class.c

gcc库的原代码,对编程有很大帮助.

tree
build_vfn_ref (ptr_to_instptr, instance, idx)
     tree *ptr_to_instptr, instance;
     tree idx;
{
  extern int building_cleanup;
  tree vtbl, aref;
  tree basetype = TREE_TYPE (instance);

  if (TREE_CODE (basetype) == REFERENCE_TYPE)
    basetype = TREE_TYPE (basetype);

  if (instance == C_C_D)
    vtbl = build_indirect_ref (build_vfield_ref (instance, basetype),
			       NULL_PTR);
  else
    {
      if (optimize)
	{
	  /* Try to figure out what a reference refers to, and
	     access its virtual function table directly.  */
	  tree ref = NULL_TREE;

	  if (TREE_CODE (instance) == INDIRECT_REF
	      && TREE_CODE (TREE_TYPE (TREE_OPERAND (instance, 0))) == REFERENCE_TYPE)
	    ref = TREE_OPERAND (instance, 0);
	  else if (TREE_CODE (TREE_TYPE (instance)) == REFERENCE_TYPE)
	    ref = instance;

	  if (ref && TREE_CODE (ref) == VAR_DECL
	      && DECL_INITIAL (ref))
	    {
	      tree init = DECL_INITIAL (ref);

	      while (TREE_CODE (init) == NOP_EXPR
		     || TREE_CODE (init) == NON_LVALUE_EXPR)
		init = TREE_OPERAND (init, 0);
	      if (TREE_CODE (init) == ADDR_EXPR)
		{
		  init = TREE_OPERAND (init, 0);
		  if (IS_AGGR_TYPE (TREE_TYPE (init))
		      && (TREE_CODE (init) == PARM_DECL
			  || TREE_CODE (init) == VAR_DECL))
		    instance = init;
		}
	    }
	}

      if (IS_AGGR_TYPE (TREE_TYPE (instance))
	  && (TREE_CODE (instance) == RESULT_DECL
	      || TREE_CODE (instance) == PARM_DECL
	      || TREE_CODE (instance) == VAR_DECL))
	vtbl = TYPE_BINFO_VTABLE (basetype);
      else
	vtbl = build_indirect_ref (build_vfield_ref (instance, basetype),
				   NULL_PTR);
    }
  assemble_external (vtbl);
  aref = build_array_ref (vtbl, idx);

  /* Save the intermediate result in a SAVE_EXPR so we don't have to
     compute each component of the virtual function pointer twice.  */ 
  if (!building_cleanup && TREE_CODE (aref) == INDIRECT_REF)
    TREE_OPERAND (aref, 0) = save_expr (TREE_OPERAND (aref, 0));

  if (flag_vtable_thunks)
    return aref;
  else
    {
      if (ptr_to_instptr)
	*ptr_to_instptr
	  = build (PLUS_EXPR, TREE_TYPE (*ptr_to_instptr),
		   *ptr_to_instptr,
		   convert (ptrdiff_type_node,
			    build_component_ref (aref, delta_identifier, 0, 0)));
      return build_component_ref (aref, pfn_identifier, 0, 0);
    }
}

/* Return the name of the virtual function table (as an IDENTIFIER_NODE)
   for the given TYPE.  */
static tree
get_vtable_name (type)
     tree type;
{
  tree type_id = build_typename_overload (type);
  char *buf = (char *)alloca (strlen (VTABLE_NAME_FORMAT)
			      + IDENTIFIER_LENGTH (type_id) + 2);
  char *ptr = IDENTIFIER_POINTER (type_id);
  int i;
  for (i = 0; ptr[i] == OPERATOR_TYPENAME_FORMAT[i]; i++) ;
#if 0
  /* We don't take off the numbers; prepare_fresh_vtable uses the
     DECL_ASSEMBLER_NAME for the type, which includes the number
     in `3foo'.  If we were to pull them off here, we'd end up with
     something like `_vt.foo.3bar', instead of a uniform definition.  */
  while (ptr[i] >= '0' && ptr[i] <= '9')
    i += 1;
#endif
  sprintf (buf, VTABLE_NAME_FORMAT, ptr+i);
  return get_identifier (buf);
}

