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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 --- - Subexpression not valid in a constant expression even when it is valid"
href="https://llvm.org/bugs/show_bug.cgi?id=27989">27989</a>
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<th>Summary</th>
<td>Subexpression not valid in a constant expression even when it is valid
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>3.8
</td>
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<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>C++14
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>michele.caini@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Consider the following code:
template<int... V>
static constexpr int f(int v) {
int a[] = { (v ^= V, 0)... }; // Line 3
return v;
}
static constexpr int i = f<0x00>(0x11); // Line 7
int main() { }
It doesn't compile with the following error:
main.cpp:7:22: error: constexpr variable 'i' must be initialized by a constant
expression
[...]
main.cpp:3:23: note: subexpression not valid in a constant expression
Note that it doesn't work as well even if no templates are involved:
static constexpr int mix(int v, int u) {
int a[] = { (v ^= u, 0) };
return v;
}
static constexpr int mf = mix(0x11, 0x00);
int main() { }
For such kind of assignments are allowed in constant expressions, it should
compile.</pre>
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