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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Incorrect Cost Calculations for Shuffle Ports on Icelake-client / Icelake-server"
href="https://bugs.llvm.org/show_bug.cgi?id=48110">48110</a>
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<th>Summary</th>
<td>Incorrect Cost Calculations for Shuffle Ports on Icelake-client / Icelake-server
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<th>Product</th>
<td>tools
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<th>Version</th>
<td>trunk
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<th>Hardware</th>
<td>All
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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>normal
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>llvm-mca
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>dweber@gmail.com
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<th>CC</th>
<td>andrea.dibiagio@gmail.com, llvm-bugs@lists.llvm.org, matthew.davis@sony.com
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<pre>Hi there,
It looks like llvm-mca is treating icelake-client and icelake-server as having
only one shuffle port. This causes incorrect cost calculations for any
operation that would use said shuffle ports. A block diagram showing the
architecture can be found here:
<a href="https://en.wikichip.org/wiki/intel/microarchitectures/sunny_cove">https://en.wikichip.org/wiki/intel/microarchitectures/sunny_cove</a> (sunny cove is
the core used by both icelake-server and icelake-client). Similarly, you can
find the uops usage for any given shuffle here:
<a href="https://uops.info/table.html?search=shuf&cb_lat=on&cb_tp=on&cb_uops=on&cb_ports=on&cb_SKL=on&cb_ICL=on&cb_measurements=on&cb_base=on&cb_avx=on">https://uops.info/table.html?search=shuf&cb_lat=on&cb_tp=on&cb_uops=on&cb_ports=on&cb_SKL=on&cb_ICL=on&cb_measurements=on&cb_base=on&cb_avx=on</a>
If the code generating the costs for LLVM-MCA is used by anything else in the
toolchain, it's likely this will yield a performance benefit for other users
targeting icelake-server and icelake-client.</pre>
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