/* Build a virtual function for type TYPE.
   If BINFO is non-NULL, build the vtable starting with the initial
   approximation that it is the same as the one which is the head of
   the association list.  */
static tree
build_vtable (binfo, type)
     tree binfo, type;
{
  tree name = get_vtable_name (type);
  tree virtuals, decl;

  if (binfo)
    {
      virtuals = copy_list (BINFO_VIRTUALS (binfo));
      decl = build_decl (VAR_DECL, name, TREE_TYPE (BINFO_VTABLE (binfo)));
    }
  else
    {
      virtuals = NULL_TREE;
      decl = build_decl (VAR_DECL, name, void_type_node);
    }

#ifdef GATHER_STATISTICS
  n_vtables += 1;
  n_vtable_elems += list_length (virtuals);
#endif

  /* Set TREE_PUBLIC and TREE_EXTERN as appropriate.  */
  import_export_vtable (decl, type, 0);

  IDENTIFIER_GLOBAL_VALUE (name) = decl = pushdecl_top_level (decl);
  /* Initialize the association list for this type, based
     on our first approximation.  */
  TYPE_BINFO_VTABLE (type) = decl;
  TYPE_BINFO_VIRTUALS (type) = virtuals;

  TREE_STATIC (decl) = 1;
#ifndef WRITABLE_VTABLES
  /* Make them READONLY by default. (mrs) */
  TREE_READONLY (decl) = 1;
#endif
  /* At one time the vtable info was grabbed 2 words at a time.  This
     fails on sparc unless you have 8-byte alignment.  (tiemann) */
  DECL_ALIGN (decl) = MAX (TYPE_ALIGN (double_type_node),
			   DECL_ALIGN (decl));

  /* Why is this conditional? (mrs) */
  if (binfo && write_virtuals >= 0)
    DECL_VIRTUAL_P (decl) = 1;
  DECL_CONTEXT (decl) = type;

  binfo = TYPE_BINFO (type);
  SET_BINFO_NEW_VTABLE_MARKED (binfo);
  return decl;
}

/* Given a base type PARENT, and a derived type TYPE, build
   a name which distinguishes exactly the PARENT member of TYPE's type.

   FORMAT is a string which controls how sprintf formats the name
   we have generated.

   For example, given

	class A; class B; class C : A, B;

   it is possible to distinguish "A" from "C's A".  And given

	class L;
	class A : L; class B : L; class C : A, B;

   it is possible to distinguish "L" from "A's L", and also from
   "C's L from A".

   Make sure to use the DECL_ASSEMBLER_NAME of the TYPE_NAME of the
   type, as template have DECL_NAMEs like: X<int>, whereas the
   DECL_ASSEMBLER_NAME is set to be something the assembler can handle.
  */
static tree
build_type_pathname (format, parent, type)
     char *format;
     tree parent, type;
{
  extern struct obstack temporary_obstack;
  char *first, *base, *name;
  int i;
  tree id;

  parent = TYPE_MAIN_VARIANT (parent);

  /* Remember where to cut the obstack to.  */
  first = obstack_base (&temporary_obstack);

  /* Put on TYPE+PARENT.  */
  obstack_grow (&temporary_obstack,
		TYPE_ASSEMBLER_NAME_STRING (type),
		TYPE_ASSEMBLER_NAME_LENGTH (type));
#ifdef JOINER
  obstack_1grow (&temporary_obstack, JOINER);
#else
  obstack_1grow (&temporary_obstack, '_');
#endif
  obstack_grow0 (&temporary_obstack,
		 TYPE_ASSEMBLER_NAME_STRING (parent),
		 TYPE_ASSEMBLER_NAME_LENGTH (parent));
  i = obstack_object_size (&temporary_obstack);
  base = obstack_base (&temporary_obstack);
  obstack_finish (&temporary_obstack);

