Re: ping: [PATCH, ARM] attribute target (thumb,arm) [0-6]

[Ramana Radhakrishnan <ramana dot radhakrishnan at arm dot com>]

> > > Christian
> >
> >
> > A general note, please reply to each of the patches with a rebased
> > patch as a separate email. Further more all your patches appear to
> > have dos line endings so they don't seem to apply cleanly. Please
> > don't have spurious headers in your patch submission - it then makes
> > it hard to , please create it in a way that it is easily applied by
> > someone trying it out. It looks like p4 needs a respin as I got a
> > reject trying to apply the documentation patch to my tree while trying
> > to apply it.
>
> OK, thanks for the suggestions and sorry for the p4 reject. The sources
> are moving fast and I have hard times catching up with re-bases.

I understand.

> > I tried the following decoration on foo in gcc.target/arm/attr_arm.c
> >
> >
> > int __attribute__((target("arm, fpu=vfpv4")))
> > foo(int a)
> > {
> >    return a ? 1 : 5;
> > }
> >
> >
> > And the compiler accepts it just fine.
>
> Indeed, it's a mistake for now. attributes other the arm/thumb ones
> shall be rejected (eventually with a "not yet implemented" warning for
> the fpu, error for the others.) until we extend it.

Yep - funnily enough if you remove "arm" and just use "fpu=vfpv4", I 
think you get an error.

> > Given that with LTO we are now using target attributes to decide
> > inlining - I'm not convinced that the inline asm case goes away. In
> > fact it only makes things worse so I'm almost convinced to forbid
> > inlining from "arm" to "thumb" or vice-versa, which is a reversal of
> > my earlier position. I hadn't twigged that LTO would reuse this
> > infrastructure and it's probably simpler to prevent inlining in those
> > cases.
>
> I can resurrect the inline check chunk. FYI, with a few small examples
> arm/thumb attribute is correctly handled by LTO

Yes it would work with normal C code as it does normally - I'm worried 
about functions with inline asm. We've just increased the inlining scope 
with lto and that would mean things are a bit more painful ?


> > Thoughts ?
> >
> > So in essence I'm still playing with this and would like to iterate
> > towards a quick solution.
>
> thanks, that would be good if we could land the arm/thumb attribute and
> start the fpu extensions separately. (I'm currently playing with
> fpu=neon but it will take time to have something solid).

Absolutely - I'd rather spend the time first in polishing this up. 
Extending it for other options can be something you look at separately.

BTW I was pointed at a PR for this yesterday by a colleague - 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59884

So, lets use that as the PR for this work.

regards
Ramana

> Christian
>
> > Ramana