From 854f0984f0b7ab9a9a541a4bcda7ea173e4113d3 Mon Sep 17 00:00:00 2001 From: James Player Date: Wed, 13 Jan 2021 14:17:31 -0800 Subject: [PATCH] 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::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::NodeSubset> *,llvm::Optional::ChildIterator>>> &llvm::Optional::NodeSubset> *,llvm::Optional::ChildIterator>>>::operator =(const llvm::Optional::NodeSubset> *,llvm::Optional::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 ::value && std::is_trivially_copy_assignable::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 --- llvm/include/llvm/ADT/Optional.h | 7 +- llvm/unittests/ADT/OptionalTest.cpp | 121 ++++++++++++++++++++++++++++ 2 files changed, 127 insertions(+), 1 deletion(-) 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 ::value> +template ::value && + std::is_trivially_copy_assignable::value && + (std::is_trivially_move_constructible::value || + !std::is_move_constructible::value) && + (std::is_trivially_move_assignable::value || + !std::is_move_assignable::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 + 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::value, + "Expect NonTCopy to be trivially copyable"); + +static_assert(!std::is_trivially_copy_constructible::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; + 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 + 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::value, + "Expect NonTAssign to be trivially copyable"); + +static_assert(!std::is_trivially_copy_assignable::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; + 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; + + NoTMoveOptT NonTMove1; + NoTMoveOptT NonTMove2{std::move(NonTMove1)}; + + NonTMove1 = std::move(NonTMove2); + + static_assert( + std::is_trivially_copyable::value, + "Expect Optional to still use the trivial specialization " + "of OptionalStorage despite the deleted move constructor / assignment."); +} + #if LLVM_HAS_RVALUE_REFERENCE_THIS TEST(OptionalTest, MoveGetValueOr) {