[PATCH] Enable GCC support for AVX512_VP2INTERSECT.

[Hongtao Liu]

On Sat, Jun 22, 2019 at 3:38 PM Uros Bizjak <ubizjak@gmail.com> wrote:
>
> On Fri, Jun 21, 2019 at 8:38 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> > > > > > > > > > >> > > +/* Register pair.  */
> > > > > > > > > > >> > > +VECTOR_MODES_WITH_PREFIX (P, INT, 2); /* P2QI */
> > > > > > > > > > >> > > +VECTOR_MODES_WITH_PREFIX (P, INT, 4); /* P2HI P4QI */
> > > > > > > > > > >> > >
> > > > > > > > > > >> > > I think
> > > > > > > > > > >> > >
> > > > > > > > > > >> > > INT_MODE (P2QI, 16);
> > > > > > > > > > >> > > INT_MODE (P2HI, 32);
> > > > > Why P2QI need 16 bytes but not 2 bytes?
> > > > > Same question with P2HI.
> > > >
> > > > Because we made a mistake. It should be 2 and 4, since these arguments
> > > Then it will run into internal comiler error when building libgcc.
> > > I'm still invertigating it.
> > > > are bytes, not bits.
> >
> > I don't think we can have 2 integer modes with the same number of bytes since
> > it breaks things like
> >
> > scalar_int_mode wider_mode = GET_MODE_WIDER_MODE (mode).require ();
> >
> > We can get
> >
> > (gdb) p mode
> > $2 = {m_mode = E_SImode}
> > (gdb) p wider_mode
> > $3 = {m_mode = E_P2HImode}
> > (gdb)
> >
> > Neither middle-end nor backend support it.
>
> Ouch... It looks we hit the limitation of the middle end (which should
> at least warn/error out if two modes of the same width are declared).
>
> OTOH, we can't solve this problem by using two HI/QImode registers,
> since a consecutive register pair has to be allocated It is also not
> possible to overload existing SI/HImode mode with different
> requirements w.r.t register pair allocation (e.g. sometimes the whole
> register is allocated, and sometimes a register pair is allocated).
>
> I think we have to invent something like SPECIAL_INT_MODE, which would
> avoid mode promotion functionality (basically, it should not be listed
> in mode_wider and similar arrays). This would prevent mode promotion
> issues, while it would still allow to have mode, having the same width
> as existing mode, but with special properties.
>
> I'm adding Jeff and Jakub to the discussion about SPECIAL_INT_MODE.
>
> Uros.

Patch from H.J using PARTIAL_INT_MODE fixed this issue.

+/* Register pair.  */
+PARTIAL_INT_MODE (HI, 16, P2QI);
+PARTIAL_INT_MODE (SI, 32, P2HI);
+

Here is updated patch.
-- 
BR,
Hongtao
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