  /* Put on FORMAT+TYPE+PARENT.  */
  obstack_blank (&temporary_obstack, strlen (format) + i + 1);
  name = obstack_base (&temporary_obstack);
  sprintf (name, format, base);
  id = get_identifier (name);
  obstack_free (&temporary_obstack, first);

  return id;
}

/* Update the rtti info for this class.  */
static void
set_rtti_entry (virtuals, offset, type)
     tree virtuals, offset, type;
{
  if (! flag_vtable_thunks)
    TREE_VALUE (virtuals)
      = build_vtable_entry (offset,
			    (flag_rtti
			     ? build_t_desc (type, 0)
			     : integer_zero_node));
  else
    {
      tree vfn = build1 (NOP_EXPR, vfunc_ptr_type_node, offset);
      TREE_CONSTANT (vfn) = 1;

      TREE_VALUE (virtuals)
	= build_vtable_entry (integer_zero_node, vfn);
      /* The second slot is for the tdesc pointer when thunks are used.  */
      vfn = flag_rtti
	     ? build_t_desc (type, 0)
	     : integer_zero_node;
      vfn = build1 (NOP_EXPR, vfunc_ptr_type_node, vfn);
      TREE_CONSTANT (vfn) = 1;

      TREE_VALUE (TREE_CHAIN (virtuals))
	= build_vtable_entry (integer_zero_node, vfn);
    }
}

/* Give TYPE a new virtual function table which is initialized
   with a skeleton-copy of its original initialization.  The only
   entry that changes is the `delta' entry, so we can really
   share a lot of structure.

   FOR_TYPE is the derived type which caused this table to
   be needed.

   BINFO is the type association which provided TYPE for FOR_TYPE.  */
static void
prepare_fresh_vtable (binfo, for_type)
     tree binfo, for_type;
{
  tree basetype = BINFO_TYPE (binfo);
  tree orig_decl = BINFO_VTABLE (binfo);
  /* This name is too simplistic.  We can have multiple basetypes for
     for_type, and we really want different names.  (mrs) */
  tree name = build_type_pathname (VTABLE_NAME_FORMAT, basetype, for_type);
  tree new_decl = build_decl (VAR_DECL, name, TREE_TYPE (orig_decl));
  tree path, offset;
  int result;

  /* Remember which class this vtable is really for.  */
  DECL_CONTEXT (new_decl) = for_type;

  TREE_STATIC (new_decl) = 1;
  BINFO_VTABLE (binfo) = pushdecl_top_level (new_decl);
  DECL_VIRTUAL_P (new_decl) = 1;
#ifndef WRITABLE_VTABLES
  /* Make them READONLY by default. (mrs) */
  TREE_READONLY (new_decl) = 1;
#endif
  DECL_ALIGN (new_decl) = DECL_ALIGN (orig_decl);

  /* Make fresh virtual list, so we can smash it later.  */
  BINFO_VIRTUALS (binfo) = copy_list (BINFO_VIRTUALS (binfo));

  if (TREE_VIA_VIRTUAL (binfo))
    offset = BINFO_OFFSET (binfo_member (BINFO_TYPE (binfo), 
			    CLASSTYPE_VBASECLASSES (for_type)));
  else
    offset = BINFO_OFFSET (binfo);

  set_rtti_entry (BINFO_VIRTUALS (binfo),
		  size_binop (MINUS_EXPR, integer_zero_node, offset),
		  for_type);

#ifdef GATHER_STATISTICS
  n_vtables += 1;
  n_vtable_elems += list_length (BINFO_VIRTUALS (binfo));
#endif

  /* Set TREE_PUBLIC and TREE_EXTERN as appropriate.  */
  import_export_vtable (new_decl, for_type, 0);

  if (TREE_VIA_VIRTUAL (binfo))
    my_friendly_assert (binfo == binfo_member (BINFO_TYPE (binfo),
				   CLASSTYPE_VBASECLASSES (current_class_type)),
			170);
  SET_BINFO_NEW_VTABLE_MARKED (binfo);
}

