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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 --- - Add -mskip-rax-setup option for x86-64"
href="https://llvm.org/bugs/show_bug.cgi?id=23258">23258</a>
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<th>Summary</th>
<td>Add -mskip-rax-setup option for x86-64
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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
</td>
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<th>Component</th>
<td>new bugs
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>hjl.tools@gmail.com
</td>
</tr>
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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
</td>
</tr></table>
<p>
<div>
<pre>GCC 5 added a compiler option, -mskip-rax-setup, for x86-64. It skips
setting up the RAX register when SSE is disabled and there are no
variable arguments passed in vector registers. Since kernel doesn't
pass vector registers to functions with variable arguments, this option
can be used to optimize the x86-64 kernel. For kernel 3.17:
text data bss dec hex filename
11455921 2204048 5853184 19513153 129bf41 vmlinux #with -mskip-rax-setup
11480079 2204048 5853184 19537311 12a1d9f vmlinux
It will be nice to implement it in clang.</pre>
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</p>
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