>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)));
+ }
+#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
