diff --git a/src/Func.cc b/src/Func.cc
index 6a85623ad5..7464f76ece 100644
--- a/src/Func.cc
+++ b/src/Func.cc
@@ -322,7 +322,7 @@ ScriptFunc::ScriptFunc(std::string _name, FuncTypePtr ft,
 	auto n = bs.size();
 	ASSERT(n == priorities.size());
 
-	for ( auto i = 0; i < n; ++i )
+	for ( auto i = 0u; i < n; ++i )
 		{
 		Body b;
 		b.stmts = std::move(bs[i]);
diff --git a/src/script_opt/CPP/Attrs.cc b/src/script_opt/CPP/Attrs.cc
index 5412daf813..e6361f2df3 100644
--- a/src/script_opt/CPP/Attrs.cc
+++ b/src/script_opt/CPP/Attrs.cc
@@ -86,9 +86,8 @@ void CPPCompile::GenAttrs(const AttributesPtr& attrs)
 
 	AddInit(attrs);
 
-	for ( auto i = 0; i < avec.size(); ++i )
+	for ( const auto& attr : avec )
 		{
-		const auto& attr = avec[i];
 		const auto& e = attr->GetExpr();
 
 		if ( ! e )
@@ -171,7 +170,7 @@ const char* CPPCompile::AttrName(const AttrPtr& attr)
 	case ATTR_IS_ASSIGNED:	return "ATTR_IS_ASSIGNED";
 	case ATTR_IS_USED:	return "ATTR_IS_USED";
 
-	case NUM_ATTRS:	return "<busted>";
+	default:	return "<busted>";
 	}
 	}
 
diff --git a/src/script_opt/CPP/CPP-load.bif b/src/script_opt/CPP/CPP-load.bif
index eafdcf232b..8260dfd012 100644
--- a/src/script_opt/CPP/CPP-load.bif
+++ b/src/script_opt/CPP/CPP-load.bif
@@ -4,6 +4,8 @@
 
 %%{ // C segment
 
+#include <cinttypes>
+#
 #include "zeek/Reporter.h"
 #include "zeek/script_opt/ScriptOpt.h"
 #include "zeek/script_opt/CPP/Func.h"
@@ -22,7 +24,7 @@ function load_CPP%(h: count%): bool
 
 	if ( cb == detail::standalone_callbacks.end() )
 		{
-		reporter->Error("load of non-existing C++ code (%llu)", h);
+		reporter->Error("load of non-existing C++ code (%" PRIu64 ")", h);
 		return zeek::val_mgr->False();
 		}
 
diff --git a/src/script_opt/CPP/Consts.cc b/src/script_opt/CPP/Consts.cc
index 1a1ab29528..e6af4c4c84 100644
--- a/src/script_opt/CPP/Consts.cc
+++ b/src/script_opt/CPP/Consts.cc
@@ -233,14 +233,14 @@ void CPPCompile::AddRecordConstant(const ValPtr& v, string& const_name)
 	auto r = cast_intrusive<RecordVal>(v);
 	auto n = r->NumFields();
 
-	for ( auto i = 0; i < n; ++i )
+	for ( auto i = 0u; i < n; ++i )
 		{
 		const auto& r_i = r->GetField(i);
 
 		if ( r_i )
 			{
 			auto r_i_c = BuildConstant(v, r_i);
-			AddInit(v, const_name + "->Assign(" + Fmt(i) +
+			AddInit(v, const_name + "->Assign(" + Fmt(static_cast<int>(i)) +
 			        ", " + r_i_c + ");");
 			}
 		}
@@ -282,7 +282,7 @@ void CPPCompile::AddVectorConstant(const ValPtr& v, string& const_name)
 	auto vv = cast_intrusive<VectorVal>(v);
 	auto n = vv->Size();
 
-	for ( auto i = 0; i < n; ++i )
+	for ( auto i = 0u; i < n; ++i )
 		{
 		const auto& v_i = vv->ValAt(i);
 		auto v_i_c = BuildConstant(v, v_i);
diff --git a/src/script_opt/CPP/DeclFunc.cc b/src/script_opt/CPP/DeclFunc.cc
index 0189b81ac7..02674029ca 100644
--- a/src/script_opt/CPP/DeclFunc.cc
+++ b/src/script_opt/CPP/DeclFunc.cc
@@ -19,7 +19,7 @@ void CPPCompile::DeclareFunc(const FuncInfo& func)
 	auto fname = Canonicalize(BodyName(func).c_str()) + "_zf";
 	auto pf = func.Profile();
 	auto f = func.Func();
-	auto body = func.Body();
+	const auto& body = func.Body();
 	auto priority = func.Priority();
 
