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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - `llvm::is_trivially_copyable` -- static assertion failure after DR 1734"
href="https://bugs.llvm.org/show_bug.cgi?id=47160">47160</a>
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<th>Summary</th>
<td>`llvm::is_trivially_copyable` -- static assertion failure after DR 1734
</td>
</tr>
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<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<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>release blocker
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Support Libraries
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>npmazzuca@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<pre>I believe only VC++ 19.27 (latest version) actually implements DR 1734, but
`llvm::is_trivially_copyable` doesn't agree with `std::is_trivially_copyable`
on `pair<void*, size_t>` after DR 1734. This results in a build error:
C:\...\llvm\include\llvm/Support/type_traits.h(181): error C2338: inconsistent
behavior between llvm:: and std:: implementation of is_trivially_copyable
C:\...\llvm\include\llvm/ADT/SmallVector.h(315): note: see reference to class
template instantiation 'llvm::is_trivially_copyable<T>' being compiled
with
[
T=std::pair<void *,size_t>
]
C:\...\llvm\include\llvm/ADT/SmallVector.h(837): note: see reference to class
template instantiation 'llvm::SmallVectorImpl<T>' being compiled
with
[
T=std::pair<void *,size_t>
]
C:\...\llvm\include\llvm/Support/Allocator.h(378): note: see reference to class
template instantiation 'llvm::SmallVector<std::pair<void *,size_t>,0>' being
compiled
C:\...\llvm\include\llvm/Support/Allocator.h(435): note: see reference to class
template instantiation
'llvm::BumpPtrAllocatorImpl<AllocatorT,SlabSize,SizeThreshold>' being compiled
C:\...\llvm\include\llvm/ADT/SmallVector.h(315): error C2976:
'llvm::SmallVectorTemplateBase': too few template arguments
C:\...\llvm\include\llvm/ADT/SmallVector.h(179): note: see declaration of
'llvm::SmallVectorTemplateBase'
A simple example of a program that changes behavior after DR 1734 is the
following:
struct meow {
meow(const meow&) = default;
meow& operator=(const volatile meow&) = delete;
template <class U = meow>
meow& operator=(const U&) {}
};
static_assert(__is_trivially_copyable(meow));</pre>
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