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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - UBSan: missing checks for invalid arguments of __builtin_clz and friends"
href="https://llvm.org/bugs/show_bug.cgi?id=26979">26979</a>
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<th>Summary</th>
<td>UBSan: missing checks for invalid arguments of __builtin_clz and friends
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>LLVM Codegen
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>vonosmas@gmail.com
</td>
</tr>
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<th>CC</th>
<td>kcc@google.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<th>Classification</th>
<td>Unclassified
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<p>
<div>
<pre>@llvm.ctlz and @llvm.cttz intrinsics have argument "i1 <is_zero_undef>" which
is defined by the target. If passing zero is considered an undefined behavior
(e.g. this is often the case for __builtin_ctz), UBSan can emit a runtime
check, that would print an error report if the argument happens to be zero.
The code in question is CodeGenFunction::EmitBuiltinExpr: if we figure out that
getTarget().isCLZForZeroUndef() is true, we can emit a regular UBSan check.
It's possible we will need to introduce a separate handler for that.</pre>
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