[Bug c++/110441] c++17: temporary causes static member function call to confuse required copy elision

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110441

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:0de651db45c758f54e9ed917069795a3835499de

commit r14-2539-g0de651db45c758f54e9ed917069795a3835499de
Author: Patrick Palka <ppalka@redhat.com>
Date:   Sat Jul 15 09:50:51 2023 -0400

    c++: copy elision w/ obj arg and static memfn call [PR110441]

    Here the call A().f() is represented as a COMPOUND_EXPR whose first
    operand is the otherwise unused object argument A() and second operand
    is the call result (both are TARGET_EXPRs).  Within the return statement,
    this outermost COMPOUND_EXPR ends up foiling the copy elision check in
    build_special_member_call, resulting in us introducing a bogus call to the
    deleted move constructor.  (Within the variable initialization, which goes
    through ocp_convert instead of convert_for_initialization, we've already
    been eliding the copy -- despite the outermost COMPOUND_EXPR -- ever since
    r10-7410-g72809d6fe8e085 made ocp_convert look through COMPOUND_EXPR).

    In contrast I noticed '(A(), A::f())' (which should be equivalent to
    the above call) is represented with the COMPOUND_EXPR inside the RHS's
    TARGET_EXPR initializer thanks to a special case in cp_build_compound_expr.

    So this patch fixes this by making keep_unused_object_arg use
    cp_build_compound_expr as well.

            PR c++/110441

    gcc/cp/ChangeLog:

            * call.cc (keep_unused_object_arg): Use cp_build_compound_expr
            instead of building a COMPOUND_EXPR directly.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp1z/elide8.C: New test.