diff options
author | James Player <jplayer@nvidia.com> | 2021-01-13 14:17:31 -0800 |
---|---|---|
committer | David Blaikie <dblaikie@gmail.com> | 2021-01-13 15:23:48 -0800 |
commit | 854f0984f0b7ab9a9a541a4bcda7ea173e4113d3 (patch) | |
tree | 736a76537885174ab6db434498ed216752a41f81 | |
parent | 7ec8f43659861be42f9d600422678196849b6e90 (diff) | |
download | llvm-854f0984f0b7ab9a9a541a4bcda7ea173e4113d3.tar.gz |
Fix llvm::Optional build breaks in MSVC using std::is_trivially_copyable
Current code breaks this version of MSVC due to a mismatch between `std::is_trivially_copyable` and `llvm::is_trivially_copyable` for `std::pair` instantiations. Hence I was attempting to use `std::is_trivially_copyable` to set `llvm::is_trivially_copyable<T>::value`.
I spent some time root causing an `llvm::Optional` build error on MSVC 16.8.3 related to the change described above:
```
62>C:\src\ocg_llvm\llvm-project\llvm\include\llvm/ADT/BreadthFirstIterator.h(96,12): error C2280: 'llvm::Optional<std::pair<std::pair<unsigned int,llvm::Graph<4>::NodeSubset> *,llvm::Optional<llvm::Graph<4>::ChildIterator>>> &llvm::Optional<std::pair<std::pair<unsigned int,llvm::Graph<4>::NodeSubset> *,llvm::Optional<llvm::Graph<4>::ChildIterator>>>::operator =(const llvm::Optional<std::pair<std::pair<unsigned int,llvm::Graph<4>::NodeSubset> *,llvm::Optional<llvm::Graph<4>::ChildIterator>>> &)': attempting to reference a deleted function (compiling source file C:\src\ocg_llvm\llvm-project\llvm\unittests\ADT\BreadthFirstIteratorTest.cpp)
...
```
The "trivial" specialization of `optional_detail::OptionalStorage` assumes that the value type is trivially copy constructible and trivially copy assignable. The specialization is invoked based on a check of `is_trivially_copyable` alone, which does not imply both `is_trivially_copy_assignable` and `is_trivially_copy_constructible` are true.
[[ https://en.cppreference.com/w/cpp/named_req/TriviallyCopyable | According to the spec ]], a deleted assignment operator does not make `is_trivially_copyable` false. So I think all these properties need to be checked explicitly in order to specialize `OptionalStorage` to the "trivial" version:
```
/// Storage for any type.
template <typename T, bool = std::is_trivially_copy_constructible<T>::value
&& std::is_trivially_copy_assignable<T>::value>
class OptionalStorage {
```
Above fixed my build break in MSVC, but I think we need to explicitly check `is_trivially_copy_constructible` too since it might be possible the copy constructor is deleted. Also would be ideal to move over to `std::is_trivially_copyable` instead of the `llvm` namespace verson.
Reviewed By: dblaikie
Differential Revision: https://reviews.llvm.org/D93510
-rw-r--r-- | llvm/include/llvm/ADT/Optional.h | 7 | ||||
-rw-r--r-- | llvm/unittests/ADT/OptionalTest.cpp | 121 |
2 files changed, 127 insertions, 1 deletions
diff --git a/llvm/include/llvm/ADT/Optional.h b/llvm/include/llvm/ADT/Optional.h index daa9ee627fa9..820e586ff7dd 100644 --- a/llvm/include/llvm/ADT/Optional.h +++ b/llvm/include/llvm/ADT/Optional.h @@ -33,7 +33,12 @@ namespace optional_detail { struct in_place_t {}; /// Storage for any type. -template <typename T, bool = is_trivially_copyable<T>::value> +template <typename T, bool = (std::is_trivially_copy_constructible<T>::value && + std::is_trivially_copy_assignable<T>::value && + (std::is_trivially_move_constructible<T>::value || + !std::is_move_constructible<T>::value) && + (std::is_trivially_move_assignable<T>::value || + !std::is_move_assignable<T>::value))> class OptionalStorage { union { char empty; diff --git a/llvm/unittests/ADT/OptionalTest.cpp b/llvm/unittests/ADT/OptionalTest.cpp index c7fa796a2d7f..235b834887d1 100644 --- a/llvm/unittests/ADT/OptionalTest.cpp +++ b/llvm/unittests/ADT/OptionalTest.cpp @@ -390,6 +390,127 @@ TEST(OptionalTest, ImmovableEmplace) { EXPECT_EQ(0u, Immovable::Destructions); } +// Craft