 	DeclareSubclass(f->GetType(), pf, fname, body, priority, nullptr,
@@ -133,7 +133,7 @@ void CPPCompile::DeclareSubclass(const FuncTypePtr& ft, const ProfileFunc* pf,
 	body_hashes[fname] = h;
 	body_priorities[fname] = priority;
 	body_names.emplace(body.get(), fname);
-	names_to_bodies.emplace(move(fname), body.get());
+	names_to_bodies.emplace(fname, body.get());
 
 	total_hash = merge_p_hashes(total_hash, h);
 	}
diff --git a/src/script_opt/CPP/Driver.cc b/src/script_opt/CPP/Driver.cc
index 0af00b7063..92a8e21cd6 100644
--- a/src/script_opt/CPP/Driver.cc
+++ b/src/script_opt/CPP/Driver.cc
@@ -63,7 +63,9 @@ void CPPCompile::Compile()
 	// as a way to identify this compilation.  Only germane when doing
 	// incremental compilation (particularly of the test suite).
 	char buf[8192];
-	getcwd(buf, sizeof buf);
+	if ( ! getcwd(buf, sizeof buf) )
+		reporter->FatalError("getcwd failed: %s", strerror(errno));
+
 	working_dir = buf;
 
 	if ( update && addl_tag > 0 && CheckForCollisions() )
@@ -212,7 +214,7 @@ void CPPCompile::RegisterCompiledBody(const string& f)
 	// Build up an initializer of the events relevant to the function.
 	string events;
 	if ( body_events.count(f) > 0 )
-		for ( auto e : body_events[f] )
+		for ( const auto& e : body_events[f] )
 			{
 			if ( events.size() > 0 )
 				events += ", ";
diff --git a/src/script_opt/CPP/Exprs.cc b/src/script_opt/CPP/Exprs.cc
index 9fd36da203..b21d12b77d 100644
--- a/src/script_opt/CPP/Exprs.cc
+++ b/src/script_opt/CPP/Exprs.cc
@@ -638,7 +638,7 @@ string CPPCompile::GenSetConstructorExpr(const Expr* e)
 	{
 	auto sc = static_cast<const SetConstructorExpr*>(e);
 	const auto& t = sc->GetType();
-	auto attrs = sc->GetAttrs();
+	const auto& attrs = sc->GetAttrs();
 
 	string attr_tags;
 	string attr_vals;
@@ -654,7 +654,7 @@ string CPPCompile::GenTableConstructorExpr(const Expr* e)
 	{
 	auto tc = static_cast<const TableConstructorExpr*>(e);
 	const auto& t = tc->GetType();
-	auto attrs = tc->GetAttrs();
+	const auto& attrs = tc->GetAttrs();
 
 	string attr_tags;
 	string attr_vals;
@@ -1126,7 +1126,7 @@ string CPPCompile::GenIntVector(const vector<int>& vec)
 	{
 	string res("{ ");
 
-	for ( auto i = 0; i < vec.size(); ++i )
+	for ( auto i = 0u; i < vec.size(); ++i )
 		{
 		res += Fmt(vec[i]);
 
diff --git a/src/script_opt/CPP/Func.cc b/src/script_opt/CPP/Func.cc
index 7267d83e3d..9c7c8c7a36 100644
--- a/src/script_opt/CPP/Func.cc
+++ b/src/script_opt/CPP/Func.cc
@@ -36,9 +36,8 @@ broker::expected<broker::data> CPPLambdaFunc::SerializeClosure() const
 
 	broker::vector body;
 
-	for ( int i = 0; i < vals.size(); ++i )
+	for ( const auto& val : vals )
 		{
-		const auto& val = vals[i];
 		auto expected = Broker::detail::val_to_data(val.get());
 		if ( ! expected )
 			return broker::ec::invalid_data;
diff --git a/src/script_opt/CPP/GenFunc.cc b/src/script_opt/CPP/GenFunc.cc
index 38e3a04e71..4889c81f1c 100644
--- a/src/script_opt/CPP/GenFunc.cc
+++ b/src/script_opt/CPP/GenFunc.cc
@@ -19,7 +19,7 @@ void CPPCompile::CompileFunc(const FuncInfo& func)
 	auto fname = Canonicalize(BodyName(func).c_str()) + "_zf";
 	auto pf = func.Profile();
 	auto f = func.Func();
-	auto body = func.Body();
+	const auto& body = func.Body();
 
 	DefineBody(f->GetType(), pf, fname, body, nullptr, f->Flavor());
 	}
@@ -223,7 +223,7 @@ string CPPCompile::BodyName(const FuncInfo& func)
 
 	// Make the name distinct-per-body.
 
