diff --git a/src/analyses/goto_check.cpp b/src/analyses/goto_check.cpp
index 354d12503ec..75c039343b2 100644
--- a/src/analyses/goto_check.cpp
+++ b/src/analyses/goto_check.cpp
@@ -1689,21 +1689,21 @@ void goto_checkt::goto_check(
       {
         i_it->source_location.id(irep_idt());
 
-        if(it->source_location.get_file()!=irep_idt())
+        if(!it->source_location.get_file().empty())
           i_it->source_location.set_file(it->source_location.get_file());
 
-        if(it->source_location.get_line()!=irep_idt())
+        if(!it->source_location.get_line().empty())
           i_it->source_location.set_line(it->source_location.get_line());
 
-        if(it->source_location.get_function()!=irep_idt())
+        if(!it->source_location.get_function().empty())
           i_it->source_location.set_function(
             it->source_location.get_function());
 
-        if(it->source_location.get_column()!=irep_idt())
+        if(!it->source_location.get_column().empty())
           i_it->source_location.set_column(it->source_location.get_column());
       }
 
-      if(i_it->function==irep_idt())
+      if(i_it->function.empty())
         i_it->function=it->function;
     }
 
diff --git a/src/ansi-c/ansi_c_declaration.cpp b/src/ansi-c/ansi_c_declaration.cpp
index 75726b7471e..74915af0f42 100644
--- a/src/ansi-c/ansi_c_declaration.cpp
+++ b/src/ansi-c/ansi_c_declaration.cpp
@@ -33,7 +33,7 @@ void ansi_c_declaratort::build(irept &src)
       t.make_nil();
       break;
     }
-    else if(t.id()==irep_idt() ||
+    else if(t.id().empty() ||
             t.is_nil())
     {
       assert(0);
diff --git a/src/ansi-c/c_typecheck_base.cpp b/src/ansi-c/c_typecheck_base.cpp
index f508c952322..74a0f33f962 100644
--- a/src/ansi-c/c_typecheck_base.cpp
+++ b/src/ansi-c/c_typecheck_base.cpp
@@ -539,7 +539,7 @@ void c_typecheck_baset::typecheck_function_body(symbolt &symbol)
       p_it++)
   {
     // may be anonymous
-    if(p_it->get_base_name()==irep_idt())
+    if(p_it->get_base_name().empty())
     {
       irep_idt base_name="#anon"+std::to_string(anon_counter++);
       p_it->set_base_name(base_name);
diff --git a/src/ansi-c/c_typecheck_expr.cpp b/src/ansi-c/c_typecheck_expr.cpp
index 58806f5f6b1..185c576e401 100644
--- a/src/ansi-c/c_typecheck_expr.cpp
+++ b/src/ansi-c/c_typecheck_expr.cpp
@@ -1522,7 +1522,7 @@ void c_typecheck_baset::typecheck_expr_member(exprt &expr)
   // copy method identifier
   const irep_idt &identifier=component.get(ID_C_identifier);
 
-  if(identifier!=irep_idt())
+  if(!identifier.empty())
     expr.set(ID_C_identifier, identifier);
 
   const irep_idt &access=component.get_access();
diff --git a/src/ansi-c/c_typecheck_type.cpp b/src/ansi-c/c_typecheck_type.cpp
index 8a6ec9e154c..448df44cef4 100644
--- a/src/ansi-c/c_typecheck_type.cpp
+++ b/src/ansi-c/c_typecheck_type.cpp
@@ -428,7 +428,7 @@ void c_typecheck_baset::typecheck_code_type(code_typet &type)
         irep_idt identifier=declaration.declarator().get_name();
 
         // abstract or not?
-        if(identifier==irep_idt())
+        if(identifier.empty())
         {
           // abstract
           parameter.add_source_location()=declaration.type().source_location();
@@ -550,7 +550,7 @@ void c_typecheck_baset::typecheck_array_type(array_typet &type)
     {
       // not a constant and not infinity
 
-      assert(current_symbol_id!=irep_idt());
+      assert(!current_symbol_id.empty());
 
       const symbolt &base_symbol=lookup(current_symbol_id);
 
@@ -862,7 +862,7 @@ void c_typecheck_baset::typecheck_compound_body(
   // scan for anonymous members, and name them
   for(auto &member : components)
   {
-    if(member.get_name()!=irep_idt())
+    if(!member.get_name().empty())
       continue;
 
     member.set_name("$anon"+std::to_string(anon_member_counter++));
diff --git a/src/ansi-c/type2name.cpp b/src/ansi-c/type2name.cpp
index 6e3ce05b757..e9a564d35b2 100644
--- a/src/ansi-c/type2name.cpp
+++ b/src/ansi-c/type2name.cpp
@@ -110,7 +110,7 @@ static std::string type2name(
   if(!type.source_location().get_function().empty())
     result+='l';
 
