Re: [PATCH 2/3] MATCH: `a | C -> C` when we know that `a & ~C == 0`

[Richard Biener <richard.guenther@gmail.com>]

On Thu, Aug 24, 2023 at 9:16 PM Andrew Pinski via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Even though this is handled by other code inside both VRP and CCP,
> sometimes we want to optimize this outside of VRP and CCP.
> An example is given in PR 106677 where phiopt will happen
> after VRP (which removes a cast for a comparison) and then
> phiopt will optimize the phi to be `a | 1` which can then
> be optimized to `1` due to this patch.

Also works for xor, no?

> OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.

OK with or without adding XOR.

Richard.

> Note Similar code already exists in simplify_rtx for the RTL level;
> it was moved from combine to simplify_rtx in r0-72539-gbd1ef757767f6d.
> gcc/ChangeLog:
>
>         * match.pd (`a | C -> C`): New pattern.
> ---
>  gcc/match.pd | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index c87a0795667..3bbeceb37b4 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -1456,6 +1456,12 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>   (if (INTEGRAL_TYPE_P (TREE_TYPE (@0))
>        && wi::bit_and_not (get_nonzero_bits (@0), wi::to_wide (@1)) == 0)
>    @0))
> +/* x | C -> C if we know that x & ~C == 0.  */
> +(simplify
> + (bit_ior SSA_NAME@0 INTEGER_CST@1)
> + (if (INTEGRAL_TYPE_P (TREE_TYPE (@0))
> +      && wi::bit_and_not (get_nonzero_bits (@0), wi::to_wide (@1)) == 0)
> +  @1))
>  #endif
>
>  /* ~(~X - Y) -> X + Y and ~(~X + Y) -> X - Y.  */
> --
> 2.31.1
>