Re: [PATCH] tree-optimization/106379 - add missing ~(a ^ b) folding for _Bool

["H.J. Lu" <hjl.tools@gmail.com>]

On Thu, Jul 21, 2022 at 4:24 AM Richard Biener via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> The following makes sure to fold ~(a ^ b) to a == b for truth
> values (but not vectors, we'd have to check for vector support of
> equality).  That turns the PR106379 testcase into a ranger one.
>
> Note that while we arrive at ~(a ^ b) in a convoluted way from
> original !a == !b one can eventually write the expression this
> way directly as well.
>
> Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.
>
>         PR tree-optimization/106379
>         * match.pd (~(a ^ b) -> a == b): New pattern.
>
>         * gcc.dg/pr106379-1.c: New testcase.
> ---
>  gcc/match.pd                      | 6 ++++++
>  gcc/testsuite/gcc.dg/pr106379-1.c | 9 +++++++++
>  2 files changed, 15 insertions(+)
>  create mode 100644 gcc/testsuite/gcc.dg/pr106379-1.c
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index 8bbc0dbd5cd..88a1a5aa9cc 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -1938,6 +1938,12 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>   (if (tree_nop_conversion_p (type, TREE_TYPE (@0)))
>    (bit_not (bit_xor (view_convert @0) @1))))
>
> +/* ~(a ^ b) is a == b for truth valued a and b.  */
> +(simplify
> + (bit_not (bit_xor:s truth_valued_p@0 truth_valued_p@1))
> + (if (!VECTOR_TYPE_P (type))
> +  (convert (eq @0 @1))))

For integers, isn't it wrong to convert ~(boolean exp) to boolean exp?


>  /* (x & ~m) | (y & m) -> ((x ^ y) & m) ^ x */
>  (simplify
>   (bit_ior:c (bit_and:cs @0 (bit_not @2)) (bit_and:cs @1 @2))
> diff --git a/gcc/testsuite/gcc.dg/pr106379-1.c b/gcc/testsuite/gcc.dg/pr106379-1.c
> new file mode 100644
> index 00000000000..7f2575e02dc
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/pr106379-1.c
> @@ -0,0 +1,9 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O -fdump-tree-forwprop1" } */
> +
> +_Bool foo (_Bool a, _Bool b)
> +{
> +  return !a == !b;
> +}
> +
> +/* { dg-final { scan-tree-dump "\[ab\]_\[0-9\]+\\(D\\) == \[ba\]_\[0-9\]+\\(D\\)" "forwprop1" } } */
> --
> 2.35.3



--
H.J.