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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/101539] [C++20] Implement builtins for layout-compatibility
 and pointer-interconvertibility traits
Date: Wed, 21 Jul 2021 13:58:47 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101539

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 51186
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D51186&action=3Dedit
gcc12-pr101539.patch

So, I've tried to play with the __is_layout_compatible trait, here is the
result.  There is one known bug, the C++ FE unfortunately removes zero sized
bit-fields early, for layout compatibility we need them (and now just that =
they
were present but how many as well and their types).  Can we not remove them=
 or
remove them when the FE parses the whole TU?

The testcase also contains various cornercases where layout-compatibility as
currently defined is just weird.=