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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 - Consteval functions in unevaluted context"
href="https://bugs.llvm.org/show_bug.cgi?id=47350">47350</a>
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<th>Summary</th>
<td>Consteval functions in unevaluted context
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>11.0
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Windows NT
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>C++2a
</td>
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<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>dudkindaniilm2@yandex.ru
</td>
</tr>
<tr>
<th>CC</th>
<td>blitzrakete@gmail.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
</td>
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<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=23903" name="attach_23903" title="The code">attachment 23903</a> <a href="attachment.cgi?id=23903&action=edit" title="The code">[details]</a></span>
The code
The problem is reproducible with clang 11 and clang trunk
Code:
struct N {
constexpr N() {}
N(N const&) = delete;
};
template <typename T> constexpr void bad_assert_copyable() { T t; T t2 = t; }
using ineffective = decltype(bad_assert_copyable<N>());
template <typename T> consteval void assert_copyable() { T t; T t2 = t; }
using check = decltype(assert_copyable<N>());
int main() {}
Link 1. <a href="https://godbolt.org/z/j9TTed">https://godbolt.org/z/j9TTed</a>
Link 2. <a href="https://wandbox.org/permlink/jYwoQg7pKd4mMMwv">https://wandbox.org/permlink/jYwoQg7pKd4mMMwv</a>
Before P1937R2 were merged into C++20 draft it really was an illegal code
because in unevaluted context consteval function must be evaluted. But now it's
totally legal code.
Link 3. P1937R2:
<a href="http://open-std.org/JTC1/SC22/WG21/docs/papers/2020/p1937r2.html">http://open-std.org/JTC1/SC22/WG21/docs/papers/2020/p1937r2.html</a>
Local compile using clang build from LLVM 11.0.0-rc2:
$ ./clang++ -v
clang version 11.0.0 (<a href="https://github.com/llvm/llvm-project.git">https://github.com/llvm/llvm-project.git</a>
0160ad802e899c2922bc9b29564080c22eb0908c)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /mnt/c/clang+llvm-11.0.0-rc2-x86_64-linux-gnu-ubuntu-20.04/bin/.
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/10
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/10
Candidate multilib: .;@m64
Selected multilib: .;@m64
$ ./clang++ test/bug.cpp -std=c++2a
test/bug.cpp:10:24: error: call to consteval function 'assert_copyable<N>' is
not a constant expression
using check = decltype(assert_copyable<N>());
^
test/bug.cpp:10:24: note: undefined function 'assert_copyable<N>' cannot be
used in a constant expression
test/bug.cpp:9:37: note: declared here
template<typename T> consteval void assert_copyable() { T t; T t2 = t; }
^
1 error generated.</pre>
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