Add $check cell to represent assertions with messages

backends/cxxrtl/runtime/cxxrtl/cxxrtl.h

@@ -952,7 +952,23 @@ struct lazy_fmt {
 	virtual std::string operator() () const = 0;
 };
 
-// An object that can be passed to a `eval()` method in order to act on side effects.
+// Flavor of a `$check` cell.
+enum class flavor {
+	// Corresponds to a `$assert` cell in other flows, and a Verilog `assert ()` statement.
+	ASSERT,
+	// Corresponds to a `$assume` cell in other flows, and a Verilog `assume ()` statement.
+	ASSUME,
+	// Corresponds to a `$live` cell in other flows, and a Verilog `assert (eventually)` statement.
+	ASSERT_EVENTUALLY,
+	// Corresponds to a `$fair` cell in other flows, and a Verilog `assume (eventually)` statement.
+	ASSUME_EVENTUALLY,
+	// Corresponds to a `$cover` cell in other flows, and a Verilog `cover ()` statement.
+	COVER,
+};
+
+// An object that can be passed to a `eval()` method in order to act on side effects. The default behavior implemented
+// below is the same as the behavior of `eval(nullptr)`, except that `-print-output` option of `write_cxxrtl` is not
+// taken into account.
 struct performer {
 	// Called by generated formatting code to evaluate a Verilog `$time` expression.
 	virtual int64_t vlog_time() const { return 0; }
@@ -964,6 +980,15 @@ struct performer {
 	virtual void on_print(const lazy_fmt &formatter, const metadata_map &attributes) {
 		std::cout << formatter();
 	}
+
+	// Called when a `$check` cell is triggered.
+	virtual void on_check(flavor type, bool condition, const lazy_fmt &formatter, const metadata_map &attributes) {
+		if (type == flavor::ASSERT || type == flavor::ASSUME) {
+			if (!condition)
+				std::cerr << formatter();
+			CXXRTL_ASSERT(condition && "Check failed");
+		}
+	}
 };
 
 // An object that can be passed to a `commit()` method in order to produce a replay log of every state change in

backends/verilog/verilog_backend.cc

@@ -1008,7 +1008,7 @@ void dump_cell_expr_binop(std::ostream &f, std::string indent, RTLIL::Cell *cell
 
 void dump_cell_expr_print(std::ostream &f, std::string indent, const RTLIL::Cell *cell)
 {
-	Fmt fmt = {};
+	Fmt fmt;
 	fmt.parse_rtlil(cell);
 	std::vector<VerilogFmtArg> args = fmt.emit_verilog();
 
@@ -1041,6 +1041,23 @@ void dump_cell_expr_print(std::ostream &f, std::string indent, const RTLIL::Cell
 	f << stringf(");\n");
 }
 
+void dump_cell_expr_check(std::ostream &f, std::string indent, const RTLIL::Cell *cell)
+{
+	std::string flavor = cell->getParam(ID(FLAVOR)).decode_string();
+	if (flavor == "assert")
+		f << stringf("%s" "assert (", indent.c_str());
+	else if (flavor == "assume")
+		f << stringf("%s" "assume (", indent.c_str());
+	else if (flavor == "live")
+		f << stringf("%s" "assert (eventually ", indent.c_str());
+	else if (flavor == "fair")
+		f << stringf("%s" "assume (eventually ", indent.c_str());
+	else if (flavor == "cover")
+		f << stringf("%s" "cover (", indent.c_str());
+	dump_sigspec(f, cell->getPort(ID::A));
+	f << stringf(");\n");
+}
+
 bool dump_cell_expr(std::ostream &f, std::string indent, RTLIL::Cell *cell)
 {
 	if (cell->type == ID($_NOT_)) {
@@ -1814,6 +1831,39 @@ bool dump_cell_expr(std::ostream &f, std::string indent, RTLIL::Cell *cell)
 		return true;
 	}
 
+	if (cell->type == ID($check))
+	{
+		// Sync $check cells are accumulated and handled in dump_module.
+		if (cell->getParam(ID::TRG_ENABLE).as_bool())
+			return true;
+
+		f << stringf("%s" "always @*\n", indent.c_str());
+
+		f << stringf("%s" "  if (", indent.c_str());
+		dump_sigspec(f, cell->getPort(ID::EN));
+		f << stringf(") begin\n");
+
+		std::string flavor = cell->getParam(ID::FLAVOR).decode_string();
+		if (flavor == "assert" || flavor == "assume") {
+			Fmt fmt;
+			fmt.parse_rtlil(cell);
+			if (!fmt.parts.empty()) {
+				f << stringf("%s" "    if (!", indent.c_str());
+				dump_sigspec(f, cell->getPort(ID::A));
+				f << stringf(")\n");
+				dump_cell_expr_print(f, indent + "      ", cell);
+			}
+		} else {
+			f << stringf("%s" "  /* message omitted */\n", indent.c_str());
+		}
+
+		dump_cell_expr_check(f, indent + "    ", cell);
+
+		f << stringf("%s" "  end\n", indent.c_str());
+
+		return true;
+	}
+
 	// FIXME: $fsm
 
 	return false;
@@ -1903,7 +1953,7 @@ void dump_cell(std::ostream &f, std::string indent, RTLIL::Cell *cell)
 	}
 }
 
