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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - An rvalue-rerefence to a bit-field should be bound to a prvalue."
href="http://llvm.org/bugs/show_bug.cgi?id=21386">21386</a>
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<th>Summary</th>
<td>An rvalue-rerefence to a bit-field should be bound to a prvalue.
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<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>
</tr>
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<th>Component</th>
<td>C++11
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>kariya_mitsuru@hotmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>dgregor@apple.com, llvmbugs@cs.uiuc.edu
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>The sample code below should output "1, 5, 6" but it outputs "2, 5, 42" (from
clang 3.3).
=================================================================
#include <iostream>
struct S {
int i:3;
int j:5;
};
int main()
{
S s{1, 5};
int&& rrj = static_cast<int&&>(s.j);
++rrj;
std::cout << s.i << ", " << s.j << ", " << rrj << std::endl;
}
=================================================================
cf. <a href="http://melpon.org/wandbox/permlink/flLfdof281ToOQCL">http://melpon.org/wandbox/permlink/flLfdof281ToOQCL</a>
Latest C++ standard (N4140) [expr.static.cast]/p.3 says that
If the value is not a bit-field, the result refers to the object or the
specified base class subobject thereof; otherwise, the lvalue-to-rvalue
conversion (4.1) is applied to the bit-field and the resulting prvalue is used
as the expression of the static_cast for the remainder of this section.
So, the rvalue-reference rrj should be initialized to a prvalue 5, s.i should
output 1, and rrj should output 6(even though "the answer to life the universe
and everything" is 42 ;)).</pre>
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