introduce instructiont::dead_symbol()

This mirrors the change in #5861 by replacing the use of code_deadt by
directly returning the symbol_exprt.  The client code is simplified.

Author: kroening

src/analyses/constant_propagator.cpp

@@ -191,8 +191,7 @@ void constant_propagator_domaint::transform(
   }
   else if(from->is_dead())
   {
-    const auto &code_dead = from->get_dead();
-    values.set_to_top(code_dead.symbol());
+    values.set_to_top(from->dead_symbol());
   }
   else if(from->is_function_call())
   {

src/goto-instrument/goto_program2code.cpp

@@ -94,7 +94,7 @@ void goto_program2codet::build_dead_map()
   {
     if(instruction.is_dead())
     {
-      dead_map[instruction.get_dead().get_identifier()] =
+      dead_map[instruction.dead_symbol().get_identifier()] =
         instruction.location_number;
     }
   }

src/goto-programs/goto_program.cpp

@@ -884,9 +884,9 @@ void goto_programt::instructiont::validate(
       source_location);
     DATA_CHECK_WITH_DIAGNOSTICS(
       vm,
-      !ns.lookup(get_dead().get_identifier(), table_symbol),
+      !ns.lookup(dead_symbol().get_identifier(), table_symbol),
       "removed symbols should be known",
-      id2string(get_dead().get_identifier()),
+      id2string(dead_symbol().get_identifier()),
       source_location);
     break;
   case FUNCTION_CALL:
@@ -966,13 +966,9 @@ void goto_programt::instructiont::transform(
 
   case DEAD:
   {
-    auto new_symbol = f(get_dead().symbol());
+    auto new_symbol = f(dead_symbol());
     if(new_symbol.has_value())
-    {
-      auto new_dead = get_dead();
-      new_dead.symbol() = to_symbol_expr(*new_symbol);
-      set_dead(new_dead);
-    }
+      dead_symbol() = to_symbol_expr(*new_symbol);
   }
   break;
 
@@ -1050,7 +1046,7 @@ void goto_programt::instructiont::apply(
     break;
 
   case DEAD:
-    f(get_dead().symbol());
+    f(dead_symbol());
     break;
 
   case FUNCTION_CALL:

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>
@@ -218,13 +219,29 @@ class goto_programt
     }
 
     /// Get the dead statement for DEAD
+    DEPRECATED(SINCE(2021, 2, 24, "Use dead_symbol instead"))
     const code_deadt &get_dead() const
     {
       PRECONDITION(is_dead());
       return to_code_dead(code);
     }
 
+    /// Get the symbol for DEAD
+    const symbol_exprt &dead_symbol() const
+    {
+      PRECONDITION(is_dead());
+      return to_code_dead(code).symbol();
+    }
+
+    /// Get the symbol for DEAD
+    symbol_exprt &dead_symbol()
+    {
+      PRECONDITION(is_dead());
+      return to_code_dead(code).symbol();
+    }
+
     /// Set the dead statement for DEAD
+    DEPRECATED(SINCE(2021, 2, 24, "Use dead_symbol instead"))
     void set_dead(code_deadt c)
     {
       PRECONDITION(is_dead());

src/goto-symex/symex_dead.cpp

@@ -19,9 +19,7 @@ Author: Daniel Kroening, [email protected]
 void goto_symext::symex_dead(statet &state)
 {
   const goto_programt::instructiont &instruction=*state.source.pc;
-
-  const code_deadt &code = instruction.get_dead();
-  symex_dead(state, code.symbol());
+  symex_dead(state, instruction.dead_symbol());
 }
 
 void goto_symext::symex_dead(statet &state, const symbol_exprt &symbol_expr)