[Bug c/65145] size of atomic object is not correct

["joseph at codesourcery dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65145

--- Comment #3 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
On Fri, 20 Feb 2015, alexey.lapshin at oracle dot com wrote:

> Hi Joseph,
> 
>     Could you help me with a link to the correct description of atomic ABI,
> which in fact used by gcc/g++, please ?

I don't believe it's documented, but I think the general rule for C is: if 
a type's size is 1, 2, 4, 8, 16, its alignment is increased by _Atomic to 
that of the atomic integer type of that size, which is the same as that of 
the non-atomic integer type unless increased by 
TARGET_ATOMIC_ALIGN_FOR_MODE; the size is never increased by _Atomic, and 
alignment of types not of those sizes is unchanged.  If the code differs, 
likely the code should take precedence over that description.  (But of 
course if a type is under-aligned for the instructions used to operate on 
it, there's a bug, whether in the alignment or in the instruction choice.)