">https://twitter.com/damageboy/status/1270266352406802432</a>
We combined
t45: v16i32 = vector_shuffle<3,2,1,0,7,6,5,4,11,10,9,8,15,14,13,12> t44,
undef:v16i32
t46: v16i32 = vector_shuffle<8,9,10,11,12,13,14,15,0,1,2,3,4,5,6,7> t45,
undef:v16i32
into
t258: v16i32 = vector_shuffle<11,10,9,8,15,14,13,12,3,2,1,0,7,6,5,4>
Which then required vpermd.
This happened before lowering and lowering doesn't know to recreate the two
shuffles. Simon, would hasFastVariableShuffle() also have created a VPERMD if
lowering had managed to make 2 immediate shuffles?</pre>
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