[Bug c++/88337] Implement P1002R1, P1327R1, P1330R0, C++20 relaxations of constexpr restrictions.

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88337

--- Comment #11 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Author: mpolacek
Date: Sun Dec 29 16:44:41 2019
New Revision: 279755

URL: https://gcc.gnu.org/viewcvs?rev=279755&root=gcc&view=rev
Log:
        PR c++/88337 - Implement P1327R1: Allow dynamic_cast in constexpr.

This patch implements
<http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p1327r1.html>.

When build_dynamic_cast realizes that a dynamic_cast needs a run-time check, it
generates a call to __dynamic_cast -- see dyncast.cc in libsupc++ for its
definition.  The gist of my approach is to evaluate such a call at compile
time.

        * constexpr.c (cxx_dynamic_cast_fn_p): New function.
        (extract_obj_from_addr_offset): New function.
        (get_component_with_type): New function.
        (cxx_eval_dynamic_cast_fn): New function.
        (cxx_eval_call_expression): Call cxx_eval_dynamic_cast_fn for a call
        to __dynamic_cast.
        (potential_constant_expression_1): Don't give up on
        cxx_dynamic_cast_fn_p.
        * rtti.c (build_dynamic_cast_1): When creating a call to
        __dynamic_cast, use the location of the original expression.

        * g++.dg/cpp2a/constexpr-dynamic1.C: New test.
        * g++.dg/cpp2a/constexpr-dynamic10.C: New test.
        * g++.dg/cpp2a/constexpr-dynamic11.C: New test.
        * g++.dg/cpp2a/constexpr-dynamic12.C: New test.
        * g++.dg/cpp2a/constexpr-dynamic13.C: New test.
        * g++.dg/cpp2a/constexpr-dynamic14.C: New test.
        * g++.dg/cpp2a/constexpr-dynamic15.C: New test.
        * g++.dg/cpp2a/constexpr-dynamic16.C: New test.
        * g++.dg/cpp2a/constexpr-dynamic17.C: New test.
        * g++.dg/cpp2a/constexpr-dynamic2.C: New test.
        * g++.dg/cpp2a/constexpr-dynamic3.C: New test.
        * g++.dg/cpp2a/constexpr-dynamic4.C: New test.
        * g++.dg/cpp2a/constexpr-dynamic5.C: New test.
        * g++.dg/cpp2a/constexpr-dynamic6.C: New test.
        * g++.dg/cpp2a/constexpr-dynamic7.C: New test.
        * g++.dg/cpp2a/constexpr-dynamic8.C: New test.
        * g++.dg/cpp2a/constexpr-dynamic9.C: New test.

Added:
    trunk/gcc/testsuite/g++.dg/cpp2a/constexpr-dynamic1.C
    trunk/gcc/testsuite/g++.dg/cpp2a/constexpr-dynamic10.C
    trunk/gcc/testsuite/g++.dg/cpp2a/constexpr-dynamic11.C
    trunk/gcc/testsuite/g++.dg/cpp2a/constexpr-dynamic12.C
    trunk/gcc/testsuite/g++.dg/cpp2a/constexpr-dynamic13.C
    trunk/gcc/testsuite/g++.dg/cpp2a/constexpr-dynamic14.C
    trunk/gcc/testsuite/g++.dg/cpp2a/constexpr-dynamic15.C
    trunk/gcc/testsuite/g++.dg/cpp2a/constexpr-dynamic16.C
    trunk/gcc/testsuite/g++.dg/cpp2a/constexpr-dynamic17.C
    trunk/gcc/testsuite/g++.dg/cpp2a/constexpr-dynamic2.C
    trunk/gcc/testsuite/g++.dg/cpp2a/constexpr-dynamic3.C
    trunk/gcc/testsuite/g++.dg/cpp2a/constexpr-dynamic4.C
    trunk/gcc/testsuite/g++.dg/cpp2a/constexpr-dynamic5.C
    trunk/gcc/testsuite/g++.dg/cpp2a/constexpr-dynamic6.C
    trunk/gcc/testsuite/g++.dg/cpp2a/constexpr-dynamic7.C
    trunk/gcc/testsuite/g++.dg/cpp2a/constexpr-dynamic8.C
    trunk/gcc/testsuite/g++.dg/cpp2a/constexpr-dynamic9.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/constexpr.c
    trunk/gcc/cp/rtti.c
    trunk/gcc/testsuite/ChangeLog