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Subject: [Bug c++/100370] [11/12 Regression] Incorrect -Wplacement-new with
 union
Date: Mon, 11 Apr 2022 12:38:34 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100370

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jason Merrill <jason@gcc.gnu.org>:

https://gcc.gnu.org/g:790b02af6a1fcfa07dba6129909b3578a55a51fa

commit r12-8079-g790b02af6a1fcfa07dba6129909b3578a55a51fa
Author: Jason Merrill <jason@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 whate=
ver
    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 d=
eref
    =3D=3D -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]: Req=
uire
            deref =3D=3D -1.

    gcc/testsuite/ChangeLog:

            * g++.dg/warn/Wplacement-new-size-11.C: New test.=