Merge pull request #7 from YosysHQ/master

Syncing with official repo

16 files changed, 4182 insertions, 1083 deletions

diff --git a/passes/opt/Makefile.inc b/passes/opt/Makefile.inc
index 0d01e9d35..eb07e9452 100644
--- a/passes/opt/Makefile.inc
+++ b/passes/opt/Makefile.inc
@@ -4,6 +4,7 @@ OBJS += passes/opt/opt_merge.o
 OBJS += passes/opt/opt_muxtree.o
 OBJS += passes/opt/opt_reduce.o
 OBJS += passes/opt/opt_rmdff.o
+OBJS += passes/opt/opt_share.o
 OBJS += passes/opt/opt_clean.o
 OBJS += passes/opt/opt_expr.o
 
@@ -12,5 +13,7 @@ OBJS += passes/opt/share.o
 OBJS += passes/opt/wreduce.o
 OBJS += passes/opt/opt_demorgan.o
 OBJS += passes/opt/rmports.o
+OBJS += passes/opt/opt_lut.o
+OBJS += passes/opt/pmux2shiftx.o
+OBJS += passes/opt/muxpack.o
 endif
-
diff --git a/passes/opt/muxpack.cc b/passes/opt/muxpack.cc
new file mode 100644
index 000000000..c40c02acd
--- /dev/null
+++ b/passes/opt/muxpack.cc
@@ -0,0 +1,368 @@
+/*
+ *  yosys -- Yosys Open SYnthesis Suite
+ *
+ *  Copyright (C) 2012  Clifford Wolf <clifford@clifford.at>
+ *                2019  Eddie Hung    <eddie@fpgeh.com>
+ *
+ *  Permission to use, copy, modify, and/or distribute this software for any
+ *  purpose with or without fee is hereby granted, provided that the above
+ *  copyright notice and this permission notice appear in all copies.
+ *
+ *  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ *  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ *  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ *  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ *  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ *  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ *  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ */
+
+#include "kernel/yosys.h"
+#include "kernel/sigtools.h"
+
+USING_YOSYS_NAMESPACE
+PRIVATE_NAMESPACE_BEGIN
+
+struct ExclusiveDatabase
+{
+	Module *module;
+	const SigMap &sigmap;
+
+	dict<SigBit, std::pair<SigSpec,std::vector<Const>>> sig_cmp_prev;
+
+	ExclusiveDatabase(Module *module, const SigMap &sigmap) : module(module), sigmap(sigmap)
+	{
+		SigSpec const_sig, nonconst_sig;
+		SigBit y_port;
+		pool<Cell*> reduce_or;
+		for (auto cell : module->cells()) {
+			if (cell->type == ID($eq)) {
+				nonconst_sig = sigmap(cell->getPort(ID::A));
+				const_sig = sigmap(cell->getPort(ID::B));
+				if (!const_sig.is_fully_const()) {
+					if (!nonconst_sig.is_fully_const())
+						continue;
+					std::swap(nonconst_sig, const_sig);
+				}
+				y_port = sigmap(cell->getPort(ID::Y));
+			}
+			else if (cell->type == ID($logic_not)) {
+				nonconst_sig = sigmap(cell->getPort(ID::A));
+				const_sig = Const(State::S0, GetSize(nonconst_sig));
+				y_port = sigmap(cell->getPort(ID::Y));
+			}
+			else if (cell->type == ID($reduce_or)) {
+				reduce_or.insert(cell);
+				continue;
+			}
+			else continue;
+
+			log_assert(!nonconst_sig.empty());
+			log_assert(!const_sig.empty());
+			sig_cmp_prev[y_port] = std::make_pair(nonconst_sig,std::vector<Const>{const_sig.as_const()});
+		}
+
+		for (auto cell : reduce_or) {
+			nonconst_sig = SigSpec();
+			std::vector<Const> values;
+			SigSpec a_port = sigmap(cell->getPort(ID::A));
+			for (auto bit : a_port) {
+				auto it = sig_cmp_prev.find(bit);
+				if (it == sig_cmp_prev.end()) {
+					nonconst_sig = SigSpec();
+					break;
+				}
+				if (nonconst_sig.empty())
+					nonconst_sig = it->second.first;
+				else if (nonconst_sig != it->second.first) {
+					nonconst_sig = SigSpec();
+					break;
+				}
+				for (auto value : it->second.second)
+					values.push_back(value);
+			}
+			if (nonconst_sig.empty())
+				continue;
+			y_port = sigmap(cell->getPort(ID::Y));
+			sig_cmp_prev[y_port] = std::make_pair(nonconst_sig,std::move(values));
+		}
+	}
+
+	bool query(const SigSpec &sig) const
+	{
+		SigSpec nonconst_sig;
+		pool<Const> const_values;
+
+		for (auto bit : sig.bits()) {
+			auto it = sig_cmp_prev.find(bit);
+			if (it == sig_cmp_prev.end())
+				return false;
+
+			if (nonconst_sig.empty())
+				nonconst_sig = it->second.first;
+			else if (nonconst_sig != it->second.first)
+				return false;
+
+			for (auto value : it->second.second)
+				if (!const_values.insert(value).second)
+					return false;
+		}
+
+		return true;
+	}
+};
+
+
+struct MuxpackWorker
+{
+	Module *module;
+	SigMap sigmap;
+
+	int mux_count, pmux_count;
+
+	pool<Cell*> remove_cells;
+
+	dict<SigSpec, Cell*> sig_chain_next;
+	dict<SigSpec, Cell*> sig_chain_prev;
+	pool<SigBit> sigbit_with_non_chain_users;
+	pool<Cell*> chain_start_cells;
+	pool<Cell*> candidate_cells;
+
+	ExclusiveDatabase excl_db;
+
+	void make_sig_chain_next_prev()
+	{
+		for (auto wire : module->wires())
+		{
+			if (wire->port_output || wire->get_bool_attribute(ID::keep)) {
+				for (auto bit : sigmap(wire))
+					sigbit_with_non_chain_users.insert(bit);
+			}
+		}
+
+		for (auto cell : module->cells())
+		{
+			if (cell->type.in(ID($mux), ID($pmux)) && !cell->get_bool_attribute(ID::keep))
+			{
+				SigSpec a_sig = sigmap(cell->getPort(ID::A));
+				SigSpec b_sig;
+				if (cell->type == ID($mux))
+					b_sig = sigmap(cell->getPort(ID::B));
+				SigSpec y_sig = sigmap(cell->getPort(ID::Y));
+   
+				if (sig_chain_next.count(a_sig))
+					for (auto a_bit : a_sig.bits())
+						sigbit_with_non_chain_users.insert(a_bit);
+				else {
+					sig_chain_next[a_sig] = cell;
+					candidate_cells.insert(cell);
+				}
+
+				if (!b_sig.empty()) {
+					if (sig_chain_next.count(b_sig))
+						for (auto b_bit : b_sig.bits())
+							sigbit_with_non_chain_users.insert(b_bit);
+					else {
+						sig_chain_next[b_sig] = cell;
+						candidate_cells.insert(cell);
+					}
+				}
+
+				sig_chain_prev[y_sig] = cell;
+				continue;
+			}
+
+			for (auto conn : cell->connections())
+				if (cell->input(conn.first))
+					for (auto bit : sigmap(conn.second))
+						sigbit_with_non_chain_users.insert(bit);
+		}
+	}
+
+	void find_chain_start_cells()
+	{
+		for (auto cell : candidate_cells)
+		{
+			log_debug("Considering %s (%s)\n", log_id(cell), log_id(cell->type));
+
+			SigSpec a_sig = sigmap(cell->getPort(ID::A));
+			if (cell->type == ID($mux)) {
+				SigSpec b_sig = sigmap(cell->getPort(ID::B));
+				if (sig_chain_prev.count(a_sig) + sig_chain_prev.count(b_sig) != 1)
+					goto start_cell;
+
+				if (!sig_chain_prev.count(a_sig))
+					a_sig = b_sig;
+			}
+			else if (cell->type == ID($pmux)) {
+				if (!sig_chain_prev.count(a_sig))
+					goto start_cell;
+			}
+			else log_abort();
+
+			for (auto bit : a_sig.bits())
+				if (sigbit_with_non_chain_users.count(bit))
+					goto start_cell;
+
+			{
+				Cell *prev_cell = sig_chain_prev.at(a_sig);
+				log_assert(prev_cell);
+				SigSpec s_sig = sigmap(cell->getPort(ID(S)));
+				s_sig.append(sigmap(prev_cell->getPort(ID(S))));
+				if (!excl_db.query(s_sig))
+					goto start_cell;
+			}
+
+			continue;
+
+		start_cell:
+			chain_start_cells.insert(cell);
+		}
+	}
+
+	vector<Cell*> create_chain(Cell *start_cell)
+	{
+		vector<Cell*> chain;
+
+		Cell *c = start_cell;
+		while (c != nullptr)
+		{
+			chain.push_back(c);
+
+			SigSpec y_sig = sigmap(c->getPort(ID::Y));
+
+			if (sig_chain_next.count(y_sig) == 0)
+				break;
+
+			c = sig_chain_next.at(y_sig);
+			if (chain_start_cells.count(c) != 0)
+				break;
+		}
+
+		return chain;
+	}
+
+	void process_chain(vector<Cell*> &chain)
+	{
+		if (GetSize(chain) < 2)
+			return;
+
+		int cursor = 0;
+		while (cursor < GetSize(chain))
+		{
+			int cases = GetSize(chain) - cursor;
+
+			Cell *first_cell = chain[cursor];
+			dict<int, SigBit> taps_dict;
+
+			if (cases < 2) {
+				cursor++;
+				continue;
+			}
+
+			Cell *last_cell = chain[cursor+cases-1];
+
+			log("Converting %s.%s ... %s.%s to a pmux with %d cases.\n",
+				log_id(module), log_id(first_cell), log_id(module), log_id(last_cell), cases);
+
+			mux_count += cases;
+			pmux_count += 1;
+
+			first_cell->type = ID($pmux);
+			SigSpec b_sig = first_cell->getPort(ID::B);
+			SigSpec s_sig = first_cell->getPort(ID(S));
+
+			for (int i = 1; i < cases; i++) {
+				Cell* prev_cell = chain[cursor+i-1];
+				Cell* cursor_cell = chain[cursor+i];
+				if (sigmap(prev_cell->getPort(ID::Y)) == sigmap(cursor_cell->getPort(ID::A))) {
+					b_sig.append(cursor_cell->getPort(ID::B));
+					s_sig.append(cursor_cell->getPort(ID(S)));
+				}
+				else {
+					log_assert(cursor_cell->type == ID($mux));
+					b_sig.append(cursor_cell->getPort(ID::A));
+					s_sig.append(module->LogicNot(NEW_ID, cursor_cell->getPort(ID(S))));
+				}
+				remove_cells.insert(cursor_cell);
+			}
+
+			first_cell->setPort(ID::B, b_sig);
+			first_cell->setPort(ID(S), s_sig);
+			first_cell->setParam(ID(S_WIDTH), GetSize(s_sig));
+			first_cell->setPort(ID::Y, last_cell->getPort(ID::Y));
+
+			cursor += cases;
+		}
+	}
+
+	void cleanup()
+	{
+		for (auto cell : remove_cells)
+			module->remove(cell);
+
+		remove_cells.clear();
+		sig_chain_next.clear();
+		sig_chain_prev.clear();
+		chain_start_cells.clear();
+		candidate_cells.clear();
+	}
+
+	MuxpackWorker(Module *module) :
+			module(module), sigmap(module), mux_count(0), pmux_count(0), excl_db(module, sigmap)
+	{
+		make_sig_chain_next_prev();
+		find_chain_start_cells();
+
+		for (auto c : chain_start_cells) {
+			vector<Cell*> chain = create_chain(c);
+			process_chain(chain);
+		}
+
+		cleanup();
+	}
+};
+
+struct MuxpackPass : public Pass {
+	MuxpackPass() : Pass("muxpack", "$mux/$pmux cascades to $pmux") { }
+	void help() YS_OVERRIDE
+	{
+		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
+		log("\n");
+		log("    muxpack [selection]\n");
+		log("\n");
+		log("This pass converts cascaded chains of $pmux cells (e.g. those create from case\n");
+		log("constructs) and $mux cells (e.g. those created by if-else constructs) into\n");
+		log("$pmux cells.\n");
+		log("\n");
+		log("This optimisation is conservative --- it will only pack $mux or $pmux cells\n");
+		log("whose select lines are driven by '$eq' cells with other such cells if it can be\n");
+		log("certain that their select inputs are mutually exclusive.\n");
+		log("\n");
+	}
+	void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
+	{
+		log_header(design, "Executing MUXPACK pass ($mux cell cascades to $pmux).\n");
+
+		size_t argidx;
+		for (argidx = 1; argidx < args.size(); argidx++)
+		{
+			break;
+		}
+		extra_args(args, argidx, design);
+
+		int mux_count = 0;
+		int pmux_count = 0;
+
+		for (auto module : design->selected_modules()) {
+			MuxpackWorker worker(module);
+			mux_count += worker.mux_count;
+			pmux_count += worker.pmux_count;
+		}
+
+		log("Converted %d (p)mux cells into %d pmux cells.\n", mux_count, pmux_count);
+	}
+} MuxpackPass;
+
+PRIVATE_NAMESPACE_END
diff --git a/passes/opt/opt.cc b/passes/opt/opt.cc
index 021c1a03f..396819883 100644
--- a/passes/opt/opt.cc
+++ b/passes/opt/opt.cc
@@ -27,7 +27,7 @@ PRIVATE_NAMESPACE_BEGIN
 
 struct OptPass : public Pass {
 	OptPass() : Pass("opt", "perform simple optimizations") { }
-	virtual void help()
+	void help() YS_OVERRIDE
 	{
 		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
 		log("\n");
@@ -44,7 +44,8 @@ struct OptPass : public Pass {
 		log("        opt_muxtree\n");
 		log("        opt_reduce [-fine] [-full]\n");
 		log("        opt_merge [-share_all]\n");
-		log("        opt_rmdff [-keepdc]\n");
+		log("        opt_share (-full only)\n");
+		log("        opt_rmdff [-keepdc] [-sat]\n");
 		log("        opt_clean [-purge]\n");
 		log("        opt_expr [-mux_undef] [-mux_bool] [-undriven] [-clkinv] [-fine] [-full] [-keepdc]\n");
 		log("    while <changed design>\n");
@@ -54,7 +55,7 @@ struct OptPass : public Pass {
 		log("    do\n");
 		log("        opt_expr [-mux_undef] [-mux_bool] [-undriven] [-clkinv] [-fine] [-full] [-keepdc]\n");
 		log("        opt_merge [-share_all]\n");
-		log("        opt_rmdff [-keepdc]\n");
+		log("        opt_rmdff [-keepdc] [-sat]\n");
 		log("        opt_clean [-purge]\n");
 		log("    while <changed design in opt_rmdff>\n");
 		log("\n");
@@ -63,13 +64,14 @@ struct OptPass : public Pass {
 		log("\n");
 		log("\n");
 	}
-	virtual void execute(std::vector<std::string> args, RTLIL::Design *design)
+	void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
 	{
 		std::string opt_clean_args;
 		std::string opt_expr_args;
 		std::string opt_reduce_args;
 		std::string opt_merge_args;
 		std::string opt_rmdff_args;
+		bool opt_share = false;
 		bool fast_mode = false;
 
 		log_header(design, "Executing OPT pass (performing simple optimizations).\n");
@@ -105,6 +107,7 @@ struct OptPass : public Pass {
 			if (args[argidx] == "-full") {
 				opt_expr_args += " -full";
 				opt_reduce_args += " -full";
+				opt_share = true;
 				continue;
 			}
 			if (args[argidx] == "-keepdc") {
@@ -112,6 +115,10 @@ struct OptPass : public Pass {
 				opt_rmdff_args += " -keepdc";
 				continue;
 			}
+			if (args[argidx] == "-sat") {
+				opt_rmdff_args += " -sat";
+				continue;
+			}
 			if (args[argidx] == "-share_all") {
 				opt_merge_args += " -share_all";
 				continue;
@@ -147,6 +154,8 @@ struct OptPass : public Pass {
 				Pass::call(design, "opt_muxtree");
 				Pass::call(design, "opt_reduce" + opt_reduce_args);
 				Pass::call(design, "opt_merge" + opt_merge_args);
+				if (opt_share)
+					Pass::call(design, "opt_share");
 				Pass::call(design, "opt_rmdff" + opt_rmdff_args);
 				Pass::call(design, "opt_clean" + opt_clean_args);
 				Pass::call(design, "opt_expr" + opt_expr_args);
diff --git a/passes/opt/opt_clean.cc b/passes/opt/opt_clean.cc
index 25d462ada..2f69b3d4c 100644
--- a/passes/opt/opt_clean.cc
+++ b/passes/opt/opt_clean.cc
@@ -52,7 +52,7 @@ struct keep_cache_t
 			return cache.at(module);
 
 		cache[module] = true;
-		if (!module->get_bool_attribute("\\keep")) {
+		if (!module->get_bool_attribute(ID::keep)) {
 			bool found_keep = false;
 			for (auto cell : module->cells())
 				if (query(cell)) found_keep = true;
@@ -64,7 +64,7 @@ struct keep_cache_t
 
 	bool query(Cell *cell)
 	{
-		if (cell->type.in("$memwr", "$meminit", "$assert", "$assume", "$live", "$fair", "$cover"))
+		if (cell->type.in(ID($memwr), ID($meminit), ID($assert), ID($assume), ID($live), ID($fair), ID($cover), ID($specify2), ID($specify3), ID($specrule)))
 			return true;
 
 		if (cell->has_keep_attr())
@@ -85,22 +85,34 @@ void rmunused_module_cells(Module *module, bool verbose)
 {
 	SigMap sigmap(module);
 	pool<Cell*> queue, unused;
+	pool<SigBit> used_raw_bits;
 	dict<SigBit, pool<Cell*>> wire2driver;
+	dict<SigBit, vector<string>> driver_driver_logs;
+
+	SigMap raw_sigmap;
+	for (auto &it : module->connections_) {
+		for (int i = 0; i < GetSize(it.second); i++) {
+			if (it.second[i].wire != nullptr)
+				raw_sigmap.add(it.first[i], it.second[i]);
+		}
+	}
 
 	for (auto &it : module->cells_) {
 		Cell *cell = it.second;
 		for (auto &it2 : cell->connections()) {
-			if (!ct_all.cell_known(cell->type) || ct_all.cell_output(cell->type, it2.first))
-				for (auto raw_bit : it2.second) {
-					if (raw_bit.wire == nullptr)
-						continue;
-					auto bit = sigmap(raw_bit);
-					if (bit.wire == nullptr)
-						log_warning("Driver-driver conflict for %s between cell %s.%s and constant %s in %s: Resolved using constant.\n",
-								log_signal(raw_bit), log_id(cell), log_id(it2.first), log_signal(bit), log_id(module));
-					if (bit.wire != nullptr)
-						wire2driver[bit].insert(cell);
-				}
+			if (ct_all.cell_known(cell->type) && !ct_all.cell_output(cell->type, it2.first))
+				continue;
+			for (auto raw_bit : it2.second) {
+				if (raw_bit.wire == nullptr)
+					continue;
+				auto bit = sigmap(raw_bit);
+				if (bit.wire == nullptr && ct_all.cell_known(cell->type))
+					driver_driver_logs[raw_sigmap(raw_bit)].push_back(stringf("Driver-driver conflict "
+							"for %s between cell %s.%s and constant %s in %s: Resolved using constant.",
+							log_signal(raw_bit), log_id(cell), log_id(it2.first), log_signal(bit), log_id(module)));
+				if (bit.wire != nullptr)
+					wire2driver[bit].insert(cell);
+			}
 		}
 		if (keep_cache.query(cell))
 			queue.insert(cell);
@@ -110,10 +122,12 @@ void rmunused_module_cells(Module *module, bool verbose)
 
 	for (auto &it : module->wires_) {
 		Wire *wire = it.second;
-		if (wire->port_output || wire->get_bool_attribute("\\keep")) {
+		if (wire->port_output || wire->get_bool_attribute(ID::keep)) {
 			for (auto bit : sigmap(wire))
 			for (auto c : wire2driver[bit])
 				queue.insert(c), unused.erase(c);
+			for (auto raw_bit : SigSpec(wire))
+				used_raw_bits.insert(raw_sigmap(raw_bit));
 		}
 	}
 
@@ -137,18 +151,34 @@ void rmunused_module_cells(Module *module, bool verbose)
 
 	for (auto cell : unused) {
 		if (verbose)
-			log("  removing unused `%s' cell `%s'.\n", cell->type.c_str(), cell->name.c_str());
+			log_debug("  removing unused `%s' cell `%s'.\n", cell->type.c_str(), cell->name.c_str());
 		module->design->scratchpad_set_bool("opt.did_something", true);
 		module->remove(cell);
 		count_rm_cells++;
 	}
+
+	for (auto &it : module->cells_) {
+		Cell *cell = it.second;
+		for (auto &it2 : cell->connections()) {
+			if (ct_all.cell_known(cell->type) && !ct_all.cell_input(cell->type, it2.first))
+				continue;
+			for (auto raw_bit : raw_sigmap(it2.second))
+				used_raw_bits.insert(raw_bit);
+		}
+	}
+
+	for (auto it : driver_driver_logs) {
+		if (used_raw_bits.count(it.first))
+			for (auto msg : it.second)
+				log_warning("%s\n", msg.c_str());
+	}
 }
 
 int count_nontrivial_wire_attrs(RTLIL::Wire *w)
 {
 	int count = w->attributes.size();
-	count -= w->attributes.count("\\src");
-	count -= w->attributes.count("\\unused_bits");
+	count -= w->attributes.count(ID(src));
+	count -= w->attributes.count(ID(unused_bits));
 	return count;
 }
 
@@ -192,17 +222,17 @@ bool compare_signals(RTLIL::SigBit &s1, RTLIL::SigBit &s2, SigPool &regs, SigPoo
 
 bool check_public_name(RTLIL::IdString id)
 {
-	const std::string &id_str = id.str();
-	if (id_str[0] == '$')
+	if (id.begins_with("$"))
 		return false;
-	if (id_str.substr(0, 2) == "\\_" && (id_str[id_str.size()-1] == '_' || id_str.find("_[") != std::string::npos))
+	const std::string &id_str = id.str();
+	if (id.begins_with("\\_") && (id.ends_with("_") || id_str.find("_[") != std::string::npos))
 		return false;
 	if (id_str.find(".$") != std::string::npos)
 		return false;
 	return true;
 }
 
-void rmunused_module_signals(RTLIL::Module *module, bool purge_mode, bool verbose)
+bool rmunused_module_signals(RTLIL::Module *module, bool purge_mode, bool verbose)
 {
 	SigPool register_signals;
 	SigPool connected_signals;
@@ -245,11 +275,13 @@ void rmunused_module_signals(RTLIL::Module *module, bool purge_mode, bool verbos
 	module->connections_.clear();
 
 	SigPool used_signals;
+	SigPool raw_used_signals;
 	SigPool used_signals_nodrivers;
 	for (auto &it : module->cells_) {
 		RTLIL::Cell *cell = it.second;
 		for (auto &it2 : cell->connections_) {
 			assign_map.apply(it2.second);
+			raw_used_signals.add(it2.second);
 			used_signals.add(it2.second);
 			if (!ct_all.cell_output(cell->type, it2.first))
 				used_signals_nodrivers.add(it2.second);
@@ -259,84 +291,116 @@ void rmunused_module_signals(RTLIL::Module *module, bool purge_mode, bool verbos
 		RTLIL::Wire *wire = it.second;
 		if (wire->port_id > 0) {
 			RTLIL::SigSpec sig = RTLIL::SigSpec(wire);
+			raw_used_signals.add(sig);
 			assign_map.apply(sig);
 			used_signals.add(sig);
 			if (!wire->port_input)
 				used_signals_nodrivers.add(sig);
 		}
-		if (wire->get_bool_attribute("\\keep")) {
+		if (wire->get_bool_attribute(ID::keep)) {
 			RTLIL::SigSpec sig = RTLIL::SigSpec(wire);
 			assign_map.apply(sig);
 			used_signals.add(sig);
 		}
 	}
 
-	std::vector<RTLIL::Wire*> maybe_del_wires;
+	pool<RTLIL::Wire*> del_wires_queue;
 	for (auto wire : module->wires())
 	{
-		if ((!purge_mode && check_public_name(wire->name)) || wire->port_id != 0 || wire->get_bool_attribute("\\keep") || wire->attributes.count("\\init")) {
-			RTLIL::SigSpec s1 = RTLIL::SigSpec(wire), s2 = s1;
-			assign_map.apply(s2);
-			if (!used_signals.check_any(s2) && wire->port_id == 0 && !wire->get_bool_attribute("\\keep")) {
-				maybe_del_wires.push_back(wire);
-			} else {
-				log_assert(GetSize(s1) == GetSize(s2));
-				RTLIL::SigSig new_conn;
-				for (int i = 0; i < GetSize(s1); i++)
-					if (s1[i] != s2[i]) {
-						new_conn.first.append_bit(s1[i]);
-						new_conn.second.append_bit(s2[i]);
+		SigSpec s1 = SigSpec(wire), s2 = assign_map(s1);
+		log_assert(GetSize(s1) == GetSize(s2));
+
+		Const initval;
+		if (wire->attributes.count(ID(init)))
+			initval = wire->attributes.at(ID(init));
+		if (GetSize(initval) != GetSize(wire))
+			initval.bits.resize(GetSize(wire), State::Sx);
+		if (initval.is_fully_undef())
+			wire->attributes.erase(ID(init));
+
+		if (GetSize(wire) == 0) {
+			// delete zero-width wires, unless they are module ports
+			if (wire->port_id == 0)
+				goto delete_this_wire;
+		} else
+		if (wire->port_id != 0 || wire->get_bool_attribute(ID::keep) || !initval.is_fully_undef()) {
+			// do not delete anything with "keep" or module ports or initialized wires
+		} else
+		if (!purge_mode && check_public_name(wire->name) && (raw_used_signals.check_any(s1) || used_signals.check_any(s2) || s1 != s2)) {
+			// do not get rid of public names unless in purge mode or if the wire is entirely unused, not even aliased
+		} else
+		if (!raw_used_signals.check_any(s1)) {
+			// delete wires that aren't used by anything directly
+			goto delete_this_wire;
+		} else
+		if (!used_signals.check_any(s2)) {
+			// delete wires that aren't used by anything indirectly, even though other wires may alias it
+			goto delete_this_wire;
+		}
+
+		if (0)
+		{
+	delete_this_wire:
+			del_wires_queue.insert(wire);
+		}
+		else
+		{
+			RTLIL::SigSig new_conn;
+			for (int i = 0; i < GetSize(s1); i++)
+				if (s1[i] != s2[i]) {
+					if (s2[i] == State::Sx && (initval[i] == State::S0 || initval[i] == State::S1)) {
+						s2[i] = initval[i];
+						initval[i] = State::Sx;
 					}
-				if (new_conn.first.size() > 0) {
-					used_signals.add(new_conn.first);
-					used_signals.add(new_conn.second);
-					module->connect(new_conn);
+					new_conn.first.append_bit(s1[i]);
+					new_conn.second.append_bit(s2[i]);
 				}
+			if (new_conn.first.size() > 0) {
+				if (initval.is_fully_undef())
+					wire->attributes.erase(ID(init));
+				else
+					wire->attributes.at(ID(init)) = initval;
+				used_signals.add(new_conn.first);
+				used_signals.add(new_conn.second);
+				module->connect(new_conn);
 			}
-		} else {
-			if (!used_signals.check_any(RTLIL::SigSpec(wire)))
-				maybe_del_wires.push_back(wire);
-		}
 
-		RTLIL::SigSpec sig = assign_map(RTLIL::SigSpec(wire));
-		if (!used_signals_nodrivers.check_any(sig)) {
-			std::string unused_bits;
-			for (int i = 0; i < GetSize(sig); i++) {
-				if (sig[i].wire == NULL)
-					continue;
-				if (!used_signals_nodrivers.check(sig[i])) {
-					if (!unused_bits.empty())
-						unused_bits += " ";
-					unused_bits += stringf("%d", i);
+			if (!used_signals_nodrivers.check_all(s2)) {
+				std::string unused_bits;
+				for (int i = 0; i < GetSize(s2); i++) {
+					if (s2[i].wire == NULL)
+						continue;
+					if (!used_signals_nodrivers.check(s2[i])) {
+						if (!unused_bits.empty())
+							unused_bits += " ";
+						unused_bits += stringf("%d", i);
+					}
 				}
+				if (unused_bits.empty() || wire->port_id != 0)
+					wire->attributes.erase(ID(unused_bits));
+				else
+					wire->attributes[ID(unused_bits)] = RTLIL::Const(unused_bits);
+			} else {
+				wire->attributes.erase(ID(unused_bits));
 			}
-			if (unused_bits.empty() || wire->port_id != 0)
-				wire->attributes.erase("\\unused_bits");
-			else
-				wire->attributes["\\unused_bits"] = RTLIL::Const(unused_bits);
-		} else {
-			wire->attributes.erase("\\unused_bits");
 		}
 	}
 
+	int del_temp_wires_count = 0;
+	for (auto wire : del_wires_queue) {
+		if (ys_debug() || (check_public_name(wire->name) && verbose))
+			log_debug("  removing unused non-port wire %s.\n", wire->name.c_str());
+		else
+			del_temp_wires_count++;
+	}
 
-	pool<RTLIL::Wire*> del_wires;
+	module->remove(del_wires_queue);
+	count_rm_wires += GetSize(del_wires_queue);
 
-	int del_wires_count = 0;
-	for (auto wire : maybe_del_wires)
-		if (!used_signals.check_any(RTLIL::SigSpec(wire))) {
-			if (check_public_name(wire->name) && verbose) {
-				log("  removing unused non-port wire %s.\n", wire->name.c_str());
-			}
-			del_wires.insert(wire);
-			del_wires_count++;
-		}
+	if (verbose && del_temp_wires_count)
+		log_debug("  removed %d unused temporary wires.\n", del_temp_wires_count);
 
-	module->remove(del_wires);
-	count_rm_wires += del_wires.size();
-
-	if (verbose && del_wires_count > 0)
-		log("  removed %d unused temporary wires.\n", del_wires_count);
+	return !del_wires_queue.empty();
 }
 
 bool rmunused_module_init(RTLIL::Module *module, bool purge_mode, bool verbose)
@@ -349,18 +413,18 @@ bool rmunused_module_init(RTLIL::Module *module, bool purge_mode, bool verbose)
 	dict<SigBit, State> qbits;
 
 	for (auto cell : module->cells())
-		if (fftypes.cell_known(cell->type) && cell->hasPort("\\Q"))
+		if (fftypes.cell_known(cell->type) && cell->hasPort(ID(Q)))
 		{
-			SigSpec sig = cell->getPort("\\Q");
+			SigSpec sig = cell->getPort(ID(Q));
 
 			for (int i = 0; i < GetSize(sig); i++)
 			{
 				SigBit bit = sig[i];
 
-				if (bit.wire == nullptr || bit.wire->attributes.count("\\init") == 0)
+				if (bit.wire == nullptr || bit.wire->attributes.count(ID(init)) == 0)
 					continue;
 
-				Const init = bit.wire->attributes.at("\\init");
+				Const init = bit.wire->attributes.at(ID(init));
 
 				if (i >= GetSize(init) || init[i] == State::Sx || init[i] == State::Sz)
 					continue;
@@ -375,10 +439,10 @@ bool rmunused_module_init(RTLIL::Module *module, bool purge_mode, bool verbose)
 		if (!purge_mode && wire->name[0] == '\\')
 			continue;
 
-		if (wire->attributes.count("\\init") == 0)
+		if (wire->attributes.count(ID(init)) == 0)
 			continue;
 
-		Const init = wire->attributes.at("\\init");
+		Const init = wire->attributes.at(ID(init));
 
 		for (int i = 0; i < GetSize(wire) && i < GetSize(init); i++)
 		{
@@ -399,9 +463,9 @@ bool rmunused_module_init(RTLIL::Module *module, bool purge_mode, bool verbose)
 		}
 
 		if (verbose)
-			log("  removing redundant init attribute on %s.\n", log_id(wire));
+			log_debug("  removing redundant init attribute on %s.\n", log_id(wire));
 
-		wire->attributes.erase("\\init");
+		wire->attributes.erase(ID(init));
 		did_something = true;
 	next_wire:;
 	}
@@ -416,33 +480,33 @@ void rmunused_module(RTLIL::Module *module, bool purge_mode, bool verbose, bool
 
 	std::vector<RTLIL::Cell*> delcells;
 	for (auto cell : module->cells())
-		if (cell->type.in("$pos", "$_BUF_")) {
-			bool is_signed = cell->type == "$pos" && cell->getParam("\\A_SIGNED").as_bool();
-			RTLIL::SigSpec a = cell->getPort("\\A");
-			RTLIL::SigSpec y = cell->getPort("\\Y");
+		if (cell->type.in(ID($pos), ID($_BUF_)) && !cell->has_keep_attr()) {
+			bool is_signed = cell->type == ID($pos) && cell->getParam(ID(A_SIGNED)).as_bool();
+			RTLIL::SigSpec a = cell->getPort(ID::A);
+			RTLIL::SigSpec y = cell->getPort(ID::Y);
 			a.extend_u0(GetSize(y), is_signed);
 			module->connect(y, a);
 			delcells.push_back(cell);
 		}
 	for (auto cell : delcells) {
 		if (verbose)
-			log("  removing buffer cell `%s': %s = %s\n", cell->name.c_str(),
-					log_signal(cell->getPort("\\Y")), log_signal(cell->getPort("\\A")));
+			log_debug("  removing buffer cell `%s': %s = %s\n", cell->name.c_str(),
+					log_signal(cell->getPort(ID::Y)), log_signal(cell->getPort(ID::A)));
 		module->remove(cell);
 	}
 	if (!delcells.empty())
 		module->design->scratchpad_set_bool("opt.did_something", true);
 
 	rmunused_module_cells(module, verbose);
-	rmunused_module_signals(module, purge_mode, verbose);
+	while (rmunused_module_signals(module, purge_mode, verbose)) { }
 
 	if (rminit && rmunused_module_init(module, purge_mode, verbose))
-		rmunused_module_signals(module, purge_mode, verbose);
+		while (rmunused_module_signals(module, purge_mode, verbose)) { }
 }
 
 struct OptCleanPass : public Pass {
 	OptCleanPass() : Pass("opt_clean", "remove unused cells and wires") { }
-	virtual void help()
+	void help() YS_OVERRIDE
 	{
 		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
 		log("\n");
@@ -459,7 +523,7 @@ struct OptCleanPass : public Pass {
 		log("        also remove internal nets if they have a public name\n");
 		log("\n");
 	}
-	virtual void execute(std::vector<std::string> args, RTLIL::Design *design)
+	void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
 	{
 		bool purge_mode = false;
 
@@ -483,6 +547,9 @@ struct OptCleanPass : public Pass {
 
 		ct_all.setup(design);
 
+		count_rm_cells = 0;
+		count_rm_wires = 0;
+
 		for (auto module : design->selected_whole_modules_warn()) {
 			if (module->has_processes_warn())
 				continue;
@@ -505,7 +572,7 @@ struct OptCleanPass : public Pass {
 
 struct CleanPass : public Pass {
 	CleanPass() : Pass("clean", "remove unused cells and wires") { }
-	virtual void help()
+	void help() YS_OVERRIDE
 	{
 		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
 		log("\n");
@@ -520,7 +587,7 @@ struct CleanPass : public Pass {
 		log("in -purge mode between the commands.\n");
 		log("\n");
 	}
-	virtual void execute(std::vector<std::string> args, RTLIL::Design *design)
+	void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
 	{
 		bool purge_mode = false;
 
@@ -548,9 +615,10 @@ struct CleanPass : public Pass {
 		for (auto module : design->selected_whole_modules()) {
 			if (module->has_processes())
 				continue;
-			rmunused_module(module, purge_mode, false, false);
+			rmunused_module(module, purge_mode, ys_debug(), false);
 		}
 
+		log_suppressed();
 		if (count_rm_cells > 0 || count_rm_wires > 0)
 			log("Removed %d unused cells and %d unused wires.\n", count_rm_cells, count_rm_wires);
 
diff --git a/passes/opt/opt_demorgan.cc b/passes/opt/opt_demorgan.cc
index f2af1cb93..4bc82815b 100644
--- a/passes/opt/opt_demorgan.cc
+++ b/passes/opt/opt_demorgan.cc
@@ -35,10 +35,10 @@ void demorgan_worker(
 	//TODO: Add support for reduce_xor
 	//DeMorgan of XOR is either XOR (if even number of inputs) or XNOR (if odd number)
 
-	if( (cell->type != "$reduce_and") && (cell->type != "$reduce_or") )
+	if( (cell->type != ID($reduce_and)) && (cell->type != ID($reduce_or)) )
 		return;
 
-	auto insig = sigmap(cell->getPort("\\A"));
+	auto insig = sigmap(cell->getPort(ID::A));
 	log("Inspecting %s cell %s (%d inputs)\n", log_id(cell->type), log_id(cell->name), GetSize(insig));
 	int num_inverted = 0;
 	for(int i=0; i<GetSize(insig); i++)
@@ -51,7 +51,7 @@ void demorgan_worker(
 		bool inverted = false;
 		for(auto x : ports)
 		{
-			if(x.port == "\\Y" && x.cell->type == "$_NOT_")
+			if(x.port == ID::Y && x.cell->type == ID($_NOT_))
 			{
 				inverted = true;
 				break;
@@ -85,7 +85,7 @@ void demorgan_worker(
 		RTLIL::Cell* srcinv = NULL;
 		for(auto x : ports)
 		{
-			if(x.port == "\\Y" && x.cell->type == "$_NOT_")
+			if(x.port == ID::Y && x.cell->type == ID($_NOT_))
 			{
 				srcinv = x.cell;
 				break;
@@ -103,7 +103,7 @@ void demorgan_worker(
 		//We ARE inverted - bypass it
 		//Don't automatically delete the inverter since other stuff might still use it
 		else
-			insig[i] = srcinv->getPort("\\A");
+			insig[i] = srcinv->getPort(ID::A);
 	}
 
 	//Cosmetic fixup: If our input is just a scrambled version of one bus, rearrange it
@@ -151,25 +151,25 @@ void demorgan_worker(
 	}
 
 	//Push the new input signal back to the reduction (after bypassing/adding inverters)
-	cell->setPort("\\A", insig);
+	cell->setPort(ID::A, insig);
 
 	//Change the cell type
-	if(cell->type == "$reduce_and")
-		cell->type = "$reduce_or";
-	else if(cell->type == "$reduce_or")
-		cell->type = "$reduce_and";
+	if(cell->type == ID($reduce_and))
+		cell->type = ID($reduce_or);
+	else if(cell->type == ID($reduce_or))
+		cell->type = ID($reduce_and);
 	//don't change XOR
 
 	//Add an inverter to the output
-	auto inverted_output = cell->getPort("\\Y");
+	auto inverted_output = cell->getPort(ID::Y);
 	auto uninverted_output = m->addWire(NEW_ID);
 	m->addNot(NEW_ID, RTLIL::SigSpec(uninverted_output), inverted_output);
-	cell->setPort("\\Y", uninverted_output);
+	cell->setPort(ID::Y, uninverted_output);
 }
 
 struct OptDemorganPass : public Pass {
 	OptDemorganPass() : Pass("opt_demorgan", "Optimize reductions with DeMorgan equivalents") { }
-	virtual void help()
+	void help() YS_OVERRIDE
 	{
 		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
 		log("\n");
@@ -179,7 +179,7 @@ struct OptDemorganPass : public Pass {
 		log("overall gate count of the circuit\n");
 		log("\n");
 	}
-	virtual void execute(std::vector<std::string> args, RTLIL::Design *design)
+	void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
 	{
 		log_header(design, "Executing OPT_DEMORGAN pass (push inverters through $reduce_* cells).\n");
 
diff --git a/passes/opt/opt_expr.cc b/passes/opt/opt_expr.cc
index a54a5c6b8..6cf66fb95 100644
--- a/passes/opt/opt_expr.cc
+++ b/passes/opt/opt_expr.cc
@@ -39,6 +39,9 @@ void replace_undriven(RTLIL::Design *design, RTLIL::Module *module)
 	SigPool used_signals;
 	SigPool all_signals;
 
+	dict<SigBit, pair<Wire*, State>> initbits;
+	pool<Wire*> revisit_initwires;
+
 	for (auto cell : module->cells())
 	for (auto &conn : cell->connections()) {
 		if (!ct.cell_known(cell->type) || ct.cell_output(cell->type, conn.first))
@@ -48,9 +51,17 @@ void replace_undriven(RTLIL::Design *design, RTLIL::Module *module)
 	}
 
 	for (auto wire : module->wires()) {
+		if (wire->attributes.count(ID(init))) {
+			SigSpec sig = sigmap(wire);
+			Const initval = wire->attributes.at(ID(init));
+			for (int i = 0; i < GetSize(initval) && i < GetSize(wire); i++) {
+				if (initval[i] == State::S0 || initval[i] == State::S1)
+					initbits[sig[i]] = make_pair(wire, initval[i]);
+			}
+		}
 		if (wire->port_input)
 			driven_signals.add(sigmap(wire));
-		if (wire->port_output)
+		if (wire->port_output || wire->get_bool_attribute(ID::keep))
 			used_signals.add(sigmap(wire));
 		all_signals.add(sigmap(wire));
 	}
@@ -67,18 +78,52 @@ void replace_undriven(RTLIL::Design *design, RTLIL::Module *module)
 		if (sig.size() == 0)
 			continue;
 
-		log("Setting undriven signal in %s to undef: %s\n", RTLIL::id2cstr(module->name), log_signal(c));
-		module->connect(RTLIL::SigSig(c, RTLIL::SigSpec(RTLIL::State::Sx, c.width)));
+		Const val(RTLIL::State::Sx, GetSize(sig));
+		for (int i = 0; i < GetSize(sig); i++) {
+			SigBit bit = sigmap(sig[i]);
+			auto cursor = initbits.find(bit);
+			if (cursor != initbits.end()) {
+				revisit_initwires.insert(cursor->second.first);
+				val[i] = cursor->second.second;
+			}
+		}
+
+		log_debug("Setting undriven signal in %s to constant: %s = %s\n", log_id(module), log_signal(sig), log_signal(val));
+		module->connect(sig, val);
 		did_something = true;
 	}
+
+	if (!revisit_initwires.empty())
+	{
+		SigMap sm2(module);
+
+		for (auto wire : revisit_initwires) {
+			SigSpec sig = sm2(wire);
+			Const initval = wire->attributes.at(ID(init));
+			for (int i = 0; i < GetSize(initval) && i < GetSize(wire); i++) {
+				if (SigBit(initval[i]) == sig[i])
+					initval[i] = State::Sx;
+			}
+			if (initval.is_fully_undef()) {
+				log_debug("Removing init attribute from %s/%s.\n", log_id(module), log_id(wire));
+				wire->attributes.erase(ID(init));
+				did_something = true;
+			} else if (initval != wire->attributes.at(ID(init))) {
+				log_debug("Updating init attribute on %s/%s: %s\n", log_id(module), log_id(wire), log_signal(initval));
+				wire->attributes[ID(init)] = initval;
+				did_something = true;
+			}
+		}
+	}
 }
 
