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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [Regression] nullptr_t lvalue-to-rvalue conversion bogusly constexpr"
href="https://bugs.llvm.org/show_bug.cgi?id=42440">42440</a>
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<th>Summary</th>
<td>[Regression] nullptr_t lvalue-to-rvalue conversion bogusly constexpr
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>All
</td>
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>C++
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>hstong@ca.ibm.com
</td>
</tr>
<tr>
<th>CC</th>
<td>blitzrakete@gmail.com, dgregor@apple.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<pre>This should not compile:
volatile decltype(nullptr) n;
extern constexpr void *p = n;
The type of the id-expression `n` is `volatile std::nullptr_t` prior to
lvalue-to-rvalue conversion. An lvalue-to-rvalue conversion occurs before we
get a null pointer constant.
N4820 subclause 7.7 [expr.const] paragraph 4, bullet 4.7 prohibits such an
lvalue-to-rvalue conversion during constant expression evaluation.
Recent comments in this area include r363429, "PR23833, DR2140: an
lvalue-to-rvalue conversion on a glvalue of type nullptr_t does not access
memory".
### COMPILE COMMAND:
clang++ -std=c++2a -Wall -Wextra -pedantic-errors -o /dev/null -c -xc++ -
### ACTUAL OUTPUT:
(Clean compile)
### EXPECTED OUTPUT:
<stdin>:2:24: error: constexpr variable 'p' must be initialized by a constant
expression
extern constexpr void *p = n;
^ ~
<stdin>:2:28: note: read of volatile-qualified type 'volatile
decltype(nullptr)' (aka 'volatile nullptr_t') is not allowed in a constant
expression
extern constexpr void *p = n;
^
1 error generated.
### COMPILER VERSION INFO (clang++ -v):
clang version 9.0.0 (trunk 364614)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /opt/compiler-explorer/clang-trunk/bin
Found candidate GCC installation:
/opt/compiler-explorer/gcc-8.3.0/lib/gcc/x86_64-linux-gnu/8.3.0
Selected GCC installation:
/opt/compiler-explorer/gcc-8.3.0/lib/gcc/x86_64-linux-gnu/8.3.0
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64</pre>
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