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LWG-3460 Unimplementable noop_coroutine_handle guarantees #1452

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merged 8 commits into from
Dec 2, 2020
Merged

LWG-3460 Unimplementable noop_coroutine_handle guarantees #1452

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601461a
Implement LWG-3460
CaseyCarter Aug 21, 2020
d744965
Derp
CaseyCarter Nov 12, 2020
dbf617a
no plan survives first contact with the enemy
CaseyCarter Nov 12, 2020
1be493b
Bah - missed noop_coroutine_handle::address
CaseyCarter Dec 1, 2020
5958b30
Add a bit more test coverage for noop_coroutine_handle
CaseyCarter Dec 1, 2020
250bf06
Oops - finish noexcept coverage
CaseyCarter Dec 1, 2020
1f60458
Verify that `explicit operator bool` is noexcept.
StephanTLavavej Dec 1, 2020
37721ce
Consistently validate that coroutine_handle<>'s conversion to bool is…
CaseyCarter Dec 2, 2020
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56 changes: 45 additions & 11 deletions stl/inc/coroutine
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Original file line number Diff line number Diff line change
Expand Up @@ -88,13 +88,14 @@ struct coroutine_handle<void> {
__builtin_coro_destroy(_Ptr);
}

protected:
private:
void* _Ptr = nullptr;
};

template <class _Promise>
struct coroutine_handle : coroutine_handle<> {
using coroutine_handle<>::coroutine_handle;
struct coroutine_handle {
constexpr coroutine_handle() noexcept = default;
constexpr coroutine_handle(nullptr_t) noexcept {}

_NODISCARD static coroutine_handle from_promise(_Promise& _Prom) noexcept { // strengthened
const auto _Prom_ptr = const_cast<void*>(static_cast<const volatile void*>(_STD addressof(_Prom)));
Expand All @@ -109,15 +110,46 @@ struct coroutine_handle : coroutine_handle<> {
return *this;
}

_NODISCARD constexpr void* address() const noexcept {
return _Ptr;
}

_NODISCARD static constexpr coroutine_handle from_address(void* const _Addr) noexcept { // strengthened
coroutine_handle _Result;
_Result._Ptr = _Addr;
return _Result;
}

constexpr operator coroutine_handle<>() const noexcept {
return coroutine_handle<>::from_address(_Ptr);
}

constexpr explicit operator bool() const noexcept {
return _Ptr != nullptr;
}

_NODISCARD bool done() const noexcept { // strengthened
return __builtin_coro_done(_Ptr);
}

void operator()() const {
__builtin_coro_resume(_Ptr);
}

void resume() const {
__builtin_coro_resume(_Ptr);
}

void destroy() const noexcept { // strengthened
__builtin_coro_destroy(_Ptr);
}

_NODISCARD _Promise& promise() const noexcept { // strengthened
return *reinterpret_cast<_Promise*>(__builtin_coro_promise(_Ptr, 0, false));
}

private:
void* _Ptr = nullptr;
};

_NODISCARD constexpr bool operator==(const coroutine_handle<> _Left, const coroutine_handle<> _Right) noexcept {
Expand Down Expand Up @@ -145,9 +177,13 @@ struct noop_coroutine_promise {};

// STRUCT coroutine_handle<noop_coroutine_promise>
template <>
struct coroutine_handle<noop_coroutine_promise> : coroutine_handle<> {
struct coroutine_handle<noop_coroutine_promise> {
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friend coroutine_handle noop_coroutine() noexcept;

constexpr operator coroutine_handle<>() const noexcept {
return coroutine_handle<>::from_address(_Ptr);
}

constexpr explicit operator bool() const noexcept {
return true;
}
Expand All @@ -159,17 +195,15 @@ struct coroutine_handle<noop_coroutine_promise> : coroutine_handle<> {
constexpr void resume() const noexcept {}
constexpr void destroy() const noexcept {}

using _Promise = noop_coroutine_promise;

_NODISCARD _Promise& promise() const noexcept {
_NODISCARD noop_coroutine_promise& promise() const noexcept {
// Returns a reference to the associated promise
return *reinterpret_cast<_Promise*>(__builtin_coro_promise(_Ptr, 0, false));
return *reinterpret_cast<noop_coroutine_promise*>(__builtin_coro_promise(_Ptr, 0, false));
}

private:
coroutine_handle() noexcept {
_Ptr = __builtin_coro_noop();
}
coroutine_handle() noexcept = default;

void* _Ptr = __builtin_coro_noop();
};

// ALIAS noop_coroutine_handle
Expand Down