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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - -Wunreachable-code/-Wunreachable-code-return is easily fooled by do{..}while(false) / macro"
href="https://bugs.llvm.org/show_bug.cgi?id=33974">33974</a>
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<th>Summary</th>
<td>-Wunreachable-code/-Wunreachable-code-return is easily fooled by do{..}while(false) / macro
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<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>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>-New Bugs
</td>
</tr>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>lebedev.ri@gmail.com
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Code:
void foo();
int main() {
do {
foo();
__builtin_unreachable();
foo();
} while(false);
foo();
return 0;
}
Clang warns only on the second foo() call, but not the last one.
7 : <source>:7:9: warning: code will never be executed [-Wunreachable-code]
foo();
^~~
Such do{stuff}while(false) pattern is used in macros to do some complicated
stuff.
And to add some more fun to it:
void foo();
#define macro() do {\
foo(); \
__builtin_unreachable(); \
foo(); \
} while(false);
int main() {
macro()
foo();
return 0;
}
clang issues no warning whatsoever for this...</pre>
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