>From 56369c999a6fe63a0ba1d1cafa7d555f4f65e7c2 Mon Sep 17 00:00:00 2001
From: Kael Andrew Alonzo Franco <[email protected]>
Date: Mon, 22 Jun 2026 22:44:06 -0400
Subject: [PATCH] match: For C != {-1, 0}, C (==,!=) (C >> a) -> a
(==,!=) 0 [PR112090]
GCC already covers C (==,!=) (C << a) -> a (==,!=) 0 for C != 0.
Bootstrapped and tested on x86_64-pc-linux-gnu
PR tree-optimization/112090
gcc/ChangeLog:
PR tree-optimization/112090
* match.pd: For C != {-1, 0}, optimize C (==,!=) (C >> a) to a (==,!=)
0.
gcc/testsuite/ChangeLog:
PR tree-optimization/112090
* gcc.dg/112090.c: New test.
Signed-off-by: Kael Franco <[email protected]>
---
gcc/match.pd | 8 ++++++++
gcc/testsuite/gcc.dg/pr112090.c | 28 ++++++++++++++++++++++++++++
2 files changed, 36 insertions(+)
create mode 100644 gcc/testsuite/gcc.dg/pr112090.c
diff --git a/gcc/match.pd b/gcc/match.pd
index 8c410c2f3b3..e765cbe3ad7 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -5120,6 +5120,14 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
(if (INTEGRAL_TYPE_P (type))
(convert (eq:boolean_type_node @2 { build_zero_cst (TREE_TYPE (@2)); }))))
+/* For C != {-1, 0}, C (==,!=) (C >> a) -> a (==,!=) 0 */
+(for neeq (ne eq)
+ (simplify
+ (neeq:c @1 (rshift INTEGER_CST@1 @0))
+ (if (integer_zerop (@1) == 0
+ && integer_all_onesp (@1) == 0)
+ (convert (neeq:boolean_type_node @0 { build_zero_cst (TREE_TYPE
(@0)); })))))
+
/* Simplify (CST << x) & 1 to 0 if CST is even or to x == 0 if it is odd. */
(simplify
(bit_and (lshift INTEGER_CST@1 @0) integer_onep)
diff --git a/gcc/testsuite/gcc.dg/pr112090.c b/gcc/testsuite/gcc.dg/pr112090.c
new file mode 100644
index 00000000000..3b22f1b5c2b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr112090.c
@@ -0,0 +1,28 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+_Bool
+pcst_ne_pcst_rshift_a (int a)
+{
+ return (11 != (11 >> a)) == (a != 0);
+}
+
+_Bool
+ncst_ne_ncst_rshift_a (int a)
+{
+ return (-11 != (-11 >> a)) == (a != 0);
+}
+
+_Bool
+pcst_eq_pcst_rshift_a (int a)
+{
+ return (11 == (11 >> a)) == (a == 0);
+}
+
+_Bool
+ncst_eq_ncst_rshift_a (int a)
+{
+ return (-11 == (-11 >> a)) == (a == 0);
+}
+
+/* { dg-final { scan-tree-dump-times "return 1;" 4 "optimized" } } */
--
2.54.0