-void replace_cell(SigMap &assign_map, RTLIL::Module *module, RTLIL::Cell *cell, std::string info, std::string out_port, RTLIL::SigSpec out_val)
+void replace_cell(SigMap &assign_map, RTLIL::Module *module, RTLIL::Cell *cell,
+		const std::string &info YS_ATTRIBUTE(unused), IdString out_port, RTLIL::SigSpec out_val)
 {
 	RTLIL::SigSpec Y = cell->getPort(out_port);
 	out_val.extend_u0(Y.size(), false);
 
-	log("Replacing %s cell `%s' (%s) in module `%s' with constant driver `%s = %s'.\n",
+	log_debug("Replacing %s cell `%s' (%s) in module `%s' with constant driver `%s = %s'.\n",
 			cell->type.c_str(), cell->name.c_str(), info.c_str(),
 			module->name.c_str(), log_signal(Y), log_signal(out_val));
 	// log_cell(cell);
@@ -90,14 +135,14 @@ void replace_cell(SigMap &assign_map, RTLIL::Module *module, RTLIL::Cell *cell,
 
 bool group_cell_inputs(RTLIL::Module *module, RTLIL::Cell *cell, bool commutative, SigMap &sigmap)
 {
-	std::string b_name = cell->hasPort("\\B") ? "\\B" : "\\A";
+	IdString b_name = cell->hasPort(ID::B) ? ID::B : ID::A;
 
-	bool a_signed = cell->parameters.at("\\A_SIGNED").as_bool();
-	bool b_signed = cell->parameters.at(b_name + "_SIGNED").as_bool();
+	bool a_signed = cell->parameters.at(ID(A_SIGNED)).as_bool();
+	bool b_signed = cell->parameters.at(b_name.str() + "_SIGNED").as_bool();
 
-	RTLIL::SigSpec sig_a = sigmap(cell->getPort("\\A"));
+	RTLIL::SigSpec sig_a = sigmap(cell->getPort(ID::A));
 	RTLIL::SigSpec sig_b = sigmap(cell->getPort(b_name));
-	RTLIL::SigSpec sig_y = sigmap(cell->getPort("\\Y"));
+	RTLIL::SigSpec sig_y = sigmap(cell->getPort(ID::Y));
 
 	sig_a.extend_u0(sig_y.size(), a_signed);
 	sig_b.extend_u0(sig_y.size(), b_signed);
@@ -112,10 +157,10 @@ bool group_cell_inputs(RTLIL::Module *module, RTLIL::Cell *cell, bool commutativ
 		int group_idx = GRP_DYN;
 		RTLIL::SigBit bit_a = bits_a[i], bit_b = bits_b[i];
 
-		if (cell->type == "$or" && (bit_a == RTLIL::State::S1 || bit_b == RTLIL::State::S1))
+		if (cell->type == ID($or) && (bit_a == RTLIL::State::S1 || bit_b == RTLIL::State::S1))
 			bit_a = bit_b = RTLIL::State::S1;
 
-		if (cell->type == "$and" && (bit_a == RTLIL::State::S0 || bit_b == RTLIL::State::S0))
+		if (cell->type == ID($and) && (bit_a == RTLIL::State::S0 || bit_b == RTLIL::State::S0))
 			bit_a = bit_b = RTLIL::State::S0;
 
 		if (bit_a.wire == NULL && bit_b.wire == NULL)
@@ -134,7 +179,7 @@ bool group_cell_inputs(RTLIL::Module *module, RTLIL::Cell *cell, bool commutativ
 		if (GetSize(grouped_bits[i]) == GetSize(bits_y))
 			return false;
 
-	log("Replacing %s cell `%s' in module `%s' with cells using grouped bits:\n",
+	log_debug("Replacing %s cell `%s' in module `%s' with cells using grouped bits:\n",
 			log_id(cell->type), log_id(cell), log_id(module));
 
 	for (int i = 0; i < GRP_N; i++)
@@ -155,28 +200,35 @@ bool group_cell_inputs(RTLIL::Module *module, RTLIL::Cell *cell, bool commutativ
 			new_b.append_bit(it.first.second);
 		}
 
+		if (cell->type.in(ID($and), ID($or)) && i == GRP_CONST_A) {
+			log_debug("  Direct Connection: %s (%s with %s)\n", log_signal(new_b), log_id(cell->type), log_signal(new_a));
+			module->connect(new_y, new_b);
+			module->connect(new_conn);
+			continue;
+		}
+
 		RTLIL::Cell *c = module->addCell(NEW_ID, cell->type);
 
-		c->setPort("\\A", new_a);
-		c->parameters["\\A_WIDTH"] = new_a.size();
-		c->parameters["\\A_SIGNED"] = false;
+		c->setPort(ID::A, new_a);
+		c->parameters[ID(A_WIDTH)] = new_a.size();
+		c->parameters[ID(A_SIGNED)] = false;
 
-		if (b_name == "\\B") {
-			c->setPort("\\B", new_b);
-			c->parameters["\\B_WIDTH"] = new_b.size();
-			c->parameters["\\B_SIGNED"] = false;
+		if (b_name == ID::B) {
+			c->setPort(ID::B, new_b);
+			c->parameters[ID(B_WIDTH)] = new_b.size();
+			c->parameters[ID(B_SIGNED)] = false;
 		}
 
-		c->setPort("\\Y", new_y);
-		c->parameters["\\Y_WIDTH"] = new_y->width;
+		c->setPort(ID::Y, new_y);
+		c->parameters[ID(Y_WIDTH)] = new_y->width;
 		c->check();
 
 		module->connect(new_conn);
 
-		log("  New cell `%s': A=%s", log_id(c), log_signal(new_a));
-		if (b_name == "\\B")
-			log(", B=%s", log_signal(new_b));
-		log("\n");
+		log_debug("  New cell `%s': A=%s", log_id(c), log_signal(new_a));
+		if (b_name == ID::B)
+			log_debug(", B=%s", log_signal(new_b));
+		log_debug("\n");
 	}
 
 	cover_list("opt.opt_expr.fine.group", "$not", "$pos", "$and", "$or", "$xor", "$xnor", cell->type.str());
@@ -190,7 +242,7 @@ void handle_polarity_inv(Cell *cell, IdString port, IdString param, const SigMap
 {
 	SigSpec sig = assign_map(cell->getPort(port));
 	if (invert_map.count(sig)) {
-		log("Inverting %s of %s cell `%s' in module `%s': %s -> %s\n",
+		log_debug("Inverting %s of %s cell `%s' in module `%s': %s -> %s\n",
 				log_id(port), log_id(cell->type), log_id(cell), log_id(cell->module),
 				log_signal(sig), log_signal(invert_map.at(sig)));
 		cell->setPort(port, (invert_map.at(sig)));
@@ -219,7 +271,7 @@ void handle_clkpol_celltype_swap(Cell *cell, string type1, string type2, IdStrin
 	if (cell->type.in(type1, type2)) {
 		SigSpec sig = assign_map(cell->getPort(port));
 		if (invert_map.count(sig)) {
-			log("Inverting %s of %s cell `%s' in module `%s': %s -> %s\n",
+			log_debug("Inverting %s of %s cell `%s' in module `%s': %s -> %s\n",
 					log_id(port), log_id(cell->type), log_id(cell), log_id(cell->module),
 					log_signal(sig), log_signal(invert_map.at(sig)));
 			cell->setPort(port, (invert_map.at(sig)));
@@ -259,6 +311,22 @@ bool is_one_or_minus_one(const Const &value, bool is_signed, bool &is_negative)
 	return last_bit_one;
 }
 
+int get_highest_hot_index(RTLIL::SigSpec signal)
+{
+	for (int i = GetSize(signal) - 1; i >= 0; i--)
+	{
+		if (signal[i] == RTLIL::State::S0)
+			continue;
+
+		if (signal[i] == RTLIL::State::S1)
+			return i;
+
+		break;
+	}
+
+	return -1;
+}
+
 // if the signal has only one bit set, return the index of that bit.
 // otherwise return -1
 int get_onehot_bit_index(RTLIL::SigSpec signal)
@@ -300,11 +368,12 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 
 	for (auto cell : module->cells())
 		if (design->selected(module, cell) && cell->type[0] == '$') {
-			if ((cell->type == "$_NOT_" || cell->type == "$not" || cell->type == "$logic_not") &&
-					cell->getPort("\\A").size() == 1 && cell->getPort("\\Y").size() == 1)
-				invert_map[assign_map(cell->getPort("\\Y"))] = assign_map(cell->getPort("\\A"));
-			if ((cell->type == "$mux" || cell->type == "$_MUX_") && cell->getPort("\\A") == SigSpec(State::S1) && cell->getPort("\\B") == SigSpec(State::S0))
-				invert_map[assign_map(cell->getPort("\\Y"))] = assign_map(cell->getPort("\\S"));
+			if (cell->type.in(ID($_NOT_), ID($not), ID($logic_not)) &&
+					GetSize(cell->getPort(ID::A)) == 1 && GetSize(cell->getPort(ID::Y)) == 1)
+				invert_map[assign_map(cell->getPort(ID::Y))] = assign_map(cell->getPort(ID::A));
+			if (cell->type.in(ID($mux), ID($_MUX_)) &&
+					cell->getPort(ID::A) == SigSpec(State::S1) && cell->getPort(ID::B) == SigSpec(State::S0))
+				invert_map[assign_map(cell->getPort(ID::Y))] = assign_map(cell->getPort(ID(S)));
 			if (ct_combinational.cell_known(cell->type))
 				for (auto &conn : cell->connections()) {
 					RTLIL::SigSpec sig = assign_map(conn.second);
@@ -328,66 +397,66 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 	for (auto cell : cells.sorted)
 	{
 #define ACTION_DO(_p_, _s_) do { cover("opt.opt_expr.action_" S__LINE__); replace_cell(assign_map, module, cell, input.as_string(), _p_, _s_); goto next_cell; } while (0)
-#define ACTION_DO_Y(_v_) ACTION_DO("\\Y", RTLIL::SigSpec(RTLIL::State::S ## _v_))
+#define ACTION_DO_Y(_v_) ACTION_DO(ID::Y, RTLIL::SigSpec(RTLIL::State::S ## _v_))
 
 		if (clkinv)
 		{
-			if (cell->type.in("$dff", "$dffe", "$dffsr", "$adff", "$fsm", "$memrd", "$memwr"))
-				handle_polarity_inv(cell, "\\CLK", "\\CLK_POLARITY", assign_map, invert_map);
+			if (cell->type.in(ID($dff), ID($dffe), ID($dffsr), ID($adff), ID($fsm), ID($memrd), ID($memwr)))
+				handle_polarity_inv(cell, ID(CLK), ID(CLK_POLARITY), assign_map, invert_map);
 
-			if (cell->type.in("$sr", "$dffsr", "$dlatchsr")) {
-				handle_polarity_inv(cell, "\\SET", "\\SET_POLARITY", assign_map, invert_map);
-				handle_polarity_inv(cell, "\\CLR", "\\CLR_POLARITY", assign_map, invert_map);
+			if (cell->type.in(ID($sr), ID($dffsr), ID($dlatchsr))) {
+				handle_polarity_inv(cell, ID(SET), ID(SET_POLARITY), assign_map, invert_map);
+				handle_polarity_inv(cell, ID(CLR), ID(CLR_POLARITY), assign_map, invert_map);
 			}
 
-			if (cell->type.in("$dffe", "$dlatch", "$dlatchsr"))
-				handle_polarity_inv(cell, "\\EN", "\\EN_POLARITY", assign_map, invert_map);
+			if (cell->type.in(ID($dffe), ID($dlatch), ID($dlatchsr)))
+				handle_polarity_inv(cell, ID(EN), ID(EN_POLARITY), assign_map, invert_map);
 
-			handle_clkpol_celltype_swap(cell, "$_SR_N?_", "$_SR_P?_", "\\S", assign_map, invert_map);
-			handle_clkpol_celltype_swap(cell, "$_SR_?N_", "$_SR_?P_", "\\R", assign_map, invert_map);
+			handle_clkpol_celltype_swap(cell, "$_SR_N?_", "$_SR_P?_", ID(S), assign_map, invert_map);
+			handle_clkpol_celltype_swap(cell, "$_SR_?N_", "$_SR_?P_", ID(R), assign_map, invert_map);
 
-			handle_clkpol_celltype_swap(cell, "$_DFF_N_", "$_DFF_P_", "\\C", assign_map, invert_map);
+			handle_clkpol_celltype_swap(cell, "$_DFF_N_", "$_DFF_P_", ID(C), assign_map, invert_map);
 
-			handle_clkpol_celltype_swap(cell, "$_DFFE_N?_", "$_DFFE_P?_", "\\C", assign_map, invert_map);
-			handle_clkpol_celltype_swap(cell, "$_DFFE_?N_", "$_DFFE_?P_", "\\E", assign_map, invert_map);
+			handle_clkpol_celltype_swap(cell, "$_DFFE_N?_", "$_DFFE_P?_", ID(C), assign_map, invert_map);
+			handle_clkpol_celltype_swap(cell, "$_DFFE_?N_", "$_DFFE_?P_", ID(E), assign_map, invert_map);
 
-			handle_clkpol_celltype_swap(cell, "$_DFF_N??_", "$_DFF_P??_", "\\C", assign_map, invert_map);
-			handle_clkpol_celltype_swap(cell, "$_DFF_?N?_", "$_DFF_?P?_", "\\R", assign_map, invert_map);
+			handle_clkpol_celltype_swap(cell, "$_DFF_N??_", "$_DFF_P??_", ID(C), assign_map, invert_map);
+			handle_clkpol_celltype_swap(cell, "$_DFF_?N?_", "$_DFF_?P?_", ID(R), assign_map, invert_map);
 
-			handle_clkpol_celltype_swap(cell, "$_DFFSR_N??_", "$_DFFSR_P??_", "\\C", assign_map, invert_map);
-			handle_clkpol_celltype_swap(cell, "$_DFFSR_?N?_", "$_DFFSR_?P?_", "\\S", assign_map, invert_map);
-			handle_clkpol_celltype_swap(cell, "$_DFFSR_??N_", "$_DFFSR_??P_", "\\R", assign_map, invert_map);
+			handle_clkpol_celltype_swap(cell, "$_DFFSR_N??_", "$_DFFSR_P??_", ID(C), assign_map, invert_map);
+			handle_clkpol_celltype_swap(cell, "$_DFFSR_?N?_", "$_DFFSR_?P?_", ID(S), assign_map, invert_map);
+			handle_clkpol_celltype_swap(cell, "$_DFFSR_??N_", "$_DFFSR_??P_", ID(R), assign_map, invert_map);
 
-			handle_clkpol_celltype_swap(cell, "$_DLATCH_N_", "$_DLATCH_P_", "\\E", assign_map, invert_map);
+			handle_clkpol_celltype_swap(cell, "$_DLATCH_N_", "$_DLATCH_P_", ID(E), assign_map, invert_map);
 
-			handle_clkpol_celltype_swap(cell, "$_DLATCHSR_N??_", "$_DLATCHSR_P??_", "\\E", assign_map, invert_map);
-			handle_clkpol_celltype_swap(cell, "$_DLATCHSR_?N?_", "$_DLATCHSR_?P?_", "\\S", assign_map, invert_map);
-			handle_clkpol_celltype_swap(cell, "$_DLATCHSR_??N_", "$_DLATCHSR_??P_", "\\R", assign_map, invert_map);
+			handle_clkpol_celltype_swap(cell, "$_DLATCHSR_N??_", "$_DLATCHSR_P??_", ID(E), assign_map, invert_map);
+			handle_clkpol_celltype_swap(cell, "$_DLATCHSR_?N?_", "$_DLATCHSR_?P?_", ID(S), assign_map, invert_map);
+			handle_clkpol_celltype_swap(cell, "$_DLATCHSR_??N_", "$_DLATCHSR_??P_", ID(R), assign_map, invert_map);
 		}
 
 		bool detect_const_and = false;
 		bool detect_const_or = false;
 
-		if (cell->type.in("$reduce_and", "$_AND_"))
+		if (cell->type.in(ID($reduce_and), ID($_AND_)))
 			detect_const_and = true;
 
-		if (cell->type.in("$and", "$logic_and") && GetSize(cell->getPort("\\A")) == 1 && GetSize(cell->getPort("\\B")) == 1 && !cell->getParam("\\A_SIGNED").as_bool())
+		if (cell->type.in(ID($and), ID($logic_and)) && GetSize(cell->getPort(ID::A)) == 1 && GetSize(cell->getPort(ID::B)) == 1 && !cell->getParam(ID(A_SIGNED)).as_bool())
 			detect_const_and = true;
 
-		if (cell->type.in("$reduce_or", "$reduce_bool", "$_OR_"))
+		if (cell->type.in(ID($reduce_or), ID($reduce_bool), ID($_OR_)))
 			detect_const_or = true;
 
-		if (cell->type.in("$or", "$logic_or") && GetSize(cell->getPort("\\A")) == 1 && GetSize(cell->getPort("\\B")) == 1 && !cell->getParam("\\A_SIGNED").as_bool())
+		if (cell->type.in(ID($or), ID($logic_or)) && GetSize(cell->getPort(ID::A)) == 1 && GetSize(cell->getPort(ID::B)) == 1 && !cell->getParam(ID(A_SIGNED)).as_bool())
 			detect_const_or = true;
 
 		if (detect_const_and || detect_const_or)
 		{
-			pool<SigBit> input_bits = assign_map(cell->getPort("\\A")).to_sigbit_pool();
+			pool<SigBit> input_bits = assign_map(cell->getPort(ID::A)).to_sigbit_pool();
 			bool found_zero = false, found_one = false, found_undef = false, found_inv = false, many_conconst = false;
 			SigBit non_const_input = State::Sm;
 
-			if (cell->hasPort("\\B")) {
-				vector<SigBit> more_bits = assign_map(cell->getPort("\\B")).to_sigbit_vector();
+			if (cell->hasPort(ID::B)) {
+				vector<SigBit> more_bits = assign_map(cell->getPort(ID::B)).to_sigbit_vector();
 				input_bits.insert(more_bits.begin(), more_bits.end());
 			}
 
@@ -410,51 +479,50 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 
 			if (detect_const_and && (found_zero || found_inv)) {
 				cover("opt.opt_expr.const_and");
-				replace_cell(assign_map, module, cell, "const_and", "\\Y", RTLIL::State::S0);
+				replace_cell(assign_map, module, cell, "const_and", ID::Y, RTLIL::State::S0);
 				goto next_cell;
 			}
 
 			if (detect_const_or && (found_one || found_inv)) {
 				cover("opt.opt_expr.const_or");
-				replace_cell(assign_map, module, cell, "const_or", "\\Y", RTLIL::State::S1);
+				replace_cell(assign_map, module, cell, "const_or", ID::Y, RTLIL::State::S1);
 				goto next_cell;
 			}
 
 			if (non_const_input != State::Sm && !found_undef) {
 				cover("opt.opt_expr.and_or_buffer");
-				replace_cell(assign_map, module, cell, "and_or_buffer", "\\Y", non_const_input);
+				replace_cell(assign_map, module, cell, "and_or_buffer", ID::Y, non_const_input);
 				goto next_cell;
 			}
 		}
 
-		if (cell->type.in("$reduce_and", "$reduce_or", "$reduce_bool", "$reduce_xor", "$reduce_xnor", "$neg") &&
-				GetSize(cell->getPort("\\A")) == 1 && GetSize(cell->getPort("\\Y")) == 1)
+		if (cell->type.in(ID($reduce_and), ID($reduce_or), ID($reduce_bool), ID($reduce_xor), ID($reduce_xnor), ID($neg)) &&
+				GetSize(cell->getPort(ID::A)) == 1 && GetSize(cell->getPort(ID::Y)) == 1)
 		{
-			if (cell->type == "$reduce_xnor") {
+			if (cell->type == ID($reduce_xnor)) {
 				cover("opt.opt_expr.reduce_xnor_not");
-				log("Replacing %s cell `%s' in module `%s' with $not cell.\n",
+				log_debug("Replacing %s cell `%s' in module `%s' with $not cell.\n",
 						log_id(cell->type), log_id(cell->name), log_id(module));
-				cell->type = "$not";
+				cell->type = ID($not);
+				did_something = true;
 			} else {
 				cover("opt.opt_expr.unary_buffer");
-				replace_cell(assign_map, module, cell, "unary_buffer", "\\Y", cell->getPort("\\A"));
+				replace_cell(assign_map, module, cell, "unary_buffer", ID::Y, cell->getPort(ID::A));
 			}
 			goto next_cell;
 		}
 
 		if (do_fine)
 		{
-			if (cell->type == "$not" || cell->type == "$pos" ||
-					cell->type == "$and" || cell->type == "$or" || cell->type == "$xor" || cell->type == "$xnor")
+			if (cell->type.in(ID($not), ID($pos), ID($and), ID($or), ID($xor), ID($xnor)))
 				if (group_cell_inputs(module, cell, true, assign_map))
 					goto next_cell;
 
-			if (cell->type == "$logic_not" || cell->type == "$logic_and" || cell->type == "$logic_or" ||
-					cell->type == "$reduce_or" || cell->type == "$reduce_and" || cell->type == "$reduce_bool")
+			if (cell->type.in(ID($logic_not), ID($logic_and), ID($logic_or), ID($reduce_or), ID($reduce_and), ID($reduce_bool)))
 			{
-				SigBit neutral_bit = cell->type == "$reduce_and" ? State::S1 : State::S0;
+				SigBit neutral_bit = cell->type == ID($reduce_and) ? State::S1 : State::S0;
 
-				RTLIL::SigSpec sig_a = assign_map(cell->getPort("\\A"));
+				RTLIL::SigSpec sig_a = assign_map(cell->getPort(ID::A));
 				RTLIL::SigSpec new_sig_a;
 
 				for (auto bit : sig_a)
@@ -465,19 +533,19 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 
 				if (GetSize(new_sig_a) < GetSize(sig_a)) {
 					cover_list("opt.opt_expr.fine.neutral_A", "$logic_not", "$logic_and", "$logic_or", "$reduce_or", "$reduce_and", "$reduce_bool", cell->type.str());
-					log("Replacing port A of %s cell `%s' in module `%s' with shorter expression: %s -> %s\n",
+					log_debug("Replacing port A of %s cell `%s' in module `%s' with shorter expression: %s -> %s\n",
 							cell->type.c_str(), cell->name.c_str(), module->name.c_str(), log_signal(sig_a), log_signal(new_sig_a));
-					cell->setPort("\\A", new_sig_a);
-					cell->parameters.at("\\A_WIDTH") = GetSize(new_sig_a);
+					cell->setPort(ID::A, new_sig_a);
+					cell->parameters.at(ID(A_WIDTH)) = GetSize(new_sig_a);
 					did_something = true;
 				}
 			}
 
-			if (cell->type == "$logic_and" || cell->type == "$logic_or")
+			if (cell->type.in(ID($logic_and), ID($logic_or)))
 			{
 				SigBit neutral_bit = State::S0;
 
-				RTLIL::SigSpec sig_b = assign_map(cell->getPort("\\B"));
+				RTLIL::SigSpec sig_b = assign_map(cell->getPort(ID::B));
 				RTLIL::SigSpec new_sig_b;
 
 				for (auto bit : sig_b)
@@ -488,17 +556,17 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 
 				if (GetSize(new_sig_b) < GetSize(sig_b)) {
 					cover_list("opt.opt_expr.fine.neutral_B", "$logic_and", "$logic_or", cell->type.str());
-					log("Replacing port B of %s cell `%s' in module `%s' with shorter expression: %s -> %s\n",
+					log_debug("Replacing port B of %s cell `%s' in module `%s' with shorter expression: %s -> %s\n",
 							cell->type.c_str(), cell->name.c_str(), module->name.c_str(), log_signal(sig_b), log_signal(new_sig_b));
-					cell->setPort("\\B", new_sig_b);
-					cell->parameters.at("\\B_WIDTH") = GetSize(new_sig_b);
+					cell->setPort(ID::B, new_sig_b);
+					cell->parameters.at(ID(B_WIDTH)) = GetSize(new_sig_b);
 					did_something = true;
 				}
 			}
 
-			if (cell->type == "$reduce_and")
+			if (cell->type == ID($reduce_and))
 			{
-				RTLIL::SigSpec sig_a = assign_map(cell->getPort("\\A"));
+				RTLIL::SigSpec sig_a = assign_map(cell->getPort(ID::A));
 
 				RTLIL::State new_a = RTLIL::State::S1;
 				for (auto &bit : sig_a.to_sigbit_vector())
@@ -514,17 +582,17 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 
 				if (new_a != RTLIL::State::Sm && RTLIL::SigSpec(new_a) != sig_a) {
 					cover("opt.opt_expr.fine.$reduce_and");
-					log("Replacing port A of %s cell `%s' in module `%s' with constant driver: %s -> %s\n",
+					log_debug("Replacing port A of %s cell `%s' in module `%s' with constant driver: %s -> %s\n",
 							cell->type.c_str(), cell->name.c_str(), module->name.c_str(), log_signal(sig_a), log_signal(new_a));
-					cell->setPort("\\A", sig_a = new_a);
-					cell->parameters.at("\\A_WIDTH") = 1;
+					cell->setPort(ID::A, sig_a = new_a);
+					cell->parameters.at(ID(A_WIDTH)) = 1;
 					did_something = true;
 				}
 			}
 
-			if (cell->type == "$logic_not" || cell->type == "$logic_and" || cell->type == "$logic_or" || cell->type == "$reduce_or" || cell->type == "$reduce_bool")
+			if (cell->type.in(ID($logic_not), ID($logic_and), ID($logic_or), ID($reduce_or), ID($reduce_bool)))
 			{
-				RTLIL::SigSpec sig_a = assign_map(cell->getPort("\\A"));
+				RTLIL::SigSpec sig_a = assign_map(cell->getPort(ID::A));
 
 				RTLIL::State new_a = RTLIL::State::S0;
 				for (auto &bit : sig_a.to_sigbit_vector())
@@ -540,17 +608,17 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 
 				if (new_a != RTLIL::State::Sm && RTLIL::SigSpec(new_a) != sig_a) {
 					cover_list("opt.opt_expr.fine.A", "$logic_not", "$logic_and", "$logic_or", "$reduce_or", "$reduce_bool", cell->type.str());
-					log("Replacing port A of %s cell `%s' in module `%s' with constant driver: %s -> %s\n",
+					log_debug("Replacing port A of %s cell `%s' in module `%s' with constant driver: %s -> %s\n",
 							cell->type.c_str(), cell->name.c_str(), module->name.c_str(), log_signal(sig_a), log_signal(new_a));
-					cell->setPort("\\A", sig_a = new_a);
-					cell->parameters.at("\\A_WIDTH") = 1;
+					cell->setPort(ID::A, sig_a = new_a);
+					cell->parameters.at(ID(A_WIDTH)) = 1;
 					did_something = true;
 				}
 			}
 
-			if (cell->type == "$logic_and" || cell->type == "$logic_or")
+			if (cell->type.in(ID($logic_and), ID($logic_or)))
 			{
-				RTLIL::SigSpec sig_b = assign_map(cell->getPort("\\B"));
+				RTLIL::SigSpec sig_b = assign_map(cell->getPort(ID::B));
 
 				RTLIL::State new_b = RTLIL::State::S0;
 				for (auto &bit : sig_b.to_sigbit_vector())
@@ -566,25 +634,95 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 
 				if (new_b != RTLIL::State::Sm && RTLIL::SigSpec(new_b) != sig_b) {
 					cover_list("opt.opt_expr.fine.B", "$logic_and", "$logic_or", cell->type.str());
-					log("Replacing port B of %s cell `%s' in module `%s' with constant driver: %s -> %s\n",
+					log_debug("Replacing port B of %s cell `%s' in module `%s' with constant driver: %s -> %s\n",
 							cell->type.c_str(), cell->name.c_str(), module->name.c_str(), log_signal(sig_b), log_signal(new_b));
-					cell->setPort("\\B", sig_b = new_b);
-					cell->parameters.at("\\B_WIDTH") = 1;
+					cell->setPort(ID::B, sig_b = new_b);
+					cell->parameters.at(ID(B_WIDTH)) = 1;
+					did_something = true;
+				}
+			}
+
+			if (cell->type.in(ID($add), ID($sub)))
+			{
+				RTLIL::SigSpec sig_a = assign_map(cell->getPort(ID::A));
+				RTLIL::SigSpec sig_b = assign_map(cell->getPort(ID::B));
+				RTLIL::SigSpec sig_y = cell->getPort(ID::Y);
+				bool sub = cell->type == ID($sub);
+
+				int i;
+				for (i = 0; i < GetSize(sig_y); i++) {
+					if (sig_b.at(i, State::Sx) == State::S0 && sig_a.at(i, State::Sx) != State::Sx)
+						module->connect(sig_y[i], sig_a[i]);
+					else if (!sub && sig_a.at(i, State::Sx) == State::S0 && sig_b.at(i, State::Sx) != State::Sx)
+						module->connect(sig_y[i], sig_b[i]);
+					else
+						break;
+				}
+				if (i > 0) {
+					cover_list("opt.opt_expr.fine", "$add", "$sub", cell->type.str());
+					cell->setPort(ID::A, sig_a.extract_end(i));
+					cell->setPort(ID::B, sig_b.extract_end(i));
+					cell->setPort(ID::Y, sig_y.extract_end(i));
+					cell->fixup_parameters();
+					did_something = true;
+				}
+			}
+
+			if (cell->type == "$alu")
+			{
+				RTLIL::SigSpec sig_a = assign_map(cell->getPort(ID::A));
+				RTLIL::SigSpec sig_b = assign_map(cell->getPort(ID::B));
+				RTLIL::SigBit sig_ci = assign_map(cell->getPort(ID(CI)));
+				RTLIL::SigBit sig_bi = assign_map(cell->getPort(ID(BI)));
+				RTLIL::SigSpec sig_x = cell->getPort(ID(X));
+				RTLIL::SigSpec sig_y = cell->getPort(ID::Y);
+				RTLIL::SigSpec sig_co = cell->getPort(ID(CO));
+
+				if (sig_ci.wire || sig_bi.wire)
+					goto next_cell;
+
+				bool sub = (sig_ci == State::S1 && sig_bi == State::S1);
+
+				// If not a subtraction, yet there is a carry or B is inverted
+				//   then no optimisation is possible as carry will not be constant
+				if (!sub && (sig_ci != State::S0 || sig_bi != State::S0))
+					goto next_cell;
+
+				int i;
+				for (i = 0; i < GetSize(sig_y); i++) {
+					if (sig_b.at(i, State::Sx) == State::S0 && sig_a.at(i, State::Sx) != State::Sx) {
+						module->connect(sig_x[i], sub ? module->Not(NEW_ID, sig_a[i]).as_bit() : sig_a[i]);
+						module->connect(sig_y[i], sig_a[i]);
+						module->connect(sig_co[i], sub ? State::S1 : State::S0);
+					}
+					else if (!sub && sig_a.at(i, State::Sx) == State::S0 && sig_b.at(i, State::Sx) != State::Sx) {
+						module->connect(sig_x[i], sig_b[i]);
+						module->connect(sig_y[i], sig_b[i]);
+						module->connect(sig_co[i], State::S0);
+					}
+					else
+						break;
+				}
+				if (i > 0) {
+					cover("opt.opt_expr.fine.$alu");
+					cell->setPort(ID::A, sig_a.extract_end(i));
+					cell->setPort(ID::B, sig_b.extract_end(i));
+					cell->setPort(ID(X), sig_x.extract_end(i));
+					cell->setPort(ID::Y, sig_y.extract_end(i));
+					cell->setPort(ID(CO), sig_co.extract_end(i));
+					cell->fixup_parameters();
 					did_something = true;
 				}
 			}
 		}
 
-		if (cell->type == "$reduce_xor" || cell->type == "$reduce_xnor" || cell->type == "$shift" || cell->type == "$shiftx" ||
-				cell->type == "$shl" || cell->type == "$shr" || cell->type == "$sshl" || cell->type == "$sshr" ||
-				cell->type == "$lt" || cell->type == "$le" || cell->type == "$ge" || cell->type == "$gt" ||
-				cell->type == "$neg" || cell->type == "$add" || cell->type == "$sub" ||
-				cell->type == "$mul" || cell->type == "$div" || cell->type == "$mod" || cell->type == "$pow")
+		if (cell->type.in(ID($reduce_xor), ID($reduce_xnor), ID($shift), ID($shiftx), ID($shl), ID($shr), ID($sshl), ID($sshr),
+					ID($lt), ID($le), ID($ge), ID($gt), ID($neg), ID($add), ID($sub), ID($mul), ID($div), ID($mod), ID($pow)))
 		{
-			RTLIL::SigSpec sig_a = assign_map(cell->getPort("\\A"));
-			RTLIL::SigSpec sig_b = cell->hasPort("\\B") ? assign_map(cell->getPort("\\B")) : RTLIL::SigSpec();
+			RTLIL::SigSpec sig_a = assign_map(cell->getPort(ID::A));
+			RTLIL::SigSpec sig_b = cell->hasPort(ID::B) ? assign_map(cell->getPort(ID::B)) : RTLIL::SigSpec();
 
-			if (cell->type == "$shl" || cell->type == "$shr" || cell->type == "$sshl" || cell->type == "$sshr" || cell->type == "$shift" || cell->type == "$shiftx")
+			if (cell->type.in(ID($shl), ID($shr), ID($sshl), ID($sshr), ID($shift), ID($shiftx)))
 				sig_a = RTLIL::SigSpec();
 
 			for (auto &bit : sig_a.to_sigbit_vector())
@@ -599,45 +737,66 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 		found_the_x_bit:
 				cover_list("opt.opt_expr.xbit", "$reduce_xor", "$reduce_xnor", "$shl", "$shr", "$sshl", "$sshr", "$shift", "$shiftx",
 						"$lt", "$le", "$ge", "$gt", "$neg", "$add", "$sub", "$mul", "$div", "$mod", "$pow", cell->type.str());
-				if (cell->type == "$reduce_xor" || cell->type == "$reduce_xnor" ||
-						cell->type == "$lt" || cell->type == "$le" || cell->type == "$ge" || cell->type == "$gt")
-					replace_cell(assign_map, module, cell, "x-bit in input", "\\Y", RTLIL::State::Sx);
+				if (cell->type.in(ID($reduce_xor), ID($reduce_xnor), ID($lt), ID($le), ID($ge), ID($gt)))
+					replace_cell(assign_map, module, cell, "x-bit in input", ID::Y, RTLIL::State::Sx);
 				else
-					replace_cell(assign_map, module, cell, "x-bit in input", "\\Y", RTLIL::SigSpec(RTLIL::State::Sx, cell->getPort("\\Y").size()));
+					replace_cell(assign_map, module, cell, "x-bit in input", ID::Y, RTLIL::SigSpec(RTLIL::State::Sx, GetSize(cell->getPort(ID::Y))));
+				goto next_cell;
+			}
+		}
+
+		if (cell->type.in(ID($shiftx), ID($shift))) {
+			SigSpec sig_a = assign_map(cell->getPort(ID::A));
+			int width;
+			bool trim_x = cell->type == ID($shiftx) || !keepdc;
+			bool trim_0 = cell->type == ID($shift);
+			for (width = GetSize(sig_a); width > 1; width--) {
+				if ((trim_x && sig_a[width-1] == State::Sx) ||
+					(trim_0 && sig_a[width-1] == State::S0))
+					continue;
+				break;
+			}
+
+			if (width < GetSize(sig_a)) {
+				cover_list("opt.opt_expr.trim", "$shiftx", "$shift", cell->type.str());
+				sig_a.remove(width, GetSize(sig_a)-width);
+				cell->setPort(ID::A, sig_a);
+				cell->setParam(ID(A_WIDTH), width);
+				did_something = true;
 				goto next_cell;
 			}
 		}
 
-		if ((cell->type == "$_NOT_" || cell->type == "$not" || cell->type == "$logic_not") && cell->getPort("\\Y").size() == 1 &&
-				invert_map.count(assign_map(cell->getPort("\\A"))) != 0) {
+		if (cell->type.in(ID($_NOT_), ID($not), ID($logic_not)) && GetSize(cell->getPort(ID::Y)) == 1 &&
+				invert_map.count(assign_map(cell->getPort(ID::A))) != 0) {
 			cover_list("opt.opt_expr.invert.double", "$_NOT_", "$not", "$logic_not", cell->type.str());
-			replace_cell(assign_map, module, cell, "double_invert", "\\Y", invert_map.at(assign_map(cell->getPort("\\A"))));
+			replace_cell(assign_map, module, cell, "double_invert", ID::Y, invert_map.at(assign_map(cell->getPort(ID::A))));
 			goto next_cell;
 		}
 
-		if ((cell->type == "$_MUX_" || cell->type == "$mux") && invert_map.count(assign_map(cell->getPort("\\S"))) != 0) {
+		if (cell->type.in(ID($_MUX_), ID($mux)) && invert_map.count(assign_map(cell->getPort(ID(S)))) != 0) {
 			cover_list("opt.opt_expr.invert.muxsel", "$_MUX_", "$mux", cell->type.str());
-			log("Optimizing away select inverter for %s cell `%s' in module `%s'.\n", log_id(cell->type), log_id(cell), log_id(module));
-			RTLIL::SigSpec tmp = cell->getPort("\\A");
-			cell->setPort("\\A", cell->getPort("\\B"));
-			cell->setPort("\\B", tmp);
-			cell->setPort("\\S", invert_map.at(assign_map(cell->getPort("\\S"))));
+			log_debug("Optimizing away select inverter for %s cell `%s' in module `%s'.\n", log_id(cell->type), log_id(cell), log_id(module));
+			RTLIL::SigSpec tmp = cell->getPort(ID::A);
+			cell->setPort(ID::A, cell->getPort(ID::B));
+			cell->setPort(ID::B, tmp);
+			cell->setPort(ID(S), invert_map.at(assign_map(cell->getPort(ID(S)))));
 			did_something = true;
 			goto next_cell;
 		}
 
-		if (cell->type == "$_NOT_") {
-			RTLIL::SigSpec input = cell->getPort("\\A");
+		if (cell->type == ID($_NOT_)) {
+			RTLIL::SigSpec input = cell->getPort(ID::A);
 			assign_map.apply(input);
 			if (input.match("1")) ACTION_DO_Y(0);
 			if (input.match("0")) ACTION_DO_Y(1);
 			if (input.match("*")) ACTION_DO_Y(x);
 		}
 
-		if (cell->type == "$_AND_") {
+		if (cell->type == ID($_AND_)) {
 			RTLIL::SigSpec input;
-			input.append(cell->getPort("\\B"));
-			input.append(cell->getPort("\\A"));
+			input.append(cell->getPort(ID::B));
+			input.append(cell->getPort(ID::A));
 			assign_map.apply(input);
 			if (input.match(" 0")) ACTION_DO_Y(0);
 			if (input.match("0 ")) ACTION_DO_Y(0);
@@ -649,14 +808,14 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 				if (input.match(" *")) ACTION_DO_Y(0);
 				if (input.match("* ")) ACTION_DO_Y(0);
 			}
-			if (input.match(" 1")) ACTION_DO("\\Y", input.extract(1, 1));
-			if (input.match("1 ")) ACTION_DO("\\Y", input.extract(0, 1));
+			if (input.match(" 1")) ACTION_DO(ID::Y, input.extract(1, 1));
+			if (input.match("1 ")) ACTION_DO(ID::Y, input.extract(0, 1));
 		}
 
-		if (cell->type == "$_OR_") {
+		if (cell->type == ID($_OR_)) {
 			RTLIL::SigSpec input;
-			input.append(cell->getPort("\\B"));
-			input.append(cell->getPort("\\A"));
+			input.append(cell->getPort(ID::B));
+			input.append(cell->getPort(ID::A));
 			assign_map.apply(input);
 			if (input.match(" 1")) ACTION_DO_Y(1);
 			if (input.match("1 ")) ACTION_DO_Y(1);
@@ -668,14 +827,14 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 				if (input.match(" *")) ACTION_DO_Y(1);
 				if (input.match("* ")) ACTION_DO_Y(1);
 			}
-			if (input.match(" 0")) ACTION_DO("\\Y", input.extract(1, 1));
-			if (input.match("0 ")) ACTION_DO("\\Y", input.extract(0, 1));
+			if (input.match(" 0")) ACTION_DO(ID::Y, input.extract(1, 1));
+			if (input.match("0 ")) ACTION_DO(ID::Y, input.extract(0, 1));
 		}
 
-		if (cell->type == "$_XOR_") {
+		if (cell->type == ID($_XOR_)) {
 			RTLIL::SigSpec input;
-			input.append(cell->getPort("\\B"));
-			input.append(cell->getPort("\\A"));
+			input.append(cell->getPort(ID::B));
+			input.append(cell->getPort(ID::A));
 			assign_map.apply(input);
 			if (input.match("00")) ACTION_DO_Y(0);
 			if (input.match("01")) ACTION_DO_Y(1);
@@ -683,27 +842,27 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 			if (input.match("11")) ACTION_DO_Y(0);
 			if (input.match(" *")) ACTION_DO_Y(x);
 			if (input.match("* ")) ACTION_DO_Y(x);
-			if (input.match(" 0")) ACTION_DO("\\Y", input.extract(1, 1));
-			if (input.match("0 ")) ACTION_DO("\\Y", input.extract(0, 1));
+			if (input.match(" 0")) ACTION_DO(ID::Y, input.extract(1, 1));
+			if (input.match("0 ")) ACTION_DO(ID::Y, input.extract(0, 1));
 		}
 