/* Access the virtual function table entry that logically
   contains BASE_FNDECL.  VIRTUALS is the virtual function table's
   initializer.  We can run off the end, when dealing with virtual
   destructors in MI situations, return NULL_TREE in that case.  */
static tree
get_vtable_entry (virtuals, base_fndecl)
     tree virtuals, base_fndecl;
{
  unsigned HOST_WIDE_INT n = (HOST_BITS_PER_WIDE_INT >= BITS_PER_WORD
	   ? (TREE_INT_CST_LOW (DECL_VINDEX (base_fndecl))
	      & (((unsigned HOST_WIDE_INT)1<<(BITS_PER_WORD-1))-1))
	   : TREE_INT_CST_LOW (DECL_VINDEX (base_fndecl)));

#ifdef GATHER_STATISTICS
  n_vtable_searches += n;
#endif

  while (n > 0 && virtuals)
    {
      --n;
      virtuals = TREE_CHAIN (virtuals);
    }
  return virtuals;
}

/* Put new entry ENTRY into virtual function table initializer
   VIRTUALS.

   Also update DECL_VINDEX (FNDECL).  */

static void
modify_vtable_entry (old_entry_in_list, new_entry, fndecl)
     tree old_entry_in_list, new_entry, fndecl;
{
  tree base_fndecl = TREE_OPERAND (FNADDR_FROM_VTABLE_ENTRY (TREE_VALUE (old_entry_in_list)), 0);

#ifdef NOTQUITE
  cp_warning ("replaced %D with %D", DECL_ASSEMBLER_NAME (base_fndecl),
	      DECL_ASSEMBLER_NAME (fndecl));
#endif
  TREE_VALUE (old_entry_in_list) = new_entry;

  /* Now assign virtual dispatch information, if unset.  */
  /* We can dispatch this, through any overridden base function. */
  if (TREE_CODE (DECL_VINDEX (fndecl)) != INTEGER_CST)
    {
      DECL_VINDEX (fndecl) = DECL_VINDEX (base_fndecl);
      DECL_CONTEXT (fndecl) = DECL_CONTEXT (base_fndecl);
    }
}

/* Access the virtual function table entry i.  VIRTUALS is the virtual
   function table's initializer.  */
static tree
get_vtable_entry_n (virtuals, n)
     tree virtuals;
     unsigned HOST_WIDE_INT n;
{
  while (n > 0)
    {
      --n;
      virtuals = TREE_CHAIN (virtuals);
    }
  return virtuals;
}

/* Add a virtual function to all the appropriate vtables for the class
   T.  DECL_VINDEX(X) should be error_mark_node, if we want to
   allocate a new slot in our table.  If it is error_mark_node, we
   know that no other function from another vtable is overridden by X.
   HAS_VIRTUAL keeps track of how many virtuals there are in our main
   vtable for the type, and we build upon the PENDING_VIRTUALS list
   and return it.  */
static tree
add_virtual_function (pending_virtuals, has_virtual, fndecl, t)
     tree pending_virtuals;
     int *has_virtual;
     tree fndecl;
     tree t; /* Structure type. */
{
  /* FUNCTION_TYPEs and OFFSET_TYPEs no longer freely
     convert to void *.  Make such a conversion here.  */
  tree vfn = build1 (ADDR_EXPR, vfunc_ptr_type_node, fndecl);
  TREE_CONSTANT (vfn) = 1;

#ifndef DUMB_USER
  if (current_class_type == 0)
    cp_warning ("internal problem, current_class_type is zero when adding `%D', please report",
		fndecl);
  if (current_class_type && t != current_class_type)
    cp_warning ("internal problem, current_class_type differs when adding `%D', please report",
		fndecl);
#endif

  /* If the virtual function is a redefinition of a prior one,
     figure out in which base class the new definition goes,
     and if necessary, make a fresh virtual function table
     to hold that entry.  */
  if (DECL_VINDEX (fndecl) == error_mark_node)
    {
      tree entry;

      if (flag_rtti && *has_virtual == 0)
	{
	  /* CLASSTYPE_RTTI is only used as a Boolean (NULL or not). */
	  CLASSTYPE_RTTI (t) = integer_one_node;
        }