Use get_fresh_aux_symbol to create $array_size and fix its type

An array_size symbol should be of type size_type(), and we can safely rely on
common logic to find fresh symbols.

Author: tautschnig

regression/cbmc/vla1/program-only.desc

@@ -0,0 +1,12 @@
+CORE
+main.c
+--program-only
+^EXIT=0$
+^SIGNAL=0$
+--
+^warning: ignoring
+--
+\(__CPROVER_size_t\)x\$array_size
+--
+There should not be any type cast of x$array_size to __CPROVER_size_t, because
+it already is of that type.

src/ansi-c/c_typecheck_type.cpp

@@ -16,6 +16,7 @@ Author: Daniel Kroening, [email protected]
 #include <util/arith_tools.h>
 #include <util/c_types.h>
 #include <util/config.h>
+#include <util/fresh_symbol.h>
 #include <util/mathematical_types.h>
 #include <util/pointer_offset_size.h>
 #include <util/simplify_expr.h>
@@ -608,44 +609,25 @@ void c_typecheck_baset::typecheck_array_type(array_typet &type)
         throw 0;
       }
 
-      // Need to pull out! We insert new symbol.
-      unsigned count=0;
-      irep_idt temp_identifier;
-      std::string suffix;
-
-      do
-      {
-        suffix="$array_size"+std::to_string(count);
-        temp_identifier=id2string(current_symbol.name)+suffix;
-        count++;
-      }
-      while(symbol_table.symbols.find(temp_identifier)!=
-            symbol_table.symbols.end());
-
-      // add the symbol to symbol table
-      auxiliary_symbolt new_symbol;
-      new_symbol.name=temp_identifier;
-      new_symbol.pretty_name=id2string(current_symbol.pretty_name)+suffix;
-      new_symbol.base_name=id2string(current_symbol.base_name)+suffix;
-      new_symbol.type=size.type();
+      symbolt &new_symbol = get_fresh_aux_symbol(
+        size_type(),
+        id2string(current_symbol.name) + "$array_size",
+        id2string(current_symbol.base_name) + "$array_size",
+        size_source_location,
+        mode,
+        symbol_table);
       new_symbol.type.set(ID_C_constant, true);
-      new_symbol.value=size;
-      new_symbol.location = size_source_location;
-      new_symbol.mode = mode;
-
-      symbol_table.add(new_symbol);
+      new_symbol.value = typecast_exprt::conditional_cast(size, size_type());
 
       // produce the code that declares and initializes the symbol
-      symbol_exprt symbol_expr;
-      symbol_expr.set_identifier(temp_identifier);
-      symbol_expr.type()=new_symbol.type;
+      symbol_exprt symbol_expr = new_symbol.symbol_expr();
 
       code_declt declaration(symbol_expr);
       declaration.add_source_location() = size_source_location;
 
       code_assignt assignment;
       assignment.lhs()=symbol_expr;
-      assignment.rhs()=size;
+      assignment.rhs() = new_symbol.value;
       assignment.add_source_location() = size_source_location;
 
       // store the code