-		if (cell->type == "$_MUX_") {
+		if (cell->type == ID($_MUX_)) {
 			RTLIL::SigSpec input;
-			input.append(cell->getPort("\\S"));
-			input.append(cell->getPort("\\B"));
-			input.append(cell->getPort("\\A"));
+			input.append(cell->getPort(ID(S)));
+			input.append(cell->getPort(ID::B));
+			input.append(cell->getPort(ID::A));
 			assign_map.apply(input);
 			if (input.extract(2, 1) == input.extract(1, 1))
-				ACTION_DO("\\Y", input.extract(2, 1));
-			if (input.match("  0")) ACTION_DO("\\Y", input.extract(2, 1));
-			if (input.match("  1")) ACTION_DO("\\Y", input.extract(1, 1));
-			if (input.match("01 ")) ACTION_DO("\\Y", input.extract(0, 1));
+				ACTION_DO(ID::Y, input.extract(2, 1));
+			if (input.match("  0")) ACTION_DO(ID::Y, input.extract(2, 1));
+			if (input.match("  1")) ACTION_DO(ID::Y, input.extract(1, 1));
+			if (input.match("01 ")) ACTION_DO(ID::Y, input.extract(0, 1));
 			if (input.match("10 ")) {
 				cover("opt.opt_expr.mux_to_inv");
-				cell->type = "$_NOT_";
-				cell->setPort("\\A", input.extract(0, 1));
-				cell->unsetPort("\\B");
-				cell->unsetPort("\\S");
+				cell->type = ID($_NOT_);
+				cell->setPort(ID::A, input.extract(0, 1));
+				cell->unsetPort(ID::B);
+				cell->unsetPort(ID(S));
 				goto next_cell;
 			}
 			if (input.match("11 ")) ACTION_DO_Y(1);
@@ -712,38 +871,38 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 			if (input.match("01*")) ACTION_DO_Y(x);
 			if (input.match("10*")) ACTION_DO_Y(x);
 			if (mux_undef) {
-				if (input.match("*  ")) ACTION_DO("\\Y", input.extract(1, 1));
-				if (input.match(" * ")) ACTION_DO("\\Y", input.extract(2, 1));
-				if (input.match("  *")) ACTION_DO("\\Y", input.extract(2, 1));
+				if (input.match("*  ")) ACTION_DO(ID::Y, input.extract(1, 1));
+				if (input.match(" * ")) ACTION_DO(ID::Y, input.extract(2, 1));
+				if (input.match("  *")) ACTION_DO(ID::Y, input.extract(2, 1));
 			}
 		}
 
-		if (cell->type == "$_TBUF_" || cell->type == "$tribuf") {
-			RTLIL::SigSpec input = cell->getPort(cell->type == "$_TBUF_" ? "\\E" : "\\EN");
-			RTLIL::SigSpec a = cell->getPort("\\A");
+		if (cell->type.in(ID($_TBUF_), ID($tribuf))) {
+			RTLIL::SigSpec input = cell->getPort(cell->type == ID($_TBUF_) ? ID(E) : ID(EN));
+			RTLIL::SigSpec a = cell->getPort(ID::A);
 			assign_map.apply(input);
 			assign_map.apply(a);
 			if (input == State::S1)
-				ACTION_DO("\\Y", cell->getPort("\\A"));
+				ACTION_DO(ID::Y, cell->getPort(ID::A));
 			if (input == State::S0 && !a.is_fully_undef()) {
 				cover("opt.opt_expr.action_" S__LINE__);
-				log("Replacing data input of %s cell `%s' in module `%s' with constant undef.\n",
+				log_debug("Replacing data input of %s cell `%s' in module `%s' with constant undef.\n",
 					cell->type.c_str(), cell->name.c_str(), module->name.c_str());
-				cell->setPort("\\A", SigSpec(State::Sx, GetSize(a)));
+				cell->setPort(ID::A, SigSpec(State::Sx, GetSize(a)));
 				did_something = true;
 				goto next_cell;
 			}
 		}
 
-		if (cell->type == "$eq" || cell->type == "$ne" || cell->type == "$eqx" || cell->type == "$nex")
+		if (cell->type.in(ID($eq), ID($ne), ID($eqx), ID($nex)))
 		{
-			RTLIL::SigSpec a = cell->getPort("\\A");
-			RTLIL::SigSpec b = cell->getPort("\\B");
+			RTLIL::SigSpec a = cell->getPort(ID::A);
+			RTLIL::SigSpec b = cell->getPort(ID::B);
 
-			if (cell->parameters["\\A_WIDTH"].as_int() != cell->parameters["\\B_WIDTH"].as_int()) {
-				int width = max(cell->parameters["\\A_WIDTH"].as_int(), cell->parameters["\\B_WIDTH"].as_int());
-				a.extend_u0(width, cell->parameters["\\A_SIGNED"].as_bool() && cell->parameters["\\B_SIGNED"].as_bool());
-				b.extend_u0(width, cell->parameters["\\A_SIGNED"].as_bool() && cell->parameters["\\B_SIGNED"].as_bool());
+			if (cell->parameters[ID(A_WIDTH)].as_int() != cell->parameters[ID(B_WIDTH)].as_int()) {
+				int width = max(cell->parameters[ID(A_WIDTH)].as_int(), cell->parameters[ID(B_WIDTH)].as_int());
+				a.extend_u0(width, cell->parameters[ID(A_SIGNED)].as_bool() && cell->parameters[ID(B_SIGNED)].as_bool());
+				b.extend_u0(width, cell->parameters[ID(A_SIGNED)].as_bool() && cell->parameters[ID(B_SIGNED)].as_bool());
 			}
 
 			RTLIL::SigSpec new_a, new_b;
@@ -752,9 +911,9 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 			for (int i = 0; i < GetSize(a); i++) {
 				if (a[i].wire == NULL && b[i].wire == NULL && a[i] != b[i] && a[i].data <= RTLIL::State::S1 && b[i].data <= RTLIL::State::S1) {
 					cover_list("opt.opt_expr.eqneq.isneq", "$eq", "$ne", "$eqx", "$nex", cell->type.str());
-					RTLIL::SigSpec new_y = RTLIL::SigSpec((cell->type == "$eq" || cell->type == "$eqx") ?  RTLIL::State::S0 : RTLIL::State::S1);
-					new_y.extend_u0(cell->parameters["\\Y_WIDTH"].as_int(), false);
-					replace_cell(assign_map, module, cell, "isneq", "\\Y", new_y);
+					RTLIL::SigSpec new_y = RTLIL::SigSpec(cell->type.in(ID($eq), ID($eqx)) ?  RTLIL::State::S0 : RTLIL::State::S1);
+					new_y.extend_u0(cell->parameters[ID(Y_WIDTH)].as_int(), false);
+					replace_cell(assign_map, module, cell, "isneq", ID::Y, new_y);
 					goto next_cell;
 				}
 				if (a[i] == b[i])
@@ -765,83 +924,87 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 
 			if (new_a.size() == 0) {
 				cover_list("opt.opt_expr.eqneq.empty", "$eq", "$ne", "$eqx", "$nex", cell->type.str());
-				RTLIL::SigSpec new_y = RTLIL::SigSpec((cell->type == "$eq" || cell->type == "$eqx") ?  RTLIL::State::S1 : RTLIL::State::S0);
-				new_y.extend_u0(cell->parameters["\\Y_WIDTH"].as_int(), false);
-				replace_cell(assign_map, module, cell, "empty", "\\Y", new_y);
+				RTLIL::SigSpec new_y = RTLIL::SigSpec(cell->type.in(ID($eq), ID($eqx)) ?  RTLIL::State::S1 : RTLIL::State::S0);
+				new_y.extend_u0(cell->parameters[ID(Y_WIDTH)].as_int(), false);
+				replace_cell(assign_map, module, cell, "empty", ID::Y, new_y);
 				goto next_cell;
 			}
 
 			if (new_a.size() < a.size() || new_b.size() < b.size()) {
 				cover_list("opt.opt_expr.eqneq.resize", "$eq", "$ne", "$eqx", "$nex", cell->type.str());
-				cell->setPort("\\A", new_a);
-				cell->setPort("\\B", new_b);
-				cell->parameters["\\A_WIDTH"] = new_a.size();
-				cell->parameters["\\B_WIDTH"] = new_b.size();
+				cell->setPort(ID::A, new_a);
+				cell->setPort(ID::B, new_b);
+				cell->parameters[ID(A_WIDTH)] = new_a.size();
+				cell->parameters[ID(B_WIDTH)] = new_b.size();
 			}
 		}
 
-		if ((cell->type == "$eq" || cell->type == "$ne") && cell->parameters["\\Y_WIDTH"].as_int() == 1 &&
-				cell->parameters["\\A_WIDTH"].as_int() == 1 && cell->parameters["\\B_WIDTH"].as_int() == 1)
+		if (cell->type.in(ID($eq), ID($ne)) && cell->parameters[ID(Y_WIDTH)].as_int() == 1 &&
+				cell->parameters[ID(A_WIDTH)].as_int() == 1 && cell->parameters[ID(B_WIDTH)].as_int() == 1)
 		{
-			RTLIL::SigSpec a = assign_map(cell->getPort("\\A"));
-			RTLIL::SigSpec b = assign_map(cell->getPort("\\B"));
+			RTLIL::SigSpec a = assign_map(cell->getPort(ID::A));
+			RTLIL::SigSpec b = assign_map(cell->getPort(ID::B));
 
 			if (a.is_fully_const() && !b.is_fully_const()) {
 				cover_list("opt.opt_expr.eqneq.swapconst", "$eq", "$ne", cell->type.str());
-				cell->setPort("\\A", b);
-				cell->setPort("\\B", a);
+				cell->setPort(ID::A, b);
+				cell->setPort(ID::B, a);
 				std::swap(a, b);
 			}
 
 			if (b.is_fully_const()) {
-				if (b.as_bool() == (cell->type == "$eq")) {
+				if (b.is_fully_undef()) {
 					RTLIL::SigSpec input = b;
-					ACTION_DO("\\Y", cell->getPort("\\A"));
+					ACTION_DO(ID::Y, Const(State::Sx, GetSize(cell->getPort(ID::Y))));
+				} else
+				if (b.as_bool() == (cell->type == ID($eq))) {
+					RTLIL::SigSpec input = b;
+					ACTION_DO(ID::Y, cell->getPort(ID::A));
 				} else {
 					cover_list("opt.opt_expr.eqneq.isnot", "$eq", "$ne", cell->type.str());
-					log("Replacing %s cell `%s' in module `%s' with inverter.\n", log_id(cell->type), log_id(cell), log_id(module));
-					cell->type = "$not";
-					cell->parameters.erase("\\B_WIDTH");
-					cell->parameters.erase("\\B_SIGNED");
-					cell->unsetPort("\\B");
+					log_debug("Replacing %s cell `%s' in module `%s' with inverter.\n", log_id(cell->type), log_id(cell), log_id(module));
+					cell->type = ID($not);
+					cell->parameters.erase(ID(B_WIDTH));
+					cell->parameters.erase(ID(B_SIGNED));
+					cell->unsetPort(ID::B);
 					did_something = true;
 				}
 				goto next_cell;
 			}
 		}
 
-		if ((cell->type == "$eq" || cell->type == "$ne") &&
-				(assign_map(cell->getPort("\\A")).is_fully_zero() || assign_map(cell->getPort("\\B")).is_fully_zero()))
+		if (cell->type.in(ID($eq), ID($ne)) &&
+				(assign_map(cell->getPort(ID::A)).is_fully_zero() || assign_map(cell->getPort(ID::B)).is_fully_zero()))
 		{
 			cover_list("opt.opt_expr.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_debug("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->type = cell->type == ID($eq) ? ID($logic_not) : ID($reduce_bool);
+			if (assign_map(cell->getPort(ID::A)).is_fully_zero()) {
+				cell->setPort(ID::A, cell->getPort(ID::B));
+				cell->setParam(ID(A_SIGNED), cell->getParam(ID(B_SIGNED)));
+				cell->setParam(ID(A_WIDTH), cell->getParam(ID(B_WIDTH)));
 			}
-			cell->unsetPort("\\B");
-			cell->unsetParam("\\B_SIGNED");
-			cell->unsetParam("\\B_WIDTH");
+			cell->unsetPort(ID::B);
+			cell->unsetParam(ID(B_SIGNED));
+			cell->unsetParam(ID(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())
+		if (cell->type.in(ID($shl), ID($shr), ID($sshl), ID($sshr), ID($shift), ID($shiftx)) && assign_map(cell->getPort(ID::B)).is_fully_const())
 		{
-			bool sign_ext = cell->type == "$sshr" && cell->getParam("\\A_SIGNED").as_bool();
-			int shift_bits = assign_map(cell->getPort("\\B")).as_int(cell->type.in("$shift", "$shiftx") && cell->getParam("\\B_SIGNED").as_bool());
+			bool sign_ext = cell->type == ID($sshr) && cell->getParam(ID(A_SIGNED)).as_bool();
+			int shift_bits = assign_map(cell->getPort(ID::B)).as_int(cell->type.in(ID($shift), ID($shiftx)) && cell->getParam(ID(B_SIGNED)).as_bool());
 
-			if (cell->type.in("$shl", "$sshl"))
+			if (cell->type.in(ID($shl), ID($sshl)))
 				shift_bits *= -1;
 
-			RTLIL::SigSpec sig_a = assign_map(cell->getPort("\\A"));
-			RTLIL::SigSpec sig_y(cell->type == "$shiftx" ? RTLIL::State::Sx : RTLIL::State::S0, cell->getParam("\\Y_WIDTH").as_int());
+			RTLIL::SigSpec sig_a = assign_map(cell->getPort(ID::A));
+			RTLIL::SigSpec sig_y(cell->type == ID($shiftx) ? RTLIL::State::Sx : RTLIL::State::S0, cell->getParam(ID(Y_WIDTH)).as_int());
 
 			if (GetSize(sig_a) < GetSize(sig_y))
-				sig_a.extend_u0(GetSize(sig_y), cell->getParam("\\A_SIGNED").as_bool());
+				sig_a.extend_u0(GetSize(sig_y), cell->getParam(ID(A_SIGNED)).as_bool());
 
 			for (int i = 0; i < GetSize(sig_y); i++) {
 				int idx = i + shift_bits;
@@ -853,10 +1016,10 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 
 			cover_list("opt.opt_expr.constshift", "$shl", "$shr", "$sshl", "$sshr", "$shift", "$shiftx", cell->type.str());
 
-			log("Replacing %s cell `%s' (B=%s, SHR=%d) in module `%s' with fixed wiring: %s\n",
-					log_id(cell->type), log_id(cell), log_signal(assign_map(cell->getPort("\\B"))), shift_bits, log_id(module), log_signal(sig_y));
+			log_debug("Replacing %s cell `%s' (B=%s, SHR=%d) in module `%s' with fixed wiring: %s\n",
+					log_id(cell->type), log_id(cell), log_signal(assign_map(cell->getPort(ID::B))), shift_bits, log_id(module), log_signal(sig_y));
 
-			module->connect(cell->getPort("\\Y"), sig_y);
+			module->connect(cell->getPort(ID::Y), sig_y);
 			module->remove(cell);
 
 			did_something = true;
@@ -869,41 +1032,41 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 			bool identity_wrt_b = false;
 			bool arith_inverse = false;
 
-			if (cell->type == "$add" || cell->type == "$sub" || cell->type == "$or" || cell->type == "$xor")
+			if (cell->type.in(ID($add), ID($sub), ID($or), ID($xor)))
 			{
-				RTLIL::SigSpec a = assign_map(cell->getPort("\\A"));
-				RTLIL::SigSpec b = assign_map(cell->getPort("\\B"));
+				RTLIL::SigSpec a = assign_map(cell->getPort(ID::A));
+				RTLIL::SigSpec b = assign_map(cell->getPort(ID::B));
 
-				if (cell->type != "$sub" && a.is_fully_const() && a.as_bool() == false)
+				if (cell->type != ID($sub) && a.is_fully_const() && a.as_bool() == false)
 					identity_wrt_b = true;
 
 				if (b.is_fully_const() && b.as_bool() == false)
 					identity_wrt_a = true;
 			}
 
-			if (cell->type == "$shl" || cell->type == "$shr" || cell->type == "$sshl" || cell->type == "$sshr" || cell->type == "$shift" || cell->type == "$shiftx")
+			if (cell->type.in(ID($shl), ID($shr), ID($sshl), ID($sshr), ID($shift), ID($shiftx)))
 			{
-				RTLIL::SigSpec b = assign_map(cell->getPort("\\B"));
+				RTLIL::SigSpec b = assign_map(cell->getPort(ID::B));
 
 				if (b.is_fully_const() && b.as_bool() == false)
 					identity_wrt_a = true;
 			}
 
-			if (cell->type == "$mul")
+			if (cell->type == ID($mul))
 			{
-				RTLIL::SigSpec a = assign_map(cell->getPort("\\A"));
-				RTLIL::SigSpec b = assign_map(cell->getPort("\\B"));
+				RTLIL::SigSpec a = assign_map(cell->getPort(ID::A));
+				RTLIL::SigSpec b = assign_map(cell->getPort(ID::B));
 
-				if (a.is_fully_const() && is_one_or_minus_one(a.as_const(), cell->getParam("\\A_SIGNED").as_bool(), arith_inverse))
+				if (a.is_fully_const() && is_one_or_minus_one(a.as_const(), cell->getParam(ID(A_SIGNED)).as_bool(), arith_inverse))
 					identity_wrt_b = true;
 				else
-				if (b.is_fully_const() && is_one_or_minus_one(b.as_const(), cell->getParam("\\B_SIGNED").as_bool(), arith_inverse))
+				if (b.is_fully_const() && is_one_or_minus_one(b.as_const(), cell->getParam(ID(B_SIGNED)).as_bool(), arith_inverse))
 					identity_wrt_a = true;
 			}
 
-			if (cell->type == "$div")
+			if (cell->type == ID($div))
 			{
-				RTLIL::SigSpec b = assign_map(cell->getPort("\\B"));
+				RTLIL::SigSpec b = assign_map(cell->getPort(ID::B));
 
 				if (b.is_fully_const() && b.size() <= 32 && b.as_int() == 1)
 					identity_wrt_a = true;
@@ -916,19 +1079,19 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 				if (identity_wrt_b)
 					cover_list("opt.opt_expr.identwrt.b", "$add", "$sub", "$or", "$xor", "$shl", "$shr", "$sshl", "$sshr", "$shift", "$shiftx", "$mul", "$div", cell->type.str());
 
-				log("Replacing %s cell `%s' in module `%s' with identity for port %c.\n",
+				log_debug("Replacing %s cell `%s' in module `%s' with identity for port %c.\n",
 					cell->type.c_str(), cell->name.c_str(), module->name.c_str(), identity_wrt_a ? 'A' : 'B');
 
 				if (!identity_wrt_a) {
-					cell->setPort("\\A", cell->getPort("\\B"));
-					cell->parameters.at("\\A_WIDTH") = cell->parameters.at("\\B_WIDTH");
-					cell->parameters.at("\\A_SIGNED") = cell->parameters.at("\\B_SIGNED");
+					cell->setPort(ID::A, cell->getPort(ID::B));
+					cell->parameters.at(ID(A_WIDTH)) = cell->parameters.at(ID(B_WIDTH));
+					cell->parameters.at(ID(A_SIGNED)) = cell->parameters.at(ID(B_SIGNED));
 				}
 
-				cell->type = arith_inverse ? "$neg" : "$pos";
-				cell->unsetPort("\\B");
-				cell->parameters.erase("\\B_WIDTH");
-				cell->parameters.erase("\\B_SIGNED");
+				cell->type = arith_inverse ? ID($neg) : ID($pos);
+				cell->unsetPort(ID::B);
+				cell->parameters.erase(ID(B_WIDTH));
+				cell->parameters.erase(ID(B_SIGNED));
 				cell->check();
 
 				did_something = true;
@@ -936,91 +1099,91 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 			}
 		}
 
-		if (mux_bool && (cell->type == "$mux" || cell->type == "$_MUX_") &&
-				cell->getPort("\\A") == RTLIL::SigSpec(0, 1) && cell->getPort("\\B") == RTLIL::SigSpec(1, 1)) {
+		if (mux_bool && cell->type.in(ID($mux), ID($_MUX_)) &&
+				cell->getPort(ID::A) == State::S0 && cell->getPort(ID::B) == State::S1) {
 			cover_list("opt.opt_expr.mux_bool", "$mux", "$_MUX_", cell->type.str());
-			replace_cell(assign_map, module, cell, "mux_bool", "\\Y", cell->getPort("\\S"));
+			replace_cell(assign_map, module, cell, "mux_bool", ID::Y, cell->getPort(ID(S)));
 			goto next_cell;
 		}
 
-		if (mux_bool && (cell->type == "$mux" || cell->type == "$_MUX_") &&
-				cell->getPort("\\A") == RTLIL::SigSpec(1, 1) && cell->getPort("\\B") == RTLIL::SigSpec(0, 1)) {
+		if (mux_bool && cell->type.in(ID($mux), ID($_MUX_)) &&
+				cell->getPort(ID::A) == State::S1 && cell->getPort(ID::B) == State::S0) {
 			cover_list("opt.opt_expr.mux_invert", "$mux", "$_MUX_", cell->type.str());
-			log("Replacing %s cell `%s' in module `%s' with inverter.\n", log_id(cell->type), log_id(cell), log_id(module));
-			cell->setPort("\\A", cell->getPort("\\S"));
-			cell->unsetPort("\\B");
-			cell->unsetPort("\\S");
-			if (cell->type == "$mux") {
-				Const width = cell->parameters["\\WIDTH"];
-				cell->parameters["\\A_WIDTH"] = width;
-				cell->parameters["\\Y_WIDTH"] = width;
-				cell->parameters["\\A_SIGNED"] = 0;
-				cell->parameters.erase("\\WIDTH");
-				cell->type = "$not";
+			log_debug("Replacing %s cell `%s' in module `%s' with inverter.\n", log_id(cell->type), log_id(cell), log_id(module));
+			cell->setPort(ID::A, cell->getPort(ID(S)));
+			cell->unsetPort(ID::B);
+			cell->unsetPort(ID(S));
+			if (cell->type == ID($mux)) {
+				Const width = cell->parameters[ID(WIDTH)];
+				cell->parameters[ID(A_WIDTH)] = width;
+				cell->parameters[ID(Y_WIDTH)] = width;
+				cell->parameters[ID(A_SIGNED)] = 0;
+				cell->parameters.erase(ID(WIDTH));
+				cell->type = ID($not);
 			} else
-				cell->type = "$_NOT_";
+				cell->type = ID($_NOT_);
 			did_something = true;
 			goto next_cell;
 		}
 
-		if (consume_x && mux_bool && (cell->type == "$mux" || cell->type == "$_MUX_") && cell->getPort("\\A") == RTLIL::SigSpec(0, 1)) {
+		if (consume_x && mux_bool && cell->type.in(ID($mux), ID($_MUX_)) && cell->getPort(ID::A) == State::S0) {
 			cover_list("opt.opt_expr.mux_and", "$mux", "$_MUX_", cell->type.str());
-			log("Replacing %s cell `%s' in module `%s' with and-gate.\n", log_id(cell->type), log_id(cell), log_id(module));
-			cell->setPort("\\A", cell->getPort("\\S"));
-			cell->unsetPort("\\S");
-			if (cell->type == "$mux") {
-				Const width = cell->parameters["\\WIDTH"];
-				cell->parameters["\\A_WIDTH"] = width;
-				cell->parameters["\\B_WIDTH"] = width;
-				cell->parameters["\\Y_WIDTH"] = width;
-				cell->parameters["\\A_SIGNED"] = 0;
-				cell->parameters["\\B_SIGNED"] = 0;
-				cell->parameters.erase("\\WIDTH");
-				cell->type = "$and";
+			log_debug("Replacing %s cell `%s' in module `%s' with and-gate.\n", log_id(cell->type), log_id(cell), log_id(module));
+			cell->setPort(ID::A, cell->getPort(ID(S)));
+			cell->unsetPort(ID(S));
+			if (cell->type == ID($mux)) {
+				Const width = cell->parameters[ID(WIDTH)];
+				cell->parameters[ID(A_WIDTH)] = width;
+				cell->parameters[ID(B_WIDTH)] = width;
+				cell->parameters[ID(Y_WIDTH)] = width;
+				cell->parameters[ID(A_SIGNED)] = 0;
+				cell->parameters[ID(B_SIGNED)] = 0;
+				cell->parameters.erase(ID(WIDTH));
+				cell->type = ID($and);
 			} else
-				cell->type = "$_AND_";
+				cell->type = ID($_AND_);
 			did_something = true;
 			goto next_cell;
 		}
 
-		if (consume_x && mux_bool && (cell->type == "$mux" || cell->type == "$_MUX_") && cell->getPort("\\B") == RTLIL::SigSpec(1, 1)) {
+		if (consume_x && mux_bool && cell->type.in(ID($mux), ID($_MUX_)) && cell->getPort(ID::B) == State::S1) {
 			cover_list("opt.opt_expr.mux_or", "$mux", "$_MUX_", cell->type.str());
-			log("Replacing %s cell `%s' in module `%s' with or-gate.\n", log_id(cell->type), log_id(cell), log_id(module));
-			cell->setPort("\\B", cell->getPort("\\S"));
-			cell->unsetPort("\\S");
-			if (cell->type == "$mux") {
-				Const width = cell->parameters["\\WIDTH"];
-				cell->parameters["\\A_WIDTH"] = width;
-				cell->parameters["\\B_WIDTH"] = width;
-				cell->parameters["\\Y_WIDTH"] = width;
-				cell->parameters["\\A_SIGNED"] = 0;
-				cell->parameters["\\B_SIGNED"] = 0;
-				cell->parameters.erase("\\WIDTH");
-				cell->type = "$or";
+			log_debug("Replacing %s cell `%s' in module `%s' with or-gate.\n", log_id(cell->type), log_id(cell), log_id(module));
+			cell->setPort(ID::B, cell->getPort(ID(S)));
+			cell->unsetPort(ID(S));
+			if (cell->type == ID($mux)) {
+				Const width = cell->parameters[ID(WIDTH)];
+				cell->parameters[ID(A_WIDTH)] = width;
+				cell->parameters[ID(B_WIDTH)] = width;
+				cell->parameters[ID(Y_WIDTH)] = width;
+				cell->parameters[ID(A_SIGNED)] = 0;
+				cell->parameters[ID(B_SIGNED)] = 0;
+				cell->parameters.erase(ID(WIDTH));
+				cell->type = ID($or);
 			} else
-				cell->type = "$_OR_";
+				cell->type = ID($_OR_);
 			did_something = true;
 			goto next_cell;
 		}
 
-		if (mux_undef && (cell->type == "$mux" || cell->type == "$pmux")) {
+		if (mux_undef && cell->type.in(ID($mux), ID($pmux))) {
 			RTLIL::SigSpec new_a, new_b, new_s;
-			int width = cell->getPort("\\A").size();
-			if ((cell->getPort("\\A").is_fully_undef() && cell->getPort("\\B").is_fully_undef()) ||
-					cell->getPort("\\S").is_fully_undef()) {
+			int width = GetSize(cell->getPort(ID::A));
+			if ((cell->getPort(ID::A).is_fully_undef() && cell->getPort(ID::B).is_fully_undef()) ||
+					cell->getPort(ID(S)).is_fully_undef()) {
 				cover_list("opt.opt_expr.mux_undef", "$mux", "$pmux", cell->type.str());
-				replace_cell(assign_map, module, cell, "mux_undef", "\\Y", cell->getPort("\\A"));
+				replace_cell(assign_map, module, cell, "mux_undef", ID::Y, cell->getPort(ID::A));
 				goto next_cell;
 			}
-			for (int i = 0; i < cell->getPort("\\S").size(); i++) {
-				RTLIL::SigSpec old_b = cell->getPort("\\B").extract(i*width, width);
-				RTLIL::SigSpec old_s = cell->getPort("\\S").extract(i, 1);
+			for (int i = 0; i < cell->getPort(ID(S)).size(); i++) {
+				RTLIL::SigSpec old_b = cell->getPort(ID::B).extract(i*width, width);
+				RTLIL::SigSpec old_s = cell->getPort(ID(S)).extract(i, 1);
 				if (old_b.is_fully_undef() || old_s.is_fully_undef())
 					continue;
 				new_b.append(old_b);
 				new_s.append(old_s);
 			}
-			new_a = cell->getPort("\\A");
+			new_a = cell->getPort(ID::A);
 			if (new_a.is_fully_undef() && new_s.size() > 0) {
 				new_a = new_b.extract((new_s.size()-1)*width, width);
 				new_b = new_b.extract(0, (new_s.size()-1)*width);
@@ -1028,27 +1191,27 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 			}
 			if (new_s.size() == 0) {
 				cover_list("opt.opt_expr.mux_empty", "$mux", "$pmux", cell->type.str());
-				replace_cell(assign_map, module, cell, "mux_empty", "\\Y", new_a);
+				replace_cell(assign_map, module, cell, "mux_empty", ID::Y, new_a);
 				goto next_cell;
 			}
 			if (new_a == RTLIL::SigSpec(RTLIL::State::S0) && new_b == RTLIL::SigSpec(RTLIL::State::S1)) {
 				cover_list("opt.opt_expr.mux_sel01", "$mux", "$pmux", cell->type.str());
-				replace_cell(assign_map, module, cell, "mux_sel01", "\\Y", new_s);
+				replace_cell(assign_map, module, cell, "mux_sel01", ID::Y, new_s);
 				goto next_cell;
 			}
-			if (cell->getPort("\\S").size() != new_s.size()) {
+			if (cell->getPort(ID(S)).size() != new_s.size()) {
 				cover_list("opt.opt_expr.mux_reduce", "$mux", "$pmux", cell->type.str());
-				log("Optimized away %d select inputs of %s cell `%s' in module `%s'.\n",
-						GetSize(cell->getPort("\\S")) - GetSize(new_s), log_id(cell->type), log_id(cell), log_id(module));
-				cell->setPort("\\A", new_a);
-				cell->setPort("\\B", new_b);
-				cell->setPort("\\S", new_s);
+				log_debug("Optimized away %d select inputs of %s cell `%s' in module `%s'.\n",
+						GetSize(cell->getPort(ID(S))) - GetSize(new_s), log_id(cell->type), log_id(cell), log_id(module));
+				cell->setPort(ID::A, new_a);
+				cell->setPort(ID::B, new_b);
+				cell->setPort(ID(S), new_s);
 				if (new_s.size() > 1) {
-					cell->type = "$pmux";
-					cell->parameters["\\S_WIDTH"] = new_s.size();
+					cell->type = ID($pmux);
+					cell->parameters[ID(S_WIDTH)] = new_s.size();
 				} else {
-					cell->type = "$mux";
-					cell->parameters.erase("\\S_WIDTH");
+					cell->type = ID($mux);
+					cell->parameters.erase(ID(S_WIDTH));
 				}
 				did_something = true;
 			}
@@ -1056,30 +1219,30 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 
 #define FOLD_1ARG_CELL(_t) \
 		if (cell->type == "$" #_t) { \
-			RTLIL::SigSpec a = cell->getPort("\\A"); \
+			RTLIL::SigSpec a = cell->getPort(ID::A); \
 			assign_map.apply(a); \
 			if (a.is_fully_const()) { \
 				RTLIL::Const dummy_arg(RTLIL::State::S0, 1); \
 				RTLIL::SigSpec y(RTLIL::const_ ## _t(a.as_const(), dummy_arg, \
-						cell->parameters["\\A_SIGNED"].as_bool(), false, \
-						cell->parameters["\\Y_WIDTH"].as_int())); \
+						cell->parameters[ID(A_SIGNED)].as_bool(), false, \
+						cell->parameters[ID(Y_WIDTH)].as_int())); \
 				cover("opt.opt_expr.const.$" #_t); \
-				replace_cell(assign_map, module, cell, stringf("%s", log_signal(a)), "\\Y", y); \
+				replace_cell(assign_map, module, cell, stringf("%s", log_signal(a)), ID::Y, y); \
 				goto next_cell; \
 			} \
 		}
 #define FOLD_2ARG_CELL(_t) \
 		if (cell->type == "$" #_t) { \
-			RTLIL::SigSpec a = cell->getPort("\\A"); \
-			RTLIL::SigSpec b = cell->getPort("\\B"); \
+			RTLIL::SigSpec a = cell->getPort(ID::A); \
+			RTLIL::SigSpec b = cell->getPort(ID::B); \
 			assign_map.apply(a), assign_map.apply(b); \
 			if (a.is_fully_const() && b.is_fully_const()) { \
 				RTLIL::SigSpec y(RTLIL::const_ ## _t(a.as_const(), b.as_const(), \
-						cell->parameters["\\A_SIGNED"].as_bool(), \
-						cell->parameters["\\B_SIGNED"].as_bool(), \
-						cell->parameters["\\Y_WIDTH"].as_int())); \
+						cell->parameters[ID(A_SIGNED)].as_bool(), \
+						cell->parameters[ID(B_SIGNED)].as_bool(), \
+						cell->parameters[ID(Y_WIDTH)].as_int())); \
 				cover("opt.opt_expr.const.$" #_t); \
-				replace_cell(assign_map, module, cell, stringf("%s, %s", log_signal(a), log_signal(b)), "\\Y", y); \
+				replace_cell(assign_map, module, cell, stringf("%s, %s", log_signal(a), log_signal(b)), ID::Y, y); \
 				goto next_cell; \
 			} \
 		}
@@ -1125,25 +1288,25 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 		FOLD_1ARG_CELL(neg)
 
 		// be very conservative with optimizing $mux cells as we do not want to break mux trees
-		if (cell->type == "$mux") {
-			RTLIL::SigSpec input = assign_map(cell->getPort("\\S"));
-			RTLIL::SigSpec inA = assign_map(cell->getPort("\\A"));
-			RTLIL::SigSpec inB = assign_map(cell->getPort("\\B"));
+		if (cell->type == ID($mux)) {
+			RTLIL::SigSpec input = assign_map(cell->getPort(ID(S)));
+			RTLIL::SigSpec inA = assign_map(cell->getPort(ID::A));
+			RTLIL::SigSpec inB = assign_map(cell->getPort(ID::B));
 			if (input.is_fully_const())
-				ACTION_DO("\\Y", input.as_bool() ? cell->getPort("\\B") : cell->getPort("\\A"));
+				ACTION_DO(ID::Y, input.as_bool() ? cell->getPort(ID::B) : cell->getPort(ID::A));
 			else if (inA == inB)
-				ACTION_DO("\\Y", cell->getPort("\\A"));
+				ACTION_DO(ID::Y, cell->getPort(ID::A));
 		}
 
-		if (!keepdc && cell->type == "$mul")
+		if (!keepdc && cell->type == ID($mul))
 		{
-			bool a_signed = cell->parameters["\\A_SIGNED"].as_bool();
-			bool b_signed = cell->parameters["\\B_SIGNED"].as_bool();
+			bool a_signed = cell->parameters[ID(A_SIGNED)].as_bool();
+			bool b_signed = cell->parameters[ID(B_SIGNED)].as_bool();
 			bool swapped_ab = false;
 
-			RTLIL::SigSpec sig_a = assign_map(cell->getPort("\\A"));
-			RTLIL::SigSpec sig_b = assign_map(cell->getPort("\\B"));
-			RTLIL::SigSpec sig_y = assign_map(cell->getPort("\\Y"));
+			RTLIL::SigSpec sig_a = assign_map(cell->getPort(ID::A));
+			RTLIL::SigSpec sig_b = assign_map(cell->getPort(ID::B));
+			RTLIL::SigSpec sig_y = assign_map(cell->getPort(ID::Y));
 
 			if (sig_b.is_fully_const() && sig_b.size() <= 32)
 				std::swap(sig_a, sig_b), std::swap(a_signed, b_signed), swapped_ab = true;
@@ -1156,7 +1319,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 				{
 					cover("opt.opt_expr.mul_shift.zero");
 
-					log("Replacing multiply-by-zero cell `%s' in module `%s' with zero-driver.\n",
+					log_debug("Replacing multiply-by-zero cell `%s' in module `%s' with zero-driver.\n",
 							cell->name.c_str(), module->name.c_str());
 
 					module->connect(RTLIL::SigSig(sig_y, RTLIL::SigSpec(0, sig_y.size())));
@@ -1174,13 +1337,13 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 						else
 							cover("opt.opt_expr.mul_shift.unswapped");
 
-						log("Replacing multiply-by-%d cell `%s' in module `%s' with shift-by-%d.\n",
+						log_debug("Replacing multiply-by-%d cell `%s' in module `%s' with shift-by-%d.\n",
 								a_val, cell->name.c_str(), module->name.c_str(), i);
 
 						if (!swapped_ab) {
-							cell->setPort("\\A", cell->getPort("\\B"));
-							cell->parameters.at("\\A_WIDTH") = cell->parameters.at("\\B_WIDTH");
-							cell->parameters.at("\\A_SIGNED") = cell->parameters.at("\\B_SIGNED");
+							cell->setPort(ID::A, cell->getPort(ID::B));
+							cell->parameters.at(ID(A_WIDTH)) = cell->parameters.at(ID(B_WIDTH));
+							cell->parameters.at(ID(A_SIGNED)) = cell->parameters.at(ID(B_SIGNED));
 						}
 
 						std::vector<RTLIL::SigBit> new_b = RTLIL::SigSpec(i, 6);
@@ -1188,10 +1351,10 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 						while (GetSize(new_b) > 1 && new_b.back() == RTLIL::State::S0)
 							new_b.pop_back();
 
-						cell->type = "$shl";
-						cell->parameters["\\B_WIDTH"] = GetSize(new_b);
-						cell->parameters["\\B_SIGNED"] = false;
-						cell->setPort("\\B", new_b);
+						cell->type = ID($shl);
+						cell->parameters[ID(B_WIDTH)] = GetSize(new_b);
+						cell->parameters[ID(B_SIGNED)] = false;
+						cell->setPort(ID::B, new_b);
 						cell->check();
 
 						did_something = true;
@@ -1200,11 +1363,11 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 			}
 		}
 
-		if (!keepdc && cell->type.in("$div", "$mod"))
+		if (!keepdc && cell->type.in(ID($div), ID($mod)))
 		{
-			bool b_signed = cell->parameters["\\B_SIGNED"].as_bool();
-			SigSpec sig_b = assign_map(cell->getPort("\\B"));
-			SigSpec sig_y = assign_map(cell->getPort("\\Y"));
+			bool b_signed = cell->parameters[ID(B_SIGNED)].as_bool();
+			SigSpec sig_b = assign_map(cell->getPort(ID::B));
+			SigSpec sig_y = assign_map(cell->getPort(ID::Y));
 
 			if (sig_b.is_fully_def() && sig_b.size() <= 32)
 			{
@@ -1214,7 +1377,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 				{
 					cover("opt.opt_expr.divmod_zero");
 
-					log("Replacing divide-by-zero cell `%s' in module `%s' with undef-driver.\n",
+					log_debug("Replacing divide-by-zero cell `%s' in module `%s' with undef-driver.\n",
 							cell->name.c_str(), module->name.c_str());
 
 					module->connect(RTLIL::SigSig(sig_y, RTLIL::SigSpec(State::Sx, sig_y.size())));
@@ -1227,11 +1390,11 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 				for (int i = 1; i < (b_signed ? sig_b.size()-1 : sig_b.size()); i++)
 					if (b_val == (1 << i))
 					{
-						if (cell->type == "$div")
+						if (cell->type == ID($div))
 						{
 							cover("opt.opt_expr.div_shift");
 
-							log("Replacing divide-by-%d cell `%s' in module `%s' with shift-by-%d.\n",
+							log_debug("Replacing divide-by-%d cell `%s' in module `%s' with shift-by-%d.\n",
 									b_val, cell->name.c_str(), module->name.c_str(), i);
 
 							std::vector<RTLIL::SigBit> new_b = RTLIL::SigSpec(i, 6);
@@ -1239,17 +1402,17 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 							while (GetSize(new_b) > 1 && new_b.back() == RTLIL::State::S0)
 								new_b.pop_back();
 
-							cell->type = "$shr";
-							cell->parameters["\\B_WIDTH"] = GetSize(new_b);
-							cell->parameters["\\B_SIGNED"] = false;
-							cell->setPort("\\B", new_b);
+							cell->type = ID($shr);
+							cell->parameters[ID(B_WIDTH)] = GetSize(new_b);
+							cell->parameters[ID(B_SIGNED)] = false;
+							cell->setPort(ID::B, new_b);
 							cell->check();
 						}
 						else
 						{
 							cover("opt.opt_expr.mod_mask");
 
-							log("Replacing modulo-by-%d cell `%s' in module `%s' with bitmask.\n",
+							log_debug("Replacing modulo-by-%d cell `%s' in module `%s' with bitmask.\n",
 									b_val, cell->name.c_str(), module->name.c_str());
 
 							std::vector<RTLIL::SigBit> new_b = RTLIL::SigSpec(State::S1, i);
@@ -1257,9 +1420,9 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 							if (b_signed)
 								new_b.push_back(State::S0);
 
-							cell->type = "$and";
-							cell->parameters["\\B_WIDTH"] = GetSize(new_b);
-							cell->setPort("\\B", new_b);
+							cell->type = ID($and);
+							cell->parameters[ID(B_WIDTH)] = GetSize(new_b);
+							cell->setPort(ID::B, new_b);
 							cell->check();
 						}
 
@@ -1271,7 +1434,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 
 		// remove redundant pairs of bits in ==, ===, !=, and !==
 		// replace cell with const driver if inputs can't be equal
-		if (do_fine && cell->type.in("$eq", "$ne", "$eqx", "$nex"))
+		if (do_fine && cell->type.in(ID($eq), ID($ne), ID($eqx), ID($nex)))
 		{
 			pool<pair<SigBit, SigBit>> redundant_cache;
 			mfp<SigBit> contradiction_cache;
@@ -1279,14 +1442,14 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 			contradiction_cache.promote(State::S0);
 			contradiction_cache.promote(State::S1);
 
-			int a_width = cell->getParam("\\A_WIDTH").as_int();
-			int b_width = cell->getParam("\\B_WIDTH").as_int();
+			int a_width = cell->getParam(ID(A_WIDTH)).as_int();
+			int b_width = cell->getParam(ID(B_WIDTH)).as_int();
 
-			bool is_signed = cell->getParam("\\A_SIGNED").as_bool();
+			bool is_signed = cell->getParam(ID(A_SIGNED)).as_bool();
 			int width = is_signed ? std::min(a_width, b_width) : std::max(a_width, b_width);
 
-			SigSpec sig_a = cell->getPort("\\A");
-			SigSpec sig_b = cell->getPort("\\B");
+			SigSpec sig_a = cell->getPort(ID::A);
+			SigSpec sig_b = cell->getPort(ID::B);
 
 			int redundant_bits = 0;
 
@@ -1316,10 +1479,10 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 
 			if (contradiction_cache.find(State::S0) == contradiction_cache.find(State::S1))
 			{
-				SigSpec y_sig = cell->getPort("\\Y");
-				Const y_value(cell->type.in("$eq", "$eqx") ? 0 : 1, GetSize(y_sig));
+				SigSpec y_sig = cell->getPort(ID::Y);
+				Const y_value(cell->type.in(ID($eq), ID($eqx)) ? 0 : 1, GetSize(y_sig));
 
-				log("Replacing cell `%s' in module `%s' with constant driver %s.\n",
+				log_debug("Replacing cell `%s' in module `%s' with constant driver %s.\n",
 					log_id(cell), log_id(module), log_signal(y_value));
 
 				module->connect(y_sig, y_value);
@@ -1331,131 +1494,152 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 
 			if (redundant_bits)
 			{
-				log("Removed %d redundant input bits from %s cell `%s' in module `%s'.\n",
+				log_debug("Removed %d redundant input bits from %s cell `%s' in module `%s'.\n",
 						redundant_bits, log_id(cell->type), log_id(cell), log_id(module));
 
