[PATCH 2/6] factorize SEL(x, OP(y,z), y) into OP(SEL(x, z, 0), y)

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

'Factorize' and expression like:
	x ? (y | z) : y;
into
	(x ? z : 0) | y;

and some positional variants as well as replacing '|' by '+' or '^'.

Note: it's not very clear if this is really an improvement but it
      allows some very nice simplification of 'bits translations'.
Note: the same can be done for others operations, for example it can
      be done for '&' if '0' (the neuter value for '|', '+' and '^')
      by '~0' (same with '*' and '1').

Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
---
 simplify.c                       | 40 ++++++++++++++++++++++++++++++++
 validation/optim/fact-select01.c |  1 -
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/simplify.c b/simplify.c
index 89a064b93e85..d729b390ae76 100644
--- a/simplify.c
+++ b/simplify.c
@@ -554,6 +554,16 @@ static inline int swap_insn(struct instruction *out, struct instruction *in, pse
 	return replace_insn_pair(out, in->opcode, in, out->opcode, a, b, c);
 }
 
+///
+// create an instruction pair OUT(SELECT(a, b, c), d)
+static int swap_select(struct instruction *out, struct instruction *in, pseudo_t a, pseudo_t b, pseudo_t c, pseudo_t d)
+{
+	use_pseudo(in, c, &in->src3);
+	swap_insn(out, in, a, b, d);
+	kill_use(&out->src3);
+	return REPEAT_CSE;
+}
+
 static inline int def_opcode(pseudo_t p)
 {
 	if (p->type != PSEUDO_REG)
@@ -2254,6 +2264,36 @@ static int simplify_select(struct instruction *insn)
 		}
 		break;
 	}
+
+	switch (DEF_OPCODE(def, src1)) {
+	case OP_ADD: case OP_OR: case OP_XOR:
+		if ((def->src1 == src2) && can_move_to(cond, def)) {
+			// SEL(x, OP(y,z), y) --> OP(SEL(x, z, 0), y)
+			swap_select(insn, def, cond, def->src2, value_pseudo(0), src2);
+			return REPEAT_CSE;
+		}
+		if ((def->src2 == src2) && can_move_to(cond, def)) {
+			// SEL(x, OP(z,y), y) --> OP(SEL(x, z, 0), y)
+			swap_select(insn, def, cond, def->src1, value_pseudo(0), src2);
+			return REPEAT_CSE;
+		}
+		break;
+	}
+
+	switch (DEF_OPCODE(def, src2)) {
+	case OP_ADD: case OP_OR: case OP_XOR:
+		if ((def->src1 == src1) && can_move_to(cond, def)) {
+			// SEL(x, y, OP(y,z)) --> OP(SEL(x, 0, z), y)
+			swap_select(insn, def, cond, value_pseudo(0), def->src2, src1);
+			return REPEAT_CSE;
+		}
+		if ((def->src2 == src1) && can_move_to(cond, def)) {
+			// SEL(x, y, OP(z,y)) --> OP(SEL(x, 0, z), y)
+			swap_select(insn, def, cond, value_pseudo(0), def->src1, src1);
+			return REPEAT_CSE;
+		}
+		break;
+	}
 	return 0;
 }
 
diff --git a/validation/optim/fact-select01.c b/validation/optim/fact-select01.c
index ef4e5e89a7be..9232fc908e34 100644
--- a/validation/optim/fact-select01.c
+++ b/validation/optim/fact-select01.c
@@ -19,7 +19,6 @@ int xor_y_yx(int p, int x, int y) { return (p ? y : (y^x)) == ((p ? 0 : x) ^ y);
 /*
  * check-name: fact-select01
  * check-command: test-linearize -Wno-decl $file
- * check-known-to-fail
  *
  * check-output-ignore
  * check-output-returns: 1
-- 
2.29.2