diff --git a/passes/opt/Makefile.inc b/passes/opt/Makefile.inc
index c3e0a2a40..337fee9e4 100644
--- a/passes/opt/Makefile.inc
+++ b/passes/opt/Makefile.inc
@@ -13,5 +13,6 @@ 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
 endif
 
diff --git a/passes/opt/pmux2shiftx.cc b/passes/opt/pmux2shiftx.cc
new file mode 100644
index 000000000..5f897b131
--- /dev/null
+++ b/passes/opt/pmux2shiftx.cc
@@ -0,0 +1,831 @@
+/*
+ *  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("\\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("$adff", "$dff", "$dffe", "$dlatch", "$ff"))
+			{
+				output = cell->getPort("\\Q");
+				if (cell->type == "$adff")
+					inputs.push_back(cell->getParam("\\ARST_VALUE"));
+				inputs.push_back(cell->getPort("\\D"));
+			}
+
+			if (cell->type.in("$mux", "$pmux"))
+			{
+				output = cell->getPort("\\Y");
+				inputs.push_back(cell->getPort("\\A"));
+				SigSpec B = cell->getPort("\\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");
+	}
+	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;
+
+		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;
+			}
+			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 == "$eq")
+				{
+					dict<SigBit, State> bits;
+
+					SigSpec A = sigmap(cell->getPort("\\A"));
+					SigSpec B = sigmap(cell->getPort("\\B"));
+
+					int a_width = cell->getParam("\\A_WIDTH").as_int();
+					int b_width = cell->getParam("\\B_WIDTH").as_int();
+
+					if (a_width < b_width) {
+						bool a_signed = cell->getParam("\\A_SIGNED").as_int();
+						A.extend_u0(b_width, a_signed);
+					}
+
+					if (b_width < a_width) {
+						bool b_signed = cell->getParam("\\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("\\Y")[0])] = entry;
+					goto next_cell;
+				}
+
+				if (cell->type == "$logic_not")
+				{
+					dict<SigBit, State> bits;
+
+					SigSpec A = sigmap(cell->getPort("\\A"));
+
+					for (int i = 0; i < GetSize(A); i++)
+						bits[A[i]] = State::S0;
+
+					bits.sort();
+					pair<SigSpec, Const> entry;
+
+					for (auto it : bits) {
+						entry.first.append_bit(it.first);
+						entry.second.bits.push_back(it.second);
+					}
+
+					eqdb[sigmap(cell->getPort("\\Y")[0])] = entry;
+					goto next_cell;
+				}
+		next_cell:;
+			}
+
+			for (auto cell : module->selected_cells())
+			{
+				if (cell->type != "$pmux")
+					continue;
+
+				string src = cell->get_src_attribute();
+				int width = cell->getParam("\\WIDTH").as_int();
+				int width_bits = ceil_log2(width);
+				int extwidth = width;
+
+				while (extwidth & (extwidth-1))
+					extwidth++;
+
+				dict<SigSpec, pool<int>> seldb;
+
+				SigSpec B = cell->getPort("\\B");
+				SigSpec S = sigmap(cell->getPort("\\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("\\S");
+				SigSpec updated_B = cell->getPort("\\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;
+					}
+
+					// 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 (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 (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);
+
+					bool full_case = (min_choice == 0) && (max_choice == (1 << GetSize(sig))-1) && (max_choice+1 == GetSize(choices));
+					log("    full case: %s\n", full_case ? "true" : "false");
+
+					// check density percentages
+					Const offset(State::S0, GetSize(sig));
+					if (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);
