Merge pull request #1258 from YosysHQ/eddie/cleanup

Cleanup a few barnacles across codebase

69 files changed, 405 insertions, 414 deletions

diff --git a/Makefile b/Makefile
index a697e9844..95b5d451b 100644
--- a/Makefile
+++ b/Makefile
@@ -781,7 +781,7 @@ clean:
 	rm -rf kernel/*.pyh
 	if test -d manual; then cd manual && sh clean.sh; fi
 	rm -f $(OBJS) $(GENFILES) $(TARGETS) $(EXTRA_TARGETS) $(EXTRA_OBJS) $(PY_WRAP_INCLUDES) $(PY_WRAPPER_FILE).cc
-	rm -f kernel/version_*.o kernel/version_*.cc abc/abc-[0-9a-f]* abc/libabc-[0-9a-f]*.a
+	rm -f kernel/version_*.o kernel/version_*.cc
 	rm -f libs/*/*.d frontends/*/*.d passes/*/*.d backends/*/*.d kernel/*.d techlibs/*/*.d
 	rm -rf tests/asicworld/*.out tests/asicworld/*.log
 	rm -rf tests/hana/*.out tests/hana/*.log
diff --git a/backends/aiger/xaiger.cc b/backends/aiger/xaiger.cc
index 36a379e34..f49ecbeda 100644
--- a/backends/aiger/xaiger.cc
+++ b/backends/aiger/xaiger.cc
@@ -388,11 +388,11 @@ struct XAigerWriter
 						RTLIL::SigSpec rhs;
 						if (it != cell->connections_.end()) {
 							if (GetSize(it->second) < GetSize(w))
-								it->second.append(RTLIL::SigSpec(RTLIL::S0, GetSize(w)-GetSize(it->second)));
+								it->second.append(RTLIL::SigSpec(State::S0, GetSize(w)-GetSize(it->second)));
 							rhs = it->second;
 						}
 						else {
-							rhs = RTLIL::SigSpec(RTLIL::S0, GetSize(w));
+							rhs = RTLIL::SigSpec(State::S0, GetSize(w));
 							cell->setPort(port_name, rhs);
 						}
 
@@ -400,10 +400,10 @@ struct XAigerWriter
 						for (auto b : rhs.bits()) {
 							SigBit I = sigmap(b);
 							if (b == RTLIL::Sx)
-								b = RTLIL::S0;
+								b = State::S0;
 							else if (I != b) {
 								if (I == RTLIL::Sx)
-									alias_map[b] = RTLIL::S0;
+									alias_map[b] = State::S0;
 								else
 									alias_map[b] = I;
 							}
@@ -671,7 +671,7 @@ struct XAigerWriter
 							if (holes_cell)
 								port_wire.append(holes_wire);
 							else
-								holes_module->connect(holes_wire, RTLIL::S0);
+								holes_module->connect(holes_wire, State::S0);
 						}
 						if (!port_wire.empty())
 							holes_cell->setPort(w->name, port_wire);
diff --git a/backends/blif/blif.cc b/backends/blif/blif.cc
index f32b0f533..b6e38c16c 100644
--- a/backends/blif/blif.cc
+++ b/backends/blif/blif.cc
@@ -377,7 +377,7 @@ struct BlifDumper
 				f << stringf("\n");
 				RTLIL::SigSpec mask = cell->parameters.at("\\LUT");
 				for (int i = 0; i < (1 << width); i++)
-					if (mask[i] == RTLIL::S1) {
+					if (mask[i] == State::S1) {
 						for (int j = width-1; j >= 0; j--) {
 							f << ((i>>j)&1 ? '1' : '0');
 						}
diff --git a/backends/btor/btor.cc b/backends/btor/btor.cc
index 7bacce2af..7c054d655 100644
--- a/backends/btor/btor.cc
+++ b/backends/btor/btor.cc
@@ -616,8 +616,8 @@ struct BtorWorker
 			if (initstate_nid < 0)
 			{
 				int sid = get_bv_sid(1);
-				int one_nid = get_sig_nid(Const(1, 1));
-				int zero_nid = get_sig_nid(Const(0, 1));
+				int one_nid = get_sig_nid(State::S1);
+				int zero_nid = get_sig_nid(State::S0);
 				initstate_nid = next_nid++;
 				btorf("%d state %d\n", initstate_nid, sid);
 				btorf("%d init %d %d %d\n", next_nid++, sid, initstate_nid, one_nid);
diff --git a/backends/firrtl/firrtl.cc b/backends/firrtl/firrtl.cc
index ad4b37353..87db0edf7 100644
--- a/backends/firrtl/firrtl.cc
+++ b/backends/firrtl/firrtl.cc
@@ -122,9 +122,9 @@ struct FirrtlWorker
 			// Current (3/13/2019) conventions:
 			//  generate a constant 0 for clock and a constant 1 for enable if they are undefined.
 			if (!clk.is_fully_def())
-				this->clk = SigSpec(RTLIL::Const(0, 1));
+				this->clk = SigSpec(State::S0);
 			if (!ena.is_fully_def())
-				this->ena = SigSpec(RTLIL::Const(1, 1));
+				this->ena = SigSpec(State::S1);
 		}
 		string gen_read(const char * indent) {
 			string addr_expr = make_expr(addr);
@@ -297,7 +297,7 @@ struct FirrtlWorker
 		std::string cell_type = fid(cell->type);
 		std::string instanceOf;
 		// If this is a parameterized module, its parent module is encoded in the cell type
-		if (cell->type.substr(0, 8) == "$paramod")
+		if (cell->type.begins_with("$paramod"))
 		{
 			std::string::iterator it;
 			for (it = cell_type.begin(); it < cell_type.end(); it++)
@@ -363,7 +363,7 @@ struct FirrtlWorker
 				}
 				// Check for subfield assignment.
 				std::string bitsString = "bits(";
-				if (sinkExpr.substr(0, bitsString.length()) == bitsString ) {
+				if (sinkExpr.compare(0, bitsString.length(), bitsString) == 0) {
 					if (sinkSig == nullptr)
 						log_error("Unknown subfield %s.%s\n", cell_type.c_str(), sinkExpr.c_str());
 					// Don't generate the assignment here.
@@ -877,7 +877,7 @@ struct FirrtlWorker
 			}
 
 			// This may be a parameterized module - paramod.
-			if (cell->type.substr(0, 8) == "$paramod")
+			if (cell->type.begins_with("$paramod"))
 			{
 				process_instance(cell, wire_exprs);
 				continue;
diff --git a/backends/ilang/ilang_backend.cc b/backends/ilang/ilang_backend.cc
index 313af7d5c..e06786220 100644
--- a/backends/ilang/ilang_backend.cc
+++ b/backends/ilang/ilang_backend.cc
@@ -40,8 +40,8 @@ void ILANG_BACKEND::dump_const(std::ostream &f, const RTLIL::Const &data, int wi
 			for (int i = 0; i < width; i++) {
 				log_assert(offset+i < (int)data.bits.size());
 				switch (data.bits[offset+i]) {
-				case RTLIL::S0: break;
-				case RTLIL::S1: val |= 1 << i; break;
+				case State::S0: break;
+				case State::S1: val |= 1 << i; break;
 				default: val = -1; break;
 				}
 			}
@@ -54,8 +54,8 @@ void ILANG_BACKEND::dump_const(std::ostream &f, const RTLIL::Const &data, int wi
 		for (int i = offset+width-1; i >= offset; i--) {
 			log_assert(i < (int)data.bits.size());
 			switch (data.bits[i]) {
-			case RTLIL::S0: f << stringf("0"); break;
-			case RTLIL::S1: f << stringf("1"); break;
+			case State::S0: f << stringf("0"); break;
+			case State::S1: f << stringf("1"); break;
 			case RTLIL::Sx: f << stringf("x"); break;
 			case RTLIL::Sz: f << stringf("z"); break;
 			case RTLIL::Sa: f << stringf("-"); break;
diff --git a/backends/intersynth/intersynth.cc b/backends/intersynth/intersynth.cc
index b0e3cd252..809a0fa09 100644
--- a/backends/intersynth/intersynth.cc
+++ b/backends/intersynth/intersynth.cc
@@ -108,7 +108,7 @@ struct IntersynthBackend : public Backend {
 			if (f.fail())
 				log_error("Can't open lib file `%s'.\n", filename.c_str());
 			RTLIL::Design *lib = new RTLIL::Design;
-			Frontend::frontend_call(lib, &f, filename, (filename.size() > 3 && filename.substr(filename.size()-3) == ".il") ? "ilang" : "verilog");
+			Frontend::frontend_call(lib, &f, filename, (filename.size() > 3 && filename.compare(filename.size()-3, std::string::npos, ".il") == 0 ? "ilang" : "verilog"));
 			libs.push_back(lib);
 		}
 
@@ -183,7 +183,7 @@ struct IntersynthBackend : public Backend {
 					if (param.second.bits.size() != 32) {
 						node_code += stringf(" %s '", RTLIL::id2cstr(param.first));
 						for (int i = param.second.bits.size()-1; i >= 0; i--)
-							node_code += param.second.bits[i] == RTLIL::S1 ? "1" : "0";
+							node_code += param.second.bits[i] == State::S1 ? "1" : "0";
 					} else
 						node_code += stringf(" %s 0x%x", RTLIL::id2cstr(param.first), param.second.as_int());
 				}
diff --git a/backends/smt2/smt2.cc b/backends/smt2/smt2.cc
index ddd680782..081dcda99 100644
--- a/backends/smt2/smt2.cc
+++ b/backends/smt2/smt2.cc
@@ -601,7 +601,7 @@ struct Smt2Worker
 			if (cell->type == "$logic_and") return export_reduce(cell, "(and (or A) (or B))", false);
 			if (cell->type == "$logic_or") return export_reduce(cell, "(or A B)", false);
 
-			if (cell->type == "$mux" || cell->type == "$pmux")
+			if (cell->type.in("$mux", "$pmux"))
 			{
 				int width = GetSize(cell->getPort("\\Y"));
 				std::string processed_expr = get_bv(cell->getPort("\\A"));
@@ -1476,7 +1476,7 @@ struct Smt2Backend : public Backend {
 				int indent = 0;
 				while (indent < GetSize(line) && (line[indent] == ' ' || line[indent] == '\t'))
 					indent++;
-				if (line.substr(indent, 2) == "%%")
+				if (line.compare(indent, 2, "%%") == 0)
 					break;
 				*f << line << std::endl;
 			}
diff --git a/backends/smv/smv.cc b/backends/smv/smv.cc
index e9586fae0..f755307bf 100644
--- a/backends/smv/smv.cc
+++ b/backends/smv/smv.cc
@@ -61,7 +61,7 @@ struct SmvWorker
 		{
 			string name = stringf("_%s", id.c_str());
 
-			if (name.substr(0, 2) == "_\\")
+			if (name.compare(0, 2, "_\\") == 0)
 				name = "_" + name.substr(2);
 
 			for (auto &c : name) {
diff --git a/backends/verilog/verilog_backend.cc b/backends/verilog/verilog_backend.cc
index 776f4eacb..7b1db4776 100644
--- a/backends/verilog/verilog_backend.cc
+++ b/backends/verilog/verilog_backend.cc
@@ -200,9 +200,9 @@ void dump_const(std::ostream &f, const RTLIL::Const &data, int width = -1, int o
 			int32_t val = 0;
 			for (int i = offset+width-1; i >= offset; i--) {
 				log_assert(i < (int)data.bits.size());
-				if (data.bits[i] != RTLIL::S0 && data.bits[i] != RTLIL::S1)
+				if (data.bits[i] != State::S0 && data.bits[i] != State::S1)
 					goto dump_hex;
-				if (data.bits[i] == RTLIL::S1)
+				if (data.bits[i] == State::S1)
 					val |= 1 << (i - offset);
 			}
 			if (decimal)
@@ -219,8 +219,8 @@ void dump_const(std::ostream &f, const RTLIL::Const &data, int width = -1, int o
 			for (int i = offset; i < offset+width; i++) {
 				log_assert(i < (int)data.bits.size());
 				switch (data.bits[i]) {
-				case RTLIL::S0: bin_digits.push_back('0'); break;
-				case RTLIL::S1: bin_digits.push_back('1'); break;
+				case State::S0: bin_digits.push_back('0'); break;
+				case State::S1: bin_digits.push_back('1'); break;
 				case RTLIL::Sx: bin_digits.push_back('x'); break;
 				case RTLIL::Sz: bin_digits.push_back('z'); break;
 				case RTLIL::Sa: bin_digits.push_back('?'); break;
@@ -273,8 +273,8 @@ void dump_const(std::ostream &f, const RTLIL::Const &data, int width = -1, int o
 			for (int i = offset+width-1; i >= offset; i--) {
 				log_assert(i < (int)data.bits.size());
 				switch (data.bits[i]) {
-				case RTLIL::S0: f << stringf("0"); break;
-				case RTLIL::S1: f << stringf("1"); break;
+				case State::S0: f << stringf("0"); break;
+				case State::S1: f << stringf("1"); break;
 				case RTLIL::Sx: f << stringf("x"); break;
 				case RTLIL::Sz: f << stringf("z"); break;
 				case RTLIL::Sa: f << stringf("?"); break;
@@ -380,9 +380,9 @@ void dump_attributes(std::ostream &f, std::string indent, dict<RTLIL::IdString,
 	for (auto it = attributes.begin(); it != attributes.end(); ++it) {
 		f << stringf("%s" "%s %s", indent.c_str(), as_comment ? "/*" : "(*", id(it->first).c_str());
 		f << stringf(" = ");
-		if (modattr && (it->second == Const(0, 1) || it->second == Const(0)))
+		if (modattr && (it->second == State::S0 || it->second == Const(0)))
 			f << stringf(" 0 ");
-		else if (modattr && (it->second == Const(1, 1) || it->second == Const(1)))
+		else if (modattr && (it->second == State::S1 || it->second == Const(1)))
 			f << stringf(" 1 ");
 		else
 			dump_const(f, it->second, -1, 0, false, as_comment);
@@ -604,7 +604,7 @@ bool dump_cell_expr(std::ostream &f, std::string indent, RTLIL::Cell *cell)
 		return true;
 	}
 
-	if (cell->type.substr(0, 6) == "$_DFF_")
+	if (cell->type.begins_with("$_DFF_"))
 	{
 		std::string reg_name = cellname(cell);
 		bool out_is_reg_wire = is_reg_wire(cell->getPort("\\Q"), reg_name);
@@ -645,7 +645,7 @@ bool dump_cell_expr(std::ostream &f, std::string indent, RTLIL::Cell *cell)
 		return true;
 	}
 
-	if (cell->type.substr(0, 8) == "$_DFFSR_")
+	if (cell->type.begins_with("$_DFFSR_"))
 	{
 		char pol_c = cell->type[8], pol_s = cell->type[9], pol_r = cell->type[10];
 
@@ -949,7 +949,7 @@ bool dump_cell_expr(std::ostream &f, std::string indent, RTLIL::Cell *cell)
 		return true;
 	}
 
-	if (cell->type == "$dff" || cell->type == "$adff" || cell->type == "$dffe")
+	if (cell->type.in("$dff", "$adff", "$dffe"))
 	{
 		RTLIL::SigSpec sig_clk, sig_arst, sig_en, val_arst;
 		bool pol_clk, pol_arst = false, pol_en = false;
diff --git a/frontends/aiger/aigerparse.cc b/frontends/aiger/aigerparse.cc
index f8ac2724f..bd0596cc0 100644
--- a/frontends/aiger/aigerparse.cc
+++ b/frontends/aiger/aigerparse.cc
@@ -152,12 +152,12 @@ struct ConstEvalAig
 
 		RTLIL::State eval_ret = RTLIL::Sx;
 		if (cell->type == "$_NOT_") {
-			if (sig_a == RTLIL::S0) eval_ret = RTLIL::S1;
-			else if (sig_a == RTLIL::S1) eval_ret = RTLIL::S0;
+			if (sig_a == State::S0) eval_ret = State::S1;
+			else if (sig_a == State::S1) eval_ret = State::S0;
 		}
 		else if (cell->type == "$_AND_") {
-			if (sig_a == RTLIL::S0) {
-				eval_ret = RTLIL::S0;
+			if (sig_a == State::S0) {
+				eval_ret = State::S0;
 				goto eval_end;
 			}
 
@@ -165,15 +165,15 @@ struct ConstEvalAig
 				RTLIL::SigBit sig_b = cell->getPort("\\B");
 				if (!eval(sig_b))
 					return false;
-				if (sig_b == RTLIL::S0) {
-					eval_ret = RTLIL::S0;
+				if (sig_b == State::S0) {
+					eval_ret = State::S0;
 					goto eval_end;
 				}
 
-				if (sig_a != RTLIL::S1 || sig_b != RTLIL::S1)
+				if (sig_a != State::S1 || sig_b != State::S1)
 					goto eval_end;
 
-				eval_ret = RTLIL::S1;
+				eval_ret = State::S1;
 			}
 		}
 		else log_abort();
@@ -257,7 +257,7 @@ end_of_header:
 
 	RTLIL::Wire* n0 = module->wire("\\__0__");
 	if (n0)
-		module->connect(n0, RTLIL::S0);
+		module->connect(n0, State::S0);
 
 	// Parse footer (symbol table, comments, etc.)
 	unsigned l1;
@@ -372,7 +372,7 @@ void AigerReader::parse_xaiger(const dict<int,IdString> &box_lookup)
 
 	RTLIL::Wire* n0 = module->wire("\\__0__");
 	if (n0)
-		module->connect(n0, RTLIL::S0);
+		module->connect(n0, State::S0);
 
