1 /* Functions related to the Boehm garbage collector.
2 Copyright (C) 2000, 2003, 2004, 2006 Free Software Foundation, Inc.
4 This file is part of GCC.
6 GCC 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 3, or (at your option)
11 GCC 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 GCC; see the file COPYING3. If not see
18 <http://www.gnu.org/licenses/>.
20 Java and all Java-based marks are trademarks or registered trademarks
21 of Sun Microsystems, Inc. in the United States and other countries.
22 The Free Software Foundation is independent of Sun Microsystems, Inc. */
24 /* Written by Tom Tromey <tromey@cygnus.com>. */
29 #include "coretypes.h"
32 #include "java-tree.h"
36 static void mark_reference_fields (tree, unsigned HOST_WIDE_INT *,
37 unsigned HOST_WIDE_INT *, unsigned int,
38 int *, int *, int *, HOST_WIDE_INT *);
39 static void set_bit (unsigned HOST_WIDE_INT *, unsigned HOST_WIDE_INT *,
42 /* A procedure-based object descriptor. We know that our
43 `kind' is 0, and `env' is likewise 0, so we have a simple
44 computation. From the GC sources:
45 (((((env) << LOG_MAX_MARK_PROCS) | (proc_index)) << DS_TAG_BITS) \
48 #define PROCEDURE_OBJECT_DESCRIPTOR 2
50 /* Treat two HOST_WIDE_INT's as a contiguous bitmap, with bit 0 being
51 the least significant. This function sets bit N in the bitmap. */
53 set_bit (unsigned HOST_WIDE_INT *low, unsigned HOST_WIDE_INT *high,
56 unsigned HOST_WIDE_INT *which;
58 if (n >= HOST_BITS_PER_WIDE_INT)
60 n -= HOST_BITS_PER_WIDE_INT;
66 *which |= (unsigned HOST_WIDE_INT) 1 << n;
69 /* Recursively mark reference fields. */
71 mark_reference_fields (tree field,
72 unsigned HOST_WIDE_INT *low,
73 unsigned HOST_WIDE_INT *high,
75 int *pointer_after_end,
78 HOST_WIDE_INT *last_view_index)
80 /* See if we have fields from our superclass. */
81 if (DECL_NAME (field) == NULL_TREE)
83 mark_reference_fields (TYPE_FIELDS (TREE_TYPE (field)),
85 pointer_after_end, all_bits_set,
86 last_set_index, last_view_index);
87 field = TREE_CHAIN (field);
90 for (; field != NULL_TREE; field = TREE_CHAIN (field))
93 HOST_WIDE_INT size_bytes;
95 if (FIELD_STATIC (field))
98 offset = int_byte_position (field);
99 size_bytes = int_size_in_bytes (TREE_TYPE (field));
100 if (JREFERENCE_TYPE_P (TREE_TYPE (field))
101 /* An `object' of type gnu.gcj.RawData is actually non-Java
103 && TREE_TYPE (field) != rawdata_ptr_type_node)
106 unsigned int size_words;
109 /* If this reference slot appears to overlay a slot we think
110 we already covered, then we are doomed. */
111 gcc_assert (offset > *last_view_index);
113 count = offset * BITS_PER_UNIT / POINTER_SIZE;
114 size_words = size_bytes * BITS_PER_UNIT / POINTER_SIZE;
116 *last_set_index = count;
118 /* First word in object corresponds to most significant byte of
121 In the case of a multiple-word record, we set pointer
122 bits for all words in the record. This is conservative, but the
123 size_words != 1 case is impossible in regular java code. */
124 for (i = 0; i < size_words; ++i)
125 set_bit (low, high, ubit - count - i - 1);
127 if (count >= ubit - 2)
128 *pointer_after_end = 1;
130 /* If we saw a non-reference field earlier, then we can't
131 use the count representation. We keep track of that in
136 else if (*all_bits_set > 0)
139 *last_view_index = offset;
