gc.c

gcc库的原代码,对编程有很大帮助.

/* Garbage collection primitives for GNU C++.
   Copyright (C) 1992, 1993, 1994, 1995 Free Software Foundation, Inc.
   Contributed by Michael Tiemann ([e-mail])

This file is part of GNU CC.

GNU CC is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

GNU CC is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU CC; see the file COPYING.  If not, write to
the Free Software Foundation, 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.  */


#include "config.h"
#include "tree.h"
#include "cp-tree.h"
#include "flags.h"
#include "output.h"

#undef NULL
#define NULL 0

extern tree define_function ();
extern tree build_t_desc_overload ();
extern struct obstack *permanent_obstack;

/* This is the function decl for the (pseudo-builtin) __gc_protect
   function.  Args are (class *value, int index); Returns value.  */
tree gc_protect_fndecl;

/* This is the function decl for the (pseudo-builtin) __gc_unprotect
   function.  Args are (int index); void return.  */
tree gc_unprotect_fndecl;

/* This is the function decl for the (pseudo-builtin) __gc_push
   function.  Args are (int length); void return.  */
tree gc_push_fndecl;

/* This is the function decl for the (pseudo-builtin) __gc_pop
   function.  Args are void; void return.  */
tree gc_pop_fndecl;

/* Special integers that are used to represent bits in gc-safe objects.  */
tree gc_nonobject;
tree gc_visible;
tree gc_white;
tree gc_offwhite;
tree gc_grey;
tree gc_black;

/* in c-common.c */
extern tree combine_strings PROTO((tree));

/* Predicate that returns non-zero if TYPE needs some kind of
   entry for the GC.  Returns zero otherwise.  */
int
type_needs_gc_entry (type)
     tree type;
{
  tree ttype = type;

  if (! flag_gc || type == error_mark_node)
    return 0;

  /* Aggregate types need gc entries if any of their members
     need gc entries.  */
  if (IS_AGGR_TYPE (type))
    {
      tree binfos;
      tree fields = TYPE_FIELDS (type);
      int i;

      /* We don't care about certain pointers.  Pointers
	 to virtual baseclasses are always up front.  We also
	 cull out virtual function table pointers because it's
	 easy, and it simplifies the logic.*/
      while (fields
	     && (DECL_NAME (fields) == NULL_TREE
		 || VFIELD_NAME_P (DECL_NAME (fields))
		 || VBASE_NAME_P (DECL_NAME (fields))
		 || !strcmp (IDENTIFIER_POINTER (DECL_NAME (fields)), "__bits")))
	fields = TREE_CHAIN (fields);

      while (fields)
	{
	  if (type_needs_gc_entry (TREE_TYPE (fields)))
	    return 1;
	  fields = TREE_CHAIN (fields);
	}

      binfos = TYPE_BINFO_BASETYPES (type);
      if (binfos)
	for (i = TREE_VEC_LENGTH (binfos)-1; i >= 0; i--)
	  if (type_needs_gc_entry (BINFO_TYPE (TREE_VEC_ELT (binfos, i))))
	    return 1;

      return 0;
    }

  while (TREE_CODE (ttype) == ARRAY_TYPE
	 && TREE_CODE (TREE_TYPE (ttype)) == ARRAY_TYPE)
    ttype = TREE_TYPE (ttype);
  if ((TREE_CODE (ttype) == POINTER_TYPE
       || TREE_CODE (ttype) == ARRAY_TYPE
       || TREE_CODE (ttype) == REFERENCE_TYPE)
      && IS_AGGR_TYPE (TREE_TYPE (ttype))
      && CLASSTYPE_RTTI (TREE_TYPE (ttype)))
    return 1;

  return 0;
}

/* Predicate that returns non-zero iff FROM is safe from the GC.
   