-				cell->setPort("\\A", sig_a);
-				cell->setPort("\\B", sig_b);
-				cell->setParam("\\A_WIDTH", GetSize(sig_a));
-				cell->setParam("\\B_WIDTH", GetSize(sig_b));
+				cell->setPort(ID::A, sig_a);
+				cell->setPort(ID::B, sig_b);
+				cell->setParam(ID(A_WIDTH), GetSize(sig_a));
+				cell->setParam(ID(B_WIDTH), GetSize(sig_b));
 
 				did_something = true;
 				goto next_cell;
 			}
 		}
 
-		// replace a<0 or a>=0 with the top bit of a
-		if (do_fine && (cell->type == "$lt" || cell->type == "$ge" || cell->type == "$gt" || cell->type == "$le"))
+		// simplify comparisons
+		if (do_fine && cell->type.in(ID($lt), ID($ge), ID($gt), ID($le)))
 		{
-			//used to decide whether the signal needs to be negated
-			bool is_lt = false;
-
-			//references the variable signal in the comparison
-			RTLIL::SigSpec sigVar;
-
-			//references the constant signal in the comparison
-			RTLIL::SigSpec sigConst;
-
-			// note that this signal must be constant for the optimization
-			// to take place, but it is not checked beforehand.
-			// If new passes are added, this signal must be checked for const-ness
-
-			//width of the variable port
-			int width;
-			int const_width;
-
-			bool var_signed;
-
-			if (cell->type == "$lt" || cell->type == "$ge") {
-				is_lt = cell->type == "$lt" ? 1 : 0;
-				sigVar = cell->getPort("\\A");
-				sigConst = cell->getPort("\\B");
-				width = cell->parameters["\\A_WIDTH"].as_int();
-				const_width = cell->parameters["\\B_WIDTH"].as_int();
-				var_signed = cell->parameters["\\A_SIGNED"].as_bool();
-			} else
-			if (cell->type == "$gt" || cell->type == "$le") {
-				is_lt = cell->type == "$gt" ? 1 : 0;
-				sigVar = cell->getPort("\\B");
-				sigConst = cell->getPort("\\A");
-				width = cell->parameters["\\B_WIDTH"].as_int();
-				const_width = cell->parameters["\\A_WIDTH"].as_int();
-				var_signed = cell->parameters["\\B_SIGNED"].as_bool();
-			} else
-				log_abort();
-
-			// replace a(signed) < 0 with the high bit of a
-			if (sigConst.is_fully_const() && sigConst.is_fully_zero() && var_signed == true)
+			IdString cmp_type = cell->type;
+			SigSpec var_sig = cell->getPort(ID::A);
+			SigSpec const_sig = cell->getPort(ID::B);
+			int var_width = cell->parameters[ID(A_WIDTH)].as_int();
+			int const_width = cell->parameters[ID(B_WIDTH)].as_int();
+			bool is_signed = cell->getParam(ID(A_SIGNED)).as_bool();
+
+			if (!const_sig.is_fully_const())
 			{
-				RTLIL::SigSpec a_prime(RTLIL::State::S0, cell->parameters["\\Y_WIDTH"].as_int());
-				a_prime[0] = sigVar[width - 1];
-				if (is_lt) {
-					log("Replacing %s cell `%s' (implementing X<0) with X[%d]: %s\n",
-							log_id(cell->type), log_id(cell), width-1, log_signal(a_prime));
-					module->connect(cell->getPort("\\Y"), a_prime);
-					module->remove(cell);
-				} else {
-					log("Replacing %s cell `%s' (implementing X>=0) with ~X[%d]: %s\n",
-							log_id(cell->type), log_id(cell), width-1, log_signal(a_prime));
-					module->addNot(NEW_ID, a_prime, cell->getPort("\\Y"));
-					module->remove(cell);
-				}
-				did_something = true;
-				goto next_cell;
-			} else
-			if (sigConst.is_fully_const() && sigConst.is_fully_def() && var_signed == false)
+				std::swap(var_sig, const_sig);
+				std::swap(var_width, const_width);
+				if (cmp_type == ID($gt))
+					cmp_type = ID($lt);
+				else if (cmp_type == ID($lt))
+					cmp_type = ID($gt);
+				else if (cmp_type == ID($ge))
+					cmp_type = ID($le);
+				else if (cmp_type == ID($le))
+					cmp_type = ID($ge);
+			}
+
+			if (const_sig.is_fully_def() && const_sig.is_fully_const())
 			{
-				if (sigConst.is_fully_zero()) {
-					RTLIL::SigSpec a_prime(RTLIL::State::S0, 1);
-					if (is_lt) {
-						log("Replacing %s cell `%s' (implementing unsigned X<0) with constant false.\n",
-								log_id(cell->type), log_id(cell));
-						a_prime[0] = RTLIL::State::S0;
-					} else {
-						log("Replacing %s cell `%s' (implementing unsigned X>=0) with constant true.\n",
-								log_id(cell->type), log_id(cell));
-						a_prime[0] = RTLIL::State::S1;
+				std::string condition, replacement;
+				SigSpec replace_sig(State::S0, GetSize(cell->getPort(ID::Y)));
+				bool replace = false;
+				bool remove = false;
+
+				if (!is_signed)
+				{ /* unsigned */
+					if (const_sig.is_fully_zero() && cmp_type == ID($lt)) {
+						condition   = "unsigned X<0";
+						replacement = "constant 0";
+						replace_sig[0] = State::S0;
+						replace = true;
+					}
+					if (const_sig.is_fully_zero() && cmp_type == ID($ge)) {
+						condition   = "unsigned X>=0";
+						replacement = "constant 1";
+						replace_sig[0] = State::S1;
+						replace = true;
+					}
+					if (const_width == var_width && const_sig.is_fully_ones() && cmp_type == ID($gt)) {
+						condition   = "unsigned X>~0";
+						replacement = "constant 0";
+						replace_sig[0] = State::S0;
+						replace = true;
+					}
+					if (const_width == var_width && const_sig.is_fully_ones() && cmp_type == ID($le)) {
+						condition   = "unsigned X<=~0";
+						replacement = "constant 1";
+						replace_sig[0] = State::S1;
+						replace = true;
 					}
-					module->connect(cell->getPort("\\Y"), a_prime);
-					module->remove(cell);
-					did_something = true;
-					goto next_cell;
-				}
 
-				int const_bit_set = get_onehot_bit_index(sigConst);
-				if (const_bit_set >= 0 && const_bit_set < width) {
-					int bit_set = const_bit_set;
-					RTLIL::SigSpec a_prime(RTLIL::State::S0, width - bit_set);
-					for (int i = bit_set; i < width; i++) {
-						a_prime[i - bit_set] = sigVar[i];
+					int const_bit_hot = get_onehot_bit_index(const_sig);
+					if (const_bit_hot >= 0 && const_bit_hot < var_width)
+					{
+						RTLIL::SigSpec var_high_sig(RTLIL::State::S0, var_width - const_bit_hot);
+						for (int i = const_bit_hot; i < var_width; i++) {
+							var_high_sig[i - const_bit_hot] = var_sig[i];
+						}
+
+						if (cmp_type == ID($lt))
+						{
+							condition   = stringf("unsigned X<%s", log_signal(const_sig));
+							replacement = stringf("!X[%d:%d]", var_width - 1, const_bit_hot);
+							module->addLogicNot(NEW_ID, var_high_sig, cell->getPort(ID::Y));
+							remove = true;
+						}
+						if (cmp_type == ID($ge))
+						{
+							condition   = stringf("unsigned X>=%s", log_signal(const_sig));
+							replacement = stringf("|X[%d:%d]", var_width - 1, const_bit_hot);
+							module->addReduceOr(NEW_ID, var_high_sig, cell->getPort(ID::Y));
+							remove = true;
+						}
 					}
-					if (is_lt) {
-						log("Replacing %s cell `%s' (implementing unsigned X<%s) with !X[%d:%d]: %s.\n",
-								log_id(cell->type), log_id(cell), log_signal(sigConst), width - 1, bit_set, log_signal(a_prime));
-						module->addLogicNot(NEW_ID, a_prime, cell->getPort("\\Y"));
-					} else {
-						log("Replacing %s cell `%s' (implementing unsigned X>=%s) with |X[%d:%d]: %s.\n",
-								log_id(cell->type), log_id(cell), log_signal(sigConst), width - 1, bit_set, log_signal(a_prime));
-						module->addReduceOr(NEW_ID, a_prime, cell->getPort("\\Y"));
+
+					int const_bit_set = get_highest_hot_index(const_sig);
+					if(const_bit_set >= var_width)
+					{
+						string cmp_name;
+						if (cmp_type == ID($lt) || cmp_type == ID($le))
+						{
+							if (cmp_type == ID($lt)) cmp_name = "<";
+							if (cmp_type == ID($le)) cmp_name = "<=";
+							condition   = stringf("unsigned X[%d:0]%s%s", var_width - 1, cmp_name.c_str(), log_signal(const_sig));
+							replacement = "constant 1";
+							replace_sig[0] = State::S1;
+							replace = true;
+						}
+						if (cmp_type == ID($gt) || cmp_type == ID($ge))
+						{
+							if (cmp_type == ID($gt)) cmp_name = ">";
+							if (cmp_type == ID($ge)) cmp_name = ">=";
+							condition   = stringf("unsigned X[%d:0]%s%s", var_width - 1, cmp_name.c_str(), log_signal(const_sig));
+							replacement = "constant 0";
+							replace_sig[0] = State::S0;
+							replace = true;
+						}
 					}
-					module->remove(cell);
-					did_something = true;
-					goto next_cell;
 				}
-				else if(const_bit_set >= width && const_bit_set >= 0){
-					RTLIL::SigSpec a_prime(RTLIL::State::S0, 1);
-					if(is_lt){
-						a_prime[0] = RTLIL::State::S1;
-						log("Replacing %s cell `%s' (implementing unsigned X[%d:0] < %s[%d:0]) with constant 0.\n", log_id(cell->type), log_id(cell), width-1, log_signal(sigConst),const_width-1);
+				else
+				{ /* signed */
+					if (const_sig.is_fully_zero() && cmp_type == ID($lt))
+					{
+						condition   = "signed X<0";
+						replacement = stringf("X[%d]", var_width - 1);
+						replace_sig[0] = var_sig[var_width - 1];
+						replace = true;
 					}
-					else{
-						log("Replacing %s cell `%s' (implementing unsigned X[%d:0]>= %s[%d:0]) with constant 1.\n", log_id(cell->type), log_id(cell), width-1, log_signal(sigConst),const_width-1);
+					if (const_sig.is_fully_zero() && cmp_type == ID($ge))
+					{
+						condition   = "signed X>=0";
+						replacement = stringf("X[%d]", var_width - 1);
+						module->addNot(NEW_ID, var_sig[var_width - 1], cell->getPort(ID::Y));
+						remove = true;
 					}
-					module->connect(cell->getPort("\\Y"), a_prime);
+				}
+
+				if (replace || remove)
+				{
+					log_debug("Replacing %s cell `%s' (implementing %s) with %s.\n",
+							log_id(cell->type), log_id(cell), condition.c_str(), replacement.c_str());
+					if (replace)
+						module->connect(cell->getPort(ID::Y), replace_sig);
 					module->remove(cell);
 					did_something = true;
 					goto next_cell;
-
 				}
 			}
 		}
@@ -1470,14 +1654,14 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 
 struct OptExprPass : public Pass {
 	OptExprPass() : Pass("opt_expr", "perform const folding and simple expression rewriting") { }
-	virtual void help()
+	void help() YS_OVERRIDE
 	{
 		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
 		log("\n");
 		log("    opt_expr [options] [selection]\n");
 		log("\n");
 		log("This pass performs const folding on internal cell types with constant inputs.\n");
-		log("It also performs some simple expression rewritring.\n");
+		log("It also performs some simple expression rewriting.\n");
 		log("\n");
 		log("    -mux_undef\n");
 		log("        remove 'undef' inputs from $mux, $pmux and $_MUX_ cells\n");
@@ -1504,7 +1688,7 @@ struct OptExprPass : public Pass {
 		log("        replaced by 'a'. the -keepdc option disables all such optimizations.\n");
 		log("\n");
 	}
-	virtual void execute(std::vector<std::string> args, RTLIL::Design *design)
+	void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
 	{
 		bool mux_undef = false;
 		bool mux_bool = false;
@@ -1555,8 +1739,14 @@ struct OptExprPass : public Pass {
 
 		for (auto module : design->selected_modules())
 		{
-			if (undriven)
+			log("Optimizing module %s.\n", log_id(module));
+
+			if (undriven) {
+				did_something = false;
 				replace_undriven(design, module);
+				if (did_something)
+					design->scratchpad_set_bool("opt.did_something", true);
+			}
 
 			do {
 				do {
@@ -1566,7 +1756,11 @@ struct OptExprPass : public Pass {
 						design->scratchpad_set_bool("opt.did_something", true);
 				} while (did_something);
 				replace_const_cells(design, module, true, mux_undef, mux_bool, do_fine, keepdc, clkinv);
+				if (did_something)
+					design->scratchpad_set_bool("opt.did_something", true);
 			} while (did_something);
+
+			log_suppressed();
 		}
 
 		log_pop();
diff --git a/passes/opt/opt_lut.cc b/passes/opt/opt_lut.cc
new file mode 100644
index 000000000..c4f278706
--- /dev/null
+++ b/passes/opt/opt_lut.cc
@@ -0,0 +1,595 @@
+/*
+ *  yosys -- Yosys Open SYnthesis Suite
+ *
+ *  Copyright (C) 2018  whitequark <whitequark@whitequark.org>
+ *
+ *  Permission to use, copy, modify, and/or distribute this software for any
+ *  purpose with or without fee is hereby granted, provided that the above
+ *  copyright notice and this permission notice appear in all copies.
+ *
+ *  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ *  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ *  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ *  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ *  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ *  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ *  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ */
+
+#include "kernel/yosys.h"
+#include "kernel/sigtools.h"
+#include "kernel/modtools.h"
+
+USING_YOSYS_NAMESPACE
+PRIVATE_NAMESPACE_BEGIN
+
+struct OptLutWorker
+{
+	dict<IdString, dict<int, IdString>> &dlogic;
+	RTLIL::Module *module;
+	ModIndex index;
+	SigMap sigmap;
+
+	pool<RTLIL::Cell*> luts;
+	dict<RTLIL::Cell*, int> luts_arity;
+	dict<RTLIL::Cell*, pool<RTLIL::Cell*>> luts_dlogics;
+	dict<RTLIL::Cell*, pool<int>> luts_dlogic_inputs;
+
+	int eliminated_count = 0, combined_count = 0;
+
+	bool evaluate_lut(RTLIL::Cell *lut, dict<SigBit, bool> inputs)
+	{
+		SigSpec lut_input = sigmap(lut->getPort(ID::A));
+		int lut_width = lut->getParam(ID(WIDTH)).as_int();
+		Const lut_table = lut->getParam(ID(LUT));
+		int lut_index = 0;
+
+		for (int i = 0; i < lut_width; i++)
+		{
+			SigBit input = sigmap(lut_input[i]);
+			if (inputs.count(input))
+			{
+				lut_index |= inputs[input] << i;
+			}
+			else
+			{
+				lut_index |= SigSpec(lut_input[i]).as_bool() << i;
+			}
+		}
+
+		return lut_table.extract(lut_index).as_bool();
+	}
+
+	void show_stats_by_arity()
+	{
+		dict<int, int> arity_counts;
+		dict<IdString, int> dlogic_counts;
+		int max_arity = 0;
+
+		for (auto lut_arity : luts_arity)
+		{
+			max_arity = max(max_arity, lut_arity.second);
+			arity_counts[lut_arity.second]++;
+		}
+
+		for (auto &lut_dlogics : luts_dlogics)
+		{
+			for (auto &lut_dlogic : lut_dlogics.second)
+			{
+				dlogic_counts[lut_dlogic->type]++;
+			}
+		}
+
+		log("Number of LUTs: %8d\n", GetSize(luts));
+		for (int arity = 1; arity <= max_arity; arity++)
+		{
+			if (arity_counts[arity])
+				log("  %d-LUT %16d\n", arity, arity_counts[arity]);
+		}
+		for (auto &dlogic_count : dlogic_counts)
+		{
+			log("  with %-12s %4d\n", dlogic_count.first.c_str(), dlogic_count.second);
+		}
+	}
+
+	OptLutWorker(dict<IdString, dict<int, IdString>> &dlogic, RTLIL::Module *module, int limit) :
+		dlogic(dlogic), module(module), index(module), sigmap(module)
+	{
+		log("Discovering LUTs.\n");
+		for (auto cell : module->selected_cells())
+		{
+			if (cell->type == ID($lut))
+			{
+				if (cell->has_keep_attr())
+					continue;
+				SigBit lut_output = cell->getPort(ID::Y);
+				if (lut_output.wire->get_bool_attribute(ID::keep))
+					continue;
+
+				int lut_width = cell->getParam(ID(WIDTH)).as_int();
+				SigSpec lut_input = cell->getPort(ID::A);
+				int lut_arity = 0;
+
+				log_debug("Found $lut\\WIDTH=%d cell %s.%s.\n", lut_width, log_id(module), log_id(cell));
+				luts.insert(cell);
+
+				// First, find all dedicated logic we're connected to. This results in an overapproximation
+				// of such connections.
+				pool<RTLIL::Cell*> lut_all_dlogics;
+				for (int i = 0; i < lut_width; i++)
+				{
+					SigBit bit = lut_input[i];
+					for (auto &port : index.query_ports(bit))
+					{
+						if (dlogic.count(port.cell->type))
+						{
+							auto &dlogic_map = dlogic[port.cell->type];
+							if (dlogic_map.count(i))
+							{
+								if (port.port == dlogic_map[i])
+								{
+									lut_all_dlogics.insert(port.cell);
+								}
+							}
+						}
+					}
+				}
+
+				// Second, make sure that the connection to dedicated logic is legal. If it is not legal,
+				// it means one of the two things:
+				//   * The connection is spurious. I.e. this is dedicated logic that will be packed
+				//     with some other LUT, and it just happens to be connected to this LUT as well.
+				//   * The connection is illegal.
+				// In either of these cases, we don't need to concern ourselves with preserving the connection
+				// between this LUT and this dedicated logic cell.
+				pool<RTLIL::Cell*> lut_legal_dlogics;
+				pool<int> lut_dlogic_inputs;
+				for (auto lut_dlogic : lut_all_dlogics)
+				{
+					auto &dlogic_map = dlogic[lut_dlogic->type];
+					bool legal = true;
+					for (auto &dlogic_conn : dlogic_map)
+					{
+						if (lut_width <= dlogic_conn.first)
+						{
+							log_debug("  LUT has illegal connection to %s cell %s.%s.\n", lut_dlogic->type.c_str(), log_id(module), log_id(lut_dlogic));
+							log_debug("    LUT input A[%d] not present.\n", dlogic_conn.first);
+							legal = false;
+							break;
+						}
+						if (sigmap(lut_input[dlogic_conn.first]) != sigmap(lut_dlogic->getPort(dlogic_conn.second)))
+						{
+							log_debug("  LUT has illegal connection to %s cell %s.%s.\n", lut_dlogic->type.c_str(), log_id(module), log_id(lut_dlogic));
+							log_debug("    LUT input A[%d] (wire %s) not connected to %s port %s (wire %s).\n", dlogic_conn.first, log_signal(lut_input[dlogic_conn.first]), lut_dlogic->type.c_str(), dlogic_conn.second.c_str(), log_signal(lut_dlogic->getPort(dlogic_conn.second)));
+							legal = false;
+							break;
+						}
+					}
+
+					if (legal)
+					{
+						log_debug("  LUT has legal connection to %s cell %s.%s.\n", lut_dlogic->type.c_str(), log_id(module), log_id(lut_dlogic));
+						lut_legal_dlogics.insert(lut_dlogic);
+						for (auto &dlogic_conn : dlogic_map)
+							lut_dlogic_inputs.insert(dlogic_conn.first);
+					}
+				}
+
+				// Third, determine LUT arity. An n-wide LUT that has k constant inputs and m inputs shared with dedicated
+				// logic implements an (n-k-m)-ary function.
+				for (int i = 0; i < lut_width; i++)
+				{
+					SigBit bit = lut_input[i];
+					if (bit.wire || lut_dlogic_inputs.count(i))
+						lut_arity++;
+				}
+
+				log_debug("  Cell implements a %d-LUT.\n", lut_arity);
+				luts_arity[cell] = lut_arity;
+				luts_dlogics[cell] = lut_legal_dlogics;
+				luts_dlogic_inputs[cell] = lut_dlogic_inputs;
+			}
+		}
+		show_stats_by_arity();
+
+		log("\n");
+		log("Eliminating LUTs.\n");
+		pool<RTLIL::Cell*> worklist = luts;
+		while (worklist.size())
+		{
+			if (limit == 0)
+			{
+				log("Limit reached.\n");
+				break;
+			}
+
+			auto lut = worklist.pop();
+			SigSpec lut_input = sigmap(lut->getPort(ID::A));
+			pool<int> &lut_dlogic_inputs = luts_dlogic_inputs[lut];
+
+			vector<SigBit> lut_inputs;
+			for (auto &bit : lut_input)
+			{
+				if (bit.wire)
+					lut_inputs.push_back(sigmap(bit));
+			}
+
+			bool const0_match = true;
+			bool const1_match = true;
+			vector<bool> input_matches;
+			for (size_t i = 0; i < lut_inputs.size(); i++)
+				input_matches.push_back(true);
+
+			for (int eval = 0; eval < 1 << lut_inputs.size(); eval++)
+			{
+				dict<SigBit, bool> eval_inputs;
+				for (size_t i = 0; i < lut_inputs.size(); i++)
+					eval_inputs[lut_inputs[i]] = (eval >> i) & 1;
+				bool value = evaluate_lut(lut, eval_inputs);
+				if (value != 0)
+					const0_match = false;
+				if (value != 1)
+					const1_match = false;
+				for (size_t i = 0; i < lut_inputs.size(); i++)
+				{
+					if (value != eval_inputs[lut_inputs[i]])
+						input_matches[i] = false;
+				}
+			}
+
+			int input_match = -1;
+			for (size_t i = 0; i < lut_inputs.size(); i++)
+				if (input_matches[i])
+					input_match = i;
+
+			if (const0_match || const1_match || input_match != -1)
+			{
+				log_debug("Found redundant cell %s.%s.\n", log_id(module), log_id(lut));
+
+				SigBit value;
+				if (const0_match)
+				{
+					log_debug("  Cell evaluates constant 0.\n");
+					value = State::S0;
+				}
+				if (const1_match)
+				{
+					log_debug("  Cell evaluates constant 1.\n");
+					value = State::S1;
+				}
+				if (input_match != -1) {
+					log_debug("  Cell evaluates signal %s.\n", log_signal(lut_inputs[input_match]));
+					value = lut_inputs[input_match];
+				}
+
+				if (lut_dlogic_inputs.size())
+					log_debug("  Not eliminating cell (connected to dedicated logic).\n");
+				else
+				{
+					SigSpec lut_output = lut->getPort(ID::Y);
+					for (auto &port : index.query_ports(lut_output))
+					{
+						if (port.cell != lut && luts.count(port.cell))
+							worklist.insert(port.cell);
+					}
+
+					module->connect(lut_output, value);
+					sigmap.add(lut_output, value);
+
+					module->remove(lut);
+					luts.erase(lut);
+					luts_arity.erase(lut);
+					luts_dlogics.erase(lut);
+					luts_dlogic_inputs.erase(lut);
+
+					eliminated_count++;
+					if (limit > 0)
+						limit--;
+				}
+			}
+		}
+		show_stats_by_arity();
+
+		log("\n");
+		log("Combining LUTs.\n");
+		worklist = luts;
+		while (worklist.size())
+		{
+			if (limit == 0)
+			{
+				log("Limit reached.\n");
+				break;
+			}
+
+			auto lutA = worklist.pop();
+			SigSpec lutA_input = sigmap(lutA->getPort(ID::A));
+			SigSpec lutA_output = sigmap(lutA->getPort(ID::Y)[0]);
+			int lutA_width = lutA->getParam(ID(WIDTH)).as_int();
+			int lutA_arity = luts_arity[lutA];
+			pool<int> &lutA_dlogic_inputs = luts_dlogic_inputs[lutA];
+
+			auto lutA_output_ports = index.query_ports(lutA->getPort(ID::Y));
+			if (lutA_output_ports.size() != 2)
+				continue;
+
+			for (auto &port : lutA_output_ports)
+			{
+				if (port.cell == lutA)
+					continue;
+
+				if (luts.count(port.cell))
+				{
+					auto lutB = port.cell;
+					SigSpec lutB_input = sigmap(lutB->getPort(ID::A));
+					SigSpec lutB_output = sigmap(lutB->getPort(ID::Y)[0]);
+					int lutB_width = lutB->getParam(ID(WIDTH)).as_int();
+					int lutB_arity = luts_arity[lutB];
+					pool<int> &lutB_dlogic_inputs = luts_dlogic_inputs[lutB];
+
+					log_debug("Found %s.%s (cell A) feeding %s.%s (cell B).\n", log_id(module), log_id(lutA), log_id(module), log_id(lutB));
+
+					if (index.query_is_output(lutA->getPort(ID::Y)))
+					{
+						log_debug("  Not combining LUTs (cascade connection feeds module output).\n");
+						continue;
+					}
+
+					pool<SigBit> lutA_inputs;
+					pool<SigBit> lutB_inputs;
+					for (auto &bit : lutA_input)
+					{
+						if (bit.wire)
+							lutA_inputs.insert(sigmap(bit));
+					}
+					for (auto &bit : lutB_input)
+					{
+						if (bit.wire)
+							lutB_inputs.insert(sigmap(bit));
+					}
+
+					pool<SigBit> common_inputs;
+					for (auto &bit : lutA_inputs)
+					{
+						if (lutB_inputs.count(bit))
+							common_inputs.insert(bit);
+					}
+
+					int lutM_arity = lutA_arity + lutB_arity - 1 - common_inputs.size();
+					if (lutA_dlogic_inputs.size())
+						log_debug("  Cell A is a %d-LUT with %d dedicated connections. ", lutA_arity, GetSize(lutA_dlogic_inputs));
+					else
+						log_debug("  Cell A is a %d-LUT. ", lutA_arity);
+					if (lutB_dlogic_inputs.size())
+						log_debug("Cell B is a %d-LUT with %d dedicated connections.\n", lutB_arity, GetSize(lutB_dlogic_inputs));
+					else
+						log_debug("Cell B is a %d-LUT.\n", lutB_arity);
+					log_debug("  Cells share %d input(s) and can be merged into one %d-LUT.\n", GetSize(common_inputs), lutM_arity);
+
+					const int COMBINE_A = 1, COMBINE_B = 2, COMBINE_EITHER = COMBINE_A | COMBINE_B;
+					int combine_mask = 0;
+					if (lutM_arity > lutA_width)
+						log_debug("  Not combining LUTs into cell A (combined LUT wider than cell A).\n");
+					else if (lutB_dlogic_inputs.size() > 0)
+						log_debug("  Not combining LUTs into cell A (cell B is connected to dedicated logic).\n");
+					else if (lutB->get_bool_attribute(ID(lut_keep)))
+						log_debug("  Not combining LUTs into cell A (cell B has attribute \\lut_keep).\n");
+					else
+						combine_mask |= COMBINE_A;
+					if (lutM_arity > lutB_width)
+						log_debug("  Not combining LUTs into cell B (combined LUT wider than cell B).\n");
+					else if (lutA_dlogic_inputs.size() > 0)
+						log_debug("  Not combining LUTs into cell B (cell A is connected to dedicated logic).\n");
+					else if (lutA->get_bool_attribute(ID(lut_keep)))
+						log_debug("  Not combining LUTs into cell B (cell A has attribute \\lut_keep).\n");
+					else
+						combine_mask |= COMBINE_B;
+
+					int combine = combine_mask;
+					if (combine == COMBINE_EITHER)
+					{
+						log_debug("  Can combine into either cell.\n");
+						if (lutA_arity == 1)
+						{
+							log_debug("    Cell A is a buffer or inverter, combining into cell B.\n");
+							combine = COMBINE_B;
+						}
+						else if (lutB_arity == 1)
+						{
+							log_debug("    Cell B is a buffer or inverter, combining into cell A.\n");
+							combine = COMBINE_A;
+						}
+						else
+						{
+							log_debug("    Arbitrarily combining into cell A.\n");
+							combine = COMBINE_A;
+						}
+					}
+
+					RTLIL::Cell *lutM, *lutR;
+					pool<SigBit> lutM_inputs, lutR_inputs;
+					pool<int> lutM_dlogic_inputs;
+					if (combine == COMBINE_A)
+					{
+						log_debug("  Combining LUTs into cell A.\n");
+						lutM = lutA;
+						lutM_inputs = lutA_inputs;
+						lutM_dlogic_inputs = lutA_dlogic_inputs;
+						lutR = lutB;
+						lutR_inputs = lutB_inputs;
+					}
+					else if (combine == COMBINE_B)
+					{
+						log_debug("  Combining LUTs into cell B.\n");
+						lutM = lutB;
+						lutM_inputs = lutB_inputs;
+						lutM_dlogic_inputs = lutB_dlogic_inputs;
+						lutR = lutA;
+						lutR_inputs = lutA_inputs;
+					}
+					else
+					{
+						log_debug("  Cannot combine LUTs.\n");
+						continue;
+					}
+
+					pool<SigBit> lutR_unique;
+					for (auto &bit : lutR_inputs)
+					{
+						if (!common_inputs.count(bit) && bit != lutA_output)
+							lutR_unique.insert(bit);
+					}
+
+					int lutM_width = lutM->getParam(ID(WIDTH)).as_int();
+					SigSpec lutM_input = sigmap(lutM->getPort(ID::A));
+					std::vector<SigBit> lutM_new_inputs;
+					for (int i = 0; i < lutM_width; i++)
+					{
+						bool input_unused = false;
+						if (sigmap(lutM_input[i]) == lutA_output)
+							input_unused = true;
+						if (!lutM_input[i].wire && !lutM_dlogic_inputs.count(i))
+							input_unused = true;
+
+						if (input_unused && lutR_unique.size())
+						{
+							SigBit new_input = lutR_unique.pop();
+							log_debug("    Connecting input %d as %s.\n", i, log_signal(new_input));
+							lutM_new_inputs.push_back(new_input);
+						}
+						else if (sigmap(lutM_input[i]) == lutA_output)
+						{
+							log_debug("    Disconnecting cascade input %d.\n", i);
+							lutM_new_inputs.push_back(SigBit());
+						}
+						else
+						{
+							log_debug("    Leaving input %d as %s.\n", i, log_signal(lutM_input[i]));
+							lutM_new_inputs.push_back(lutM_input[i]);
+						}
+					}
+					log_assert(lutR_unique.size() == 0);
+
+					RTLIL::Const lutM_new_table(State::Sx, 1 << lutM_width);
+					for (int eval = 0; eval < 1 << lutM_width; eval++)
+					{
+						dict<SigBit, bool> eval_inputs;
+						for (size_t i = 0; i < lutM_new_inputs.size(); i++)
+						{
+							eval_inputs[lutM_new_inputs[i]] = (eval >> i) & 1;
+						}
+						eval_inputs[lutA_output] = evaluate_lut(lutA, eval_inputs);
+						lutM_new_table[eval] = (RTLIL::State) evaluate_lut(lutB, eval_inputs);
+					}
+
+					log_debug("  Cell A truth table: %s.\n", lutA->getParam(ID(LUT)).as_string().c_str());
+					log_debug("  Cell B truth table: %s.\n", lutB->getParam(ID(LUT)).as_string().c_str());
+					log_debug("  Merged truth table: %s.\n", lutM_new_table.as_string().c_str());
+
+					lutM->setParam(ID(LUT), lutM_new_table);
+					lutM->setPort(ID::A, lutM_new_inputs);
+					lutM->setPort(ID::Y, lutB_output);
+
+					luts_arity[lutM] = lutM_arity;
+					luts.erase(lutR);
+					luts_arity.erase(lutR);
+					lutR->module->remove(lutR);
+
+					worklist.insert(lutM);
+					worklist.erase(lutR);
+
+					combined_count++;
+					if (limit > 0)
+						limit--;
+				}
+			}
+		}
+		show_stats_by_arity();
+	}
+};
+
+static void split(std::vector<std::string> &tokens, const std::string &text, char sep)
+{
+	size_t start = 0, end = 0;
+	while ((end = text.find(sep, start)) != std::string::npos) {
+		tokens.push_back(text.substr(start, end - start));
+		start = end + 1;
+	}
+	tokens.push_back(text.substr(start));
+}
+
+struct OptLutPass : public Pass {
+	OptLutPass() : Pass("opt_lut", "optimize LUT cells") { }
+	void help() YS_OVERRIDE
+	{
+		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
+		log("\n");
+		log("    opt_lut [options] [selection]\n");
+		log("\n");
+		log("This pass combines cascaded $lut cells with unused inputs.\n");
+		log("\n");
+		log("    -dlogic <type>:<cell-port>=<LUT-input>[:<cell-port>=<LUT-input>...]\n");
+		log("        preserve connections to dedicated logic cell <type> that has ports\n");
+		log("        <cell-port> connected to LUT inputs <LUT-input>. this includes\n");
+		log("        the case where both LUT and dedicated logic input are connected to\n");
+		log("        the same constant.\n");
+		log("\n");
+		log("    -limit N\n");
+		log("        only perform the first N combines, then stop. useful for debugging.\n");
+		log("\n");
+	}
+	void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
+	{
+		log_header(design, "Executing OPT_LUT pass (optimize LUTs).\n");
+
+		dict<IdString, dict<int, IdString>> dlogic;
+		int limit = -1;
+
+		size_t argidx;
+		for (argidx = 1; argidx < args.size(); argidx++)
+		{
+			if (args[argidx] == "-dlogic" && argidx+1 < args.size())
+			{
+				std::vector<std::string> tokens;
+				split(tokens, args[++argidx], ':');
+				if (tokens.size() < 2)
+					log_cmd_error("The -dlogic option requires at least one connection.\n");
+				IdString type = "\\" + tokens[0];
+				for (auto it = tokens.begin() + 1; it != tokens.end(); ++it) {
+					std::vector<std::string> conn_tokens;
+					split(conn_tokens, *it, '=');
+					if (conn_tokens.size() != 2)
+						log_cmd_error("Invalid format of -dlogic signal mapping.\n");
+					IdString logic_port = "\\" + conn_tokens[0];
+					int lut_input = atoi(conn_tokens[1].c_str());
+					dlogic[type][lut_input] = logic_port;
+				}
+				continue;
+			}
+			if (args[argidx] == "-limit" && argidx + 1 < args.size())
+			{
+				limit = atoi(args[++argidx].c_str());
+				continue;
+			}
+			break;
+		}
+		extra_args(args, argidx, design);
+
+		int eliminated_count = 0, combined_count = 0;
+		for (auto module : design->selected_modules())
+		{
+			OptLutWorker worker(dlogic, module, limit - eliminated_count - combined_count);
+			eliminated_count += worker.eliminated_count;
+			combined_count   += worker.combined_count;
+		}
+		if (eliminated_count)
+			design->scratchpad_set_bool("opt.did_something", true);
+		if (combined_count)
+			design->scratchpad_set_bool("opt.did_something", true);
+		log("\n");
+		log("Eliminated %d LUTs.\n", eliminated_count);
+		log("Combined %d LUTs.\n", combined_count);
+	}
+} OptLutPass;
+
+PRIVATE_NAMESPACE_END
diff --git a/passes/opt/opt_merge.cc b/passes/opt/opt_merge.cc
index 2aeb514e4..aaea6159e 100644
--- a/passes/opt/opt_merge.cc
+++ b/passes/opt/opt_merge.cc
@@ -47,8 +47,8 @@ struct OptMergeWorker
 
 	static void sort_pmux_conn(dict<RTLIL::IdString, RTLIL::SigSpec> &conn)
 	{
-		SigSpec sig_s = conn.at("\\S");
-		SigSpec sig_b = conn.at("\\B");
+		SigSpec sig_s = conn.at(ID(S));
+		SigSpec sig_b = conn.at(ID::B);
 
 		int s_width = GetSize(sig_s);
 		int width = GetSize(sig_b) / s_width;
@@ -59,12 +59,12 @@ struct OptMergeWorker
 
 		std::sort(sb_pairs.begin(), sb_pairs.end());
 
-		conn["\\S"] = SigSpec();
-		conn["\\B"] = SigSpec();
+		conn[ID(S)] = SigSpec();
+		conn[ID::B] = SigSpec();
 
 		for (auto &it : sb_pairs) {
-			conn["\\S"].append(it.first);
-			conn["\\B"].append(it.second);
+			conn[ID(S)].append(it.first);
+			conn[ID::B].append(it.second);
 		}
 	}
 
@@ -94,32 +94,32 @@ struct OptMergeWorker
 		const dict<RTLIL::IdString, RTLIL::SigSpec> *conn = &cell->connections();
 		dict<RTLIL::IdString, RTLIL::SigSpec> alt_conn;
 
-		if (cell->type == "$and" || cell->type == "$or" || cell->type == "$xor" || cell->type == "$xnor" || cell->type == "$add" || cell->type == "$mul" ||
-				cell->type == "$logic_and" || cell->type == "$logic_or" || cell->type == "$_AND_" || cell->type == "$_OR_" || cell->type == "$_XOR_") {
+		if (cell->type.in(ID($and), ID($or), ID($xor), ID($xnor), ID($add), ID($mul),
+				ID($logic_and), ID($logic_or), ID($_AND_), ID($_OR_), ID($_XOR_))) {
 			alt_conn = *conn;
-			if (assign_map(alt_conn.at("\\A")) < assign_map(alt_conn.at("\\B"))) {
-				alt_conn["\\A"] = conn->at("\\B");
-				alt_conn["\\B"] = conn->at("\\A");
+			if (assign_map(alt_conn.at(ID::A)) < assign_map(alt_conn.at(ID::B))) {
+				alt_conn[ID::A] = conn->at(ID::B);
+				alt_conn[ID::B] = conn->at(ID::A);
 			}
 			conn = &alt_conn;
 		} else
-		if (cell->type == "$reduce_xor" || cell->type == "$reduce_xnor") {
+		if (cell->type.in(ID($reduce_xor), ID($reduce_xnor))) {
 			alt_conn = *conn;
-			assign_map.apply(alt_conn.at("\\A"));
-			alt_conn.at("\\A").sort();
+			assign_map.apply(alt_conn.at(ID::A));
+			alt_conn.at(ID::A).sort();
 			conn = &alt_conn;
 		} else
-		if (cell->type == "$reduce_and" || cell->type == "$reduce_or" || cell->type == "$reduce_bool") {
+		if (cell->type.in(ID($reduce_and), ID($reduce_or), ID($reduce_bool))) {
 			alt_conn = *conn;
-			assign_map.apply(alt_conn.at("\\A"));
-			alt_conn.at("\\A").sort_and_unify();
+			assign_map.apply(alt_conn.at(ID::A));
+			alt_conn.at(ID::A).sort_and_unify();
 			conn = &alt_conn;
 		} else
-		if (cell->type == "$pmux") {
+		if (cell->type == ID($pmux)) {
 			alt_conn = *conn;
-			assign_map.apply(alt_conn.at("\\A"));
-			assign_map.apply(alt_conn.at("\\B"));
-			assign_map.apply(alt_conn.at("\\S"));
+			assign_map.apply(alt_conn.at(ID::A));
+			assign_map.apply(alt_conn.at(ID::B));
+			assign_map.apply(alt_conn.at(ID(S)));
 			sort_pmux_conn(alt_conn);
 			conn = &alt_conn;
 		}
@@ -189,28 +189,28 @@ struct OptMergeWorker
 				assign_map.apply(it.second);
 		}
 
-		if (cell1->type == "$and" || cell1->type == "$or" || cell1->type == "$xor" || cell1->type == "$xnor" || cell1->type == "$add" || cell1->type == "$mul" ||
-				cell1->type == "$logic_and" || cell1->type == "$logic_or" || cell1->type == "$_AND_" || cell1->type == "$_OR_" || cell1->type == "$_XOR_") {
-			if (conn1.at("\\A") < conn1.at("\\B")) {
-				RTLIL::SigSpec tmp = conn1["\\A"];
-				conn1["\\A"] = conn1["\\B"];
-				conn1["\\B"] = tmp;
+		if (cell1->type == ID($and) || cell1->type == ID($or) || cell1->type == ID($xor) || cell1->type == ID($xnor) || cell1->type == ID($add) || cell1->type == ID($mul) ||
+				cell1->type == ID($logic_and) || cell1->type == ID($logic_or) || cell1->type == ID($_AND_) || cell1->type == ID($_OR_) || cell1->type == ID($_XOR_)) {
+			if (conn1.at(ID::A) < conn1.at(ID::B)) {
+				RTLIL::SigSpec tmp = conn1[ID::A];
+				conn1[ID::A] = conn1[ID::B];
+				conn1[ID::B] = tmp;
 			}
-			if (conn2.at("\\A") < conn2.at("\\B")) {
-				RTLIL::SigSpec tmp = conn2["\\A"];
-				conn2["\\A"] = conn2["\\B"];
-				conn2["\\B"] = tmp;
+			if (conn2.at(ID::A) < conn2.at(ID::B)) {
+				RTLIL::SigSpec tmp = conn2[ID::A];
+				conn2[ID::A] = conn2[ID::B];
+				conn2[ID::B] = tmp;
 			}
 		} else
-		if (cell1->type == "$reduce_xor" || cell1->type == "$reduce_xnor") {
-			conn1["\\A"].sort();
-			conn2["\\A"].sort();
+		if (cell1->type == ID($reduce_xor) || cell1->type == ID($reduce_xnor)) {
+			conn1[ID::A].sort();
+			conn2[ID::A].sort();
 		} else
-		if (cell1->type == "$reduce_and" || cell1->type == "$reduce_or" || cell1->type == "$reduce_bool") {
-			conn1["\\A"].sort_and_unify();
-			conn2["\\A"].sort_and_unify();
+		if (cell1->type == ID($reduce_and) || cell1->type == ID($reduce_or) || cell1->type == ID($reduce_bool)) {
+			conn1[ID::A].sort_and_unify();
+			conn2[ID::A].sort_and_unify();
 		} else
-		if (cell1->type == "$pmux") {
+		if (cell1->type == ID($pmux)) {
 			sort_pmux_conn(conn1);
 			sort_pmux_conn(conn2);
 		}
@@ -222,9 +222,9 @@ struct OptMergeWorker
 			return true;
 		}
 
