Re: [PATCH v2] match: 1 / X -> X == 1 for positive X. [PR125735]

On Sat, Aug 8, 2026 at 4:05 AM Kael Andrew Franco <[email protected]> wrote:
>
> Bootstrap and tested with
> https://gcc.gnu.org/pipermail/gcc-patches/2026-August/726688.html
>
>
> From 21c1ad7db9cce4061d30162e98a8baa8109c48b4 Mon Sep 17 00:00:00 2001
> From: Kael Andrew Alonzo Franco <[email protected]>
> Date: Fri, 7 Aug 2026 18:24:36 -0400
> Subject: [PATCH] match: 1 / X -> X == 1 for positive X. [PR125735]
>
> TYPE_UNSIGNED (type) doesn't cover positive signed types
> so use tree_expr_nonnegative_p ().
>
> Bootstrapped and tested on x86_64-pc-linux-gnu.
>
> PR tree-optimization/125735
>
> gcc/ChangeLog:
>
> * match.pd: 1 / X -> X == 1 for positive X. [PR125735]

Ok, once my patch gets pushed.

>
> gcc/testsuite/ChangeLog:
>
> * gcc.dg/pr125735.c: New test.
>
> Signed-off-by: Kael Andrew Franco <[email protected]>
> ---
>  gcc/match.pd                    |  7 ++++---
>  gcc/testsuite/gcc.dg/pr125735.c | 11 +++++++++++
>  2 files changed, 15 insertions(+), 3 deletions(-)
>  create mode 100644 gcc/testsuite/gcc.dg/pr125735.c
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index a2a48e1b475..8850e993425 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -628,8 +628,8 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>         && TYPE_UNSIGNED (type))
>     (trunc_divmod @0 @1))))
>
> -/* 1 / X -> X == 1 for unsigned integer X.
> -   1 / X -> X >= -1 && X <= 1 ? X : 0 for signed integer X.
> +/* 1 / X -> X == 1 for positive integer X.
> +   1 / X -> X >= -1 && X <= 1 ? X : 0 for when X could be negative.
>     But not for 1 / 0 so that we can get proper warnings and errors,
>     and not for 1-bit integers as they are edge cases better handled
>     elsewhere.  Delay the conversion of the signed division until late
> @@ -640,7 +640,8 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>        && TYPE_PRECISION (type) > 1
>        && !integer_zerop (@1)
>        && (!flag_non_call_exceptions || tree_expr_nonzero_p (@1)))
> -  (if (TYPE_UNSIGNED (type))
> +  (if (TYPE_UNSIGNED (type)
> +       || tree_expr_nonnegative_p (@1))
>     (convert (eq:boolean_type_node @1 @0))
>     (if (fold_before_rtl_expansion_p ())
>      (with { tree utype = unsigned_type_for (type); }
> diff --git a/gcc/testsuite/gcc.dg/pr125735.c b/gcc/testsuite/gcc.dg/pr125735.c
> new file mode 100644
> index 00000000000..b94d95c0de7
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/pr125735.c
> @@ -0,0 +1,11 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-optimized" } */
> +
> +_Bool
> +one_div_positive (int b)
> +{
> +  if (b < 1) return 0;
> +  return (1 / b);
> +}
> +
> +/* { dg-final { scan-tree-dump "b_\[0-9\]+.D. == 1" "optimized" } } */
> --
> 2.55.0
>
>