-void dump_sync_print(std::ostream &f, std::string indent, const RTLIL::SigSpec &trg, const RTLIL::Const &polarity, std::vector<const RTLIL::Cell*> &cells)
+void dump_sync_effect(std::ostream &f, std::string indent, const RTLIL::SigSpec &trg, const RTLIL::Const &polarity, std::vector<const RTLIL::Cell*> &cells)
 {
 	if (trg.size() == 0) {
 		f << stringf("%s" "initial begin\n", indent.c_str());
@@ -1927,9 +1977,29 @@ void dump_sync_print(std::ostream &f, std::string indent, const RTLIL::SigSpec &
 	for (auto cell : cells) {
 		f << stringf("%s" "  if (", indent.c_str());
 		dump_sigspec(f, cell->getPort(ID::EN));
-		f << stringf(")\n");
+		f << stringf(") begin\n");
+
+		if (cell->type == ID($print)) {
+			dump_cell_expr_print(f, indent + "    ", cell);
+		} else if (cell->type == ID($check)) {
+			std::string flavor = cell->getParam(ID::FLAVOR).decode_string();
+			if (flavor == "assert" || flavor == "assume") {
+				Fmt fmt;
+				fmt.parse_rtlil(cell);
+				if (!fmt.parts.empty()) {
+					f << stringf("%s" "    if (!", indent.c_str());
+					dump_sigspec(f, cell->getPort(ID::A));
+					f << stringf(")\n");
+					dump_cell_expr_print(f, indent + "      ", cell);
+				}
+			} else {
+				f << stringf("%s" "  /* message omitted */\n", indent.c_str());
+			}
 
-		dump_cell_expr_print(f, indent + "    ", cell);
+			dump_cell_expr_check(f, indent + "    ", cell);
+		}
+
+		f << stringf("%s" "  end\n", indent.c_str());
 	}
 
 	f << stringf("%s" "end\n", indent.c_str());
@@ -2182,7 +2252,7 @@ void dump_process(std::ostream &f, std::string indent, RTLIL::Process *proc, boo
 
 void dump_module(std::ostream &f, std::string indent, RTLIL::Module *module)
 {
-	std::map<std::pair<RTLIL::SigSpec, RTLIL::Const>, std::vector<const RTLIL::Cell*>> sync_print_cells;
+	std::map<std::pair<RTLIL::SigSpec, RTLIL::Const>, std::vector<const RTLIL::Cell*>> sync_effect_cells;
 
 	reg_wires.clear();
 	reset_auto_counter(module);
@@ -2214,8 +2284,8 @@ void dump_module(std::ostream &f, std::string indent, RTLIL::Module *module)
 		std::set<std::pair<RTLIL::Wire*,int>> reg_bits;
 		for (auto cell : module->cells())
 		{
-			if (cell->type == ID($print) && cell->getParam(ID::TRG_ENABLE).as_bool()) {
-				sync_print_cells[make_pair(cell->getPort(ID::TRG), cell->getParam(ID::TRG_POLARITY))].push_back(cell);
+			if (cell->type.in(ID($print), ID($check)) && cell->getParam(ID::TRG_ENABLE).as_bool()) {
+				sync_effect_cells[make_pair(cell->getPort(ID::TRG), cell->getParam(ID::TRG_POLARITY))].push_back(cell);
 				continue;
 			}
 
@@ -2274,8 +2344,8 @@ void dump_module(std::ostream &f, std::string indent, RTLIL::Module *module)
 	for (auto cell : module->cells())
 		dump_cell(f, indent + "  ", cell);
 
-	for (auto &it : sync_print_cells)
-		dump_sync_print(f, indent + "  ", it.first.first, it.first.second, it.second);
+	for (auto &it : sync_effect_cells)
+		dump_sync_effect(f, indent + "  ", it.first.first, it.first.second, it.second);
 
 	for (auto it = module->processes.begin(); it != module->processes.end(); ++it)
 		dump_process(f, indent + "  ", it->second);

docs/source/CHAPTER_CellLib.rst

@@ -621,7 +621,7 @@ Add information about ``$specify2``, ``$specify3``, and ``$specrule`` cells.
 Formal verification cells
 ~~~~~~~~~~~~~~~~~~~~~~~~~
 
-Add information about ``$assert``, ``$assume``, ``$live``, ``$fair``,
+Add information about ``$check``, ``$assert``, ``$assume``, ``$live``, ``$fair``,
 ``$cover``, ``$equiv``, ``$initstate``, ``$anyconst``, ``$anyseq``,
 ``$anyinit``, ``$allconst``, ``$allseq`` cells.
 
@@ -654,8 +654,8 @@ If ``\TRG_ENABLE`` is true, the following parameters also apply:
 	negative-edge triggered.
 
 ``\PRIORITY``
-	When multiple ``$print`` cells fire on the same trigger, they execute in
-	descending priority order.
+	When multiple ``$print`` or ``$$check`` cells fire on the same trigger, they\
+	execute in descending priority order.
 
 Ports: