[libstdc++/65033] Give alignment info to libatomic

[Jonathan Wakely]

On 07/04/15 10:51 -0400, Hans-Peter Nilsson wrote:
>I was more thinking of something like:
>
>#include <atomic>
>#include <iostream>
>using std::cout;
>using std::endl;
>
>struct SoSo {
> double d;
> int x alignas(sizeof(int));
>};
>
>SoSo s __attribute__((__aligned__(16)));
>
>int main(void)
>{
>  cout << "alignof(s): " << alignof(s) << endl;
>  cout << "alignof(s.d): " << alignof(s.d) << endl;
>  cout << "alignof(s.x): " << alignof(s.x) << endl;
>}
>
>in which I fear s.x would get an alignof the same as the s.d or
>s, now or after a while, i.e. higher than specified.
>
>(I get for cris-elf at revision 221891:
>alignof(s): 16
>alignof(s.d): 1
>alignof(s.x): 4
>which is kind-of-expected except I thought s.d would get the s
>alignment so that just leaves it open whether that could
>possibly change.)

The docs are clear that alignof(s.x) is not related to its position in
struct SoSo: https://gcc.gnu.org/onlinedocs/gcc/Alignment.html

I'm not going to worry about that behaviour changing.