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Primary motivation: is that after #84651 msan will complain if fields accessed after ~__no_destroy. My understanding of the https://eel.is/c++draft/basic.life#10 Static object with trivial destruction has program lifetime. Static object with empty destuctor has implicit lifetime, and accessing the object after lifetime is UB. It was UB before #84651, it's just msan ignored union members. Existing code with unions uses empty destructor, so accessing after the main() can cause UB. "placement new" version can have trivial destructor, so there is no end of lifetime. Secondary motivation: empty destructor will register __cxa_atexit with -O0. https://gcc.godbolt.org/z/hce587b65 We can not remove the destructor with union where _Tp can have non-trivial destructor. But we can remove destructor if we use in-place new instead of union. https://gcc.godbolt.org/z/Yqxx57eEd - empty even with -O0. New test fails without the patch on https://lab.llvm.org/buildbot/#/builders/sanitizer-x86_64-linux-bootstrap-msan