class.c

gcc-2.95.3 Linux下最常用的C编译器

   Note that the index (DELTA2) in the virtual function table
   is always 0.  */

static tree
build_vtable_entry (delta, pfn)
     tree delta, pfn;
{
  if (flag_vtable_thunks)
    {
      HOST_WIDE_INT idelta = TREE_INT_CST_LOW (delta);
      if (idelta && ! DECL_ABSTRACT_VIRTUAL_P (TREE_OPERAND (pfn, 0)))
	{
	  pfn = build1 (ADDR_EXPR, vtable_entry_type,
			make_thunk (pfn, idelta));
	  TREE_READONLY (pfn) = 1;
	  TREE_CONSTANT (pfn) = 1;
	}
#ifdef GATHER_STATISTICS
      n_vtable_entries += 1;
#endif
      return pfn;
    }
  else
    {
      extern int flag_huge_objects;
      tree elems = expr_tree_cons (NULL_TREE, delta,
			      expr_tree_cons (NULL_TREE, integer_zero_node,
					 build_expr_list (NULL_TREE, pfn)));
      tree entry = build (CONSTRUCTOR, vtable_entry_type, NULL_TREE, elems);

      /* DELTA used to be constructed by `size_int' and/or size_binop,
	 which caused overflow problems when it was negative.  That should
	 be fixed now.  */

      if (! int_fits_type_p (delta, delta_type_node))
	{
	  if (flag_huge_objects)
	    sorry ("object size exceeds built-in limit for virtual function table implementation");
	  else
	    sorry ("object size exceeds normal limit for virtual function table implementation, recompile all source and use -fhuge-objects");
	}
      
      TREE_CONSTANT (entry) = 1;
      TREE_STATIC (entry) = 1;
      TREE_READONLY (entry) = 1;

#ifdef GATHER_STATISTICS
      n_vtable_entries += 1;
#endif

      return entry;
    }
}

/* We want to give the assembler the vtable identifier as well as
   the offset to the function pointer.  So we generate

   __asm__ __volatile__ (".vtable_entry %c0, %c1"
      : : "s"(&class_vtable),
          "i"((long)&vtbl[idx].pfn - (long)&vtbl[0])); */

static void
build_vtable_entry_ref (basetype, vtbl, idx)
     tree basetype, vtbl, idx;
{
  static char asm_stmt[] = ".vtable_entry %c0, %c1";
  tree s, i, i2;

  s = build_unary_op (ADDR_EXPR, TYPE_BINFO_VTABLE (basetype), 0);
  s = build_tree_list (build_string (1, "s"), s);

  i = build_array_ref (vtbl, idx);
  if (!flag_vtable_thunks)
    i = build_component_ref (i, pfn_identifier, vtable_entry_type, 0);
  i = build_c_cast (ptrdiff_type_node, build_unary_op (ADDR_EXPR, i, 0));
  i2 = build_array_ref (vtbl, build_int_2(0,0));
  i2 = build_c_cast (ptrdiff_type_node, build_unary_op (ADDR_EXPR, i2, 0));
  i = build_binary_op (MINUS_EXPR, i, i2);
  i = build_tree_list (build_string (1, "i"), i);

  expand_asm_operands (build_string (sizeof(asm_stmt)-1, asm_stmt),
		       NULL_TREE, chainon (s, i), NULL_TREE, 1, NULL, 0);
}

/* Given an object INSTANCE, return an expression which yields the
   virtual function vtable element corresponding to INDEX.  There are
   many special cases for INSTANCE which we take care of here, mainly
   to avoid creating extra tree nodes when we don't have to.  */

tree
build_vtbl_ref (instance, idx)
     tree instance, idx;
{
  tree vtbl, aref;
  tree basetype = TREE_TYPE (instance);

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

  if (instance == current_class_ref)
    vtbl = build_vfield_ref (instance, basetype);
  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_vfield_ref (instance, basetype);
    }

  assemble_external (vtbl);

  if (flag_vtable_gc)
    build_vtable_entry_ref (basetype, vtbl, idx);

  aref = build_array_ref (vtbl, idx);

  return aref;
}

/* Given an object INSTANCE, return an expression which yields the
   virtual function corresponding to INDEX.  There are many special
   cases for INSTANCE which we take care of here, mainly to avoid
   creating extra tree nodes when we don't have to.  */

tree
build_vfn_ref (ptr_to_instptr, instance, idx)
     tree *ptr_to_instptr, instance;
     tree idx;
{
  tree aref = build_vtbl_ref (instance, idx);

  /* When using thunks, there is no extra delta, and we get the pfn
     directly.  */
  if (flag_vtable_thunks)
    return aref;

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

      *ptr_to_instptr
	= build (PLUS_EXPR, TREE_TYPE (*ptr_to_instptr),
		 *ptr_to_instptr,
		 cp_convert (ptrdiff_type_node,
			     build_component_ref (aref, delta_identifier, NULL_TREE, 0)));
    }

  return build_component_ref (aref, pfn_identifier, NULL_TREE, 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);
  const 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);
}

/* Return the offset to the main vtable for a given base BINFO.  */

tree
get_vfield_offset (binfo)
     tree binfo;
{
  tree tmp
    = size_binop (FLOOR_DIV_EXPR,
		  DECL_FIELD_BITPOS (CLASSTYPE_VFIELD (BINFO_TYPE (binfo))),
		  size_int (BITS_PER_UNIT));
  tmp = convert (sizetype, tmp);
  return size_binop (PLUS_EXPR, tmp, BINFO_OFFSET (binfo));
}

