https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100370
--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jason Merrill <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:790b02af6a1fcfa07dba6129909b3578a55a51fa commit r12-8079-g790b02af6a1fcfa07dba6129909b3578a55a51fa Author: Jason Merrill <ja...@redhat.com> Date: Tue Apr 5 22:29:06 2022 -0400 c++: -Wplacement-new and anon union member [PR100370] This bug was an object/value confusion; we are interested in the size of *b.ip, but instead the code was calculating the size of b.ip itself. This seems to be because compute_objsize will compute the size of whatever object it can find in the argument: if you pass it a VAR_DECL, it gives you the size of that variable. If you pass it an ADDR_EXPR of a VAR_DECL, it again gives you the size of the variable. The way you can tell the difference is by looking at the deref member of access_ref: if it's -1, the argument is a pointer to the object. Since that's what we're interested in, we should check for that, like check_dangling_stores does. This regressed some tests because compute_objsize_r was wrongly zeroing deref in the POINTER_PLUS_EXPR handling; adding an offset to a pointer doesn't change whether the pointer is itself a variable or a pointer to one. In fact, handling POINTER_PLUS_EXPR only really makes sense for deref == -1, where we're adjusting a pointer to the variable. PR c++/100370 gcc/cp/ChangeLog: * init.cc (warn_placement_new_too_small): Check deref. gcc/ChangeLog: * pointer-query.cc (compute_objsize_r) [POINTER_PLUS_EXPR]: Require deref == -1. gcc/testsuite/ChangeLog: * g++.dg/warn/Wplacement-new-size-11.C: New test.
