<memory>: Make algorithms properly destroy objects in constant evaluation
#5449
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StephanTLavavej
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May 2, 2025
tests/std/tests/P0784R7_library_support_for_more_constexpr_containers/test.cpp
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tests/std/tests/P0784R7_library_support_for_more_constexpr_containers/test.cpp
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Currently, MSVC STL's destroying algorithms skip ranges whose element types are trivially destructible. This is slightly non-conforming, because further access to the destroyed objects should cause core language UB and in turn cause constant evaluation failure.
This PR makes
std::(ranges::)destroy(_at, _n)always destroy objects during constant evaluation. The behavior difference is currently only observable by Clang due to bugs of MSVC (DevCom-10642767) and EDG (DevCom-10896316).The allocator-aware
_Destroy_rangeis not yet touched, because any attempt to access an element destroyed by that overload will raise library UB first.Related to #5225, although the "vectorized implementation" is no-op in these algorithms.The change aboutif constevalare dropped. See the review comments.