/* Get the offset to the start of the original binfo that we derived
   this binfo from.  If we find TYPE first, return the offset only
   that far.  The shortened search is useful because the this pointer
   on method calling is expected to point to a DECL_CONTEXT (fndecl)
   object, and not a baseclass of it.  */

static tree
get_derived_offset (binfo, type)
     tree binfo, type;
{
  tree offset1 = get_vfield_offset (TYPE_BINFO (BINFO_TYPE (binfo)));
  tree offset2;
  int i;
  while (BINFO_BASETYPES (binfo)
	 && (i=CLASSTYPE_VFIELD_PARENT (BINFO_TYPE (binfo))) != -1)
    {
      tree binfos = BINFO_BASETYPES (binfo);
      if (BINFO_TYPE (binfo) == type)
	break;
      binfo = TREE_VEC_ELT (binfos, i);
    }
  offset2 = get_vfield_offset (TYPE_BINFO (BINFO_TYPE (binfo)));
  return size_binop (MINUS_EXPR, offset1, offset2);
}

/* Update the rtti info for this class.  */

static void
set_rtti_entry (virtuals, offset, type)
     tree virtuals, offset, type;
{
  tree vfn;

  if (CLASSTYPE_COM_INTERFACE (type))
    return;

  if (flag_rtti)
    vfn = build1 (ADDR_EXPR, vfunc_ptr_type_node, get_tinfo_fn_unused (type));
  else
    vfn = build1 (NOP_EXPR, vfunc_ptr_type_node, size_zero_node);
  TREE_CONSTANT (vfn) = 1;

  if (! flag_vtable_thunks)
    TREE_VALUE (virtuals) = build_vtable_entry (offset, vfn);
  else
    {
      tree voff = build1 (NOP_EXPR, vfunc_ptr_type_node, offset);
      TREE_CONSTANT (voff) = 1;

      TREE_VALUE (virtuals) = build_vtable_entry (integer_zero_node, voff);

      /* The second slot is for the tdesc pointer when thunks are used.  */
      TREE_VALUE (TREE_CHAIN (virtuals))
	= build_vtable_entry (integer_zero_node, vfn);
    }
}

/* 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)
    {
      tree offset;

      virtuals = copy_list (BINFO_VIRTUALS (binfo));
      decl = build_lang_decl (VAR_DECL, name, TREE_TYPE (BINFO_VTABLE (binfo)));

      /* Now do rtti stuff.  */
      offset = get_derived_offset (TYPE_BINFO (type), NULL_TREE);
      offset = ssize_binop (MINUS_EXPR, integer_zero_node, offset);
      set_rtti_entry (virtuals, offset, type);
    }
  else
    {
      virtuals = NULL_TREE;
      decl = build_lang_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);

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

  DECL_ARTIFICIAL (decl) = 1;
  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));

  DECL_VIRTUAL_P (decl) = 1;
  DECL_CONTEXT (decl) = type;

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

extern tree signed_size_zero_node;

/* 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.

   The order in which vtables are built (by calling this function) for
   an object must remain the same, otherwise a binary incompatibility
   can result.  */

static void
prepare_fresh_vtable (binfo, for_type)
     tree binfo, for_type;
{
  tree basetype;
  tree orig_decl = BINFO_VTABLE (binfo);
  tree name;
  tree new_decl;
  tree offset;
  tree path = binfo;
  char *buf, *buf2;
  char joiner = '_';
  int i;

#ifdef JOINER
  joiner = JOINER;
#endif

  basetype = TYPE_MAIN_VARIANT (BINFO_TYPE (binfo));

  buf2 = TYPE_ASSEMBLER_NAME_STRING (basetype);
  i = TYPE_ASSEMBLER_NAME_LENGTH (basetype) + 1;

  /* We know that the vtable that we are going to create doesn't exist
     yet in the global namespace, and when we finish, it will be
     pushed into the global namespace.  In complex MI hierarchies, we
     have to loop while the name we are thinking of adding is globally
     defined, adding more name components to the vtable name as we
     loop, until the name is unique.  This is because in complex MI
     cases, we might have the same base more than once.  This means
     that the order in which this function is called for vtables must
     remain the same, otherwise binary compatibility can be
     compromised.  */

  while (1)
    {
      char *buf1 = (char *) alloca (TYPE_ASSEMBLER_NAME_LENGTH (for_type)
				    + 1 + i);
      char *new_buf2;

      sprintf (buf1, "%s%c%s", TYPE_ASSEMBLER_NAME_STRING (for_type), joiner,
	       buf2);
      buf = (char *) alloca (strlen (VTABLE_NAME_FORMAT) + strlen (buf1) + 1);
      sprintf (buf, VTABLE_NAME_FORMAT, buf1);
      name = get_identifier (buf);

      /* If this name doesn't clash, then we can use it, otherwise
	 we add more to the name until it is unique.  */

      if (! IDENTIFIER_GLOBAL_VALUE (name))
	break;

      /* Set values for next loop through, if the name isn't unique.  */

      path = BINFO_INHERITANCE_CHAIN (path);