gcc/java/boehm.c

   1 /* Functions related to the Boehm garbage collector.
   2    Copyright (C) 2000-2015 Free Software Foundation, Inc.
   3
   4 This file is part of GCC.
   5
   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)
   9 any later version.
  10
  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.
  15
  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/>.
  19
  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.  */
  23
  24 /* Written by Tom Tromey <tromey@cygnus.com>.  */
  25
  26 #include "config.h"
  27 #include "system.h"
  28 #include "coretypes.h"
  29 #include "tm.h"
  30 #include "alias.h"
  31 #include "symtab.h"
  32 #include "options.h"
  33 #include "tree.h"
  34 #include "java-tree.h"
  35 #include "parse.h"
  36 #include "diagnostic-core.h"
  37
  38 static void mark_reference_fields (tree, wide_int *, unsigned int,
  39                                    int *, int *, int *, HOST_WIDE_INT *);
  40
  41 /* A procedure-based object descriptor.  We know that our
  42    `kind' is 0, and `env' is likewise 0, so we have a simple
  43    computation.  From the GC sources:
  44    (((((env) << LOG_MAX_MARK_PROCS) | (proc_index)) << DS_TAG_BITS)     \
  45    | DS_PROC)
  46    Here DS_PROC == 2.  */
  47 #define PROCEDURE_OBJECT_DESCRIPTOR 2
  48
  49 /* Recursively mark reference fields.  */
  50 static void
  51 mark_reference_fields (tree field,
  52                        wide_int *mask,
  53                        unsigned int ubit,
  54                        int *pointer_after_end,
  55                        int *all_bits_set,
  56                        int *last_set_index,
  57                        HOST_WIDE_INT *last_view_index)
  58 {
  59   /* See if we have fields from our superclass.  */
  60   if (DECL_NAME (field) == NULL_TREE)
  61     {
  62       mark_reference_fields (TYPE_FIELDS (TREE_TYPE (field)),
  63                              mask, ubit,
  64                              pointer_after_end, all_bits_set,
  65                              last_set_index, last_view_index);
  66       field = DECL_CHAIN (field);
  67     }
  68
  69   for (; field != NULL_TREE; field = DECL_CHAIN (field))
  70     {
  71       HOST_WIDE_INT offset;
  72       HOST_WIDE_INT size_bytes;
  73
  74       if (FIELD_STATIC (field))
  75         continue;
  76
  77       offset = int_byte_position (field);
  78       size_bytes = int_size_in_bytes (TREE_TYPE (field));
  79
  80       if (JREFERENCE_TYPE_P (TREE_TYPE (field))
  81           /* An `object' of type gnu.gcj.RawData is actually non-Java
  82              data.  */
  83           && TREE_TYPE (field) != rawdata_ptr_type_node)
  84         {
  85           unsigned int count;
  86           unsigned int size_words;
  87           unsigned int i;
  88
  89           /* If this reference slot appears to overlay a slot we think
  90              we already covered, then we are doomed.  */
  91           gcc_assert (offset > *last_view_index);
  92
  93           if (offset % (HOST_WIDE_INT) (POINTER_SIZE / BITS_PER_UNIT))
  94             {
  95               *all_bits_set = -1;
  96               *pointer_after_end = 1;
  97               break;
  98             }
  99
 100           count = offset * BITS_PER_UNIT / POINTER_SIZE;
 101           size_words = size_bytes * BITS_PER_UNIT / POINTER_SIZE;
 102
 103           *last_set_index = count;
 104
 105           if (count >= ubit - 2)
 106             *pointer_after_end = 1;
 107           else
 108             /* First word in object corresponds to most significant byte of
 109                bitmap.
