[llvm-dev] [llvm] r322838 - [ADT] Split optional to only include copy mechanics and dtor for non-trivial types.
Benjamin Kramer via llvm-dev
llvm-dev at lists.llvm.org
Wed Jan 24 14:47:38 PST 2018
That's an unintentional change. However, the reason for this change
was to make optional of trivially copyable types trivially copyable,
adding a user-provided move ctor would break that again :(
I'm leaning towards making the non-trivial version of llvm::Optional
more like std::optional. In the long term std::optional is going to
replace llvm::Optional. How bad would that be for your use case?
On Wed, Jan 24, 2018 at 9:20 PM, Sam McCall <sammccall at google.com> wrote:
> Hey Ben,
>
> This change broke some clangd code (no failing test, mea culpa), because it
> changed the move semantics.
>
> Previously: a moved-from llvm::Optional was None (for all types).
> Now: a moved-from llvm::Optional is None (for non-trivial types), and has
> the old value (for trivial types).
>
> FWIW, a moved-from std::optional is *not* nullopt, and contains the
> moved-from value.
> This seems sad to me, and kills a nice use of optional (this one), but
> there's some value in consistency with std.
>
> Either way, I wanted to bring this up because
> - I wasn't sure it was explicitly considered, and should probably be
> documented
> - I think we should have either the old llvm behavior or the std behavior,
> the new hybrid is a gotcha I think.
>
> WDYT?
>
> On Thu, Jan 18, 2018 at 12:26 PM, Benjamin Kramer via llvm-commits
> <llvm-commits at lists.llvm.org> wrote:
>>
>> Author: d0k
>> Date: Thu Jan 18 03:26:24 2018
>> New Revision: 322838
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=322838&view=rev
>> Log:
>> [ADT] Split optional to only include copy mechanics and dtor for
>> non-trivial types.
>>
>> This makes uses of Optional more transparent to the compiler (and
>> clang-tidy) and generates slightly smaller code.
>>
>> This is a re-land of r317019, which had issues with GCC 4.8 back then.
>> Those issues don't reproduce anymore, but I'll watch the buildbots
>> closely in case anything goes wrong.
>>
>> Modified:
>> llvm/trunk/include/llvm/ADT/Optional.h
>> llvm/trunk/unittests/ADT/OptionalTest.cpp
>>
>> Modified: llvm/trunk/include/llvm/ADT/Optional.h
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/Optional.h?rev=322838&r1=322837&r2=322838&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/include/llvm/ADT/Optional.h (original)
>> +++ llvm/trunk/include/llvm/ADT/Optional.h Thu Jan 18 03:26:24 2018
>> @@ -27,139 +27,173 @@
>>
>> namespace llvm {
>>
>> -template <typename T> class Optional {
>> +namespace optional_detail {
>> +/// Storage for any type.
>> +template <typename T, bool IsPodLike> struct OptionalStorage {
>> AlignedCharArrayUnion<T> storage;
>> bool hasVal = false;
>>
>> -public:
>> - using value_type = T;
>> -
>> - Optional(NoneType) {}
>> - explicit Optional() {}
>> -
>> - Optional(const T &y) : hasVal(true) { new (storage.buffer) T(y); }
>> + OptionalStorage() = default;
>>
>> - Optional(const Optional &O) : hasVal(O.hasVal) {
>> + 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);
>> + new (storage.buffer) T(*O.getPointer());
>> }
>> -
>> - Optional(T &&y) : hasVal(true) { new (storage.buffer)
>> T(std::forward<T>(y)); }
>> -
>> - Optional(Optional<T> &&O) : hasVal(O) {
>> - if (O) {
>> - new (storage.buffer) T(std::move(*O));
>> + OptionalStorage(T &&y) : hasVal(true) {
>> + new (storage.buffer) T(std::forward<T>(y));
>> + }
>> + OptionalStorage(OptionalStorage &&O) : hasVal(O.hasVal) {
>> + if (O.hasVal) {
>> + new (storage.buffer) T(std::move(*O.getPointer()));
>> O.reset();
>> }
>> }
>>
>> - ~Optional() { reset(); }
>> -
>> - Optional &operator=(T &&y) {
>> + OptionalStorage &operator=(T &&y) {
>> if (hasVal)
>> - **this = std::move(y);
>> + *getPointer() = std::move(y);
>> else {
>> new (storage.buffer) T(std::move(y));
>> hasVal = true;
>> }
>> return *this;
>> }
>> -
>> - Optional &operator=(Optional &&O) {
>> - if (!O)
>> + OptionalStorage &operator=(OptionalStorage &&O) {
>> + if (!O.hasVal)
>> reset();
>> else {
>> - *this = std::move(*O);
>> + *this = std::move(*O.getPointer());
>> O.reset();
>> }
>> return *this;
>> }
>>
>> - /// Create a new object by constructing it in place with the given
>> arguments.
