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

  From 205a0d397c3099a273fc792c1d906cd0b7b4545a Mon Sep 17 00:00:00 2001
From: Kael Andrew Alonzo Franco <kaelfandrew@gmail.com>
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 <kaelfandrew@gmail.com>
---
 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
  

On Thu, Jul 16, 2026 at 9:31 AM Kael Andrew Franco
<kaelfandrew@gmail.com> wrote:
>
> From 205a0d397c3099a273fc792c1d906cd0b7b4545a Mon Sep 17 00:00:00 2001
> From: Kael Andrew Alonzo Franco <kaelfandrew@gmail.com>
> 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 <kaelfandrew@gmail.com>
> ---
>  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
>
>
  

From 113cada55a1a87c748f9e2bc763f740a2f9ec16a Mon Sep 17 00:00:00 2001
From: Kael Andrew Alonzo Franco <kaelfandrew@gmail.com>
Date: Fri, 17 Jul 2026 07:49:13 -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 vr0.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]

gcc/testsuite/ChangeLog:

	* gcc.dg/pr125735.c: New test.

Signed-off-by: Kael Andrew Franco <kaelfandrew@gmail.com>
---
 gcc/match.pd                    | 19 +++++++++++++++----
 gcc/testsuite/gcc.dg/pr125735.c | 11 +++++++++++
 2 files changed, 26 insertions(+), 4 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/pr125735.c

diff --git a/gcc/match.pd b/gcc/match.pd
index cb8c68bd915..9f26a6458dd 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 +640,24 @@ 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.nonnegative_p ())
+      positive_p = true;
+#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" } } */