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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [x86] Less optimized multi-byte nop instructions are generated"
href="https://llvm.org/bugs/show_bug.cgi?id=22965">22965</a>
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<th>Summary</th>
<td>[x86] Less optimized multi-byte nop instructions are generated
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<th>Product</th>
<td>new-bugs
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>new bugs
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>hjl.tools@gmail.com
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu, michael.m.kuperstein@intel.com
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<th>Classification</th>
<td>Unclassified
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<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=14080" name="attach_14080" title="A testcase">attachment 14080</a> <a href="attachment.cgi?id=14080&action=edit" title="A testcase">[details]</a></span>
A testcase
llvm generates multi-byte nop instructions greater than 10 bytes,
which have performance on x86 processors. GNU assembler has been
changed to limit multi-byte nop instructions to 10 bytes:
<a href="https://sourceware.org/ml/binutils/2015-03/msg00260.html">https://sourceware.org/ml/binutils/2015-03/msg00260.html</a>
to avoid nops like:
66 66 66 66 66 66 2e 0f 1f 84 00 00 00 00 00 data16 data16 data16 data16
data16 nopw %cs:0x0(%rax,%rax,1)
66 66 66 66 66 2e 0f 1f 84 00 00 00 00 00 data16 data16 data16 data16
data16 nopw %cs:0x0(%rax,%rax,1)
66 66 66 66 2e 0f 1f 84 00 00 00 00 00 data16 data16 data16 nopw
%cs:0x0(%rax,%rax,1)
66 66 66 2e 0f 1f 84 00 00 00 00 00 data16 data16 nopw %cs:0x0(%rax,%rax,1)
66 66 2e 0f 1f 84 00 00 00 00 00 data16 nopw %cs:0x0(%rax,%rax,1)
llvm should also be updated.</pre>
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