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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - __compressed_pair doesn't correctly forward constructor arguments."
href="https://llvm.org/bugs/show_bug.cgi?id=31051">31051</a>
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<th>Summary</th>
<td>__compressed_pair doesn't correctly forward constructor arguments.
</td>
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<th>Product</th>
<td>libc++
</td>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Windows NT
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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>All Bugs
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>eric@efcs.ca
</td>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org, mclow.lists@gmail.com
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<th>Classification</th>
<td>Unclassified
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<p>
<div>
<pre>__compressed_pair takes it's arguments by value, which incurs an additional
copy or move. This needs to be fixed.
Reproducer:
#include <memory>
#include <cassert>
int A_moved = 0;
struct A {
A() = default;
A(A const&) = default;
A(A&&) { ++A_moved; };
};
int main() {
std::__compressed_pair<A, int> p(A{});
assert(A_moved == 3); // Assert passes
assert(A_moved == 1); // Assert fails
}</pre>
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