 	// Parse footer (symbol table, comments, etc.)
 	std::string s;
@@ -521,9 +521,9 @@ void AigerReader::parse_aiger_ascii()
 				log_error("Line %u cannot be interpreted as a latch!\n", line_count);
 
 			if (l3 == 0)
-				q_wire->attributes["\\init"] = RTLIL::S0;
+				q_wire->attributes["\\init"] = State::S0;
 			else if (l3 == 1)
-				q_wire->attributes["\\init"] = RTLIL::S1;
+				q_wire->attributes["\\init"] = State::S1;
 			else if (l3 == l1) {
 				//q_wire->attributes["\\init"] = RTLIL::Sx;
 			}
@@ -532,7 +532,7 @@ void AigerReader::parse_aiger_ascii()
 		}
 		else {
 			// AIGER latches are assumed to be initialized to zero
-			q_wire->attributes["\\init"] = RTLIL::S0;
+			q_wire->attributes["\\init"] = State::S0;
 		}
 		latches.push_back(q_wire);
 	}
@@ -646,9 +646,9 @@ void AigerReader::parse_aiger_binary()
 				log_error("Line %u cannot be interpreted as a latch!\n", line_count);
 
 			if (l3 == 0)
-				q_wire->attributes["\\init"] = RTLIL::S0;
+				q_wire->attributes["\\init"] = State::S0;
 			else if (l3 == 1)
-				q_wire->attributes["\\init"] = RTLIL::S1;
+				q_wire->attributes["\\init"] = State::S1;
 			else if (l3 == l1) {
 				//q_wire->attributes["\\init"] = RTLIL::Sx;
 			}
@@ -657,7 +657,7 @@ void AigerReader::parse_aiger_binary()
 		}
 		else {
 			// AIGER latches are assumed to be initialized to zero
-			q_wire->attributes["\\init"] = RTLIL::S0;
+			q_wire->attributes["\\init"] = State::S0;
 		}
 		latches.push_back(q_wire);
 	}
diff --git a/frontends/ast/ast.cc b/frontends/ast/ast.cc
index c8ca6d164..0d6626b19 100644
--- a/frontends/ast/ast.cc
+++ b/frontends/ast/ast.cc
@@ -283,8 +283,8 @@ void AstNode::dumpAst(FILE *f, std::string indent) const
 	if (!bits.empty()) {
 		fprintf(f, " bits='");
 		for (size_t i = bits.size(); i > 0; i--)
-			fprintf(f, "%c", bits[i-1] == RTLIL::S0 ? '0' :
-					bits[i-1] == RTLIL::S1 ? '1' :
+			fprintf(f, "%c", bits[i-1] == State::S0 ? '0' :
+					bits[i-1] == State::S1 ? '1' :
 					bits[i-1] == RTLIL::Sx ? 'x' :
 					bits[i-1] == RTLIL::Sz ? 'z' : '?');
 		fprintf(f, "'(%d)", GetSize(bits));
@@ -716,7 +716,7 @@ AstNode *AstNode::mkconst_int(uint32_t v, bool is_signed, int width)
 	node->integer = v;
 	node->is_signed = is_signed;
 	for (int i = 0; i < width; i++) {
-		node->bits.push_back((v & 1) ? RTLIL::S1 : RTLIL::S0);
+		node->bits.push_back((v & 1) ? State::S1 : State::S0);
 		v = v >> 1;
 	}
 	node->range_valid = true;
@@ -733,9 +733,9 @@ AstNode *AstNode::mkconst_bits(const std::vector<RTLIL::State> &v, bool is_signe
 	node->bits = v;
 	for (size_t i = 0; i < 32; i++) {
 		if (i < node->bits.size())
-			node->integer |= (node->bits[i] == RTLIL::S1) << i;
+			node->integer |= (node->bits[i] == State::S1) << i;
 		else if (is_signed && !node->bits.empty())
-			node->integer |= (node->bits.back() == RTLIL::S1) << i;
+			node->integer |= (node->bits.back() == State::S1) << i;
 	}
 	node->range_valid = true;
 	node->range_left = node->bits.size()-1;
@@ -767,7 +767,7 @@ AstNode *AstNode::mkconst_str(const std::string &str)
 	for (size_t i = 0; i < str.size(); i++) {
 		unsigned char ch = str[str.size() - i - 1];
 		for (int j = 0; j < 8; j++) {
-			data.push_back((ch & 1) ? RTLIL::S1 : RTLIL::S0);
+			data.push_back((ch & 1) ? State::S1 : State::S0);
 			ch = ch >> 1;
 		}
 	}
@@ -780,7 +780,7 @@ AstNode *AstNode::mkconst_str(const std::string &str)
 bool AstNode::bits_only_01() const
 {
 	for (auto bit : bits)
-		if (bit != RTLIL::S0 && bit != RTLIL::S1)
+		if (bit != State::S0 && bit != State::S1)
 			return false;
 	return true;
 }
@@ -1164,7 +1164,7 @@ void AST::process(RTLIL::Design *design, AstNode *ast, bool dump_ast1, bool dump
 				}
 			}
 
-			if (flag_icells && (*it)->str.substr(0, 2) == "\\$")
+			if (flag_icells && (*it)->str.compare(0, 2, "\\$") == 0)
 				(*it)->str = (*it)->str.substr(1);
 
 			if (defer)
@@ -1463,7 +1463,7 @@ std::string AstModule::derive_common(RTLIL::Design *design, dict<RTLIL::IdString
 {
 	std::string stripped_name = name.str();
 
-	if (stripped_name.substr(0, 9) == "$abstract")
+	if (stripped_name.compare(0, 9, "$abstract") == 0)
 		stripped_name = stripped_name.substr(9);
 
 	log_header(design, "Executing AST frontend in derive mode using pre-parsed AST for module `%s'.\n", stripped_name.c_str());
diff --git a/frontends/ast/genrtlil.cc b/frontends/ast/genrtlil.cc
index 571ddd988..407a34472 100644
--- a/frontends/ast/genrtlil.cc
+++ b/frontends/ast/genrtlil.cc
@@ -1516,7 +1516,7 @@ RTLIL::SigSpec AstNode::genRTLIL(int width_hint, bool sign_hint)
 				AstNode *child = *it;
 				if (child->type == AST_CELLTYPE) {
 					cell->type = child->str;
-					if (flag_icells && cell->type.substr(0, 2) == "\\$")
+					if (flag_icells && cell->type.begins_with("\\$"))
 						cell->type = cell->type.substr(1);
 					continue;
 				}
diff --git a/frontends/ast/simplify.cc b/frontends/ast/simplify.cc
index 6fb94d80b..54b9efaad 100644
--- a/frontends/ast/simplify.cc
+++ b/frontends/ast/simplify.cc
@@ -2319,7 +2319,7 @@ skip_dynamic_range_lvalue_expansion:;
 				if (attr.first.str().rfind("\\via_celltype_defparam_", 0) == 0)
 				{
 					AstNode *cell_arg = new AstNode(AST_PARASET, attr.second->clone());
-					cell_arg->str = RTLIL::escape_id(attr.first.str().substr(strlen("\\via_celltype_defparam_")));
+					cell_arg->str = RTLIL::escape_id(attr.first.substr(strlen("\\via_celltype_defparam_")));
 					cell->children.push_back(cell_arg);
 				}
 
@@ -2793,13 +2793,13 @@ AstNode *AstNode::readmem(bool is_readmemh, std::string mem_filename, AstNode *m
 		std::getline(f, line);
 
 		for (int i = 0; i < GetSize(line); i++) {
-			if (in_comment && line.substr(i, 2) == "*/") {
+			if (in_comment && line.compare(i, 2, "*/") == 0) {
 				line[i] = ' ';
 				line[i+1] = ' ';
 				in_comment = false;
 				continue;
 			}
-			if (!in_comment && line.substr(i, 2) == "/*")
+			if (!in_comment && line.compare(i, 2, "/*") == 0)
 				in_comment = true;
 			if (in_comment)
 				line[i] = ' ';
@@ -2808,7 +2808,7 @@ AstNode *AstNode::readmem(bool is_readmemh, std::string mem_filename, AstNode *m
 		while (1)
 		{
 			token = next_token(line, " \t\r\n");
-			if (token.empty() || token.substr(0, 2) == "//")
+			if (token.empty() || token.compare(0, 2, "//") == 0)
 				break;
 
 			if (token[0] == '@') {
diff --git a/frontends/verific/verific.cc b/frontends/verific/verific.cc
index 39a5a6b50..17c4a1e5b 100644
--- a/frontends/verific/verific.cc
+++ b/frontends/verific/verific.cc
@@ -2189,7 +2189,7 @@ struct VerificPass : public Pass {
 			veri_file::DefineMacro("VERIFIC");
 			veri_file::DefineMacro(args[argidx] == "-formal" ? "FORMAL" : "SYNTHESIS");
 
-			for (argidx++; argidx < GetSize(args) && GetSize(args[argidx]) >= 2 && args[argidx].substr(0, 2) == "-D"; argidx++) {
+			for (argidx++; argidx < GetSize(args) && GetSize(args[argidx]) >= 2 && args[argidx].compare(0, 2, "-D") == 0; argidx++) {
 				std::string name = args[argidx].substr(2);
 				if (args[argidx] == "-D") {
 					if (++argidx >= GetSize(args))
@@ -2336,7 +2336,7 @@ struct VerificPass : public Pass {
 				break;
 			}
 
-			if (argidx > GetSize(args) && args[argidx].substr(0, 1) == "-")
+			if (argidx > GetSize(args) && args[argidx].compare(0, 1, "-") == 0)
 				cmd_error(args, argidx, "unknown option");
 
 			if (mode_all)
diff --git a/frontends/verific/verificsva.cc b/frontends/verific/verificsva.cc
index 8ea8372d3..909e9b4f1 100644
--- a/frontends/verific/verificsva.cc
+++ b/frontends/verific/verificsva.cc
@@ -357,7 +357,7 @@ struct SvaFsm
 		for (int i = 0; i < GetSize(nodes); i++)
 		{
 			if (next_state_sig[i] != State::S0) {
-				clocking.addDff(NEW_ID, next_state_sig[i], state_wire[i], Const(0, 1));
+				clocking.addDff(NEW_ID, next_state_sig[i], state_wire[i], State::S0);
 			} else {
 				module->connect(state_wire[i], State::S0);
 			}
diff --git a/frontends/verilog/const2ast.cc b/frontends/verilog/const2ast.cc
index f6a17b242..4bf5b1cf5 100644
--- a/frontends/verilog/const2ast.cc
+++ b/frontends/verilog/const2ast.cc
@@ -99,7 +99,7 @@ static void my_strtobin(std::vector<RTLIL::State> &data, const char *str, int le
 
 	if (base == 10) {
 		while (!digits.empty())
-			data.push_back(my_decimal_div_by_two(digits) ? RTLIL::S1 : RTLIL::S0);
+			data.push_back(my_decimal_div_by_two(digits) ? State::S1 : State::S0);
 	} else {
 		int bits_per_digit = my_ilog2(base-1);
 		for (auto it = digits.rbegin(), e = digits.rend(); it != e; it++) {
@@ -115,17 +115,17 @@ static void my_strtobin(std::vector<RTLIL::State> &data, const char *str, int le
 				else if (*it == 0xf2)
 					data.push_back(RTLIL::Sa);
 				else
-					data.push_back((*it & bitmask) ? RTLIL::S1 : RTLIL::S0);
+					data.push_back((*it & bitmask) ? State::S1 : State::S0);
 			}
 		}
 	}
 
 	int len = GetSize(data);
-	RTLIL::State msb = data.empty() ? RTLIL::S0 : data.back();
+	RTLIL::State msb = data.empty() ? State::S0 : data.back();
 
 	if (len_in_bits < 0) {
 		if (len < 32)
-			data.resize(32, msb == RTLIL::S0 || msb == RTLIL::S1 ? RTLIL::S0 : msb);
+			data.resize(32, msb == State::S0 || msb == State::S1 ? RTLIL::S0 : msb);
 		return;
 	}
 
@@ -133,11 +133,11 @@ static void my_strtobin(std::vector<RTLIL::State> &data, const char *str, int le
 		log_file_error(current_filename, get_line_num(), "Unsized constant must have width of 1 bit, but have %d bits!\n", len);
 
 	for (len = len - 1; len >= 0; len--)
-		if (data[len] == RTLIL::S1)
+		if (data[len] == State::S1)
 			break;
-	if (msb == RTLIL::S0 || msb == RTLIL::S1) {
+	if (msb == State::S0 || msb == State::S1) {
 		len += 1;
-		data.resize(len_in_bits, RTLIL::S0);
+		data.resize(len_in_bits, State::S0);
 	} else {
 		len += 2;
 		data.resize(len_in_bits, msb);
@@ -169,7 +169,7 @@ AstNode *VERILOG_FRONTEND::const2ast(std::string code, char case_type, bool warn
 		for (int i = 0; i < len; i++) {
 			unsigned char ch = str[len - i];
 			for (int j = 0; j < 8; j++) {
-				data.push_back((ch & 1) ? RTLIL::S1 : RTLIL::S0);
+				data.push_back((ch & 1) ? State::S1 : State::S0);
 				ch = ch >> 1;
 			}
 		}
@@ -190,8 +190,8 @@ AstNode *VERILOG_FRONTEND::const2ast(std::string code, char case_type, bool warn
 	if (*endptr == 0) {
 		std::vector<RTLIL::State> data;
 		my_strtobin(data, str, -1, 10, case_type, false);
-		if (data.back() == RTLIL::S1)
-			data.push_back(RTLIL::S0);
+		if (data.back() == State::S1)
+			data.push_back(State::S0);
 		return AstNode::mkconst_bits(data, true);
 	}
 
@@ -237,8 +237,8 @@ AstNode *VERILOG_FRONTEND::const2ast(std::string code, char case_type, bool warn
 			}
 		}
 		if (len_in_bits < 0) {
-			if (is_signed && data.back() == RTLIL::S1)
-				data.push_back(RTLIL::S0);
+			if (is_signed && data.back() == State::S1)
+				data.push_back(State::S0);
 		}
 		return AstNode::mkconst_bits(data, is_signed, is_unsized);
 	}
diff --git a/frontends/verilog/verilog_parser.y b/frontends/verilog/verilog_parser.y
index 0fec445fa..4afd72b73 100644
--- a/frontends/verilog/verilog_parser.y
+++ b/frontends/verilog/verilog_parser.y
@@ -274,7 +274,7 @@ hierarchical_id:
 		$$ = $1;
 	} |
 	hierarchical_id TOK_PACKAGESEP TOK_ID {
-		if ($3->substr(0, 1) == "\\")
+		if ($3->compare(0, 1, "\\") == 0)
 			*$1 += "::" + $3->substr(1);
 		else
 			*$1 += "::" + *$3;
@@ -282,7 +282,7 @@ hierarchical_id:
 		$$ = $1;
 	} |
 	hierarchical_id '.' TOK_ID {
-		if ($3->substr(0, 1) == "\\")
+		if ($3->compare(0, 1, "\\") == 0)
 			*$1 += "." + $3->substr(1);
 		else
 			*$1 += "." + *$3;
@@ -2184,7 +2184,7 @@ basic_expr:
 		$$ = $1;
 	} |
 	'(' expr ')' TOK_CONSTVAL {
-		if ($4->substr(0, 1) != "'")
+		if ($4->compare(0, 1, "'") != 0)
 			frontend_verilog_yyerror("Cast operation must be applied on sized constants e.g. (<expr>)<constval> , while %s is not a sized constant.", $4->c_str());
 		AstNode *bits = $2;
 		AstNode *val = const2ast(*$4, case_type_stack.size() == 0 ? 0 : case_type_stack.back(), !lib_mode);
@@ -2194,7 +2194,7 @@ basic_expr:
 		delete $4;
 	} |
 	hierarchical_id TOK_CONSTVAL {
-		if ($2->substr(0, 1) != "'")
+		if ($2->compare(0, 1, "'") != 0)
 			frontend_verilog_yyerror("Cast operation must be applied on sized constants, e.g. <ID>\'d0, while %s is not a sized constant.", $2->c_str());
 		AstNode *bits = new AstNode(AST_IDENTIFIER);
 		bits->str = *$1;
diff --git a/kernel/celltypes.h b/kernel/celltypes.h
index d1d9bf943..1256fbcba 100644
--- a/kernel/celltypes.h
+++ b/kernel/celltypes.h
@@ -282,8 +282,8 @@ struct CellTypes
 	static RTLIL::Const eval_not(RTLIL::Const v)
 	{
 		for (auto &bit : v.bits)
-			if (bit == RTLIL::S0) bit = RTLIL::S1;
-			else if (bit == RTLIL::S1) bit = RTLIL::S0;
+			if (bit == State::S0) bit = State::S1;
+			else if (bit == State::S1) bit = State::S0;
 		return v;
 	}
 
@@ -389,15 +389,15 @@ struct CellTypes
 
 			std::vector<RTLIL::State> t = cell->parameters.at("\\LUT").bits;
 			while (GetSize(t) < (1 << width))
-				t.push_back(RTLIL::S0);
+				t.push_back(State::S0);
 			t.resize(1 << width);
 
 			for (int i = width-1; i >= 0; i--) {
 				RTLIL::State sel = arg1.bits.at(i);
 				std::vector<RTLIL::State> new_t;
-				if (sel == RTLIL::S0)
+				if (sel == State::S0)
 					new_t = std::vector<RTLIL::State>(t.begin(), t.begin() + GetSize(t)/2);
-				else if (sel == RTLIL::S1)
+				else if (sel == State::S1)
 					new_t = std::vector<RTLIL::State>(t.begin() + GetSize(t)/2, t.end());
 				else
 					for (int j = 0; j < GetSize(t)/2; j++)
@@ -416,7 +416,7 @@ struct CellTypes
 			std::vector<RTLIL::State> t = cell->parameters.at("\\TABLE").bits;
 
 			while (GetSize(t) < width*depth*2)
-				t.push_back(RTLIL::S0);
+				t.push_back(State::S0);
 
 			RTLIL::State default_ret = State::S0;
 
diff --git a/kernel/consteval.h b/kernel/consteval.h
index f70dfa0fb..521ce96d4 100644
--- a/kernel/consteval.h
+++ b/kernel/consteval.h
@@ -114,8 +114,8 @@ struct ConstEval
 				bool carry = sig_ci.as_bool();
 
 				for (int i = 0; i < GetSize(coval); i++) {
-					carry = (sig_g[i] == RTLIL::S1) || (sig_p[i] == RTLIL::S1 && carry);
-					coval.bits[i] = carry ? RTLIL::S1 : RTLIL::S0;
+					carry = (sig_g[i] == State::S1) || (sig_p[i] == RTLIL::S1 && carry);
+					coval.bits[i] = carry ? State::S1 : State::S0;
 				}
 
 				set(sig_co, coval);
@@ -254,8 +254,8 @@ struct ConstEval
 			sig_a.extend_u0(GetSize(sig_y), signed_a);
 			sig_b.extend_u0(GetSize(sig_y), signed_b);
 
-			bool carry = sig_ci[0] == RTLIL::S1;
-			bool b_inv = sig_bi[0] == RTLIL::S1;
+			bool carry = sig_ci[0] == State::S1;
+			bool b_inv = sig_bi[0] == State::S1;
 
 			for (int i = 0; i < GetSize(sig_y); i++)
 			{
@@ -264,22 +264,22 @@ struct ConstEval
 				if (!x_inputs.is_fully_def()) {
 					set(sig_x[i], RTLIL::Sx);
 				} else {
-					bool bit_a = sig_a[i] == RTLIL::S1;
-					bool bit_b = (sig_b[i] == RTLIL::S1) != b_inv;
+					bool bit_a = sig_a[i] == State::S1;
+					bool bit_b = (sig_b[i] == State::S1) != b_inv;
 					bool bit_x = bit_a != bit_b;
-					set(sig_x[i], bit_x ? RTLIL::S1 : RTLIL::S0);
+					set(sig_x[i], bit_x ? State::S1 : State::S0);
 				}
 
 				if (any_input_undef) {
 					set(sig_y[i], RTLIL::Sx);
 					set(sig_co[i], RTLIL::Sx);
 				} else {
-					bool bit_a = sig_a[i] == RTLIL::S1;
-					bool bit_b = (sig_b[i] == RTLIL::S1) != b_inv;
+					bool bit_a = sig_a[i] == State::S1;
+					bool bit_b = (sig_b[i] == State::S1) != b_inv;
 					bool bit_y = (bit_a != bit_b) != carry;
 					carry = (bit_a && bit_b) || (bit_a && carry) || (bit_b && carry);
-					set(sig_y[i], bit_y ? RTLIL::S1 : RTLIL::S0);
-					set(sig_co[i], carry ? RTLIL::S1 : RTLIL::S0);
+					set(sig_y[i], bit_y ? State::S1 : State::S0);
+					set(sig_co[i], carry ? State::S1 : State::S0);
 				}
 			}
 		}
diff --git a/kernel/macc.h b/kernel/macc.h
index 286ce567f..c7595ebc1 100644
--- a/kernel/macc.h
+++ b/kernel/macc.h
@@ -70,9 +70,9 @@ struct Macc
 				while (GetSize(port.in_b) > 1 && port.in_b[GetSize(port.in_b)-1] == port.in_b[GetSize(port.in_b)-2])
 					port.in_b.remove(GetSize(port.in_b)-1);
 			} else {
-				while (GetSize(port.in_a) > 1 && port.in_a[GetSize(port.in_a)-1] == RTLIL::S0)
+				while (GetSize(port.in_a) > 1 && port.in_a[GetSize(port.in_a)-1] == State::S0)
 					port.in_a.remove(GetSize(port.in_a)-1);
-				while (GetSize(port.in_b) > 1 && port.in_b[GetSize(port.in_b)-1] == RTLIL::S0)
+				while (GetSize(port.in_b) > 1 && port.in_b[GetSize(port.in_b)-1] == State::S0)
 					port.in_b.remove(GetSize(port.in_b)-1);
 			}
 
