On Thu, Jun 03, 2021 at 11:03:43AM +0000, Liu, Hongtao via Gcc-patches wrote:
> In simplify_rtx, no simplication occurs, there is just the difference between
> (vec_duplicate (not REG)) and (not (vec_duplicate (REG)). So here tem will
> only be 0.
> Basically we don't know it's a simplication until combine successfully split
> the
> 3->2 instructions (not + broadcast + and to andnot + broadcast), but it's
> pretty awkward
> to do this in combine.
>
> Consider andnot is existed for many backends, I think a canonicalization is
> needed here.
> Maybe we can add insn canonicalization for transforming (and (vect_duplicate
> (not A)) B) to
> (and (not (duplicate (not A)) B) instead of (vec_duplicate (not A)) to (not
> (vec_duplicate A))?
For the (not (vec_duplicate)) vs. (vec_duplicate (not)) it isn't clear which
one is generally a win on major targets, so I'd say it is better to add a
combine splitter to swap it in backends that want that.
Jakub
