[Bug libstdc++/88101] Implement P0528R3, C++20 cmpxchg and padding bits

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88101

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

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

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 49563
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=49563&action=edit
gcc11-pr88101-wip.patch

Here is completely untested WIP of __builtin_clear_padding builtin, so far
doesn't handle bit-fields, unions, VLAs and has a couple of other FIXMEs.
I'll try to complete this virtually from Baker Island (AoE timezone) tonight
before stage1 closes there.  Also I'll probably need to remember the originally
passed pointer type in e.g. second artificial argument of the builtin (NULL),
in case already before or during lower pass something would forward propagate
the argument.