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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - clang c compiler produces wrong result for the attached c code with -O2 optimzation"
href="https://llvm.org/bugs/show_bug.cgi?id=26110">26110</a>
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<th>Summary</th>
<td>clang c compiler produces wrong result for the attached c code with -O2 optimzation
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>3.7
</td>
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<th>Hardware</th>
<td>Macintosh
</td>
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<th>OS</th>
<td>MacOS X
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>release blocker
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>LLVM Codegen
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>garunsrinivasan@gmail.com
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</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=15602" name="attach_15602" title="C file that reproduces the problem">attachment 15602</a> <a href="attachment.cgi?id=15602&action=edit" title="C file that reproduces the problem">[details]</a></span>
C file that reproduces the problem
A bug in the llvm auto vectoizer produces wrong results for the attached c
file. Turning off auto vectorizer produces the right results, but makes the
bigger test cases run much slower.
Compile the attached c file with xcode 7.0x or later with (clang-700.1.81)
(based on LLVM 3.7.0svn) with the following command:
bad result:
===============================
% clang -O2 bug.c -Wall -o bad
% ./bad
dbg = 10 10 10 10 10 10 10 10
good result:
===============================
% clang -O2 -fno-vectorize bug.c -Wall -o bad
%./bad
dbg = 15 15 15 15 15 15 15 15
gcc 4.7
% gcc -O2 bug.c -Wall -o bad
% ./bad
dbg = 15 15 15 15 15 15 15 15</pre>
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