https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79024
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution|--- |INVALID
--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Xidorn Quan from comment #2)
> ABI requires a different alignment than in struct?
Yes.
> That's interesting. But I
> think developers (I mean, users of compilers) are generally more interested
> on alignment requirement in struct rather than that for ABI, and most
> description of the concept "alignment" refers to that in struct, so it is
> probably better make alignof / alignas report that value.
It's arguable whether that would be standard conforming. alignas(T) tells you
the alignment needed for an obejct of type T. If you want the alignment for a
subobject of type T that's a different question, and you can get it by doing:
struct S { T t; };
alignas(S)
Or more generally:
template<typename T>
struct alignof_subobject
{
struct S { T t; };
static constexpr std::size_t value = alignof(S);
};
struct Test2 { char c; alignas(alignof_subobject<uint64_t>::value) uint64_t u;
};