   If TO is nonzero, it means we know that FROM is being stored
   in TO, which make make it safe.  */
int
value_safe_from_gc (to, from)
     tree to, from;
{
  /* First, return non-zero for easy cases: parameters,
     static variables.  */
  if (TREE_CODE (from) == PARM_DECL
      || (TREE_CODE (from) == VAR_DECL
	  && TREE_STATIC (from)))
    return 1;

  /* If something has its address taken, it cannot be
     in the heap, so it doesn't need to be protected.  */
  if (TREE_CODE (from) == ADDR_EXPR || TREE_REFERENCE_EXPR (from))
    return 1;

  /* If we are storing into a static variable, then what
     we store will be safe from the gc.  */
  if (to && TREE_CODE (to) == VAR_DECL
      && TREE_STATIC (to))
    return 1;

  /* Now recurse on structure of FROM.  */
  switch (TREE_CODE (from))
    {
    case COMPONENT_REF:
      /* These guys are special, and safe.  */
      if (TREE_CODE (TREE_OPERAND (from, 1)) == FIELD_DECL
	  && (VFIELD_NAME_P (DECL_NAME (TREE_OPERAND (from, 1)))
	      || VBASE_NAME_P (DECL_NAME (TREE_OPERAND (from, 1)))))
	return 1;
      /* fall through...  */
    case NOP_EXPR:
    case CONVERT_EXPR:
    case NON_LVALUE_EXPR:
    case WITH_CLEANUP_EXPR:
    case SAVE_EXPR:
    case PREDECREMENT_EXPR:
    case PREINCREMENT_EXPR:
    case POSTDECREMENT_EXPR:
    case POSTINCREMENT_EXPR:
      if (value_safe_from_gc (to, TREE_OPERAND (from, 0)))
	return 1;
      break;

    case VAR_DECL:
    case PARM_DECL:
      /* We can safely pass these things as parameters to functions.  */
      if (to == 0)
	return 1;

    case ARRAY_REF:
    case INDIRECT_REF:
    case RESULT_DECL:
    case OFFSET_REF:
    case CALL_EXPR:
    case METHOD_CALL_EXPR:
      break;

    case COMPOUND_EXPR:
    case TARGET_EXPR:
      if (value_safe_from_gc (to, TREE_OPERAND (from, 1)))
	return 1;
      break;

    case COND_EXPR:
      if (value_safe_from_gc (to, TREE_OPERAND (from, 1))
	  && value_safe_from_gc (to, TREE_OPERAND (from, 2)))
	return 1;
      break;

    case PLUS_EXPR:
    case MINUS_EXPR:
      if ((type_needs_gc_entry (TREE_TYPE (TREE_OPERAND (from, 0)))
	   || value_safe_from_gc (to, TREE_OPERAND (from, 0)))
	  && (type_needs_gc_entry (TREE_TYPE (TREE_OPERAND (from, 1))) == 0
	      || value_safe_from_gc (to, TREE_OPERAND (from, 1))))
	return 1;
      break;

    case RTL_EXPR:
      /* Every time we build an RTL_EXPR in the front-end, we must
	 ensure that everything in it is safe from the garbage collector.
	 ??? This has only been done for `build_new'.  */
      return 1;

    default:
      my_friendly_abort (41);
    }

  if (to == 0)
    return 0;

  /* FROM wasn't safe.  But other properties of TO might make it safe.  */
  switch (TREE_CODE (to))
    {
    case VAR_DECL:
    case PARM_DECL:
      /* We already culled out static VAR_DECLs above.  */
      return 0;

    case COMPONENT_REF:
      /* These guys are special, and safe.  */
      if (TREE_CODE (TREE_OPERAND (to, 1)) == FIELD_DECL
	  && (VFIELD_NAME_P (DECL_NAME (TREE_OPERAND (to, 1)))
	      || VBASE_NAME_P (DECL_NAME (TREE_OPERAND (to, 1)))))
	return 1;
      /* fall through...  */

    case NOP_EXPR:
    case NON_LVALUE_EXPR:
    case WITH_CLEANUP_EXPR:
    case SAVE_EXPR:
    case PREDECREMENT_EXPR:
    case PREINCREMENT_EXPR:
    case POSTDECREMENT_EXPR:
    case POSTINCREMENT_EXPR:
      return value_safe_from_gc (TREE_OPERAND (to, 0), from);

    case COMPOUND_EXPR:
    case TARGET_EXPR:
      return value_safe_from_gc (TREE_OPERAND (to, 1), from);

    case COND_EXPR:
      return (value_safe_from_gc (TREE_OPERAND (to, 1), from)
	      && value_safe_from_gc (TREE_OPERAND (to, 2), from));

    case INDIRECT_REF:
    case ARRAY_REF:
      /* This used to be 0, but our current restricted model
	 allows this to be 1.  We'll never get arrays this way.  */
      return 1;

    default:
      my_friendly_abort (42);
    }

  /* Catch-all case is that TO/FROM is not safe.  */
  return 0;
}

/* Function to build a static GC entry for DECL.  TYPE is DECL's type.

