Re: [PATCH v2 1/2] Allow vec_duplicate_optab to fail

[Richard Biener <richard.guenther@gmail.com>]

On Mon, Jun 7, 2021 at 4:19 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Mon, Jun 7, 2021 at 12:12 AM Richard Sandiford
> <richard.sandiford@arm.com> wrote:
> >
> > "H.J. Lu" <hjl.tools@gmail.com> writes:
> > > Update vec_duplicate to allow to fail so that backend can only allow
> > > broadcasting an integer constant to a vector when broadcast instruction
> > > is available.
> >
> > I'm not sure why we need this to fail though.  Once the optab is defined
> > for target X, the optab should handle all duplicates for target X,
> > even if there are different strategies it can use.
> >
> > AIUI the case you want to make conditional is the constant case.
> > I guess the first question is: why don't we simplify those CONSTRUCTORs
> > to VECTOR_CSTs in gimple?  I'm surprised we still see the constant case
> > as a constructor here.
>
> The particular testcase for vec_duplicate is gcc.dg/pr100239.c.
>
> > If we can't rely on that happening, then would it work to change:
> >
> >         /* Try using vec_duplicate_optab for uniform vectors.  */
> >         if (!TREE_SIDE_EFFECTS (exp)
> >             && VECTOR_MODE_P (mode)
> >             && eltmode == GET_MODE_INNER (mode)
> >             && ((icode = optab_handler (vec_duplicate_optab, mode))
> >                 != CODE_FOR_nothing)
> >             && (elt = uniform_vector_p (exp)))
> >
> > to something like:
> >
> >         /* Try using vec_duplicate_optab for uniform vectors.  */
> >         if (!TREE_SIDE_EFFECTS (exp)
> >             && VECTOR_MODE_P (mode)
> >             && eltmode == GET_MODE_INNER (mode)
> >             && (elt = uniform_vector_p (exp)))
> >           {
> >             if (TREE_CODE (elt) == INTEGER_CST
> >                 || TREE_CODE (elt) == POLY_INT_CST
> >                 || TREE_CODE (elt) == REAL_CST
> >                 || TREE_CODE (elt) == FIXED_CST)
> >               {
> >                 rtx src = gen_const_vec_duplicate (mode, expand_normal (node));
> >                 emit_move_insn (target, src);
> >                 break;
> >               }
> >             …
> >           }
>
> I will give it a try.

I can confirm that veclower leaves us with an unfolded constant CTOR.
If you file a PR to remind me I'll fix that.

Richard.

> Thanks.
>
> --
> H.J.