[10/10] cmps: canonicalize SEL(x > 0, a, -a) --> SEL(x >= 0, a, -a)

Commit Message

Luc Van Oostenryck Jan. 26, 2021, 10:04 p.m. UTC

When computing the absolute value using an expression like:
	(a > 0) ? a : -a
it's irrelevant to use '>' or '>=', both will give the same
result since 0 is its own negation.

Canonicalize these equivalent expressions, such that OP_GE
is always used.

Signed-off-by: Luc Van Oostenryck <[e-mail]>
---
 simplify.c                       | 14 ++++++++++++++
 validation/optim/canonical-abs.c |  1 -
 2 files changed, 14 insertions(+), 1 deletion(-)

Patch

diff --git a/simplify.c b/simplify.c
index 10cdf50dcbf1..584078ddca89 100644
--- a/simplify.c
+++ b/simplify.c
@@ -454,6 +454,13 @@  static inline pseudo_t is_same_op(pseudo_t src, int op, unsigned osize)
 	return def->src;
 }
 
+static bool is_negate_of(pseudo_t p, pseudo_t ref)
+{
+	struct instruction *def;
+
+	return (DEF_OPCODE(def, p) == OP_NEG) && (def->src == ref);
+}
+
 ///
 // replace the operand of an instruction
 // @insn: the instruction
@@ -2308,6 +2315,13 @@  static int simplify_select(struct instruction *insn)
 		// SEL(x {<,<=} y, a, b) --> SEL(x {>=,>} y, b, a)
 		def->opcode = opcode_negate(def->opcode);
 		return switch_pseudo(insn, &insn->src2, insn, &insn->src3);
+	case OP_SET_GT:
+		if (one_use(cond) && is_zero(def->src2)) {
+			if (is_negate_of(src2, src1))
+				// SEL(x > 0, a, -a) --> SEL(x >= 0, a, -a)
+				return replace_opcode(def, OP_SET_GE);
+		}
+		break;
 	case OP_SEL:
 		if (constant(def->src2) && constant(def->src3)) {
 			// Is the def of the conditional another select?
diff --git a/validation/optim/canonical-abs.c b/validation/optim/canonical-abs.c
index 0809a52d445b..1bd6d89a3ad5 100644
--- a/validation/optim/canonical-abs.c
+++ b/validation/optim/canonical-abs.c
@@ -5,7 +5,6 @@  _Bool abs2(int a) { return (a < 0 ? -a : a) == (a <= 0 ? -a : a); }
 /*
  * check-name: canonical-abs1
  * check-command: test-linearize -Wno-decl $file
- * check-known-to-fail
  *
  * check-output-ignore
  * check-output-returns: 1