 110
 111                In the case of a multiple-word record, we set pointer
 112                bits for all words in the record. This is conservative, but the
 113                size_words != 1 case is impossible in regular java code. */
 114             for (i = 0; i < size_words; ++i)
 115               *mask = wi::set_bit (*mask, ubit - count - i - 1);
 116
 117           /* If we saw a non-reference field earlier, then we can't
 118              use the count representation.  We keep track of that in
 119              *ALL_BITS_SET.  */
 120           if (! *all_bits_set)
 121             *all_bits_set = -1;
 122         }
 123       else if (*all_bits_set > 0)
 124         *all_bits_set = 0;
 125
 126       *last_view_index = offset;
 127     }
 128 }
 129
 130 /* Return the marking bitmap for the class TYPE.  For now this is a
 131    single word describing the type.  */
 132 tree
 133 get_boehm_type_descriptor (tree type)
 134 {
 135   unsigned int count, log2_size, ubit;
 136   int bit;
 137   int all_bits_set = 1;
 138   int last_set_index = 0;
 139   HOST_WIDE_INT last_view_index = -1;
 140   int pointer_after_end = 0;
 141   tree field, value, value_type;
 142
 143   /* If the GC wasn't requested, just use a null pointer.  */
 144   if (! flag_use_boehm_gc)
 145     return null_pointer_node;
 146
 147   value_type = java_type_for_mode (ptr_mode, 1);
 148   wide_int mask = wi::zero (TYPE_PRECISION (value_type));
 149
 150   /* If we have a type of unknown size, use a proc.  */
 151   if (int_size_in_bytes (type) == -1)
 152     goto procedure_object_descriptor;
 153
 154   bit = POINTER_SIZE / BITS_PER_UNIT;
 155   /* The size of this node has to be known.  And, we only support 32
 156      and 64 bit targets, so we need to know that the log2 is one of
 157      our values.  */
 158   log2_size = exact_log2 (bit);
 159   if (bit == -1 || (log2_size != 2 && log2_size != 3))
 160     {
 161       /* This means the GC isn't supported.  We should probably
 162          abort or give an error.  Instead, for now, we just silently
 163          revert.  FIXME.  */
 164       return null_pointer_node;
 165     }
 166   bit *= BITS_PER_UNIT;
 167
 168   /* Warning avoidance.  */
 169   ubit = (unsigned int) bit;
 170
 171   if (type == class_type_node)
 172     goto procedure_object_descriptor;
 173
 174   field = TYPE_FIELDS (type);
 175   mark_reference_fields (field, &mask, ubit,
 176                          &pointer_after_end, &all_bits_set,
 177                          &last_set_index, &last_view_index);
 178
 179   /* If the object is all pointers, or if the part with pointers fits
 180      in our bitmap, then we are ok.  Otherwise we have to allocate it
 181      a different way.  */
 182   if (all_bits_set != -1 || (pointer_after_end && flag_reduced_reflection))
 183     {
 184       /* In this case the initial part of the object is all reference
 185          fields, and the end of the object is all non-reference
 186          fields.  We represent the mark as a count of the fields,
 187          shifted.  In the GC the computation looks something like
 188          this:
 189          value = DS_LENGTH | WORDS_TO_BYTES (last_set_index + 1);
 190          DS_LENGTH is 0.
 191          WORDS_TO_BYTES shifts by log2(bytes-per-pointer).
 192
 193          In the case of flag_reduced_reflection and the bitmap would
 194          overflow, we tell the gc that the object is all pointers so
 195          that we don't have to emit reflection data for run time
 196          marking. */
 197       count = 0;
 198       mask = wi::zero (TYPE_PRECISION (value_type));
 199       ++last_set_index;
 200       while (last_set_index)
 201         {
 202           if ((last_set_index & 1))
 203             mask = wi::set_bit (mask, log2_size + count);
 204           last_set_index >>= 1;
 205           ++count;
 206         }
 207       value = wide_int_to_tree (value_type, mask);
 208     }
 209   else if (! pointer_after_end)
 210     {
 211       /* Bottom two bits for bitmap mark type are 01.  */
 212       mask = wi::set_bit (mask, 0);
 213       value = wide_int_to_tree (value_type, mask);
 214     }
 215   else
 216     {
 217     procedure_object_descriptor:
 218       value = build_int_cst (value_type, PROCEDURE_OBJECT_DESCRIPTOR);
 219     }
 220
 221   return value;
 222 }
 223
 224 /* The fourth (index of 3) element in the vtable is the GC descriptor.
 225    A value of 2 indicates that the class uses _Jv_MarkObj. */
 226 bool
 227 uses_jv_markobj_p (tree dtable)
 228 {
 229   tree v;
 230   /* FIXME: what do we return if !flag_use_boehm_gc ? */
 231   gcc_assert (flag_use_boehm_gc);
 232   /* FIXME: this is wrong if TARGET_VTABLE_USES_DESCRIPTORS.  However,
 233      this function is only used with flag_reduced_reflection.  No
 234      point in asserting unless we hit the bad case.  */
 235   gcc_assert (!flag_reduced_reflection || TARGET_VTABLE_USES_DESCRIPTORS == 0);
 236   v = (*CONSTRUCTOR_ELTS (dtable))[3].value;
 237   return (PROCEDURE_OBJECT_DESCRIPTOR == TREE_INT_CST_LOW (v));
 238 }