>> - template <typename... ArgTypes> void emplace(ArgTypes &&... Args) {
>> - reset();
>> - hasVal = true;
>> - new (storage.buffer) T(std::forward<ArgTypes>(Args)...);
>> - }
>> -
>> - static inline Optional create(const T *y) {
>> - return y ? Optional(*y) : Optional();
>> - }
>> -
>> // FIXME: these assignments (& the equivalent const T&/const Optional&
>> ctors)
>> // could be made more efficient by passing by value, possibly unifying
>> them
>> // with the rvalue versions above - but this could place a different
>> set of
>> // requirements (notably: the existence of a default ctor) when
>> implemented
>> // in that way. Careful SFINAE to avoid such pitfalls would be
>> required.
>> - Optional &operator=(const T &y) {
>> + OptionalStorage &operator=(const T &y) {
>> if (hasVal)
>> - **this = y;
>> + *getPointer() = y;
>> else {
>> new (storage.buffer) T(y);
>> hasVal = true;
>> }
>> return *this;
>> }
>> -
>> - Optional &operator=(const Optional &O) {
>> - if (!O)
>> + OptionalStorage &operator=(const OptionalStorage &O) {
>> + if (!O.hasVal)
>> reset();
>> else
>> - *this = *O;
>> + *this = *O.getPointer();
>> return *this;
>> }
>>
>> + ~OptionalStorage() { reset(); }
>> +
>> void reset() {
>> if (hasVal) {
>> - (**this).~T();
>> + (*getPointer()).~T();
>> hasVal = false;
>> }
>> }
>>
>> - const T *getPointer() const {
>> - assert(hasVal);
>> - return reinterpret_cast<const T *>(storage.buffer);
>> - }
>> T *getPointer() {
>> assert(hasVal);
>> return reinterpret_cast<T *>(storage.buffer);
>> }
>> - const T &getValue() const LLVM_LVALUE_FUNCTION {
>> + const T *getPointer() const {
>> assert(hasVal);
>> - return *getPointer();
>> + return reinterpret_cast<const T *>(storage.buffer);
>> }
>> - T &getValue() LLVM_LVALUE_FUNCTION {
>> - assert(hasVal);
>> - return *getPointer();
>> +};
>> +
>> +/// Storage for trivially copyable types only.
>> +template <typename T> struct OptionalStorage<T, true> {
>> + AlignedCharArrayUnion<T> storage;
>> + bool hasVal = false;
>> +
>> + OptionalStorage() = default;
>> +
>> + OptionalStorage(const T &y) : hasVal(true) { new (storage.buffer) T(y);
>> }
>> + OptionalStorage &operator=(const T &y) {
>> + new (storage.buffer) T(y);
>> + hasVal = true;
>> + return *this;
>> }
>>
>> - explicit operator bool() const { return hasVal; }
>> - bool hasValue() const { return hasVal; }
>> - const T *operator->() const { return getPointer(); }
>> - T *operator->() { return getPointer(); }
>> - const T &operator*() const LLVM_LVALUE_FUNCTION {
>> - assert(hasVal);
>> - return *getPointer();
>> + void reset() { hasVal = false; }
>> +};
>> +} // namespace optional_detail
>> +
>> +template <typename T> class Optional {
>> + optional_detail::OptionalStorage<T, isPodLike<T>::value> Storage;
>> +
>> +public:
>> + using value_type = T;
>> +
>> + constexpr Optional() {}
>> + constexpr Optional(NoneType) {}
>> +
>> + Optional(const T &y) : Storage(y) {}
>> + Optional(const Optional &O) = default;
>> +
>> + Optional(T &&y) : Storage(std::forward<T>(y)) {}
>> + Optional(Optional &&O) = default;
>> +
>> + Optional &operator=(T &&y) {
>> + Storage = std::move(y);
>> + return *this;
>> }
>> - T &operator*() LLVM_LVALUE_FUNCTION {
>> - assert(hasVal);
>> - return *getPointer();
>> + Optional &operator=(Optional &&O) = default;
>> +
>> + /// Create a new object by constructing it in place with the given
>> arguments.