-  if(type.id()==irep_idt())
+  if(type.id().empty())
     throw "empty type encountered";
   else if(type.id()==ID_empty)
     result+='V';
diff --git a/src/cpp/cpp_declarator.cpp b/src/cpp/cpp_declarator.cpp
index aa671c45a5f..cbf97d6a06e 100644
--- a/src/cpp/cpp_declarator.cpp
+++ b/src/cpp/cpp_declarator.cpp
@@ -49,7 +49,7 @@ typet cpp_declaratort::merge_type(const typet &declaration_type) const
     }
     else
     {
-      assert(t.id()!=irep_idt());
+      assert(!t.id().empty());
       p=&t.subtype();
     }
   }
diff --git a/src/cpp/cpp_exception_id.cpp b/src/cpp/cpp_exception_id.cpp
index d3a4b8f7081..18649696f53 100644
--- a/src/cpp/cpp_exception_id.cpp
+++ b/src/cpp/cpp_exception_id.cpp
@@ -59,7 +59,7 @@ void cpp_exception_list_rec(
     // grab C/C++ type
     irep_idt c_type=src.get(ID_C_c_type);
 
-    if(c_type!=irep_idt())
+    if(!c_type.empty())
     {
       dest.push_back(id2string(c_type)+suffix);
       return;
diff --git a/src/cpp/cpp_instantiate_template.cpp b/src/cpp/cpp_instantiate_template.cpp
index e4ee0403ed6..79e3de89b06 100644
--- a/src/cpp/cpp_instantiate_template.cpp
+++ b/src/cpp/cpp_instantiate_template.cpp
@@ -485,7 +485,7 @@ const symbolt &cpp_typecheckt::instantiate_template(
     bool is_static=new_decl.storage_spec().is_static();
     irep_idt access = new_decl.get(ID_C_access);
 
-    assert(access != irep_idt());
+    assert(!access.empty());
     assert(symb.type.id()==ID_struct);
 
     typecheck_compound_declarator(
diff --git a/src/cpp/cpp_type2name.cpp b/src/cpp/cpp_type2name.cpp
index 6a938a9a4f0..c92c32eb2a2 100644
--- a/src/cpp/cpp_type2name.cpp
+++ b/src/cpp/cpp_type2name.cpp
@@ -119,7 +119,7 @@ std::string cpp_type2name(const typet &type)
     // we try to use #c_type
     const irep_idt c_type=type.get(ID_C_c_type);
 
-    if(c_type!=irep_idt())
+    if(!c_type.empty())
       result+=id2string(c_type);
     else if(type.id()==ID_unsignedbv)
       result+="unsigned_int";
@@ -131,7 +131,7 @@ std::string cpp_type2name(const typet &type)
     // we try to use #c_type
     const irep_idt c_type=type.get(ID_C_c_type);
 
-    if(c_type!=irep_idt())
+    if(!c_type.empty())
       result+=id2string(c_type);
     else
       result+="double";
diff --git a/src/cpp/cpp_typecheck_bases.cpp b/src/cpp/cpp_typecheck_bases.cpp
index 7432b7a382b..9d8060301d5 100644
--- a/src/cpp/cpp_typecheck_bases.cpp
+++ b/src/cpp/cpp_typecheck_bases.cpp
@@ -71,7 +71,7 @@ void cpp_typecheckt::typecheck_compound_bases(struct_typet &type)
     bool virtual_base = base_it->get_bool(ID_virtual);
     irep_idt class_access = base_it->get(ID_protection);
 
-    if(class_access==irep_idt())
+    if(class_access.empty())
       class_access = default_class_access;
 
     base_symbol_expr.id(ID_base);
diff --git a/src/cpp/cpp_typecheck_compound_type.cpp b/src/cpp/cpp_typecheck_compound_type.cpp
index 0549197fc90..6e2cce31d74 100644
--- a/src/cpp/cpp_typecheck_compound_type.cpp
+++ b/src/cpp/cpp_typecheck_compound_type.cpp
@@ -602,7 +602,7 @@ void cpp_typecheckt::typecheck_compound_declarator(
         {
           irep_idt base_name=arg.get_base_name();
 
