diff --git a/passes/opt/muxpack.cc b/passes/opt/muxpack.cc
index ac47f6bf7..250352656 100644
--- a/passes/opt/muxpack.cc
+++ b/passes/opt/muxpack.cc
@@ -159,7 +159,7 @@ struct MuxpackWorker
 				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)
 						sigbit_with_non_chain_users.insert(a_bit);
@@ -189,45 +189,43 @@ struct MuxpackWorker
 		}
 	}
 
+	bool is_start_cell(Cell* cell)
+	{
+		SigSpec a_sig = sigmap(cell->getPort(ID::A));
+		if (cell->type == ID($mux)) {
+			SigSpec b_sig = sigmap(cell->getPort(ID::B));
+			if (sig_chain_prev.count(a_sig) + sig_chain_prev.count(b_sig) != 1)
+				return true;
+
+			if (!sig_chain_prev.count(a_sig))
+				a_sig = b_sig;
+		}
+		else if (cell->type == ID($pmux)) {
+			if (!sig_chain_prev.count(a_sig))
+				return true;
+		}
+		else log_abort();
+
+		for (auto bit : a_sig)
+			if (sigbit_with_non_chain_users.count(bit))
+				return true;
+
+		{
+			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))
+				return true;
+		}
+		return false;
+	}
+
 	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)
-				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);
-		}
+			if (is_start_cell(cell))
+				chain_start_cells.insert(cell);
 	}
 
 	vector<Cell*> create_chain(Cell *start_cell)
@@ -235,7 +233,7 @@ struct MuxpackWorker
 		vector<Cell*> chain;
 
 		Cell *c = start_cell;
-		while (c != nullptr)
+		while (true)
 		{
 			chain.push_back(c);
 
@@ -257,53 +255,39 @@ struct MuxpackWorker
 		if (GetSize(chain) < 2)
 			return;
 
-		int cursor = 0;
-		while (cursor < GetSize(chain))
-		{
-			int cases = GetSize(chain) - cursor;
+		int cases = GetSize(chain);
+		Cell *first_cell = chain.front();
+		Cell *last_cell = chain.back();
 
-			Cell *first_cell = chain[cursor];
-			dict<int, SigBit> taps_dict;
+		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);
 
-			if (cases < 2) {
-				cursor++;
-				continue;
+		mux_count += cases;
+		pmux_count += 1;
+
+		first_cell->type = ID($pmux);
+
+		SigSpec b_sig = first_cell->getPort(ID::B);
+		SigSpec s_sig = first_cell->getPort(ID::S);
+
+		for (int i = 1; i < cases; i++) {
+			Cell* prev_cell = chain[i-1];
+			Cell* cursor_cell = chain[i];
+			if (sigmap(prev_cell->getPort(ID::Y)) == sigmap(cursor_cell->getPort(ID::A))) {
+				b_sig.append(cursor_cell->getPort(ID::B));
+				s_sig.append(cursor_cell->getPort(ID::S));
+			} else {
+				log_assert(cursor_cell->type == ID($mux));
+				b_sig.append(cursor_cell->getPort(ID::A));
+				s_sig.append(module->LogicNot(NEW_ID, cursor_cell->getPort(ID::S)));
 			}
-
-			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;
+			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));
 	}
 
 	void cleanup()