+					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("\\S", updated_S);
+				cell->setPort("\\B", updated_B);
+				cell->setParam("\\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 $eq cells that compare one-hot signals against constants\n");
+		log("\n");
+		log("    -v, -vv\n");
+		log("        verbose output\n");
+		log("\n");
+	}
+	void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
+	{
+		bool verbose = false;
+		bool verbose_onehot = false;
+
+		log_header(design, "Executing ONEHOT pass.\n");
+
+		size_t argidx;
+		for (argidx = 1; argidx < args.size(); argidx++) {
+			if (args[argidx] == "-v") {
+				verbose = true;
+				continue;
+			}
+			if (args[argidx] == "-vv") {
+				verbose = true;
+				verbose_onehot = true;
+				continue;
+			}
+			break;
+		}
+		extra_args(args, argidx, design);
+
+		for (auto module : design->selected_modules())
+		{
+			SigMap sigmap(module);
+			OnehotDatabase onehot_db(module, sigmap);
+			onehot_db.verbose = verbose_onehot;
+
+			for (auto cell : module->selected_cells())
+			{
+				if (cell->type != "$eq")
+					continue;
+
+				SigSpec A = sigmap(cell->getPort("\\A"));
+				SigSpec B = sigmap(cell->getPort("\\B"));
+
+				int a_width = cell->getParam("\\A_WIDTH").as_int();
+				int b_width = cell->getParam("\\B_WIDTH").as_int();
+
+				if (a_width < b_width) {
+					bool a_signed = cell->getParam("\\A_SIGNED").as_int();
+					A.extend_u0(b_width, a_signed);
+				}
+
+				if (b_width < a_width) {
+					bool b_signed = cell->getParam("\\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("\\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 $eq(%s, %s) cell %s/%s with signal %s.\n",log_signal(A), log_signal(B), log_id(module), log_id(cell), log_signal(sig));
+					sig.extend_u0(GetSize(Y));
+					module->connect(Y, sig);
+				}
+
+				module->remove(cell);
+			}
+		}
+	}
+} OnehotPass;
+
+PRIVATE_NAMESPACE_END
diff --git a/tests/various/pmux2shiftx.v b/tests/various/pmux2shiftx.v
new file mode 100644
index 000000000..fec84187b
--- /dev/null
+++ b/tests/various/pmux2shiftx.v
@@ -0,0 +1,34 @@
+module pmux2shiftx_test (
+	input [2:0] S1,
+	input [5:0] S2,
+	input [1:0] S3,
+	input [9:0] A, B, C, D, D, E, F, G, H,
+	input [9:0] I, J, K, L, M, N, O, P, Q,
+	output reg [9:0] X
+);
+	always @* begin
+		case (S1)
+			3'd 0: X = A;
+			3'd 1: X = B;
+			3'd 2: X = C;
+			3'd 3: X = D;
+			3'd 4: X = E;
+			3'd 5: X = F;
+			3'd 6: X = G;
+			3'd 7: X = H;
+		endcase
+		case (S2)
+			6'd 45: X = I;
+			6'd 47: X = J;
+			6'd 49: X = K;
+			6'd 55: X = L;
+			6'd 57: X = M;
+			6'd 59: X = N;
+		endcase
+		case (S3)
+			2'd 1: X = O;
+			2'd 2: X = P;
+			2'd 3: X = Q;
+		endcase
+	end
+endmodule
diff --git a/tests/various/pmux2shiftx.ys b/tests/various/pmux2shiftx.ys
new file mode 100644
index 000000000..6bb9626eb
--- /dev/null
+++ b/tests/various/pmux2shiftx.ys
@@ -0,0 +1,28 @@
+read_verilog pmux2shiftx.v
+prep
+design -save gold
+
+pmux2shiftx -min_density 70
+
+opt
+
+stat
+# show -width
+select -assert-count 1 t:$sub
+select -assert-count 2 t:$mux
+select -assert-count 2 t:$shift
+select -assert-count 3 t:$shiftx
+
+design -stash gate
+
+design -import gold -as gold
+design -import gate -as gate
+
+miter -equiv -flatten -make_assert -make_outputs gold gate miter
+sat -verify -prove-asserts -show-ports miter
+
+design -load gold
+stat
+
+design -load gate
+stat