Re: [PATCH] middle-end: Fold popcount(x&4) to (x>>2)&1 and friends.

[Richard Biener via Gcc-patches]

On Thu, Jul 23, 2020 at 10:15 AM Marc Glisse <marc.gli...@inria.fr> wrote:
>
> On Wed, 22 Jul 2020, Roger Sayle wrote:
>
> > Many thanks for the peer review and feedback.  I completely agree that 
> > POPCOUNT
> > and PARITY iterators simplifies things and handle the IFN_ variants.
>
> Is there a reason why the iterators cannot be used for this one?
>
> +(for popcount (BUILT_IN_POPCOUNT BUILT_IN_POPCOUNTL BUILT_IN_POPCOUNTLL
> +              BUILT_IN_POPCOUNTIMAX)
> +     parity (BUILT_IN_PARITY BUILT_IN_PARITYL BUILT_IN_PARITYLL
> +            BUILT_IN_PARITYIMAX)
> +  (simplify
> +    (bit_and (popcount @0) integer_onep)
> +    (parity @0)))

I should indeed work fine to even do

 (simplify
   (bit_and (POPCOUNT @0) integer_onep)
   (PARITY @0))

Likewise for the existing

+/* popcount(X) == 0 is X == 0, and related (in)equalities.  */
+(for popcount (POPCOUNT)
   (for cmp (le eq ne gt)
        rep (eq eq ne ne)
     (simplify
       (cmp (popcount @0) integer_zerop)
       (rep @0 { build_zero_cst (TREE_TYPE (@0)); }))))

you can elide the (for ...)

OK with those changes.

Richard.

>
> --
> Marc Glisse