a class which is_trivially_copyable, but not +// is_trivially_copy_constructible. +struct NonTCopy { + NonTCopy() = default; + + // Delete the volatile copy constructor to engage the "rule of 3" and delete + // any unspecified copy assignment or constructor. + NonTCopy(volatile NonTCopy const &) = delete; + + // Leave the non-volatile default copy constructor unspecified (deleted by + // rule of 3) + + // This template can serve as the copy constructor, but isn't chosen + // by =default in a class with a 'NonTCopy' member. + template <typename Self = NonTCopy> + NonTCopy(Self const &Other) : Val(Other.Val) {} + + NonTCopy &operator=(NonTCopy const &) = default; + + int Val{0}; +}; + +#if defined(_MSC_VER) && _MSC_VER >= 1927 +// Currently only true on recent MSVC releases. +static_assert(std::is_trivially_copyable<NonTCopy>::value, + "Expect NonTCopy to be trivially copyable"); + +static_assert(!std::is_trivially_copy_constructible<NonTCopy>::value, + "Expect NonTCopy not to be trivially copy constructible."); +#endif // defined(_MSC_VER) && _MSC_VER >= 1927 + +TEST(OptionalTest, DeletedCopyConstructor) { + + // Expect compile to fail if 'trivial' version of + // optional_detail::OptionalStorage is chosen. + using NonTCopyOptT = Optional<NonTCopy>; + NonTCopyOptT NonTCopy1; + + // Check that the Optional can be copy constructed. + NonTCopyOptT NonTCopy2{NonTCopy1}; + + // Check that the Optional can be copy assigned. + NonTCopy1 = NonTCopy2; +} + +// Craft a class which is_trivially_copyable, but not +// is_trivially_copy_assignable. +class NonTAssign { +public: + NonTAssign() = default; + NonTAssign(NonTAssign const &) = default; + + // Delete the volatile copy assignment to engage the "rule of 3" and delete + // any unspecified copy assignment or constructor. + NonTAssign &operator=(volatile NonTAssign const &) = delete; + + // Leave the non-volatile default copy assignment unspecified (deleted by rule + // of 3). + + // This template can serve as the copy assignment, but isn't chosen + // by =default in a class with a 'NonTAssign' member. + template <typename Self = NonTAssign> + NonTAssign &operator=(Self const &Other) { + A = Other.A; + return *this; + } + + int A{0}; +}; + +#if defined(_MSC_VER) && _MSC_VER >= 1927 +// Currently only true on recent MSVC releases. +static_assert(std::is_trivially_copyable<NonTAssign>::value, + "Expect NonTAssign to be trivially copyable"); + +static_assert(!std::is_trivially_copy_assignable<NonTAssign>::value, + "Expect NonTAssign not to be trivially assignable."); +#endif // defined(_MSC_VER) && _MSC_VER >= 1927 + +TEST(OptionalTest, DeletedCopyAssignment) { + + // Expect compile to fail if 'trivial' version of + // optional_detail::OptionalStorage is chosen. + using NonTAssignOptT = Optional<NonTAssign>; + NonTAssignOptT NonTAssign1; + + // Check that the Optional can be copy constructed. + NonTAssignOptT NonTAssign2{NonTAssign1}; + + // Check that the Optional can be copy assigned. + NonTAssign1 = NonTAssign2; +} + +struct NoTMove { + NoTMove() = default; + NoTMove(NoTMove const &) = default; + NoTMove &operator=(NoTMove const &) = default; + + // Delete move constructor / assignment. Compiler should fall-back to the + // trivial copy constructor / assignment in the trivial OptionalStorage + // specialization. + NoTMove(NoTMove &&) = delete; + NoTMove &operator=(NoTMove &&) = delete; + + int Val{0}; +}; + +TEST(OptionalTest, DeletedMoveConstructor) { + using NoTMoveOptT = Optional<NoTMove>; + + NoTMoveOptT NonTMove1; + NoTMoveOptT NonTMove2{std::move(NonTMove1)}; + + NonTMove1 = std::move(NonTMove2); + + static_assert( + std::is_trivially_copyable<NoTMoveOptT>::value, + "Expect Optional<NoTMove> to still use the trivial specialization " + "of OptionalStorage despite the deleted move constructor / assignment."); +} + #if LLVM_HAS_RVALUE_REFERENCE_THIS TEST(OptionalTest, MoveGetValueOr) { |