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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Missed constant propagation optimization in simple while loop"
href="https://bugs.llvm.org/show_bug.cgi?id=44679">44679</a>
</td>
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<tr>
<th>Summary</th>
<td>Missed constant propagation optimization in simple while loop
</td>
</tr>
<tr>
<th>Product</th>
<td>new-bugs
</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>All
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>new bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>klrehm123@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>htmldeveloper@gmail.com, llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>//////////////////
int foo(int a) {
int num = 0;
int n = 1;
while (true) {
if (n == 1) {
num++;
n = 2;
} else if(n == 2) {
num += 2;
n = 3;
}
else if(n == 3) {
return num;
}
}
}
//////////////////
Optimized away in GCC, but not with LLVM trunk.
Interestingly, copying the loop body twice does get optimized:
//////////////////
int bar(int a) {
int num = 0;
int n = 1;
while (true) {
if (n == 1) {
num++;
n = 2;
} else if(n == 2) {
num += 2;
n = 3;
}
else if(n == 3) {
return num;
}
if (n == 1) {
num++;
n = 2;
} else if(n == 2) {
num += 2;
n = 3;
}
else if(n == 3) {
return num;
}
}
}
//////////////////</pre>
</div>
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