https://bugs.llvm.org/show_bug.cgi?id=47160
Bug ID: 47160
Summary: `llvm::is_trivially_copyable` -- static assertion
failure after DR 1734
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: release blocker
Priority: P
Component: Support Libraries
Assignee: unassignedb...@nondot.org
Reporter: npmazz...@gmail.com
CC: llvm-bugs@lists.llvm.org
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));
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