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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Wrong code generation at -O2 leading to division by zero"
href="https://llvm.org/bugs/show_bug.cgi?id=30806">30806</a>
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</tr>
<tr>
<th>Summary</th>
<td>Wrong code generation at -O2 leading to division by zero
</td>
</tr>
<tr>
<th>Product</th>
<td>new-bugs
</td>
</tr>
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<th>Version</th>
<td>3.9
</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>
<tr>
<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>new bugs
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>clang@martinien.de
</td>
</tr>
<tr>
<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=17500" name="attach_17500" title="Repro">attachment 17500</a> <a href="attachment.cgi?id=17500&action=edit" title="Repro">[details]</a></span>
Repro
Attached repro causes a division by zero although it shouldn't (I tried my best
to rule out undefined behavior, but if I missed something let me know).
Build with build.sh and run "div_by_zero"
In run.cpp "array" is only being assigned a non-NULL pointer when both a and b
are both > 0:
if(a > 0 && b > 0) // false at runtime!
{
try {
array.reset(new size_t[b]());
}
catch (...)
{
}
}
But later on the following code gets executed even though array.get() must
return NULL:
if (array.get() != 0) // Should be false at runtime; even adding "&& a > 0"
here does not help
{
// Also this crashes:
//const size_t partSize = a != 0 ? b / a : 0;
const size_t partSize = b / a; // Crash here - Division by zero
Side note:
It works at -O1. I know that for earlier clang versions (I think 3.6) this
broke even at -O1, but the workaround seen above ("Also this crashes") worked
there.
Best regards,
Martin</pre>
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