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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 --- - cast-expression from lvalue to rvalue reference fails while reinterpret_cast for the same conversion works" href="https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_bugs_show-5Fbug.cgi-3Fid-3D23802&d=AwMBaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=pF93YEPyB-J_PERP4DUZOJDzFVX5ZQ57vQk33wu0vio&m=nb5Vdgs6K51-TlURXvUKx2LfSpzHuOjM1t0I5a3hVyk&s=MCF43ku8COqfE8bpYZXxJm_gmSZveya6noEH6vLXJg0&e=">23802</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>cast-expression from lvalue to rvalue reference fails while reinterpret_cast for the same conversion works
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>3.6
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>C++11
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>andrey.vul@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>dgregor@apple.com, llvmbugs@cs.uiuc.edu
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Consider the following example:
// begin a.cc
struct S {};
int x;
S&& y1 = (S&&)x;
S&& y2 = reinterpret_cast<S&&>(x);
S& z1 = (S&)x;
//end a.cc
The casts initializing y1 and y2 should behave the same but the cast-expression
gives the diagnostic:
"error: cannot cast from lvalue of type 'int' to rvalue reference type 'S
&&'; types are not compatible"
The expression initializing z1 works as intended.
I conclude that reinterpret_cast is neglected as a candidate in a
cast-expression when the target is a rvalue reference, violating 5.4p4.4.
clang++ -v output:
clang version 3.6.1 (tags/RELEASE_361/final)
Target: x86_64-pc-linux-gnu
Thread model: posix
Selected GCC installation: /usr/lib/gcc/x86_64-pc-linux-gnu/4.9.2
"/usr/bin/x86_64-pc-linux-gnu-clang-3.6.1" -cc1 -triple x86_64-pc-linux-gnu
-emit-obj -mrelax-all -disable-free -disable-llvm-verifier -main-file-name a.cc
-mrelocation-model static -mthread-model posix -mdisable-fp-elim -fmath-errno
-masm-verbose -mconstructor-aliases -munwind-tables -fuse-init-array
-target-cpu x86-64 -target-linker-version 2.25 -v -dwarf-column-info
-resource-dir /usr/bin/../lib/clang/3.6.1 -internal-isystem
/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.2/include/g++-v4 -internal-isystem
/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.2/include/g++-v4/x86_64-pc-linux-gnu
-internal-isystem
/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.2/include/g++-v4/backward
-internal-isystem /usr/local/include -internal-isystem
/usr/bin/../lib/clang/3.6.1/include -internal-externc-isystem /include
-internal-externc-isystem /usr/include -Wall -Wextra -std=c++11
-fdeprecated-macro -fdebug-compilation-dir /tmp -ferror-limit 19
-fmessage-length 132 -mstackrealign -fobjc-runtime=gcc -fcxx-exceptions
-fexceptions -fdiagnostics-show-option -fcolor-diagnostics -o /tmp/a-85edcb.o
-x c++ a.cc
clang -cc1 version 3.6.1 based upon LLVM 3.6.1 default target
x86_64-pc-linux-gnu
ignoring nonexistent directory "/usr/local/include"
ignoring nonexistent directory "/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.2/include/g++-v4
/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.2/include/g++-v4/x86_64-pc-linux-gnu
/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.2/include/g++-v4/backward
/usr/bin/../lib/clang/3.6.1/include
/usr/include
End of search list.
a.cc:3:10: error: cannot cast from lvalue of type 'int' to rvalue reference
type 'S &&'; types are not compatible
S&& y1 = (S&&)x;
^~~~~~
1 error generated.</pre>
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