[cfe-dev] libc++ std::cout alignment trouble (was: Re: [llvm] r240144 - [SLP] Vectorize for all-constant entries.)

[Tim Northover via cfe-dev]

On 10 October 2015 at 14:22, Joerg Sonnenberger via cfe-dev
<cfe-dev at lists.llvm.org> wrote:
> On Sat, Oct 10, 2015 at 02:17:38PM -0700, Michael Zolotukhin via cfe-dev wrote:
>> it looks like you relatively recently touched code in
>> enforceKnownAlignment. Could you please comment on whether it’s correct
>> behavior or not?
>
> This looks entirely correct to me as long as PrefAlign <= 16 for AMD64.

I'm not so sure, especially when we get to other targets that don't
have the special AMD64 rule about objects > 16 bytes in size getting
that alignment.

It seems that the way ELF's R_..._COPY relocations work make an
externally visible object's alignment part of a .so's ABI whether we
like it or not. I just don't see a way around that which allows us to
increase it at the moment.

Tim.