https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110619
--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The trunk branch has been updated by Jason Merrill <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:b8266af71c19a0bd7db4d08c8d2ee3c33214508c commit r14-2772-gb8266af71c19a0bd7db4d08c8d2ee3c33214508c Author: Nathaniel Shead <nathanielosh...@gmail.com> Date: Sun Jul 23 01:14:37 2023 +1000 c++: Prevent dangling pointers from becoming nullptr in constexpr [PR110619] Currently, when typeck discovers that a return statement will refer to a local variable it rewrites to return a null pointer. This causes the error messages for using the return value in a constant expression to be unhelpful, especially for reference return values, and is also a visible change to otherwise valid code (as in the linked PR). The transformation is nonetheless important, however, both as a safety guard against attackers being able to gain a handle to other data on the stack, and to prevent duplicate warnings from later null-dereference warning passes. As such, this patch just delays the transformation until cp_genericize, after constexpr function definitions have been generated. PR c++/110619 gcc/cp/ChangeLog: * cp-gimplify.cc (cp_genericize_r): Transform RETURN_EXPRs to not return dangling pointers. * cp-tree.h (RETURN_EXPR_LOCAL_ADDR_P): New flag. (check_return_expr): Add a new parameter. * semantics.cc (finish_return_stmt): Set flag on RETURN_EXPR when referring to dangling pointer. * typeck.cc (check_return_expr): Disable transformation of dangling pointers, instead pass this information to caller. gcc/testsuite/ChangeLog: * g++.dg/cpp1y/constexpr-110619.C: New test. Signed-off-by: Nathaniel Shead <nathanielosh...@gmail.com>