@@ -80,9 +80,9 @@ struct Macc
 		}
 
 		for (auto &bit : bit_ports)
-			if (bit == RTLIL::S1)
+			if (bit == State::S1)
 				off = const_add(off, RTLIL::Const(1, width), false, false, width);
-			else if (bit != RTLIL::S0)
+			else if (bit != State::S0)
 				new_bit_ports.append(bit);
 
 		if (off.as_bool()) {
@@ -113,10 +113,10 @@ struct Macc
 #endif
 
 		int num_bits = 0;
-		if (config_bits[config_cursor++] == RTLIL::S1) num_bits |= 1;
-		if (config_bits[config_cursor++] == RTLIL::S1) num_bits |= 2;
-		if (config_bits[config_cursor++] == RTLIL::S1) num_bits |= 4;
-		if (config_bits[config_cursor++] == RTLIL::S1) num_bits |= 8;
+		if (config_bits[config_cursor++] == State::S1) num_bits |= 1;
+		if (config_bits[config_cursor++] == State::S1) num_bits |= 2;
+		if (config_bits[config_cursor++] == State::S1) num_bits |= 4;
+		if (config_bits[config_cursor++] == State::S1) num_bits |= 8;
 
 		int port_a_cursor = 0;
 		while (port_a_cursor < GetSize(port_a))
@@ -124,12 +124,12 @@ struct Macc
 			log_assert(config_cursor + 2 + 2*num_bits <= config_width);
 
 			port_t this_port;
-			this_port.is_signed = config_bits[config_cursor++] == RTLIL::S1;
-			this_port.do_subtract = config_bits[config_cursor++] == RTLIL::S1;
+			this_port.is_signed = config_bits[config_cursor++] == State::S1;
+			this_port.do_subtract = config_bits[config_cursor++] == State::S1;
 
 			int size_a = 0;
 			for (int i = 0; i < num_bits; i++)
-				if (config_bits[config_cursor++] == RTLIL::S1)
+				if (config_bits[config_cursor++] == State::S1)
 					size_a |= 1 << i;
 
 			this_port.in_a = port_a.extract(port_a_cursor, size_a);
@@ -137,7 +137,7 @@ struct Macc
 
 			int size_b = 0;
 			for (int i = 0; i < num_bits; i++)
-				if (config_bits[config_cursor++] == RTLIL::S1)
+				if (config_bits[config_cursor++] == State::S1)
 					size_b |= 1 << i;
 
 			this_port.in_b = port_a.extract(port_a_cursor, size_b);
@@ -166,26 +166,26 @@ struct Macc
 			num_bits++, max_size /= 2;
 
 		log_assert(num_bits < 16);
-		config_bits.push_back(num_bits & 1 ? RTLIL::S1 : RTLIL::S0);
-		config_bits.push_back(num_bits & 2 ? RTLIL::S1 : RTLIL::S0);
-		config_bits.push_back(num_bits & 4 ? RTLIL::S1 : RTLIL::S0);
-		config_bits.push_back(num_bits & 8 ? RTLIL::S1 : RTLIL::S0);
+		config_bits.push_back(num_bits & 1 ? State::S1 : State::S0);
+		config_bits.push_back(num_bits & 2 ? State::S1 : State::S0);
+		config_bits.push_back(num_bits & 4 ? State::S1 : State::S0);
+		config_bits.push_back(num_bits & 8 ? State::S1 : State::S0);
 
 		for (auto &port : ports)
 		{
 			if (GetSize(port.in_a) == 0)
 				continue;
 
-			config_bits.push_back(port.is_signed ? RTLIL::S1 : RTLIL::S0);
-			config_bits.push_back(port.do_subtract ? RTLIL::S1 : RTLIL::S0);
+			config_bits.push_back(port.is_signed ? State::S1 : State::S0);
+			config_bits.push_back(port.do_subtract ? State::S1 : State::S0);
 
 			int size_a = GetSize(port.in_a);
 			for (int i = 0; i < num_bits; i++)
-				config_bits.push_back(size_a & (1 << i) ? RTLIL::S1 : RTLIL::S0);
+				config_bits.push_back(size_a & (1 << i) ? State::S1 : State::S0);
 
 			int size_b = GetSize(port.in_b);
 			for (int i = 0; i < num_bits; i++)
-				config_bits.push_back(size_b & (1 << i) ? RTLIL::S1 : RTLIL::S0);
+				config_bits.push_back(size_b & (1 << i) ? State::S1 : State::S0);
 
 			port_a.append(port.in_a);
 			port_a.append(port.in_b);
@@ -202,7 +202,7 @@ struct Macc
 	bool eval(RTLIL::Const &result) const
 	{
 		for (auto &bit : result.bits)
-			bit = RTLIL::S0;
+			bit = State::S0;
 
 		for (auto &port : ports)
 		{
diff --git a/kernel/register.cc b/kernel/register.cc
index e4237cac4..1fd1bad1d 100644
--- a/kernel/register.cc
+++ b/kernel/register.cc
@@ -200,7 +200,7 @@ void Pass::extra_args(std::vector<std::string> args, size_t argidx, RTLIL::Desig
 	{
 		std::string arg = args[argidx];
 
-		if (arg.substr(0, 1) == "-")
+		if (arg.compare(0, 1, "-") == 0)
 			cmd_error(args, argidx, "Unknown option or option in arguments.");
 
 		if (!select)
@@ -449,7 +449,7 @@ void Frontend::extra_args(std::istream *&f, std::string &filename, std::vector<s
 	{
 		std::string arg = args[argidx];
 
-		if (arg.substr(0, 1) == "-")
+		if (arg.compare(0, 1, "-") == 0)
 			cmd_error(args, argidx, "Unknown option or option in arguments.");
 		if (f != NULL)
 			cmd_error(args, argidx, "Extra filename argument in direct file mode.");
@@ -457,7 +457,7 @@ void Frontend::extra_args(std::istream *&f, std::string &filename, std::vector<s
 		filename = arg;
 		if (filename == "<<" && argidx+1 < args.size())
 			filename += args[++argidx];
-		if (filename.substr(0, 2) == "<<") {
+		if (filename.compare(0, 2, "<<") == 0) {
 			if (Frontend::current_script_file == NULL)
 				log_error("Unexpected here document '%s' outside of script!\n", filename.c_str());
 			if (filename.size() <= 2)
@@ -475,7 +475,7 @@ void Frontend::extra_args(std::istream *&f, std::string &filename, std::vector<s
 						break;
 				}
 				size_t indent = buffer.find_first_not_of(" \t\r\n");
-				if (indent != std::string::npos && buffer.substr(indent, eot_marker.size()) == eot_marker)
+				if (indent != std::string::npos && buffer.compare(indent, eot_marker.size(), eot_marker) == 0)
 					break;
 				last_here_document += buffer;
 			}
@@ -522,7 +522,7 @@ void Frontend::extra_args(std::istream *&f, std::string &filename, std::vector<s
 			log_cmd_error("Can't open input file `%s' for reading: %s\n", filename.c_str(), strerror(errno));
 
 		for (size_t i = argidx+1; i < args.size(); i++)
-			if (args[i].substr(0, 1) == "-")
+			if (args[i].compare(0, 1, "-") == 0)
 				cmd_error(args, i, "Found option, expected arguments.");
 
 		if (argidx+1 < args.size()) {
@@ -612,7 +612,7 @@ void Backend::extra_args(std::ostream *&f, std::string &filename, std::vector<st
 	{
 		std::string arg = args[argidx];
 
-		if (arg.substr(0, 1) == "-" && arg != "-")
+		if (arg.compare(0, 1, "-") == 0 && arg != "-")
 			cmd_error(args, argidx, "Unknown option or option in arguments.");
 		if (f != NULL)
 			cmd_error(args, argidx, "Extra filename argument in direct file mode.");
@@ -625,7 +625,7 @@ void Backend::extra_args(std::ostream *&f, std::string &filename, std::vector<st
 
 		filename = arg;
 		rewrite_filename(filename);
-		if (filename.size() > 3 && filename.substr(filename.size()-3) == ".gz") {
+		if (filename.size() > 3 && filename.compare(filename.size()-3, std::string::npos, ".gz") == 0) {
 #ifdef YOSYS_ENABLE_ZLIB
 			gzip_ostream *gf = new gzip_ostream;
 			if (!gf->open(filename)) {
diff --git a/kernel/rtlil.cc b/kernel/rtlil.cc
index ba8472ec1..fade0bc36 100644
--- a/kernel/rtlil.cc
+++ b/kernel/rtlil.cc
@@ -47,7 +47,7 @@ RTLIL::Const::Const(std::string str)
 	for (int i = str.size()-1; i >= 0; i--) {
 		unsigned char ch = str[i];
 		for (int j = 0; j < 8; j++) {
-			bits.push_back((ch & 1) != 0 ? RTLIL::S1 : RTLIL::S0);
+			bits.push_back((ch & 1) != 0 ? State::S1 : State::S0);
 			ch = ch >> 1;
 		}
 	}
@@ -57,7 +57,7 @@ RTLIL::Const::Const(int val, int width)
 {
 	flags = RTLIL::CONST_FLAG_NONE;
 	for (int i = 0; i < width; i++) {
-		bits.push_back((val & 1) != 0 ? RTLIL::S1 : RTLIL::S0);
+		bits.push_back((val & 1) != 0 ? State::S1 : State::S0);
 		val = val >> 1;
 	}
 }
@@ -73,7 +73,7 @@ RTLIL::Const::Const(const std::vector<bool> &bits)
 {
 	flags = RTLIL::CONST_FLAG_NONE;
 	for (auto b : bits)
-		this->bits.push_back(b ? RTLIL::S1 : RTLIL::S0);
+		this->bits.push_back(b ? State::S1 : State::S0);
 }
 
 RTLIL::Const::Const(const RTLIL::Const &c)
@@ -106,7 +106,7 @@ bool RTLIL::Const::operator !=(const RTLIL::Const &other) const
 bool RTLIL::Const::as_bool() const
 {
 	for (size_t i = 0; i < bits.size(); i++)
-		if (bits[i] == RTLIL::S1)
+		if (bits[i] == State::S1)
 			return true;
 	return false;
 }
@@ -115,9 +115,9 @@ int RTLIL::Const::as_int(bool is_signed) const
 {
 	int32_t ret = 0;
 	for (size_t i = 0; i < bits.size() && i < 32; i++)
-		if (bits[i] == RTLIL::S1)
+		if (bits[i] == State::S1)
 			ret |= 1 << i;
-	if (is_signed && bits.back() == RTLIL::S1)
+	if (is_signed && bits.back() == State::S1)
 		for (size_t i = bits.size(); i < 32; i++)
 			ret |= 1 << i;
 	return ret;
@@ -828,8 +828,8 @@ namespace {
 
 		void check()
 		{
-			if (cell->type.substr(0, 1) != "$" || cell->type.substr(0, 3) == "$__" || cell->type.substr(0, 8) == "$paramod" || cell->type.substr(0,10) == "$fmcombine" ||
-					cell->type.substr(0, 9) == "$verific$" || cell->type.substr(0, 7) == "$array:" || cell->type.substr(0, 8) == "$extern:")
+			if (!cell->type.begins_with("$") || cell->type.begins_with("$__") || cell->type.begins_with("$paramod") || cell->type.begins_with("$fmcombine") ||
+					cell->type.begins_with("$verific$") || cell->type.begins_with("$array:") || cell->type.begins_with("$extern:"))
 				return;
 
 			if (cell->type.in("$not", "$pos", "$neg")) {
@@ -940,7 +940,7 @@ namespace {
 				return;
 			}
 
-			if (cell->type == "$logic_and" || cell->type == "$logic_or") {
+			if (cell->type.in("$logic_and", "$logic_or")) {
 				param_bool("\\A_SIGNED");
 				param_bool("\\B_SIGNED");
 				port("\\A", param("\\A_WIDTH"));
@@ -2553,8 +2553,8 @@ void RTLIL::Cell::check()
 
 void RTLIL::Cell::fixup_parameters(bool set_a_signed, bool set_b_signed)
 {
-	if (type.substr(0, 1) != "$" || type.substr(0, 2) == "$_" || type.substr(0, 8) == "$paramod" || type.substr(0,10) == "$fmcombine" ||
-			type.substr(0, 9) == "$verific$" || type.substr(0, 7) == "$array:" || type.substr(0, 8) == "$extern:")
+	if (!type.begins_with("$") || type.begins_with("$_") || type.begins_with("$paramod") || type.begins_with("$fmcombine") ||
+			type.begins_with("$verific$") || type.begins_with("$array:") || type.begins_with("$extern:"))
 		return;
 
 	if (type == "$mux" || type == "$pmux") {
diff --git a/kernel/rtlil.h b/kernel/rtlil.h
index c07d39c65..37b5f984c 100644
--- a/kernel/rtlil.h
+++ b/kernel/rtlil.h
@@ -276,20 +276,24 @@ namespace RTLIL
 				return std::string(c_str() + pos, len);
 		}
 
+		int compare(size_t pos, size_t len, const char* s) const {
+			return strncmp(c_str()+pos, s, len);
+		}
+
 		bool begins_with(const char* prefix) const {
 			size_t len = strlen(prefix);
 			if (size() < len) return false;
-			return substr(0, len) == prefix;
+			return compare(0, len, prefix) == 0;
 		}
 
 		bool ends_with(const char* suffix) const {
 			size_t len = strlen(suffix);
 			if (size() < len) return false;
-			return substr(size()-len) == suffix;
+			return compare(size()-len, len, suffix) == 0;
 		}
 
 		size_t size() const {
-			return str().size();
+			return strlen(c_str());
 		}
 
 		bool empty() const {
@@ -1404,7 +1408,7 @@ struct RTLIL::Process : public RTLIL::AttrObject
 
 inline RTLIL::SigBit::SigBit() : wire(NULL), data(RTLIL::State::S0) { }
 inline RTLIL::SigBit::SigBit(RTLIL::State bit) : wire(NULL), data(bit) { }
-inline RTLIL::SigBit::SigBit(bool bit) : wire(NULL), data(bit ? RTLIL::S1 : RTLIL::S0) { }
+inline RTLIL::SigBit::SigBit(bool bit) : wire(NULL), data(bit ? State::S1 : State::S0) { }
 inline RTLIL::SigBit::SigBit(RTLIL::Wire *wire) : wire(wire), offset(0) { log_assert(wire && wire->width == 1); }
 inline RTLIL::SigBit::SigBit(RTLIL::Wire *wire, int offset) : wire(wire), offset(offset) { log_assert(wire != nullptr); }
 inline RTLIL::SigBit::SigBit(const RTLIL::SigChunk &chunk) : wire(chunk.wire) { log_assert(chunk.width == 1); if (wire) offset = chunk.offset; else data = chunk.data[0]; }
diff --git a/kernel/satgen.h b/kernel/satgen.h
index e9f3ecd44..596f522ec 100644
--- a/kernel/satgen.h
+++ b/kernel/satgen.h
@@ -1023,7 +1023,7 @@ struct SatGen
 
 			std::vector<int> lut;
 			for (auto bit : cell->getParam("\\LUT").bits)
-				lut.push_back(bit == RTLIL::S1 ? ez->CONST_TRUE : ez->CONST_FALSE);
+				lut.push_back(bit == State::S1 ? ez->CONST_TRUE : ez->CONST_FALSE);
 			while (GetSize(lut) < (1 << GetSize(a)))
 				lut.push_back(ez->CONST_FALSE);
 			lut.resize(1 << GetSize(a));
diff --git a/kernel/yosys.cc b/kernel/yosys.cc
index a4cc53f1a..5a53f90fd 100644
--- a/kernel/yosys.cc
+++ b/kernel/yosys.cc
@@ -647,12 +647,12 @@ std::vector<std::string> glob_filename(const std::string &filename_pattern)
 
 void rewrite_filename(std::string &filename)
 {
-	if (filename.substr(0, 1) == "\"" && filename.substr(GetSize(filename)-1) == "\"")
+	if (filename.compare(0, 1, "\"") == 0 && filename.compare(GetSize(filename)-1, std::string::npos, "\"") == 0)
 		filename = filename.substr(1, GetSize(filename)-2);
-	if (filename.substr(0, 2) == "+/")
+	if (filename.compare(0, 2, "+/") == 0)
 		filename = proc_share_dirname() + filename.substr(2);
 #ifndef _WIN32
-	if (filename.substr(0, 2) == "~/")
+	if (filename.compare(0, 2, "~/") == 0)
 		filename = filename.replace(0, 1, getenv("HOME"));
 #endif
 }
@@ -895,25 +895,25 @@ void run_frontend(std::string filename, std::string command, std::string *backen
 
 	if (command == "auto") {
 		std::string filename_trim = filename;
-		if (filename_trim.size() > 3 && filename_trim.substr(filename_trim.size()-3) == ".gz")
+		if (filename_trim.size() > 3 && filename_trim.compare(filename_trim.size()-3, std::string::npos, ".gz") == 0)
 			filename_trim.erase(filename_trim.size()-3);
-		if (filename_trim.size() > 2 && filename_trim.substr(filename_trim.size()-2) == ".v")
+		if (filename_trim.size() > 2 && filename_trim.compare(filename_trim.size()-2, std::string::npos, ".v") == 0)
 			command = "verilog";
-		else if (filename_trim.size() > 2 && filename_trim.substr(filename_trim.size()-3) == ".sv")
+		else if (filename_trim.size() > 2 && filename_trim.compare(filename_trim.size()-3, std::string::npos, ".sv") == 0)
 			command = "verilog -sv";
-		else if (filename_trim.size() > 3 && filename_trim.substr(filename_trim.size()-4) == ".vhd")
+		else if (filename_trim.size() > 3 && filename_trim.compare(filename_trim.size()-4, std::string::npos, ".vhd") == 0)
 			command = "vhdl";
-		else if (filename_trim.size() > 4 && filename_trim.substr(filename_trim.size()-5) == ".blif")
+		else if (filename_trim.size() > 4 && filename_trim.compare(filename_trim.size()-5, std::string::npos, ".blif") == 0)
 			command = "blif";
-		else if (filename_trim.size() > 5 && filename_trim.substr(filename_trim.size()-6) == ".eblif")
+		else if (filename_trim.size() > 5 && filename_trim.compare(filename_trim.size()-6, std::string::npos, ".eblif") == 0)
 			command = "blif";
-		else if (filename_trim.size() > 4 && filename_trim.substr(filename_trim.size()-5) == ".json")
+		else if (filename_trim.size() > 4 && filename_trim.compare(filename_trim.size()-5, std::string::npos, ".json") == 0)
 			command = "json";
-		else if (filename_trim.size() > 3 && filename_trim.substr(filename_trim.size()-3) == ".il")
+		else if (filename_trim.size() > 3 && filename_trim.compare(filename_trim.size()-3, std::string::npos, ".il") == 0)
 			command = "ilang";
-		else if (filename_trim.size() > 3 && filename_trim.substr(filename_trim.size()-3) == ".ys")
+		else if (filename_trim.size() > 3 && filename_trim.compare(filename_trim.size()-3, std::string::npos, ".ys") == 0)
 			command = "script";
-		else if (filename_trim.size() > 3 && filename_trim.substr(filename_trim.size()-4) == ".tcl")
+		else if (filename_trim.size() > 3 && filename_trim.compare(filename_trim.size()-4, std::string::npos, ".tcl") == 0)
 			command = "tcl";
 		else if (filename == "-")
 			command = "script";
@@ -1028,17 +1028,17 @@ void run_backend(std::string filename, std::string command, RTLIL::Design *desig
 		design = yosys_design;
 