-          if(base_name==irep_idt())
+          if(base_name.empty())
             base_name="arg"+std::to_string(i++);
 
           symbolt arg_symb;
@@ -769,7 +769,7 @@ void cpp_typecheckt::put_compound_into_scope(
   const irep_idt &name=compound.get_name();
 
   // nothing to do if no base_name (e.g., an anonymous bitfield)
-  if(base_name==irep_idt())
+  if(base_name.empty())
     return;
 
   if(compound.type().id()==ID_code)
@@ -983,7 +983,7 @@ void cpp_typecheckt::typecheck_compound_body(symbolt &symbol)
         continue;
       }
 
-      if(declaration.type().id()==irep_idt()) // empty?
+      if(declaration.type().id().empty())
         continue;
 
       bool is_typedef=declaration.is_typedef();
@@ -1259,7 +1259,7 @@ void cpp_typecheckt::typecheck_member_function(
 
   if(component.get_bool(ID_is_static))
   {
-    if(method_qualifier.id()!=irep_idt())
+    if(!method_qualifier.id().empty())
     {
       error().source_location=component.source_location();
       error() << "method is static -- no qualifiers allowed" << eom;
diff --git a/src/cpp/cpp_typecheck_expr.cpp b/src/cpp/cpp_typecheck_expr.cpp
index fb2981ce188..979572c717e 100644
--- a/src/cpp/cpp_typecheck_expr.cpp
+++ b/src/cpp/cpp_typecheck_expr.cpp
@@ -571,7 +571,7 @@ bool cpp_typecheckt::operator_is_overloaded(exprt &expr)
   }
 
   for(const operator_entryt *e=operators;
-      e->id!=irep_idt();
+      !e->id.empty();
       e++)
     if(expr.id()==e->id)
     {
diff --git a/src/cpp/cpp_typecheck_type.cpp b/src/cpp/cpp_typecheck_type.cpp
index 24dc19c74dd..376efd6f9e1 100644
--- a/src/cpp/cpp_typecheck_type.cpp
+++ b/src/cpp/cpp_typecheck_type.cpp
@@ -20,7 +20,7 @@ Author: Daniel Kroening, kroening@cs.cmu.edu
 
 void cpp_typecheckt::typecheck_type(typet &type)
 {
-  assert(type.id()!=irep_idt());
+  assert(!type.id().empty());
   assert(type.is_not_nil());
 
   try
diff --git a/src/cpp/expr2cpp.cpp b/src/cpp/expr2cpp.cpp
index c5169aebf80..1ed9ff738c4 100644
--- a/src/cpp/expr2cpp.cpp
+++ b/src/cpp/expr2cpp.cpp
@@ -150,7 +150,7 @@ std::string expr2cppt::convert_rec(
   {
     return q+convert(src.subtype())+" &&"+d;
   }
-  else if(src.get(ID_C_c_type)!=irep_idt())
+  else if(!src.get(ID_C_c_type).empty())
   {
     const irep_idt c_type=src.get(ID_C_c_type);
 
@@ -208,7 +208,7 @@ std::string expr2cppt::convert_rec(
       else
         dest+="struct";
 
-      if(symbol.pretty_name!=irep_idt())
+      if(!symbol.pretty_name.empty())
         dest+=" "+id2string(symbol.pretty_name);
 
       dest+=d;
@@ -221,7 +221,7 @@ std::string expr2cppt::convert_rec(
 
       dest+="enum";
 
-      if(symbol.pretty_name!=irep_idt())
+      if(!symbol.pretty_name.empty())
         dest+=" "+id2string(symbol.pretty_name);
 
       dest+=d;
diff --git a/src/cpp/parse.cpp b/src/cpp/parse.cpp
index ff59d80ebf5..190e9e1e8ce 100644
--- a/src/cpp/parse.cpp
+++ b/src/cpp/parse.cpp
@@ -398,7 +398,7 @@ class Parser // NOLINT(readability/identifiers)
   {
     typet *p=&dest;
 
-    while(p->id()!=irep_idt() && p->is_not_nil())
+    while(!p->id().empty() && p->is_not_nil())
     {
       if(p->id()==ID_merged_type)
       {
@@ -2224,7 +2224,7 @@ bool Parser::optIntegralTypeOrClassSpec(typet &p)
     default: type_id=irep_idt();
     }
 
-    if(type_id!=irep_idt())
+    if(!type_id.empty())
     {
       cpp_tokent tk;
       typet kw;
@@ -3467,7 +3467,7 @@ bool Parser::rOperatorName(irept &name)
     return rCastOperatorName(name);
   }
 
