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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 - [concepts] requires expression wrongly evaluates to true within a class template"
href="https://bugs.llvm.org/show_bug.cgi?id=45162">45162</a>
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<th>Summary</th>
<td>[concepts] requires expression wrongly evaluates to true within a class template
</td>
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<th>Product</th>
<td>clang
</td>
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<tr>
<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>Windows NT
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<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++2a
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>heavenandhell171@gmail.com
</td>
</tr>
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<th>CC</th>
<td>blitzrakete@gmail.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk, saar@raz.email
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<p>
<div>
<pre>$ clang++.exe --version
clang version 11.0.0 (<a href="https://github.com/llvm/llvm-project.git">https://github.com/llvm/llvm-project.git</a>
fc3c80c38643aff6c4744433ab485c7550ee77b9)
$ cat test.cpp
#ifdef BUG
template <typename T>
#endif
struct test_t {
template <typename U>
int exec(U) {
if constexpr (requires { this->is_memmovable<U>(); })
return 1;
else
return 0;
}
template <typename>
requires false
auto is_memmovable() -> void;
};
int test() {
#ifdef BUG
using test_type = test_t<int>;
#else
using test_type = test_t;
#endif
return test_type{}.exec(0);
}
$ clang++.exe -std=c++2a -O3 -c -S -o - test.cpp -DBUG
"?test@@YAHXZ": # @"?test@@YAHXZ"
# %bb.0:
movl $1, %eax
retl
$ clang++.exe -std=c++2a -O3 -c -S -o - test.cpp
"?test@@YAHXZ": # @"?test@@YAHXZ"
# %bb.0:
xorl %eax, %eax
retl
The requires expression only gives the wrong result if test_t is a template.
Otherwise it correctly evaluates to false.</pre>
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