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<base href="http://llvm.org/bugs/" />
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Bad O2,O3 optimization in some cases"
href="http://llvm.org/bugs/show_bug.cgi?id=19157">19157</a>
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<th>Summary</th>
<td>Bad O2,O3 optimization in some cases
</td>
</tr>
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<th>Product</th>
<td>new-bugs
</td>
</tr>
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<th>Version</th>
<td>3.3
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
</tr>
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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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</tr>
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<th>Reporter</th>
<td>kostya27@gmail.com
</td>
</tr>
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<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>I have two almost similar programs 1.bc and 2.bc which generated by crystal:
<a href="https://gist.github.com/kostya/c1748e5dde4aefa4cb14">https://gist.github.com/kostya/c1748e5dde4aefa4cb14</a>
and perfomance for both should be the same, but:
/usr/lib/llvm-3.3/bin/opt 1.bc -o 1.obc -O3 && /usr/lib/llvm-3.3/bin/llc 1.obc
-o 1.s && gcc -c 1.s -o 1.o && gcc 1.o -o 1 -lm -lpcre -lgc -lrt -lunwind &&
./1
1.42804
/usr/lib/llvm-3.3/bin/opt 2.bc -o 2.obc -O3 && /usr/lib/llvm-3.3/bin/llc 2.obc
-o 2.s && gcc -c 2.s -o 2.o && gcc 2.o -o 2 -lm -lpcre -lgc -lrt -lunwind &&
./2
0.321645
1.bc 4.4 times slower than 2.bc with O3.
But if i add: -scalarrepl -instcombine, it became the same:
/usr/lib/llvm-3.3/bin/opt 1.bc -o 1.obc -O3 -scalarrepl -instcombine &&
/usr/lib/llvm-3.3/bin/llc 1.obc -o 1.s && gcc -c 1.s -o 1.o && gcc 1.o -o 1
-lm -lpcre -lgc -lrt -lunwind && ./1
0.310694
/usr/lib/llvm-3.3/bin/opt 2.bc -o 2.obc -O3 -scalarrepl -instcombine &&
/usr/lib/llvm-3.3/bin/llc 2.obc -o 2.s && gcc -c 2.s -o 2.o && gcc 2.o -o 2
-lm -lpcre -lgc -lrt -lunwind && ./2
0.317292</pre>
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