introduce instructiont::return_value()

This mirrors the change in #5861 by replacing the use of code_returnt by
directly returning the return value expression.  The client code is
simplified considerably.

Author: kroening

src/goto-instrument/goto_program2code.cpp

@@ -418,14 +418,11 @@ goto_programt::const_targett goto_program2codet::convert_return(
   goto_programt::const_targett upper_bound,
   code_blockt &dest)
 {
-  const code_returnt &ret = target->get_return();
-
   // add return instruction unless original code was missing a return
-  if(!ret.has_return_value() ||
-     ret.return_value().id()!=ID_side_effect ||
-     to_side_effect_expr(ret.return_value()).get_statement()!=ID_nondet)
+  if(target->return_value().id()!=ID_side_effect ||
+     to_side_effect_expr(target->return_value()).get_statement()!=ID_nondet)
   {
-    dest.add(ret);
+    dest.add(code_returnt{target->return_value()});
   }
 
   // all v3 (or later) goto programs have an explicit GOTO after return

src/goto-programs/goto_inline_class.cpp

@@ -165,31 +165,21 @@ void goto_inlinet::replace_return(
   {
     if(it->is_return())
     {
-      const auto &code_return = it->get_return();
-
       if(lhs.is_not_nil())
       {
-        if(!code_return.has_return_value())
-        {
-          log.warning().source_location = it->code.find_source_location();
-          log.warning() << "return expects one operand!\n"
-                        << it->code.pretty() << messaget::eom;
-          continue;
-        }
-
         // a typecast may be necessary if the declared return type at the call
         // site differs from the defined return type
         it->code = code_assignt(
           lhs,
           typecast_exprt::conditional_cast(
-            code_return.return_value(), lhs.type()));
+            it->return_value(), lhs.type()));
         it->type=ASSIGN;
 
         it++;
       }
-      else if(code_return.has_return_value())
+      else
       {
-        it->code = code_expressiont(code_return.return_value());
+        it->code = code_expressiont(it->return_value());
         it->type=OTHER;
         it++;
       }

src/goto-programs/goto_program.cpp

@@ -285,8 +285,7 @@ std::list<exprt> expressions_read(
     break;
 
   case RETURN:
-    if(instruction.get_return().return_value().is_not_nil())
-      dest.push_back(instruction.get_return().return_value());
+    dest.push_back(instruction.return_value());
     break;
 
   case FUNCTION_CALL:
@@ -928,13 +927,9 @@ void goto_programt::instructiont::transform(
 
   case RETURN:
   {
-    auto new_return_value = f(get_return().return_value());
+    auto new_return_value = f(return_value());
     if(new_return_value.has_value())
-    {
-      auto new_return = get_return();
-      new_return.return_value() = *new_return_value;
-      set_return(new_return);
-    }
+      return_value() = *new_return_value;
   }
   break;
 
@@ -1037,7 +1032,7 @@ void goto_programt::instructiont::apply(
     break;
 
   case RETURN:
-    f(get_return().return_value());
+    f(return_value());
     break;
 
   case ASSIGN:

src/goto-programs/goto_program.h

@@ -18,6 +18,7 @@ Author: Daniel Kroening, [email protected]
 #include <sstream>
 #include <string>
 
+#include <util/deprecate.h>
 #include <util/invariant.h>
 #include <util/namespace.h>
 #include <util/source_location.h>
@@ -231,19 +232,39 @@ class goto_programt
       code = std::move(c);
     }
 
+#if 0
     /// Get the return statement for READ
+    DEPRECATED(SINCE(2021, 2, 24, "Use return_value instead"))
     const code_returnt &get_return() const
     {
       PRECONDITION(is_return());
       return to_code_return(code);
     }
+#endif
 
+    /// Get the return value of a RETURN instruction
+    const exprt &return_value() const
+    {
+      PRECONDITION(is_return());
+      return to_code_return(code).return_value();
+    }
+
+    /// Get the return value of a RETURN instruction
+    exprt &return_value()
+    {
+      PRECONDITION(is_return());
+      return to_code_return(code).return_value();
+    }
+
+#if 0
     /// Set the return statement for READ
+    DEPRECATED(SINCE(2021, 2, 24, "Use return_value instead"))
     void set_return(code_returnt c)
     {
       PRECONDITION(is_return());
       code = std::move(c);
     }
+#endif
 
     /// Get the function call for FUNCTION_CALL
     const code_function_callt &get_function_call() const

src/pointer-analysis/goto_program_dereference.cpp

@@ -228,13 +228,7 @@ void goto_program_dereferencet::dereference_instruction(
   }
   else if(i.is_return())
   {
-    auto r = i.get_return();
-
-    if(r.return_value().is_not_nil())
-    {
-      dereference_expr(r.return_value(), checks_only);
-      i.set_return(r);
-    }
+    dereference_expr(i.return_value(), checks_only);
   }
   else if(i.is_other())
   {