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Workaround for MSVC's constexpr array allocation bug for vector #6177

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Merged
Stephan T. Lavavej (StephanTLavavej) merged 2 commits into from
Mar 27, 2026
Merged

Workaround for MSVC's constexpr array allocation bug for vector #6177

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109b7ca
Workaround for MSVC's `constexpr` array allocation bug for `vector`
frederick-vs-ja Mar 22, 2026
2f53a15
Merge branch 'microsoft:main' into workaround-dev-11060638
frederick-vs-ja Mar 25, 2026
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4 changes: 4 additions & 0 deletions stl/inc/vector
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Original file line number Diff line number Diff line change
Expand Up @@ -1656,7 +1656,11 @@ private:
_Newvec = _Allocate_at_least_helper(_Al, _Newcapacity);
} else {
_STL_INTERNAL_STATIC_ASSERT(_Policy == _Reallocation_policy::_Exactly);
#if !defined(__clang__) && !defined(__EDG__) // TRANSITION, DevCom-11060638
_Newvec = _Al.allocate(_Newcapacity) + decltype(pointer{} - pointer{}){0};
#else // ^^^ workaround / no workaround vvv
_Newvec = _Al.allocate(_Newcapacity);
#endif // ^^^ no workaround ^^^
}

_Allocation_guard<_Alty> _Guard{_Al, _Newvec, _Newcapacity};
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9 changes: 9 additions & 0 deletions stl/inc/xmemory
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Expand Up @@ -2320,11 +2320,20 @@ _NODISCARD_RAW_PTR_ALLOC _CONSTEXPR20 typename allocator_traits<_Alloc>::pointer
if constexpr (_Should_allocate_at_least<_Alloc>) {
auto [_Ptr, _Allocated] = _Al.allocate_at_least(_Count);
_Count = _Allocated;
#if !defined(__clang__) && !defined(__EDG__) // TRANSITION, DevCom-11060638
return _Ptr + decltype(_Ptr - _Ptr){0};
#else // ^^^ workaround / no workaround vvv
return _Ptr;
#endif // ^^^ no workaround ^^^
} else
#endif // _HAS_CXX23
{
#if !defined(__clang__) && !defined(__EDG__) // TRANSITION, DevCom-11060638
using _Pointer = decltype(_Al.allocate(_Count));
return _Al.allocate(_Count) + decltype(_Pointer{} - _Pointer{}){0};
#else // ^^^ workaround / no workaround vvv
return _Al.allocate(_Count);
#endif // ^^^ no workaround ^^^
}
}

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4 changes: 0 additions & 4 deletions tests/std/tests/P1004R2_constexpr_vector/test.cpp
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Expand Up @@ -679,15 +679,11 @@ constexpr bool test_vector_of_array() {
#endif // !_HAS_CXX23
{
test_vector_of_array_impl<unique_ptr<vector<char>>, 1>();
#if defined(__clang__) || defined(__EDG__) // TRANSITION, GH-6155 (not yet reported to MSVC)
test_vector_of_array_impl<unique_ptr<vector<char>>, 42>();
#endif // ^^^ no workaround ^^^
}

test_vector_of_array_impl<vector<long>, 1>();
#if defined(__clang__) || defined(__EDG__) // TRANSITION, GH-6155 (not yet reported to MSVC)
test_vector_of_array_impl<vector<long>, 42>();
#endif // ^^^ no workaround ^^^

return true;
}
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