Keep keep wires in abc.

backends/aiger2/aiger.cc

@@ -1607,6 +1607,20 @@ struct XAigerWriter : AigerWriter {
 		}
 	}
 
+	static bool is_keep_po(Wire *w)
+	{
+		return !w->port_input && !w->port_output && w->get_bool_attribute(ID::keep);
+	}
+
+	void add_proper_po(Wire *w, int i, const char *symbol)
+	{
+		if (map_file.is_open())
+			map_file << symbol << " " << proper_pos_counter << " " << w->start_offset + i
+				<< " " << w->name.c_str() << "\n";
+		proper_pos_counter++;
+		pos.push_back(std::make_pair(SigBit(w, i), HierCursor{}));
+	}
+
 	void write(std::ostream *f) {
 		reset_counters();
 
@@ -1620,20 +1634,21 @@ struct XAigerWriter : AigerWriter {
 
 		int proper_po_num = 0;
 		for (auto w : top->wires())
-			if (w->port_output)
+			if (w->port_output || is_keep_po(w))
 				proper_po_num += w->width;
 
 		prep_boxes(proper_po_num);
 		for (auto w : top->wires())
 			if (w->port_output)
-				for (int i = 0; i < w->width; i++) {
-					if (map_file.is_open()) {
-						map_file << "output " << proper_pos_counter << " " << w->start_offset + i
-									<< " " << w->name.c_str() << "\n";
-					}
-					proper_pos_counter++;
-					pos.push_back(std::make_pair(SigBit(w, i), HierCursor{}));
-				}
+				for (int i = 0; i < w->width; i++)
+					add_proper_po(w, i, "output");
+
+		for (auto w : top->wires())
+			if (is_keep_po(w)) {
+				keep_wires.insert(w);
+				for (int i = 0; i < w->width; i++)
+					add_proper_po(w, i, "keepwire");
+			}
 
 		this->f = f;
 		// start with the header

passes/techmap/abc_ops_reintegrate.cc

@@ -40,6 +40,11 @@ struct PseudoPo {
 	int offset;
 };
 
+struct KeptWire {
+	RTLIL::IdString wire;
+	int offset;
+};
+
 void reintegrate(RTLIL::Module *module, bool dff_mode, std::string map_filename)
 {
 	auto design = module->design;
@@ -57,6 +62,7 @@ void reintegrate(RTLIL::Module *module, bool dff_mode, std::string map_filename)
 
 	dict<RTLIL::IdString, std::pair<int,int>> wideports_cache;
 	dict<RTLIL::IdString, PseudoPo> pseudopos;
+	dict<RTLIL::IdString, KeptWire> keptwires;
 
 	if (!map_filename.empty()) {
 		std::ifstream mf(map_filename);
@@ -172,6 +178,17 @@ void reintegrate(RTLIL::Module *module, bool dff_mode, std::string map_filename)
 				pseudopos.insert({wire_name, PseudoPo{escaped_s, escaped_p, index}});
 				log_debug(" -> %s.%s[%d]\n", escaped_s, escaped_p, index);
 			}
+			else if (type == "keepwire") {
+				log_assert(variable + co_count < output_count);
+				RTLIL::IdString wire_name = stringf("$aiger$o%d", variable + co_count);
+				RTLIL::Wire* wire = mapped_mod->wire(wire_name);
+				log_assert(wire);
+				log_assert(wire->port_output);
+				log_debug("Mapping kept wire %s", wire);
+
+				keptwires.insert({wire_name, KeptWire{escaped_s, index}});
+				log_debug(" -> %s[%d]\n", escaped_s, index);
+			}
 			else if (type == "box") {
 				RTLIL::Cell* cell = mapped_mod->cell(stringf("$box%d", variable));
 				if (!cell)
@@ -548,6 +565,20 @@ void reintegrate(RTLIL::Module *module, bool dff_mode, std::string map_filename)
 		mapped_wire->port_output = false;
 	}
 
+	// Drive the kept wires from the nets that replaced them
+	for (auto &[wire_name, kept] : keptwires) {
+		RTLIL::Wire *mapped_wire = mapped_mod->wire(wire_name);
+		log_assert(mapped_wire);
+		RTLIL::Wire *remap_wire = module->wire(remap_name(wire_name));
+		log_assert(remap_wire);
+
+		RTLIL::Wire *wire = module->wire(kept.wire);
+		log_assert(wire);
+		module->connect(SigBit(wire, kept.offset - wire->start_offset), remap_wire);
+
+		mapped_wire->port_output = false;
+	}
+
 	mapped_mod->fixup_ports();
 
 	// Stitch in mapped_mod's inputs/outputs into module

tests/abc_new/generate_mk.py

@@ -9,7 +9,6 @@ import gen_tests_makefile
 
 skip = [
     "hier_check.ys",
-    "keep_wire.ys",
 ]
 
 def create_tests():

tests/abc_new/keep_wire.ys

@@ -3,7 +3,8 @@ read_verilog <<EOT
 module top(input [3:0] a, b, output y);
 	(* keep *) wire t = &a;
 	(* keep *) wire u = |b;
-	assign y = t ^ u ^ (a[0] & b[0]);
+	(* keep *) wire [2:1] v = a[2:1] & b[2:1];
+	assign y = t ^ u ^ ^v ^ (a[0] & b[0]);
 endmodule
 EOT
 
@@ -15,6 +16,7 @@ techmap
 abc_new -liberty openroad/cm_test_cells.lib
 select -assert-count 1 w:t a:keep %i
 select -assert-count 1 w:u a:keep %i
+select -assert-count 1 w:v a:keep %i
 select -assert-none t:$_*_
 check -assert
 read_verilog openroad/cells_sim.v