>> + template <typename... ArgTypes> void emplace(ArgTypes &&... Args) {
>> + reset();
>> + Storage.hasVal = true;
>> + new (getPointer()) T(std::forward<ArgTypes>(Args)...);
>> }
>>
>> + static inline Optional create(const T *y) {
>> + return y ? Optional(*y) : Optional();
>> + }
>> +
>> + Optional &operator=(const T &y) {
>> + Storage = y;
>> + return *this;
>> + }
>> + Optional &operator=(const Optional &O) = default;
>> +
>> + void reset() { Storage.reset(); }
>> +
>> + const T *getPointer() const {
>> + assert(Storage.hasVal);
>> + return reinterpret_cast<const T *>(Storage.storage.buffer);
>> + }
>> + T *getPointer() {
>> + assert(Storage.hasVal);
>> + return reinterpret_cast<T *>(Storage.storage.buffer);
>> + }
>> + const T &getValue() const LLVM_LVALUE_FUNCTION { return *getPointer();
>> }
>> + T &getValue() LLVM_LVALUE_FUNCTION { return *getPointer(); }
>> +
>> + explicit operator bool() const { return Storage.hasVal; }
>> + bool hasValue() const { return Storage.hasVal; }
>> + const T *operator->() const { return getPointer(); }
>> + T *operator->() { return getPointer(); }
>> + const T &operator*() const LLVM_LVALUE_FUNCTION { return *getPointer();
>> }
>> + T &operator*() LLVM_LVALUE_FUNCTION { return *getPointer(); }
>> +
>> template <typename U>
>> constexpr T getValueOr(U &&value) const LLVM_LVALUE_FUNCTION {
>> return hasValue() ? getValue() : std::forward<U>(value);
>> }
>>
>> #if LLVM_HAS_RVALUE_REFERENCE_THIS
>> - T &&getValue() && {
>> - assert(hasVal);
>> - return std::move(*getPointer());
>> - }
>> - T &&operator*() && {
>> - assert(hasVal);
>> - return std::move(*getPointer());
>> - }
>> + T &&getValue() && { return std::move(*getPointer()); }
>> + T &&operator*() && { return std::move(*getPointer()); }
>>
>> template <typename U>
>> T getValueOr(U &&value) && {
>>
>> Modified: llvm/trunk/unittests/ADT/OptionalTest.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/ADT/OptionalTest.cpp?rev=322838&r1=322837&r2=322838&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/unittests/ADT/OptionalTest.cpp (original)
>> +++ llvm/trunk/unittests/ADT/OptionalTest.cpp Thu Jan 18 03:26:24 2018
>> @@ -518,5 +518,14 @@ TEST_F(OptionalTest, OperatorGreaterEqua
>> CheckRelation<GreaterEqual>(InequalityLhs, InequalityRhs, !IsLess);
>> }
>>
>> +#if (__has_feature(is_trivially_copyable) && defined(_LIBCPP_VERSION)) ||
>> \
>> + (defined(__GNUC__) && __GNUC__ >= 5)
>> +static_assert(std::is_trivially_copyable<Optional<int>>::value,
>> + "Should be trivially copyable");
>> +static_assert(
>> +
>> !std::is_trivially_copyable<Optional<NonDefaultConstructible>>::value,
>> + "Shouldn't be trivially copyable");
>> +#endif
>> +
>> } // end anonymous namespace
>>
>>
>>
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