[cfe-dev] Does clang now emit [abi:cxx11] unconditionally when used with libstdc++?

Richard Smith via cfe-dev cfe-dev at lists.llvm.org
Mon Aug 15 15:05:19 PDT 2016

On Mon, Aug 15, 2016 at 2:53 PM, Renato Golin via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> On 15 August 2016 at 22:43, Maria Gottschalk <gottschalk_maria at yahoo.de>
> wrote:
> > But actually, there were abi tags already in 4.9.2, e.g.
> >
> > But then gcc-4.9.2 doesn't emit any, while now clang-3.9.0 does!
> I'd risk say this is a bug in GCC. Or at least a pretty ugly
> implementation of something that should be simple.

If it's only applied to an inline function, and that function did in fact
take an ABI break in libstdc++ 4.9.2, then this seems unproblematic. If
anything, our results will be marginally better than GCC 4.9.2's, because
we'll do the right thing when mixing libstdc++ 4.9.2 and an earlier
version. It looks like there is nothing to fix here.

> We can't be compatible with all versions of GCC on what attributes
> they support and the compile-time flags that they use. This just
> doesn't scale.
> In a way, if you don't want ABI tags, use Clang 3.8 or before. If you
> do, use Clang 3.9 or after.
> I'm not sure there's a better way of doing this and creating a
> compile-time flag just to imitate GCC seems like the wrong way to go,
> IMO.
> cheers,
> --renato
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