introduce instructiont::decl_symbol()

This addresses the issue of the ambiguous dual-use of code_declt in both the
C front-end and the goto-program API by replacing the use of code_declt by
directly returning the symbol_exprt.  The client code is simplified.

Author: kroening

jbmc/src/java_bytecode/remove_exceptions.cpp

@@ -512,8 +512,7 @@ void remove_exceptionst::instrument_exceptions(
   {
     if(instr_it->is_decl())
     {
-      code_declt decl = instr_it->get_decl();
-      locals.push_back(decl.symbol());
+      locals.push_back(instr_it->decl_symbol());
     }
     // Is it a handler push/pop or catch landing-pad?
     else if(instr_it->type==CATCH)

src/analyses/constant_propagator.cpp

@@ -158,8 +158,7 @@ void constant_propagator_domaint::transform(
 
   if(from->is_decl())
   {
-    const auto &code_decl = from->get_decl();
-    const symbol_exprt &symbol = code_decl.symbol();
+    const symbol_exprt &symbol = from->decl_symbol();
     values.set_to_top(symbol);
   }
   else if(from->is_assign())

src/analyses/custom_bitvector_analysis.cpp

@@ -294,12 +294,12 @@ void custom_bitvector_domaint::transform(
 
   case DECL:
     {
-      const code_declt &code_decl=to_code_decl(instruction.code);
-      assign_lhs(code_decl.symbol(), vectorst());
+      const auto &decl_symbol = instruction.decl_symbol();
+      assign_lhs(decl_symbol, vectorst());
 
       // is it a pointer?
-      if(code_decl.symbol().type().id()==ID_pointer)
-        assign_lhs(dereference_exprt(code_decl.symbol()), vectorst());
+      if(decl_symbol.type().id() == ID_pointer)
+        assign_lhs(dereference_exprt(decl_symbol), vectorst());
     }
     break;
 

src/analyses/escape_analysis.cpp

@@ -202,11 +202,8 @@ void escape_domaint::transform(
     break;
 
   case DECL:
-    {
-      const code_declt &code_decl=to_code_decl(instruction.code);
-      aliases.isolate(code_decl.get_identifier());
-      assign_lhs_cleanup(code_decl.symbol(), std::set<irep_idt>());
-    }
+    aliases.isolate(instruction.decl_symbol().get_identifier());
+    assign_lhs_cleanup(instruction.decl_symbol(), std::set<irep_idt>());
     break;
 
   case DEAD:

src/analyses/global_may_alias.cpp

@@ -120,11 +120,8 @@ void global_may_alias_domaint::transform(
   }
 
   case DECL:
-  {
-    const code_declt &code_decl = to_code_decl(instruction.code);
-    aliases.isolate(code_decl.get_identifier());
+    aliases.isolate(instruction.decl_symbol().get_identifier());
     break;
-  }
 
   case DEAD:
   {

src/analyses/goto_rw.cpp

@@ -822,13 +822,9 @@ void goto_rw(
     break;
 
   case DECL:
+    rw_set.get_objects_rec(function, target, target->decl_symbol().type());
     rw_set.get_objects_rec(
-      function, target, to_code_decl(target->code).symbol().type());
-    rw_set.get_objects_rec(
-      function,
-      target,
-      rw_range_sett::get_modet::LHS_W,
-      to_code_decl(target->code).symbol());
+      function, target, rw_range_sett::get_modet::LHS_W, target->decl_symbol());
     break;
 
   case FUNCTION_CALL:

src/analyses/interval_domain.cpp

@@ -71,7 +71,7 @@ void interval_domaint::transform(
   switch(instruction.type)
   {
   case DECL:
-    havoc_rec(to_code_decl(instruction.code).symbol());
+    havoc_rec(instruction.decl_symbol());
     break;
 
   case DEAD:

src/analyses/local_bitvector_analysis.cpp

@@ -282,15 +282,12 @@ void local_bitvector_analysist::build()
     }
 
     case DECL:
-    {
-      const code_declt &code_decl = to_code_decl(instruction.code);
       assign_lhs(
-        code_decl.symbol(),
+        instruction.decl_symbol(),
         exprt(ID_uninitialized),
         loc_info_src,
         loc_info_dest);
       break;
-    }
 
     case DEAD:
     {

src/analyses/local_may_alias.cpp

@@ -383,11 +383,9 @@ void local_may_aliast::build(const goto_functiont &goto_function)
     }
 
     case DECL:
-    {
-      const code_declt &code_decl = to_code_decl(instruction.code);
-      assign_lhs(code_decl.symbol(), nil_exprt(), loc_info_src, loc_info_dest);
+      assign_lhs(
+        instruction.decl_symbol(), nil_exprt(), loc_info_src, loc_info_dest);
       break;
-    }
 
     case DEAD:
     {

src/analyses/locals.cpp

@@ -20,7 +20,7 @@ void localst::build(const goto_functiont &goto_function)
   for(const auto &instruction : goto_function.body.instructions)
   {
     if(instruction.is_decl())
-      locals.insert(instruction.get_decl().get_identifier());
+      locals.insert(instruction.decl_symbol().get_identifier());
   }
 
   locals.insert(