-		if (cell1->type.substr(0, 1) == "$" && conn1.count("\\Q") != 0) {
-			std::vector<RTLIL::SigBit> q1 = dff_init_map(cell1->getPort("\\Q")).to_sigbit_vector();
-			std::vector<RTLIL::SigBit> q2 = dff_init_map(cell2->getPort("\\Q")).to_sigbit_vector();
+		if (cell1->type.begins_with("$") && conn1.count(ID(Q)) != 0) {
+			std::vector<RTLIL::SigBit> q1 = dff_init_map(cell1->getPort(ID(Q))).to_sigbit_vector();
+			std::vector<RTLIL::SigBit> q2 = dff_init_map(cell2->getPort(ID(Q))).to_sigbit_vector();
 			for (size_t i = 0; i < q1.size(); i++)
 				if ((q1.at(i).wire == NULL || q2.at(i).wire == NULL) && q1.at(i) != q2.at(i)) {
 					lt = q1.at(i) < q2.at(i);
@@ -271,24 +271,24 @@ struct OptMergeWorker
 		ct.setup_stdcells_mem();
 
 		if (mode_nomux) {
-			ct.cell_types.erase("$mux");
-			ct.cell_types.erase("$pmux");
+			ct.cell_types.erase(ID($mux));
+			ct.cell_types.erase(ID($pmux));
 		}
 
-		ct.cell_types.erase("$tribuf");
-		ct.cell_types.erase("$_TBUF_");
-		ct.cell_types.erase("$anyseq");
-		ct.cell_types.erase("$anyconst");
-		ct.cell_types.erase("$allseq");
-		ct.cell_types.erase("$allconst");
+		ct.cell_types.erase(ID($tribuf));
+		ct.cell_types.erase(ID($_TBUF_));
+		ct.cell_types.erase(ID($anyseq));
+		ct.cell_types.erase(ID($anyconst));
+		ct.cell_types.erase(ID($allseq));
+		ct.cell_types.erase(ID($allconst));
 
 		log("Finding identical cells in module `%s'.\n", module->name.c_str());
 		assign_map.set(module);
 
 		dff_init_map.set(module);
 		for (auto &it : module->wires_)
-			if (it.second->attributes.count("\\init") != 0) {
-				Const initval = it.second->attributes.at("\\init");
+			if (it.second->attributes.count(ID(init)) != 0) {
+				Const initval = it.second->attributes.at(ID(init));
 				for (int i = 0; i < GetSize(initval) && i < GetSize(it.second); i++)
 					if (initval[i] == State::S0 || initval[i] == State::S1)
 						dff_init_map.add(SigBit(it.second, i), initval[i]);
@@ -315,17 +315,17 @@ struct OptMergeWorker
 			{
 				if (sharemap.count(cell) > 0) {
 					did_something = true;
-					log("  Cell `%s' is identical to cell `%s'.\n", cell->name.c_str(), sharemap[cell]->name.c_str());
+					log_debug("  Cell `%s' is identical to cell `%s'.\n", cell->name.c_str(), sharemap[cell]->name.c_str());
 					for (auto &it : cell->connections()) {
 						if (cell->output(it.first)) {
 							RTLIL::SigSpec other_sig = sharemap[cell]->getPort(it.first);
-							log("    Redirecting output %s: %s = %s\n", it.first.c_str(),
+							log_debug("    Redirecting output %s: %s = %s\n", it.first.c_str(),
 									log_signal(it.second), log_signal(other_sig));
 							module->connect(RTLIL::SigSig(it.second, other_sig));
 							assign_map.add(it.second, other_sig);
 						}
 					}
-					log("    Removing %s cell `%s' from module `%s'.\n", cell->type.c_str(), cell->name.c_str(), module->name.c_str());
+					log_debug("    Removing %s cell `%s' from module `%s'.\n", cell->type.c_str(), cell->name.c_str(), module->name.c_str());
 #ifdef USE_CELL_HASH_CACHE
 					cell_hash_cache.erase(cell);
 #endif
@@ -336,12 +336,14 @@ struct OptMergeWorker
 				}
 			}
 		}
+
+		log_suppressed();
 	}
 };
 
 struct OptMergePass : public Pass {
 	OptMergePass() : Pass("opt_merge", "consolidate identical cells") { }
-	virtual void help()
+	void help() YS_OVERRIDE
 	{
 		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
 		log("\n");
@@ -357,7 +359,7 @@ struct OptMergePass : public Pass {
 		log("        Operate on all cell types, not just built-in types.\n");
 		log("\n");
 	}
-	virtual void execute(std::vector<std::string> args, RTLIL::Design *design)
+	void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
 	{
 		log_header(design, "Executing OPT_MERGE pass (detect identical cells).\n");
 
diff --git a/passes/opt/opt_muxtree.cc b/passes/opt/opt_muxtree.cc
index f5ddc2af9..3c486bbcc 100644
--- a/passes/opt/opt_muxtree.cc
+++ b/passes/opt/opt_muxtree.cc
@@ -36,6 +36,7 @@ struct OptMuxtreeWorker
 	RTLIL::Module *module;
 	SigMap assign_map;
 	int removed_count;
+	int glob_abort_cnt = 100000;
 
 	struct bitinfo_t {
 		bool seen_non_mux;
@@ -83,12 +84,12 @@ struct OptMuxtreeWorker
 		//	.const_deactivated
 		for (auto cell : module->cells())
 		{
-			if (cell->type == "$mux" || cell->type == "$pmux")
+			if (cell->type.in(ID($mux), ID($pmux)))
 			{
-				RTLIL::SigSpec sig_a = cell->getPort("\\A");
-				RTLIL::SigSpec sig_b = cell->getPort("\\B");
-				RTLIL::SigSpec sig_s = cell->getPort("\\S");
-				RTLIL::SigSpec sig_y = cell->getPort("\\Y");
+				RTLIL::SigSpec sig_a = cell->getPort(ID::A);
+				RTLIL::SigSpec sig_b = cell->getPort(ID::B);
+				RTLIL::SigSpec sig_s = cell->getPort(ID(S));
+				RTLIL::SigSpec sig_y = cell->getPort(ID::Y);
 
 				muxinfo_t muxinfo;
 				muxinfo.cell = cell;
@@ -136,7 +137,7 @@ struct OptMuxtreeWorker
 			}
 		}
 		for (auto wire : module->wires()) {
-			if (wire->port_output || wire->get_bool_attribute("\\keep"))
+			if (wire->port_output || wire->get_bool_attribute(ID::keep))
 				for (int idx : sig2bits(RTLIL::SigSpec(wire)))
 					bit2info[idx].seen_non_mux = true;
 		}
@@ -180,20 +181,29 @@ struct OptMuxtreeWorker
 
 		for (int mux_idx = 0; mux_idx < GetSize(root_muxes); mux_idx++)
 			if (root_muxes.at(mux_idx)) {
-				log("    Root of a mux tree: %s%s\n", log_id(mux2info[mux_idx].cell), root_enable_muxes.at(mux_idx) ? " (pure)" : "");
+				log_debug("    Root of a mux tree: %s%s\n", log_id(mux2info[mux_idx].cell), root_enable_muxes.at(mux_idx) ? " (pure)" : "");
 				root_mux_rerun.erase(mux_idx);
 				eval_root_mux(mux_idx);
+				if (glob_abort_cnt == 0) {
+					log("  Giving up (too many iterations)\n");
+					return;
+				}
 			}
 
 		while (!root_mux_rerun.empty()) {
 			int mux_idx = *root_mux_rerun.begin();
-			log("    Root of a mux tree: %s (rerun as non-pure)\n", log_id(mux2info[mux_idx].cell));
+			log_debug("    Root of a mux tree: %s (rerun as non-pure)\n", log_id(mux2info[mux_idx].cell));
 			log_assert(root_enable_muxes.at(mux_idx));
 			root_mux_rerun.erase(mux_idx);
 			eval_root_mux(mux_idx);
+			if (glob_abort_cnt == 0) {
+				log("  Giving up (too many iterations)\n");
+				return;
+			}
 		}
 
 		log("  Analyzing evaluation results.\n");
+		log_assert(glob_abort_cnt > 0);
 
 		for (auto &mi : mux2info)
 		{
@@ -217,10 +227,10 @@ struct OptMuxtreeWorker
 				continue;
 			}
 
-			RTLIL::SigSpec sig_a = mi.cell->getPort("\\A");
-			RTLIL::SigSpec sig_b = mi.cell->getPort("\\B");
-			RTLIL::SigSpec sig_s = mi.cell->getPort("\\S");
-			RTLIL::SigSpec sig_y = mi.cell->getPort("\\Y");
+			RTLIL::SigSpec sig_a = mi.cell->getPort(ID::A);
+			RTLIL::SigSpec sig_b = mi.cell->getPort(ID::B);
+			RTLIL::SigSpec sig_s = mi.cell->getPort(ID(S));
+			RTLIL::SigSpec sig_y = mi.cell->getPort(ID::Y);
 
 			RTLIL::SigSpec sig_ports = sig_b;
 			sig_ports.append(sig_a);
@@ -245,14 +255,14 @@ struct OptMuxtreeWorker
 					}
 				}
 
-				mi.cell->setPort("\\A", new_sig_a);
-				mi.cell->setPort("\\B", new_sig_b);
-				mi.cell->setPort("\\S", new_sig_s);
+				mi.cell->setPort(ID::A, new_sig_a);
+				mi.cell->setPort(ID::B, new_sig_b);
+				mi.cell->setPort(ID(S), new_sig_s);
 				if (GetSize(new_sig_s) == 1) {
-					mi.cell->type = "$mux";
-					mi.cell->parameters.erase("\\S_WIDTH");
+					mi.cell->type = ID($mux);
+					mi.cell->parameters.erase(ID(S_WIDTH));
 				} else {
-					mi.cell->parameters["\\S_WIDTH"] = RTLIL::Const(GetSize(new_sig_s));
+					mi.cell->parameters[ID(S_WIDTH)] = RTLIL::Const(GetSize(new_sig_s));
 				}
 			}
 		}
@@ -293,6 +303,9 @@ struct OptMuxtreeWorker
 
 	void eval_mux_port(knowledge_t &knowledge, int mux_idx, int port_idx, bool do_replace_known, bool do_enable_ports, int abort_count)
 	{
+		if (glob_abort_cnt == 0)
+			return;
+
 		muxinfo_t &muxinfo = mux2info[mux_idx];
 
 		if (do_enable_ports)
@@ -315,18 +328,21 @@ struct OptMuxtreeWorker
 			knowledge.visited_muxes[m] = true;
 			parent_muxes.push_back(m);
 		}
-		for (int m : parent_muxes)
+		for (int m : parent_muxes) {
 			if (root_enable_muxes.at(m))
 				continue;
 			else if (root_muxes.at(m)) {
 				if (abort_count == 0) {
 					root_mux_rerun.insert(m);
 					root_enable_muxes.at(m) = true;
-					log("      Removing pure flag from root mux %s.\n", log_id(mux2info[m].cell));
+					log_debug("      Removing pure flag from root mux %s.\n", log_id(mux2info[m].cell));
 				} else
 					eval_mux(knowledge, m, false, do_enable_ports, abort_count - 1);
 			} else
 				eval_mux(knowledge, m, do_replace_known, do_enable_ports, abort_count);
+			if (glob_abort_cnt == 0)
+				return;
+		}
 		for (int m : parent_muxes)
 			knowledge.visited_muxes[m] = false;
 
@@ -348,9 +364,9 @@ struct OptMuxtreeWorker
 
 		int width = 0;
 		idict<int> ctrl_bits;
-		if (portname == "\\B")
-			width = GetSize(muxinfo.cell->getPort("\\A"));
-		for (int bit : sig2bits(muxinfo.cell->getPort("\\S"), false))
+		if (portname == ID::B)
+			width = GetSize(muxinfo.cell->getPort(ID::A));
+		for (int bit : sig2bits(muxinfo.cell->getPort(ID(S)), false))
 			ctrl_bits(bit);
 
 		int port_idx = 0, port_off = 0;
@@ -390,12 +406,16 @@ struct OptMuxtreeWorker
 
 	void eval_mux(knowledge_t &knowledge, int mux_idx, bool do_replace_known, bool do_enable_ports, int abort_count)
 	{
+		if (glob_abort_cnt == 0)
+			return;
+		glob_abort_cnt--;
+
 		muxinfo_t &muxinfo = mux2info[mux_idx];
 
 		// set input ports to constants if we find known active or inactive signals
 		if (do_replace_known) {
-			replace_known(knowledge, muxinfo, "\\A");
-			replace_known(knowledge, muxinfo, "\\B");
+			replace_known(knowledge, muxinfo, ID::A);
+			replace_known(knowledge, muxinfo, ID::B);
 		}
 
 		// if there is a constant activated port we just use it
@@ -433,11 +453,15 @@ struct OptMuxtreeWorker
 				if (knowledge.known_inactive.at(portinfo.ctrl_sig))
 					continue;
 			eval_mux_port(knowledge, mux_idx, port_idx, do_replace_known, do_enable_ports, abort_count);
+
+			if (glob_abort_cnt == 0)
+				return;
 		}
 	}
 
 	void eval_root_mux(int mux_idx)
 	{
+		log_assert(glob_abort_cnt > 0);
 		knowledge_t knowledge;
 		knowledge.known_inactive.resize(GetSize(bit2info));
 		knowledge.known_active.resize(GetSize(bit2info));
@@ -449,7 +473,7 @@ struct OptMuxtreeWorker
 
 struct OptMuxtreePass : public Pass {
 	OptMuxtreePass() : Pass("opt_muxtree", "eliminate dead trees in multiplexer trees") { }
-	virtual void help()
+	void help() YS_OVERRIDE
 	{
 		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
 		log("\n");
@@ -462,7 +486,7 @@ struct OptMuxtreePass : public Pass {
 		log("This pass only operates on completely selected modules without processes.\n");
 		log("\n");
 	}
-	virtual void execute(vector<std::string> args, RTLIL::Design *design)
+	void execute(vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
 	{
 		log_header(design, "Executing OPT_MUXTREE pass (detect dead branches in mux trees).\n");
 		extra_args(args, 1, design);
diff --git a/passes/opt/opt_reduce.cc b/passes/opt/opt_reduce.cc
index eb9d02ad5..6a8d8cabd 100644
--- a/passes/opt/opt_reduce.cc
+++ b/passes/opt/opt_reduce.cc
@@ -43,13 +43,13 @@ struct OptReduceWorker
 			return;
 		cells.erase(cell);
 
-		RTLIL::SigSpec sig_a = assign_map(cell->getPort("\\A"));
+		RTLIL::SigSpec sig_a = assign_map(cell->getPort(ID::A));
 		pool<RTLIL::SigBit> new_sig_a_bits;
 
 		for (auto &bit : sig_a.to_sigbit_set())
 		{
 			if (bit == RTLIL::State::S0) {
-				if (cell->type == "$reduce_and") {
+				if (cell->type == ID($reduce_and)) {
 					new_sig_a_bits.clear();
 					new_sig_a_bits.insert(RTLIL::State::S0);
 					break;
@@ -57,7 +57,7 @@ struct OptReduceWorker
 				continue;
 			}
 			if (bit == RTLIL::State::S1) {
-				if (cell->type == "$reduce_or") {
+				if (cell->type == ID($reduce_or)) {
 					new_sig_a_bits.clear();
 					new_sig_a_bits.insert(RTLIL::State::S1);
 					break;
@@ -73,8 +73,8 @@ struct OptReduceWorker
 			for (auto child_cell : drivers.find(bit)) {
 				if (child_cell->type == cell->type) {
 					opt_reduce(cells, drivers, child_cell);
-					if (child_cell->getPort("\\Y")[0] == bit) {
-						pool<RTLIL::SigBit> child_sig_a_bits = assign_map(child_cell->getPort("\\A")).to_sigbit_pool();
+					if (child_cell->getPort(ID::Y)[0] == bit) {
+						pool<RTLIL::SigBit> child_sig_a_bits = assign_map(child_cell->getPort(ID::A)).to_sigbit_pool();
 						new_sig_a_bits.insert(child_sig_a_bits.begin(), child_sig_a_bits.end());
 					} else
 						new_sig_a_bits.insert(RTLIL::State::S0);
@@ -87,22 +87,22 @@ struct OptReduceWorker
 
 		RTLIL::SigSpec new_sig_a(new_sig_a_bits);
 
-		if (new_sig_a != sig_a || sig_a.size() != cell->getPort("\\A").size()) {
+		if (new_sig_a != sig_a || sig_a.size() != cell->getPort(ID::A).size()) {
 			log("    New input vector for %s cell %s: %s\n", cell->type.c_str(), cell->name.c_str(), log_signal(new_sig_a));
 			did_something = true;
 			total_count++;
 		}
 
-		cell->setPort("\\A", new_sig_a);
-		cell->parameters["\\A_WIDTH"] = RTLIL::Const(new_sig_a.size());
+		cell->setPort(ID::A, new_sig_a);
+		cell->parameters[ID(A_WIDTH)] = RTLIL::Const(new_sig_a.size());
 		return;
 	}
 
 	void opt_mux(RTLIL::Cell *cell)
 	{
-		RTLIL::SigSpec sig_a = assign_map(cell->getPort("\\A"));
-		RTLIL::SigSpec sig_b = assign_map(cell->getPort("\\B"));
-		RTLIL::SigSpec sig_s = assign_map(cell->getPort("\\S"));
+		RTLIL::SigSpec sig_a = assign_map(cell->getPort(ID::A));
+		RTLIL::SigSpec sig_b = assign_map(cell->getPort(ID::B));
+		RTLIL::SigSpec sig_s = assign_map(cell->getPort(ID(S)));
 
 		RTLIL::SigSpec new_sig_b, new_sig_s;
 		pool<RTLIL::SigSpec> handled_sig;
@@ -123,15 +123,15 @@ struct OptReduceWorker
 
 			if (this_s.size() > 1)
 			{
-				RTLIL::Cell *reduce_or_cell = module->addCell(NEW_ID, "$reduce_or");
-				reduce_or_cell->setPort("\\A", this_s);
-				reduce_or_cell->parameters["\\A_SIGNED"] = RTLIL::Const(0);
-				reduce_or_cell->parameters["\\A_WIDTH"] = RTLIL::Const(this_s.size());
-				reduce_or_cell->parameters["\\Y_WIDTH"] = RTLIL::Const(1);
+				RTLIL::Cell *reduce_or_cell = module->addCell(NEW_ID, ID($reduce_or));
+				reduce_or_cell->setPort(ID::A, this_s);
+				reduce_or_cell->parameters[ID(A_SIGNED)] = RTLIL::Const(0);
+				reduce_or_cell->parameters[ID(A_WIDTH)] = RTLIL::Const(this_s.size());
+				reduce_or_cell->parameters[ID(Y_WIDTH)] = RTLIL::Const(1);
 
 				RTLIL::Wire *reduce_or_wire = module->addWire(NEW_ID);
 				this_s = RTLIL::SigSpec(reduce_or_wire);
-				reduce_or_cell->setPort("\\Y", this_s);
+				reduce_or_cell->setPort(ID::Y, this_s);
 			}
 
 			new_sig_b.append(this_b);
@@ -147,28 +147,28 @@ struct OptReduceWorker
 
 		if (new_sig_s.size() == 0)
 		{
-			module->connect(RTLIL::SigSig(cell->getPort("\\Y"), cell->getPort("\\A")));
-			assign_map.add(cell->getPort("\\Y"), cell->getPort("\\A"));
+			module->connect(RTLIL::SigSig(cell->getPort(ID::Y), cell->getPort(ID::A)));
+			assign_map.add(cell->getPort(ID::Y), cell->getPort(ID::A));
 			module->remove(cell);
 		}
 		else
 		{
-			cell->setPort("\\B", new_sig_b);
-			cell->setPort("\\S", new_sig_s);
+			cell->setPort(ID::B, new_sig_b);
+			cell->setPort(ID(S), new_sig_s);
 			if (new_sig_s.size() > 1) {
-				cell->parameters["\\S_WIDTH"] = RTLIL::Const(new_sig_s.size());
+				cell->parameters[ID(S_WIDTH)] = RTLIL::Const(new_sig_s.size());
 			} else {
-				cell->type = "$mux";
-				cell->parameters.erase("\\S_WIDTH");
+				cell->type = ID($mux);
+				cell->parameters.erase(ID(S_WIDTH));
 			}
 		}
 	}
 
 	void opt_mux_bits(RTLIL::Cell *cell)
 	{
-		std::vector<RTLIL::SigBit> sig_a = assign_map(cell->getPort("\\A")).to_sigbit_vector();
-		std::vector<RTLIL::SigBit> sig_b = assign_map(cell->getPort("\\B")).to_sigbit_vector();
-		std::vector<RTLIL::SigBit> sig_y = assign_map(cell->getPort("\\Y")).to_sigbit_vector();
+		std::vector<RTLIL::SigBit> sig_a = assign_map(cell->getPort(ID::A)).to_sigbit_vector();
+		std::vector<RTLIL::SigBit> sig_b = assign_map(cell->getPort(ID::B)).to_sigbit_vector();
+		std::vector<RTLIL::SigBit> sig_y = assign_map(cell->getPort(ID::Y)).to_sigbit_vector();
 
 		std::vector<RTLIL::SigBit> new_sig_y;
 		RTLIL::SigSig old_sig_conn;
@@ -209,29 +209,29 @@ struct OptReduceWorker
 		if (new_sig_y.size() != sig_y.size())
 		{
 			log("    Consolidated identical input bits for %s cell %s:\n", cell->type.c_str(), cell->name.c_str());
-			log("      Old ports: A=%s, B=%s, Y=%s\n", log_signal(cell->getPort("\\A")),
-					log_signal(cell->getPort("\\B")), log_signal(cell->getPort("\\Y")));
+			log("      Old ports: A=%s, B=%s, Y=%s\n", log_signal(cell->getPort(ID::A)),
+					log_signal(cell->getPort(ID::B)), log_signal(cell->getPort(ID::Y)));
 
-			cell->setPort("\\A", RTLIL::SigSpec());
+			cell->setPort(ID::A, RTLIL::SigSpec());
 			for (auto &in_tuple : consolidated_in_tuples) {
-				RTLIL::SigSpec new_a = cell->getPort("\\A");
+				RTLIL::SigSpec new_a = cell->getPort(ID::A);
 				new_a.append(in_tuple.at(0));
-				cell->setPort("\\A", new_a);
+				cell->setPort(ID::A, new_a);
 			}
 
-			cell->setPort("\\B", RTLIL::SigSpec());
-			for (int i = 1; i <= cell->getPort("\\S").size(); i++)
+			cell->setPort(ID::B, RTLIL::SigSpec());
+			for (int i = 1; i <= cell->getPort(ID(S)).size(); i++)
 				for (auto &in_tuple : consolidated_in_tuples) {
-					RTLIL::SigSpec new_b = cell->getPort("\\B");
+					RTLIL::SigSpec new_b = cell->getPort(ID::B);
 					new_b.append(in_tuple.at(i));
-					cell->setPort("\\B", new_b);
+					cell->setPort(ID::B, new_b);
 				}
 
-			cell->parameters["\\WIDTH"] = RTLIL::Const(new_sig_y.size());
-			cell->setPort("\\Y", new_sig_y);
+			cell->parameters[ID(WIDTH)] = RTLIL::Const(new_sig_y.size());
+			cell->setPort(ID::Y, new_sig_y);
 
-			log("      New ports: A=%s, B=%s, Y=%s\n", log_signal(cell->getPort("\\A")),
-					log_signal(cell->getPort("\\B")), log_signal(cell->getPort("\\Y")));
+			log("      New ports: A=%s, B=%s, Y=%s\n", log_signal(cell->getPort(ID::A)),
+					log_signal(cell->getPort(ID::B)), log_signal(cell->getPort(ID::Y)));
 			log("      New connections: %s = %s\n", log_signal(old_sig_conn.first), log_signal(old_sig_conn.second));
 
 			module->connect(old_sig_conn);
@@ -253,15 +253,15 @@ struct OptReduceWorker
 		SigPool mem_wren_sigs;
 		for (auto &cell_it : module->cells_) {
 			RTLIL::Cell *cell = cell_it.second;
-			if (cell->type == "$mem")
-				mem_wren_sigs.add(assign_map(cell->getPort("\\WR_EN")));
-			if (cell->type == "$memwr")
-				mem_wren_sigs.add(assign_map(cell->getPort("\\EN")));
+			if (cell->type == ID($mem))
+				mem_wren_sigs.add(assign_map(cell->getPort(ID(WR_EN))));
+			if (cell->type == ID($memwr))
+				mem_wren_sigs.add(assign_map(cell->getPort(ID(EN))));
 		}
 		for (auto &cell_it : module->cells_) {
 			RTLIL::Cell *cell = cell_it.second;
-			if (cell->type == "$dff" && mem_wren_sigs.check_any(assign_map(cell->getPort("\\Q"))))
-				mem_wren_sigs.add(assign_map(cell->getPort("\\D")));
+			if (cell->type == ID($dff) && mem_wren_sigs.check_any(assign_map(cell->getPort(ID(Q)))))
+				mem_wren_sigs.add(assign_map(cell->getPort(ID(D))));
 		}
 
 		bool keep_expanding_mem_wren_sigs = true;
@@ -269,12 +269,12 @@ struct OptReduceWorker
 			keep_expanding_mem_wren_sigs = false;
 			for (auto &cell_it : module->cells_) {
 				RTLIL::Cell *cell = cell_it.second;
-				if (cell->type == "$mux" && mem_wren_sigs.check_any(assign_map(cell->getPort("\\Y")))) {
-					if (!mem_wren_sigs.check_all(assign_map(cell->getPort("\\A"))) ||
-							!mem_wren_sigs.check_all(assign_map(cell->getPort("\\B"))))
+				if (cell->type == ID($mux) && mem_wren_sigs.check_any(assign_map(cell->getPort(ID::Y)))) {
+					if (!mem_wren_sigs.check_all(assign_map(cell->getPort(ID::A))) ||
+							!mem_wren_sigs.check_all(assign_map(cell->getPort(ID::B))))
 						keep_expanding_mem_wren_sigs = true;
-					mem_wren_sigs.add(assign_map(cell->getPort("\\A")));
-					mem_wren_sigs.add(assign_map(cell->getPort("\\B")));
+					mem_wren_sigs.add(assign_map(cell->getPort(ID::A)));
+					mem_wren_sigs.add(assign_map(cell->getPort(ID::B)));
 				}
 			}
 		}
@@ -286,7 +286,7 @@ struct OptReduceWorker
 			// merge trees of reduce_* cells to one single cell and unify input vectors
 			// (only handle reduce_and and reduce_or for various reasons)
 
-			const char *type_list[] = { "$reduce_or", "$reduce_and" };
+			const IdString type_list[] = { ID($reduce_or), ID($reduce_and) };
 			for (auto type : type_list)
 			{
 				SigSet<RTLIL::Cell*> drivers;
@@ -296,7 +296,7 @@ struct OptReduceWorker
 					RTLIL::Cell *cell = cell_it.second;
 					if (cell->type != type || !design->selected(module, cell))
 						continue;
-					drivers.insert(assign_map(cell->getPort("\\Y")), cell);
+					drivers.insert(assign_map(cell->getPort(ID::Y)), cell);
 					cells.insert(cell);
 				}
 
@@ -311,14 +311,14 @@ struct OptReduceWorker
 			std::vector<RTLIL::Cell*> cells;
 
 			for (auto &it : module->cells_)
-				if ((it.second->type == "$mux" || it.second->type == "$pmux") && design->selected(module, it.second))
+				if ((it.second->type == ID($mux) || it.second->type == ID($pmux)) && design->selected(module, it.second))
 					cells.push_back(it.second);
 
 			for (auto cell : cells)
 			{
 				// this optimization is to aggressive for most coarse-grain applications.
 				// but we always want it for multiplexers driving write enable ports.
-				if (do_fine || mem_wren_sigs.check_any(assign_map(cell->getPort("\\Y"))))
+				if (do_fine || mem_wren_sigs.check_any(assign_map(cell->getPort(ID::Y))))
 					opt_mux_bits(cell);
 
 				opt_mux(cell);
@@ -329,7 +329,7 @@ struct OptReduceWorker
 
 struct OptReducePass : public Pass {
 	OptReducePass() : Pass("opt_reduce", "simplify large MUXes and AND/OR gates") { }
-	virtual void help()
+	void help() YS_OVERRIDE
 	{
 		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
 		log("\n");
@@ -350,7 +350,7 @@ struct OptReducePass : public Pass {
 		log("      alias for -fine\n");
 		log("\n");
 	}
-	virtual void execute(std::vector<std::string> args, RTLIL::Design *design)
+	void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
 	{
 		bool do_fine = false;
 
diff --git a/passes/opt/opt_rmdff.cc b/passes/opt/opt_rmdff.cc
index b5edb357b..0bf74098a 100644
--- a/passes/opt/opt_rmdff.cc
+++ b/passes/opt/opt_rmdff.cc
@@ -17,26 +17,31 @@
  *
  */
 
+#include "kernel/log.h"
 #include "kernel/register.h"
+#include "kernel/rtlil.h"
+#include "kernel/satgen.h"
 #include "kernel/sigtools.h"
-#include "kernel/log.h"
-#include <stdlib.h>
 #include <stdio.h>
+#include <stdlib.h>
 
 USING_YOSYS_NAMESPACE
 PRIVATE_NAMESPACE_BEGIN
 
 SigMap assign_map, dff_init_map;
 SigSet<RTLIL::Cell*> mux_drivers;
+dict<SigBit, RTLIL::Cell*> bit2driver;
 dict<SigBit, pool<SigBit>> init_attributes;
+
 bool keepdc;
+bool sat;
 
 void remove_init_attr(SigSpec sig)
 {
 	for (auto bit : assign_map(sig))
 		if (init_attributes.count(bit))
 			for (auto wbit : init_attributes.at(bit))
-				wbit.wire->attributes.at("\\init")[wbit.offset] = State::Sx;
+				wbit.wire->attributes.at(ID(init))[wbit.offset] = State::Sx;
 }
 
 bool handle_dffsr(RTLIL::Module *mod, RTLIL::Cell *cell)
@@ -44,39 +49,39 @@ bool handle_dffsr(RTLIL::Module *mod, RTLIL::Cell *cell)
 	SigSpec sig_set, sig_clr;
 	State pol_set, pol_clr;
 
-	if (cell->hasPort("\\S"))
-		sig_set = cell->getPort("\\S");
+	if (cell->hasPort(ID(S)))
+		sig_set = cell->getPort(ID(S));
 
-	if (cell->hasPort("\\R"))
-		sig_clr = cell->getPort("\\R");
+	if (cell->hasPort(ID(R)))
+		sig_clr = cell->getPort(ID(R));
 
-	if (cell->hasPort("\\SET"))
-		sig_set = cell->getPort("\\SET");
+	if (cell->hasPort(ID(SET)))
+		sig_set = cell->getPort(ID(SET));
 
-	if (cell->hasPort("\\CLR"))
-		sig_clr = cell->getPort("\\CLR");
+	if (cell->hasPort(ID(CLR)))
+		sig_clr = cell->getPort(ID(CLR));
 
 	log_assert(GetSize(sig_set) == GetSize(sig_clr));
 
-	if (cell->type.substr(0,8) == "$_DFFSR_") {
+	if (cell->type.begins_with("$_DFFSR_")) {
 		pol_set = cell->type[9] == 'P' ? State::S1 : State::S0;
 		pol_clr = cell->type[10] == 'P' ? State::S1 : State::S0;
 	} else
-	if (cell->type.substr(0,11) == "$_DLATCHSR_") {
+	if (cell->type.begins_with("$_DLATCHSR_")) {
 		pol_set = cell->type[12] == 'P' ? State::S1 : State::S0;
 		pol_clr = cell->type[13] == 'P' ? State::S1 : State::S0;
 	} else
-	if (cell->type == "$dffsr" || cell->type == "$dlatchsr") {
-		pol_set = cell->parameters["\\SET_POLARITY"].as_bool() ? State::S1 : State::S0;
-		pol_clr = cell->parameters["\\CLR_POLARITY"].as_bool() ? State::S1 : State::S0;
+	if (cell->type.in(ID($dffsr), ID($dlatchsr))) {
+		pol_set = cell->parameters[ID(SET_POLARITY)].as_bool() ? State::S1 : State::S0;
+		pol_clr = cell->parameters[ID(CLR_POLARITY)].as_bool() ? State::S1 : State::S0;
 	} else
 		log_abort();
 
 	State npol_set = pol_set == State::S0 ? State::S1 : State::S0;
 	State npol_clr = pol_clr == State::S0 ? State::S1 : State::S0;
 
-	SigSpec sig_d = cell->getPort("\\D");
-	SigSpec sig_q = cell->getPort("\\Q");
+	SigSpec sig_d = cell->getPort(ID(D));
+	SigSpec sig_q = cell->getPort(ID(Q));
 
 	bool did_something = false;
 	bool proper_sr = false;
@@ -132,20 +137,20 @@ bool handle_dffsr(RTLIL::Module *mod, RTLIL::Cell *cell)
 		return true;
 	}
 
-	if (cell->type == "$dffsr" || cell->type == "$dlatchsr")
+	if (cell->type.in(ID($dffsr), ID($dlatchsr)))
 	{
-		cell->setParam("\\WIDTH", GetSize(sig_d));
-		cell->setPort("\\SET", sig_set);
-		cell->setPort("\\CLR", sig_clr);
-		cell->setPort("\\D", sig_d);
-		cell->setPort("\\Q", sig_q);
+		cell->setParam(ID(WIDTH), GetSize(sig_d));
+		cell->setPort(ID(SET), sig_set);
+		cell->setPort(ID(CLR), sig_clr);
+		cell->setPort(ID(D), sig_d);
+		cell->setPort(ID(Q), sig_q);
 	}
 	else
 	{
-		cell->setPort("\\S", sig_set);
-		cell->setPort("\\R", sig_clr);
-		cell->setPort("\\D", sig_d);
-		cell->setPort("\\Q", sig_q);
+		cell->setPort(ID(S), sig_set);
+		cell->setPort(ID(R), sig_clr);
+		cell->setPort(ID(D), sig_d);
+		cell->setPort(ID(Q), sig_q);
 	}
 
 	if (proper_sr)
@@ -154,49 +159,48 @@ bool handle_dffsr(RTLIL::Module *mod, RTLIL::Cell *cell)
 	if (used_pol_set && used_pol_clr && pol_set != pol_clr)
 		return did_something;
 
-	if (cell->type == "$dlatchsr")
+	if (cell->type == ID($dlatchsr))
 		return did_something;
 
 	State unified_pol = used_pol_set ? pol_set : pol_clr;
 
-	if (cell->type == "$dffsr")
+	if (cell->type == ID($dffsr))
 	{
 		if (hasreset)
 		{
 			log("Converting %s (%s) to %s in module %s.\n", log_id(cell), log_id(cell->type), "$adff", log_id(mod));
 
-			cell->type = "$adff";
-			cell->setParam("\\ARST_POLARITY", unified_pol);
-			cell->setParam("\\ARST_VALUE", reset_val);
-			cell->setPort("\\ARST", sig_reset);
+			cell->type = ID($adff);
+			cell->setParam(ID(ARST_POLARITY), unified_pol);
+			cell->setParam(ID(ARST_VALUE), reset_val);
+			cell->setPort(ID(ARST), sig_reset);
 
-			cell->unsetParam("\\SET_POLARITY");
-			cell->unsetParam("\\CLR_POLARITY");
-			cell->unsetPort("\\SET");
-			cell->unsetPort("\\CLR");
-
-			return true;
+			cell->unsetParam(ID(SET_POLARITY));
+			cell->unsetParam(ID(CLR_POLARITY));
+			cell->unsetPort(ID(SET));
+			cell->unsetPort(ID(CLR));
 		}
 		else
 		{
 			log("Converting %s (%s) to %s in module %s.\n", log_id(cell), log_id(cell->type), "$dff", log_id(mod));
 
-			cell->type = "$dff";
-			cell->unsetParam("\\SET_POLARITY");
-			cell->unsetParam("\\CLR_POLARITY");
-			cell->unsetPort("\\SET");
-			cell->unsetPort("\\CLR");
-
-			return true;
+			cell->type = ID($dff);
+			cell->unsetParam(ID(SET_POLARITY));
+			cell->unsetParam(ID(CLR_POLARITY));
+			cell->unsetPort(ID(SET));
+			cell->unsetPort(ID(CLR));
 		}
+
+		return true;
 	}
-	else
+
+	if (!hasreset)
 	{
 		IdString new_type;
 
-		if (cell->type.substr(0,8) == "$_DFFSR_")
+		if (cell->type.begins_with("$_DFFSR_"))
 			new_type = stringf("$_DFF_%c_", cell->type[8]);
-		else if (cell->type.substr(0,11) == "$_DLATCHSR_")
+		else if (cell->type.begins_with("$_DLATCHSR_"))
 			new_type = stringf("$_DLATCH_%c_", cell->type[11]);
 		else
 			log_abort();
@@ -204,11 +208,13 @@ bool handle_dffsr(RTLIL::Module *mod, RTLIL::Cell *cell)
 		log("Converting %s (%s) to %s in module %s.\n", log_id(cell), log_id(cell->type), log_id(new_type), log_id(mod));
 
 		cell->type = new_type;
-		cell->unsetPort("\\S");
-		cell->unsetPort("\\R");
+		cell->unsetPort(ID(S));
+		cell->unsetPort(ID(R));
 
-		return did_something;
+		return true;
 	}
+
+	return did_something;
 }
 
 bool handle_dlatch(RTLIL::Module *mod, RTLIL::Cell *dlatch)
@@ -216,18 +222,18 @@ bool handle_dlatch(RTLIL::Module *mod, RTLIL::Cell *dlatch)
 	SigSpec sig_e;
 	State on_state, off_state;
 
-	if (dlatch->type == "$dlatch") {
-		sig_e = assign_map(dlatch->getPort("\\EN"));
-		on_state = dlatch->getParam("\\EN_POLARITY").as_bool() ? State::S1 : State::S0;
-		off_state = dlatch->getParam("\\EN_POLARITY").as_bool() ? State::S0 : State::S1;
+	if (dlatch->type == ID($dlatch)) {
+		sig_e = assign_map(dlatch->getPort(ID(EN)));
+		on_state = dlatch->getParam(ID(EN_POLARITY)).as_bool() ? State::S1 : State::S0;
+		off_state = dlatch->getParam(ID(EN_POLARITY)).as_bool() ? State::S0 : State::S1;
 	} else
-	if (dlatch->type == "$_DLATCH_P_") {
-		sig_e = assign_map(dlatch->getPort("\\E"));
+	if (dlatch->type == ID($_DLATCH_P_)) {
+		sig_e = assign_map(dlatch->getPort(ID(E)));
 		on_state = State::S1;
 		off_state = State::S0;
 	} else
-	if (dlatch->type == "$_DLATCH_N_") {
-		sig_e = assign_map(dlatch->getPort("\\E"));
+	if (dlatch->type == ID($_DLATCH_N_)) {
+		sig_e = assign_map(dlatch->getPort(ID(E)));
 		on_state = State::S0;
 		off_state = State::S1;
 	} else
@@ -236,15 +242,15 @@ bool handle_dlatch(RTLIL::Module *mod, RTLIL::Cell *dlatch)
 	if (sig_e == off_state)
 	{
 		RTLIL::Const val_init;
-		for (auto bit : dff_init_map(dlatch->getPort("\\Q")))
+		for (auto bit : dff_init_map(dlatch->getPort(ID(Q))))
 			val_init.bits.push_back(bit.wire == NULL ? bit.data : State::Sx);
-		mod->connect(dlatch->getPort("\\Q"), val_init);
+		mod->connect(dlatch->getPort(ID(Q)), val_init);
 		goto delete_dlatch;
 	}
 
 	if (sig_e == on_state)
 	{
-		mod->connect(dlatch->getPort("\\Q"), dlatch->getPort("\\D"));
+		mod->connect(dlatch->getPort(ID(Q)), dlatch->getPort(ID(D)));
 		goto delete_dlatch;
 	}
 
@@ -252,56 +258,74 @@ bool handle_dlatch(RTLIL::Module *mod, RTLIL::Cell *dlatch)
 
 delete_dlatch:
 	log("Removing %s (%s) from module %s.\n", log_id(dlatch), log_id(dlatch->type), log_id(mod));
-	remove_init_attr(dlatch->getPort("\\Q"));
+	remove_init_attr(dlatch->getPort(ID(Q)));
 	mod->remove(dlatch);
 	return true;
 }
 
 bool handle_dff(RTLIL::Module *mod, RTLIL::Cell *dff)
 {
-	RTLIL::SigSpec sig_d, sig_q, sig_c, sig_r;
-	RTLIL::Const val_cp, val_rp, val_rv;
+	RTLIL::SigSpec sig_d, sig_q, sig_c, sig_r, sig_e;
+	RTLIL::Const val_cp, val_rp, val_rv, val_ep;
 
