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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW " title="NEW --- - No warning on shifting a negative value" href="https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_bugs_show-5Fbug.cgi-3Fid-3D24026&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=pF93YEPyB-J_PERP4DUZOJDzFVX5ZQ57vQk33wu0vio&m=Ao9iqdcxm3kaUGayW5jfJNjsfJppFZLahOCMDlJY-T4&s=xqjan5_JB8CJZIsX0Nuh1fN2BGGCdBTUiX8fh_bAGm0&e=">24026</a>
</td>
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<th>Summary</th>
<td>No warning on shifting a negative value
</td>
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<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>3.6
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Windows NT
</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
</td>
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<th>Component</th>
<td>Frontend
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
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<th>Reporter</th>
<td>chengniansun@gmail.com
</td>
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>When we shift a negative number, clang does not emit a warning. This is
undefined behavior, which is already captured by ubsan.
$: cat t.c
#include <stdio.h>
int main(int argc, char **argv) {
int a = -1 << 3;
printf("%d\n", a);
return a;
}
$: clang-3.6 t.c ; ./a.out
-8
$: clang-3.6 -fsanitize=undefined t.c ; ./a.out
t.c:3:14: runtime error: left shift of negative value -1
-8
$:
$: gcc-trunk -pedantic -Wshift-negative-value t.c
t.c: In function ‘main’:
t.c:3:14: warning: left shift of negative value [-Wshift-negative-value]
int a = -1 << 3;
^</pre>
</div>
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