[PATCH v2 6/8] transform (A & M) >> S to (A >> S) & (M >> S)

[Luc Van Oostenryck <luc.vanoostenryck@gmail.com>]

This is especially usefull when simplifying code
accessing bitfields.

Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
---
 simplify.c                 | 29 ++++++++++++++++++++++++++++-
 validation/bitfield-size.c |  4 +---
 2 files changed, 29 insertions(+), 4 deletions(-)

diff --git a/simplify.c b/simplify.c
index 9893613da..f1a898700 100644
--- a/simplify.c
+++ b/simplify.c
@@ -412,6 +412,32 @@ static int simplify_asr(struct instruction *insn, pseudo_t pseudo, long long val
 	return 0;
 }
 
+static int simplify_lsr(struct instruction *insn, pseudo_t pseudo, long long value)
+{
+	struct instruction *def;
+	unsigned long long mask;
+
+	if (!value)
+		return replace_with_pseudo(insn, pseudo);
+	switch (def_opcode(insn->src1)) {
+	case OP_AND:
+		// replace (A & M) >> S
+		// by      (A >> S) & (M >> S)
+		def = insn->src1->def;
+		if (!constant(def->src2))
+			break;
+		if (nbr_pseudo_users(insn->src1) > 1)
+			break;
+		mask = def->src2->value;
+		def->opcode = OP_LSR;
+		def->src2 = value_pseudo(value);
+		insn->opcode = OP_AND;
+		insn->src2 = value_pseudo(mask >> value);
+		return REPEAT_CSE;
+	}
+	return 0;
+}
+
 static int simplify_mul_div(struct instruction *insn, long long value)
 {
 	unsigned long long sbit = 1ULL << (insn->size - 1);
@@ -562,13 +588,14 @@ static int simplify_constant_rightside(struct instruction *insn)
 	case OP_ADD:
 	case OP_OR: case OP_XOR:
 	case OP_SHL:
-	case OP_LSR:
 	case_neutral_zero:
 		if (!value)
 			return replace_with_pseudo(insn, insn->src1);
 		return 0;
 	case OP_ASR:
 		return simplify_asr(insn, insn->src1, value);
+	case OP_LSR:
+		return simplify_lsr(insn, insn->src1, value);
 
 	case OP_MODU: case OP_MODS:
 		if (value == 1)
diff --git a/validation/bitfield-size.c b/validation/bitfield-size.c
index c8c94bb15..34400479a 100644
--- a/validation/bitfield-size.c
+++ b/validation/bitfield-size.c
@@ -36,8 +36,6 @@ unsigned int get_pbfi_b(struct bfi *bf) { return bf->b; }
  * check-output-ignore
  *
  * check-output-excludes: cast\\.4
- * check-output-pattern-6-times: cast\\.
  * check-output-pattern-6-times: lsr\\..*\\$6
- * check-output-pattern-6-times: and\\..*\\$15
- * check-output-pattern-6-times: and\\..*\\$960
+ * check-output-pattern-12-times: and\\..*\\$15
  */
-- 
2.13.2