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

Ping of https://gcc.gnu.org/pipermail/gcc-patches/2026-July/724387.html.
Updated patch still works:

From a8dad89050597f075c197bba9b0da2703277671e Mon Sep 17 00:00:00 2001
From: Kael Andrew Alonzo Franco <[email protected]>
Date: Thu, 30 Jul 2026 21:59:35 -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 <[email protected]>
---
 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 dd223dc4553..9c022224bc5 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" } } */
-- 
2.55.0