-	int i;
+	size_t i;
 	for ( i = 0; i < bodies.size(); ++i )
 		if ( bodies[i].stmts == body )
 			break;
@@ -231,7 +231,7 @@ string CPPCompile::BodyName(const FuncInfo& func)
 	if ( i >= bodies.size() )
 		reporter->InternalError("can't find body in CPPCompile::BodyName");
 
-	return fname + "__" + Fmt(i);
+	return fname + "__" + Fmt(static_cast<int>(i));
 	}
 
 string CPPCompile::GenArgs(const RecordTypePtr& params, const Expr* e)
@@ -258,7 +258,7 @@ string CPPCompile::GenArgs(const RecordTypePtr& params, const Expr* e)
 		if ( ! param_any && arg_any )
 			expr_gen = GenericValPtrToGT(expr_gen, param_t, GEN_NATIVE);
 
-		gen = gen + expr_gen;
+		gen += expr_gen;
 		if ( i < n - 1 )
 			gen += ", ";
 		}
diff --git a/src/script_opt/CPP/Inits.cc b/src/script_opt/CPP/Inits.cc
index 0335d86f43..40f7e9da4e 100644
--- a/src/script_opt/CPP/Inits.cc
+++ b/src/script_opt/CPP/Inits.cc
@@ -161,7 +161,7 @@ void CPPCompile::GenFuncVarInits()
 
 		string hashes = "{";
 
-		for ( auto b : bodies )
+		for ( const auto& b : bodies )
 			{
 			auto body = b.stmts.get();
 
diff --git a/src/script_opt/CPP/RuntimeOps.cc b/src/script_opt/CPP/RuntimeOps.cc
index 76b3317cb6..2e21f7dfdf 100644
--- a/src/script_opt/CPP/RuntimeOps.cc
+++ b/src/script_opt/CPP/RuntimeOps.cc
@@ -31,7 +31,7 @@ ListValPtr index_val__CPP(vector<ValPtr> indices)
 
 	// In the future, we could provide N versions of this that
 	// unroll the loop.
-	for ( auto i : indices )
+	for ( const auto& i : indices )
 		ind_v->Append(i);
 
 	return ind_v;
@@ -61,7 +61,7 @@ ValPtr index_string__CPP(const StringValPtr& svp, vector<ValPtr> indices)
 
 ValPtr set_event__CPP(IDPtr g, ValPtr v, EventHandlerPtr& gh)
 	{
-	g->SetVal(move(v));
+	g->SetVal(v);
 	gh = event_registry->Register(g->Name());
 	return v;
 	}
@@ -116,15 +116,15 @@ ValPtr assign_to_index__CPP(T v1, ValPtr v2, ValPtr v3)
 
 ValPtr assign_to_index__CPP(TableValPtr v1, ValPtr v2, ValPtr v3)
 	{
-	return assign_to_index__CPP<TableValPtr>(v1, v2, v3);
+	return assign_to_index__CPP<TableValPtr>(std::move(v1), std::move(v2), std::move(v3));
 	}
 ValPtr assign_to_index__CPP(VectorValPtr v1, ValPtr v2, ValPtr v3)
 	{
-	return assign_to_index__CPP<VectorValPtr>(v1, v2, v3);
+	return assign_to_index__CPP<VectorValPtr>(std::move(v1), std::move(v2), std::move(v3));
 	}
 ValPtr assign_to_index__CPP(StringValPtr v1, ValPtr v2, ValPtr v3)
 	{
-	return assign_to_index__CPP<StringValPtr>(v1, v2, v3);
+	return assign_to_index__CPP<StringValPtr>(std::move(v1), std::move(v2), std::move(v3));
 	}
 
 void add_element__CPP(TableValPtr aggr, ListValPtr indices)
@@ -172,7 +172,7 @@ TableValPtr set_constructor__CPP(vector<ValPtr> elements, TableTypePtr t,
 	auto attrs = build_attrs__CPP(move(attr_tags), move(attr_vals));
 	auto aggr = make_intrusive<TableVal>(move(t), move(attrs));
 
-	for ( const auto& elem : elements )
+	for ( auto& elem : elements )
 		aggr->Assign(move(elem), nullptr);
 
 	return aggr;
@@ -188,7 +188,7 @@ TableValPtr table_constructor__CPP(vector<ValPtr> indices, vector<ValPtr> vals,
 	auto attrs = build_attrs__CPP(move(attr_tags), move(attr_vals));
 	auto aggr = make_intrusive<TableVal>(move(t), move(attrs));
 
-	for ( auto i = 0; i < n; ++i )
+	for ( auto i = 0u; i < n; ++i )
 		{
 		auto v = check_and_promote(vals[i], yt, true);
 		if ( v )
@@ -205,7 +205,7 @@ RecordValPtr record_constructor__CPP(vector<ValPtr> vals, RecordTypePtr t)
 
 	rv->Reserve(n);
 
-	for ( auto i = 0; i < n; ++i )
+	for ( auto i = 0u; i < n; ++i )
 		rv->Assign(i, vals[i]);
 
 	return rv;
@@ -216,7 +216,7 @@ VectorValPtr vector_constructor__CPP(vector<ValPtr> vals, VectorTypePtr t)
 	auto vv = make_intrusive<VectorVal>(move(t));
 	auto n = vals.size();
 
