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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug bootstrap/98340] gcc trunk build with clang failure, part 2
Date: Thu, 17 Dec 2020 08:45:52 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98340

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Before r0-99643-g2defb926479247a61fe0fffbcf95597722a94c40 this used to be
rejected with:
pr98340.C: In member function =E2=80=98int uintset<T>::hash::foo() [with T =
=3D int]=E2=80=99:
pr98340.C:33:18:   instantiated from here
pr98340.C:29:33: error: type =E2=80=98uintset<int>=E2=80=99 is not a base t=
ype for type
=E2=80=98uintset<int>::hash=E2=80=99

clang++ rejects the above testcase even if it is just struct traits {};
i.e. not derived from delete_ptr_hash <uintset>, but accepts it if
uintptr<T>::hash isn't derived from hash_table<traits> but say hash_table<i=
nt>
(rejects if it is derived
from hash_table<uintptr<T>::traits> though).
I guess a C++ language lawyer would need to have a look if it is a clang++ =
bug
or g++ bug in accepting it.  Of course, even if it is clang++ bug, a workar=
ound
is possible, e.g. it could use sizeof (T) rather than sizeof (uintset::valu=
es),
after all, when it multiplicates by n, I guess it wants sizeof
(uintset<T>::values[0]) anyway, because it uses trailing array of Ts rather
than T[1]s.=