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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - LLVM no longer honours -stack-alignment=4"
href="http://llvm.org/bugs/show_bug.cgi?id=21435">21435</a>
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<tr>
<th>Summary</th>
<td>LLVM no longer honours -stack-alignment=4
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>All
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Backend: X86
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>jfonseca@vmware.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=13268" name="attach_13268" title="bug1347703.ll">attachment 13268</a> <a href="attachment.cgi?id=13268&action=edit" title="bug1347703.ll">[details]</a></span>
bug1347703.ll
LLVM stoped honouring
This can easily be reproduced with the attached bug1347703.ll doing
$ llc -o - -mtriple=i686-pc-mingw32 -mattr=+avx -stack-alignment=4
bug1347703.ll | grep '\<and.*[er]sp'
$
which produces nothing showing that the stack pointer is never aligned.
However if one disables frame-pointer elimination then it works again:
$
/home/jfonseca/work/vmware/llvm/llvm/build/linux-x86_64/Debug+Asserts/bin/llc
-disable-fp-elim -o - -mtriple=i686-pc-mingw32 -mattr=+avx -stack-alignment=4
bug1347703.ll | grep '\<and.*[er]sp'
andl $-32, %esp
andl $-32, %esp
$
Which doesn't seem the right behavior -- using the frame-pointer to align the
stack seems an implementation detail -- there are probably other ways, and if
frame-pointer is indeed necessary it should be automatically employed as
necessary.
This regression happened between LLVM release 3.2 and release 3.3. I strongly
suspect r168627 --
<a href="https://github.com/llvm-mirror/llvm/commit/1243922fc1a1e3d2681ed9e78503eeabd875ba93">https://github.com/llvm-mirror/llvm/commit/1243922fc1a1e3d2681ed9e78503eeabd875ba93</a></pre>
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