-  assert(operator_id!=irep_idt());
+  assert(!operator_id.empty());
   lex.get_token(tk);
   name=irept(operator_id);
   set_location(name, tk);
diff --git a/src/goto-programs/goto_inline_class.cpp b/src/goto-programs/goto_inline_class.cpp
index 1e4dd8d99d5..592630f1443 100644
--- a/src/goto-programs/goto_inline_class.cpp
+++ b/src/goto-programs/goto_inline_class.cpp
@@ -57,7 +57,7 @@ void goto_inlinet::parameter_assignments(
 
     const irep_idt &identifier=parameter.get_identifier();
 
-    if(identifier==irep_idt())
+    if(identifier.empty())
     {
       error().source_location=source_location;
       error() << "no identifier for function parameter" << eom;
@@ -182,7 +182,7 @@ void goto_inlinet::parameter_destruction(
 
     const irep_idt &identifier=parameter.get_identifier();
 
-    if(identifier==irep_idt())
+    if(identifier.empty())
     {
       error().source_location=source_location;
       error() << "no identifier for function parameter" << eom;
@@ -328,13 +328,13 @@ void replace_location(
 
   dest=new_location;
 
-  if(comment!=irep_idt())
+  if(!comment.empty())
     dest.set_comment(comment);
 
-  if(property_class!=irep_idt())
+  if(!property_class.empty())
     dest.set_property_class(property_class);
 
-  if(property_id!=irep_idt())
+  if(!property_id.empty())
     dest.set_property_id(property_id);
 }
 
diff --git a/src/goto-symex/symex_builtin_functions.cpp b/src/goto-symex/symex_builtin_functions.cpp
index 44e7d532c42..a85d6e5b18d 100644
--- a/src/goto-symex/symex_builtin_functions.cpp
+++ b/src/goto-symex/symex_builtin_functions.cpp
@@ -221,7 +221,7 @@ void goto_symext::symex_gcc_builtin_va_arg_next(
 
   exprt rhs=zero_initializer(lhs.type(), code.source_location(), ns);
 
-  if(id!=irep_idt())
+  if(!id.empty())
   {
     // strip last name off id to get function name
     std::size_t pos=id2string(id).rfind("::");
diff --git a/src/goto-symex/symex_function_call.cpp b/src/goto-symex/symex_function_call.cpp
index 18813a9ec97..e50d1c8ea7f 100644
--- a/src/goto-symex/symex_function_call.cpp
+++ b/src/goto-symex/symex_function_call.cpp
@@ -62,7 +62,7 @@ void goto_symext::parameter_assignments(
 
     const irep_idt &identifier=parameter.get_identifier();
 
-    if(identifier==irep_idt())
+    if(identifier.empty())
       throw "no identifier for function parameter";
 
     const symbolt &symbol=ns.lookup(identifier);
diff --git a/src/java_bytecode/java_bytecode_convert_method.cpp b/src/java_bytecode/java_bytecode_convert_method.cpp
index 1aaeac39005..f9f75e45dbe 100644
--- a/src/java_bytecode/java_bytecode_convert_method.cpp
+++ b/src/java_bytecode/java_bytecode_convert_method.cpp
@@ -2309,7 +2309,7 @@ codet java_bytecode_convert_methodt::convert_instructions(
     if(v.is_parameter)
       continue;
     // Skip anonymous variables:
-    if(v.symbol_expr.get_identifier()==irep_idt())
+    if(v.symbol_expr.get_identifier().empty())
       continue;
     auto &block=get_block_for_pcrange(
       root,
diff --git a/src/java_bytecode/java_bytecode_language.cpp b/src/java_bytecode/java_bytecode_language.cpp
index 7fb765f1a4c..7ba75b1d8f4 100644
--- a/src/java_bytecode/java_bytecode_language.cpp
+++ b/src/java_bytecode/java_bytecode_language.cpp
@@ -203,9 +203,9 @@ static void get_virtual_method_targets(
   assert(called_function.id()==ID_virtual_function);
 
   const auto &call_class=called_function.get(ID_C_class);
-  assert(call_class!=irep_idt());
+  assert(!call_class.empty());
   const auto &call_basename=called_function.get(ID_component_name);
-  assert(call_basename!=irep_idt());
+  assert(!call_basename.empty());
 
   auto old_size=needed_methods.size();
 