 	if (command == "auto") {
-		if (filename.size() > 2 && filename.substr(filename.size()-2) == ".v")
+		if (filename.size() > 2 && filename.compare(filename.size()-2, std::string::npos, ".v") == 0)
 			command = "verilog";
-		else if (filename.size() > 3 && filename.substr(filename.size()-3) == ".il")
+		else if (filename.size() > 3 && filename.compare(filename.size()-3, std::string::npos, ".il") == 0)
 			command = "ilang";
-		else if (filename.size() > 4 && filename.substr(filename.size()-4) == ".aig")
+		else if (filename.size() > 4 && filename.compare(filename.size()-4, std::string::npos, ".aig") == 0)
 			command = "aiger";
-		else if (filename.size() > 5 && filename.substr(filename.size()-5) == ".blif")
+		else if (filename.size() > 5 && filename.compare(filename.size()-5, std::string::npos, ".blif") == 0)
 			command = "blif";
-		else if (filename.size() > 5 && filename.substr(filename.size()-5) == ".edif")
+		else if (filename.size() > 5 && filename.compare(filename.size()-5, std::string::npos, ".edif") == 0)
 			command = "edif";
-		else if (filename.size() > 5 && filename.substr(filename.size()-5) == ".json")
+		else if (filename.size() > 5 && filename.compare(filename.size()-5, std::string::npos, ".json") == 0)
 			command = "json";
 		else if (filename == "-")
 			command = "ilang";
@@ -1072,7 +1072,7 @@ static char *readline_cmd_generator(const char *text, int state)
 	}
 
 	for (; it != pass_register.end(); it++) {
-		if (it->first.substr(0, len) == text)
+		if (it->first.compare(0, len, text) == 0)
 			return strdup((it++)->first.c_str());
 	}
 	return NULL;
@@ -1094,7 +1094,7 @@ static char *readline_obj_generator(const char *text, int state)
 		if (design->selected_active_module.empty())
 		{
 			for (auto &it : design->modules_)
-				if (RTLIL::unescape_id(it.first).substr(0, len) == text)
+				if (RTLIL::unescape_id(it.first).compare(0, len, text) == 0)
 					obj_names.push_back(strdup(RTLIL::id2cstr(it.first)));
 		}
 		else
@@ -1103,19 +1103,19 @@ static char *readline_obj_generator(const char *text, int state)
 			RTLIL::Module *module = design->modules_.at(design->selected_active_module);
 
 			for (auto &it : module->wires_)
-				if (RTLIL::unescape_id(it.first).substr(0, len) == text)
+				if (RTLIL::unescape_id(it.first).compare(0, len, text) == 0)
 					obj_names.push_back(strdup(RTLIL::id2cstr(it.first)));
 
 			for (auto &it : module->memories)
-				if (RTLIL::unescape_id(it.first).substr(0, len) == text)
+				if (RTLIL::unescape_id(it.first).compare(0, len, text) == 0)
 					obj_names.push_back(strdup(RTLIL::id2cstr(it.first)));
 
 			for (auto &it : module->cells_)
-				if (RTLIL::unescape_id(it.first).substr(0, len) == text)
+				if (RTLIL::unescape_id(it.first).compare(0, len, text) == 0)
 					obj_names.push_back(strdup(RTLIL::id2cstr(it.first)));
 
 			for (auto &it : module->processes)
-				if (RTLIL::unescape_id(it.first).substr(0, len) == text)
+				if (RTLIL::unescape_id(it.first).compare(0, len, text) == 0)
 					obj_names.push_back(strdup(RTLIL::id2cstr(it.first)));
 		}
 
diff --git a/passes/cmds/cover.cc b/passes/cmds/cover.cc
index 1128116b4..628ac4c5e 100644
--- a/passes/cmds/cover.cc
+++ b/passes/cmds/cover.cc
@@ -121,7 +121,7 @@ struct CoverPass : public Pass {
 			}
 			break;
 		}
-		while (argidx < args.size() && args[argidx].substr(0, 1) != "-")
+		while (argidx < args.size() && args[argidx].compare(0, 1, "-") != 0)
 			patterns.push_back(args[argidx++]);
 		extra_args(args, argidx, design);
 
diff --git a/passes/cmds/select.cc b/passes/cmds/select.cc
index b5e8ef1af..59d10a1b8 100644
--- a/passes/cmds/select.cc
+++ b/passes/cmds/select.cc
@@ -34,7 +34,7 @@ static bool match_ids(RTLIL::IdString id, std::string pattern)
 {
 	if (id == pattern)
 		return true;
-	if (id.size() > 0 && id[0] == '\\' && id.substr(1) == pattern)
+	if (id.size() > 0 && id[0] == '\\' && id.compare(1, std::string::npos, pattern.c_str()) == 0)
 		return true;
 	if (patmatch(pattern.c_str(), id.c_str()))
 		return true;
@@ -124,11 +124,11 @@ static bool match_attr(const dict<RTLIL::IdString, RTLIL::Const> &attributes, st
 	size_t pos = match_expr.find_first_of("<!=>");
 
 	if (pos != std::string::npos) {
-		if (match_expr.substr(pos, 2) == "!=")
+		if (match_expr.compare(pos, 2, "!=") == 0)
 			return match_attr(attributes, match_expr.substr(0, pos), match_expr.substr(pos+2), '!');
-		if (match_expr.substr(pos, 2) == "<=")
+		if (match_expr.compare(pos, 2, "<=") == 0)
 			return match_attr(attributes, match_expr.substr(0, pos), match_expr.substr(pos+2), '[');
-		if (match_expr.substr(pos, 2) == ">=")
+		if (match_expr.compare(pos, 2, ">=") == 0)
 			return match_attr(attributes, match_expr.substr(0, pos), match_expr.substr(pos+2), ']');
 		return match_attr(attributes, match_expr.substr(0, pos), match_expr.substr(pos+1), match_expr[pos]);
 	}
@@ -711,32 +711,32 @@ static void select_stmt(RTLIL::Design *design, std::string arg)
 				log_cmd_error("Must have at least one element on the stack for operator %%a.\n");
 			select_op_alias(design, work_stack[work_stack.size()-1]);
 		} else
-		if (arg == "%x" || (arg.size() > 2 && arg.substr(0, 2) == "%x" && (arg[2] == ':' || arg[2] == '*' || arg[2] == '.' || ('0' <= arg[2] && arg[2] <= '9')))) {
+		if (arg == "%x" || (arg.size() > 2 && arg.compare(0, 2, "%x") == 0 && (arg[2] == ':' || arg[2] == '*' || arg[2] == '.' || ('0' <= arg[2] && arg[2] <= '9')))) {
 			if (work_stack.size() < 1)
 				log_cmd_error("Must have at least one element on the stack for operator %%x.\n");
 			select_op_expand(design, arg, 'x', false);
 		} else
-		if (arg == "%ci" || (arg.size() > 3 && arg.substr(0, 3) == "%ci" && (arg[3] == ':' || arg[3] == '*' || arg[3] == '.' || ('0' <= arg[3] && arg[3] <= '9')))) {
+		if (arg == "%ci" || (arg.size() > 3 && arg.compare(0, 3, "%ci") == 0 && (arg[3] == ':' || arg[3] == '*' || arg[3] == '.' || ('0' <= arg[3] && arg[3] <= '9')))) {
 			if (work_stack.size() < 1)
 				log_cmd_error("Must have at least one element on the stack for operator %%ci.\n");
 			select_op_expand(design, arg, 'i', false);
 		} else
-		if (arg == "%co" || (arg.size() > 3 && arg.substr(0, 3) == "%co" && (arg[3] == ':' || arg[3] == '*' || arg[3] == '.' || ('0' <= arg[3] && arg[3] <= '9')))) {
+		if (arg == "%co" || (arg.size() > 3 && arg.compare(0, 3, "%co") == 0 && (arg[3] == ':' || arg[3] == '*' || arg[3] == '.' || ('0' <= arg[3] && arg[3] <= '9')))) {
 			if (work_stack.size() < 1)
 				log_cmd_error("Must have at least one element on the stack for operator %%co.\n");
 			select_op_expand(design, arg, 'o', false);
 		} else
-		if (arg == "%xe" || (arg.size() > 3 && arg.substr(0, 3) == "%xe" && (arg[3] == ':' || arg[3] == '*' || arg[3] == '.' || ('0' <= arg[3] && arg[3] <= '9')))) {
+		if (arg == "%xe" || (arg.size() > 3 && arg.compare(0, 3, "%xe") == 0 && (arg[3] == ':' || arg[3] == '*' || arg[3] == '.' || ('0' <= arg[3] && arg[3] <= '9')))) {
 			if (work_stack.size() < 1)
 				log_cmd_error("Must have at least one element on the stack for operator %%xe.\n");
 			select_op_expand(design, arg, 'x', true);
 		} else
-		if (arg == "%cie" || (arg.size() > 4 && arg.substr(0, 4) == "%cie" && (arg[4] == ':' || arg[4] == '*' || arg[4] == '.' || ('0' <= arg[4] && arg[4] <= '9')))) {
+		if (arg == "%cie" || (arg.size() > 4 && arg.compare(0, 4, "%cie") == 0 && (arg[4] == ':' || arg[4] == '*' || arg[4] == '.' || ('0' <= arg[4] && arg[4] <= '9')))) {
 			if (work_stack.size() < 1)
 				log_cmd_error("Must have at least one element on the stack for operator %%cie.\n");
 			select_op_expand(design, arg, 'i', true);
 		} else
-		if (arg == "%coe" || (arg.size() > 4 && arg.substr(0, 4) == "%coe" && (arg[4] == ':' || arg[4] == '*' || arg[4] == '.' || ('0' <= arg[4] && arg[4] <= '9')))) {
+		if (arg == "%coe" || (arg.size() > 4 && arg.compare(0, 4, "%coe") == 0 && (arg[4] == ':' || arg[4] == '*' || arg[4] == '.' || ('0' <= arg[4] && arg[4] <= '9')))) {
 			if (work_stack.size() < 1)
 				log_cmd_error("Must have at least one element on the stack for operator %%coe.\n");
 			select_op_expand(design, arg, 'o', true);
@@ -766,7 +766,7 @@ static void select_stmt(RTLIL::Design *design, std::string arg)
 	} else {
 		size_t pos = arg.find('/');
 		if (pos == std::string::npos) {
-			if (arg.find(':') == std::string::npos || arg.substr(0, 1) == "A")
+			if (arg.find(':') == std::string::npos || arg.compare(0, 1, "A") == 0)
 				arg_mod = arg;
 			else
 				arg_mod = "*", arg_memb = arg;
@@ -787,7 +787,7 @@ static void select_stmt(RTLIL::Design *design, std::string arg)
 	sel.full_selection = false;
 	for (auto &mod_it : design->modules_)
 	{
-		if (arg_mod.substr(0, 2) == "A:") {
+		if (arg_mod.compare(0, 2, "A:") == 0) {
 			if (!match_attr(mod_it.second->attributes, arg_mod.substr(2)))
 				continue;
 		} else
@@ -800,27 +800,27 @@ static void select_stmt(RTLIL::Design *design, std::string arg)
 		}
 
 		RTLIL::Module *mod = mod_it.second;
-		if (arg_memb.substr(0, 2) == "w:") {
+		if (arg_memb.compare(0, 2, "w:") == 0) {
 			for (auto &it : mod->wires_)
 				if (match_ids(it.first, arg_memb.substr(2)))
 					sel.selected_members[mod->name].insert(it.first);
 		} else
-		if (arg_memb.substr(0, 2) == "i:") {
+		if (arg_memb.compare(0, 2, "i:") == 0) {
 			for (auto &it : mod->wires_)
 				if (it.second->port_input && match_ids(it.first, arg_memb.substr(2)))
 					sel.selected_members[mod->name].insert(it.first);
 		} else
-		if (arg_memb.substr(0, 2) == "o:") {
+		if (arg_memb.compare(0, 2, "o:") == 0) {
 			for (auto &it : mod->wires_)
 				if (it.second->port_output && match_ids(it.first, arg_memb.substr(2)))
 					sel.selected_members[mod->name].insert(it.first);
 		} else
-		if (arg_memb.substr(0, 2) == "x:") {
+		if (arg_memb.compare(0, 2, "x:") == 0) {
 			for (auto &it : mod->wires_)
 				if ((it.second->port_input || it.second->port_output) && match_ids(it.first, arg_memb.substr(2)))
 					sel.selected_members[mod->name].insert(it.first);
 		} else
-		if (arg_memb.substr(0, 2) == "s:") {
+		if (arg_memb.compare(0, 2, "s:") == 0) {
 			size_t delim = arg_memb.substr(2).find(':');
 			if (delim == std::string::npos) {
 				int width = atoi(arg_memb.substr(2).c_str());
@@ -837,27 +837,27 @@ static void select_stmt(RTLIL::Design *design, std::string arg)
 						sel.selected_members[mod->name].insert(it.first);
 			}
 		} else
-		if (arg_memb.substr(0, 2) == "m:") {
+		if (arg_memb.compare(0, 2, "m:") == 0) {
 			for (auto &it : mod->memories)
 				if (match_ids(it.first, arg_memb.substr(2)))
 					sel.selected_members[mod->name].insert(it.first);
 		} else
-		if (arg_memb.substr(0, 2) == "c:") {
+		if (arg_memb.compare(0, 2, "c:") ==0) {
 			for (auto &it : mod->cells_)
 				if (match_ids(it.first, arg_memb.substr(2)))
 					sel.selected_members[mod->name].insert(it.first);
 		} else
-		if (arg_memb.substr(0, 2) == "t:") {
+		if (arg_memb.compare(0, 2, "t:") == 0) {
 			for (auto &it : mod->cells_)
 				if (match_ids(it.second->type, arg_memb.substr(2)))
 					sel.selected_members[mod->name].insert(it.first);
 		} else
-		if (arg_memb.substr(0, 2) == "p:") {
+		if (arg_memb.compare(0, 2, "p:") == 0) {
 			for (auto &it : mod->processes)
 				if (match_ids(it.first, arg_memb.substr(2)))
 					sel.selected_members[mod->name].insert(it.first);
 		} else
-		if (arg_memb.substr(0, 2) == "a:") {
+		if (arg_memb.compare(0, 2, "a:") == 0) {
 			for (auto &it : mod->wires_)
 				if (match_attr(it.second->attributes, arg_memb.substr(2)))
 					sel.selected_members[mod->name].insert(it.first);
@@ -871,12 +871,12 @@ static void select_stmt(RTLIL::Design *design, std::string arg)
 				if (match_attr(it.second->attributes, arg_memb.substr(2)))
 					sel.selected_members[mod->name].insert(it.first);
 		} else
-		if (arg_memb.substr(0, 2) == "r:") {
+		if (arg_memb.compare(0, 2, "r:") == 0) {
 			for (auto &it : mod->cells_)
 				if (match_attr(it.second->parameters, arg_memb.substr(2)))
 					sel.selected_members[mod->name].insert(it.first);
 		} else {
-			if (arg_memb.substr(0, 2) == "n:")
+			if (arg_memb.compare(0, 2, "n:") == 0)
 				arg_memb = arg_memb.substr(2);
 			for (auto &it : mod->wires_)
 				if (match_ids(it.first, arg_memb))
@@ -927,7 +927,7 @@ void handle_extra_select_args(Pass *pass, vector<string> args, size_t argidx, si
 {
 	work_stack.clear();
 	for (; argidx < args_size; argidx++) {
-		if (args[argidx].substr(0, 1) == "-") {
+		if (args[argidx].compare(0, 1, "-") == 0) {
 			if (pass != NULL)
 				pass->cmd_error(args, argidx, "Unexpected option in selection arguments.");
 			else
diff --git a/passes/cmds/setattr.cc b/passes/cmds/setattr.cc
index b9fcc3e7a..1ccfc2e86 100644
--- a/passes/cmds/setattr.cc
+++ b/passes/cmds/setattr.cc
@@ -34,7 +34,7 @@ struct setunset_t
 
 	setunset_t(std::string set_name, std::string set_value) : name(RTLIL::escape_id(set_name)), value(), unset(false)
 	{
-		if (set_value.substr(0, 1) == "\"" && set_value.substr(GetSize(set_value)-1) == "\"") {
+		if (set_value.compare(0, 1, "\"") == 0 && set_value.compare(GetSize(set_value)-1, std::string::npos, "\"") == 0) {
 			value = RTLIL::Const(set_value.substr(1, GetSize(set_value)-2));
 		} else {
 			RTLIL::SigSpec sig_value;
diff --git a/passes/cmds/show.cc b/passes/cmds/show.cc
index cf729215f..2e9fc72af 100644
--- a/passes/cmds/show.cc
+++ b/passes/cmds/show.cc
@@ -527,11 +527,11 @@ struct ShowWorker
 		{
 			currentColor = xorshift32(currentColor);
 			if (wires_on_demand.count(it.first) > 0) {
-				if (it.second.in.size() == 1 && it.second.out.size() > 1 && it.second.in.begin()->substr(0, 1) == "p")
+				if (it.second.in.size() == 1 && it.second.out.size() > 1 && it.second.in.begin()->compare(0, 1, "p") == 0)
 					it.second.out.erase(*it.second.in.begin());
 				if (it.second.in.size() == 1 && it.second.out.size() == 1) {
 					std::string from = *it.second.in.begin(), to = *it.second.out.begin();
-					if (from != to || from.substr(0, 1) != "p")
+					if (from != to || from.compare(0, 1, "p") != 0)
 						fprintf(f, "%s:e -> %s:w [%s, %s];\n", from.c_str(), to.c_str(), nextColor(it.second.color).c_str(), widthLabel(it.second.bits).c_str());
 					continue;
 				}
@@ -808,7 +808,7 @@ struct ShowPass : public Pass {
 			if (f.fail())
 				log_error("Can't open lib file `%s'.\n", filename.c_str());
 			RTLIL::Design *lib = new RTLIL::Design;
-			Frontend::frontend_call(lib, &f, filename, (filename.size() > 3 && filename.substr(filename.size()-3) == ".il") ? "ilang" : "verilog");
+			Frontend::frontend_call(lib, &f, filename, (filename.size() > 3 && filename.compare(filename.size()-3, std::string::npos, ".il") == 0 ? "ilang" : "verilog"));
 			libs.push_back(lib);
 		}
 
diff --git a/passes/equiv/equiv_opt.cc b/passes/equiv/equiv_opt.cc
index 3596dfd7b..19d1c25ac 100644
--- a/passes/equiv/equiv_opt.cc
+++ b/passes/equiv/equiv_opt.cc
@@ -97,7 +97,7 @@ struct EquivOptPass:public ScriptPass
 
 		for (; argidx < args.size(); argidx++) {
 			if (command.empty()) {
-				if (args[argidx].substr(0, 1) == "-")
+				if (args[argidx].compare(0, 1, "-") == 0)
 					cmd_error(args, argidx, "Unknown option.");
 			} else {
 				command += " ";
diff --git a/passes/equiv/equiv_struct.cc b/passes/equiv/equiv_struct.cc
index a7973fd04..6672948b9 100644
--- a/passes/equiv/equiv_struct.cc
+++ b/passes/equiv/equiv_struct.cc
@@ -215,9 +215,9 @@ struct EquivStructWorker
 					if (c != nullptr) {
 						string n = cell_name.str();
 						cells_type = c->type;
-						if (GetSize(n) > 5 && n.substr(GetSize(n)-5) == "_gold")
+						if (GetSize(n) > 5 && n.compare(GetSize(n)-5, std::string::npos, "_gold") == 0)
 							gold_cells.push_back(c);
-						else if (GetSize(n) > 5 && n.substr(GetSize(n)-5) == "_gate")
+						else if (GetSize(n) > 5 && n.compare(GetSize(n)-5, std::string::npos, "_gate") == 0)
 							gate_cells.push_back(c);
 						else
 							other_cells.push_back(c);
diff --git a/passes/fsm/fsm_expand.cc b/passes/fsm/fsm_expand.cc
index c34d0c15c..1610ec751 100644
--- a/passes/fsm/fsm_expand.cc
+++ b/passes/fsm/fsm_expand.cc
@@ -50,7 +50,7 @@ struct FsmExpand
 		if (full_mode || cell->type == "$_MUX_")
 			return true;
 
