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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - valueless_by_exception() should unconditionally return false if all the constructors are noexcept"
href="https://bugs.llvm.org/show_bug.cgi?id=39072">39072</a>
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<th>Summary</th>
<td>valueless_by_exception() should unconditionally return false if all the constructors are noexcept
</td>
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<th>Product</th>
<td>libc++
</td>
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<th>Version</th>
<td>7.0
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>All Bugs
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>antoshkka@gmail.com
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org, mclow.lists@gmail.com
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<p>
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<pre>Right now the variant::valueless_by_exception() is defined like that:
constexpr bool valueless_by_exception() const noexcept {
return index() == variant_npos;
}
Above code is quite complex for the optimizer. It may be profitable to detect
variant types that never have valueless_by_exception() state and re-implement
the function:
constexpr bool valueless_by_exception() const noexcept {
return !__always_valid::value /*compile-time constant*/ && index() ==
variant_npos;
}
Such change would improve assembly for multiple functions including
comparisons, swap, get and constructors.</pre>
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