substr() -> compare()

31 files changed, 127 insertions, 127 deletions

diff --git a/backends/firrtl/firrtl.cc b/backends/firrtl/firrtl.cc
index 5be6d60fd..73b1e7d53 100644
--- a/backends/firrtl/firrtl.cc
+++ b/backends/firrtl/firrtl.cc
@@ -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.
diff --git a/backends/intersynth/intersynth.cc b/backends/intersynth/intersynth.cc
index 98746809c..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);
 		}
 
diff --git a/backends/smt2/smt2.cc b/backends/smt2/smt2.cc
index db849882e..081dcda99 100644
--- a/backends/smt2/smt2.cc
+++ b/backends/smt2/smt2.cc
@@ -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 6065a71ff..7b1db4776 100644
--- a/backends/verilog/verilog_backend.cc
+++ b/backends/verilog/verilog_backend.cc
@@ -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];
 
diff --git a/frontends/ast/ast.cc b/frontends/ast/ast.cc
index e707f435a..07ef0a86e 100644
--- a/frontends/ast/ast.cc
+++ b/frontends/ast/ast.cc
@@ -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 467b2e5c0..54b9efaad 100644
--- a/frontends/ast/simplify.cc
+++ b/frontends/ast/simplify.cc
@@ -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 06d58a44a..594da45eb 100644
--- a/frontends/verific/verific.cc
+++ b/frontends/verific/verific.cc
@@ -2140,7 +2140,7 @@ 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))
@@ -2283,7 +2283,7 @@ 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/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/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/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/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_merge.cc b/passes/opt/opt_merge.cc
index 8964171e6..cac7c0a6f 100644
--- a/passes/opt/opt_merge.cc
+++ b/passes/opt/opt_merge.cc
@@ -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_rmdff.cc b/passes/opt/opt_rmdff.cc
index 450626f4a..8d42a37c3 100644
--- a/passes/opt/opt_rmdff.cc
+++ b/passes/opt/opt_rmdff.cc
@@ -278,7 +278,7 @@ bool handle_dff(RTLIL::Module *mod, RTLIL::Cell *dff)
 		sig_c = dff->getPort("\\C");
 		val_cp = RTLIL::Const(dff->type == "$_DFF_P_", 1);
 	}
-	else if (dff->type.begins_with("$_DFF_") && dff->type.substr(9) == "_" &&
+	else if (dff->type.begins_with("$_DFF_") && dff->type.compare(9, 1, "_") == 0 &&
 			(dff->type[6] == 'N' || dff->type[6] == 'P') &&
 			(dff->type[7] == 'N' || dff->type[7] == 'P') &&
 			(dff->type[8] == '0' || dff->type[8] == '1')) {
@@ -290,7 +290,7 @@ bool handle_dff(RTLIL::Module *mod, RTLIL::Cell *dff)
 		val_rp = RTLIL::Const(dff->type[7] == 'P', 1);
 		val_rv = RTLIL::Const(dff->type[8] == '1', 1);
 	}
-	else if (dff->type.begins_with("$_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");
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 e1da1a9e6..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++]);
@@ -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 7cb784505..9db8aafa7 100644
--- a/passes/techmap/abc.cc
+++ b/passes/techmap/abc.cc
@@ -333,12 +333,12 @@ 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)))
@@ -1562,10 +1562,10 @@ struct AbcPass : public Pass {
 				size_t pos = arg.find_first_of(':');
 				int lut_mode = 0, lut_mode2 = 0;
 				if (pos != string::npos) {
-					lut_mode = std::atoi(arg.substr(0, pos).c_str());
-					lut_mode2 = std::atoi(arg.substr(pos+1).c_str());
+					lut_mode = atoi(arg.substr(0, pos).c_str());
+					lut_mode2 = atoi(arg.substr(pos+1).c_str());
 				} else {
-					lut_mode = std::atoi(arg.c_str());
+					lut_mode = atoi(arg.c_str());
 					lut_mode2 = lut_mode;
 				}
 				lut_costs.clear();
diff --git a/passes/techmap/dff2dffe.cc b/passes/techmap/dff2dffe.cc
index 2dc577c73..c0bf3a665 100644
--- a/passes/techmap/dff2dffe.cc
+++ b/passes/techmap/dff2dffe.cc
@@ -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/muxcover.cc b/passes/techmap/muxcover.cc
index 45987392e..81546249c 100644
--- a/passes/techmap/muxcover.cc
+++ b/passes/techmap/muxcover.cc
@@ -675,11 +675,11 @@ 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=") {
+			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;
@@ -687,7 +687,7 @@ struct MuxcoverPass : public Pass {
 				}
 				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;
@@ -695,7 +695,7 @@ struct MuxcoverPass : public Pass {
 				}
 				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;
@@ -703,7 +703,7 @@ struct MuxcoverPass : public Pass {
 				}
 				continue;
 			}
-			if (arg.size() >= 6 && arg.substr(0,6) == "-dmux=") {
+			if (arg.size() >= 6 && arg.compare(0,6,"-dmux=") == 0) {
 				cost_dmux = atoi(arg.substr(6).c_str());
 				continue;
 			}
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 cea247dc7..319669955 100644
--- a/passes/tests/test_cell.cc
+++ b/passes/tests/test_cell.cc
@@ -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/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] == '@') {