Turn the ID_C_typedef into a comment

This means that it will not be used to check types are equal, fixing the
failing regression tests that were validating the types were equal (and
they only differed by a typedef'd name).

Author: thk123

src/ansi-c/c_typecheck_base.h

@@ -262,10 +262,6 @@ class c_typecheck_baset:
   asm_label_mapt asm_label_map;
 
   void apply_asm_label(const irep_idt &asm_label, symbolt &symbol);
-
-private:
-  static bool are_types_equal_ignoring_typedef(
-    const typet type1, const typet &type2);
 };
 
 #endif // CPROVER_ANSI_C_C_TYPECHECK_BASE_H

src/ansi-c/c_typecheck_expr.cpp

@@ -140,8 +140,6 @@ bool c_typecheck_baset::gcc_types_compatible_p(
   if(type1.id()==ID_c_enum)
   {
     if(type2.id()==ID_c_enum) // both are enums
-      // We don't need to remove the typedef flag here since as it is an enum
-      // we have already followed the enum tag to get to the underlying enum
       return type1==type2; // compares the tag
     else if(type2==type1.subtype())
       return true;
@@ -186,13 +184,12 @@ bool c_typecheck_baset::gcc_types_compatible_p(
   }
   else
   {
-    if(are_types_equal_ignoring_typedef(type1, type2))
+    if(type1==type2)
     {
       // Need to distinguish e.g. long int from int or
       // long long int from long int.
       // The rules appear to match those of C++.
-      // Isn't this explictly handled by checking type1==type2 (since
-      // operator== recursively checks all sub types).
+
       if(type1.get(ID_C_c_type)==type2.get(ID_C_c_type))
         return true;
     }
@@ -203,38 +200,6 @@ bool c_typecheck_baset::gcc_types_compatible_p(
 
 /*******************************************************************\
 
-Function: c_typecheck_baset::are_types_equal_ignoring_typedef
-
-  Inputs:
-   type1 - the first type to compare
-   type2 - the second type to compare
-
- Outputs: True if the types are equal
-
- Purpose: To check whether two types are equal, ignoring if they have a
-          different typedef tag. We do this by explictly removing the
-          ID_C_typedef from the type before comparing. Then we just use
-          operator== to compare the resultant types.
-
-\*******************************************************************/
-bool c_typecheck_baset::are_types_equal_ignoring_typedef(
-  const typet type1, const typet &type2)
-{
-  typet non_typedefd_type1=type1;
-  typet non_typedefd_type2=type2;
-  if(type1.get(ID_C_typedef)!=ID_nil)
-  {
-    non_typedefd_type1.remove(ID_C_typedef);
-  }
-  if(type2.get(ID_C_typedef)!=ID_nil)
-  {
-    non_typedefd_type2.remove(ID_C_typedef);
-  }
-  return non_typedefd_type1==non_typedefd_type2;
-}
-
-/*******************************************************************\
-
 Function: c_typecheck_baset::typecheck_expr_main
 
   Inputs:

src/util/irep_ids.txt

@@ -251,7 +251,7 @@ concatenation
 infinity
 return_type
 typedef
-C_typedef
+C_typedef #typedef
 extern
 static
 auto