Replace redundant pointer-and-boolean with just a pointer

It's already implicit in a bare pointer (rather than a reference) that it could be null,
so let's just use that to express whether we have an answer or not.

Author: smowton

src/goto-symex/symex_dereference_state.cpp

@@ -28,9 +28,8 @@ Author: Daniel Kroening, [email protected]
 /// \param expr: expression to get or create a failed symbol for
 /// \param [out] symbol: failed symbol result
 /// \return true if we populated \p symbol
-bool symex_dereference_statet::get_or_create_failed_symbol(
-  const exprt &expr,
-  const symbolt *&symbol)
+const symbolt *symex_dereference_statet::get_or_create_failed_symbol(
+  const exprt &expr)
 {
   const namespacet &ns=goto_symex.ns;
 
@@ -39,13 +38,14 @@ bool symex_dereference_statet::get_or_create_failed_symbol(
   {
     const ssa_exprt &ssa_expr=to_ssa_expr(expr);
     if(ssa_expr.get_original_expr().id()!=ID_symbol)
-      return false;
+      return nullptr;
 
     const symbolt &ptr_symbol=
       ns.lookup(to_ssa_expr(expr).get_object_name());
 
     const irep_idt &failed_symbol = ptr_symbol.type.get(ID_C_failed_symbol);
 
+    const symbolt *symbol;
     if(failed_symbol!="" &&
         !ns.lookup(failed_symbol, symbol))
     {
@@ -55,8 +55,7 @@ bool symex_dereference_statet::get_or_create_failed_symbol(
       state.rename(sym_expr, ns, goto_symex_statet::L1);
       sym.name=to_ssa_expr(sym_expr).get_identifier();
       state.symbol_table.move(sym, sym_ptr);
-      symbol=sym_ptr;
-      return true;
+      return sym_ptr;
     }
   }
   else if(expr.id()==ID_symbol)
@@ -66,6 +65,7 @@ bool symex_dereference_statet::get_or_create_failed_symbol(
 
     const irep_idt &failed_symbol = ptr_symbol.type.get(ID_C_failed_symbol);
 
+    const symbolt *symbol;
     if(failed_symbol!="" &&
         !ns.lookup(failed_symbol, symbol))
     {
@@ -75,12 +75,11 @@ bool symex_dereference_statet::get_or_create_failed_symbol(
       state.rename(sym_expr, ns, goto_symex_statet::L1);
       sym.name=to_ssa_expr(sym_expr).get_identifier();
       state.symbol_table.move(sym, sym_ptr);
-      symbol=sym_ptr;
-      return true;
+      return sym_ptr;
     }
   }
 
-  return false;
+  return nullptr;
 }
 
 /// Just forwards a value-set query to `state.value_set`

src/goto-symex/symex_dereference_state.h

@@ -39,8 +39,7 @@ class symex_dereference_statet:
   void get_value_set(const exprt &expr, value_setst::valuest &value_set)
     const override;
 
-  bool get_or_create_failed_symbol(const exprt &expr, const symbolt *&symbol)
-    override;
+  const symbolt *get_or_create_failed_symbol(const exprt &expr) override;
 };
 
 #endif // CPROVER_GOTO_SYMEX_SYMEX_DEREFERENCE_STATE_H

src/pointer-analysis/dereference_callback.h

@@ -32,8 +32,7 @@ class dereference_callbackt
   virtual void
   get_value_set(const exprt &expr, value_setst::valuest &value_set) const = 0;
 
-  virtual bool
-  get_or_create_failed_symbol(const exprt &expr, const symbolt *&symbol) = 0;
+  virtual const symbolt *get_or_create_failed_symbol(const exprt &expr) = 0;
 };
 
 #endif // CPROVER_POINTER_ANALYSIS_DEREFERENCE_CALLBACK_H

src/pointer-analysis/goto_program_dereference.cpp

@@ -24,26 +24,27 @@ Author: Daniel Kroening, [email protected]
 ///   `failed_symbol` comment
 /// \return true when `expr` is a symbol, whose type contains a `failed_symbol`
 ///   comment which exists in the namespace.
-bool goto_program_dereferencet::get_or_create_failed_symbol(
-  const exprt &expr,
-  const symbolt *&symbol)
+const symbolt *goto_program_dereferencet::get_or_create_failed_symbol(
+  const exprt &expr)
 {
   if(expr.id()==ID_symbol)
   {
     if(expr.get_bool(ID_C_invalid_object))
-      return false;
+      return nullptr;
 
     const symbolt &ptr_symbol = ns.lookup(to_symbol_expr(expr));
 
     const irep_idt &failed_symbol = ptr_symbol.type.get(ID_C_failed_symbol);
 
     if(failed_symbol.empty())
-      return false;
+      return nullptr;
 
-    return !ns.lookup(failed_symbol, symbol);
+    const symbolt *symbol = nullptr;
+    ns.lookup(failed_symbol, symbol);
+    return symbol;
   }
 
-  return false;
+  return nullptr;
 }
 
 /// \deprecated

src/pointer-analysis/goto_program_dereference.h

@@ -69,8 +69,7 @@ class goto_program_dereferencet:protected dereference_callbackt
   DEPRECATED("Unused")
   virtual bool is_valid_object(const irep_idt &identifier);
 
-  bool get_or_create_failed_symbol(const exprt &expr, const symbolt *&symbol)
-    override;
+  const symbolt *get_or_create_failed_symbol(const exprt &expr) override;
 
   DEPRECATED("Unused")
   virtual void dereference_failure(

src/pointer-analysis/value_set_dereference.cpp

@@ -122,10 +122,12 @@ exprt value_set_dereferencet::dereference(
   {
     // first see if we have a "failed object" for this pointer
 
-    const symbolt *failed_symbol;
+
     exprt failure_value;
 
-    if(dereference_callback.get_or_create_failed_symbol(pointer, failed_symbol))
+    if(
+      const symbolt *failed_symbol =
+      dereference_callback.get_or_create_failed_symbol(pointer))
     {
       // yes!
       failure_value=failed_symbol->symbol_expr();