-	if (dff->type == "$_FF_") {
-		sig_d = dff->getPort("\\D");
-		sig_q = dff->getPort("\\Q");
+	if (dff->type == ID($_FF_)) {
+		sig_d = dff->getPort(ID(D));
+		sig_q = dff->getPort(ID(Q));
 	}
-	else if (dff->type == "$_DFF_N_" || dff->type == "$_DFF_P_") {
-		sig_d = dff->getPort("\\D");
-		sig_q = dff->getPort("\\Q");
-		sig_c = dff->getPort("\\C");
-		val_cp = RTLIL::Const(dff->type == "$_DFF_P_", 1);
+	else if (dff->type == ID($_DFF_N_) || dff->type == ID($_DFF_P_)) {
+		sig_d = dff->getPort(ID(D));
+		sig_q = dff->getPort(ID(Q));
+		sig_c = dff->getPort(ID(C));
+		val_cp = RTLIL::Const(dff->type == ID($_DFF_P_), 1);
 	}
-	else if (dff->type.substr(0,6) == "$_DFF_" && dff->type.substr(9) == "_" &&
+	else if (dff->type.begins_with("$_DFF_") && dff->type.compare(9, 1, "_") == 0 &&
 			(dff->type[6] == 'N' || dff->type[6] == 'P') &&
 			(dff->type[7] == 'N' || dff->type[7] == 'P') &&
 			(dff->type[8] == '0' || dff->type[8] == '1')) {
-		sig_d = dff->getPort("\\D");
-		sig_q = dff->getPort("\\Q");
-		sig_c = dff->getPort("\\C");
-		sig_r = dff->getPort("\\R");
+		sig_d = dff->getPort(ID(D));
+		sig_q = dff->getPort(ID(Q));
+		sig_c = dff->getPort(ID(C));
+		sig_r = dff->getPort(ID(R));
 		val_cp = RTLIL::Const(dff->type[6] == 'P', 1);
 		val_rp = RTLIL::Const(dff->type[7] == 'P', 1);
 		val_rv = RTLIL::Const(dff->type[8] == '1', 1);
 	}
-	else if (dff->type == "$ff") {
-		sig_d = dff->getPort("\\D");
-		sig_q = dff->getPort("\\Q");
+	else if (dff->type.begins_with("$_DFFE_") && dff->type.compare(9, 1, "_") == 0 &&
+			(dff->type[7] == 'N' || dff->type[7] == 'P') &&
+			(dff->type[8] == 'N' || dff->type[8] == 'P')) {
+		sig_d = dff->getPort(ID(D));
+		sig_q = dff->getPort(ID(Q));
+		sig_c = dff->getPort(ID(C));
+		sig_e = dff->getPort(ID(E));
+		val_cp = RTLIL::Const(dff->type[7] == 'P', 1);
+		val_ep = RTLIL::Const(dff->type[8] == 'P', 1);
+	}
+	else if (dff->type == ID($ff)) {
+		sig_d = dff->getPort(ID(D));
+		sig_q = dff->getPort(ID(Q));
 	}
-	else if (dff->type == "$dff") {
-		sig_d = dff->getPort("\\D");
-		sig_q = dff->getPort("\\Q");
-		sig_c = dff->getPort("\\CLK");
-		val_cp = RTLIL::Const(dff->parameters["\\CLK_POLARITY"].as_bool(), 1);
+	else if (dff->type == ID($dff)) {
+		sig_d = dff->getPort(ID(D));
+		sig_q = dff->getPort(ID(Q));
+		sig_c = dff->getPort(ID(CLK));
+		val_cp = RTLIL::Const(dff->parameters[ID(CLK_POLARITY)].as_bool(), 1);
 	}
-	else if (dff->type == "$adff") {
-		sig_d = dff->getPort("\\D");
-		sig_q = dff->getPort("\\Q");
-		sig_c = dff->getPort("\\CLK");
-		sig_r = dff->getPort("\\ARST");
-		val_cp = RTLIL::Const(dff->parameters["\\CLK_POLARITY"].as_bool(), 1);
-		val_rp = RTLIL::Const(dff->parameters["\\ARST_POLARITY"].as_bool(), 1);
-		val_rv = dff->parameters["\\ARST_VALUE"];
+	else if (dff->type == ID($dffe)) {
+		sig_e = dff->getPort(ID(EN));
+		sig_d = dff->getPort(ID(D));
+		sig_q = dff->getPort(ID(Q));
+		sig_c = dff->getPort(ID(CLK));
+		val_cp = RTLIL::Const(dff->parameters[ID(CLK_POLARITY)].as_bool(), 1);
+		val_ep = RTLIL::Const(dff->parameters[ID(EN_POLARITY)].as_bool(), 1);
+	}
+	else if (dff->type == ID($adff)) {
+		sig_d = dff->getPort(ID(D));
+		sig_q = dff->getPort(ID(Q));
+		sig_c = dff->getPort(ID(CLK));
+		sig_r = dff->getPort(ID(ARST));
+		val_cp = RTLIL::Const(dff->parameters[ID(CLK_POLARITY)].as_bool(), 1);
+		val_rp = RTLIL::Const(dff->parameters[ID(ARST_POLARITY)].as_bool(), 1);
+		val_rv = dff->parameters[ID(ARST_VALUE)];
 	}
 	else
 		log_abort();
@@ -319,12 +343,12 @@ bool handle_dff(RTLIL::Module *mod, RTLIL::Cell *dff)
 		val_init.bits.push_back(bit.wire == NULL ? bit.data : RTLIL::State::Sx);
 	}
 
-	if (dff->type.in("$ff", "$dff") && mux_drivers.has(sig_d)) {
+	if (dff->type.in(ID($ff), ID($dff)) && mux_drivers.has(sig_d)) {
 		std::set<RTLIL::Cell*> muxes;
 		mux_drivers.find(sig_d, muxes);
 		for (auto mux : muxes) {
-			RTLIL::SigSpec sig_a = assign_map(mux->getPort("\\A"));
-			RTLIL::SigSpec sig_b = assign_map(mux->getPort("\\B"));
+			RTLIL::SigSpec sig_a = assign_map(mux->getPort(ID::A));
+			RTLIL::SigSpec sig_b = assign_map(mux->getPort(ID::B));
 			if (sig_a == sig_q && sig_b.is_fully_const() && (!has_init || val_init == sig_b.as_const())) {
 				mod->connect(sig_q, sig_b);
 				goto delete_dff;
@@ -336,85 +360,207 @@ bool handle_dff(RTLIL::Module *mod, RTLIL::Cell *dff)
 		}
 	}
 
+	// If clock is driven by a constant and (i) no reset signal
+	//                                      (ii) Q has no initial value
+	//                                      (iii) initial value is same as reset value
 	if (!sig_c.empty() && sig_c.is_fully_const() && (!sig_r.size() || !has_init || val_init == val_rv)) {
 		if (val_rv.bits.size() == 0)
 			val_rv = val_init;
+		// Q is permanently reset value or initial value
 		mod->connect(sig_q, val_rv);
 		goto delete_dff;
 	}
 
+	// If D is fully undefined and reset signal present and (i) Q has no initial value
+	//                                                     (ii) initial value is same as reset value
 	if (sig_d.is_fully_undef() && sig_r.size() && (!has_init || val_init == val_rv)) {
+		// Q is permanently reset value
 		mod->connect(sig_q, val_rv);
 		goto delete_dff;
 	}
 
+	// If D is fully undefined and no reset signal and Q has an initial value
 	if (sig_d.is_fully_undef() && !sig_r.size() && has_init) {
+		// Q is permanently initial value
 		mod->connect(sig_q, val_init);
 		goto delete_dff;
 	}
 
+	// If D is fully constant and (i) no reset signal
+	//                            (ii) reset value is same as constant D
+	//                        and (a) has no initial value
+	//                            (b) initial value same as constant D
 	if (sig_d.is_fully_const() && (!sig_r.size() || val_rv == sig_d.as_const()) && (!has_init || val_init == sig_d.as_const())) {
+		// Q is permanently D
 		mod->connect(sig_q, sig_d);
 		goto delete_dff;
 	}
 
+	// If D input is same as Q output and (i) no reset signal
+	//                                    (ii) no initial signal
+	//                                    (iii) initial value is same as reset value
 	if (sig_d == sig_q && (sig_r.empty() || !has_init || val_init == val_rv)) {
+		// Q is permanently reset value or initial value
 		if (sig_r.size())
 			mod->connect(sig_q, val_rv);
-		if (has_init)
+		else if (has_init)
 			mod->connect(sig_q, val_init);
 		goto delete_dff;
 	}
 
+	// If reset signal is present, and is fully constant
 	if (!sig_r.empty() && sig_r.is_fully_const())
 	{
+		// If reset value is permanently active or if reset is undefined
 		if (sig_r == val_rp || sig_r.is_fully_undef()) {
+			// Q is permanently reset value
 			mod->connect(sig_q, val_rv);
 			goto delete_dff;
 		}
 
 		log("Removing unused reset from %s (%s) from module %s.\n", log_id(dff), log_id(dff->type), log_id(mod));
 
-		if (dff->type == "$adff") {
-			dff->type = "$dff";
-			dff->unsetPort("\\ARST");
-			dff->unsetParam("\\ARST_POLARITY");
-			dff->unsetParam("\\ARST_VALUE");
+		if (dff->type == ID($adff)) {
+			dff->type = ID($dff);
+			dff->unsetPort(ID(ARST));
+			dff->unsetParam(ID(ARST_POLARITY));
+			dff->unsetParam(ID(ARST_VALUE));
 			return true;
 		}
 
-		log_assert(dff->type.substr(0,6) == "$_DFF_");
+		log_assert(dff->type.begins_with("$_DFF_"));
 		dff->type = stringf("$_DFF_%c_", + dff->type[6]);
-		dff->unsetPort("\\R");
+		dff->unsetPort(ID(R));
+	}
+
+	// If enable signal is present, and is fully constant
+	if (!sig_e.empty() && sig_e.is_fully_const())
+	{
+		// If enable value is permanently inactive
+		if (sig_e != val_ep) {
+			// Q is permanently initial value
+			mod->connect(sig_q, val_init);
+			goto delete_dff;
+		}
+
+		log("Removing unused enable from %s (%s) from module %s.\n", log_id(dff), log_id(dff->type), log_id(mod));
+
+		if (dff->type == ID($dffe)) {
+			dff->type = ID($dff);
+			dff->unsetPort(ID(EN));
+			dff->unsetParam(ID(EN_POLARITY));
+			return true;
+		}
+
+		log_assert(dff->type.begins_with("$_DFFE_"));
+		dff->type = stringf("$_DFF_%c_", + dff->type[7]);
+		dff->unsetPort(ID(E));
 	}
 
+	if (sat && has_init && (!sig_r.size() || val_init == val_rv))
+	{
+		bool removed_sigbits = false;
+
+		ezSatPtr ez;
+		SatGen satgen(ez.get(), &assign_map);
+		pool<Cell*> sat_cells;
+
+		std::function<void(Cell*)> sat_import_cell = [&](Cell *c) {
+			if (!sat_cells.insert(c).second)
+				return;
+			if (!satgen.importCell(c))
+				return;
+			for (auto &conn : c->connections()) {
+				if (!c->input(conn.first))
+					continue;
+				for (auto bit : assign_map(conn.second))
+					if (bit2driver.count(bit))
+						sat_import_cell(bit2driver.at(bit));
+			}
+		};
+
+		// For each register bit, try to prove that it cannot change from the initial value. If so, remove it
+		for (int position = 0; position < GetSize(sig_d); position += 1) {
+			RTLIL::SigBit q_sigbit = sig_q[position];
+			RTLIL::SigBit d_sigbit = sig_d[position];
+
+			if ((!q_sigbit.wire) || (!d_sigbit.wire))
+				continue;
+
+			if (!bit2driver.count(d_sigbit))
+				continue;
+
+			sat_import_cell(bit2driver.at(d_sigbit));
+
+			RTLIL::State sigbit_init_val = val_init[position];
+			if (sigbit_init_val != State::S0 && sigbit_init_val != State::S1)
+				continue;
+
+			int init_sat_pi = satgen.importSigSpec(sigbit_init_val).front();
+			int q_sat_pi = satgen.importSigBit(q_sigbit);
+			int d_sat_pi = satgen.importSigBit(d_sigbit);
+
+			// Try to find out whether the register bit can change under some circumstances
+			bool counter_example_found = ez->solve(ez->IFF(q_sat_pi, init_sat_pi), ez->NOT(ez->IFF(d_sat_pi, init_sat_pi)));
+
+			// If the register bit cannot change, we can replace it with a constant
+			if (!counter_example_found)
+			{
+				log("Setting constant %d-bit at position %d on %s (%s) from module %s.\n", sigbit_init_val ? 1 : 0,
+						position, log_id(dff), log_id(dff->type), log_id(mod));
+
+				SigSpec tmp = dff->getPort(ID(D));
+				tmp[position] = sigbit_init_val;
+				dff->setPort(ID(D), tmp);
+
+				removed_sigbits = true;
+			}
+		}
+
+		if (removed_sigbits) {
+			handle_dff(mod, dff);
+			return true;
+		}
+	}
+
+
 	return false;
 
 delete_dff:
 	log("Removing %s (%s) from module %s.\n", log_id(dff), log_id(dff->type), log_id(mod));
-	remove_init_attr(dff->getPort("\\Q"));
+	remove_init_attr(dff->getPort(ID(Q)));
 	mod->remove(dff);
+
+	for (auto &entry : bit2driver)
+		if (entry.second == dff)
+			bit2driver.erase(entry.first);
+
 	return true;
 }
 
 struct OptRmdffPass : public Pass {
 	OptRmdffPass() : Pass("opt_rmdff", "remove DFFs with constant inputs") { }
-	virtual void help()
+	void help() YS_OVERRIDE
 	{
 		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
 		log("\n");
-		log("    opt_rmdff [-keepdc] [selection]\n");
+		log("    opt_rmdff [-keepdc] [-sat] [selection]\n");
 		log("\n");
 		log("This pass identifies flip-flops with constant inputs and replaces them with\n");
 		log("a constant driver.\n");
 		log("\n");
+		log("    -sat\n");
+		log("        additionally invoke SAT solver to detect and remove flip-flops (with \n");
+		log("        non-constant inputs) that can also be replaced with a constant driver\n");
+		log("\n");
 	}
-	virtual void execute(std::vector<std::string> args, RTLIL::Design *design)
+	void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
 	{
 		int total_count = 0, total_initdrv = 0;
 		log_header(design, "Executing OPT_RMDFF pass (remove dff with constant values).\n");
 
 		keepdc = false;
+		sat = false;
 
 		size_t argidx;
 		for (argidx = 1; argidx < args.size(); argidx++) {
@@ -422,24 +568,28 @@ struct OptRmdffPass : public Pass {
 				keepdc = true;
 				continue;
 			}
+			if (args[argidx] == "-sat") {
+				sat = true;
+				continue;
+			}
 			break;
 		}
 		extra_args(args, argidx, design);
 
-		for (auto module : design->selected_modules())
-		{
+		for (auto module : design->selected_modules()) {
 			pool<SigBit> driven_bits;
 			dict<SigBit, State> init_bits;
 
 			assign_map.set(module);
 			dff_init_map.set(module);
 			mux_drivers.clear();
+			bit2driver.clear();
 			init_attributes.clear();
 
 			for (auto wire : module->wires())
 			{
-				if (wire->attributes.count("\\init") != 0) {
-					Const initval = wire->attributes.at("\\init");
+				if (wire->attributes.count(ID(init)) != 0) {
+					Const initval = wire->attributes.at(ID(init));
 					for (int i = 0; i < GetSize(initval) && i < GetSize(wire); i++)
 						if (initval[i] == State::S0 || initval[i] == State::S1)
 							dff_init_map.add(SigBit(wire, i), initval[i]);
@@ -458,40 +608,45 @@ struct OptRmdffPass : public Pass {
 						driven_bits.insert(bit);
 				}
 			}
-			mux_drivers.clear();
 
 			std::vector<RTLIL::IdString> dff_list;
 			std::vector<RTLIL::IdString> dffsr_list;
 			std::vector<RTLIL::IdString> dlatch_list;
 			for (auto cell : module->cells())
 			{
-				for (auto &conn : cell->connections())
-					if (cell->output(conn.first) || !cell->known())
-						for (auto bit : assign_map(conn.second))
+				for (auto &conn : cell->connections()) {
+					bool is_output = cell->output(conn.first);
+					if (is_output || !cell->known())
+						for (auto bit : assign_map(conn.second)) {
+							if (is_output)
+								bit2driver[bit] = cell;
 							driven_bits.insert(bit);
+						}
+				}
 
-				if (cell->type == "$mux" || cell->type == "$pmux") {
-					if (cell->getPort("\\A").size() == cell->getPort("\\B").size())
-						mux_drivers.insert(assign_map(cell->getPort("\\Y")), cell);
+				if (cell->type.in(ID($mux), ID($pmux))) {
+					if (cell->getPort(ID::A).size() == cell->getPort(ID::B).size())
+						mux_drivers.insert(assign_map(cell->getPort(ID::Y)), cell);
 					continue;
 				}
 
 				if (!design->selected(module, cell))
 					continue;
 
-				if (cell->type.in("$_DFFSR_NNN_", "$_DFFSR_NNP_", "$_DFFSR_NPN_", "$_DFFSR_NPP_",
-						"$_DFFSR_PNN_", "$_DFFSR_PNP_", "$_DFFSR_PPN_", "$_DFFSR_PPP_", "$dffsr",
-						"$_DLATCHSR_NNN_", "$_DLATCHSR_NNP_", "$_DLATCHSR_NPN_", "$_DLATCHSR_NPP_",
-						"$_DLATCHSR_PNN_", "$_DLATCHSR_PNP_", "$_DLATCHSR_PPN_", "$_DLATCHSR_PPP_", "$dlatchsr"))
+				if (cell->type.in(ID($_DFFSR_NNN_), ID($_DFFSR_NNP_), ID($_DFFSR_NPN_), ID($_DFFSR_NPP_),
+						ID($_DFFSR_PNN_), ID($_DFFSR_PNP_), ID($_DFFSR_PPN_), ID($_DFFSR_PPP_), ID($dffsr),
+						ID($_DLATCHSR_NNN_), ID($_DLATCHSR_NNP_), ID($_DLATCHSR_NPN_), ID($_DLATCHSR_NPP_),
+						ID($_DLATCHSR_PNN_), ID($_DLATCHSR_PNP_), ID($_DLATCHSR_PPN_), ID($_DLATCHSR_PPP_), ID($dlatchsr)))
 					dffsr_list.push_back(cell->name);
 
-				if (cell->type.in("$_FF_", "$_DFF_N_", "$_DFF_P_",
-						"$_DFF_NN0_", "$_DFF_NN1_", "$_DFF_NP0_", "$_DFF_NP1_",
-						"$_DFF_PN0_", "$_DFF_PN1_", "$_DFF_PP0_", "$_DFF_PP1_",
-						"$ff", "$dff", "$adff"))
+				if (cell->type.in(ID($_FF_), ID($_DFF_N_), ID($_DFF_P_),
+						ID($_DFF_NN0_), ID($_DFF_NN1_), ID($_DFF_NP0_), ID($_DFF_NP1_),
+						ID($_DFF_PN0_), ID($_DFF_PN1_), ID($_DFF_PP0_), ID($_DFF_PP1_),
+						ID($_DFFE_NN_), ID($_DFFE_NP_), ID($_DFFE_PN_), ID($_DFFE_PP_),
+						ID($ff), ID($dff), ID($dffe), ID($adff)))
 					dff_list.push_back(cell->name);
 
-				if (cell->type.in("$dlatch", "$_DLATCH_P_", "$_DLATCH_N_"))
+				if (cell->type.in(ID($dlatch), ID($_DLATCH_P_), ID($_DLATCH_N_)))
 					dlatch_list.push_back(cell->name);
 			}
 
@@ -539,6 +694,7 @@ struct OptRmdffPass : public Pass {
 
 		assign_map.clear();
 		mux_drivers.clear();
+		bit2driver.clear();
 		init_attributes.clear();
 
