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canonicalize ((x & M) == M) --> ((x & M) != 0) when M is a power-of-2

Message ID 20210418184622.54994-1-luc.vanoostenryck@gmail.com (mailing list archive)
State Mainlined, archived
Headers show
Series canonicalize ((x & M) == M) --> ((x & M) != 0) when M is a power-of-2 | expand

Commit Message

Luc Van Oostenryck April 18, 2021, 6:46 p.m. UTC 
and same for its dual: ((x & M) != M) --> ((x & M) == 0)

Beside the canonicalization itself, these simplifications are
useful because the compare against 0 can often be further
simplified (for example when it is used by OP_CBR or OP_SELECT).

Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
---
 simplify.c                      |  4 ++++
 validation/optim/cmp-and-pow2.c | 12 ++++++++++++
 2 files changed, 16 insertions(+)
 create mode 100644 validation/optim/cmp-and-pow2.c
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Patch

diff --git a/simplify.c b/simplify.c
index 9e3514d838a9..99f1d0454633 100644
--- a/simplify.c
+++ b/simplify.c
@@ -1266,10 +1266,14 @@  static int simplify_compare_constant(struct instruction *insn, long long value)
 		case OP_SET_EQ:
 			if ((value & bits) != value)
 				return replace_with_value(insn, 0);
+			if (value == bits && is_power_of_2(bits))
+				return replace_binop_value(insn, OP_SET_NE, 0);
 			break;
 		case OP_SET_NE:
 			if ((value & bits) != value)
 				return replace_with_value(insn, 1);
+			if (value == bits && is_power_of_2(bits))
+				return replace_binop_value(insn, OP_SET_EQ, 0);
 			break;
 		case OP_SET_LE:
 			value = sign_extend(value, def->size);
diff --git a/validation/optim/cmp-and-pow2.c b/validation/optim/cmp-and-pow2.c
new file mode 100644
index 000000000000..01ba2537521f
--- /dev/null
+++ b/validation/optim/cmp-and-pow2.c
@@ -0,0 +1,12 @@ 
+#define M 32
+
+_Bool eq(int a) { return ((a & M) != M) == ((a & M) == 0); }
+_Bool ne(int a) { return ((a & M) == M) == ((a & M) != 0); }
+
+/*
+ * check-name: cmp-and-pow2
+ * check-command: test-linearize -Wno-decl $file
+ *
+ * check-output-ignore
+ * check-output-returns: 1
+ */