From: Andrew MacLeod <amacleod@redhat.com>
Date: Wed, 10 Jun 2026 13:41:27 +0000 (-0400)
Subject: Refine modulo range operations with fixed quotient.
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=cd52e71e8aea258342deca45868bf2529d4fdd76;p=thirdparty%2Fgcc.git

Refine modulo range operations with fixed quotient.

When all combines of x / y produce the same quotient Q, further refine
modulo operations by treating x % y ==  x - Q * y

	PR tree-optimization/125706
	gcc/
	* range-op.cc (operator_trunc_mod::wi_fold): Apply fixed
	quotient refinement.
	gcc/testsuite/
	* gcc.dg/pr125706.c: New.
---

diff --git a/gcc/range-op.cc b/gcc/range-op.cc
index 5eb3582a235..94edfdc9870 100644
--- a/gcc/range-op.cc
+++ b/gcc/range-op.cc
@@ -4367,6 +4367,24 @@ operator_trunc_mod::wi_fold (irange &r, tree type,
   new_ub = wi::min (new_ub, tmp, sign);
 
   value_range_with_overflow (r, type, new_lb, new_ub);
+
+  // When all positive and all X/Y combinations produce the same quotient
+  // we can refine the result with    X % Y == X - Q * Y.
+  // Ensure that division by 0 is not an option.
+  if (wi::gt_p (rh_lb, 0, sign) && wi::ge_p (lh_lb, 0, sign))
+    {
+      wide_int q_lb = wi::div_trunc (lh_lb, rh_ub, sign);
+      wide_int q_ub = wi::div_trunc (lh_ub, rh_lb, sign);
+
+      if (q_lb == q_ub)
+	{
+	  new_lb = lh_lb - q_lb * rh_ub;
+	  new_ub = lh_ub - q_lb * rh_lb;
+
+	  int_range<2> refined (type, new_lb, new_ub);
+	  r.intersect (refined);
+	}
+    }
 }
 
 bool
diff --git a/gcc/testsuite/gcc.dg/pr125706.c b/gcc/testsuite/gcc.dg/pr125706.c
new file mode 100644
index 00000000000..d71c5ac613c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr125706.c
@@ -0,0 +1,14 @@
+// { dg-do compile }
+// { dg-options "-O2 -fdump-tree-evrp" }
+
+#include <stdint.h>
+
+int8_t src(uint8_t v2_u8, int8_t v4_i8, int8_t v5_i8) {
+  if (!(((uint8_t)6 <= v2_u8) && (v2_u8 <= (uint8_t)7))) __builtin_unreachable();
+  if (!(((int8_t)65 <= v4_i8) && (v4_i8 <= (int8_t)80))) __builtin_unreachable();
+  if (!(((int8_t)100 <= v5_i8) && (v5_i8 <= (int8_t)101))) __builtin_unreachable();
+  int8_t i0_i8 = (int8_t)(v5_i8 % v4_i8);
+  int8_t i1_i8 = (int8_t)((int8_t)i0_i8 >> (uint8_t)v2_u8);
+  return i1_i8;
+}
+// { dg-final { scan-tree-dump "20, 36" "evrp" } }