simplify LSR + SEXT into ASR

Commit Message

Luc Van Oostenryck Jan. 24, 2021, 11:18 p.m. UTC

A logical shift right followed by a sign extension is equivalent
to an arithmetic shift. Teach this to sparse.

Signed-off-by: Luc Van Oostenryck <[e-mail]>
---
 simplify.c                    | 13 ++++++++++++-
 validation/optim/lsr-to-asr.c | 27 +++++++++++++++++++++++++++
 2 files changed, 39 insertions(+), 1 deletion(-)
 create mode 100644 validation/optim/lsr-to-asr.c

Patch

diff --git a/simplify.c b/simplify.c
index 1e7648486c49..3d398292f172 100644
--- a/simplify.c
+++ b/simplify.c
@@ -2066,7 +2066,7 @@  static int simplify_memop(struct instruction *insn)
 static int simplify_cast(struct instruction *insn)
 {
 	unsigned long long mask;
-	struct instruction *def;
+	struct instruction *def, *def2;
 	pseudo_t src = insn->src;
 	pseudo_t val;
 	int osize;
@@ -2163,6 +2163,17 @@  static int simplify_cast(struct instruction *insn)
 		case OP_TRUNC:
 			insn->orig_type = def->orig_type;
 			return replace_pseudo(insn, &insn->src1, def->src);
+		case OP_SEXT:
+			if (size != def->orig_type->bit_size)
+				break;
+			if (DEF_OPCODE(def2, def->src) != OP_LSR)
+				break;
+			if (def2->src2 != value_pseudo(size - def->size))
+				break;
+			// SEXT(TRUNC(LSR(x, N))) --> ASR(x, N)
+			insn->opcode = OP_ASR;
+			insn->src2 = def2->src2;
+			return replace_pseudo(insn, &insn->src1, def2->src1);
 		case OP_ZEXT:
 			if (size != def->orig_type->bit_size)
 				break;
diff --git a/validation/optim/lsr-to-asr.c b/validation/optim/lsr-to-asr.c
new file mode 100644
index 000000000000..269277396429
--- /dev/null
+++ b/validation/optim/lsr-to-asr.c
@@ -0,0 +1,27 @@ 
+int lsr_to_asr24(int x)
+{
+	return ((signed char)(((unsigned)x) >> 24)) == (x >> 24);
+}
+
+
+struct s {
+	int :30;
+	signed int f:2;
+};
+
+int lsr_to_asr30(int a)
+{
+	union {
+		int i;
+		struct s s;
+	} u = { .i = a };
+	return u.s.f == (a >> 30);
+}
+
+/*
+ * check-name: lsr-to-asr
+ * check-command: test-linearize -Wno-decl $file
+ *
+ * check-output-ignore
+ * check-output-returns: 1
+ */