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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [X86] Possibly incorrect throughput for vpshufb/vpperm on bdver2 model"
href="https://bugs.llvm.org/show_bug.cgi?id=51539">51539</a>
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<th>Summary</th>
<td>[X86] Possibly incorrect throughput for vpshufb/vpperm on bdver2 model
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<th>Product</th>
<td>libraries
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
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<th>OS</th>
<td>Windows NT
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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>llvm-dev@redking.me.uk
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<th>CC</th>
<td>craig.topper@gmail.com, lebedev.ri@gmail.com, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk, pengfei.wang@intel.com, spatel+llvm@rotateright.com
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<pre>I noticed this while working on the D103695 cost model helper script, the
llvm-mca reported bdver2 throughput for codegen containing vpshufb/vpperm is
often higher than expected.
Instruction Info:
[1]: #uOps
[2]: Latency
[3]: RThroughput
[4]: MayLoad
[5]: MayStore
[6]: HasSideEffects (U)
[1] [2] [3] [4] [5] [6] Instructions:
1 3 1.50 vpshufb %xmm0, %xmm1, %xmm2
1 2 1.50 vpperm %xmm0, %xmm1, %xmm2,
%xmm3
<a href="https://llvm.godbolt.org/z/Tsc5P4zox">https://llvm.godbolt.org/z/Tsc5P4zox</a>
All the docs I can find (AMDFam15h SoG, Agner, instlatx64 etc) indicate these
are fastpath (tp = 1.0) but just on pipe1 (xbr):
<a href="https://www.amd.com/system/files/TechDocs/47414_15h_sw_opt_guide.pdf">https://www.amd.com/system/files/TechDocs/47414_15h_sw_opt_guide.pdf</a></pre>
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