On Fri, Sep 24, 2021 at 9:08 PM Segher Boessenkool
<seg...@kernel.crashing.org> wrote:
>
> On Mon, Sep 13, 2021 at 04:24:13PM +0200, Richard Biener wrote:
> > On Mon, Sep 13, 2021 at 4:10 PM Jeff Law via Gcc-patches
> > <gcc-patches@gcc.gnu.org> wrote:
> > > I'm not convinced that we need the inner mode to match anything. As
> > > long as the vec_concat's mode is twice the size of the vec_select modes
> > > and the vec_select mode is <= the mode of its operands ISTM this is
> > > fine. We might want the modes of the vec_select to match, but I don't
> > > think that's strictly necessary either, they just need to be the same
> > > size. ie, we could have somethig like
> > >
> > > (vec_concat:V2DF (vec_select:DF (reg:V4DF)) (vec_select:DI (reg:V4DI)))
> > >
> > > I'm not sure if that level of generality is useful though. If we want
> > > the modes of the vec_selects to match I think we could still support
> > >
> > > (vec_concat:V2DF (vec_select:DF (reg:V4DF)) (vec_select:DF (reg:V8DF)))
> > >
> > > Thoughts?
> >
> > I think the component or scalar modes of the elements to concat need to
> > match
> > the component mode of the result. I don't think you example involving
> > a cat of DF and DI is too useful - but you could use a subreg around the DI
> > value ;)
>
> I agree.
>
> If you want to concatenate components of different modes, you should
> change mode first, using subregs for example.
I don't really understand.
for
> > > (vec_concat:V2DF (vec_select:DF (reg:V4DF)) (vec_select:DF (reg:V8DF)))
> > >
> > > Thoughts?
how can it be simplified when reg:V4DF is different from (reg:V8DF)
to
(vec_select: (vec_concat:(subreg V8DF (reg:V4DF) 0) (reg:V8DF))
(paralle[...])
?, which doesn't look like a simpication.
Similar for
> > > (vec_concat:V2DF (vec_select:DF (reg:V4DF)) (vec_select:DI (reg:V4DI)))
here we require rtx_equal_p (XEXP (trueop0, 0), XEXP (trueop1, 0)) so
vec_concat (vec_select vec_select) can be simplified to just
vec_select.
>
> ("Inner mode" is something of subregs btw, "component mode" is what this
> concept of modes is called, the name GET_MODE_INNER is a bit confusing
> though :-) )
>
> Btw, the documentation for "concat" says
> @findex concat
> @item (concat@var{m} @var{rtx} @var{rtx})
> This RTX represents the concatenation of two other RTXs. This is used
> for complex values. It should only appear in the RTL attached to
> declarations and during RTL generation. It should not appear in the
> ordinary insn chain.
> which needs some updating (in many ways).
>
>
> Segher
--
BR,
Hongtao