 		if (total_count || total_initdrv)
diff --git a/passes/opt/opt_share.cc b/passes/opt/opt_share.cc
new file mode 100644
index 000000000..2c456705c
--- /dev/null
+++ b/passes/opt/opt_share.cc
@@ -0,0 +1,650 @@
+/*
+ *  yosys -- Yosys Open SYnthesis Suite
+ *
+ *  Copyright (C) 2012  Clifford Wolf <clifford@clifford.at>
+ *                2019  Bogdan Vukobratovic <bogdan.vukobratovic@gmail.com>
+ *
+ *  Permission to use, copy, modify, and/or distribute this software for any
+ *  purpose with or without fee is hereby granted, provided that the above
+ *  copyright notice and this permission notice appear in all copies.
+ *
+ *  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ *  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ *  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ *  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ *  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ *  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ *  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ */
+
+#include "kernel/log.h"
+#include "kernel/register.h"
+#include "kernel/rtlil.h"
+#include "kernel/sigtools.h"
+#include <algorithm>
+
+#include <stdio.h>
+#include <stdlib.h>
+
+USING_YOSYS_NAMESPACE
+PRIVATE_NAMESPACE_BEGIN
+
+SigMap assign_map;
+
+struct OpMuxConn {
+	RTLIL::SigSpec sig;
+	RTLIL::Cell *mux;
+	RTLIL::Cell *op;
+	int mux_port_id;
+	int mux_port_offset;
+	int op_outsig_offset;
+
+	bool operator<(const OpMuxConn &other) const
+	{
+		if (mux != other.mux)
+			return mux < other.mux;
+
+		if (mux_port_id != other.mux_port_id)
+			return mux_port_id < other.mux_port_id;
+
+		return mux_port_offset < other.mux_port_offset;
+	}
+};
+
+// Helper class to track additiona information about a SigSpec, like whether it is signed and the semantics of the port it is connected to
+struct ExtSigSpec {
+	RTLIL::SigSpec sig;
+	RTLIL::SigSpec sign;
+	bool is_signed;
+	RTLIL::IdString semantics;
+
+	ExtSigSpec() {}
+
+	ExtSigSpec(RTLIL::SigSpec s, RTLIL::SigSpec sign = RTLIL::Const(0, 1), bool is_signed = false, RTLIL::IdString semantics = RTLIL::IdString()) : sig(s), sign(sign), is_signed(is_signed), semantics(semantics) {}
+
+	bool empty() const { return sig.empty(); }
+
+	bool operator<(const ExtSigSpec &other) const
+	{
+		if (sig != other.sig)
+			return sig < other.sig;
+
+		if (sign != other.sign)
+			return sign < other.sign;
+
+		if (is_signed != other.is_signed)
+			return is_signed < other.is_signed;
+
+		return semantics < other.semantics;
+	}
+
+	bool operator==(const RTLIL::SigSpec &other) const { return (sign != RTLIL::Const(0, 1)) ? false : sig == other; }
+	bool operator==(const ExtSigSpec &other) const { return is_signed == other.is_signed && sign == other.sign && sig == other.sig && semantics == other.semantics; }
+};
+
+#define BITWISE_OPS ID($_AND_), ID($_NAND_), ID($_OR_), ID($_NOR_), ID($_XOR_), ID($_XNOR_), ID($_ANDNOT_), ID($_ORNOT_), ID($and), ID($or), ID($xor), ID($xnor)
+
+#define REDUCTION_OPS ID($reduce_and), ID($reduce_or), ID($reduce_xor), ID($reduce_xnor), ID($reduce_bool), ID($reduce_nand)
+
+#define LOGICAL_OPS ID($logic_and), ID($logic_or)
+
+#define SHIFT_OPS ID($shl), ID($shr), ID($sshl), ID($sshr), ID($shift), ID($shiftx)
+
+#define RELATIONAL_OPS ID($lt), ID($le), ID($eq), ID($ne), ID($eqx), ID($nex), ID($ge), ID($gt)
+
+bool cell_supported(RTLIL::Cell *cell)
+{
+	if (cell->type.in(ID($alu))) {
+		RTLIL::SigSpec sig_bi = cell->getPort(ID(BI));
+		RTLIL::SigSpec sig_ci = cell->getPort(ID(CI));
+
+		if (sig_bi.is_fully_const() && sig_ci.is_fully_const() && sig_bi == sig_ci)
+			return true;
+	} else if (cell->type.in(LOGICAL_OPS, SHIFT_OPS, BITWISE_OPS, RELATIONAL_OPS, ID($add), ID($sub), ID($mul), ID($div), ID($mod), ID($concat))) {
+		return true;
+	}
+
+	return false;
+}
+
+std::map<IdString, IdString> mergeable_type_map;
+
+bool mergeable(RTLIL::Cell *a, RTLIL::Cell *b)
+{
+	if (mergeable_type_map.empty()) {
+		mergeable_type_map.insert({ID($sub), ID($add)});
+	}
+	auto a_type = a->type;
+	if (mergeable_type_map.count(a_type))
+		a_type = mergeable_type_map.at(a_type);
+
+	auto b_type = b->type;
+	if (mergeable_type_map.count(b_type))
+		b_type = mergeable_type_map.at(b_type);
+
+	return a_type == b_type;
+}
+
+RTLIL::IdString decode_port_semantics(RTLIL::Cell *cell, RTLIL::IdString port_name)
+{
+	if (cell->type.in(ID($lt), ID($le), ID($ge), ID($gt), ID($div), ID($mod), ID($concat), SHIFT_OPS) && port_name == ID::B)
+		return port_name;
+
+	return "";
+}
+
+RTLIL::SigSpec decode_port_sign(RTLIL::Cell *cell, RTLIL::IdString port_name) {
+
+	if (cell->type == ID($alu) && port_name == ID::B)
+		return cell->getPort(ID(BI));
+	else if (cell->type == ID($sub) && port_name == ID::B)
+		return RTLIL::Const(1, 1);
+
+	return RTLIL::Const(0, 1);
+}
+
+bool decode_port_signed(RTLIL::Cell *cell, RTLIL::IdString port_name)
+{
+	if (cell->type.in(BITWISE_OPS, LOGICAL_OPS))
+		return false;
+
+	if (cell->hasParam(port_name.str() + "_SIGNED"))
+		return cell->getParam(port_name.str() + "_SIGNED").as_bool();
+
+	return false;
+}
+
+ExtSigSpec decode_port(RTLIL::Cell *cell, RTLIL::IdString port_name, SigMap *sigmap)
+{
+	auto sig = (*sigmap)(cell->getPort(port_name));
+
+	RTLIL::SigSpec sign = decode_port_sign(cell, port_name);
+	RTLIL::IdString semantics = decode_port_semantics(cell, port_name);
+
+	bool is_signed = decode_port_signed(cell, port_name);
+
+	return ExtSigSpec(sig, sign, is_signed, semantics);
+}
+
+void merge_operators(RTLIL::Module *module, RTLIL::Cell *mux, const std::vector<OpMuxConn> &ports, const ExtSigSpec &operand)
+{
+	std::vector<ExtSigSpec> muxed_operands;
+	int max_width = 0;
+	for (const auto& p : ports) {
+		auto op = p.op;
+
+		RTLIL::IdString muxed_port_name = ID::A;
+		if (decode_port(op, ID::A, &assign_map) == operand)
+			muxed_port_name = ID::B;
+
+		auto operand = decode_port(op, muxed_port_name, &assign_map);
+		if (operand.sig.size() > max_width)
+			max_width = operand.sig.size();
+
+		muxed_operands.push_back(operand);
+	}
+
+	auto shared_op = ports[0].op;
+
+	if (std::any_of(muxed_operands.begin(), muxed_operands.end(), [&](ExtSigSpec &op) { return op.sign != muxed_operands[0].sign; }))
+        max_width = std::max(max_width, shared_op->getParam(ID(Y_WIDTH)).as_int());
+
+
+	for (auto &operand : muxed_operands)
+		operand.sig.extend_u0(max_width, operand.is_signed);
+
+	for (const auto& p : ports) {
+		auto op = p.op;
+		if (op == shared_op)
+			continue;
+		module->remove(op);
+	}
+
+	for (auto &muxed_op : muxed_operands)
+		if (muxed_op.sign != muxed_operands[0].sign)
+			muxed_op = ExtSigSpec(module->Neg(NEW_ID, muxed_op.sig, muxed_op.is_signed));
+
+	RTLIL::SigSpec mux_y = mux->getPort(ID::Y);
+	RTLIL::SigSpec mux_a = mux->getPort(ID::A);
+	RTLIL::SigSpec mux_b = mux->getPort(ID::B);
+	RTLIL::SigSpec mux_s = mux->getPort(ID(S));
+
+	RTLIL::SigSpec shared_pmux_a = RTLIL::Const(RTLIL::State::Sx, max_width);
+	RTLIL::SigSpec shared_pmux_b;
+	RTLIL::SigSpec shared_pmux_s;
+
+	int conn_width = ports[0].sig.size();
+	int conn_offset = ports[0].mux_port_offset;
+
+	shared_op->setPort(ID::Y, shared_op->getPort(ID::Y).extract(0, conn_width));
+
+	if (mux->type == ID($pmux)) {
+		shared_pmux_s = RTLIL::SigSpec();
+
+		for (const auto &p : ports) {
+			shared_pmux_s.append(mux_s[p.mux_port_id]);
+			mux_b.replace(p.mux_port_id * mux_a.size() + conn_offset, shared_op->getPort(ID::Y));
+		}
+	} else {
+		shared_pmux_s = RTLIL::SigSpec{mux_s, module->Not(NEW_ID, mux_s)};
+		mux_a.replace(conn_offset, shared_op->getPort(ID::Y));
+		mux_b.replace(conn_offset, shared_op->getPort(ID::Y));
+	}
+
+	mux->setPort(ID::A, mux_a);
+	mux->setPort(ID::B, mux_b);
+	mux->setPort(ID::Y, mux_y);
+	mux->setPort(ID(S), mux_s);
+
+	for (const auto &op : muxed_operands)
+		shared_pmux_b.append(op.sig);
+
+	auto mux_to_oper = module->Pmux(NEW_ID, shared_pmux_a, shared_pmux_b, shared_pmux_s);
+
+	if (shared_op->type.in(ID($alu))) {
+		RTLIL::SigSpec alu_x = shared_op->getPort(ID(X));
+		RTLIL::SigSpec alu_co = shared_op->getPort(ID(CO));
+
+		shared_op->setPort(ID(X), alu_x.extract(0, conn_width));
+		shared_op->setPort(ID(CO), alu_co.extract(0, conn_width));
+	}
+
+	shared_op->setParam(ID(Y_WIDTH), conn_width);
+
+	if (decode_port(shared_op, ID::A, &assign_map) == operand) {
+		shared_op->setPort(ID::B, mux_to_oper);
+		shared_op->setParam(ID(B_WIDTH), max_width);
+	} else {
+		shared_op->setPort(ID::A, mux_to_oper);
+		shared_op->setParam(ID(A_WIDTH), max_width);
+	}
+}
+
+typedef struct {
+	RTLIL::Cell *mux;
+	std::vector<OpMuxConn> ports;
+	ExtSigSpec shared_operand;
+} merged_op_t;
+
+
+template <typename T> void remove_val(std::vector<T> &v, const std::vector<T> &vals)
+{
+	auto val_iter = vals.rbegin();
+	for (auto i = v.rbegin(); i != v.rend(); ++i)
+		if ((val_iter != vals.rend()) && (*i == *val_iter)) {
+			v.erase(i.base() - 1);
+			++val_iter;
+		}
+}
+
+void check_muxed_operands(std::vector<const OpMuxConn *> &ports, const ExtSigSpec &shared_operand)
+{
+	auto it = ports.begin();
+	ExtSigSpec seed;
+
+	while (it != ports.end()) {
+		auto p = *it;
+		auto op = p->op;
+
+		RTLIL::IdString muxed_port_name = ID::A;
+		if (decode_port(op, ID::A, &assign_map) == shared_operand) {
+			muxed_port_name = ID::B;
+		}
+
+		auto operand = decode_port(op, muxed_port_name, &assign_map);
+
+		if (seed.empty())
+			seed = operand;
+
+		if (operand.is_signed != seed.is_signed) {
+			ports.erase(it);
+		} else {
+			++it;
+		}
+	}
+}
+
+ExtSigSpec find_shared_operand(const OpMuxConn* seed, std::vector<const OpMuxConn *> &ports, const std::map<ExtSigSpec, std::set<RTLIL::Cell *>> &operand_to_users)
+{
+	std::set<RTLIL::Cell *> ops_using_operand;
+	std::set<RTLIL::Cell *> ops_set;
+	for(const auto& p: ports)
+		ops_set.insert(p->op);
+
+	ExtSigSpec oper;
+
+	auto op_a = seed->op;
+
+	for (RTLIL::IdString port_name : {ID::A, ID::B}) {
+		oper = decode_port(op_a, port_name, &assign_map);
+		auto operand_users = operand_to_users.at(oper);
+
+		if (operand_users.size() == 1)
+			continue;
+
+		ops_using_operand.clear();
+		for (auto mux_ops: ops_set)
+			if (operand_users.count(mux_ops))
+				ops_using_operand.insert(mux_ops);
+
+		if (ops_using_operand.size() > 1) {
+			ports.erase(std::remove_if(ports.begin(), ports.end(), [&](const OpMuxConn *p) { return !ops_using_operand.count(p->op); }),
+						ports.end());
+			return oper;
+		}
+	}
+
+	return ExtSigSpec();
+}
+
+dict<RTLIL::SigSpec, OpMuxConn> find_valid_op_mux_conns(RTLIL::Module *module, dict<RTLIL::SigBit, RTLIL::SigSpec> &op_outbit_to_outsig,
+							dict<RTLIL::SigSpec, RTLIL::Cell *> outsig_to_operator,
+							dict<RTLIL::SigBit, RTLIL::SigSpec> &op_aux_to_outsig)
+{
+	dict<RTLIL::SigSpec, int> op_outsig_user_track;
+	dict<RTLIL::SigSpec, OpMuxConn> op_mux_conn_map;
+
+	std::function<void(RTLIL::SigSpec)> remove_outsig = [&](RTLIL::SigSpec outsig) {
+		for (auto op_outbit : outsig)
+			op_outbit_to_outsig.erase(op_outbit);
+
+		if (op_mux_conn_map.count(outsig))
+			op_mux_conn_map.erase(outsig);
+	};
+
+	std::function<void(RTLIL::SigBit)> remove_outsig_from_aux_bit = [&](RTLIL::SigBit auxbit) {
+		auto aux_outsig = op_aux_to_outsig.at(auxbit);
+		auto op = outsig_to_operator.at(aux_outsig);
+		auto op_outsig = assign_map(op->getPort(ID::Y));
+		remove_outsig(op_outsig);
+
+		for (auto aux_outbit : aux_outsig)
+			op_aux_to_outsig.erase(aux_outbit);
+	};
+
+	std::function<void(RTLIL::Cell *)> find_op_mux_conns = [&](RTLIL::Cell *mux) {
+		RTLIL::SigSpec sig;
+		int mux_port_size;
+
+		if (mux->type.in(ID($mux), ID($_MUX_))) {
+			mux_port_size = mux->getPort(ID::A).size();
+			sig = RTLIL::SigSpec{mux->getPort(ID::B), mux->getPort(ID::A)};
+		} else {
+			mux_port_size = mux->getPort(ID::A).size();
+			sig = mux->getPort(ID::B);
+		}
+
+		auto mux_insig = assign_map(sig);
+
+		for (int i = 0; i < mux_insig.size(); ++i) {
+			if (op_aux_to_outsig.count(mux_insig[i])) {
+				remove_outsig_from_aux_bit(mux_insig[i]);
+				continue;
+			}
+
+			if (!op_outbit_to_outsig.count(mux_insig[i]))
+				continue;
+
+			auto op_outsig = op_outbit_to_outsig.at(mux_insig[i]);
+
+			if (op_mux_conn_map.count(op_outsig)) {
+				remove_outsig(op_outsig);
+				continue;
+			}
+
+			int mux_port_id = i / mux_port_size;
+			int mux_port_offset = i % mux_port_size;
+
+			int op_outsig_offset;
+			for (op_outsig_offset = 0; op_outsig[op_outsig_offset] != mux_insig[i]; ++op_outsig_offset)
+				;
+
+			int j = op_outsig_offset;
+			do {
+				if (!op_outbit_to_outsig.count(mux_insig[i]))
+					break;
+
+				if (op_outbit_to_outsig.at(mux_insig[i]) != op_outsig)
+					break;
+
+				++i;
+				++j;
+			} while ((i / mux_port_size == mux_port_id) && (j < op_outsig.size()));
+
+			int op_conn_width = j - op_outsig_offset;
+			OpMuxConn inp = {
+				op_outsig.extract(op_outsig_offset, op_conn_width),
+				mux,
+				outsig_to_operator.at(op_outsig),
+				mux_port_id,
+				mux_port_offset,
+				op_outsig_offset,
+			};
+
+			op_mux_conn_map[op_outsig] = inp;
+
+			--i;
+		}
+	};
+
+	std::function<void(RTLIL::SigSpec)> remove_connected_ops = [&](RTLIL::SigSpec sig) {
+		auto mux_insig = assign_map(sig);
+		for (auto outbit : mux_insig) {
+			if (op_aux_to_outsig.count(outbit)) {
+				remove_outsig_from_aux_bit(outbit);
+				continue;
+			}
+
+			if (!op_outbit_to_outsig.count(outbit))
+				continue;
+
+			remove_outsig(op_outbit_to_outsig.at(outbit));
+		}
+	};
+
+	for (auto cell : module->cells()) {
+		if (cell->type.in(ID($mux), ID($_MUX_), ID($pmux))) {
+			remove_connected_ops(cell->getPort(ID(S)));
+			find_op_mux_conns(cell);
+		} else {
+			for (auto &conn : cell->connections())
+				if (cell->input(conn.first))
+					remove_connected_ops(conn.second);
+		}
+	}
+
+	for (auto w : module->wires()) {
+		if (!w->port_output)
+			continue;
+
+		remove_connected_ops(w);
+	}
+
+	return op_mux_conn_map;
+}
+
+struct OptSharePass : public Pass {
+	OptSharePass() : Pass("opt_share", "merge mutually exclusive cells of the same type that share an input signal") {}
+	void help() YS_OVERRIDE
+	{
+		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
+		log("\n");
+		log("    opt_share [selection]\n");
+		log("\n");
+
+		log("This pass identifies mutually exclusive cells of the same type that:\n");
+		log("    (a) share an input signal,\n");
+		log("    (b) drive the same $mux, $_MUX_, or $pmux multiplexing cell,\n");
+		log("\n");
+		log("allowing the cell to be merged and the multiplexer to be moved from\n");
+		log("multiplexing its output to multiplexing the non-shared input signals.\n");
+		log("\n");
+	}
+	void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
+	{
+
+		log_header(design, "Executing OPT_SHARE pass.\n");
+
+		extra_args(args, 1, design);
+		for (auto module : design->selected_modules()) {
+			assign_map.clear();
+			assign_map.set(module);
+
+			std::map<ExtSigSpec, std::set<RTLIL::Cell *>> operand_to_users;
+			dict<RTLIL::SigSpec, RTLIL::Cell *> outsig_to_operator;
+			dict<RTLIL::SigBit, RTLIL::SigSpec> op_outbit_to_outsig;
+			dict<RTLIL::SigBit, RTLIL::SigSpec> op_aux_to_outsig;
+			bool any_shared_operands = false;
+			std::vector<ExtSigSpec> op_insigs;
+
+			for (auto cell : module->cells()) {
+				if (!cell_supported(cell))
+					continue;
+
+				if (cell->type == ID($alu)) {
+					for (RTLIL::IdString port_name : {ID(X), ID(CO)}) {
+						auto mux_insig = assign_map(cell->getPort(port_name));
+						outsig_to_operator[mux_insig] = cell;
+						for (auto outbit : mux_insig)
+							op_aux_to_outsig[outbit] = mux_insig;
+					}
+				}
+
+				auto mux_insig = assign_map(cell->getPort(ID::Y));
+				outsig_to_operator[mux_insig] = cell;
+				for (auto outbit : mux_insig)
+					op_outbit_to_outsig[outbit] = mux_insig;
+
+				for (RTLIL::IdString port_name : {ID::A, ID::B}) {
+					auto op_insig = decode_port(cell, port_name, &assign_map);
+					op_insigs.push_back(op_insig);
+					operand_to_users[op_insig].insert(cell);
+					if (operand_to_users[op_insig].size() > 1)
+						any_shared_operands = true;
+				}
+			}
+
+			if (!any_shared_operands)
+				continue;
+
+			// Operator outputs need to be exclusively connected to the $mux inputs in order to be mergeable. Hence we count to
+			// how many points are operator output bits connected.
+			dict<RTLIL::SigSpec, OpMuxConn> op_mux_conn_map =
+			  find_valid_op_mux_conns(module, op_outbit_to_outsig, outsig_to_operator, op_aux_to_outsig);
+
+			// Group op connections connected to same ports of the same $mux. Sort them in ascending order of their port offset
+			dict<RTLIL::Cell*, std::vector<std::set<OpMuxConn>>> mux_port_op_conns;
+			for (auto& val: op_mux_conn_map) {
+				OpMuxConn p = val.second;
+				auto& mux_port_conns = mux_port_op_conns[p.mux];
+
+				if (mux_port_conns.size() == 0) {
+					int mux_port_num;
+
+					if (p.mux->type.in(ID($mux), ID($_MUX_)))
+						mux_port_num = 2;
+					else
+						mux_port_num = p.mux->getPort(ID(S)).size();
+
+					mux_port_conns.resize(mux_port_num);
+				}
+
+				mux_port_conns[p.mux_port_id].insert(p);
+			}
+
+			std::vector<merged_op_t> merged_ops;
+			for (auto& val: mux_port_op_conns) {
+
+				RTLIL::Cell* cell = val.first;
+				auto &mux_port_conns = val.second;
+
+				const OpMuxConn *seed = NULL;
+
+				// Look through the bits of the $mux inputs and see which of them are connected to the operator
+				// results. Operator results can be concatenated with other signals before led to the $mux.
+				while (true) {
+
+					// Remove either the merged ports from the last iteration or the seed that failed to yield a merger
+					if (seed != NULL) {
+						mux_port_conns[seed->mux_port_id].erase(*seed);
+						seed = NULL;
+					}
+
+					// For a new merger, find the seed op connection that starts at lowest port offset among port connections
+					for (auto &port_conns : mux_port_conns) {
+						if (!port_conns.size())
+							continue;
+
+						const OpMuxConn *next_p = &(*port_conns.begin());
+
+						if ((seed == NULL) || (seed->mux_port_offset > next_p->mux_port_offset))
+							seed = next_p;
+					}
+
+					// Cannot find the seed -> nothing to do for this $mux anymore
+					if (seed == NULL)
+						break;
+
+					// Find all other op connections that start from the same port offset, and whose ops can be merged with the seed op
+					std::vector<const OpMuxConn *> mergeable_conns;
+					for (auto &port_conns : mux_port_conns) {
+						if (!port_conns.size())
+							continue;
+
+						const OpMuxConn *next_p = &(*port_conns.begin());
+
+						if ((next_p->op_outsig_offset == seed->op_outsig_offset) &&
+						    (next_p->mux_port_offset == seed->mux_port_offset) && mergeable(next_p->op, seed->op) &&
+						    next_p->sig.size() == seed->sig.size())
+							mergeable_conns.push_back(next_p);
+					}
+
+					// We need at least two mergeable connections for the merger
+					if (mergeable_conns.size() < 2)
+						continue;
+
+					// Filter mergeable connections whose ops share an operand with seed connection's op
+					auto shared_operand = find_shared_operand(seed, mergeable_conns, operand_to_users);
+
+					if (shared_operand.empty())
+						continue;
+
+					check_muxed_operands(mergeable_conns, shared_operand);
+
+					if (mergeable_conns.size() < 2)
+						continue;
+
+					// Remember the combination for the merger
+					std::vector<OpMuxConn> merged_ports;
+					for (auto p : mergeable_conns) {
+						merged_ports.push_back(*p);
+						mux_port_conns[p->mux_port_id].erase(*p);
+					}
+
+					seed = NULL;
+
+					merged_ops.push_back(merged_op_t{cell, merged_ports, shared_operand});
+
+					design->scratchpad_set_bool("opt.did_something", true);
+				}
+
+			}
+
+			for (auto &shared : merged_ops) {
+				log("    Found cells that share an operand and can be merged by moving the %s %s in front "
+				    "of "
+				    "them:\n",
+				    log_id(shared.mux->type), log_id(shared.mux));
+				for (const auto& op : shared.ports)
+					log("        %s\n", log_id(op.op));
+				log("\n");
+
+				merge_operators(module, shared.mux, shared.ports, shared.shared_operand);
+			}
+		}
+	}
+
+} OptSharePass;
+
+PRIVATE_NAMESPACE_END
diff --git a/passes/opt/pmux2shiftx.cc b/passes/opt/pmux2shiftx.cc
new file mode 100644
index 000000000..92b5794ac
--- /dev/null
+++ b/passes/opt/pmux2shiftx.cc
@@ -0,0 +1,860 @@
+/*
+ *  yosys -- Yosys Open SYnthesis Suite
+ *
+ *  Copyright (C) 2012  Clifford Wolf <clifford@clifford.at>
+ *
+ *  Permission to use, copy, modify, and/or distribute this software for any
+ *  purpose with or without fee is hereby granted, provided that the above
+ *  copyright notice and this permission notice appear in all copies.
+ *
+ *  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ *  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ *  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ *  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ *  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ *  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ *  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ */
+
+#include "kernel/yosys.h"
+#include "kernel/sigtools.h"
+
+USING_YOSYS_NAMESPACE
+PRIVATE_NAMESPACE_BEGIN
+
+struct OnehotDatabase
+{
+	Module *module;
+	const SigMap &sigmap;
+	bool verbose = false;
+	bool initialized = false;
+
+	pool<SigBit> init_ones;
+	dict<SigSpec, pool<SigSpec>> sig_sources_db;
+	dict<SigSpec, bool> sig_onehot_cache;
+	pool<SigSpec> recursion_guard;
+
+	OnehotDatabase(Module *module, const SigMap &sigmap) : module(module), sigmap(sigmap)
+	{
+	}
+
+	void initialize()
+	{
+		log_assert(!initialized);
+		initialized = true;
+
+		for (auto wire : module->wires())
+		{
+			auto it = wire->attributes.find(ID(init));
+			if (it == wire->attributes.end())
+				continue;
+
+			auto &val = it->second;
+			int width = std::max(GetSize(wire), GetSize(val));
+
+			for (int i = 0; i < width; i++)
+				if (val[i] == State::S1)
+					init_ones.insert(sigmap(SigBit(wire, i)));
+		}
+
+		for (auto cell : module->cells())
+		{
+			vector<SigSpec> inputs;
+			SigSpec output;
+
+			if (cell->type.in(ID($adff), ID($dff), ID($dffe), ID($dlatch), ID($ff)))
+			{
+				output = cell->getPort(ID(Q));
+				if (cell->type == ID($adff))
+					inputs.push_back(cell->getParam(ID(ARST_VALUE)));
+				inputs.push_back(cell->getPort(ID(D)));
+			}
+
+			if (cell->type.in(ID($mux), ID($pmux)))
+			{
+				output = cell->getPort(ID::Y);
+				inputs.push_back(cell->getPort(ID::A));
+				SigSpec B = cell->getPort(ID::B);
+				for (int i = 0; i < GetSize(B); i += GetSize(output))
+					inputs.push_back(B.extract(i, GetSize(output)));
+			}
+
+			if (!output.empty())
+			{
+				output = sigmap(output);
+				auto &srcs = sig_sources_db[output];
+				for (auto src : inputs) {
+					while (!src.empty() && src[GetSize(src)-1] == State::S0)
+						src.remove(GetSize(src)-1);
+					srcs.insert(sigmap(src));
+				}
+			}
+		}
+	}
+
+	void query_worker(const SigSpec &sig, bool &retval, bool &cache, int indent)
+	{
+		if (verbose)
+			log("%*s %s\n", indent, "", log_signal(sig));
+		log_assert(retval);
+
+		if (recursion_guard.count(sig)) {
+			if (verbose)
+				log("%*s   - recursion\n", indent, "");
+			cache = false;
+			return;
+		}
+
+		auto it = sig_onehot_cache.find(sig);
+		if (it != sig_onehot_cache.end()) {
+			if (verbose)
+				log("%*s   - cached (%s)\n", indent, "", it->second ? "true" : "false");
+			if (!it->second)
+				retval = false;
+			return;
+		}
+
+		bool found_init_ones = false;
+		for (auto bit : sig) {
+			if (init_ones.count(bit)) {
+				if (found_init_ones) {
+					if (verbose)
+						log("%*s   - non-onehot init value\n", indent, "");
+					retval = false;
+					break;
+				}
+				found_init_ones = true;
+			}
+		}
+
+		if (retval)
+		{
+			if (sig.is_fully_const())
+			{
+				bool found_ones = false;
+				for (auto bit : sig) {
+					if (bit == State::S1) {
+						if (found_ones) {
+							if (verbose)
+								log("%*s   - non-onehot constant\n", indent, "");
+							retval = false;
+							break;
+						}
+						found_ones = true;
+					}
+				}
+			}
+			else
+			{
+				auto srcs = sig_sources_db.find(sig);
+				if (srcs == sig_sources_db.end()) {
+					if (verbose)
+						log("%*s   - no sources for non-const signal\n", indent, "");
+					retval = false;
+				} else {
+					for (auto &src : srcs->second) {
+						bool child_cache = true;
+						recursion_guard.insert(sig);
+						query_worker(src, retval, child_cache, indent+4);
+						recursion_guard.erase(sig);
+						if (!child_cache)
+							cache = false;
+						if (!retval)
+							break;
+					}
+				}
+			}
+		}
+
+		// it is always safe to cache a negative result
+		if (cache || !retval)
+			sig_onehot_cache[sig] = retval;
+	}
+
+	bool query(const SigSpec &sig)
+	{
+		bool retval = true;
+		bool cache = true;
+
+		if (verbose)
+			log("** ONEHOT QUERY START (%s)\n", log_signal(sig));
+
+		if (!initialized)
+			initialize();
+
+		query_worker(sig, retval, cache, 3);
+
+		if (verbose)
+			log("** ONEHOT QUERY RESULT = %s\n", retval ? "true" : "false");
+
+		// it is always safe to cache the root result of a query
+		if (!cache)
+			sig_onehot_cache[sig] = retval;
+
+		return retval;
+	}
+};
+
+struct Pmux2ShiftxPass : public Pass {
+	Pmux2ShiftxPass() : Pass("pmux2shiftx", "transform $pmux cells to $shiftx cells") { }
+	void help() YS_OVERRIDE
+	{
+		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
+		log("\n");
+		log("    pmux2shiftx [options] [selection]\n");
+		log("\n");
+		log("This pass transforms $pmux cells to $shiftx cells.\n");
+		log("\n");
+		log("    -v, -vv\n");
+		log("        verbose output\n");
+		log("\n");
+		log("    -min_density <percentage>\n");
+		log("        specifies the minimum density for the shifter\n");
+		log("        default: 50\n");
+		log("\n");
+		log("    -min_choices <int>\n");
+		log("        specified the minimum number of choices for a control signal\n");
+		log("        default: 3\n");
+		log("\n");
+		log("    -onehot ignore|pmux|shiftx\n");
+		log("        select strategy for one-hot encoded control signals\n");
+		log("        default: pmux\n");
+		log("\n");
+		log("    -norange\n");
+		log("        disable $sub inference for \"range decoders\"\n");
+		log("\n");
+	}
+	void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
+	{
+		int min_density = 50;
+		int min_choices = 3;
+		bool allow_onehot = false;
+		bool optimize_onehot = true;
+		bool verbose = false;
+		bool verbose_onehot = false;
+		bool norange = false;
+
+		log_header(design, "Executing PMUX2SHIFTX pass.\n");
+
+		size_t argidx;
+		for (argidx = 1; argidx < args.size(); argidx++) {
+			if (args[argidx] == "-min_density" && argidx+1 < args.size()) {
+				min_density = atoi(args[++argidx].c_str());
+				continue;
+			}
+			if (args[argidx] == "-min_choices" && argidx+1 < args.size()) {
+				min_choices = atoi(args[++argidx].c_str());
+				continue;
+			}
+			if (args[argidx] == "-onehot" && argidx+1 < args.size() && args[argidx+1] == "ignore") {
+				argidx++;
+				allow_onehot = false;
+				optimize_onehot = false;
+				continue;
+			}
+			if (args[argidx] == "-onehot" && argidx+1 < args.size() && args[argidx+1] == "pmux") {
+				argidx++;
+				allow_onehot = false;
+				optimize_onehot = true;
+				continue;
+			}
+			if (args[argidx] == "-onehot" && argidx+1 < args.size() && args[argidx+1] == "shiftx") {
+				argidx++;
+				allow_onehot = true;
+				optimize_onehot = false;
+				continue;
+			}
+			if (args[argidx] == "-v") {
+				verbose = true;
+				continue;
+			}
+			if (args[argidx] == "-vv") {
+				verbose = true;
+				verbose_onehot = true;
+				continue;
+			}
+			if (args[argidx] == "-norange") {
+				norange = true;
+				continue;
+			}
+			break;
+		}
+		extra_args(args, argidx, design);
+
+		for (auto module : design->selected_modules())
+		{
+			SigMap sigmap(module);
+			OnehotDatabase onehot_db(module, sigmap);
+			onehot_db.verbose = verbose_onehot;
+
+			dict<SigBit, pair<SigSpec, Const>> eqdb;
+
+			for (auto cell : module->cells())
+			{
+				if (cell->type == ID($eq))
+				{
+					dict<SigBit, State> bits;
+
+					SigSpec A = sigmap(cell->getPort(ID::A));
+					SigSpec B = sigmap(cell->getPort(ID::B));
+
+					int a_width = cell->getParam(ID(A_WIDTH)).as_int();
+					int b_width = cell->getParam(ID(B_WIDTH)).as_int();
+
+					if (a_width < b_width) {
+						bool a_signed = cell->getParam(ID(A_SIGNED)).as_int();
+						A.extend_u0(b_width, a_signed);
+					}
+
+					if (b_width < a_width) {
+						bool b_signed = cell->getParam(ID(B_SIGNED)).as_int();
+						B.extend_u0(a_width, b_signed);
+					}
+
+					for (int i = 0; i < GetSize(A); i++) {
+						SigBit a_bit = A[i], b_bit = B[i];
+						if (b_bit.wire && !a_bit.wire) {
+							std::swap(a_bit, b_bit);
+						}
+						if (!a_bit.wire || b_bit.wire)
+							goto next_cell;
+						if (bits.count(a_bit))
+							goto next_cell;
+						bits[a_bit] = b_bit.data;
+					}
+
+					if (GetSize(bits) > 20)
+						goto next_cell;
+
+					bits.sort();
+					pair<SigSpec, Const> entry;
+
+					for (auto it : bits) {
+						entry.first.append_bit(it.first);
+						entry.second.bits.push_back(it.second);
+					}
+
+					eqdb[sigmap(cell->getPort(ID::Y)[0])] = entry;
+					goto next_cell;
+				}
+
+				if (cell->type == ID($logic_not))
+				{
+					dict<SigBit, State> bits;
+
+					SigSpec A = sigmap(cell->getPort(ID::A));
+
+					for (int i = 0; i < GetSize(A); i++)
+						bits[A[i]] = State::S0;
+
+					bits.sort();
+					pair<SigSpec, Const> entry;
+
+					for (auto it : bits) {
+						entry.first.append_bit(it.first);
+						entry.second.bits.push_back(it.second);
+					}
+
+					eqdb[sigmap(cell->getPort(ID::Y)[0])] = entry;
+					goto next_cell;
+				}
+		next_cell:;
+			}
+
+			for (auto cell : module->selected_cells())
+			{
+				if (cell->type != ID($pmux))
+					continue;
+
+				string src = cell->get_src_attribute();
+				int width = cell->getParam(ID(WIDTH)).as_int();
+				int width_bits = ceil_log2(width);
+				int extwidth = width;
+
+				while (extwidth & (extwidth-1))
+					extwidth++;
+
+				dict<SigSpec, pool<int>> seldb;
+
+				SigSpec A = cell->getPort(ID::A);
+				SigSpec B = cell->getPort(ID::B);
+				SigSpec S = sigmap(cell->getPort(ID(S)));
+				for (int i = 0; i < GetSize(S); i++)
+				{
+					if (!eqdb.count(S[i]))
+						continue;
+
+					auto &entry = eqdb.at(S[i]);
+					seldb[entry.first].insert(i);
+				}
+
+				if (seldb.empty())
+					continue;
+
+				bool printed_pmux_header = false;
+
+				if (verbose) {
+					printed_pmux_header = true;
+					log("Inspecting $pmux cell %s/%s.\n", log_id(module), log_id(cell));
+					log("  data width: %d (next power-of-2 = %d, log2 = %d)\n", width, extwidth, width_bits);
+				}
+
+				SigSpec updated_S = cell->getPort(ID(S));
+				SigSpec updated_B = cell->getPort(ID::B);
+
+				while (!seldb.empty())
+				{
+					// pick the largest entry in seldb
+					SigSpec sig = seldb.begin()->first;
+					for (auto &it : seldb) {
+						if (GetSize(sig) < GetSize(it.first))
+							sig = it.first;
+						else if (GetSize(seldb.at(sig)) < GetSize(it.second))
+							sig = it.first;
+					}
+
+					// find the relevant choices
+					bool is_onehot = GetSize(sig) > 2;
+					dict<Const, int> choices;
+					for (int i : seldb.at(sig)) {
+						Const val = eqdb.at(S[i]).second;
+						int onebits = 0;
+						for (auto b : val.bits)
+							if (b == State::S1)
+								onebits++;
+						if (onebits > 1)
+							is_onehot = false;
+						choices[val] = i;
+					}
+
+					bool full_pmux = GetSize(choices) == GetSize(S);
+
+					// TBD: also find choices that are using signals that are subsets of the bits in "sig"
+
+					if (!verbose)
+					{
+						if (is_onehot && !allow_onehot && !optimize_onehot) {
+							seldb.erase(sig);
+							continue;
+						}
+
+						if (GetSize(choices) < min_choices) {
+							seldb.erase(sig);
+							continue;
+						}
+					}
+
+					if (!printed_pmux_header) {
+						printed_pmux_header = true;
+						log("Inspecting $pmux cell %s/%s.\n", log_id(module), log_id(cell));
+						log("  data width: %d (next power-of-2 = %d, log2 = %d)\n", width, extwidth, width_bits);
+					}
+
+					log("  checking ctrl signal %s\n", log_signal(sig));
+
+					auto print_choices = [&]() {
+						log("    table of choices:\n");
+						for (auto &it : choices)
+							log("    %3d: %s: %s\n", it.second, log_signal(it.first),
+									log_signal(B.extract(it.second*width, width)));
+					};
+
+					if (verbose)
+					{
+						if (is_onehot && !allow_onehot && !optimize_onehot) {
+							print_choices();
+							log("    ignoring one-hot encoding.\n");
+							seldb.erase(sig);
+							continue;
+						}
+
+						if (GetSize(choices) < min_choices) {
+							print_choices();
+							log("    insufficient choices.\n");
+							seldb.erase(sig);
+							continue;
+						}
+					}
+
+					if (is_onehot && optimize_onehot)
+					{
+						print_choices();
+						if (!onehot_db.query(sig))
+						{
+							log("    failed to detect onehot driver. do not optimize.\n");
+						}
+						else
+						{
+							log("    optimizing one-hot encoding.\n");
+							for (auto &it : choices)
+							{
+								const Const &val = it.first;
+								int index = -1;
+
+								for (int i = 0; i < GetSize(val); i++)
+									if (val[i] == State::S1) {
+										log_assert(index < 0);
+										index = i;
+									}
+
+								if (index < 0) {
+									log("    %3d: zero encoding.\n", it.second);
+									continue;
+								}
+
+								SigBit new_ctrl = sig[index];
+								log("    %3d: new crtl signal is %s.\n", it.second, log_signal(new_ctrl));
+								updated_S[it.second] = new_ctrl;
+							}
+						}
+						seldb.erase(sig);
+						continue;
+					}
+
+					// find the best permutation
+					vector<int> perm_new_from_old(GetSize(sig));
+					Const perm_xormask(State::S0, GetSize(sig));
+					{
+						vector<int> values(GetSize(choices));
+						vector<bool> used_src_columns(GetSize(sig));
+						vector<vector<bool>> columns(GetSize(sig), vector<bool>(GetSize(values)));
+
+						for (int i = 0; i < GetSize(choices); i++) {
+							Const val = choices.element(i)->first;
+							for (int k = 0; k < GetSize(val); k++)
+								if (val[k] == State::S1)
+									columns[k][i] = true;
+						}
+
+						for (int dst_col = GetSize(sig)-1; dst_col >= 0; dst_col--)
+						{
+							int best_src_col = -1;
+							bool best_inv = false;
+							int best_maxval = 0;
+							int best_delta = 0;
+
+							// find best src column for this dst column
+							for (int src_col = 0; src_col < GetSize(sig); src_col++)
+							{
+								if (used_src_columns[src_col])
+									continue;
+
+								int this_maxval = 0;
+								int this_minval = 1 << 30;
+
+								int this_inv_maxval = 0;
+								int this_inv_minval = 1 << 30;
+
+								for (int i = 0; i < GetSize(values); i++)
+								{
+									int val = values[i];
+									int inv_val = val;
+
+									if (columns[src_col][i])
+										val |= 1 << dst_col;
+									else
+										inv_val |= 1 << dst_col;
+
+									this_maxval = std::max(this_maxval, val);
+									this_minval = std::min(this_minval, val);
+
+									this_inv_maxval = std::max(this_inv_maxval, inv_val);
+									this_inv_minval = std::min(this_inv_minval, inv_val);
+								}
+
+								int this_delta = this_maxval - this_minval;
+								int this_inv_delta = this_maxval - this_minval;
+								bool this_inv = false;
+
+								if (!norange && this_delta != this_inv_delta)
+									this_inv = this_inv_delta < this_delta;
+								else if (this_maxval != this_inv_maxval)
+									this_inv = this_inv_maxval < this_maxval;
+
+								if (this_inv) {
+									this_delta = this_inv_delta;
+									this_maxval = this_inv_maxval;
+									this_minval = this_inv_minval;
+								}
+
+								bool this_is_better = false;
+
+								if (best_src_col < 0)
+									this_is_better = true;
+								else if (!norange && this_delta != best_delta)
+									this_is_better = this_delta < best_delta;
+								else if (this_maxval != best_maxval)
+									this_is_better = this_maxval < best_maxval;
+								else
+									this_is_better = sig[best_src_col] < sig[src_col];
+
+								if (this_is_better) {
+									best_src_col = src_col;
+									best_inv = this_inv;
+									best_maxval = this_maxval;
+									best_delta = this_delta;
+								}
+							}
+
+							used_src_columns[best_src_col] = true;
+							perm_new_from_old[dst_col] = best_src_col;
+							perm_xormask[dst_col] = best_inv ? State::S1 : State::S0;
+						}
+					}
+
+					// permutated sig
+					SigSpec perm_sig(State::S0, GetSize(sig));
+					for (int i = 0; i < GetSize(sig); i++)
+						perm_sig[i] = sig[perm_new_from_old[i]];
+
+					log("    best permutation: %s\n", log_signal(perm_sig));
+					log("    best xor mask: %s\n", log_signal(perm_xormask));
+
+					// permutated choices
+					int min_choice = 1 << 30;
+					int max_choice = -1;
+					dict<Const, int> perm_choices;
+
+					for (auto &it : choices)
+					{
+						Const &old_c = it.first;
+						Const new_c(State::S0, GetSize(old_c));
+
+						for (int i = 0; i < GetSize(old_c); i++)
+							new_c[i] = old_c[perm_new_from_old[i]];
+
+						Const new_c_before_xor = new_c;
+						new_c = const_xor(new_c, perm_xormask, false, false, GetSize(new_c));
+
+						perm_choices[new_c] = it.second;
+
+						min_choice = std::min(min_choice, new_c.as_int());
+						max_choice = std::max(max_choice, new_c.as_int());
+
+						log("    %3d: %s -> %s -> %s: %s\n", it.second, log_signal(old_c), log_signal(new_c_before_xor),
+								log_signal(new_c), log_signal(B.extract(it.second*width, width)));
+					}
+
+					int range_density = 100*GetSize(choices) / (max_choice-min_choice+1);
+					int absolute_density = 100*GetSize(choices) / (max_choice+1);
+
+					log("    choices: %d\n", GetSize(choices));
+					log("    min choice: %d\n", min_choice);
+					log("    max choice: %d\n", max_choice);
+					log("    range density: %d%%\n", range_density);
+					log("    absolute density: %d%%\n", absolute_density);
+
+					if (full_pmux) {
+						int full_density = 100*GetSize(choices) / (1 << GetSize(sig));
+						log("    full density: %d%%\n", full_density);
+						if (full_density < min_density) {
+							full_pmux = false;
+						} else {
+							min_choice = 0;
+							max_choice = (1 << GetSize(sig))-1;
+							log("    update to full case.\n");
+							log("    new min choice: %d\n", min_choice);
+							log("    new max choice: %d\n", max_choice);
+						}
+					}
+
+					bool full_case = (min_choice == 0) && (max_choice == (1 << GetSize(sig))-1) && (full_pmux || max_choice+1 == GetSize(choices));
+					log("    full case: %s\n", full_case ? "true" : "false");
+
+					// check density percentages
+					Const offset(State::S0, GetSize(sig));
+					if (!norange && absolute_density < min_density && range_density >= min_density)
+					{
+						offset = Const(min_choice, GetSize(sig));
+						log("    offset: %s\n", log_signal(offset));
+
+						min_choice -= offset.as_int();
+						max_choice -= offset.as_int();
+
+						dict<Const, int> new_perm_choices;
+						for (auto &it : perm_choices)
+							new_perm_choices[const_sub(it.first, offset, false, false, GetSize(sig))] = it.second;
+						perm_choices.swap(new_perm_choices);
+					} else
+					if (absolute_density < min_density) {
+						log("    insufficient density.\n");
+						seldb.erase(sig);
+						continue;
+					}
+
+					// creat cmp signal
+					SigSpec cmp = perm_sig;
+					if (perm_xormask.as_bool())
+						cmp = module->Xor(NEW_ID, cmp, perm_xormask, false, src);
+					if (offset.as_bool())
+						cmp = module->Sub(NEW_ID, cmp, offset, false, src);
+
+					// create enable signal
+					SigBit en = State::S1;
+					if (!full_case) {
+						Const enable_mask(State::S0, max_choice+1);
+						for (auto &it : perm_choices)
+							enable_mask[it.first.as_int()] = State::S1;
+						en = module->addWire(NEW_ID);
+						module->addShift(NEW_ID, enable_mask, cmp, en, false, src);
+					}
+
+					// create data signal
+					SigSpec data(State::Sx, (max_choice+1)*extwidth);
+					if (full_pmux) {
+						for (int i = 0; i <= max_choice; i++)
+							data.replace(i*extwidth, A);
+					}
+					for (auto &it : perm_choices) {
+						int position = it.first.as_int()*extwidth;
+						int data_index = it.second;
+						data.replace(position, B.extract(data_index*width, width));
+						updated_S[data_index] = State::S0;
+						updated_B.replace(data_index*width, SigSpec(State::Sx, width));
+					}
+
+					// create shiftx cell
+					SigSpec shifted_cmp = {cmp, SigSpec(State::S0, width_bits)};
+					SigSpec outsig = module->addWire(NEW_ID, width);
+					Cell *c = module->addShiftx(NEW_ID, data, shifted_cmp, outsig, false, src);
+					updated_S.append(en);
+					updated_B.append(outsig);
+					log("    created $shiftx cell %s.\n", log_id(c));
+
+					// remove this sig and continue with the next block
+					seldb.erase(sig);
+				}
+
+				// update $pmux cell
+				cell->setPort(ID(S), updated_S);
+				cell->setPort(ID::B, updated_B);
+				cell->setParam(ID(S_WIDTH), GetSize(updated_S));
+			}
+		}
+	}
+} Pmux2ShiftxPass;
+
+struct OnehotPass : public Pass {
+	OnehotPass() : Pass("onehot", "optimize $eq cells for onehot signals") { }
+	void help() YS_OVERRIDE
+	{
+		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
+		log("\n");
+		log("    onehot [options] [selection]\n");
+		log("\n");
+		log("This pass optimizes $eq cells that compare one-hot signals against constants\n");
+		log("\n");
+		log("    -v, -vv\n");
+		log("        verbose output\n");
+		log("\n");
+	}
+	void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
+	{
+		bool verbose = false;
+		bool verbose_onehot = false;
+
+		log_header(design, "Executing ONEHOT pass.\n");
+
+		size_t argidx;
+		for (argidx = 1; argidx < args.size(); argidx++) {
+			if (args[argidx] == "-v") {
+				verbose = true;
+				continue;
+			}
+			if (args[argidx] == "-vv") {
+				verbose = true;
+				verbose_onehot = true;
+				continue;
+			}
+			break;
+		}
+		extra_args(args, argidx, design);
+
+		for (auto module : design->selected_modules())
+		{
+			SigMap sigmap(module);
+			OnehotDatabase onehot_db(module, sigmap);
+			onehot_db.verbose = verbose_onehot;
+
+			for (auto cell : module->selected_cells())
+			{
+				if (cell->type != ID($eq))
+					continue;
+
+				SigSpec A = sigmap(cell->getPort(ID::A));
+				SigSpec B = sigmap(cell->getPort(ID::B));
+
+				int a_width = cell->getParam(ID(A_WIDTH)).as_int();
+				int b_width = cell->getParam(ID(B_WIDTH)).as_int();
+
+				if (a_width < b_width) {
+					bool a_signed = cell->getParam(ID(A_SIGNED)).as_int();
+					A.extend_u0(b_width, a_signed);
+				}
+
+				if (b_width < a_width) {
+					bool b_signed = cell->getParam(ID(B_SIGNED)).as_int();
+					B.extend_u0(a_width, b_signed);
+				}
+
+				if (A.is_fully_const())
+					std::swap(A, B);
+
+				if (!B.is_fully_const())
+					continue;
+
+				if (verbose)
+					log("Checking $eq(%s, %s) cell %s/%s.\n", log_signal(A), log_signal(B), log_id(module), log_id(cell));
+
+				if (!onehot_db.query(A)) {
+					if (verbose)
+						log("  onehot driver test on %s failed.\n", log_signal(A));
+					continue;
+				}
+
+				int index = -1;
+				bool not_onehot = false;
+
+				for (int i = 0; i < GetSize(B); i++) {
+					if (B[i] != State::S1)
+						continue;
+					if (index >= 0)
+						not_onehot = true;
+					index = i;
+				}
+
+				if (index < 0) {
+					if (verbose)
+						log("  not optimizing the zero pattern.\n");
+					continue;
+				}
+
+				SigSpec Y = cell->getPort(ID::Y);
+
+				if (not_onehot)
+				{
+					if (verbose)
+						log("  replacing with constant 0 driver.\n");
+					else
+						log("Replacing one-hot $eq(%s, %s) cell %s/%s with constant 0 driver.\n", log_signal(A), log_signal(B), log_id(module), log_id(cell));
+					module->connect(Y, SigSpec(1, GetSize(Y)));
+				}
+				else
+				{
+					SigSpec sig = A[index];
+					if (verbose)
+						log("  replacing with signal %s.\n", log_signal(sig));
+					else
+						log("Replacing one-hot $eq(%s, %s) cell %s/%s with signal %s.\n",log_signal(A), log_signal(B), log_id(module), log_id(cell), log_signal(sig));
+					sig.extend_u0(GetSize(Y));
+					module->connect(Y, sig);
+				}
+
+				module->remove(cell);
+			}
+		}
+	}
+} OnehotPass;
+
+PRIVATE_NAMESPACE_END
diff --git a/passes/opt/rmports.cc b/passes/opt/rmports.cc
index 756be7473..32363dd68 100644
--- a/passes/opt/rmports.cc
+++ b/passes/opt/rmports.cc
@@ -28,7 +28,7 @@ PRIVATE_NAMESPACE_BEGIN
 
 struct RmportsPassPass : public Pass {
 	RmportsPassPass() : Pass("rmports", "remove module ports with no connections") { }
-	virtual void help()
+	void help() YS_OVERRIDE
 	{
 		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
 		log("\n");
@@ -39,7 +39,7 @@ struct RmportsPassPass : public Pass {
 		log("\n");
 	}
 
-	virtual void execute(std::vector<std::string> args, RTLIL::Design *design)
+	void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
 	{
 		log_header(design, "Executing RMPORTS pass (remove ports with no connections).\n");
 
@@ -171,7 +171,7 @@ struct RmportsPassPass : public Pass {
 			wire->port_output = false;
 			wire->port_id = 0;
 		}
-		log("Removed %zu unused ports.\n", unused_ports.size());
+		log("Removed %d unused ports.\n", GetSize(unused_ports));
 
 		// Re-number all of the wires that DO have ports still on them
 		for(size_t i=0; i<module->ports.size(); i++)
diff --git a/passes/opt/share.cc b/passes/opt/share.cc
index 22914eaa7..92ce3fd11 100644
--- a/passes/opt/share.cc
+++ b/passes/opt/share.cc
@@ -89,8 +89,8 @@ struct ShareWorker
 			queue_bits.clear();
 
 			for (auto &pbit : portbits) {
-				if (pbit.cell->type == "$mux" || pbit.cell->type == "$pmux") {
-					pool<RTLIL::SigBit> bits = modwalker.sigmap(pbit.cell->getPort("\\S")).to_sigbit_pool();
+				if (pbit.cell->type == ID($mux) || pbit.cell->type == ID($pmux)) {
+					pool<RTLIL::SigBit> bits = modwalker.sigmap(pbit.cell->getPort(ID(S))).to_sigbit_pool();
 					terminal_bits.insert(bits.begin(), bits.end());
 					queue_bits.insert(bits.begin(), bits.end());
 					visited_cells.insert(pbit.cell);
@@ -128,7 +128,7 @@ struct ShareWorker
 	static int bits_macc(RTLIL::Cell *c)
 	{
 		Macc m(c);
-		int width = GetSize(c->getPort("\\Y"));
+		int width = GetSize(c->getPort(ID::Y));
 		return bits_macc(m, width);
 	}
 
@@ -242,7 +242,7 @@ struct ShareWorker
 	{
 		Macc m1(c1), m2(c2), supermacc;
 
-		int w1 = GetSize(c1->getPort("\\Y")), w2 = GetSize(c2->getPort("\\Y"));
+		int w1 = GetSize(c1->getPort(ID::Y)), w2 = GetSize(c2->getPort(ID::Y));
 		int width = max(w1, w2);
 
 		m1.optimize(w1);
@@ -328,11 +328,11 @@ struct ShareWorker
 		{
 			RTLIL::SigSpec sig_y = module->addWire(NEW_ID, width);
 
-			supercell_aux->insert(module->addPos(NEW_ID, sig_y, c1->getPort("\\Y")));
-			supercell_aux->insert(module->addPos(NEW_ID, sig_y, c2->getPort("\\Y")));
+			supercell_aux->insert(module->addPos(NEW_ID, sig_y, c1->getPort(ID::Y)));
+			supercell_aux->insert(module->addPos(NEW_ID, sig_y, c2->getPort(ID::Y)));
 
-			supercell->setParam("\\Y_WIDTH", width);
-			supercell->setPort("\\Y", sig_y);
+			supercell->setParam(ID(Y_WIDTH), width);
+			supercell->setPort(ID::Y, sig_y);
 
 			supermacc.optimize(width);
 			supermacc.to_cell(supercell);
@@ -368,22 +368,22 @@ struct ShareWorker
 				continue;
 			}
 
-			if (cell->type == "$memrd") {
-				if (cell->parameters.at("\\CLK_ENABLE").as_bool())
+			if (cell->type == ID($memrd)) {
+				if (cell->parameters.at(ID(CLK_ENABLE)).as_bool())
 					continue;
-				if (config.opt_aggressive || !modwalker.sigmap(cell->getPort("\\ADDR")).is_fully_const())
+				if (config.opt_aggressive || !modwalker.sigmap(cell->getPort(ID(ADDR))).is_fully_const())
 					shareable_cells.insert(cell);
 				continue;
 			}
 
-			if (cell->type == "$mul" || cell->type == "$div" || cell->type == "$mod") {
-				if (config.opt_aggressive || cell->parameters.at("\\Y_WIDTH").as_int() >= 4)
+			if (cell->type.in(ID($mul), ID($div), ID($mod))) {
+				if (config.opt_aggressive || cell->parameters.at(ID(Y_WIDTH)).as_int() >= 4)
 					shareable_cells.insert(cell);
 				continue;
 			}
 
-			if (cell->type == "$shl" || cell->type == "$shr" || cell->type == "$sshl" || cell->type == "$sshr") {
-				if (config.opt_aggressive || cell->parameters.at("\\Y_WIDTH").as_int() >= 8)
+			if (cell->type.in(ID($shl), ID($shr), ID($sshl), ID($sshr))) {
+				if (config.opt_aggressive || cell->parameters.at(ID(Y_WIDTH)).as_int() >= 8)
 					shareable_cells.insert(cell);
 				continue;
 			}
@@ -401,9 +401,9 @@ struct ShareWorker
 		if (c1->type != c2->type)
 			return false;
 
-		if (c1->type == "$memrd")
+		if (c1->type == ID($memrd))
 		{
-			if (c1->parameters.at("\\MEMID").decode_string() != c2->parameters.at("\\MEMID").decode_string())
+			if (c1->parameters.at(ID(MEMID)).decode_string() != c2->parameters.at(ID(MEMID)).decode_string())
 				return false;
 
 			return true;
@@ -413,11 +413,11 @@ struct ShareWorker
 		{
 			if (!config.opt_aggressive)
 			{
-				int a1_width = c1->parameters.at("\\A_WIDTH").as_int();
-				int y1_width = c1->parameters.at("\\Y_WIDTH").as_int();
+				int a1_width = c1->parameters.at(ID(A_WIDTH)).as_int();
+				int y1_width = c1->parameters.at(ID(Y_WIDTH)).as_int();
 
-				int a2_width = c2->parameters.at("\\A_WIDTH").as_int();
-				int y2_width = c2->parameters.at("\\Y_WIDTH").as_int();
+				int a2_width = c2->parameters.at(ID(A_WIDTH)).as_int();
+				int y2_width = c2->parameters.at(ID(Y_WIDTH)).as_int();
 
 				if (max(a1_width, a2_width) > 2 * min(a1_width, a2_width)) return false;
 				if (max(y1_width, y2_width) > 2 * min(y1_width, y2_width)) return false;
@@ -426,17 +426,17 @@ struct ShareWorker
 			return true;
 		}
 
-		if (config.generic_bin_ops.count(c1->type) || c1->type == "$alu")
+		if (config.generic_bin_ops.count(c1->type) || c1->type == ID($alu))
 		{
 			if (!config.opt_aggressive)
 			{
-				int a1_width = c1->parameters.at("\\A_WIDTH").as_int();
-				int b1_width = c1->parameters.at("\\B_WIDTH").as_int();
-				int y1_width = c1->parameters.at("\\Y_WIDTH").as_int();
+				int a1_width = c1->parameters.at(ID(A_WIDTH)).as_int();
+				int b1_width = c1->parameters.at(ID(B_WIDTH)).as_int();
+				int y1_width = c1->parameters.at(ID(Y_WIDTH)).as_int();
 
-				int a2_width = c2->parameters.at("\\A_WIDTH").as_int();
-				int b2_width = c2->parameters.at("\\B_WIDTH").as_int();
-				int y2_width = c2->parameters.at("\\Y_WIDTH").as_int();
+				int a2_width = c2->parameters.at(ID(A_WIDTH)).as_int();
+				int b2_width = c2->parameters.at(ID(B_WIDTH)).as_int();
+				int y2_width = c2->parameters.at(ID(Y_WIDTH)).as_int();
 
 				if (max(a1_width, a2_width) > 2 * min(a1_width, a2_width)) return false;
 				if (max(b1_width, b2_width) > 2 * min(b1_width, b2_width)) return false;
@@ -450,13 +450,13 @@ struct ShareWorker
 		{
 			if (!config.opt_aggressive)
 			{
-				int a1_width = c1->parameters.at("\\A_WIDTH").as_int();
-				int b1_width = c1->parameters.at("\\B_WIDTH").as_int();
-				int y1_width = c1->parameters.at("\\Y_WIDTH").as_int();
+				int a1_width = c1->parameters.at(ID(A_WIDTH)).as_int();
+				int b1_width = c1->parameters.at(ID(B_WIDTH)).as_int();
+				int y1_width = c1->parameters.at(ID(Y_WIDTH)).as_int();
 
-				int a2_width = c2->parameters.at("\\A_WIDTH").as_int();
-				int b2_width = c2->parameters.at("\\B_WIDTH").as_int();
-				int y2_width = c2->parameters.at("\\Y_WIDTH").as_int();
+				int a2_width = c2->parameters.at(ID(A_WIDTH)).as_int();
+				int b2_width = c2->parameters.at(ID(B_WIDTH)).as_int();
+				int y2_width = c2->parameters.at(ID(Y_WIDTH)).as_int();
 
 				int min1_width = min(a1_width, b1_width);
 				int max1_width = max(a1_width, b1_width);
@@ -472,7 +472,7 @@ struct ShareWorker
 			return true;
 		}
 
-		if (c1->type == "$macc")
+		if (c1->type == ID($macc))
 		{
 			if (!config.opt_aggressive)
 				if (share_macc(c1, c2) > 2 * min(bits_macc(c1), bits_macc(c2))) return false;
@@ -510,27 +510,27 @@ struct ShareWorker
 
 		if (config.generic_uni_ops.count(c1->type))
 		{
-			if (c1->parameters.at("\\A_SIGNED").as_bool() != c2->parameters.at("\\A_SIGNED").as_bool())
+			if (c1->parameters.at(ID(A_SIGNED)).as_bool() != c2->parameters.at(ID(A_SIGNED)).as_bool())
 			{
-				RTLIL::Cell *unsigned_cell = c1->parameters.at("\\A_SIGNED").as_bool() ? c2 : c1;
-				if (unsigned_cell->getPort("\\A").to_sigbit_vector().back() != RTLIL::State::S0) {
-					unsigned_cell->parameters.at("\\A_WIDTH") = unsigned_cell->parameters.at("\\A_WIDTH").as_int() + 1;
-					RTLIL::SigSpec new_a = unsigned_cell->getPort("\\A");
+				RTLIL::Cell *unsigned_cell = c1->parameters.at(ID(A_SIGNED)).as_bool() ? c2 : c1;
+				if (unsigned_cell->getPort(ID::A).to_sigbit_vector().back() != RTLIL::State::S0) {
+					unsigned_cell->parameters.at(ID(A_WIDTH)) = unsigned_cell->parameters.at(ID(A_WIDTH)).as_int() + 1;
+					RTLIL::SigSpec new_a = unsigned_cell->getPort(ID::A);
 					new_a.append_bit(RTLIL::State::S0);
-					unsigned_cell->setPort("\\A", new_a);
+					unsigned_cell->setPort(ID::A, new_a);
 				}
-				unsigned_cell->parameters.at("\\A_SIGNED") = true;
+				unsigned_cell->parameters.at(ID(A_SIGNED)) = true;
 				unsigned_cell->check();
 			}
 
-			bool a_signed = c1->parameters.at("\\A_SIGNED").as_bool();
-			log_assert(a_signed == c2->parameters.at("\\A_SIGNED").as_bool());
+			bool a_signed = c1->parameters.at(ID(A_SIGNED)).as_bool();
+			log_assert(a_signed == c2->parameters.at(ID(A_SIGNED)).as_bool());
 
-			RTLIL::SigSpec a1 = c1->getPort("\\A");
-			RTLIL::SigSpec y1 = c1->getPort("\\Y");
+			RTLIL::SigSpec a1 = c1->getPort(ID::A);
+			RTLIL::SigSpec y1 = c1->getPort(ID::Y);
 
-			RTLIL::SigSpec a2 = c2->getPort("\\A");
-			RTLIL::SigSpec y2 = c2->getPort("\\Y");
+			RTLIL::SigSpec a2 = c2->getPort(ID::A);
+			RTLIL::SigSpec y2 = c2->getPort(ID::Y);
 
 			int a_width = max(a1.size(), a2.size());
 			int y_width = max(y1.size(), y2.size());
@@ -544,11 +544,11 @@ struct ShareWorker
 			RTLIL::Wire *y = module->addWire(NEW_ID, y_width);
 
 			RTLIL::Cell *supercell = module->addCell(NEW_ID, c1->type);
-			supercell->parameters["\\A_SIGNED"] = a_signed;
-			supercell->parameters["\\A_WIDTH"] = a_width;
-			supercell->parameters["\\Y_WIDTH"] = y_width;
-			supercell->setPort("\\A", a);
-			supercell->setPort("\\Y", y);
+			supercell->parameters[ID(A_SIGNED)] = a_signed;
+			supercell->parameters[ID(A_WIDTH)] = a_width;
+			supercell->parameters[ID(Y_WIDTH)] = y_width;
+			supercell->setPort(ID::A, a);
+			supercell->setPort(ID::Y, y);
 
 			supercell_aux.insert(module->addPos(NEW_ID, y, y1));
 			supercell_aux.insert(module->addPos(NEW_ID, y, y2));
@@ -557,54 +557,54 @@ struct ShareWorker
 			return supercell;
 		}
 
-		if (config.generic_bin_ops.count(c1->type) || config.generic_cbin_ops.count(c1->type) || c1->type == "$alu")
+		if (config.generic_bin_ops.count(c1->type) || config.generic_cbin_ops.count(c1->type) || c1->type == ID($alu))
 		{
 			bool modified_src_cells = false;
 
 			if (config.generic_cbin_ops.count(c1->type))
 			{
-				int score_unflipped = max(c1->parameters.at("\\A_WIDTH").as_int(), c2->parameters.at("\\A_WIDTH").as_int()) +
-						max(c1->parameters.at("\\B_WIDTH").as_int(), c2->parameters.at("\\B_WIDTH").as_int());
+				int score_unflipped = max(c1->parameters.at(ID(A_WIDTH)).as_int(), c2->parameters.at(ID(A_WIDTH)).as_int()) +
+						max(c1->parameters.at(ID(B_WIDTH)).as_int(), c2->parameters.at(ID(B_WIDTH)).as_int());
 
-				int score_flipped = max(c1->parameters.at("\\A_WIDTH").as_int(), c2->parameters.at("\\B_WIDTH").as_int()) +
-						max(c1->parameters.at("\\B_WIDTH").as_int(), c2->parameters.at("\\A_WIDTH").as_int());
+				int score_flipped = max(c1->parameters.at(ID(A_WIDTH)).as_int(), c2->parameters.at(ID(B_WIDTH)).as_int()) +
+						max(c1->parameters.at(ID(B_WIDTH)).as_int(), c2->parameters.at(ID(A_WIDTH)).as_int());
 
 				if (score_flipped < score_unflipped)
 				{
-					RTLIL::SigSpec tmp = c2->getPort("\\A");
-					c2->setPort("\\A", c2->getPort("\\B"));
-					c2->setPort("\\B", tmp);
+					RTLIL::SigSpec tmp = c2->getPort(ID::A);
+					c2->setPort(ID::A, c2->getPort(ID::B));
+					c2->setPort(ID::B, tmp);
 
-					std::swap(c2->parameters.at("\\A_WIDTH"), c2->parameters.at("\\B_WIDTH"));
-					std::swap(c2->parameters.at("\\A_SIGNED"), c2->parameters.at("\\B_SIGNED"));
+					std::swap(c2->parameters.at(ID(A_WIDTH)), c2->parameters.at(ID(B_WIDTH)));
+					std::swap(c2->parameters.at(ID(A_SIGNED)), c2->parameters.at(ID(B_SIGNED)));
 					modified_src_cells = true;
 				}
 			}
 
