The patch simplifies expressions (a - 1) & -a, (a - 1) | -a, and (a - 1) ^ -a
to the constants 0, -1, and -1, respectively.
Currently, GCC does not perform these simplifications.
Bootstrapped and tested on x86-linux-gnu with no regressions.
gcc/ChangeLog:
* match.pd: New pattern.
gcc/testsuite/ChangeLog:
* gcc.dg/tree-ssa/bitops-11.c: New test.
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---
gcc/match.pd | 11 +++++++++++
gcc/testsuite/gcc.dg/tree-ssa/bitops-11.c | 23 +++++++++++++++++++++++
2 files changed, 34 insertions(+)
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/bitops-11.c
diff --git a/gcc/match.pd b/gcc/match.pd
index c10bf9a7b80..6d95ceaa194 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -1472,6 +1472,17 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
(bit_and:c @0 (bit_not (bit_xor:c @0 @1)))
(bit_and @0 @1))
+/* Transform:
+ (a - 1) & -a -> 0.
+ (a - 1) | -a -> -1.
+ (a - 1) ^ -a -> -1. */
+(for bit_op (bit_ior bit_xor bit_and)
+ (simplify
+ (bit_op:c (plus @0 integer_minus_onep) (negate @0))
+ (if (bit_op == BIT_AND_EXPR)
+ { build_zero_cst (type); }
+ { build_minus_one_cst (type); })))
+
/* a & (a == b) --> a & b (boolean version of the above). */
(simplify
(bit_and:c @0 (nop_convert? (eq:c @0 @1)))
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/bitops-11.c b/gcc/testsuite/gcc.dg/tree-ssa/bitops-11.c
new file mode 100644
index 00000000000..c2d646e2b8d
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/bitops-11.c
@@ -0,0 +1,23 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized-raw" } */
+
+int foo1(int a)
+{
+ return (a - 1) & -a;
+}
+
+int foo2(int a)
+{
+ return (a - 1) | -a;
+}
+
+int foo3(int a)
+{
+ return (a - 1) ^ -a;
+}
+
+/* { dg-final { scan-tree-dump-not "bit_and_expr, " "optimized" } } */
+/* { dg-final { scan-tree-dump-not "bit_ior_expr, " "optimized" } } */
+/* { dg-final { scan-tree-dump-not "bit_xor_expr, " "optimized" } } */
+/* { dg-final { scan-tree-dump-not "negate_expr, " "optimized" } } */
+
--
2.43.0