   For objects of type `class *', this is just an entry in the
   static vector __PTR_LIST__.

   For objects of type `class[]', this requires building an entry
   in the static vector __ARR_LIST__.

   For aggregates, this records all fields of type `class *'
   and `class[]' in the respective lists above.  */
void
build_static_gc_entry (decl, type)
     tree decl;
     tree type;
{
  /* Now, figure out what sort of entry to build.  */
  if (TREE_CODE (type) == POINTER_TYPE
      || TREE_CODE (type) == REFERENCE_TYPE)
    assemble_gc_entry (IDENTIFIER_POINTER (DECL_NAME (decl)));
  else if (TREE_CODE (type) == RECORD_TYPE)
    {
      tree ref = get_temp_name (build_reference_type (type), 1);
      DECL_INITIAL (ref) = build1 (ADDR_EXPR, TREE_TYPE (ref), decl);
      TREE_CONSTANT (DECL_INITIAL (ref)) = 1;
      cp_finish_decl (ref, DECL_INITIAL (ref), NULL_TREE, 0, 0);
    }
  else
    {
      /* Not yet implemented.
	 
	 Cons up a static variable that holds address and length info
	 and add that to ___ARR_LIST__.  */
      my_friendly_abort (43);
    }
}

/* Protect FROM from the GC, assuming FROM is going to be
   stored into TO.  We handle three cases for TO here:

   case 1: TO is a stack variable.
   case 2: TO is zero (which means it is a parameter).
   case 3: TO is a return value.  */

tree
protect_value_from_gc (to, from)
     tree to, from;
{
  if (to == 0)
    {
      tree cleanup;

      to = get_temp_regvar (TREE_TYPE (from), from);

      /* Convert from integer to list form since we'll use it twice.  */
      DECL_GC_OFFSET (to) = build_tree_list (NULL_TREE, DECL_GC_OFFSET (to));
      cleanup = build_function_call (gc_unprotect_fndecl,
				     DECL_GC_OFFSET (to));

      if (! cp_expand_decl_cleanup (to, cleanup))
	{
	  compiler_error ("cannot unprotect parameter in this scope");
	  return error_mark_node;
	}
    }

  /* Should never need to protect a value that's headed for static storage.  */
  if (TREE_STATIC (to))
    my_friendly_abort (44);

  switch (TREE_CODE (to))
    {
    case COMPONENT_REF:
    case INDIRECT_REF:
      return protect_value_from_gc (TREE_OPERAND (to, 0), from);

    case VAR_DECL:
    case PARM_DECL:
      {
	tree rval;
	if (DECL_GC_OFFSET (to) == NULL_TREE)
	  {
	    /* Because of a cast or a conversion, we might stick
	       a value into a variable that would not normally
	       have a GC entry.  */
	    DECL_GC_OFFSET (to) = size_int (++current_function_obstack_index);
	  }

	if (TREE_CODE (DECL_GC_OFFSET (to)) != TREE_LIST)
	  {
	    DECL_GC_OFFSET (to)
	      = build_tree_list (NULL_TREE, DECL_GC_OFFSET (to));
	  }

	current_function_obstack_usage = 1;
	rval = build_function_call (gc_protect_fndecl,
				    tree_cons (NULL_TREE, from,
					       DECL_GC_OFFSET (to)));
	TREE_TYPE (rval) = TREE_TYPE (from);
	return rval;
      }
    }

  /* If we fall through the switch, assume we lost.  */
  my_friendly_abort (45);
  /* NOTREACHED */
  return NULL_TREE;
}

/* Given the expression EXP of type `class *', return the head
   of the object pointed to by EXP.  */
tree
build_headof (exp)
     tree exp;
{
  tree type = TREE_TYPE (exp);
  tree vptr, offset;

  if (TREE_CODE (type) != POINTER_TYPE)
    {
      error ("`headof' applied to non-pointer type");
      return error_mark_node;
    }