Added $eq/$neq -> $logic_not/$reduce_bool optimization

kernel/rtlil.cc

@@ -3000,6 +3000,21 @@ bool RTLIL::SigSpec::is_fully_const() const
 	return true;
 }
 
+bool RTLIL::SigSpec::is_fully_zero() const
+{
+	cover("kernel.rtlil.sigspec.is_fully_zero");
+
+	pack();
+	for (auto it = chunks_.begin(); it != chunks_.end(); it++) {
+		if (it->width > 0 && it->wire != NULL)
+			return false;
+		for (size_t i = 0; i < it->data.size(); i++)
+			if (it->data[i] != RTLIL::State::S0)
+				return false;
+	}
+	return true;
+}
+
 bool RTLIL::SigSpec::is_fully_def() const
 {
 	cover("kernel.rtlil.sigspec.is_fully_def");

kernel/rtlil.h

@@ -692,6 +692,7 @@ public:
 	bool is_chunk() const;
 
 	bool is_fully_const() const;
+	bool is_fully_zero() const;
 	bool is_fully_def() const;
 	bool is_fully_undef() const;
 	bool has_const() const;

passes/fsm/fsm_extract.cc

@@ -305,7 +305,9 @@ static void extract_fsm(RTLIL::Wire *wire)
 	for (auto &cellport : cellport_list) {
 		RTLIL::Cell *cell = module->cells_.at(cellport.first);
 		RTLIL::SigSpec sig_a = assign_map(cell->getPort("\\A"));
-		RTLIL::SigSpec sig_b = assign_map(cell->getPort("\\B"));
+		RTLIL::SigSpec sig_b;
+		if (cell->hasPort("\\B"))
+			sig_b = assign_map(cell->getPort("\\B"));
 		RTLIL::SigSpec sig_y = assign_map(cell->getPort("\\Y"));
 		if (cellport.second == "\\A" && !sig_b.is_fully_const())
 			continue;

passes/opt/opt_const.cc

@@ -548,6 +548,25 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 			}
 		}
 
+		if ((cell->type == "$eq" || cell->type == "$ne") &&
+				(assign_map(cell->getPort("\\A")).is_fully_zero() || assign_map(cell->getPort("\\B")).is_fully_zero()))
+		{
+			cover_list("opt.opt_const.eqneq.cmpzero", "$eq", "$ne", cell->type.str());
+			log("Replacing %s cell `%s' in module `%s' with %s.\n", log_id(cell->type), log_id(cell),
+					log_id(module), "$eq" ? "$logic_not" : "$reduce_bool");
+			cell->type = cell->type == "$eq" ? "$logic_not" : "$reduce_bool";
+			if (assign_map(cell->getPort("\\A")).is_fully_zero()) {
+				cell->setPort("\\A", cell->getPort("\\B"));
+				cell->setParam("\\A_SIGNED", cell->getParam("\\B_SIGNED"));
+				cell->setParam("\\A_WIDTH", cell->getParam("\\B_WIDTH"));
+			}
+			cell->unsetPort("\\B");
+			cell->unsetParam("\\B_SIGNED");
+			cell->unsetParam("\\B_WIDTH");
+			did_something = true;
+			goto next_cell;
+		}
+
 		if (cell->type.in("$shl", "$shr", "$sshl", "$sshr", "$shift", "$shiftx") && assign_map(cell->getPort("\\B")).is_fully_const())
 		{
 			bool sign_ext = cell->type == "$sshr" && cell->getParam("\\A_SIGNED").as_bool();