@@ -218,7 +218,7 @@ static void get_virtual_method_targets(
         call_basename,
         child_class,
         symbol_table);
-    if(child_method!=irep_idt())
+    if(!child_method.empty())
       needed_methods.push_back(child_method);
   }
 
@@ -231,7 +231,7 @@ static void get_virtual_method_targets(
         call_basename,
         parent_class_id,
         symbol_table);
-    if(parent_method!=irep_idt())
+    if(!parent_method.empty())
     {
       needed_methods.push_back(parent_method);
       break;
diff --git a/src/java_bytecode/java_bytecode_parse_tree.cpp b/src/java_bytecode/java_bytecode_parse_tree.cpp
index 148e5a72212..6da1a7f1872 100644
--- a/src/java_bytecode/java_bytecode_parse_tree.cpp
+++ b/src/java_bytecode/java_bytecode_parse_tree.cpp
@@ -157,7 +157,7 @@ void java_bytecode_parse_treet::methodt::output(std::ostream &out) const
 
   for(const auto &i : instructions)
   {
-    if(i.source_location.get_line()!=irep_idt())
+    if(!i.source_location.get_line().empty())
       out << "    // " << i.source_location << '\n';
 
     out << "    " << i.address << ": ";
diff --git a/src/path-symex/build_goto_trace.cpp b/src/path-symex/build_goto_trace.cpp
index fed73f16457..eefb5361f5c 100644
--- a/src/path-symex/build_goto_trace.cpp
+++ b/src/path-symex/build_goto_trace.cpp
@@ -105,7 +105,7 @@ void build_goto_trace(
     const irep_idt &comment=
       instruction.source_location.get_comment();
 
-    if(comment!=irep_idt())
+    if(!comment.empty())
       trace_step.comment=id2string(comment);
     else
       trace_step.comment="assertion";
diff --git a/src/path-symex/path_symex.cpp b/src/path-symex/path_symex.cpp
index 356474cc294..3ae6b858b7f 100644
--- a/src/path-symex/path_symex.cpp
+++ b/src/path-symex/path_symex.cpp
@@ -699,7 +699,7 @@ void path_symext::function_call_rec(
         const code_typet::parametert &function_parameter=function_parameters[i];
         irep_idt identifier=function_parameter.get_identifier();
 
-        if(identifier==irep_idt())
+        if(identifier.empty())
           throw "function_call " + id2string(function_identifier)
               + " no identifier for function parameter";
 
diff --git a/src/path-symex/path_symex_state_read.cpp b/src/path-symex/path_symex_state_read.cpp
index 89783226300..4e60dd91ff7 100644
--- a/src/path-symex/path_symex_state_read.cpp
+++ b/src/path-symex/path_symex_state_read.cpp
@@ -407,7 +407,7 @@ exprt path_symex_statet::read_symbol_member_index(
   else
   {
     // we do some SSA symbol
-    if(var_state.ssa_symbol.get_identifier()==irep_idt())
+    if(var_state.ssa_symbol.get_identifier().empty())
     {
       // produce one
       var_state.ssa_symbol=var_info.ssa_symbol();
diff --git a/src/path-symex/var_map.cpp b/src/path-symex/var_map.cpp
index 83193f4abc5..97563e31240 100644
--- a/src/path-symex/var_map.cpp
+++ b/src/path-symex/var_map.cpp
@@ -22,7 +22,7 @@ var_mapt::var_infot &var_mapt::operator()(
   const irep_idt &suffix,
   const typet &type)
 {
-  assert(symbol!=irep_idt());
+  assert(!symbol.empty());
 
   std::string full_identifier=
     id2string(symbol)+id2string(suffix);
diff --git a/src/pointer-analysis/add_failed_symbols.cpp b/src/pointer-analysis/add_failed_symbols.cpp
index ef8688285e7..5def51a4499 100644
--- a/src/pointer-analysis/add_failed_symbols.cpp
+++ b/src/pointer-analysis/add_failed_symbols.cpp
@@ -76,7 +76,7 @@ exprt get_failed_symbol(
   const symbolt &symbol=ns.lookup(expr);
   irep_idt failed_symbol_id=symbol.type.get(ID_C_failed_symbol);
 
-  if(failed_symbol_id==irep_idt())
+  if(failed_symbol_id.empty())
     return nil_exprt();
 
   const symbolt &failed_symbol=ns.lookup(failed_symbol_id);
diff --git a/src/pointer-analysis/goto_program_dereference.cpp b/src/pointer-analysis/goto_program_dereference.cpp
index 5665816cf67..44340aa0fc4 100644
--- a/src/pointer-analysis/goto_program_dereference.cpp
+++ b/src/pointer-analysis/goto_program_dereference.cpp
@@ -32,7 +32,7 @@ bool goto_program_dereferencet::has_failed_symbol(
     const irep_idt &failed_symbol=
       ptr_symbol.type.get("#failed_symbol");
 
