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Fix call unwrapping optimization #5919

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Merged
Stephan T. Lavavej (StephanTLavavej) merged 5 commits into from
Dec 1, 2025
Merged

Fix call unwrapping optimization #5919

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ac0a703
Fix call unwrapping optimization
AlexGuteniev Nov 30, 2025
f749382
better coverage
AlexGuteniev Nov 30, 2025
2486130
Proper fix
AlexGuteniev Nov 30, 2025
2f17e32
fix comment
AlexGuteniev Nov 30, 2025
2729c74
Use aggregate init for the guard.
StephanTLavavej Dec 1, 2025
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38 changes: 32 additions & 6 deletions stl/inc/functional
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Original file line number Diff line number Diff line change
Expand Up @@ -1629,24 +1629,50 @@ public:
_STL_INTERNAL_STATIC_ASSERT(alignof(max_align_t) == alignof(void*));
// 64-bit target, can put small function into small move_only_function directly
_Data._Impl = _Create_impl_ptr<_Impl_kind::_Old_fn_small, _Vt, void>();
_Old_fn_impl->_Move(_Data._Buf_ptr<void*>());
_Func._Tidy();
if constexpr (is_lvalue_reference_v<_Fn>) {
_Old_fn_impl->_Copy(_Data._Buf_ptr<void*>());
} else {
_Old_fn_impl->_Move(_Data._Buf_ptr<void*>());
_Func._Tidy();
}
#else // ^^^ 64-bit / 32-bit vvv
_STL_INTERNAL_STATIC_ASSERT(alignof(max_align_t) > alignof(void*));
// 32-bit target, cannot put small function into small move_only_function directly
// due to potentially not enough alignment. Allocate large function
void* _Where = ::operator new((_Small_object_num_ptrs - 1) * sizeof(void*));
_Old_fn_impl->_Move(_Where);
_Func._Tidy();
if constexpr (is_lvalue_reference_v<_Fn>) {
struct _NODISCARD _Guard_type {
void* _Ptr;

~_Guard_type() {
// _Ptr is not nullptr only if an exception is thrown as a result of _Copy.
// Check _Ptr before calling operator delete to save the call in the common case.
if (_Ptr) {
::operator delete(_Ptr);
}
}
};

_Guard_type _Guard{_Where};
_Old_fn_impl->_Copy(_Where);
_Guard._Ptr = nullptr;
} else {
_Old_fn_impl->_Move(_Where);
_Func._Tidy();
}

_Data._Impl = _Create_impl_ptr<_Impl_kind::_Old_fn_small_as_large, _Vt, void>();
_Data._Set_large_fn_ptr(_Where);
#endif // ^^^ 32-bit ^^^
} else {
// Just take ownership of the inner impl pointer
_Data._Impl = _Create_impl_ptr<_Impl_kind::_Old_fn_large, _Vt, void>();
_Data._Set_large_fn_ptr(_Old_fn_impl);
_Func._Set(nullptr);
if constexpr (is_lvalue_reference_v<_Fn>) {
_Data._Set_large_fn_ptr(_Old_fn_impl->_Copy(nullptr));
} else {
_Data._Set_large_fn_ptr(_Old_fn_impl);
_Func._Set(nullptr);
}
}
}

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22 changes: 17 additions & 5 deletions tests/std/tests/GH_005504_avoid_function_call_wrapping/test.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -104,6 +104,14 @@ void test_wrapped_call(const int expected_copies) {
assert(outer(copy_counter{}) == expected_copies);
}

template <class OuterWrapper, class InnerWrapper, class Callable>
void test_wrapped_copy_call(const int expected_copies) {
InnerWrapper inner{Callable{}};
OuterWrapper outer{inner};
assert(inner);
assert(outer(copy_counter{}) == expected_copies);
}

template <class Wrapper>
void check_call_null(Wrapper& wrapper, const bool throws) {
if (throws) {
Expand Down Expand Up @@ -143,18 +151,22 @@ int main() {
// Moves to the same
alloc_checker{0}, test_wrapped_call<function<fn_type>, function<fn_type>, small_callable>(0);
alloc_checker{1}, test_wrapped_call<function<fn_type>, function<fn_type>, large_callable>(0);
alloc_checker{0}, test_wrapped_copy_call<function<fn_type>, function<fn_type>, small_callable>(0);
alloc_checker{2}, test_wrapped_copy_call<function<fn_type>, function<fn_type>, large_callable>(0);
alloc_checker{0}, test_wrapped_call<move_only_function<fn_type>, move_only_function<fn_type>, small_callable>(0);
alloc_checker{1}, test_wrapped_call<move_only_function<fn_type>, move_only_function<fn_type>, large_callable>(0);

constexpr bool is_64_bit = sizeof(void*) > 4;

// Moves from function to move_only_function
#ifdef _WIN64
alloc_checker{0},
#else
alloc_checker{1},
#endif
alloc_checker{is_64_bit ? 0 : 1},
test_wrapped_call<move_only_function<fn_type>, function<fn_type>, small_callable>(0);
alloc_checker{1}, test_wrapped_call<move_only_function<fn_type>, function<fn_type>, large_callable>(0);

alloc_checker{is_64_bit ? 0 : 1},
test_wrapped_copy_call<move_only_function<fn_type>, function<fn_type>, small_callable>(0);
alloc_checker{2}, test_wrapped_copy_call<move_only_function<fn_type>, function<fn_type>, large_callable>(0);

// nulls
alloc_checker{0}, test_plain_null<function<fn_type>>(true);
alloc_checker{0}, test_plain_null<move_only_function<fn_type>>(false);
Expand Down