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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - extend -fwrapv to apply to left shifts"
href="https://llvm.org/bugs/show_bug.cgi?id=25552">25552</a>
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<th>Summary</th>
<td>extend -fwrapv to apply to left shifts
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<th>Product</th>
<td>clang
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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>Linux
</td>
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<th>Status</th>
<td>NEW
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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>-New Bugs
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>bonzini@gnu.org
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<th>Classification</th>
<td>Unclassified
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<p>
<div>
<pre>If you pass clang -fwrapv then this causes -fsanitize=undefined to no longer
complain about signed integer overflows from addition. However the sanitizer
will still complain about left shifts of negative values.
-fwrapv should apply also to shifts. In addition -fwrapv in clang should
suppress -Wshift-negative-value.
(The GCC manuals only mention -fwrapv to affect add/sub/mult because GCC
currently _never_ treats signed left shifts as having undefined behavior. GCC
documentation however says very clearly, under -fstrict-overflow, that "Using
'-fwrapv' means that integer signed overflow is fully defined: it wraps").</pre>
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