-		if (cell->type == "$mux" || cell->type == "$pmux")
+		if (cell->type.in("$mux", "$pmux"))
 			if (cell->getPort("\\A").size() < 2)
 				return true;
 
diff --git a/passes/fsm/fsm_extract.cc b/passes/fsm/fsm_extract.cc
index 6095eaf30..a85c3bec0 100644
--- a/passes/fsm/fsm_extract.cc
+++ b/passes/fsm/fsm_extract.cc
@@ -168,7 +168,7 @@ undef_bit_in_next_state:
 			ctrl_in_bit_indices[ctrl_in[i]] = i;
 
 		for (auto &it : ctrl_in_bit_indices)
-			if (tr.ctrl_in.bits.at(it.second) == RTLIL::S1 && exclusive_ctrls.count(it.first) != 0)
+			if (tr.ctrl_in.bits.at(it.second) == State::S1 && exclusive_ctrls.count(it.first) != 0)
 				for (auto &dc_bit : exclusive_ctrls.at(it.first))
 					if (ctrl_in_bit_indices.count(dc_bit))
 						tr.ctrl_in.bits.at(ctrl_in_bit_indices.at(dc_bit)) = RTLIL::State::Sa;
@@ -216,13 +216,13 @@ undef_bit_in_next_state:
 		ce.push();
 		dont_care.append(undef);
 		ce.set(undef, constval.as_const());
-		if (exclusive_ctrls.count(undef) && constval == RTLIL::S1)
+		if (exclusive_ctrls.count(undef) && constval == State::S1)
 			for (auto &bit : exclusive_ctrls.at(undef)) {
 				RTLIL::SigSpec bitval = bit;
-				if (ce.eval(bitval) && bitval != RTLIL::S0)
+				if (ce.eval(bitval) && bitval != State::S0)
 					goto found_contradiction_1;
 				else
-					ce.set(bit, RTLIL::S0);
+					ce.set(bit, State::S0);
 			}
 		find_transitions(ce, ce_nostop, fsm_data, states, state_in, ctrl_in, ctrl_out, dff_in, dont_care);
 	found_contradiction_1:
@@ -231,21 +231,21 @@ undef_bit_in_next_state:
 	else
 	{
 		ce.push(), ce_nostop.push();
-		ce.set(undef, RTLIL::S0);
-		ce_nostop.set(undef, RTLIL::S0);
+		ce.set(undef, State::S0);
+		ce_nostop.set(undef, State::S0);
 		find_transitions(ce, ce_nostop, fsm_data, states, state_in, ctrl_in, ctrl_out, dff_in, dont_care);
 		ce.pop(), ce_nostop.pop();
 
 		ce.push(), ce_nostop.push();
-		ce.set(undef, RTLIL::S1);
-		ce_nostop.set(undef, RTLIL::S1);
+		ce.set(undef, State::S1);
+		ce_nostop.set(undef, State::S1);
 		if (exclusive_ctrls.count(undef))
 			for (auto &bit : exclusive_ctrls.at(undef)) {
 				RTLIL::SigSpec bitval = bit;
-				if ((ce.eval(bitval) || ce_nostop.eval(bitval)) && bitval != RTLIL::S0)
+				if ((ce.eval(bitval) || ce_nostop.eval(bitval)) && bitval != State::S0)
 					goto found_contradiction_2;
 				else
-					ce.set(bit, RTLIL::S0), ce_nostop.set(bit, RTLIL::S0);
+					ce.set(bit, State::S0), ce_nostop.set(bit, RTLIL::S0);
 			}
 		find_transitions(ce, ce_nostop, fsm_data, states, state_in, ctrl_in, ctrl_out, dff_in, dont_care);
 	found_contradiction_2:
@@ -263,8 +263,8 @@ static void extract_fsm(RTLIL::Wire *wire)
 	RTLIL::SigSpec dff_in(RTLIL::State::Sm, wire->width);
 	RTLIL::Const reset_state(RTLIL::State::Sx, wire->width);
 
-	RTLIL::SigSpec clk = RTLIL::S0;
-	RTLIL::SigSpec arst = RTLIL::S0;
+	RTLIL::SigSpec clk = State::S0;
+	RTLIL::SigSpec arst = State::S0;
 	bool clk_polarity = true;
 	bool arst_polarity = true;
 
@@ -371,8 +371,8 @@ static void extract_fsm(RTLIL::Wire *wire)
 	RTLIL::Cell *fsm_cell = module->addCell(stringf("$fsm$%s$%d", wire->name.c_str(), autoidx++), "$fsm");
 	fsm_cell->setPort("\\CLK", clk);
 	fsm_cell->setPort("\\ARST", arst);
-	fsm_cell->parameters["\\CLK_POLARITY"] = clk_polarity ? RTLIL::S1 : RTLIL::S0;
-	fsm_cell->parameters["\\ARST_POLARITY"] = arst_polarity ? RTLIL::S1 : RTLIL::S0;
+	fsm_cell->parameters["\\CLK_POLARITY"] = clk_polarity ? State::S1 : State::S0;
+	fsm_cell->parameters["\\ARST_POLARITY"] = arst_polarity ? State::S1 : State::S0;
 	fsm_cell->setPort("\\CTRL_IN", ctrl_in);
 	fsm_cell->setPort("\\CTRL_OUT", ctrl_out);
 	fsm_cell->parameters["\\NAME"] = RTLIL::Const(wire->name.str());
diff --git a/passes/fsm/fsm_map.cc b/passes/fsm/fsm_map.cc
index 90c958912..80913fda8 100644
--- a/passes/fsm/fsm_map.cc
+++ b/passes/fsm/fsm_map.cc
@@ -133,7 +133,7 @@ static void implement_pattern_cache(RTLIL::Module *module, std::map<RTLIL::Const
 			cases_vector.append(and_sig);
 			break;
 		case 0:
-			cases_vector.append(RTLIL::SigSpec(1, 1));
+			cases_vector.append(State::S1);
 			break;
 		default:
 			log_abort();
@@ -150,7 +150,7 @@ static void implement_pattern_cache(RTLIL::Module *module, std::map<RTLIL::Const
 	} else if (cases_vector.size() == 1) {
 		module->connect(RTLIL::SigSig(output, cases_vector));
 	} else {
-		module->connect(RTLIL::SigSig(output, RTLIL::SigSpec(0, 1)));
+		module->connect(RTLIL::SigSig(output, State::S0));
 	}
 }
 
diff --git a/passes/hierarchy/hierarchy.cc b/passes/hierarchy/hierarchy.cc
index 213437c01..fd95b94b2 100644
--- a/passes/hierarchy/hierarchy.cc
+++ b/passes/hierarchy/hierarchy.cc
@@ -48,7 +48,7 @@ void generate(RTLIL::Design *design, const std::vector<std::string> &celltypes,
 		RTLIL::Cell *cell = i2.second;
 		if (design->has(cell->type))
 			continue;
-		if (cell->type.substr(0, 1) == "$" && cell->type.substr(0, 3) != "$__")
+		if (cell->type.begins_with("$__"))
 			continue;
 		for (auto &pattern : celltypes)
 			if (patmatch(pattern.c_str(), RTLIL::unescape_id(cell->type).c_str()))
@@ -143,7 +143,7 @@ void generate(RTLIL::Design *design, const std::vector<std::string> &celltypes,
 // Return the "basic" type for an array item.
 std::string basic_cell_type(const std::string celltype, int pos[3] = nullptr) {
 	std::string basicType = celltype;
-	if (celltype.substr(0, 7) == "$array:") {
+	if (celltype.compare(0, strlen("$array:"), "$array:") == 0) {
 		int pos_idx = celltype.find_first_of(':');
 		int pos_num = celltype.find_first_of(':', pos_idx + 1);
 		int pos_type = celltype.find_first_of(':', pos_num + 1);
@@ -194,16 +194,16 @@ bool expand_module(RTLIL::Design *design, RTLIL::Module *module, bool flag_check
 		std::vector<RTLIL::IdString> connections_to_add_name;
 		std::vector<RTLIL::SigSpec> connections_to_add_signal;
 
-		if (cell->type.substr(0, 7) == "$array:") {
+		if (cell->type.begins_with("$array:")) {
 			int pos[3];
 			basic_cell_type(cell->type.str(), pos);
 			int pos_idx = pos[0];
 			int pos_num = pos[1];
 			int pos_type = pos[2];
-			int idx = atoi(cell->type.str().substr(pos_idx + 1, pos_num).c_str());
-			int num = atoi(cell->type.str().substr(pos_num + 1, pos_type).c_str());
+			int idx = atoi(cell->type.substr(pos_idx + 1, pos_num).c_str());
+			int num = atoi(cell->type.substr(pos_num + 1, pos_type).c_str());
 			array_cells[cell] = std::pair<int, int>(idx, num);
-			cell->type = cell->type.str().substr(pos_type + 1);
+			cell->type = cell->type.substr(pos_type + 1);
 		}
 		dict<RTLIL::IdString, RTLIL::Module*> interfaces_to_add_to_submodule;
 		dict<RTLIL::IdString, RTLIL::IdString> modports_used_in_submodule;
@@ -422,7 +422,7 @@ bool expand_module(RTLIL::Design *design, RTLIL::Module *module, bool flag_check
 		for (auto &conn : cell->connections_) {
 			int conn_size = conn.second.size();
 			RTLIL::IdString portname = conn.first;
-			if (portname.substr(0, 1) == "$") {
+			if (portname.begins_with("$")) {
 				int port_id = atoi(portname.substr(1).c_str());
 				for (auto &wire_it : mod->wires_)
 					if (wire_it.second->port_id == port_id) {
@@ -457,9 +457,8 @@ void hierarchy_worker(RTLIL::Design *design, std::set<RTLIL::Module*, IdString::
 
 	for (auto cell : mod->cells()) {
 		std::string celltype = cell->type.str();
-		if (celltype.substr(0, 7) == "$array:") {
+		if (celltype.compare(0, strlen("$array:"), "$array:") == 0)
 			celltype = basic_cell_type(celltype);
-		}
 		if (design->module(celltype))
 			hierarchy_worker(design, used, design->module(celltype), indent+4);
 	}
@@ -521,9 +520,8 @@ int find_top_mod_score(Design *design, Module *module, dict<Module*, int> &db)
 		for (auto cell : module->cells()) {
 			std::string celltype = cell->type.str();
 			// Is this an array instance
-			if (celltype.substr(0, 7) == "$array:") {
+			if (celltype.compare(0, strlen("$array:"), "$array:") == 0)
 				celltype = basic_cell_type(celltype);
-			}
 			// Is this cell a module instance?
 			auto instModule = design->module(celltype);
 			// If there is no instance for this, issue a warning.
diff --git a/passes/memory/memory_collect.cc b/passes/memory/memory_collect.cc
index 369fcc84e..6acbce62f 100644
--- a/passes/memory/memory_collect.cc
+++ b/passes/memory/memory_collect.cc
@@ -194,8 +194,8 @@ Cell *handle_memory(Module *module, RTLIL::Memory *memory)
 	log_assert(sig_wr_en.size() == wr_ports * memory->width);
 
 	mem->parameters["\\WR_PORTS"] = Const(wr_ports);
-	mem->parameters["\\WR_CLK_ENABLE"] = wr_ports ? sig_wr_clk_enable.as_const() : Const(0, 1);
-	mem->parameters["\\WR_CLK_POLARITY"] = wr_ports ? sig_wr_clk_polarity.as_const() : Const(0, 1);
+	mem->parameters["\\WR_CLK_ENABLE"] = wr_ports ? sig_wr_clk_enable.as_const() : State::S0;
+	mem->parameters["\\WR_CLK_POLARITY"] = wr_ports ? sig_wr_clk_polarity.as_const() : State::S0;
 
 	mem->setPort("\\WR_CLK", sig_wr_clk);
 	mem->setPort("\\WR_ADDR", sig_wr_addr);
@@ -209,9 +209,9 @@ Cell *handle_memory(Module *module, RTLIL::Memory *memory)
 	log_assert(sig_rd_data.size() == rd_ports * memory->width);
 
 	mem->parameters["\\RD_PORTS"] = Const(rd_ports);
-	mem->parameters["\\RD_CLK_ENABLE"] = rd_ports ? sig_rd_clk_enable.as_const() : Const(0, 1);
-	mem->parameters["\\RD_CLK_POLARITY"] = rd_ports ? sig_rd_clk_polarity.as_const() : Const(0, 1);
-	mem->parameters["\\RD_TRANSPARENT"] = rd_ports ? sig_rd_transparent.as_const() : Const(0, 1);
+	mem->parameters["\\RD_CLK_ENABLE"] = rd_ports ? sig_rd_clk_enable.as_const() : State::S0;
+	mem->parameters["\\RD_CLK_POLARITY"] = rd_ports ? sig_rd_clk_polarity.as_const() : State::S0;
+	mem->parameters["\\RD_TRANSPARENT"] = rd_ports ? sig_rd_transparent.as_const() : State::S0;
 
 	mem->setPort("\\RD_CLK", sig_rd_clk);
 	mem->setPort("\\RD_ADDR", sig_rd_addr);
diff --git a/passes/memory/memory_dff.cc b/passes/memory/memory_dff.cc
index 32b97f27a..be4b3c100 100644
--- a/passes/memory/memory_dff.cc
+++ b/passes/memory/memory_dff.cc
@@ -262,7 +262,7 @@ struct MemoryDffWorker
 				mux_cells_a[sigmap(cell->getPort("\\A"))] = cell;
 				mux_cells_b[sigmap(cell->getPort("\\B"))] = cell;
 			}
-			if (cell->type == "$not" || cell->type == "$_NOT_" || (cell->type == "$logic_not" && GetSize(cell->getPort("\\A")) == 1)) {
+			if (cell->type.in("$not", "$_NOT_") || (cell->type == "$logic_not" && GetSize(cell->getPort("\\A")) == 1)) {
 				SigSpec sig_a = cell->getPort("\\A");
 				SigSpec sig_y = cell->getPort("\\Y");
 				if (cell->type == "$not")
diff --git a/passes/memory/memory_map.cc b/passes/memory/memory_map.cc
index a0b808e56..65bccb5ef 100644
--- a/passes/memory/memory_map.cc
+++ b/passes/memory/memory_map.cc
@@ -301,7 +301,7 @@ struct MemoryMapWorker
 
 					RTLIL::Wire *w = w_seladdr;
 
-					if (wr_bit != RTLIL::SigSpec(1, 1))
+					if (wr_bit != State::S1)
 					{
 						RTLIL::Cell *c = module->addCell(genid(cell->name, "$wren", i, "", j, "", wr_offset), "$and");
 						c->parameters["\\A_SIGNED"] = RTLIL::Const(0);
diff --git a/passes/memory/memory_share.cc b/passes/memory/memory_share.cc
index 172afe0cb..eb912cfd4 100644
--- a/passes/memory/memory_share.cc
+++ b/passes/memory/memory_share.cc
@@ -155,7 +155,7 @@ struct MemoryShareWorker
 		{
 			bool ignore_data_port = false;
 
-			if (cell->type == "$mux" || cell->type == "$pmux")
+			if (cell->type.in("$mux", "$pmux"))
 			{
 				std::vector<RTLIL::SigBit> sig_a = sigmap(cell->getPort("\\A"));
 				std::vector<RTLIL::SigBit> sig_b = sigmap(cell->getPort("\\B"));
@@ -173,7 +173,7 @@ struct MemoryShareWorker
 				continue;
 			}
 
-			if ((cell->type == "$memwr" || cell->type == "$memrd") &&
+			if (cell->type.in("$memwr", "$memrd") &&
 					cell->parameters.at("\\MEMID").decode_string() == memid)
 				ignore_data_port = true;
 
@@ -690,7 +690,7 @@ struct MemoryShareWorker
 					sigmap_xmux.add(cell->getPort("\\Y"), sig_a);
 			}
 
-			if (cell->type == "$mux" || cell->type == "$pmux")
+			if (cell->type.in("$mux", "$pmux"))
 			{
 				std::vector<RTLIL::SigBit> sig_y = sigmap(cell->getPort("\\Y"));
 				for (int i = 0; i < int(sig_y.size()); i++)
diff --git a/passes/opt/muxpack.cc b/passes/opt/muxpack.cc
index 6697d6ca1..225c30d9a 100644
--- a/passes/opt/muxpack.cc
+++ b/passes/opt/muxpack.cc
@@ -49,7 +49,7 @@ struct ExclusiveDatabase
 			}
 			else if (cell->type == "$logic_not") {
 				nonconst_sig = sigmap(cell->getPort("\\A"));
-				const_sig = Const(RTLIL::S0, GetSize(nonconst_sig));
+				const_sig = Const(State::S0, GetSize(nonconst_sig));
 				y_port = sigmap(cell->getPort("\\Y"));
 			}
 			else if (cell->type == "$reduce_or") {
diff --git a/passes/opt/opt_clean.cc b/passes/opt/opt_clean.cc
index a8a8e0bc7..905c95b6c 100644
--- a/passes/opt/opt_clean.cc
+++ b/passes/opt/opt_clean.cc
@@ -222,10 +222,10 @@ 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;
diff --git a/passes/opt/opt_expr.cc b/passes/opt/opt_expr.cc
index acdc39937..b2dc9a448 100644
--- a/passes/opt/opt_expr.cc
+++ b/passes/opt/opt_expr.cc
@@ -367,10 +367,11 @@ 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") &&
+			if (cell->type.in("$_NOT_", "$not", "$logic_not") &&
 					cell->getPort("\\A").size() == 1 && cell->getPort("\\Y").size() == 1)
 				invert_map[assign_map(cell->getPort("\\Y"))] = assign_map(cell->getPort("\\A"));
-			if ((cell->type == "$mux" || cell->type == "$_MUX_") && cell->getPort("\\A") == SigSpec(State::S1) && cell->getPort("\\B") == SigSpec(State::S0))
+			if (cell->type.in("$mux", "$_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 (ct_combinational.cell_known(cell->type))
 				for (auto &conn : cell->connections()) {
@@ -512,13 +513,11 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 
 		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("$not", "$pos", "$and", "$or", "$xor", "$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("$logic_not", "$logic_and", "$logic_or", "$reduce_or", "$reduce_and", "$reduce_bool"))
 			{
 				SigBit neutral_bit = cell->type == "$reduce_and" ? State::S1 : State::S0;
 
@@ -541,7 +540,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 				}
 			}
 
-			if (cell->type == "$logic_and" || cell->type == "$logic_or")
+			if (cell->type.in("$logic_and", "$logic_or"))
 			{
 				SigBit neutral_bit = State::S0;
 
@@ -590,7 +589,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 				}
 			}
 
-			if (cell->type == "$logic_not" || cell->type == "$logic_and" || cell->type == "$logic_or" || cell->type == "$reduce_or" || cell->type == "$reduce_bool")
+			if (cell->type.in("$logic_not", "$logic_and", "$logic_or", "$reduce_or", "$reduce_bool"))
 			{
 				RTLIL::SigSpec sig_a = assign_map(cell->getPort("\\A"));
 
@@ -616,7 +615,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 				}
 			}
 
-			if (cell->type == "$logic_and" || cell->type == "$logic_or")
+			if (cell->type.in("$logic_and", "$logic_or"))
 			{
 				RTLIL::SigSpec sig_b = assign_map(cell->getPort("\\B"));
 
