Re: [PATCH] match.pd: Fix .PARITY(~x) simplification [PR126471]

[Andrea Pinski]

On Wed, Jul 29, 2026 at 12:07 PM Jakub Jelinek <ja...@redhat.com> wrote:
>
> Hi!
>
> The parity(~X) simpliciation to parity(X) is incorrect for types with
> odd element precision, in that case parity(~X) is equivalent to
> parity(X) ^ 1.
> The following patch fixes this.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk/16.2?

Ok.

>
> 2026-07-29  Jakub Jelinek  <ja...@redhat.com>
>
>         PR tree-optimization/126471
>         * match.pd (parity(~X) is parity(X)): Only optimize this way
>         if element_precision is even, otherwise optimize into parity(X) ^ 1.
>
>         * gcc.dg/bitint-139.c: New test.
>
> --- gcc/match.pd.jj     2026-07-28 21:02:47.836319557 +0200
> +++ gcc/match.pd        2026-07-29 16:13:46.327108421 +0200
> @@ -10777,10 +10777,12 @@ (define_operator_list SYNC_FETCH_AND_AND
>  #endif
>
>  /* PARITY simplifications.  */
> -/* parity(~X) is parity(X).  */
> +/* parity(~X) is parity(X) for even precision and parity(X) ^ 1 otherwise.  
> */
>  (simplify
>    (PARITY (bit_not @0))
> -  (PARITY @0))
> +  (if ((element_precision (TREE_TYPE (@0)) & 1) == 0)
> +   (PARITY @0)
> +   (bit_xor (PARITY:type @0) { build_one_cst (type); })))
>
>  /* parity(bswap(x)) is parity(x).  */
>  (for parity (PARITY)
> --- gcc/testsuite/gcc.dg/bitint-139.c.jj        2026-07-29 16:01:03.344808633 
> +0200
> +++ gcc/testsuite/gcc.dg/bitint-139.c   2026-07-29 16:15:17.521949013 +0200
> @@ -0,0 +1,36 @@
> +/* PR tree-optimization/126471 */
> +/* { dg-do run { target bitint575 } } */
> +/* { dg-options "-O2" } */
> +
> +[[gnu::noipa]] int
> +foo (unsigned _BitInt(129) x)
> +{
> +  return __builtin_parityg (~x);
> +}
> +
> +[[gnu::noipa]] int
> +bar (unsigned _BitInt(7) x)
> +{
> +  return __builtin_parityg (~x);
> +}
> +
> +[[gnu::noipa]] int
> +baz (unsigned _BitInt(256) x)
> +{
> +  return __builtin_parityg (~x);
> +}
> +
> +int
> +main ()
> +{
> +  if (foo (0) != 1
> +      || foo (~(unsigned _BitInt(129)) 0) != 0
> +      || foo (1) != 0
> +      || bar (0) != 1
> +      || bar (~(unsigned _BitInt(7)) 0) != 0
> +      || bar (1) != 0
> +      || baz (0) != 0
> +      || baz (~(unsigned _BitInt(256)) 0) != 0
> +      || baz (1) != 1)
> +    __builtin_abort ();
> +}
>
>         Jakub
>