>From 113cada55a1a87c748f9e2bc763f740a2f9ec16a Mon Sep 17 00:00:00 2001
From: Kael Andrew Alonzo Franco <[email protected]>
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 <[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 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" } } */
--
2.55.0
On Thu, Jul 16, 2026 at 11:44 PM Andrea Pinski <
[email protected]> wrote:
> 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
> >
> >
>