@@ -668,16 +667,13 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 			}
 		}
 
-		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 == "$pow")
+		if (cell->type.in("$reduce_xor", "$reduce_xnor", "$shift", "$shiftx", "$shl", "$shr", "$sshl", "$sshr",
+					"$lt", "$le", "$ge", "$gt", "$neg", "$add", "$sub", "$mul", "$div", "$mod", "$pow"))
 		{
 			RTLIL::SigSpec sig_a = assign_map(cell->getPort("\\A"));
 			RTLIL::SigSpec sig_b = cell->hasPort("\\B") ? assign_map(cell->getPort("\\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("$shl", "$shr", "$sshl", "$sshr", "$shift", "$shiftx"))
 				sig_a = RTLIL::SigSpec();
 
 			for (auto &bit : sig_a.to_sigbit_vector())
@@ -692,8 +688,7 @@ 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 == "$gt")
+				if (cell->type.in("$reduce_xor", "$reduce_xnor", "$lt", "$le", "$ge", "$gt"))
 					replace_cell(assign_map, module, cell, "x-bit in input", "\\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()));
@@ -701,14 +696,14 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 			}
 		}
 
-		if ((cell->type == "$_NOT_" || cell->type == "$not" || cell->type == "$logic_not") && cell->getPort("\\Y").size() == 1 &&
+		if (cell->type.in("$_NOT_", "$not", "$logic_not") && cell->getPort("\\Y").size() == 1 &&
 				invert_map.count(assign_map(cell->getPort("\\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"))));
 			goto next_cell;
 		}
 
-		if ((cell->type == "$_MUX_" || cell->type == "$mux") && invert_map.count(assign_map(cell->getPort("\\S"))) != 0) {
+		if (cell->type.in("$_MUX_", "$mux") && invert_map.count(assign_map(cell->getPort("\\S"))) != 0) {
 			cover_list("opt.opt_expr.invert.muxsel", "$_MUX_", "$mux", cell->type.str());
 			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("\\A");
@@ -811,7 +806,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 			}
 		}
 
-		if (cell->type == "$_TBUF_" || cell->type == "$tribuf") {
+		if (cell->type.in("$_TBUF_", "$tribuf")) {
 			RTLIL::SigSpec input = cell->getPort(cell->type == "$_TBUF_" ? "\\E" : "\\EN");
 			RTLIL::SigSpec a = cell->getPort("\\A");
 			assign_map.apply(input);
@@ -828,7 +823,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 			}
 		}
 
-		if (cell->type == "$eq" || cell->type == "$ne" || cell->type == "$eqx" || cell->type == "$nex")
+		if (cell->type.in("$eq", "$ne", "$eqx", "$nex"))
 		{
 			RTLIL::SigSpec a = cell->getPort("\\A");
 			RTLIL::SigSpec b = cell->getPort("\\B");
@@ -845,7 +840,7 @@ 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);
+					RTLIL::SigSpec new_y = RTLIL::SigSpec(cell->type.in("$eq", "$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);
 					goto next_cell;
@@ -858,7 +853,7 @@ 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);
+				RTLIL::SigSpec new_y = RTLIL::SigSpec(cell->type.in("$eq", "$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);
 				goto next_cell;
@@ -873,7 +868,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 			}
 		}
 
-		if ((cell->type == "$eq" || cell->type == "$ne") && cell->parameters["\\Y_WIDTH"].as_int() == 1 &&
+		if (cell->type.in("$eq", "$ne") && cell->parameters["\\Y_WIDTH"].as_int() == 1 &&
 				cell->parameters["\\A_WIDTH"].as_int() == 1 && cell->parameters["\\B_WIDTH"].as_int() == 1)
 		{
 			RTLIL::SigSpec a = assign_map(cell->getPort("\\A"));
@@ -903,7 +898,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 			}
 		}
 
-		if ((cell->type == "$eq" || cell->type == "$ne") &&
+		if (cell->type.in("$eq", "$ne") &&
 				(assign_map(cell->getPort("\\A")).is_fully_zero() || assign_map(cell->getPort("\\B")).is_fully_zero()))
 		{
 			cover_list("opt.opt_expr.eqneq.cmpzero", "$eq", "$ne", cell->type.str());
@@ -962,7 +957,7 @@ 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("$add", "$sub", "$or", "$xor"))
 			{
 				RTLIL::SigSpec a = assign_map(cell->getPort("\\A"));
 				RTLIL::SigSpec b = assign_map(cell->getPort("\\B"));
@@ -974,7 +969,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 					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("$shl", "$shr", "$sshl", "$sshr", "$shift", "$shiftx"))
 			{
 				RTLIL::SigSpec b = assign_map(cell->getPort("\\B"));
 
@@ -1029,15 +1024,15 @@ 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("$mux", "$_MUX_") &&
+				cell->getPort("\\A") == State::S0 && cell->getPort("\\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"));
 			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("$mux", "$_MUX_") &&
+				cell->getPort("\\A") == State::S1 && cell->getPort("\\B") == State::S0) {
 			cover_list("opt.opt_expr.mux_invert", "$mux", "$_MUX_", cell->type.str());
 			log_debug("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"));
@@ -1056,7 +1051,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 			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("$mux", "$_MUX_") && cell->getPort("\\A") == State::S0) {
 			cover_list("opt.opt_expr.mux_and", "$mux", "$_MUX_", cell->type.str());
 			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("\\A", cell->getPort("\\S"));
@@ -1076,7 +1071,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 			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("$mux", "$_MUX_") && cell->getPort("\\B") == State::S1) {
 			cover_list("opt.opt_expr.mux_or", "$mux", "$_MUX_", cell->type.str());
 			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("\\B", cell->getPort("\\S"));
@@ -1096,7 +1091,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 			goto next_cell;
 		}
 
-		if (mux_undef && (cell->type == "$mux" || cell->type == "$pmux")) {
+		if (mux_undef && cell->type.in("$mux", "$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()) ||
@@ -1438,7 +1433,7 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 		}
 
 		// simplify comparisons
-		if (do_fine && (cell->type == "$lt" || cell->type == "$ge" || cell->type == "$gt" || cell->type == "$le"))
+		if (do_fine && cell->type.in("$lt", "$ge", "$gt", "$le"))
 		{
 			IdString cmp_type = cell->type;
 			SigSpec var_sig = cell->getPort("\\A");
diff --git a/passes/opt/opt_merge.cc b/passes/opt/opt_merge.cc
index 7567d4657..cac7c0a6f 100644
--- a/passes/opt/opt_merge.cc
+++ b/passes/opt/opt_merge.cc
@@ -94,8 +94,8 @@ 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 == "$_XOR_") {
+		if (cell->type.in("$and", "$or", "$xor", "$xnor", "$add", "$mul",
+				"$logic_and", "$logic_or", "$_AND_", "$_OR_", "$_XOR_")) {
 			alt_conn = *conn;
 			if (assign_map(alt_conn.at("\\A")) < assign_map(alt_conn.at("\\B"))) {
 				alt_conn["\\A"] = conn->at("\\B");
@@ -103,13 +103,13 @@ struct OptMergeWorker
 			}
 			conn = &alt_conn;
 		} else
-		if (cell->type == "$reduce_xor" || cell->type == "$reduce_xnor") {
+		if (cell->type.in("$reduce_xor", "$reduce_xnor")) {
 			alt_conn = *conn;
 			assign_map.apply(alt_conn.at("\\A"));
 			alt_conn.at("\\A").sort();
 			conn = &alt_conn;
 		} else
-		if (cell->type == "$reduce_and" || cell->type == "$reduce_or" || cell->type == "$reduce_bool") {
+		if (cell->type.in("$reduce_and", "$reduce_or", "$reduce_bool")) {
 			alt_conn = *conn;
 			assign_map.apply(alt_conn.at("\\A"));
 			alt_conn.at("\\A").sort_and_unify();
@@ -222,7 +222,7 @@ struct OptMergeWorker
 			return true;
 		}
 
-		if (cell1->type.substr(0, 1) == "$" && conn1.count("\\Q") != 0) {
+		if (cell1->type.begins_with("$") && 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();
 			for (size_t i = 0; i < q1.size(); i++)
diff --git a/passes/opt/opt_muxtree.cc b/passes/opt/opt_muxtree.cc
index 6511e091b..4b96fe524 100644
--- a/passes/opt/opt_muxtree.cc
+++ b/passes/opt/opt_muxtree.cc
@@ -84,7 +84,7 @@ struct OptMuxtreeWorker
 		//	.const_deactivated
 		for (auto cell : module->cells())
 		{
-			if (cell->type == "$mux" || cell->type == "$pmux")
+			if (cell->type.in("$mux", "$pmux"))
 			{
 				RTLIL::SigSpec sig_a = cell->getPort("\\A");
 				RTLIL::SigSpec sig_b = cell->getPort("\\B");
diff --git a/passes/opt/opt_rmdff.cc b/passes/opt/opt_rmdff.cc
index be6ac2d30..8d42a37c3 100644
--- a/passes/opt/opt_rmdff.cc
+++ b/passes/opt/opt_rmdff.cc
@@ -63,15 +63,15 @@ bool handle_dffsr(RTLIL::Module *mod, RTLIL::Cell *cell)
 
 	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") {
+	if (cell->type.in("$dffsr", "$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;
 	} else
@@ -137,7 +137,7 @@ bool handle_dffsr(RTLIL::Module *mod, RTLIL::Cell *cell)
 		return true;
 	}
 
-	if (cell->type == "$dffsr" || cell->type == "$dlatchsr")
+	if (cell->type.in("$dffsr", "$dlatchsr"))
 	{
 		cell->setParam("\\WIDTH", GetSize(sig_d));
 		cell->setPort("\\SET", sig_set);
@@ -198,9 +198,9 @@ bool handle_dffsr(RTLIL::Module *mod, RTLIL::Cell *cell)
 	{
 		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();
@@ -278,7 +278,7 @@ bool handle_dff(RTLIL::Module *mod, RTLIL::Cell *dff)
 		sig_c = dff->getPort("\\C");
 		val_cp = RTLIL::Const(dff->type == "$_DFF_P_", 1);
 	}
-	else if (dff->type.substr(0,6) == "$_DFF_" && dff->type.substr(9) == "_" &&
+	else if (dff->type.begins_with("$_DFF_") && dff->type.compare(9, 1, "_") == 0 &&
 			(dff->type[6] == 'N' || dff->type[6] == 'P') &&
 			(dff->type[7] == 'N' || dff->type[7] == 'P') &&
 			(dff->type[8] == '0' || dff->type[8] == '1')) {
@@ -290,7 +290,7 @@ bool handle_dff(RTLIL::Module *mod, RTLIL::Cell *dff)
 		val_rp = RTLIL::Const(dff->type[7] == 'P', 1);
 		val_rv = RTLIL::Const(dff->type[8] == '1', 1);
 	}
-	else if (dff->type.substr(0,7) == "$_DFFE_" && dff->type.substr(9) == "_" &&
+	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("\\D");
@@ -428,7 +428,7 @@ bool handle_dff(RTLIL::Module *mod, RTLIL::Cell *dff)
 			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");
 	}
@@ -452,7 +452,7 @@ bool handle_dff(RTLIL::Module *mod, RTLIL::Cell *dff)
 			return true;
 		}
 
-		log_assert(dff->type.substr(0,7) == "$_DFFE_");
+		log_assert(dff->type.begins_with("$_DFFE_"));
 		dff->type = stringf("$_DFF_%c_", + dff->type[7]);
 		dff->unsetPort("\\E");
 	}
@@ -624,7 +624,7 @@ struct OptRmdffPass : public Pass {
 						}
 				}
 
-				if (cell->type == "$mux" || cell->type == "$pmux") {
+				if (cell->type.in("$mux", "$pmux")) {
 					if (cell->getPort("\\A").size() == cell->getPort("\\B").size())
 						mux_drivers.insert(assign_map(cell->getPort("\\Y")), cell);
 					continue;
diff --git a/passes/opt/share.cc b/passes/opt/share.cc
index c85c27427..7f66f749f 100644
--- a/passes/opt/share.cc
+++ b/passes/opt/share.cc
@@ -376,13 +376,13 @@ struct ShareWorker
 				continue;
 			}
 
-			if (cell->type == "$mul" || cell->type == "$div" || cell->type == "$mod") {
+			if (cell->type.in("$mul", "$div", "$mod")) {
 				if (config.opt_aggressive || cell->parameters.at("\\Y_WIDTH").as_int() >= 4)
 					shareable_cells.insert(cell);
 				continue;
 			}
 
-			if (cell->type == "$shl" || cell->type == "$shr" || cell->type == "$sshl" || cell->type == "$sshr") {
+			if (cell->type.in("$shl", "$shr", "$sshl", "$sshr")) {
 				if (config.opt_aggressive || cell->parameters.at("\\Y_WIDTH").as_int() >= 8)
 					shareable_cells.insert(cell);
 				continue;
diff --git a/passes/proc/proc_arst.cc b/passes/proc/proc_arst.cc
index d069f152a..c606deb88 100644
--- a/passes/proc/proc_arst.cc
+++ b/passes/proc/proc_arst.cc
@@ -55,7 +55,7 @@ bool check_signal(RTLIL::Module *mod, RTLIL::SigSpec signal, RTLIL::SigSpec ref,
 			return check_signal(mod, cell->getPort("\\A"), ref, polarity);
 		}
 
-		if ((cell->type == "$eq" || cell->type == "$eqx") && cell->getPort("\\Y") == signal) {
+		if (cell->type.in("$eq", "$eqx") && cell->getPort("\\Y") == signal) {
 			if (cell->getPort("\\A").is_fully_const()) {
 				if (!cell->getPort("\\A").as_bool())
 					polarity = !polarity;
@@ -68,7 +68,7 @@ bool check_signal(RTLIL::Module *mod, RTLIL::SigSpec signal, RTLIL::SigSpec ref,
 			}
 		}
 
-		if ((cell->type == "$ne" || cell->type == "$nex") && cell->getPort("\\Y") == signal) {
+		if (cell->type.in("$ne", "$nex") && cell->getPort("\\Y") == signal) {
 			if (cell->getPort("\\A").is_fully_const()) {
 				if (cell->getPort("\\A").as_bool())
 					polarity = !polarity;
diff --git a/passes/sat/eval.cc b/passes/sat/eval.cc
index 008cd2dfa..e0bb439f4 100644
--- a/passes/sat/eval.cc
+++ b/passes/sat/eval.cc
@@ -47,8 +47,8 @@ struct BruteForceEquivChecker
 	{
 		if (inputs.size() < mod1_inputs.size()) {
 			RTLIL::SigSpec inputs0 = inputs, inputs1 = inputs;
-			inputs0.append(RTLIL::Const(0, 1));
-			inputs1.append(RTLIL::Const(1, 1));
+			inputs0.append(State::S0);
+			inputs1.append(State::S1);
 			run_checker(inputs0);
 			run_checker(inputs1);
 			return;
diff --git a/passes/sat/expose.cc b/passes/sat/expose.cc
index 71ce1683d..7631d87e6 100644
--- a/passes/sat/expose.cc
+++ b/passes/sat/expose.cc
@@ -151,7 +151,7 @@ void create_dff_dq_map(std::map<RTLIL::IdString, dff_map_info_t> &map, RTLIL::De
 			continue;
 		}
 
-		if (info.cell->type.size() == 10 && info.cell->type.substr(0, 6) == "$_DFF_") {
+		if (info.cell->type.size() == 10 && info.cell->type.begins_with("$_DFF_")) {
 			info.bit_clk = sigmap(info.cell->getPort("\\C")).as_bit();
 			info.bit_arst = sigmap(info.cell->getPort("\\R")).as_bit();
 			info.clk_polarity = info.cell->type[6] == 'P';
diff --git a/passes/sat/miter.cc b/passes/sat/miter.cc
index 1a886af70..49ef40061 100644
--- a/passes/sat/miter.cc
+++ b/passes/sat/miter.cc
@@ -59,7 +59,7 @@ void create_miter_equiv(struct Pass *that, std::vector<std::string> args, RTLIL:
 		}
 		break;
 	}
-	if (argidx+3 != args.size() || args[argidx].substr(0, 1) == "-")
+	if (argidx+3 != args.size() || args[argidx].compare(0, 1, "-") == 0)
 		that->cmd_error(args, argidx, "command argument error");
 
 	RTLIL::IdString gold_name = RTLIL::escape_id(args[argidx++]);
@@ -236,7 +236,7 @@ void create_miter_equiv(struct Pass *that, std::vector<std::string> args, RTLIL:
 	if (flag_make_assert) {
 		RTLIL::Cell *assert_cell = miter_module->addCell(NEW_ID, "$assert");
 		assert_cell->setPort("\\A", all_conditions);
-		assert_cell->setPort("\\EN", RTLIL::SigSpec(1, 1));
+		assert_cell->setPort("\\EN", State::S1);
 	}
 
 	RTLIL::Wire *w_trigger = miter_module->addWire("\\trigger");
@@ -279,7 +279,7 @@ void create_miter_assert(struct Pass *that, std::vector<std::string> args, RTLIL
 		}
 		break;
 	}
-	if ((argidx+1 != args.size() && argidx+2 != args.size()) || args[argidx].substr(0, 1) == "-")
+	if ((argidx+1 != args.size() && argidx+2 != args.size()) || args[argidx].compare(0, 1, "-") == 0)
 		that->cmd_error(args, argidx, "command argument error");
 
 	IdString module_name = RTLIL::escape_id(args[argidx++]);
diff --git a/passes/sat/sat.cc b/passes/sat/sat.cc
index e4654d835..dd56d8c71 100644
--- a/passes/sat/sat.cc
+++ b/passes/sat/sat.cc
@@ -519,7 +519,7 @@ struct SatHelper
 					for (auto &p : d->connections()) {
 						if (d->type == "$dff" && p.first == "\\CLK")
 							continue;
-						if (d->type.substr(0, 6) == "$_DFF_" && p.first == "\\C")
+						if (d->type.begins_with("$_DFF_") && p.first == "\\C")
 							continue;
 						queued_signals.add(handled_signals.remove(sigmap(p.second)));
 					}
@@ -797,7 +797,7 @@ struct SatHelper
 
 			vector<string> data;
 			string name = wd.first.c_str();
-			while (name.substr(0, 1) == "\\")
+			while (name.compare(0, 1, "\\") == 0)
 				name = name.substr(1);
 
 			fprintf(f, "    { \"name\": \"%s\", \"wave\": \"", name.c_str());
@@ -1353,7 +1353,7 @@ struct SatPass : public Pass {
 		if (show_regs) {
 			pool<Wire*> reg_wires;
 			for (auto cell : module->cells()) {
-				if (cell->type == "$dff" || cell->type.substr(0, 6) == "$_DFF_")
+				if (cell->type == "$dff" || cell->type.begins_with("$_DFF_"))
 					for (auto bit : cell->getPort("\\Q"))
 						if (bit.wire)
 							reg_wires.insert(bit.wire);
diff --git a/passes/techmap/abc.cc b/passes/techmap/abc.cc
index cb70b3b8e..9f963a8bf 100644
--- a/passes/techmap/abc.cc
+++ b/passes/techmap/abc.cc
@@ -166,7 +166,7 @@ void mark_port(RTLIL::SigSpec sig)
 
 void extract_cell(RTLIL::Cell *cell, bool keepff)
 {
-	if (cell->type == "$_DFF_N_" || cell->type == "$_DFF_P_")
+	if (cell->type.in("$_DFF_N_", "$_DFF_P_"))
 	{
 		if (clk_polarity != (cell->type == "$_DFF_P_"))
 			return;
@@ -177,11 +177,11 @@ void extract_cell(RTLIL::Cell *cell, bool keepff)
 		goto matching_dff;
 	}
 