143 /* Return the marking bitmap for the class TYPE. For now this is a
144 single word describing the type. */
146 get_boehm_type_descriptor (tree type)
148 unsigned int count, log2_size, ubit;
150 int all_bits_set = 1;
151 int last_set_index = 0;
152 HOST_WIDE_INT last_view_index = -1;
153 int pointer_after_end = 0;
154 unsigned HOST_WIDE_INT low = 0, high = 0;
155 tree field, value, value_type;
157 /* If the GC wasn't requested, just use a null pointer. */
158 if (! flag_use_boehm_gc)
159 return null_pointer_node;
161 value_type = java_type_for_mode (ptr_mode, 1);
162 /* If we have a type of unknown size, use a proc. */
163 if (int_size_in_bytes (type) == -1)
164 goto procedure_object_descriptor;
166 bit = POINTER_SIZE / BITS_PER_UNIT;
167 /* The size of this node has to be known. And, we only support 32
168 and 64 bit targets, so we need to know that the log2 is one of
170 log2_size = exact_log2 (bit);
171 if (bit == -1 || (log2_size != 2 && log2_size != 3))
173 /* This means the GC isn't supported. We should probably
174 abort or give an error. Instead, for now, we just silently
176 return null_pointer_node;
178 bit *= BITS_PER_UNIT;
180 /* Warning avoidance. */
181 ubit = (unsigned int) bit;
183 if (type == class_type_node)
184 goto procedure_object_descriptor;
186 field = TYPE_FIELDS (type);
187 mark_reference_fields (field, &low, &high, ubit,
188 &pointer_after_end, &all_bits_set,
189 &last_set_index, &last_view_index);
191 /* If the object is all pointers, or if the part with pointers fits
192 in our bitmap, then we are ok. Otherwise we have to allocate it
194 if (all_bits_set != -1 || (pointer_after_end && flag_reduced_reflection))
196 /* In this case the initial part of the object is all reference
197 fields, and the end of the object is all non-reference
198 fields. We represent the mark as a count of the fields,
199 shifted. In the GC the computation looks something like
201 value = DS_LENGTH | WORDS_TO_BYTES (last_set_index + 1);
203 WORDS_TO_BYTES shifts by log2(bytes-per-pointer).
205 In the case of flag_reduced_reflection and the bitmap would
206 overflow, we tell the gc that the object is all pointers so
207 that we don't have to emit reflection data for run time
213 while (last_set_index)
215 if ((last_set_index & 1))
216 set_bit (&low, &high, log2_size + count);
217 last_set_index >>= 1;
220 value = build_int_cst_wide (value_type, low, high);
222 else if (! pointer_after_end)
224 /* Bottom two bits for bitmap mark type are 01. */
225 set_bit (&low, &high, 0);
226 value = build_int_cst_wide (value_type, low, high);
230 procedure_object_descriptor:
231 value = build_int_cst (value_type, PROCEDURE_OBJECT_DESCRIPTOR);
237 /* The fourth (index of 3) element in the vtable is the GC descriptor.
238 A value of 2 indicates that the class uses _Jv_MarkObj. */
240 uses_jv_markobj_p (tree dtable)
243 /* FIXME: what do we return if !flag_use_boehm_gc ? */
244 gcc_assert (flag_use_boehm_gc);
245 /* FIXME: this is wrong if TARGET_VTABLE_USES_DESCRIPTORS. However,
246 this function is only used with flag_reduced_reflection. No
247 point in asserting unless we hit the bad case. */
248 gcc_assert (!flag_reduced_reflection || TARGET_VTABLE_USES_DESCRIPTORS == 0);
249 v = VEC_index (constructor_elt, CONSTRUCTOR_ELTS (dtable), 3)->value;
250 return (PROCEDURE_OBJECT_DESCRIPTOR == TREE_INT_CST_LOW (v));