aiger2: Resolve warnings

- Remove unused statics CONST_FALSE and CONST_TRUE (which appear to have been folded into the `Index` declaration as CFALSE and CTRUE).
- Assign default value of EMPTY_LIT to `a` and `b` for comparison ops.
- Tag debug only variables with YS_MAYBE_UNUSED, don't assign unused variables (but continue to call the function because it moves the file pointer).

backends/aiger2/aiger.cc

@@ -262,7 +262,8 @@ struct Index {
 				if (cell->type.in(ID($gt), ID($ge)))
 					std::swap(aport, bport);
 				int carry = cell->type.in(ID($le), ID($ge)) ? CFALSE : CTRUE; 
-				Lit a, b;
+				Lit a = Writer::EMPTY_LIT;
+				Lit b = Writer::EMPTY_LIT;
 				// TODO: this might not be the most economic structure; revisit at a later date
 				for (int i = 0; i < width; i++) {
 					a = visit(cursor, aport[i]);
@@ -664,8 +665,6 @@ struct Index {
 struct AigerWriter : Index<AigerWriter, unsigned int, 0, 1> {
 	typedef unsigned int Lit;
 
-	const static Lit CONST_FALSE = 0;
-	const static Lit CONST_TRUE = 1;
 	const static constexpr Lit EMPTY_LIT = std::numeric_limits<Lit>::max();
 
 	static Lit negate(Lit lit) {
@@ -802,8 +801,6 @@ struct AigerWriter : Index<AigerWriter, unsigned int, 0, 1> {
 };
 
 struct XAigerAnalysis : Index<XAigerAnalysis, int, 0, 0> {
-	const static int CONST_FALSE = 0;
-	const static int CONST_TRUE = 0;
 	const static constexpr int EMPTY_LIT = -1;
 
 	XAigerAnalysis()

frontends/aiger2/xaiger.cc

@@ -198,11 +198,10 @@ struct Xaiger2Frontend : public Frontend {
 
 				int ci_counter = 0;
 				for (uint32_t i = 0; i < no_boxes; i++) {
-					uint32_t box_inputs, box_outputs, box_id, box_seq;
-					box_inputs = read_be32(*f);
-					box_outputs = read_be32(*f);
-					box_id = read_be32(*f);
-					box_seq = read_be32(*f);
+					/* unused box_inputs = */ read_be32(*f);
+					YS_MAYBE_UNUSED auto box_outputs = read_be32(*f);
+					/* unused box_id = */ read_be32(*f);
+					auto box_seq = read_be32(*f);
 
 					log("box_seq=%d boxes.size=%d\n", box_seq, (int) boxes.size());
 					log_assert(box_seq < boxes.size());
@@ -337,11 +336,10 @@ struct Xaiger2Frontend : public Frontend {
 						  len, ci_num, co_num, pi_num, po_num, no_boxes);
 
 				for (uint32_t i = 0; i < no_boxes; i++) {
-					uint32_t box_inputs, box_outputs, box_id, box_seq;
-					box_inputs = read_be32(*f);
-					box_outputs = read_be32(*f);
-					box_id = read_be32(*f);
-					box_seq = read_be32(*f);
+					YS_MAYBE_UNUSED auto box_inputs = read_be32(*f);
+					/* unused box_outputs = */ read_be32(*f);
+					/* unused box_id = */ read_be32(*f);
+					auto box_seq = read_be32(*f);
 
 					log("box_seq=%d boxes.size=%d\n", box_seq, (int) boxes.size());
 					log_assert(box_seq < boxes.size());