-	if (cell->type == "$_DFFE_NN_" || cell->type == "$_DFFE_NP_" || cell->type == "$_DFFE_PN_" || cell->type == "$_DFFE_PP_")
+	if (cell->type.in("$_DFFE_NN_", "$_DFFE_NP_", "$_DFFE_PN_", "$_DFFE_PP_"))
 	{
-		if (clk_polarity != (cell->type == "$_DFFE_PN_" || cell->type == "$_DFFE_PP_"))
+		if (clk_polarity != cell->type.in("$_DFFE_PN_", "$_DFFE_PP_"))
 			return;
-		if (en_polarity != (cell->type == "$_DFFE_NP_" || cell->type == "$_DFFE_PP_"))
+		if (en_polarity != cell->type.in("$_DFFE_NP_", "$_DFFE_PP_"))
 			return;
 		if (clk_sig != assign_map(cell->getPort("\\C")))
 			return;
@@ -333,17 +333,17 @@ std::string remap_name(RTLIL::IdString abc_name, RTLIL::Wire **orig_wire = nullp
 {
 	std::string abc_sname = abc_name.substr(1);
 	bool isnew = false;
-	if (abc_sname.substr(0, 4) == "new_")
+	if (abc_sname.compare(0, 4, "new_") == 0)
 	{
 		abc_sname.erase(0, 4);
 		isnew = true;
 	}
-	if (abc_sname.substr(0, 5) == "ys__n")
+	if (abc_sname.compare(0, 5, "ys__n") == 0)
 	{
 		abc_sname.erase(0, 5);
 		if (std::isdigit(abc_sname.at(0)))
 		{
-			int sid = std::stoi(abc_sname);
+			int sid = std::atoi(abc_sname.c_str());
 			size_t postfix_start = abc_sname.find_first_not_of("0123456789");
 			std::string postfix = postfix_start != std::string::npos ? abc_sname.substr(postfix_start) : "";
 
@@ -1590,7 +1590,7 @@ struct AbcPass : public Pass {
 					else if (GetSize(parts) == 1)
 						lut_costs.push_back(atoi(parts.at(0).c_str()));
 					else if (GetSize(parts) == 2)
-						while (GetSize(lut_costs) < atoi(parts.at(0).c_str()))
+						while (GetSize(lut_costs) < std::atoi(parts.at(0).c_str()))
 							lut_costs.push_back(atoi(parts.at(1).c_str()));
 					else
 						log_cmd_error("Invalid -luts syntax.\n");
@@ -1861,15 +1861,15 @@ struct AbcPass : public Pass {
 					}
 				}
 
-				if (cell->type == "$_DFF_N_" || cell->type == "$_DFF_P_")
+				if (cell->type.in("$_DFF_N_", "$_DFF_P_"))
 				{
 					key = clkdomain_t(cell->type == "$_DFF_P_", assign_map(cell->getPort("\\C")), true, RTLIL::SigSpec());
 				}
 				else
-				if (cell->type == "$_DFFE_NN_" || cell->type == "$_DFFE_NP_" || cell->type == "$_DFFE_PN_" || cell->type == "$_DFFE_PP_")
+				if (cell->type.in("$_DFFE_NN_", "$_DFFE_NP_" "$_DFFE_PN_", "$_DFFE_PP_"))
 				{
-					bool this_clk_pol = cell->type == "$_DFFE_PN_" || cell->type == "$_DFFE_PP_";
-					bool this_en_pol = cell->type == "$_DFFE_NP_" || cell->type == "$_DFFE_PP_";
+					bool this_clk_pol = cell->type.in("$_DFFE_PN_", "$_DFFE_PP_");
+					bool this_en_pol = cell->type.in("$_DFFE_NP_", "$_DFFE_PP_");
 					key = clkdomain_t(this_clk_pol, assign_map(cell->getPort("\\C")), this_en_pol, assign_map(cell->getPort("\\E")));
 				}
 				else
diff --git a/passes/techmap/abc9.cc b/passes/techmap/abc9.cc
index 7255e2481..7418ed4a3 100644
--- a/passes/techmap/abc9.cc
+++ b/passes/techmap/abc9.cc
@@ -593,7 +593,7 @@ void abc9_module(RTLIL::Design *design, RTLIL::Module *current_module, std::stri
 					c->setPort("\\Y", module->addWire(NEW_ID));
 					RTLIL::Wire *wire = module->wire(remap_name(y_bit.wire->name));
 					log_assert(wire);
-					module->connect(RTLIL::SigBit(wire, y_bit.offset), RTLIL::S1);
+					module->connect(RTLIL::SigBit(wire, y_bit.offset), State::S1);
 				}
 				else if (!lut_costs.empty() || !lut_file.empty()) {
 					RTLIL::Cell* driver_lut = nullptr;
@@ -1153,15 +1153,15 @@ struct Abc9Pass : public Pass {
 					}
 				}
 
-				if (cell->type == "$_DFF_N_" || cell->type == "$_DFF_P_")
+				if (cell->type.in("$_DFF_N_", "$_DFF_P_"))
 				{
 					key = clkdomain_t(cell->type == "$_DFF_P_", assign_map(cell->getPort("\\C")), true, RTLIL::SigSpec());
 				}
 				else
-				if (cell->type == "$_DFFE_NN_" || cell->type == "$_DFFE_NP_" || cell->type == "$_DFFE_PN_" || cell->type == "$_DFFE_PP_")
+				if (cell->type.in("$_DFFE_NN_", "$_DFFE_NP_", "$_DFFE_PN_", "$_DFFE_PP_"))
 				{
-					bool this_clk_pol = cell->type == "$_DFFE_PN_" || cell->type == "$_DFFE_PP_";
-					bool this_en_pol = cell->type == "$_DFFE_NP_" || cell->type == "$_DFFE_PP_";
+					bool this_clk_pol = cell->type.in("$_DFFE_PN_", "$_DFFE_PP_");
+					bool this_en_pol = cell->type.in("$_DFFE_NP_", "$_DFFE_PP_");
 					key = clkdomain_t(this_clk_pol, assign_map(cell->getPort("\\C")), this_en_pol, assign_map(cell->getPort("\\E")));
 				}
 				else
diff --git a/passes/techmap/aigmap.cc b/passes/techmap/aigmap.cc
index 35df2ff79..2423676cb 100644
--- a/passes/techmap/aigmap.cc
+++ b/passes/techmap/aigmap.cc
@@ -66,7 +66,7 @@ struct AigmapPass : public Pass {
 			{
 				Aig aig(cell);
 
-				if (cell->type == "$_AND_" || cell->type == "$_NOT_")
+				if (cell->type.in("$_AND_", "$_NOT_"))
 					aig.name.clear();
 
 				if (nand_mode && cell->type == "$_NAND_")
diff --git a/passes/techmap/alumacc.cc b/passes/techmap/alumacc.cc
index dc7d416b0..5c9e42fd4 100644
--- a/passes/techmap/alumacc.cc
+++ b/passes/techmap/alumacc.cc
@@ -315,7 +315,7 @@ struct AlumaccWorker
 			}
 
 			if (subtract_b)
-				C.append(RTLIL::S1);
+				C.append(State::S1);
 
 			if (GetSize(C) > 1)
 				goto next_macc;
@@ -402,7 +402,7 @@ struct AlumaccWorker
 			alunode_t *n = nullptr;
 
 			for (auto node : sig_alu[RTLIL::SigSig(A, B)])
-				if (node->is_signed == is_signed && node->invert_b && node->c == RTLIL::S1) {
+				if (node->is_signed == is_signed && node->invert_b && node->c == State::S1) {
 					n = node;
 					break;
 				}
@@ -411,7 +411,7 @@ struct AlumaccWorker
 				n = new alunode_t;
 				n->a = A;
 				n->b = B;
-				n->c = RTLIL::S1;
+				n->c = State::S1;
 				n->y = module->addWire(NEW_ID, max(GetSize(A), GetSize(B)));
 				n->is_signed = is_signed;
 				n->invert_b = true;
@@ -440,7 +440,7 @@ struct AlumaccWorker
 			alunode_t *n = nullptr;
 
 			for (auto node : sig_alu[RTLIL::SigSig(A, B)])
-				if (node->is_signed == is_signed && node->invert_b && node->c == RTLIL::S1) {
+				if (node->is_signed == is_signed && node->invert_b && node->c == State::S1) {
 					n = node;
 					break;
 				}
@@ -484,8 +484,8 @@ struct AlumaccWorker
 
 			n->alu_cell->setPort("\\A", n->a);
 			n->alu_cell->setPort("\\B", n->b);
-			n->alu_cell->setPort("\\CI", GetSize(n->c) ? n->c : RTLIL::S0);
-			n->alu_cell->setPort("\\BI", n->invert_b ? RTLIL::S1 : RTLIL::S0);
+			n->alu_cell->setPort("\\CI", GetSize(n->c) ? n->c : State::S0);
+			n->alu_cell->setPort("\\BI", n->invert_b ? State::S1 : State::S0);
 			n->alu_cell->setPort("\\Y", n->y);
 			n->alu_cell->setPort("\\X", module->addWire(NEW_ID, GetSize(n->y)));
 			n->alu_cell->setPort("\\CO", module->addWire(NEW_ID, GetSize(n->y)));
diff --git a/passes/techmap/deminout.cc b/passes/techmap/deminout.cc
index 47d0ff416..142d12bdc 100644
--- a/passes/techmap/deminout.cc
+++ b/passes/techmap/deminout.cc
@@ -85,7 +85,7 @@ struct DeminoutPass : public Pass {
 
 					if (conn.first == "\\Y" && cell->type.in("$mux", "$pmux", "$_MUX_", "$_TBUF_", "$tribuf"))
 					{
-						bool tribuf = (cell->type == "$_TBUF_" || cell->type == "$tribuf");
+						bool tribuf = cell->type.in("$_TBUF_", "$tribuf");
 
 						if (!tribuf) {
 							for (auto &c : cell->connections()) {
diff --git a/passes/techmap/dff2dffe.cc b/passes/techmap/dff2dffe.cc
index 7e1040963..c0bf3a665 100644
--- a/passes/techmap/dff2dffe.cc
+++ b/passes/techmap/dff2dffe.cc
@@ -52,13 +52,13 @@ struct Dff2dffeWorker
 		}
 
 		for (auto cell : module->cells()) {
-			if (cell->type == "$mux" || cell->type == "$pmux" || cell->type == "$_MUX_") {
+			if (cell->type.in("$mux", "$pmux", "$_MUX_")) {
 				RTLIL::SigSpec sig_y = sigmap(cell->getPort("\\Y"));
 				for (int i = 0; i < GetSize(sig_y); i++)
 					bit2mux[sig_y[i]] = cell_int_t(cell, i);
 			}
 			if (direct_dict.empty()) {
-				if (cell->type == "$dff" || cell->type == "$_DFF_N_" || cell->type == "$_DFF_P_")
+				if (cell->type.in("$dff", "$_DFF_N_", "$_DFF_P_"))
 					dff_cells.push_back(cell);
 			} else {
 				if (direct_dict.count(cell->type))
@@ -167,7 +167,7 @@ struct Dff2dffeWorker
 		}
 
 		if (GetSize(or_input) == 0)
-			return RTLIL::S1;
+			return State::S1;
 
 		if (GetSize(or_input) == 1)
 			return or_input;
@@ -304,7 +304,7 @@ struct Dff2dffePass : public Pass {
 			}
 			if (args[argidx] == "-unmap-mince" && argidx + 1 < args.size()) {
 				unmap_mode = true;
-				min_ce_use = std::stoi(args[++argidx]);
+				min_ce_use = atoi(args[++argidx].c_str());
 				continue;
 			}
 			if (args[argidx] == "-direct" && argidx + 2 < args.size()) {
@@ -377,7 +377,7 @@ struct Dff2dffePass : public Pass {
 							mod->remove(cell);
 							continue;
 						}
-						if (cell->type.substr(0, 7) == "$_DFFE_") {
+						if (cell->type.begins_with("$_DFFE_")) {
 							if (min_ce_use >= 0) {
 								int ce_use = 0;
 								for (auto cell_other : mod->selected_cells()) {
@@ -390,8 +390,8 @@ struct Dff2dffePass : public Pass {
 									continue;
 							}
 
-							bool clk_pol = cell->type.substr(7, 1) == "P";
-							bool en_pol = cell->type.substr(8, 1) == "P";
+							bool clk_pol = cell->type.compare(7, 1, "P") == 0;
+							bool en_pol = cell->type.compare(8, 1, "P") == 0;
 							RTLIL::SigSpec tmp = mod->addWire(NEW_ID);
 							mod->addDff(NEW_ID, cell->getPort("\\C"), tmp, cell->getPort("\\Q"), clk_pol);
 							if (en_pol)
diff --git a/passes/techmap/extract.cc b/passes/techmap/extract.cc
index fff90f13c..e3b4faba1 100644
--- a/passes/techmap/extract.cc
+++ b/passes/techmap/extract.cc
@@ -54,7 +54,7 @@ public:
 
 	RTLIL::Const unified_param(RTLIL::IdString cell_type, RTLIL::IdString param, RTLIL::Const value)
 	{
-		if (cell_type.substr(0, 1) != "$" || cell_type.substr(0, 2) == "$_")
+		if (!cell_type.begins_with("$") || cell_type.begins_with("$_"))
 			return value;
 
 	#define param_bool(_n) if (param == _n) return value.as_bool();
@@ -203,7 +203,7 @@ bool module2graph(SubCircuit::Graph &graph, RTLIL::Module *mod, bool constports,
 			continue;
 
 		std::string type = cell->type.str();
-		if (sel == NULL && type.substr(0, 2) == "\\$")
+		if (sel == NULL && type.compare(0, 2, "\\$") == 0)
 			type = type.substr(1);
 		graph.createNode(cell->name.str(), type, (void*)cell);
 
@@ -594,7 +594,7 @@ struct ExtractPass : public Pass {
 			map = new RTLIL::Design;
 			for (auto &filename : map_filenames)
 			{
-				if (filename.substr(0, 1) == "%")
+				if (filename.compare(0, 1, "%") == 0)
 				{
 					if (!saved_designs.count(filename.substr(1))) {
 						delete map;
@@ -613,10 +613,10 @@ struct ExtractPass : public Pass {
 						delete map;
 						log_cmd_error("Can't open map file `%s'.\n", filename.c_str());
 					}
-					Frontend::frontend_call(map, &f, filename, (filename.size() > 3 && filename.substr(filename.size()-3) == ".il") ? "ilang" : "verilog");
+					Frontend::frontend_call(map, &f, filename, (filename.size() > 3 && filename.compare(filename.size()-3, std::string::npos, ".il") == 0 ? "ilang" : "verilog"));
 					f.close();
 
-					if (filename.size() <= 3 || filename.substr(filename.size()-3) != ".il") {
+					if (filename.size() <= 3 || filename.compare(filename.size()-3, std::string::npos, ".il") != 0) {
 						Pass::call(map, "proc");
 						Pass::call(map, "opt_clean");
 					}
diff --git a/passes/techmap/maccmap.cc b/passes/techmap/maccmap.cc
index 3e8e59e6b..59e58e4db 100644
--- a/passes/techmap/maccmap.cc
+++ b/passes/techmap/maccmap.cc
@@ -36,7 +36,7 @@ struct MaccmapWorker
 
 	void add(RTLIL::SigBit bit, int position)
 	{
-		if (position >= width || bit == RTLIL::S0)
+		if (position >= width || bit == State::S0)
 			return;
 
 		if (bits.at(position).count(bit)) {
@@ -53,7 +53,7 @@ struct MaccmapWorker
 
 		if (do_subtract) {
 			a = module->Not(NEW_ID, a);
-			add(RTLIL::S1, 0);
+			add(State::S1, 0);
 		}
 
 		for (int i = 0; i < width; i++)
@@ -80,7 +80,7 @@ struct MaccmapWorker
 			else
 			{
 				add(module->And(NEW_ID, a, RTLIL::SigSpec(b[i], width)), false, do_subtract);
-				a = {a.extract(0, width-1), RTLIL::S0};
+				a = {a.extract(0, width-1), State::S0};
 			}
 	}
 
@@ -88,10 +88,10 @@ struct MaccmapWorker
 	{
 		int start_index = 0, stop_index = GetSize(in1);
 
-		while (start_index < stop_index && in1[start_index] == RTLIL::S0 && in2[start_index] == RTLIL::S0 && in3[start_index] == RTLIL::S0)
+		while (start_index < stop_index && in1[start_index] == State::S0 && in2[start_index] == RTLIL::S0 && in3[start_index] == RTLIL::S0)
 			start_index++;
 
-		while (start_index < stop_index && in1[stop_index-1] == RTLIL::S0 && in2[stop_index-1] == RTLIL::S0 && in3[stop_index-1] == RTLIL::S0)
+		while (start_index < stop_index && in1[stop_index-1] == State::S0 && in2[stop_index-1] == RTLIL::S0 && in3[stop_index-1] == RTLIL::S0)
 			stop_index--;
 
 		if (start_index == stop_index)
@@ -222,7 +222,7 @@ struct MaccmapWorker
 					RTLIL::SigSpec in3 = summands[i+2];
 					RTLIL::SigSpec out1, out2;
 					fulladd(in1, in2, in3, out1, out2);
-					RTLIL::SigBit extra_bit = RTLIL::S0;
+					RTLIL::SigBit extra_bit = State::S0;
 					if (!tree_sum_bits.empty()) {
 						extra_bit = tree_sum_bits.back();
 						tree_sum_bits.pop_back();
@@ -240,8 +240,8 @@ struct MaccmapWorker
 		RTLIL::Cell *c = module->addCell(NEW_ID, "$alu");
 		c->setPort("\\A", summands.front());
 		c->setPort("\\B", summands.back());
-		c->setPort("\\CI", RTLIL::S0);
-		c->setPort("\\BI", RTLIL::S0);
+		c->setPort("\\CI", State::S0);
+		c->setPort("\\BI", State::S0);
 		c->setPort("\\Y", module->addWire(NEW_ID, width));
 		c->setPort("\\X", module->addWire(NEW_ID, width));
 		c->setPort("\\CO", module->addWire(NEW_ID, width));
diff --git a/passes/techmap/muxcover.cc b/passes/techmap/muxcover.cc
index d53378a29..81546249c 100644
--- a/passes/techmap/muxcover.cc
+++ b/passes/techmap/muxcover.cc
@@ -675,36 +675,36 @@ struct MuxcoverPass : public Pass {
 		for (argidx = 1; argidx < args.size(); argidx++)
 		{
 			const auto &arg = args[argidx];
-			if (arg.size() >= 6 && arg.substr(0,6) == "-mux2=") {
-				cost_mux2 = std::stoi(arg.substr(6));
+			if (arg.size() >= 6 && arg.compare(0,6,"-mux2=") == 0) {
+				cost_mux2 = atoi(arg.substr(6).c_str());
 				continue;
 			}
-			if (arg.size() >= 5 && arg.substr(0,5) == "-mux4") {
+			if (arg.size() >= 5 && arg.compare(0,5,"-mux4") == 0) {
 				use_mux4 = true;
 				if (arg.size() > 5) {
 					if (arg[5] != '=') break;
-					cost_mux4 = std::stoi(arg.substr(6));
+					cost_mux4 = atoi(arg.substr(6).c_str());
 				}
 				continue;
 			}
-			if (arg.size() >= 5 && arg.substr(0,5) == "-mux8") {
+			if (arg.size() >= 5 && arg.compare(0,5,"-mux8") == 0) {
 				use_mux8 = true;
 				if (arg.size() > 5) {
 					if (arg[5] != '=') break;
-					cost_mux8 = std::stoi(arg.substr(6));
+					cost_mux8 = atoi(arg.substr(6).c_str());
 				}
 				continue;
 			}
-			if (arg.size() >= 6 && arg.substr(0,6) == "-mux16") {
+			if (arg.size() >= 6 && arg.compare(0,6,"-mux16") == 0) {
 				use_mux16 = true;
 				if (arg.size() > 6) {
 					if (arg[6] != '=') break;
-					cost_mux16 = std::stoi(arg.substr(7));
+					cost_mux16 = atoi(arg.substr(7).c_str());
 				}
 				continue;
 			}
-			if (arg.size() >= 6 && arg.substr(0,6) == "-dmux=") {
-				cost_dmux = std::stoi(arg.substr(6));
+			if (arg.size() >= 6 && arg.compare(0,6,"-dmux=") == 0) {
+				cost_dmux = atoi(arg.substr(6).c_str());
 				continue;
 			}
 			if (arg == "-nodecode") {
diff --git a/passes/techmap/simplemap.cc b/passes/techmap/simplemap.cc
index f3da80c66..2eaba1b09 100644
--- a/passes/techmap/simplemap.cc
+++ b/passes/techmap/simplemap.cc
@@ -185,7 +185,7 @@ static void logic_reduce(RTLIL::Module *module, RTLIL::SigSpec &sig, RTLIL::Cell
 	}
 
 	if (sig.size() == 0)
-		sig = RTLIL::SigSpec(0, 1);
+		sig = State::S0;
 }
 
 void simplemap_lognot(RTLIL::Module *module, RTLIL::Cell *cell)
@@ -245,7 +245,7 @@ void simplemap_eqne(RTLIL::Module *module, RTLIL::Cell *cell)
 	RTLIL::SigSpec sig_b = cell->getPort("\\B");
 	RTLIL::SigSpec sig_y = cell->getPort("\\Y");
 	bool is_signed = cell->parameters.at("\\A_SIGNED").as_bool();
-	bool is_ne = cell->type == "$ne" || cell->type == "$nex";
+	bool is_ne = cell->type.in("$ne", "$nex");
 
