On Tue, Jun 25, 2019 at 4:44 AM Hongtao Liu <crazy...@gmail.com> wrote:
>
> On Sat, Jun 22, 2019 at 3:38 PM Uros Bizjak <ubiz...@gmail.com> wrote:
> >
> > On Fri, Jun 21, 2019 at 8:38 PM H.J. Lu <hjl.to...@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.
OK for mainline, but please add the comment about the reason to use
PARTIAL_INT_MODE.
Thanks,
Uros.
