Re: [RFC PATCH v1 1/1] PPC64: Implement POWER Architecture Vector Function ABI.

[GT <tnggil@protonmail.com>]

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Friday, August 7, 2020 4:59 PM, Jakub Jelinek <jakub@redhat.com> wrote:

> On Fri, Aug 07, 2020 at 08:35:52PM +0000, Bert Tenjy via Gcc-patches wrote:
>
> > The document describing POWER Architecture Vector Function interface is
> > tentatively at: https://sourceware.org/glibc/wiki/Homepage?action=AttachFile&do=view&target=powerarchvectfuncabi.html
>
> Doesn't exist.

I can't tell what the issue is with the link as given above. But the one below does actually open
the page for me.

https://sourceware.org/glibc/wiki/HomePage?action=AttachFile&do=view&target=powerarchvectfuncabi.html


>
> > -   if (TARGET_VSX)
> > -   {
> > -        clonei->vecsize_mangle = 'b';
> >
> >
> > -        ret = 1;
> >
> >
> > -   }
> > -   clonei->mask_mode = VOIDmode;
> > -   switch (clonei->vecsize_mangle)
> > -   {
> > -   case 'b':
> > -        clonei->vecsize_int = 128;
> >
> >
> > -        clonei->vecsize_float = 128;
> >
> >
> > -        break;
> >
> >
> > -   case 'c':
> > -        clonei->vecsize_int = 128;
> >
> >
> > -        clonei->vecsize_float = 128;
> >
> >
>
> So what is this 'c' case here for?
>

I should have removed it. It will be deleted in the next version.

> > -        break;
> >
> >
> > -   default:
> > -        gcc_unreachable ();
> >
> >
>
> If (!TARGET_VSX), this will abort (as you only set vecsize_mangle to 'b'
> if TARGET_VSX, otherwise nothing sets it (so it remains 0).
>
> The way this works is that the caller calls the target hook with 0
> as last argument, and the hook either returns 0 (means not supported at
> all), or returns number of supported variants and provides the first one.
> If more than one are supported, the caller will keep iterating on those.
> E.g. on x86, we support 4 modes (b, c, d, e) for exported functions and
> for non-exported ones just choose a single one based on the ISA, because in
> that case it is not a matter of ABI.
>
> For PowerPC, if all you want to support is b which requires VSX, then the
> right thing is for !TREE_PUBLIC functions return 0 if !TARGET_VSX and
> otherwise set vecsize_mangle to 'b' and in the end return 1, for exported
> functions always set it to 'b' (and in the end return 1).
> Then ensure that the 'b' variants of function definitions get target ("vsx")
> attribute added if !TARGET_VSX.
>

So setting attribute "vsx" for 'b' variants of function definitions is what
should go in function rs6000_simd_clone_usable?

Bert.