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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Unswitching does not catch opportunity with -fexperimental-new-pass-manager"
href="https://bugs.llvm.org/show_bug.cgi?id=34313">34313</a>
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<th>Summary</th>
<td>Unswitching does not catch opportunity with -fexperimental-new-pass-manager
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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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>Loop Optimizer
</td>
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<th>Assignee</th>
<td>chandlerc@gmail.com
</td>
</tr>
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<th>Reporter</th>
<td>stefanp@ca.ibm.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>With the following test code:
int has_utf8 = 1;
const char AA[] = {
0, 1, 2, 3, 156, 9, 134, 17
};
int main() {
long i, count=0, num=22;
for (i=0; i<100000000; i++) {
num = i % 7;
if (!has_utf8 && AA[num] < 0x4)
count+=AA[num+1];
}
return count;
}
we can move the "if (!has_utf8)" outside of the loop and not run the loop at
all when has_utf8 = 1.
The opportunity is caught correctly with the old pass manager but not with the
new one.
Found with these options:
-m64 -mcpu=power8 -O3
Not found with these ones:
-m64 -mcpu=power8 -O3 -fexperimental-new-pass-manager
I did try the new unswitching pass from this patch:
<a href="https://reviews.llvm.org/D34200">https://reviews.llvm.org/D34200</a>
but the compiler still did not find the opportunity.</pre>
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