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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Non-trivial infinite while loops being optimized away"
href="http://llvm.org/bugs/show_bug.cgi?id=19846">19846</a>
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<th>Summary</th>
<td>Non-trivial infinite while loops being optimized away
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
</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>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>chris.a.ferguson@gmail.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>The following code fails to compile with Clang 3.2, is optimized away entirely
with Clang 3.3 using -O3, and is optimized away entirely with Clang 3.4 using
-O2 and -O3.
#include <cstdint>
int main()
{
uint32_t i = 0;
uint32_t count = 1;
while (1)
{
if( i < 5 )
count+=1;
if (i == 0xFFFFFFFF)
break;
i++;
}
return count; // should return 6
}
The assembly output from Clang 3.3 with -O3 looks like:
main: # @main
movl $1, %eax
ret
Here is an online example: <a href="http://goo.gl/PAqMny">http://goo.gl/PAqMny</a>
This is a simplified test case, the original looked like this:
<a href="http://goo.gl/RTdHN3">http://goo.gl/RTdHN3</a>
I brought this up on stackoverflow first:
<a href="http://stackoverflow.com/questions/23838661/why-is-clang-optimizing-this-code-out">http://stackoverflow.com/questions/23838661/why-is-clang-optimizing-this-code-out</a></pre>
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