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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - consteval function allows undefined behavior"
href="https://bugs.llvm.org/show_bug.cgi?id=43714">43714</a>
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<th>Summary</th>
<td>consteval function allows undefined behavior
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<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>
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<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>C++2a
</td>
</tr>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>mikhail.matrosov@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>blitzrakete@gmail.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
</td>
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<p>
<div>
<pre>Compile this program:
```
#include <iostream>
consteval int f(int n)
{
int r = n--;
for (; n > 1; --n) r *= n;
return r;
}
int main()
{
int x = f(13);
std::cout << x;
}
```
Expected: does not compile, since 13! overflows int (UB not allowed on compile
time)
Actual: compiles, runs with UB
Demo: <a href="https://wandbox.org/permlink/QJziECSrsDGuQyj4">https://wandbox.org/permlink/QJziECSrsDGuQyj4</a>
See also: <a href="https://stackoverflow.com/q/58454657/261217">https://stackoverflow.com/q/58454657/261217</a></pre>
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