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

["H.J. Lu" <hjl.tools@gmail.com>]

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.

Thanks.

-- 
H.J.