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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Duplicated warning message in -Wunused-value with "const""
href="https://bugs.llvm.org/show_bug.cgi?id=46454">46454</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Duplicated warning message in -Wunused-value with "const"
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Frontend
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>haoxintu@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org, neeilans@live.com, richard-llvm@metafoo.co.uk
</td>
</tr></table>
<p>
<div>
<pre>$cat bug.cc
int int_a = 0;
const int const_int_b = 0;
int int_c = 0;
auto var1 = reinterpret_cast <int> (int_a , const_int_b );
auto var2 = reinterpret_cast <int> (const_int_b ,const_int_b);
auto var3 = reinterpret_cast <int> (const_int_b , int_a);
auto var4 = reinterpret_cast <int> (int_c , int_a);
$clang++ -c -Wunused-value bug.cc
bug.cc:4:37: warning: expression result unused [-Wunused-value]
auto var1 = reinterpret_cast <int> (int_a , const_int_b );
^~~~~
bug.cc:4:37: warning: expression result unused [-Wunused-value]
auto var1 = reinterpret_cast <int> (int_a , const_int_b );
^~~~~
bug.cc:5:37: warning: expression result unused [-Wunused-value]
auto var2 = reinterpret_cast <int> (const_int_b ,const_int_b);
^~~~~~~~~~~
bug.cc:5:37: warning: expression result unused [-Wunused-value]
auto var2 = reinterpret_cast <int> (const_int_b ,const_int_b);
^~~~~~~~~~~
bug.cc:6:37: warning: expression result unused [-Wunused-value]
auto var3 = reinterpret_cast <int> (const_int_b , int_a);
^~~~~~~~~~~
bug.cc:7:37: warning: expression result unused [-Wunused-value]
auto var4 = reinterpret_cast <int> (int_c , int_a);
^~~~~
6 warnings generated.
While in GCC
$g++ -c -Wunused-value bug.cc
bug.cc:4:37: warning: left operand of comma operator has no effect
[-Wunused-value]
4 | auto var1 = reinterpret_cast <int> (int_a , const_int_b );
| ^~~~~
bug.cc:5:37: warning: left operand of comma operator has no effect
[-Wunused-value]
5 | auto var2 = reinterpret_cast <int> (const_int_b ,const_int_b);
| ^~~~~~~~~~~
bug.cc:6:37: warning: left operand of comma operator has no effect
[-Wunused-value]
6 | auto var3 = reinterpret_cast <int> (const_int_b , int_a);
| ^~~~~~~~~~~
bug.cc:7:37: warning: left operand of comma operator has no effect
[-Wunused-value]
7 | auto var4 = reinterpret_cast <int> (int_c , int_a);
|
Clang emits two duplicated warning messages in Line4 and Line5, while following
two lines just gives one warning message. I guess clang might have something
wrong in handling the "const" variable in reinterpret_cast expression.
I have tested in recently released Clang versions, and found that Clang-9 to
Clang-trunk versions have this issue and Clang-8 or lower versions work fine
with it.</pre>
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