-			if (c1->parameters.at("\\A_SIGNED").as_bool() != c2->parameters.at("\\A_SIGNED").as_bool())
+			if (c1->parameters.at(ID(A_SIGNED)).as_bool() != c2->parameters.at(ID(A_SIGNED)).as_bool())
 
 			{
-				RTLIL::Cell *unsigned_cell = c1->parameters.at("\\A_SIGNED").as_bool() ? c2 : c1;
-				if (unsigned_cell->getPort("\\A").to_sigbit_vector().back() != RTLIL::State::S0) {
-					unsigned_cell->parameters.at("\\A_WIDTH") = unsigned_cell->parameters.at("\\A_WIDTH").as_int() + 1;
-					RTLIL::SigSpec new_a = unsigned_cell->getPort("\\A");
+				RTLIL::Cell *unsigned_cell = c1->parameters.at(ID(A_SIGNED)).as_bool() ? c2 : c1;
+				if (unsigned_cell->getPort(ID::A).to_sigbit_vector().back() != RTLIL::State::S0) {
+					unsigned_cell->parameters.at(ID(A_WIDTH)) = unsigned_cell->parameters.at(ID(A_WIDTH)).as_int() + 1;
+					RTLIL::SigSpec new_a = unsigned_cell->getPort(ID::A);
 					new_a.append_bit(RTLIL::State::S0);
-					unsigned_cell->setPort("\\A", new_a);
+					unsigned_cell->setPort(ID::A, new_a);
 				}
-				unsigned_cell->parameters.at("\\A_SIGNED") = true;
+				unsigned_cell->parameters.at(ID(A_SIGNED)) = true;
 				modified_src_cells = true;
 			}
 
-			if (c1->parameters.at("\\B_SIGNED").as_bool() != c2->parameters.at("\\B_SIGNED").as_bool())
+			if (c1->parameters.at(ID(B_SIGNED)).as_bool() != c2->parameters.at(ID(B_SIGNED)).as_bool())
 			{
-				RTLIL::Cell *unsigned_cell = c1->parameters.at("\\B_SIGNED").as_bool() ? c2 : c1;
-				if (unsigned_cell->getPort("\\B").to_sigbit_vector().back() != RTLIL::State::S0) {
-					unsigned_cell->parameters.at("\\B_WIDTH") = unsigned_cell->parameters.at("\\B_WIDTH").as_int() + 1;
-					RTLIL::SigSpec new_b = unsigned_cell->getPort("\\B");
+				RTLIL::Cell *unsigned_cell = c1->parameters.at(ID(B_SIGNED)).as_bool() ? c2 : c1;
+				if (unsigned_cell->getPort(ID::B).to_sigbit_vector().back() != RTLIL::State::S0) {
+					unsigned_cell->parameters.at(ID(B_WIDTH)) = unsigned_cell->parameters.at(ID(B_WIDTH)).as_int() + 1;
+					RTLIL::SigSpec new_b = unsigned_cell->getPort(ID::B);
 					new_b.append_bit(RTLIL::State::S0);
-					unsigned_cell->setPort("\\B", new_b);
+					unsigned_cell->setPort(ID::B, new_b);
 				}
-				unsigned_cell->parameters.at("\\B_SIGNED") = true;
+				unsigned_cell->parameters.at(ID(B_SIGNED)) = true;
 				modified_src_cells = true;
 			}
 
@@ -613,28 +613,28 @@ struct ShareWorker
 				c2->check();
 			}
 
-			bool a_signed = c1->parameters.at("\\A_SIGNED").as_bool();
-			bool b_signed = c1->parameters.at("\\B_SIGNED").as_bool();
+			bool a_signed = c1->parameters.at(ID(A_SIGNED)).as_bool();
+			bool b_signed = c1->parameters.at(ID(B_SIGNED)).as_bool();
 
-			log_assert(a_signed == c2->parameters.at("\\A_SIGNED").as_bool());
-			log_assert(b_signed == c2->parameters.at("\\B_SIGNED").as_bool());
+			log_assert(a_signed == c2->parameters.at(ID(A_SIGNED)).as_bool());
+			log_assert(b_signed == c2->parameters.at(ID(B_SIGNED)).as_bool());
 
-			if (c1->type == "$shl" || c1->type == "$shr" || c1->type == "$sshl" || c1->type == "$sshr")
+			if (c1->type == ID($shl) || c1->type == ID($shr) || c1->type == ID($sshl) || c1->type == ID($sshr))
 				b_signed = false;
 
-			RTLIL::SigSpec a1 = c1->getPort("\\A");
-			RTLIL::SigSpec b1 = c1->getPort("\\B");
-			RTLIL::SigSpec y1 = c1->getPort("\\Y");
+			RTLIL::SigSpec a1 = c1->getPort(ID::A);
+			RTLIL::SigSpec b1 = c1->getPort(ID::B);
+			RTLIL::SigSpec y1 = c1->getPort(ID::Y);
 
-			RTLIL::SigSpec a2 = c2->getPort("\\A");
-			RTLIL::SigSpec b2 = c2->getPort("\\B");
-			RTLIL::SigSpec y2 = c2->getPort("\\Y");
+			RTLIL::SigSpec a2 = c2->getPort(ID::A);
+			RTLIL::SigSpec b2 = c2->getPort(ID::B);
+			RTLIL::SigSpec y2 = c2->getPort(ID::Y);
 
 			int a_width = max(a1.size(), a2.size());
 			int b_width = max(b1.size(), b2.size());
 			int y_width = max(y1.size(), y2.size());
 
-			if (c1->type == "$shr" && a_signed)
+			if (c1->type == ID($shr) && a_signed)
 			{
 				a_width = max(y_width, a_width);
 
@@ -660,43 +660,43 @@ struct ShareWorker
 			supercell_aux.insert(module->addMux(NEW_ID, b2, b1, act, b));
 
 			RTLIL::Wire *y = module->addWire(NEW_ID, y_width);
-			RTLIL::Wire *x = c1->type == "$alu" ? module->addWire(NEW_ID, y_width) : nullptr;
-			RTLIL::Wire *co = c1->type == "$alu" ? module->addWire(NEW_ID, y_width) : nullptr;
+			RTLIL::Wire *x = c1->type == ID($alu) ? module->addWire(NEW_ID, y_width) : nullptr;
+			RTLIL::Wire *co = c1->type == ID($alu) ? module->addWire(NEW_ID, y_width) : nullptr;
 
 			RTLIL::Cell *supercell = module->addCell(NEW_ID, c1->type);
-			supercell->parameters["\\A_SIGNED"] = a_signed;
-			supercell->parameters["\\B_SIGNED"] = b_signed;
-			supercell->parameters["\\A_WIDTH"] = a_width;
-			supercell->parameters["\\B_WIDTH"] = b_width;
-			supercell->parameters["\\Y_WIDTH"] = y_width;
-			supercell->setPort("\\A", a);
-			supercell->setPort("\\B", b);
-			supercell->setPort("\\Y", y);
-			if (c1->type == "$alu") {
+			supercell->parameters[ID(A_SIGNED)] = a_signed;
+			supercell->parameters[ID(B_SIGNED)] = b_signed;
+			supercell->parameters[ID(A_WIDTH)] = a_width;
+			supercell->parameters[ID(B_WIDTH)] = b_width;
+			supercell->parameters[ID(Y_WIDTH)] = y_width;
+			supercell->setPort(ID::A, a);
+			supercell->setPort(ID::B, b);
+			supercell->setPort(ID::Y, y);
+			if (c1->type == ID($alu)) {
 				RTLIL::Wire *ci = module->addWire(NEW_ID), *bi = module->addWire(NEW_ID);
-				supercell_aux.insert(module->addMux(NEW_ID, c2->getPort("\\CI"), c1->getPort("\\CI"), act, ci));
-				supercell_aux.insert(module->addMux(NEW_ID, c2->getPort("\\BI"), c1->getPort("\\BI"), act, bi));
-				supercell->setPort("\\CI", ci);
-				supercell->setPort("\\BI", bi);
-				supercell->setPort("\\CO", co);
-				supercell->setPort("\\X", x);
+				supercell_aux.insert(module->addMux(NEW_ID, c2->getPort(ID(CI)), c1->getPort(ID(CI)), act, ci));
+				supercell_aux.insert(module->addMux(NEW_ID, c2->getPort(ID(BI)), c1->getPort(ID(BI)), act, bi));
+				supercell->setPort(ID(CI), ci);
+				supercell->setPort(ID(BI), bi);
+				supercell->setPort(ID(CO), co);
+				supercell->setPort(ID(X), x);
 			}
 			supercell->check();
 
 			supercell_aux.insert(module->addPos(NEW_ID, y, y1));
 			supercell_aux.insert(module->addPos(NEW_ID, y, y2));
-			if (c1->type == "$alu") {
-				supercell_aux.insert(module->addPos(NEW_ID, co, c1->getPort("\\CO")));
-				supercell_aux.insert(module->addPos(NEW_ID, co, c2->getPort("\\CO")));
-				supercell_aux.insert(module->addPos(NEW_ID, x, c1->getPort("\\X")));
-				supercell_aux.insert(module->addPos(NEW_ID, x, c2->getPort("\\X")));
+			if (c1->type == ID($alu)) {
+				supercell_aux.insert(module->addPos(NEW_ID, co, c1->getPort(ID(CO))));
+				supercell_aux.insert(module->addPos(NEW_ID, co, c2->getPort(ID(CO))));
+				supercell_aux.insert(module->addPos(NEW_ID, x, c1->getPort(ID(X))));
+				supercell_aux.insert(module->addPos(NEW_ID, x, c2->getPort(ID(X))));
 			}
 
 			supercell_aux.insert(supercell);
 			return supercell;
 		}
 
-		if (c1->type == "$macc")
+		if (c1->type == ID($macc))
 		{
 			RTLIL::Cell *supercell = module->addCell(NEW_ID, c1->type);
 			supercell_aux.insert(supercell);
@@ -705,14 +705,18 @@ struct ShareWorker
 			return supercell;
 		}
 
-		if (c1->type == "$memrd")
+		if (c1->type == ID($memrd))
 		{
 			RTLIL::Cell *supercell = module->addCell(NEW_ID, c1);
-			RTLIL::SigSpec addr1 = c1->getPort("\\ADDR");
-			RTLIL::SigSpec addr2 = c2->getPort("\\ADDR");
-			if (addr1 != addr2)
-				supercell->setPort("\\ADDR", module->Mux(NEW_ID, addr2, addr1, act));
-			supercell_aux.insert(module->addPos(NEW_ID, supercell->getPort("\\DATA"), c2->getPort("\\DATA")));
+			RTLIL::SigSpec addr1 = c1->getPort(ID(ADDR));
+			RTLIL::SigSpec addr2 = c2->getPort(ID(ADDR));
+			if (GetSize(addr1) < GetSize(addr2))
+				addr1.extend_u0(GetSize(addr2));
+			else
+				addr2.extend_u0(GetSize(addr1));
+			supercell->setPort(ID(ADDR), addr1 != addr2 ? module->Mux(NEW_ID, addr2, addr1, act) : addr1);
+			supercell->parameters[ID(ABITS)] = RTLIL::Const(GetSize(addr1));
+			supercell_aux.insert(module->addPos(NEW_ID, supercell->getPort(ID(DATA)), c2->getPort(ID(DATA))));
 			supercell_aux.insert(supercell);
 			return supercell;
 		}
@@ -743,8 +747,8 @@ struct ShareWorker
 		modwalker.get_consumers(pbits, modwalker.cell_outputs[cell]);
 
 		for (auto &bit : pbits) {
-			if ((bit.cell->type == "$mux" || bit.cell->type == "$pmux") && bit.port == "\\S")
-				forbidden_controls_cache[cell].insert(bit.cell->getPort("\\S").extract(bit.offset, 1));
+			if ((bit.cell->type == ID($mux) || bit.cell->type == ID($pmux)) && bit.port == ID(S))
+				forbidden_controls_cache[cell].insert(bit.cell->getPort(ID(S)).extract(bit.offset, 1));
 			consumer_cells.insert(bit.cell);
 		}
 
@@ -870,7 +874,7 @@ struct ShareWorker
 			}
 			for (auto &pbit : modwalker.signal_consumers[bit]) {
 				log_assert(fwd_ct.cell_known(pbit.cell->type));
-				if ((pbit.cell->type == "$mux" || pbit.cell->type == "$pmux") && (pbit.port == "\\A" || pbit.port == "\\B"))
+				if ((pbit.cell->type == ID($mux) || pbit.cell->type == ID($pmux)) && (pbit.port == ID::A || pbit.port == ID::B))
 					driven_data_muxes.insert(pbit.cell);
 				else
 					driven_cells.insert(pbit.cell);
@@ -886,10 +890,10 @@ struct ShareWorker
 			bool used_in_a = false;
 			std::set<int> used_in_b_parts;
 
-			int width = c->parameters.at("\\WIDTH").as_int();
-			std::vector<RTLIL::SigBit> sig_a = modwalker.sigmap(c->getPort("\\A"));
-			std::vector<RTLIL::SigBit> sig_b = modwalker.sigmap(c->getPort("\\B"));
-			std::vector<RTLIL::SigBit> sig_s = modwalker.sigmap(c->getPort("\\S"));
+			int width = c->parameters.at(ID(WIDTH)).as_int();
+			std::vector<RTLIL::SigBit> sig_a = modwalker.sigmap(c->getPort(ID::A));
+			std::vector<RTLIL::SigBit> sig_b = modwalker.sigmap(c->getPort(ID::B));
+			std::vector<RTLIL::SigBit> sig_s = modwalker.sigmap(c->getPort(ID(S)));
 
 			for (auto &bit : sig_a)
 				if (cell_out_bits.count(bit))
@@ -1128,14 +1132,14 @@ struct ShareWorker
 		fwd_ct.setup_internals();
 
 		cone_ct.setup_internals();
-		cone_ct.cell_types.erase("$mul");
-		cone_ct.cell_types.erase("$mod");
-		cone_ct.cell_types.erase("$div");
-		cone_ct.cell_types.erase("$pow");
-		cone_ct.cell_types.erase("$shl");
-		cone_ct.cell_types.erase("$shr");
-		cone_ct.cell_types.erase("$sshl");
-		cone_ct.cell_types.erase("$sshr");
+		cone_ct.cell_types.erase(ID($mul));
+		cone_ct.cell_types.erase(ID($mod));
+		cone_ct.cell_types.erase(ID($div));
+		cone_ct.cell_types.erase(ID($pow));
+		cone_ct.cell_types.erase(ID($shl));
+		cone_ct.cell_types.erase(ID($shr));
+		cone_ct.cell_types.erase(ID($sshl));
+		cone_ct.cell_types.erase(ID($sshr));
 
 		modwalker.setup(design, module);
 
@@ -1149,9 +1153,9 @@ struct ShareWorker
 				GetSize(shareable_cells), log_id(module));
 
 		for (auto cell : module->cells())
-			if (cell->type == "$pmux")
-				for (auto bit : cell->getPort("\\S"))
-				for (auto other_bit : cell->getPort("\\S"))
+			if (cell->type == ID($pmux))
+				for (auto bit : cell->getPort(ID(S)))
+				for (auto other_bit : cell->getPort(ID(S)))
 					if (bit < other_bit)
 						exclusive_ctrls.push_back(std::pair<RTLIL::SigBit, RTLIL::SigBit>(bit, other_bit));
 
@@ -1421,7 +1425,7 @@ struct ShareWorker
 
 struct SharePass : public Pass {
 	SharePass() : Pass("share", "perform sat-based resource sharing") { }
-	virtual void help()
+	void help() YS_OVERRIDE
 	{
 		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
 		log("\n");
@@ -1453,7 +1457,7 @@ struct SharePass : public Pass {
 		log("    Only perform the first N merges, then stop. This is useful for debugging.\n");
 		log("\n");
 	}
-	virtual void execute(std::vector<std::string> args, RTLIL::Design *design)
+	void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
 	{
 		ShareWorkerConfig config;
 
@@ -1462,43 +1466,43 @@ struct SharePass : public Pass {
 		config.opt_aggressive = false;
 		config.opt_fast = false;
 
-		config.generic_uni_ops.insert("$not");
-		// config.generic_uni_ops.insert("$pos");
-		config.generic_uni_ops.insert("$neg");
-
-		config.generic_cbin_ops.insert("$and");
-		config.generic_cbin_ops.insert("$or");
-		config.generic_cbin_ops.insert("$xor");
-		config.generic_cbin_ops.insert("$xnor");
-
-		config.generic_bin_ops.insert("$shl");
-		config.generic_bin_ops.insert("$shr");
-		config.generic_bin_ops.insert("$sshl");
-		config.generic_bin_ops.insert("$sshr");
-
-		config.generic_bin_ops.insert("$lt");
-		config.generic_bin_ops.insert("$le");
-		config.generic_bin_ops.insert("$eq");
-		config.generic_bin_ops.insert("$ne");
-		config.generic_bin_ops.insert("$eqx");
-		config.generic_bin_ops.insert("$nex");
-		config.generic_bin_ops.insert("$ge");
-		config.generic_bin_ops.insert("$gt");
-
-		config.generic_cbin_ops.insert("$add");
-		config.generic_cbin_ops.insert("$mul");
-
-		config.generic_bin_ops.insert("$sub");
-		config.generic_bin_ops.insert("$div");
-		config.generic_bin_ops.insert("$mod");
-		// config.generic_bin_ops.insert("$pow");
-
-		config.generic_uni_ops.insert("$logic_not");
-		config.generic_cbin_ops.insert("$logic_and");
-		config.generic_cbin_ops.insert("$logic_or");
-
-		config.generic_other_ops.insert("$alu");
-		config.generic_other_ops.insert("$macc");
+		config.generic_uni_ops.insert(ID($not));
+		// config.generic_uni_ops.insert(ID($pos));
+		config.generic_uni_ops.insert(ID($neg));
+
+		config.generic_cbin_ops.insert(ID($and));
+		config.generic_cbin_ops.insert(ID($or));
+		config.generic_cbin_ops.insert(ID($xor));
+		config.generic_cbin_ops.insert(ID($xnor));
+
+		config.generic_bin_ops.insert(ID($shl));
+		config.generic_bin_ops.insert(ID($shr));
+		config.generic_bin_ops.insert(ID($sshl));
+		config.generic_bin_ops.insert(ID($sshr));
+
+		config.generic_bin_ops.insert(ID($lt));
+		config.generic_bin_ops.insert(ID($le));
+		config.generic_bin_ops.insert(ID($eq));
+		config.generic_bin_ops.insert(ID($ne));
+		config.generic_bin_ops.insert(ID($eqx));
+		config.generic_bin_ops.insert(ID($nex));
+		config.generic_bin_ops.insert(ID($ge));
+		config.generic_bin_ops.insert(ID($gt));
+
+		config.generic_cbin_ops.insert(ID($add));
+		config.generic_cbin_ops.insert(ID($mul));
+
+		config.generic_bin_ops.insert(ID($sub));
+		config.generic_bin_ops.insert(ID($div));
+		config.generic_bin_ops.insert(ID($mod));
+		// config.generic_bin_ops.insert(ID($pow));
+
+		config.generic_uni_ops.insert(ID($logic_not));
+		config.generic_cbin_ops.insert(ID($logic_and));
+		config.generic_cbin_ops.insert(ID($logic_or));
+
+		config.generic_other_ops.insert(ID($alu));
+		config.generic_other_ops.insert(ID($macc));
 
 		log_header(design, "Executing SHARE pass (SAT-based resource sharing).\n");
 
diff --git a/passes/opt/wreduce.cc b/passes/opt/wreduce.cc
index 07503fbb3..c02c355cb 100644
--- a/passes/opt/wreduce.cc
+++ b/passes/opt/wreduce.cc
@@ -22,23 +22,24 @@
 #include "kernel/modtools.h"
 
 USING_YOSYS_NAMESPACE
-using namespace RTLIL;
 
 PRIVATE_NAMESPACE_BEGIN
 
 struct WreduceConfig
 {
 	pool<IdString> supported_cell_types;
+	bool keepdc = false;
 
 	WreduceConfig()
 	{
 		supported_cell_types = pool<IdString>({
-			"$not", "$pos", "$neg",
-			"$and", "$or", "$xor", "$xnor",
-			"$shl", "$shr", "$sshl", "$sshr", "$shift", "$shiftx",
-			"$lt", "$le", "$eq", "$ne", "$eqx", "$nex", "$ge", "$gt",
-			"$add", "$sub", "$mul", // "$div", "$mod", "$pow",
-			"$mux", "$pmux"
+			ID($not), ID($pos), ID($neg),
+			ID($and), ID($or), ID($xor), ID($xnor),
+			ID($shl), ID($shr), ID($sshl), ID($sshr), ID($shift), ID($shiftx),
+			ID($lt), ID($le), ID($eq), ID($ne), ID($eqx), ID($nex), ID($ge), ID($gt),
+			ID($add), ID($sub), ID($mul), // ID($div), ID($mod), ID($pow),
+			ID($mux), ID($pmux),
+			ID($dff), ID($adff)
 		});
 	}
 };
@@ -52,6 +53,8 @@ struct WreduceWorker
 	std::set<Cell*, IdString::compare_ptr_by_name<Cell>> work_queue_cells;
 	std::set<SigBit> work_queue_bits;
 	pool<SigBit> keep_bits;
+	dict<SigBit, State> init_bits;
+	pool<SigBit> remove_init_bits;
 
 	WreduceWorker(WreduceConfig *config, Module *module) :
 			config(config), module(module), mi(module) { }
@@ -60,10 +63,10 @@ struct WreduceWorker
 	{
 		// Reduce size of MUX if inputs agree on a value for a bit or a output bit is unused
 
-		SigSpec sig_a = mi.sigmap(cell->getPort("\\A"));
-		SigSpec sig_b = mi.sigmap(cell->getPort("\\B"));
-		SigSpec sig_s = mi.sigmap(cell->getPort("\\S"));
-		SigSpec sig_y = mi.sigmap(cell->getPort("\\Y"));
+		SigSpec sig_a = mi.sigmap(cell->getPort(ID::A));
+		SigSpec sig_b = mi.sigmap(cell->getPort(ID::B));
+		SigSpec sig_s = mi.sigmap(cell->getPort(ID(S)));
+		SigSpec sig_y = mi.sigmap(cell->getPort(ID::Y));
 		std::vector<SigBit> bits_removed;
 
 		if (sig_y.has_const())
@@ -73,15 +76,15 @@ struct WreduceWorker
 		{
 			auto info = mi.query(sig_y[i]);
 			if (!info->is_output && GetSize(info->ports) <= 1 && !keep_bits.count(mi.sigmap(sig_y[i]))) {
-				bits_removed.push_back(Sx);
+				bits_removed.push_back(State::Sx);
 				continue;
 			}
 
 			SigBit ref = sig_a[i];
 			for (int k = 0; k < GetSize(sig_s); k++) {
-				if (ref != Sx && sig_b[k*GetSize(sig_a) + i] != Sx && ref != sig_b[k*GetSize(sig_a) + i])
+				if ((config->keepdc || (ref != State::Sx && sig_b[k*GetSize(sig_a) + i] != State::Sx)) && ref != sig_b[k*GetSize(sig_a) + i])
 					goto no_match_ab;
-				if (sig_b[k*GetSize(sig_a) + i] != Sx)
+				if (sig_b[k*GetSize(sig_a) + i] != State::Sx)
 					ref = sig_b[k*GetSize(sig_a) + i];
 			}
 			if (0)
@@ -126,20 +129,107 @@ struct WreduceWorker
 		for (auto bit : new_work_queue_bits)
 			work_queue_bits.insert(bit);
 
-		cell->setPort("\\A", new_sig_a);
-		cell->setPort("\\B", new_sig_b);
-		cell->setPort("\\Y", new_sig_y);
+		cell->setPort(ID::A, new_sig_a);
+		cell->setPort(ID::B, new_sig_b);
+		cell->setPort(ID::Y, new_sig_y);
 		cell->fixup_parameters();
 
 		module->connect(sig_y.extract(n_kept, n_removed), sig_removed);
 	}
 
+	void run_cell_dff(Cell *cell)
+	{
+		// Reduce size of FF if inputs are just sign/zero extended or output bit is not used
+
+		SigSpec sig_d = mi.sigmap(cell->getPort(ID(D)));
+		SigSpec sig_q = mi.sigmap(cell->getPort(ID(Q)));
+		Const initval;
+
+		int width_before = GetSize(sig_q);
+
+		if (width_before == 0)
+			return;
+
+		bool zero_ext = sig_d[GetSize(sig_d)-1] == State::S0;
+		bool sign_ext = !zero_ext;
+
+		for (int i = 0; i < GetSize(sig_q); i++) {
+			SigBit bit = sig_q[i];
+			if (init_bits.count(bit))
+				initval.bits.push_back(init_bits.at(bit));
+			else
+				initval.bits.push_back(State::Sx);
+		}
+
+		for (int i = GetSize(sig_q)-1; i >= 0; i--)
+		{
+			if (zero_ext && sig_d[i] == State::S0 && (initval[i] == State::S0 || initval[i] == State::Sx)) {
+				module->connect(sig_q[i], State::S0);
+				remove_init_bits.insert(sig_q[i]);
+				sig_d.remove(i);
+				sig_q.remove(i);
+				continue;
+			}
+
+			if (sign_ext && i > 0 && sig_d[i] == sig_d[i-1] && initval[i] == initval[i-1]) {
+				module->connect(sig_q[i], sig_q[i-1]);
+				remove_init_bits.insert(sig_q[i]);
+				sig_d.remove(i);
+				sig_q.remove(i);
+				continue;
+			}
+
+			auto info = mi.query(sig_q[i]);
+			if (info == nullptr)
+				return;
+			if (!info->is_output && GetSize(info->ports) == 1 && !keep_bits.count(mi.sigmap(sig_q[i]))) {
+				remove_init_bits.insert(sig_q[i]);
+				sig_d.remove(i);
+				sig_q.remove(i);
+				zero_ext = false;
+				sign_ext = false;
+				continue;
+			}
+
+			break;
+		}
+
+		if (width_before == GetSize(sig_q))
+			return;
+
+		if (GetSize(sig_q) == 0) {
+			log("Removed cell %s.%s (%s).\n", log_id(module), log_id(cell), log_id(cell->type));
+			module->remove(cell);
+			return;
+		}
+
+		log("Removed top %d bits (of %d) from FF cell %s.%s (%s).\n", width_before - GetSize(sig_q), width_before,
+				log_id(module), log_id(cell), log_id(cell->type));
+
+		for (auto bit : sig_d)
+			work_queue_bits.insert(bit);
+
+		for (auto bit : sig_q)
+			work_queue_bits.insert(bit);
+
+		// Narrow ARST_VALUE parameter to new size.
+		if (cell->parameters.count(ID(ARST_VALUE))) {
+			Const arst_value = cell->getParam(ID(ARST_VALUE));
+			arst_value.bits.resize(GetSize(sig_q));
+			cell->setParam(ID(ARST_VALUE), arst_value);
+		}
+
+		cell->setPort(ID(D), sig_d);
+		cell->setPort(ID(Q), sig_q);
+		cell->fixup_parameters();
+	}
+
 	void run_reduce_inport(Cell *cell, char port, int max_port_size, bool &port_signed, bool &did_something)
 	{
 		port_signed = cell->getParam(stringf("\\%c_SIGNED", port)).as_bool();
 		SigSpec sig = mi.sigmap(cell->getPort(stringf("\\%c", port)));
 
-		if (port == 'B' && cell->type.in("$shl", "$shr", "$sshl", "$sshr"))
+		if (port == 'B' && cell->type.in(ID($shl), ID($shr), ID($sshl), ID($sshr)))
 			port_signed = false;
 
 		int bits_removed = 0;
@@ -154,7 +244,7 @@ struct WreduceWorker
 			while (GetSize(sig) > 1 && sig[GetSize(sig)-1] == sig[GetSize(sig)-2])
 				work_queue_bits.insert(sig[GetSize(sig)-1]), sig.remove(GetSize(sig)-1), bits_removed++;
 		} else {
-			while (GetSize(sig) > 1 && sig[GetSize(sig)-1] == S0)
+			while (GetSize(sig) > 1 && sig[GetSize(sig)-1] == State::S0)
 				work_queue_bits.insert(sig[GetSize(sig)-1]), sig.remove(GetSize(sig)-1), bits_removed++;
 		}
 
@@ -173,10 +263,13 @@ struct WreduceWorker
 		if (!cell->type.in(config->supported_cell_types))
 			return;
 
-		if (cell->type.in("$mux", "$pmux"))
+		if (cell->type.in(ID($mux), ID($pmux)))
 			return run_cell_mux(cell);
 
-		SigSpec sig = mi.sigmap(cell->getPort("\\Y"));
+		if (cell->type.in(ID($dff), ID($adff)))
+			return run_cell_dff(cell);
+
+		SigSpec sig = mi.sigmap(cell->getPort(ID::Y));
 
 		if (sig.has_const())
 			return;
@@ -184,10 +277,10 @@ struct WreduceWorker
 
 		// Reduce size of ports A and B based on constant input bits and size of output port
 
-		int max_port_a_size = cell->hasPort("\\A") ? GetSize(cell->getPort("\\A")) : -1;
-		int max_port_b_size = cell->hasPort("\\B") ? GetSize(cell->getPort("\\B")) : -1;
+		int max_port_a_size = cell->hasPort(ID::A) ? GetSize(cell->getPort(ID::A)) : -1;
+		int max_port_b_size = cell->hasPort(ID::B) ? GetSize(cell->getPort(ID::B)) : -1;
 
-		if (cell->type.in("$not", "$pos", "$neg", "$and", "$or", "$xor", "$add", "$sub")) {
+		if (cell->type.in(ID($not), ID($pos), ID($neg), ID($and), ID($or), ID($xor), ID($add), ID($sub))) {
 			max_port_a_size = min(max_port_a_size, GetSize(sig));
 			max_port_b_size = min(max_port_b_size, GetSize(sig));
 		}
@@ -195,32 +288,32 @@ struct WreduceWorker
 		bool port_a_signed = false;
 		bool port_b_signed = false;
 
-		if (max_port_a_size >= 0 && cell->type != "$shiftx")
+		if (max_port_a_size >= 0 && cell->type != ID($shiftx))
 			run_reduce_inport(cell, 'A', max_port_a_size, port_a_signed, did_something);
 
 		if (max_port_b_size >= 0)
 			run_reduce_inport(cell, 'B', max_port_b_size, port_b_signed, did_something);
 
-		if (cell->hasPort("\\A") && cell->hasPort("\\B") && port_a_signed && port_b_signed) {
-			SigSpec sig_a = mi.sigmap(cell->getPort("\\A")), sig_b = mi.sigmap(cell->getPort("\\B"));
+		if (cell->hasPort(ID::A) && cell->hasPort(ID::B) && port_a_signed && port_b_signed) {
+			SigSpec sig_a = mi.sigmap(cell->getPort(ID::A)), sig_b = mi.sigmap(cell->getPort(ID::B));
 			if (GetSize(sig_a) > 0 && sig_a[GetSize(sig_a)-1] == State::S0 &&
 					GetSize(sig_b) > 0 && sig_b[GetSize(sig_b)-1] == State::S0) {
 				log("Converting cell %s.%s (%s) from signed to unsigned.\n",
 						log_id(module), log_id(cell), log_id(cell->type));
-				cell->setParam("\\A_SIGNED", 0);
-				cell->setParam("\\B_SIGNED", 0);
+				cell->setParam(ID(A_SIGNED), 0);
+				cell->setParam(ID(B_SIGNED), 0);
 				port_a_signed = false;
 				port_b_signed = false;
 				did_something = true;
 			}
 		}
 
-		if (cell->hasPort("\\A") && !cell->hasPort("\\B") && port_a_signed) {
-			SigSpec sig_a = mi.sigmap(cell->getPort("\\A"));
+		if (cell->hasPort(ID::A) && !cell->hasPort(ID::B) && port_a_signed) {
+			SigSpec sig_a = mi.sigmap(cell->getPort(ID::A));
 			if (GetSize(sig_a) > 0 && sig_a[GetSize(sig_a)-1] == State::S0) {
 				log("Converting cell %s.%s (%s) from signed to unsigned.\n",
 						log_id(module), log_id(cell), log_id(cell->type));
-				cell->setParam("\\A_SIGNED", 0);
+				cell->setParam(ID(A_SIGNED), 0);
 				port_a_signed = false;
 				did_something = true;
 			}
@@ -230,13 +323,16 @@ struct WreduceWorker
 		// Reduce size of port Y based on sizes for A and B and unused bits in Y
 
 		int bits_removed = 0;
-		if (port_a_signed && cell->type == "$shr") {
+		if (port_a_signed && cell->type == ID($shr)) {
 			// do not reduce size of output on $shr cells with signed A inputs
 		} else {
 			while (GetSize(sig) > 0)
 			{
-				auto info = mi.query(sig[GetSize(sig)-1]);
+				auto bit = sig[GetSize(sig)-1];
+				if (keep_bits.count(bit))
+					break;
 
+				auto info = mi.query(bit);
 				if (info->is_output || GetSize(info->ports) > 1)
 					break;
 
@@ -245,24 +341,24 @@ struct WreduceWorker
 			}
 		}
 
-		if (cell->type.in("$pos", "$add", "$mul", "$and", "$or", "$xor"))
+		if (cell->type.in(ID($pos), ID($add), ID($mul), ID($and), ID($or), ID($xor), ID($sub)))
 		{
-			bool is_signed = cell->getParam("\\A_SIGNED").as_bool();
+			bool is_signed = cell->getParam(ID(A_SIGNED)).as_bool() || cell->type == ID($sub);
 
 			int a_size = 0, b_size = 0;
-			if (cell->hasPort("\\A")) a_size = GetSize(cell->getPort("\\A"));
-			if (cell->hasPort("\\B")) b_size = GetSize(cell->getPort("\\B"));
+			if (cell->hasPort(ID::A)) a_size = GetSize(cell->getPort(ID::A));
+			if (cell->hasPort(ID::B)) b_size = GetSize(cell->getPort(ID::B));
 
 			int max_y_size = max(a_size, b_size);
 
-			if (cell->type == "$add")
+			if (cell->type.in(ID($add), ID($sub)))
 				max_y_size++;
 
-			if (cell->type == "$mul")
+			if (cell->type == ID($mul))
 				max_y_size = a_size + b_size;
 
 			while (GetSize(sig) > 1 && GetSize(sig) > max_y_size) {
-				module->connect(sig[GetSize(sig)-1], is_signed ? sig[GetSize(sig)-2] : S0);
+				module->connect(sig[GetSize(sig)-1], is_signed ? sig[GetSize(sig)-2] : State::S0);
 				sig.remove(GetSize(sig)-1);
 				bits_removed++;
 			}
@@ -277,7 +373,7 @@ struct WreduceWorker
 		if (bits_removed) {
 			log("Removed top %d bits (of %d) from port Y of cell %s.%s (%s).\n",
 					bits_removed, GetSize(sig) + bits_removed, log_id(module), log_id(cell), log_id(cell->type));
-			cell->setPort("\\Y", sig);
+			cell->setPort(ID::Y, sig);
 			did_something = true;
 		}
 
@@ -290,17 +386,28 @@ struct WreduceWorker
 	static int count_nontrivial_wire_attrs(RTLIL::Wire *w)
 	{
 		int count = w->attributes.size();
-		count -= w->attributes.count("\\src");
-		count -= w->attributes.count("\\unused_bits");
+		count -= w->attributes.count(ID(src));
+		count -= w->attributes.count(ID(unused_bits));
 		return count;
 	}
 
 	void run()
 	{
-		for (auto w : module->wires())
-			if (w->get_bool_attribute("\\keep"))
+		// create a copy as mi.sigmap will be updated as we process the module
+		SigMap init_attr_sigmap = mi.sigmap;
+
+		for (auto w : module->wires()) {
+			if (w->get_bool_attribute(ID::keep))
 				for (auto bit : mi.sigmap(w))
 					keep_bits.insert(bit);
+			if (w->attributes.count(ID(init))) {
+				Const initval = w->attributes.at(ID(init));
+				SigSpec initsig = init_attr_sigmap(w);
+				int width = std::min(GetSize(initval), GetSize(initsig));
+				for (int i = 0; i < width; i++)
+					init_bits[initsig[i]] = initval[i];
+			}
+		}
 
 		for (auto c : module->selected_cells())
 			work_queue_cells.insert(c);
@@ -348,12 +455,28 @@ struct WreduceWorker
 			module->connect(nw, SigSpec(w).extract(0, GetSize(nw)));
 			module->swap_names(w, nw);
 		}
+
+		if (!remove_init_bits.empty()) {
+			for (auto w : module->wires()) {
+				if (w->attributes.count(ID(init))) {
+					Const initval = w->attributes.at(ID(init));
+					Const new_initval(State::Sx, GetSize(w));
+					SigSpec initsig = init_attr_sigmap(w);
+					int width = std::min(GetSize(initval), GetSize(initsig));
+					for (int i = 0; i < width; i++) {
+						if (!remove_init_bits.count(initsig[i]))
+							new_initval[i] = initval[i];
+					}
+					w->attributes.at(ID(init)) = new_initval;
+				}
+			}
+		}
 	}
 };
 
 struct WreducePass : public Pass {
 	WreducePass() : Pass("wreduce", "reduce the word size of operations if possible") { }
-	virtual void help()
+	void help() YS_OVERRIDE
 	{
 		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
 		log("\n");
@@ -372,8 +495,11 @@ struct WreducePass : public Pass {
 		log("        Do not change the width of memory address ports. Use this options in\n");
 		log("        flows that use the 'memory_memx' pass.\n");
 		log("\n");
+		log("    -keepdc\n");
+		log("        Do not optimize explicit don't-care values.\n");
+		log("\n");
 	}
-	virtual void execute(std::vector<std::string> args, Design *design)
+	void execute(std::vector<std::string> args, Design *design) YS_OVERRIDE
 	{
 		WreduceConfig config;
 		bool opt_memx = false;
@@ -386,6 +512,10 @@ struct WreducePass : public Pass {
 				opt_memx = true;
 				continue;
 			}
+			if (args[argidx] == "-keepdc") {
+				config.keepdc = true;
+				continue;
+			}
 			break;
 		}
 		extra_args(args, argidx, design);
@@ -397,30 +527,66 @@ struct WreducePass : public Pass {
 
 			for (auto c : module->selected_cells())
 			{
-				if (c->type.in("$reduce_and", "$reduce_or", "$reduce_xor", "$reduce_xnor", "$reduce_bool",
-						"$lt", "$le", "$eq", "$ne", "$eqx", "$nex", "$ge", "$gt",
-						"$logic_not", "$logic_and", "$logic_or") && GetSize(c->getPort("\\Y")) > 1) {
-					SigSpec sig = c->getPort("\\Y");
+				if (c->type.in(ID($reduce_and), ID($reduce_or), ID($reduce_xor), ID($reduce_xnor), ID($reduce_bool),
+						ID($lt), ID($le), ID($eq), ID($ne), ID($eqx), ID($nex), ID($ge), ID($gt),
+						ID($logic_not), ID($logic_and), ID($logic_or)) && GetSize(c->getPort(ID::Y)) > 1) {
+					SigSpec sig = c->getPort(ID::Y);
 					if (!sig.has_const()) {
-						c->setPort("\\Y", sig[0]);
-						c->setParam("\\Y_WIDTH", 1);
+						c->setPort(ID::Y, sig[0]);
+						c->setParam(ID(Y_WIDTH), 1);
 						sig.remove(0);
 						module->connect(sig, Const(0, GetSize(sig)));
 					}
 				}
-				if (!opt_memx && c->type.in("$memrd", "$memwr", "$meminit")) {
-					IdString memid = c->getParam("\\MEMID").decode_string();
+
+				if (c->type.in(ID($div), ID($mod), ID($pow)))
+				{
+					SigSpec A = c->getPort(ID::A);
+					int original_a_width = GetSize(A);
+					if (c->getParam(ID(A_SIGNED)).as_bool()) {
+						while (GetSize(A) > 1 && A[GetSize(A)-1] == State::S0 && A[GetSize(A)-2] == State::S0)
+							A.remove(GetSize(A)-1, 1);
+					} else {
+						while (GetSize(A) > 0 && A[GetSize(A)-1] == State::S0)
+							A.remove(GetSize(A)-1, 1);
+					}
+					if (original_a_width != GetSize(A)) {
+						log("Removed top %d bits (of %d) from port A of cell %s.%s (%s).\n",
+								original_a_width-GetSize(A), original_a_width, log_id(module), log_id(c), log_id(c->type));
+						c->setPort(ID::A, A);
+						c->setParam(ID(A_WIDTH), GetSize(A));
+					}
+
+					SigSpec B = c->getPort(ID::B);
+					int original_b_width = GetSize(B);
+					if (c->getParam(ID(B_SIGNED)).as_bool()) {
+						while (GetSize(B) > 1 && B[GetSize(B)-1] == State::S0 && B[GetSize(B)-2] == State::S0)
+							B.remove(GetSize(B)-1, 1);
+					} else {
+						while (GetSize(B) > 0 && B[GetSize(B)-1] == State::S0)
+							B.remove(GetSize(B)-1, 1);
+					}
+					if (original_b_width != GetSize(B)) {
+						log("Removed top %d bits (of %d) from port B of cell %s.%s (%s).\n",
+								original_b_width-GetSize(B), original_b_width, log_id(module), log_id(c), log_id(c->type));
+						c->setPort(ID::B, B);
+						c->setParam(ID(B_WIDTH), GetSize(B));
+					}
+				}
+
+				if (!opt_memx && c->type.in(ID($memrd), ID($memwr), ID($meminit))) {
+					IdString memid = c->getParam(ID(MEMID)).decode_string();
 					RTLIL::Memory *mem = module->memories.at(memid);
 					if (mem->start_offset >= 0) {
-						int cur_addrbits = c->getParam("\\ABITS").as_int();
+						int cur_addrbits = c->getParam(ID(ABITS)).as_int();
 						int max_addrbits = ceil_log2(mem->start_offset + mem->size);
 						if (cur_addrbits > max_addrbits) {
 							log("Removed top %d address bits (of %d) from memory %s port %s.%s (%s).\n",
 									cur_addrbits-max_addrbits, cur_addrbits,
-									c->type == "$memrd" ? "read" : c->type == "$memwr" ? "write" : "init",
+									c->type == ID($memrd) ? "read" : c->type == ID($memwr) ? "write" : "init",
 									log_id(module), log_id(c), log_id(memid));
-							c->setParam("\\ABITS", max_addrbits);
-							c->setPort("\\ADDR", c->getPort("\\ADDR").extract(0, max_addrbits));
+							c->setParam(ID(ABITS), max_addrbits);
+							c->setPort(ID(ADDR), c->getPort(ID(ADDR)).extract(0, max_addrbits));
 						}
 					}
 				}