https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102586
--- Comment #29 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:c879b92c30d088ff01eb0c3e912eb8a01f9fc6e3 commit r12-7641-gc879b92c30d088ff01eb0c3e912eb8a01f9fc6e3 Author: Jakub Jelinek <ja...@redhat.com> Date: Mon Mar 14 10:47:38 2022 +0100 c++: Reject __builtin_clear_padding on non-trivially-copyable types with one exception [PR102586] As mentioned by Jason in the PR, non-trivially-copyable types (or non-POD for purposes of layout?) types can be base classes of derived classes in which the padding in those non-trivially-copyable types can be reused for some real data members or even the layout can change and data members can be moved to other positions. __builtin_clear_padding is right now used for multiple purposes, in <atomic> where it isn't used yet but was planned as the main spot it can be used for trivially copyable types only, ditto for std::bit_cast where we also use it. It is used for OpenMP long double atomics too but long double is trivially copyable, and lastly for -ftrivial-auto-var-init=. The following patch restricts the builtin to pointers to trivially-copyable types, with the exception when it is called directly on an address of a variable, in that case already the FE can verify it is the complete object type and so it is safe to clear all the paddings in it. 2022-03-14 Jakub Jelinek <ja...@redhat.com> PR tree-optimization/102586 gcc/ * doc/extend.texi (__builtin_clear_padding): Clearify that for C++ argument type should be pointer to trivially-copyable type unless it is address of a variable or parameter. gcc/cp/ * call.cc (build_cxx_call): Diagnose __builtin_clear_padding where first argument's type is pointer to non-trivially-copyable type unless it is address of a variable or parameter. gcc/testsuite/ * g++.dg/cpp2a/builtin-clear-padding1.C: New test.