 	RTLIL::SigSpec xor_out = module->addWire(NEW_ID, max(GetSize(sig_a), GetSize(sig_b)));
 	RTLIL::Cell *xor_cell = module->addXor(NEW_ID, sig_a, sig_b, xor_out, is_signed);
diff --git a/passes/techmap/techmap.cc b/passes/techmap/techmap.cc
index ceb053825..2708b08ae 100644
--- a/passes/techmap/techmap.cc
+++ b/passes/techmap/techmap.cc
@@ -243,7 +243,7 @@ struct TechmapWorker
 			if (positional_ports.count(portname) > 0)
 				portname = positional_ports.at(portname);
 			if (tpl->wires_.count(portname) == 0 || tpl->wires_.at(portname)->port_id == 0) {
-				if (portname.substr(0, 1) == "$")
+				if (portname.begins_with("$"))
 					log_error("Can't map port `%s' of cell `%s' to template `%s'!\n", portname.c_str(), cell->name.c_str(), tpl->name.c_str());
 				continue;
 			}
@@ -341,7 +341,7 @@ struct TechmapWorker
 			RTLIL::Cell *c = module->addCell(c_name, it.second);
 			design->select(module, c);
 
-			if (!flatten_mode && c->type.substr(0, 2) == "\\$")
+			if (!flatten_mode && c->type.begins_with("\\$"))
 				c->type = c->type.substr(1);
 
 			for (auto &it2 : c->connections_) {
@@ -406,7 +406,7 @@ struct TechmapWorker
 				continue;
 
 			std::string cell_type = cell->type.str();
-			if (in_recursion && cell_type.substr(0, 2) == "\\$")
+			if (in_recursion && cell->type.begins_with("\\$"))
 				cell_type = cell_type.substr(1);
 
 			if (celltypeMap.count(cell_type) == 0) {
@@ -468,7 +468,7 @@ struct TechmapWorker
 
 			std::string cell_type = cell->type.str();
 
-			if (in_recursion && cell_type.substr(0, 2) == "\\$")
+			if (in_recursion && cell->type.begins_with("\\$"))
 				cell_type = cell_type.substr(1);
 
 			for (auto &tpl_name : celltypeMap.at(cell_type))
@@ -602,7 +602,7 @@ struct TechmapWorker
 					}
 
 					for (auto conn : cell->connections()) {
-						if (conn.first.substr(0, 1) == "$")
+						if (conn.first.begins_with("$"))
 							continue;
 						if (tpl->wires_.count(conn.first) > 0 && tpl->wires_.at(conn.first)->port_id > 0)
 							continue;
@@ -725,7 +725,7 @@ struct TechmapWorker
 
 						for (auto &it : twd)
 						{
-							if (it.first.substr(0, 12) != "_TECHMAP_DO_" || it.second.empty())
+							if (it.first.compare(0, 12, "_TECHMAP_DO_") != 0 || it.second.empty())
 								continue;
 
 							auto &data = it.second.front();
@@ -874,7 +874,7 @@ struct TechmapWorker
 						tpl->cloneInto(m);
 
 						for (auto cell : m->cells()) {
-							if (cell->type.substr(0, 2) == "\\$")
+							if (cell->type.begins_with("\\$"))
 								cell->type = cell->type.substr(1);
 						}
 
@@ -1113,7 +1113,7 @@ struct TechmapPass : public Pass {
 			Frontend::frontend_call(map, &f, "<techmap.v>", verilog_frontend);
 		} else {
 			for (auto &fn : map_files)
-				if (fn.substr(0, 1) == "%") {
+				if (fn.compare(0, 1, "%") == 0) {
 					if (!saved_designs.count(fn.substr(1))) {
 						delete map;
 						log_cmd_error("Can't saved design `%s'.\n", fn.c_str()+1);
@@ -1128,7 +1128,7 @@ struct TechmapPass : public Pass {
 					yosys_input_files.insert(fn);
 					if (f.fail())
 						log_cmd_error("Can't open map file `%s'\n", fn.c_str());
-					Frontend::frontend_call(map, &f, fn, (fn.size() > 3 && fn.substr(fn.size()-3) == ".il") ? "ilang" : verilog_frontend);
+					Frontend::frontend_call(map, &f, fn, (fn.size() > 3 && fn.compare(fn.size()-3, std::string::npos, ".il") == 0 ? "ilang" : verilog_frontend));
 				}
 		}
 
@@ -1143,7 +1143,7 @@ struct TechmapPass : public Pass {
 				free(p);
 			} else {
 				string module_name = it.first.str();
-				if (module_name.substr(0, 2) == "\\$")
+				if (it.first.begins_with("\\$"))
 					module_name = module_name.substr(1);
 				celltypeMap[module_name].insert(it.first);
 			}
diff --git a/passes/tests/test_cell.cc b/passes/tests/test_cell.cc
index e360b5edb..319669955 100644
--- a/passes/tests/test_cell.cc
+++ b/passes/tests/test_cell.cc
@@ -186,7 +186,7 @@ static void create_gold_module(RTLIL::Design *design, RTLIL::IdString cell_type,
 
 		RTLIL::SigSpec config;
 		for (int i = 0; i < (1 << width); i++)
-			config.append(xorshift32(2) ? RTLIL::S1 : RTLIL::S0);
+			config.append(xorshift32(2) ? State::S1 : State::S0);
 
 		cell->setParam("\\LUT", config.as_const());
 	}
@@ -209,16 +209,16 @@ static void create_gold_module(RTLIL::Design *design, RTLIL::IdString cell_type,
 		for (int i = 0; i < width*depth; i++)
 			switch (xorshift32(3)) {
 				case 0:
-					config.append(RTLIL::S1);
-					config.append(RTLIL::S0);
+					config.append(State::S1);
+					config.append(State::S0);
 					break;
 				case 1:
-					config.append(RTLIL::S0);
-					config.append(RTLIL::S1);
+					config.append(State::S0);
+					config.append(State::S1);
 					break;
 				case 2:
-					config.append(RTLIL::S0);
-					config.append(RTLIL::S0);
+					config.append(State::S0);
+					config.append(State::S0);
 					break;
 			}
 
@@ -308,18 +308,18 @@ static void create_gold_module(RTLIL::Design *design, RTLIL::IdString cell_type,
 			case 0:
 				n = xorshift32(GetSize(sig) + 1);
 				for (int i = 0; i < n; i++)
-					sig[i] = xorshift32(2) == 1 ? RTLIL::S1 : RTLIL::S0;
+					sig[i] = xorshift32(2) == 1 ? State::S1 : State::S0;
 				break;
 			case 1:
 				n = xorshift32(GetSize(sig) + 1);
 				for (int i = n; i < GetSize(sig); i++)
-					sig[i] = xorshift32(2) == 1 ? RTLIL::S1 : RTLIL::S0;
+					sig[i] = xorshift32(2) == 1 ? State::S1 : State::S0;
 				break;
 			case 2:
 				n = xorshift32(GetSize(sig));
 				m = xorshift32(GetSize(sig));
 				for (int i = min(n, m); i < max(n, m); i++)
-					sig[i] = xorshift32(2) == 1 ? RTLIL::S1 : RTLIL::S0;
+					sig[i] = xorshift32(2) == 1 ? State::S1 : State::S0;
 				break;
 			}
 
@@ -491,7 +491,7 @@ static void run_eval_test(RTLIL::Design *design, bool verbose, bool nosat, std::
 
 			RTLIL::Const in_value;
 			for (int i = 0; i < GetSize(gold_wire); i++)
-				in_value.bits.push_back(xorshift32(2) ? RTLIL::S1 : RTLIL::S0);
+				in_value.bits.push_back(xorshift32(2) ? State::S1 : State::S0);
 
 			if (xorshift32(4) == 0) {
 				int inv_chance = 1 + xorshift32(8);
@@ -591,11 +591,11 @@ static void run_eval_test(RTLIL::Design *design, bool verbose, bool nosat, std::
 			}
 
 			for (int i = 0; i < GetSize(out_sig); i++) {
-				if (out_val[i] != RTLIL::S0 && out_val[i] != RTLIL::S1)
+				if (out_val[i] != State::S0 && out_val[i] != State::S1)
 					continue;
-				if (out_val[i] == RTLIL::S0 && sat1_model_value.at(i) == false)
+				if (out_val[i] == State::S0 && sat1_model_value.at(i) == false)
 					continue;
-				if (out_val[i] == RTLIL::S1 && sat1_model_value.at(i) == true)
+				if (out_val[i] == State::S1 && sat1_model_value.at(i) == true)
 					continue;
 				log_error("Mismatch in sat model 1 (no undef modeling) output!\n");
 			}
@@ -627,12 +627,12 @@ static void run_eval_test(RTLIL::Design *design, bool verbose, bool nosat, std::
 
 			for (int i = 0; i < GetSize(out_sig); i++) {
 				if (sat2_model_value.at(GetSize(out_sig) + i)) {
-					if (out_val[i] != RTLIL::S0 && out_val[i] != RTLIL::S1)
+					if (out_val[i] != State::S0 && out_val[i] != State::S1)
 						continue;
 				} else {
-					if (out_val[i] == RTLIL::S0 && sat2_model_value.at(i) == false)
+					if (out_val[i] == State::S0 && sat2_model_value.at(i) == false)
 						continue;
-					if (out_val[i] == RTLIL::S1 && sat2_model_value.at(i) == true)
+					if (out_val[i] == State::S1 && sat2_model_value.at(i) == true)
 						continue;
 				}
 				log_error("Mismatch in sat model 2 (undef modeling) output!\n");
@@ -872,7 +872,7 @@ struct TestCellPass : public Pass {
 				continue;
 			}
 
-			if (args[argidx].substr(0, 1) == "/") {
+			if (args[argidx].compare(0, 1, "/") == 0) {
 				std::vector<std::string> new_selected_cell_types;
 				for (auto it : selected_cell_types)
 					if (it != args[argidx].substr(1))
diff --git a/techlibs/coolrunner2/coolrunner2_sop.cc b/techlibs/coolrunner2/coolrunner2_sop.cc
index 48da0d8ad..de0cbb29d 100644
--- a/techlibs/coolrunner2/coolrunner2_sop.cc
+++ b/techlibs/coolrunner2/coolrunner2_sop.cc
@@ -60,10 +60,8 @@ struct Coolrunner2SopPass : public Pass {
 			dict<SigBit, pool<tuple<Cell*, std::string>>> special_pterms_inv;
 			for (auto cell : module->selected_cells())
 			{
-				if (cell->type == "\\FDCP" || cell->type == "\\FDCP_N" || cell->type == "\\FDDCP" ||
-					cell->type == "\\FTCP" || cell->type == "\\FTCP_N" || cell->type == "\\FTDCP" ||
-					cell->type == "\\FDCPE" || cell->type == "\\FDCPE_N" || cell->type == "\\FDDCPE" ||
-					cell->type == "\\LDCP" || cell->type == "\\LDCP_N")
+				if (cell->type.in("\\FDCP", "\\FDCP_N", "\\FDDCP", "\\FTCP", "\\FTCP_N", "\\FTDCP",
+							"\\FDCPE", "\\FDCPE_N", "\\FDDCPE", "\\LDCP", "\\LDCP_N"))
 				{
 					if (cell->hasPort("\\PRE"))
 						special_pterms_no_inv[sigmap(cell->getPort("\\PRE")[0])].insert(
@@ -257,10 +255,8 @@ struct Coolrunner2SopPass : public Pass {
 			pool<SigBit> sig_fed_by_ff;
 			for (auto cell : module->selected_cells())
 			{
-				if (cell->type == "\\FDCP" || cell->type == "\\FDCP_N" || cell->type == "\\FDDCP" ||
-					cell->type == "\\LDCP" || cell->type == "\\LDCP_N" ||
-					cell->type == "\\FTCP" || cell->type == "\\FTCP_N" || cell->type == "\\FTDCP" ||
-					cell->type == "\\FDCPE" || cell->type == "\\FDCPE_N" || cell->type == "\\FDDCPE")
+				if (cell->type.in("\\FDCP", "\\FDCP_N", "\\FDDCP", "\\LDCP", "\\LDCP_N",
+							"\\FTCP", "\\FTCP_N", "\\FTDCP", "\\FDCPE", "\\FDCPE_N", "\\FDDCPE"))
 				{
 					auto output = sigmap(cell->getPort("\\Q")[0]);
 					sig_fed_by_ff.insert(output);
@@ -270,13 +266,11 @@ struct Coolrunner2SopPass : public Pass {
 			// Look at all the FF inputs
 			for (auto cell : module->selected_cells())
 			{
-				if (cell->type == "\\FDCP" || cell->type == "\\FDCP_N" || cell->type == "\\FDDCP" ||
-					cell->type == "\\LDCP" || cell->type == "\\LDCP_N" ||
-					cell->type == "\\FTCP" || cell->type == "\\FTCP_N" || cell->type == "\\FTDCP" ||
-					cell->type == "\\FDCPE" || cell->type == "\\FDCPE_N" || cell->type == "\\FDDCPE")
+				if (cell->type.in("\\FDCP", "\\FDCP_N", "\\FDDCP", "\\LDCP", "\\LDCP_N",
+							"\\FTCP", "\\FTCP_N", "\\FTDCP", "\\FDCPE", "\\FDCPE_N", "\\FDDCPE"))
 				{
 					SigBit input;
-					if (cell->type == "\\FTCP" || cell->type == "\\FTCP_N" || cell->type == "\\FTDCP")
+					if (cell->type.in("\\FTCP", "\\FTCP_N", "\\FTDCP"))
 						input = sigmap(cell->getPort("\\T")[0]);
 					else
 						input = sigmap(cell->getPort("\\D")[0]);
@@ -300,7 +294,7 @@ struct Coolrunner2SopPass : public Pass {
 						xor_cell->setPort("\\IN_PTC", and_to_xor_wire);
 						xor_cell->setPort("\\OUT", xor_to_ff_wire);
 
-						if (cell->type == "\\FTCP" || cell->type == "\\FTCP_N" || cell->type == "\\FTDCP")
+						if (cell->type.in("\\FTCP", "\\FTCP_N", "\\FTDCP"))
 							cell->setPort("\\T", xor_to_ff_wire);
 						else
 							cell->setPort("\\D", xor_to_ff_wire);
diff --git a/techlibs/ice40/ice40_braminit.cc b/techlibs/ice40/ice40_braminit.cc
index 4fa6b0792..1a139ffea 100644
--- a/techlibs/ice40/ice40_braminit.cc
+++ b/techlibs/ice40/ice40_braminit.cc
@@ -69,13 +69,13 @@ static void run_ice40_braminit(Module *module)
 
 			for (int i = 0; i < GetSize(line); i++)
 			{
-				if (in_comment && line.substr(i, 2) == "*/") {
+				if (in_comment && line.compare(i, 2, "*/") == 0) {
 					line[i] = ' ';
 					line[i+1] = ' ';
 					in_comment = false;
 					continue;
 				}
-				if (!in_comment && line.substr(i, 2) == "/*")
+				if (!in_comment && line.compare(i, 2, "/*") == 0)
 					in_comment = true;
 				if (in_comment)
 					line[i] = ' ';
@@ -87,7 +87,7 @@ static void run_ice40_braminit(Module *module)
 				long value;
 
 				token = next_token(line, " \t\r\n");
-				if (token.empty() || token.substr(0, 2) == "//")
+				if (token.empty() || token.compare(0, 2, "//") == 0)
 					break;
 
 				if (token[0] == '@') {
diff --git a/techlibs/ice40/ice40_opt.cc b/techlibs/ice40/ice40_opt.cc
index e492454fb..d5106b805 100644
--- a/techlibs/ice40/ice40_opt.cc
+++ b/techlibs/ice40/ice40_opt.cc
@@ -117,7 +117,7 @@ static void run_ice40_opts(Module *module)
 				log("Optimized $__ICE40_FULL_ADDER cell back to logic (without SB_CARRY) %s.%s: CO=%s\n",
 						log_id(module), log_id(cell), log_signal(replacement_output));
 				cell->type = "$lut";
-				cell->setPort("\\A", { RTLIL::S0, inbit[0], inbit[1], inbit[2] });
+				cell->setPort("\\A", { State::S0, inbit[0], inbit[1], inbit[2] });
 				cell->setPort("\\Y", cell->getPort("\\O"));
 				cell->unsetPort("\\B");
 				cell->unsetPort("\\CI");
diff --git a/techlibs/ice40/synth_ice40.cc b/techlibs/ice40/synth_ice40.cc
index 8f4a0f377..c6de81bd9 100644
--- a/techlibs/ice40/synth_ice40.cc
+++ b/techlibs/ice40/synth_ice40.cc
@@ -183,7 +183,7 @@ struct SynthIce40Pass : public ScriptPass
 				continue;
 			}
 			if (args[argidx] == "-dffe_min_ce_use" && argidx+1 < args.size()) {
-				min_ce_use = std::stoi(args[++argidx]);
+				min_ce_use = atoi(args[++argidx].c_str());
 				continue;
 			}
 			if (args[argidx] == "-nobram") {
diff --git a/techlibs/xilinx/synth_xilinx.cc b/techlibs/xilinx/synth_xilinx.cc
index b672a0d4f..d143c6823 100644
--- a/techlibs/xilinx/synth_xilinx.cc
+++ b/techlibs/xilinx/synth_xilinx.cc
@@ -195,7 +195,7 @@ struct SynthXilinxPass : public ScriptPass
 				continue;
 			}
 			if (args[argidx] == "-widemux" && argidx+1 < args.size()) {
-				widemux = std::stoi(args[++argidx]);
+				widemux = atoi(args[++argidx].c_str());
 				continue;
 			}
 			if (args[argidx] == "-abc9") {