Re: [PATCH 2/3] Change the `zero_one ==/!= 0) ? y : z <op> y` patterns to use multiply rather than `(-zero_one) & z`

[Andrew Pinski <pinskia@gmail.com>]

On Wed, Jun 7, 2023 at 3:57 PM Jeff Law via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
>
>
> On 6/7/23 15:32, Andrew Pinski via Gcc-patches wrote:
> > Since there is a pattern to convert `(-zero_one) & z` into `zero_one * z` already,
> > it is better if we don't do a secondary transformation. This reduces the extra
> > statements produced by match-and-simplify on the gimple level too.
> >
> > gcc/ChangeLog:
> >
> >       * match.pd (`zero_one ==/!= 0) ? y : z <op> y`): Use
> >       multiply rather than negation/bit_and.
> Don't you need to check the types in a manner similar to what the A & -Y
> -> X * Y pattern does before you make this transformation?

No, because the convert is in a different order than in that
transformation; a very subtle difference which makes it work.

In A & -Y it was matching:
(bit_and  (convert? (negate
But here we have:
(bit_and (negate (convert
Notice the convert is in a different location, in the `A & -Y` case,
the convert needs to be a sign extending (or a truncation) of the
negative value. Here we are converting the one_zero_value to the new
type so we get zero_one in the new type and then doing the negation
getting us 0 or -1 value.

Thanks,
Andrew

>
> jeff
>