Merge pull request #6055 from tautschnig/short-lived

Avoid short-lived heap-allocated objects

Author: kroening

src/goto-symex/field_sensitivity.cpp

@@ -170,11 +170,10 @@ exprt field_sensitivityt::get_fields(
 
     for(const auto &comp : components)
     {
-      const member_exprt member(struct_op, comp.get_name(), comp.type());
       ssa_exprt tmp = ssa_expr;
       bool was_l2 = !tmp.get_level_2().empty();
       tmp.remove_level_2();
-      tmp.set_expression(member);
+      tmp.set_expression(member_exprt{struct_op, comp.get_name(), comp.type()});
       if(was_l2)
       {
         fields.push_back(state.rename(get_fields(ns, state, tmp), ns).get());

src/solvers/flattening/boolbv.cpp

@@ -100,12 +100,7 @@ bvt boolbvt::conversion_failed(const exprt &expr)
 bvt boolbvt::convert_bitvector(const exprt &expr)
 {
   if(expr.type().id()==ID_bool)
-  {
-    bvt bv;
-    bv.resize(1);
-    bv[0]=convert(expr);
-    return bv;
-  }
+    return {convert(expr)};
 
   if(expr.id()==ID_index)
     return convert_index(to_index_expr(expr));

src/solvers/sat/cnf.cpp

@@ -412,14 +412,10 @@ bvt cnft::new_variables(std::size_t width)
 /// \return set of literals, duplicates removed
 bvt cnft::eliminate_duplicates(const bvt &bv)
 {
-  std::set<literalt> s;
-
-  bvt dest;
-  dest.reserve(bv.size());
-
-  for(const auto &l : bv)
-    if(s.insert(l).second)
-      dest.push_back(l);
+  bvt dest = bv;
+  std::sort(dest.begin(), dest.end());
+  auto last = std::unique(dest.begin(), dest.end());
+  dest.erase(last, dest.end());
 
   return dest;
 }

src/util/pointer_expr.cpp

@@ -122,9 +122,9 @@ address_of_exprt::address_of_exprt(const exprt &_op)
 {
 }
 
-const exprt &object_descriptor_exprt::root_object() const
+const exprt &object_descriptor_exprt::root_object(const exprt &expr)
 {
-  const exprt *p = &object();
+  const exprt *p = &expr;
 
   while(true)
   {

src/util/pointer_expr.h

@@ -180,7 +180,11 @@ class object_descriptor_exprt : public binary_exprt
     return op0();
   }
 
-  const exprt &root_object() const;
+  static const exprt &root_object(const exprt &expr);
+  const exprt &root_object() const
+  {
+    return root_object(object());
+  }
 
   exprt &offset()
   {

src/util/sharing_node.h

@@ -346,8 +346,13 @@ SN_TYPE_PAR_DEF class sharing_nodet
     const to_mapt &m = get_to_map();
     typename to_mapt::const_iterator it = m.find(n);
 
+#if SN_SMALL_MAP == 1
+    if(it != m.end())
+      return &it.get_value();
+#else
     if(it != m.end())
       return &it->second;
+#endif
 
     return nullptr;
   }

src/util/small_map.h

@@ -265,6 +265,15 @@ class small_mapt
       return std::make_shared<valuet>(idx, *(m.p + ii));
     }
 
+    /// Non-standard direct access to the underlying value instead of creating a
+    /// \c valuet object. Avoids creating a very short-lived \c valuet object
+    /// when only the value is needed.
+    /// \return Reference to value stored in the map.
+    const T &get_value() const
+    {
+      return *(m.p + ii);
+    }
+
     const_iterator operator++()
     {
       idx++;

src/util/ssa_expr.cpp

@@ -134,10 +134,10 @@ static void update_identifier(ssa_exprt &ssa)
   ssa.set(ID_L1_object_identifier, idpair.second);
 }
 
-void ssa_exprt::set_expression(const exprt &expr)
+void ssa_exprt::set_expression(exprt expr)
 {
-  type() = expr.type();
-  add(ID_expression, expr);
+  type() = as_const(expr).type();
+  add(ID_expression, std::move(expr));
   ::update_identifier(*this);
 }
 
@@ -148,8 +148,8 @@ irep_idt ssa_exprt::get_object_name() const
   if(original_expr.id() == ID_symbol)
     return to_symbol_expr(original_expr).get_identifier();
 
-  object_descriptor_exprt ode(original_expr);
-  return to_symbol_expr(ode.root_object()).get_identifier();
+  return to_symbol_expr(object_descriptor_exprt::root_object(original_expr))
+    .get_identifier();
 }
 
 const ssa_exprt ssa_exprt::get_l1_object() const

src/util/ssa_expr.h

@@ -38,7 +38,7 @@ class ssa_exprt:public symbol_exprt
   /// Replace the underlying, original expression by \p expr while maintaining
   /// SSA indices.
   /// \param expr: expression to store
-  void set_expression(const exprt &expr);
+  void set_expression(exprt expr);
 
   irep_idt get_object_name() const;