On Thu, Jul 16, 2026 at 9:31 AM Kael Andrew Franco
<[email protected]> wrote:
>
> From 205a0d397c3099a273fc792c1d906cd0b7b4545a Mon Sep 17 00:00:00 2001
> From: Kael Andrew Alonzo Franco <[email protected]>
> Date: Thu, 16 Jul 2026 12:25:13 -0400
> Subject: [PATCH] match: 1 / X -> X == 1 for positive X. [PR125735]
>
> TYPE_UNSIGNED (type) doesn't cover positive signed types and
> tree_expr_nonnegative_p () doesn't work so use gimple_match_range_of_expr ().
>
> 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]
>
> gcc/testsuite/ChangeLog:
>
> * gcc.dg/pr125735.c: New test.
>
> Signed-off-by: Kael Andrew Franco <[email protected]>
> ---
> gcc/match.pd | 22 ++++++++++++++++++----
> gcc/testsuite/gcc.dg/pr125735.c | 11 +++++++++++
> 2 files changed, 29 insertions(+), 4 deletions(-)
> create mode 100644 gcc/testsuite/gcc.dg/pr125735.c
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index cb8c68bd915..900ca9f0278 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
> @@ -640,13 +640,27 @@ 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))
> + (with {
> + bool positive_p = TYPE_UNSIGNED (type);
> +#if GIMPLE
> + int_range_max vr0;
> + wide_int lower_bnd;
> + if (!positive_p
> + && gimple_match_range_of_expr (vr0, @1)
> + && !vr0.varying_p ())
> + {
> + lower_bnd = vr0.lower_bound ();
> + positive_p = wi::gt_p (lower_bnd, 0, TYPE_SIGN (TREE_TYPE (@1)));
Instead of the above you should just do:
vr0.nonnegative_p () && !range_includes_zero_p (vr0)
That is non negative and does not include zero. Or you can add a new
function which does the above check in its own function.
Something like positive_range_p?
But in this case the time we care about non-zero is with non-call exceptions.
So `vr0.nonnegative_p ()` should be enough.
We already have a check to for the non-call exceptions with non-zero earlier:
(!flag_non_call_exceptions || tree_expr_nonzero_p (@1)
Thanks,
Andrea
> + }
> +#endif
> + }
> + (if (positive_p)
> (convert (eq:boolean_type_node @1 @0))
> (if (fold_before_rtl_expansion_p ())
> (with { tree utype = unsigned_type_for (type); }
> (cond (le (plus (convert:utype @1) { build_one_cst (utype); })
> { build_int_cst (utype, 2); })
> - @1 { build_zero_cst (type); }))))))
> + @1 { build_zero_cst (type); })))))))
>
> /* Combine two successive divisions. Note that combining ceil_div
> and floor_div is trickier and combining round_div even more so. */
> 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
>
>
