cxxrtl: expose port direction in debug information.

This can be useful to distinguish e.g. a combinatorially driven wire
with type `CXXRTL_VALUE` from a module input with the same type, as
well as general introspection.

backends/cxxrtl/cxxrtl.h

@@ -452,7 +452,7 @@ struct value : public expr_base<value<Bits>> {
 		bool carry = CarryIn;
 		for (size_t n = 0; n < result.chunks; n++) {
 			result.data[n] = data[n] + (Invert ? ~other.data[n] : other.data[n]) + carry;
-			if (result.chunks - 1 == n) 
+			if (result.chunks - 1 == n)
 				result.data[result.chunks - 1] &= result.msb_mask;
 			carry = (result.data[n] <  data[n]) ||
 			        (result.data[n] == data[n] && carry);
@@ -824,6 +824,7 @@ struct debug_alias {};
 // To avoid violating strict aliasing rules, this structure has to be a subclass of the one used
 // in the C API, or it would not be possible to cast between the pointers to these.
 struct debug_item : ::cxxrtl_object {
+	// Object types.
 	enum : uint32_t {
 		VALUE  = CXXRTL_VALUE,
 		WIRE   = CXXRTL_WIRE,
@@ -831,13 +832,21 @@ struct debug_item : ::cxxrtl_object {
 		ALIAS  = CXXRTL_ALIAS,
 	};
 
+	// Object flags.
+	enum : uint32_t {
+		INPUT  = CXXRTL_INPUT,
+		OUTPUT = CXXRTL_OUTPUT,
+		INOUT  = CXXRTL_INOUT,
+	};
+
 	debug_item(const ::cxxrtl_object &object) : cxxrtl_object(object) {}
 
 	template<size_t Bits>
-	debug_item(value<Bits> &item, size_t lsb_offset = 0) {
+	debug_item(value<Bits> &item, size_t lsb_offset = 0, uint32_t flags_ = 0) {
 		static_assert(sizeof(item) == value<Bits>::chunks * sizeof(chunk_t),
 		              "value<Bits> is not compatible with C layout");
 		type    = VALUE;
+		flags   = flags_;
 		width   = Bits;
 		lsb_at  = lsb_offset;
 		depth   = 1;
@@ -847,10 +856,11 @@ struct debug_item : ::cxxrtl_object {
 	}
 
 	template<size_t Bits>
-	debug_item(const value<Bits> &item, size_t lsb_offset = 0) {
+	debug_item(const value<Bits> &item, size_t lsb_offset = 0, uint32_t flags_ = 0) {
 		static_assert(sizeof(item) == value<Bits>::chunks * sizeof(chunk_t),
 		              "value<Bits> is not compatible with C layout");
 		type    = VALUE;
+		flags   = flags_;
 		width   = Bits;
 		lsb_at  = lsb_offset;
 		depth   = 1;
@@ -860,11 +870,12 @@ struct debug_item : ::cxxrtl_object {
 	}
 
 	template<size_t Bits>
-	debug_item(wire<Bits> &item, size_t lsb_offset = 0) {
+	debug_item(wire<Bits> &item, size_t lsb_offset = 0, uint32_t flags_ = 0) {
 		static_assert(sizeof(item.curr) == value<Bits>::chunks * sizeof(chunk_t) &&
 		              sizeof(item.next) == value<Bits>::chunks * sizeof(chunk_t),
 		              "wire<Bits> is not compatible with C layout");
 		type    = WIRE;
+		flags   = flags_;
 		width   = Bits;
 		lsb_at  = lsb_offset;
 		depth   = 1;
@@ -878,6 +889,7 @@ struct debug_item : ::cxxrtl_object {
 		static_assert(sizeof(item.data[0]) == value<Width>::chunks * sizeof(chunk_t),
 		              "memory<Width> is not compatible with C layout");
 		type    = MEMORY;
+		flags   = 0;
 		width   = Width;
 		lsb_at  = 0;
 		depth   = item.data.size();
@@ -891,6 +903,7 @@ struct debug_item : ::cxxrtl_object {
 		static_assert(sizeof(item) == value<Bits>::chunks * sizeof(chunk_t),
 		              "value<Bits> is not compatible with C layout");
 		type    = ALIAS;
+		flags   = 0;
 		width   = Bits;
 		lsb_at  = lsb_offset;
 		depth   = 1;
@@ -905,6 +918,7 @@ struct debug_item : ::cxxrtl_object {
 		              sizeof(item.next) == value<Bits>::chunks * sizeof(chunk_t),
 		              "wire<Bits> is not compatible with C layout");
 		type    = ALIAS;
+		flags   = 0;
 		width   = Bits;
 		lsb_at  = lsb_offset;
 		depth   = 1;

backends/cxxrtl/cxxrtl_backend.cc

@@ -1662,7 +1662,14 @@ struct CxxrtlWorker {
 					// Member wire
 					f << indent << "items.add(path + " << escape_cxx_string(get_hdl_name(wire));
 					f << ", debug_item(" << mangle(wire) << ", ";
-					f << wire->start_offset << "));\n";
+					f << wire->start_offset;
+					if (wire->port_input && wire->port_output)
+						f << ", debug_item::INOUT";
+					else if (wire->port_input)
+						f << ", debug_item::INPUT";
+					else if (wire->port_output)
+						f << ", debug_item::OUTPUT";
+					f << "));\n";
 					count_member_wires++;
 				} else {
 					count_skipped_wires++;

backends/cxxrtl/cxxrtl_capi.h

@@ -112,6 +112,28 @@ enum cxxrtl_type {
 	// More object types may be added in the future, but the existing ones will never change.
 };
 
+// Flags of a simulated object.
+enum cxxrtl_flag {
+	// Node is a module input port.
+	//
+	// This flag can be set on objects of type `CXXRTL_VALUE` and `CXXRTL_WIRE`. It may be combined
+	// with `CXXRTL_OUTPUT`, as well as other flags.
+	CXXRTL_INPUT = 1 << 0,
+
+	// Node is a module output port.
+	//
+	// This flag can be set on objects of type `CXXRTL_WIRE`. It may be combined with `CXXRTL_INPUT`,
+	// as well as other flags.
+	CXXRTL_OUTPUT = 1 << 1,
+
+	// Node is a module inout port.
+	//
+	// This flag can be set on objects of type `CXXRTL_WIRE`. It may be combined with other flags.
+	CXXRTL_INOUT = (CXXRTL_INPUT|CXXRTL_OUTPUT),
+
+	// More object flags may be added in the future, but the existing ones will never change.
+};
+
 // Description of a simulated object.
 //
 // The `data` array can be accessed directly to inspect and, if applicable, modify the bits
@@ -123,6 +145,9 @@ struct cxxrtl_object {
 	// determines all other properties of the object.
 	uint32_t type; // actually `enum cxxrtl_type`
 
+	// Flags of the object.
+	uint32_t flags; // actually bit mask of `enum cxxrtl_flags`
+
 	// Width of the object in bits.
 	size_t width;