1 /* Functions related to the Boehm garbage collector.
2 Copyright (C) 2000 Free Software Foundation, Inc.
4 This file is part of GNU CC.
6 GNU CC is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 2, or (at your option)
11 GNU CC is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with GNU CC; see the file COPYING. If not, write to
18 the Free Software Foundation, 59 Temple Place - Suite 330,
19 Boston, MA 02111-1307, USA.
21 Java and all Java-based marks are trademarks or registered trademarks
22 of Sun Microsystems, Inc. in the United States and other countries.
23 The Free Software Foundation is independent of Sun Microsystems, Inc. */
25 /* Written by Tom Tromey <tromey@cygnus.com>. */
31 #include "java-tree.h"
34 static void mark_reference_fields PARAMS ((tree,
35 unsigned HOST_WIDE_INT *,
36 unsigned HOST_WIDE_INT *,
41 static void set_bit PARAMS ((unsigned HOST_WIDE_INT *,
42 unsigned HOST_WIDE_INT *,
45 /* Compute a procedure-based object descriptor. We know that our
46 `kind' is 0, and `env' is likewise 0, so we have a simple
47 computation. From the GC sources:
48 (((((env) << LOG_MAX_MARK_PROCS) | (proc_index)) << DS_TAG_BITS) \
51 #define PROCEDURE_OBJECT_DESCRIPTOR integer_two_node
53 /* Treat two HOST_WIDE_INT's as a contiguous bitmap, with bit 0 being
54 the least significant. This function sets bit N in the bitmap. */
56 set_bit (low, high, n)
57 unsigned HOST_WIDE_INT *low, *high;
62 if (n >= HOST_BITS_PER_WIDE_INT)
64 n -= HOST_BITS_PER_WIDE_INT;
70 *which |= (HOST_WIDE_INT) 1 << n;
73 /* Recursively mark reference fields. */
75 mark_reference_fields (field, low, high, ubit,
76 pointer_after_end, all_bits_set,
77 last_set_index, last_view_index)
79 unsigned HOST_WIDE_INT *low, *high;
81 int *pointer_after_end, *all_bits_set;
83 HOST_WIDE_INT *last_view_index;
85 /* See if we have fields from our superclass. */
86 if (DECL_NAME (field) == NULL_TREE)
88 mark_reference_fields (TYPE_FIELDS (TREE_TYPE (field)),
90 pointer_after_end, all_bits_set,
91 last_set_index, last_view_index);
92 field = TREE_CHAIN (field);
95 for (; field != NULL_TREE; field = TREE_CHAIN (field))
99 if (FIELD_STATIC (field))
102 offset = tree_low_cst (byte_position (field), 1);
103 if (JREFERENCE_TYPE_P (TREE_TYPE (field)))
107 /* If this reference slot appears to overlay a slot we think
108 we already covered, then we are doomed. */
109 if (offset <= *last_view_index)
112 count = offset * BITS_PER_UNIT / POINTER_SIZE;
114 *last_set_index = count;
115 /* First word in object corresponds to most significant byte
117 set_bit (low, high, ubit - count - 1);
118 if (count > ubit - 2)
119 *pointer_after_end = 1;
124 *last_view_index = offset;
128 /* Return the marking bitmap for the class TYPE. For now this is a
129 single word describing the type. */
131 get_boehm_type_descriptor (tree type)
133 unsigned int count, log2_size, ubit;
135 int all_bits_set = 1;
136 int last_set_index = 0;
137 HOST_WIDE_INT last_view_index = -1;
138 int pointer_after_end = 0;
139 unsigned HOST_WIDE_INT low = 0, high = 0;
142 /* If the GC wasn't requested, just use a null pointer. */
143 if (! flag_use_boehm_gc)
144 return null_pointer_node;
146 /* If we have a type of unknown size, use a proc. */
147 if (int_size_in_bytes (type) == -1)
148 return PROCEDURE_OBJECT_DESCRIPTOR;
150 bit = POINTER_SIZE / BITS_PER_UNIT;
151 /* The size of this node has to be known. And, we only support 32
152 and 64 bit targets, so we need to know that the log2 is one of
154 log2_size = exact_log2 (bit);
155 if (bit == -1 || (log2_size != 2 && log2_size != 3))
157 /* This means the GC isn't supported. We should probably
158 abort or give an error. Instead, for now, we just silently
160 return null_pointer_node;
162 bit *= BITS_PER_UNIT;
164 /* Warning avoidance. */
165 ubit = (unsigned int) bit;
167 field = TYPE_FIELDS (type);
168 mark_reference_fields (field, &low, &high, ubit,
169 &pointer_after_end, &all_bits_set,
170 &last_set_index, &last_view_index);
172 /* If the object is all pointers, or if the part with pointers fits
173 in our bitmap, then we are ok. Otherwise we have to allocate it
177 /* In the GC the computation looks something like this:
178 value = DS_LENGTH | WORDS_TO_BYTES (last_set_index + 1);
180 WORDS_TO_BYTES shifts by log2(bytes-per-pointer). */
185 while (last_set_index)
187 if ((last_set_index & 1))
188 set_bit (&low, &high, log2_size + count);
189 last_set_index >>= 1;
192 value = build_int_2 (low, high);
194 else if (! pointer_after_end)
196 /* Bottom two bits for bitmap mark type are 01. */
197 set_bit (&low, &high, 0);
198 value = build_int_2 (low, high);
201 value = PROCEDURE_OBJECT_DESCRIPTOR;