-    if(failed_symbol==irep_idt())
+    if(failed_symbol.empty())
       return false;
 
     return !ns.lookup(failed_symbol, symbol);
diff --git a/src/pointer-analysis/value_set_analysis.cpp b/src/pointer-analysis/value_set_analysis.cpp
index d1367f4e061..549fd53a348 100644
--- a/src/pointer-analysis/value_set_analysis.cpp
+++ b/src/pointer-analysis/value_set_analysis.cpp
@@ -44,7 +44,7 @@ void value_set_analysist::convert(
     if(location==previous_location)
       continue;
 
-    if(location.is_nil() || location.get_file()==irep_idt())
+    if(location.is_nil() || location.get_file().empty())
       continue;
 
     // find value set
diff --git a/src/util/find_symbols.cpp b/src/util/find_symbols.cpp
index 15501ae239a..32e10d33627 100644
--- a/src/util/find_symbols.cpp
+++ b/src/util/find_symbols.cpp
@@ -153,7 +153,7 @@ void find_symbols(kindt kind, const typet &src, find_symbols_sett &dest)
       find_symbols(kind, *it, dest);
 
       // irep_idt identifier=it->get_identifier();
-      // if(identifier!=irep_idt() && (kind==F_TYPE || kind==F_BOTH))
+      // if(!identifier.empty() && (kind==F_TYPE || kind==F_BOTH))
       //  dest.insert(identifier);
     }
   }
diff --git a/src/util/simplify_expr.cpp b/src/util/simplify_expr.cpp
index d8d62fee483..23d814b75a9 100644
--- a/src/util/simplify_expr.cpp
+++ b/src/util/simplify_expr.cpp
@@ -2322,7 +2322,7 @@ bool simplify_exprt::simplify_rec(exprt &expr)
   {
     const exprt &new_expr=cache_result.first->second;
 
-    if(new_expr.id()==irep_idt())
+    if(new_expr.id().empty())
       return true; // no change
 
     expr=new_expr;
diff --git a/src/util/simplify_utils.cpp b/src/util/simplify_utils.cpp
index d5583226f71..482d6ba4fee 100644
--- a/src/util/simplify_utils.cpp
+++ b/src/util/simplify_utils.cpp
@@ -99,7 +99,7 @@ static bool sort_and_join(
   const struct saj_tablet &saj_entry,
   const irep_idt &type_id)
 {
-  for(unsigned i=0; saj_entry.type_ids[i]!=irep_idt(); i++)
+  for(unsigned i=0; !saj_entry.type_ids[i].empty(); i++)
     if(type_id==saj_entry.type_ids[i])
       return true;
 
@@ -112,7 +112,7 @@ static const struct saj_tablet &sort_and_join(
 {
   unsigned i=0;
 
-  for( ; saj_table[i].id!=irep_idt(); i++)
+  for( ; !saj_table[i].id.empty(); i++)
     if(id==saj_table[i].id &&
        sort_and_join(saj_table[i], type_id))
       return saj_table[i];
@@ -129,7 +129,7 @@ bool sort_and_join(exprt &expr)
 
   const struct saj_tablet &saj_entry=
     sort_and_join(expr.id(), expr.type().id());
-  if(saj_entry.id==irep_idt())
+  if(saj_entry.id.empty())
     return true;
 
   // check operand types
diff --git a/src/util/std_types.cpp b/src/util/std_types.cpp
index 6da91652bc1..b06af1ecf77 100644
--- a/src/util/std_types.cpp
+++ b/src/util/std_types.cpp
@@ -15,14 +15,14 @@ Author: Daniel Kroening, kroening@kroening.com
 std::size_t fixedbv_typet::get_integer_bits() const
 {
   const irep_idt integer_bits=get(ID_integer_bits);
-  assert(integer_bits!=irep_idt());
+  assert(!integer_bits.empty());
   return unsafe_string2unsigned(id2string(integer_bits));
 }
 
 std::size_t floatbv_typet::get_f() const
 {
   const irep_idt &f=get(ID_f);
-  assert(f!=irep_idt());
+  assert(!f.empty());
   return unsafe_string2unsigned(id2string(f));
 }