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Make llvm::Optional<T> trivially copyable when T is trivially copyable

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This is an ever-recurring issue (see https://bugs.llvm.org/show_bug.cgi?id=39427 and https://bugs.llvm.org/show_bug.cgi?id=35978)
but I believe that thanks to https://reviews.llvm.org/D54472 we can now ship a decent implementation of this.

Basically the fact that llvm::is_trivially_copyable has a consistent behavior across compilers should prevent any ABI issue,
and using in-place new instead of memcpy should keep compiler bugs away.

Differential Revision: https://reviews.llvm.org/D57097

llvm-svn: 353927
This commit is contained in:
Serge Guelton 2019-02-13 09:31:22 +00:00
parent ef8b9cdabe
commit 920e69d8bf
2 changed files with 84 additions and 31 deletions
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95
include/llvm/ADT/Optional.h
View File

@ -29,36 +29,77 @@ namespace llvm {
class raw_ostream;
namespace optional_detail {
/// Storage for any type.
template <typename T, bool = is_trivially_copyable<T>::value> struct OptionalStorage {
//
template <class T> struct OptionalTrivialStorage {
AlignedCharArrayUnion<T> storage;
bool hasVal = false;
OptionalTrivialStorage() = default;
OptionalTrivialStorage(OptionalTrivialStorage const &) = default;
OptionalTrivialStorage(OptionalTrivialStorage &&) = default;
OptionalTrivialStorage &operator=(OptionalTrivialStorage const &) = default;
OptionalTrivialStorage &operator=(OptionalTrivialStorage &&) = default;
~OptionalTrivialStorage() = default;
OptionalTrivialStorage(const T &y) : hasVal(true) {
new (storage.buffer) T(y);
}
OptionalTrivialStorage(T &&y) : hasVal(true) {
new (storage.buffer) T(std::move(y));
}
OptionalTrivialStorage &operator=(const T &y) {
new (storage.buffer) T(y);
hasVal = true;
return *this;
}
OptionalTrivialStorage &operator=(T &&y) {
new (storage.buffer) T(std::move(y));
hasVal = true;
return *this;
}
T *getPointer() {
assert(hasVal);
return reinterpret_cast<T *>(storage.buffer);
}
const T *getPointer() const {
assert(hasVal);
return reinterpret_cast<const T *>(storage.buffer);
}
void reset() { hasVal = false; }
};
template <typename T> struct OptionalStorage : OptionalTrivialStorage<T> {
OptionalStorage() = default;
OptionalStorage(const T &y) : hasVal(true) { new (storage.buffer) T(y); }
OptionalStorage(const OptionalStorage &O) : hasVal(O.hasVal) {
if (hasVal)
new (storage.buffer) T(*O.getPointer());
OptionalStorage(const T &y) : OptionalTrivialStorage<T>(y) {}
OptionalStorage(T &&y) : OptionalTrivialStorage<T>(std::move(y)) {}
OptionalStorage(const OptionalStorage &O) : OptionalTrivialStorage<T>() {
this->hasVal = O.hasVal;
if (this->hasVal)
new (this->storage.buffer) T(*O.getPointer());
}
OptionalStorage(T &&y) : hasVal(true) {
new (storage.buffer) T(std::forward<T>(y));
}
OptionalStorage(OptionalStorage &&O) : hasVal(O.hasVal) {
OptionalStorage(OptionalStorage &&O) : OptionalTrivialStorage<T>() {
this->hasVal = O.hasVal;
if (O.hasVal) {
new (storage.buffer) T(std::move(*O.getPointer()));
new (this->storage.buffer) T(std::move(*O.getPointer()));
}
}
OptionalStorage &operator=(T &&y) {
if (hasVal)
*getPointer() = std::move(y);
if (this->hasVal)
*this->getPointer() = std::move(y);
else {
new (storage.buffer) T(std::move(y));
hasVal = true;
OptionalTrivialStorage<T>::operator=(std::move(y));
}
return *this;
}
OptionalStorage &operator=(OptionalStorage &&O) {
if (!O.hasVal)
reset();
@ -74,11 +115,10 @@ template <typename T, bool = is_trivially_copyable<T>::value> struct OptionalSto
// requirements (notably: the existence of a default ctor) when implemented
// in that way. Careful SFINAE to avoid such pitfalls would be required.
OptionalStorage &operator=(const T &y) {
if (hasVal)
*getPointer() = y;
if (this->hasVal)
*this->getPointer() = y;
else {
new (storage.buffer) T(y);
hasVal = true;
OptionalTrivialStorage<T>::operator=(y);
}
return *this;
}
@ -93,26 +133,19 @@ template <typename T, bool = is_trivially_copyable<T>::value> struct OptionalSto
~OptionalStorage() { reset(); }
void reset() {
if (hasVal) {
(*getPointer()).~T();
hasVal = false;
if (this->hasVal) {
(*this->getPointer()).~T();
OptionalTrivialStorage<T>::reset();
}
}
T *getPointer() {
assert(hasVal);
return reinterpret_cast<T *>(storage.buffer);
}
const T *getPointer() const {
assert(hasVal);
return reinterpret_cast<const T *>(storage.buffer);
}
};
} // namespace optional_detail
template <typename T> class Optional {
optional_detail::OptionalStorage<T> Storage;
typename std::conditional<is_trivially_copyable<T>::value,
optional_detail::OptionalTrivialStorage<T>,
optional_detail::OptionalStorage<T>>::type Storage;
public:
using value_type = T;

20
unittests/ADT/OptionalTest.cpp
View File

@ -16,6 +16,12 @@ using namespace llvm;
namespace {
static_assert(llvm::is_trivially_copyable<Optional<int>>::value,
"trivially copyable");
static_assert(llvm::is_trivially_copyable<Optional<std::array<int, 3>>>::value,
"trivially copyable");
struct NonDefaultConstructible {
static unsigned CopyConstructions;
static unsigned Destructions;
@ -43,6 +49,10 @@ unsigned NonDefaultConstructible::CopyConstructions = 0;
unsigned NonDefaultConstructible::Destructions = 0;
unsigned NonDefaultConstructible::CopyAssignments = 0;
static_assert(
!llvm::is_trivially_copyable<Optional<NonDefaultConstructible>>::value,
"not trivially copyable");
// Test fixture
class OptionalTest : public testing::Test {
};
@ -201,6 +211,10 @@ struct MultiArgConstructor {
};
unsigned MultiArgConstructor::Destructions = 0;
static_assert(
!llvm::is_trivially_copyable<Optional<MultiArgConstructor>>::value,
"not trivially copyable");
TEST_F(OptionalTest, Emplace) {
MultiArgConstructor::ResetCounts();
Optional<MultiArgConstructor> A;
@ -248,6 +262,9 @@ unsigned MoveOnly::MoveConstructions = 0;
unsigned MoveOnly::Destructions = 0;
unsigned MoveOnly::MoveAssignments = 0;
static_assert(!llvm::is_trivially_copyable<Optional<MoveOnly>>::value,
"not trivially copyable");
TEST_F(OptionalTest, MoveOnlyNull) {
MoveOnly::ResetCounts();
Optional<MoveOnly> O;
@ -349,6 +366,9 @@ private:
unsigned Immovable::Constructions = 0;
unsigned Immovable::Destructions = 0;
static_assert(!llvm::is_trivially_copyable<Optional<Immovable>>::value,
"not trivially copyable");
TEST_F(OptionalTest, ImmovableEmplace) {
Optional<Immovable> A;
Immovable::ResetCounts();