-	for ( auto i = 0; i < n; ++i )
+	for ( auto i = 0u; i < n; ++i )
 		vv->Assign(i, vals[i]);
 
 	return vv;
diff --git a/src/script_opt/CPP/Types.cc b/src/script_opt/CPP/Types.cc
index 369bb0414a..68fdf48d11 100644
--- a/src/script_opt/CPP/Types.cc
+++ b/src/script_opt/CPP/Types.cc
@@ -140,10 +140,10 @@ void CPPCompile::ExpandTypeVar(const TypePtr& t)
 
 void CPPCompile::ExpandListTypeVar(const TypePtr& t, string& tn)
 	{
-	auto tl = t->AsTypeList()->GetTypes();
+	const auto& tl = t->AsTypeList()->GetTypes();
 	auto t_name = tn + "->AsTypeList()";
 
-	for ( auto i = 0; i < tl.size(); ++i )
+	for ( auto i = 0u; i < tl.size(); ++i )
 		AddInit(t, t_name + "->Append(" +
 			GenTypeName(tl[i]) + ");");
 	}
@@ -208,7 +208,7 @@ void CPPCompile::ExpandFuncTypeVar(const TypePtr& t, string& tn)
 	auto f = t->AsFuncType();
 
 	auto args_type_accessor = GenTypeName(f->Params());
-	auto yt = f->Yield();
+	const auto& yt = f->Yield();
 
 	string yield_type_accessor;
 
@@ -447,9 +447,9 @@ void CPPCompile::RegisterType(const TypePtr& tp)
 
 void CPPCompile::RegisterListType(const TypePtr& t)
 	{
-	auto tl = t->AsTypeList()->GetTypes();
+	const auto& tl = t->AsTypeList()->GetTypes();
 
-	for ( auto i = 0; i < tl.size(); ++i )
+	for ( auto i = 0u; i < tl.size(); ++i )
 		{
 		NoteNonRecordInitDependency(t, tl[i]);
 		RegisterType(tl[i]);
diff --git a/src/script_opt/CPP/Vars.cc b/src/script_opt/CPP/Vars.cc
index d1d753a39c..0cf5e668c5 100644
--- a/src/script_opt/CPP/Vars.cc
+++ b/src/script_opt/CPP/Vars.cc
@@ -241,7 +241,7 @@ string CPPCompile::Canonicalize(const char* name) const
 		if ( c == ':' || c == '-' )
 			c = '_';
 
-		cname = cname + c;
+		cname += c;
 		}
 
 	// Add a trailing '_' to avoid conflicts with C++ keywords.
diff --git a/src/script_opt/ProfileFunc.cc b/src/script_opt/ProfileFunc.cc
index 555cb0e62d..aad6cc3004 100644
--- a/src/script_opt/ProfileFunc.cc
+++ b/src/script_opt/ProfileFunc.cc
@@ -483,7 +483,7 @@ void ProfileFuncs::MergeInProfile(ProfileFunc* pf)
 			(void) HashType(t->AsTypeType()->GetType());
 
 		auto& init_exprs = g->GetInitExprs();
-		for ( auto i_e : init_exprs )
+		for ( const auto& i_e : init_exprs )
 			if ( i_e )
 				{
 				pending_exprs.push_back(i_e.get());
@@ -550,7 +550,7 @@ void ProfileFuncs::TraverseValue(const ValPtr& v)
 		auto r = cast_intrusive<RecordVal>(v);
 		auto n = r->NumFields();
 
-		for ( auto i = 0; i < n; ++i )
+		for ( auto i = 0u; i < n; ++i )
 			TraverseValue(r->GetField(i));
 		}
 		break;
@@ -583,7 +583,7 @@ void ProfileFuncs::TraverseValue(const ValPtr& v)
 		auto vv = cast_intrusive<VectorVal>(v);
 		auto n = vv->Size();
 
-		for ( auto i = 0; i < n; ++i )
+		for ( auto i = 0u; i < n; ++i )
 			TraverseValue(vv->ValAt(i));
 		}
 		break;
diff --git a/src/script_opt/ScriptOpt.cc b/src/script_opt/ScriptOpt.cc
index 3a8ec83df9..ff20df0800 100644
--- a/src/script_opt/ScriptOpt.cc
+++ b/src/script_opt/ScriptOpt.cc
@@ -334,7 +334,7 @@ void analyze_scripts()
 
 		printf("\nAdditional C++ script bodies available:\n");
 		int addl = 0;
-		for ( auto s : compiled_scripts )
+		for ( const auto& s : compiled_scripts )
 			if ( already_reported.count(s.first) == 0 )
 				{
 				printf("%s body (hash %llu)\n",