gcc/ggc-simple.c

   1 /* Simple garbage collection for the GNU compiler.
   2    Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003
   3    Free Software Foundation, Inc.
   4
   5    This file is part of GCC.
   6
   7    GCC is free software; you can redistribute it and/or modify it
   8    under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 2, or (at your option)
  10    any later version.
  11
  12    GCC is distributed in the hope that it will be useful, but WITHOUT
  13    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  14    or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
  15    License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with GCC; see the file COPYING.  If not, write to the Free
  19    Software Foundation, 59 Temple Place - Suite 330, Boston, MA
  20    02111-1307, USA.  */
  21
  22 #include "config.h"
  23 #include "system.h"
  24 #include "coretypes.h"
  25 #include "tm.h"
  26 #include "rtl.h"
  27 #include "tree.h"
  28 #include "tm_p.h"
  29 #include "flags.h"
  30 #include "varray.h"
  31 #include "ggc.h"
  32 #include "toplev.h"
  33 #include "timevar.h"
  34 #include "params.h"
  35
  36 /* Debugging flags.  */
  37
  38 /* Zap memory before freeing to catch dangling pointers.  */
  39 #undef GGC_POISON
  40
  41 /* Collect statistics on how bushy the search tree is.  */
  42 #undef GGC_BALANCE
  43
  44 /* Always verify that the to-be-marked memory is collectable.  */
  45 #undef GGC_ALWAYS_VERIFY
  46
  47 #ifdef ENABLE_GC_CHECKING
  48 #define GGC_POISON
  49 #define GGC_ALWAYS_VERIFY
  50 #endif
  51
  52 #ifndef HOST_BITS_PER_PTR
  53 #define HOST_BITS_PER_PTR  HOST_BITS_PER_LONG
  54 #endif
  55
  56 /* We'd like a balanced tree, but we don't really want to pay for the
  57    cost of keeping the tree balanced.  We'll settle for the next best
  58    thing -- nearly balanced.
  59
  60    In this context, the most natural key is the node pointer itself,
  61    but due to the way memory managers work, we'd be virtually certain
  62    to wind up with a completely degenerate straight line.  What's needed
  63    is to make something more variable, and yet predictable, be more
  64    significant in the comparison.
  65
  66    The handiest source of variability is the low bits of the pointer
  67    value itself.  Any sort of bit/byte swap would do, but such machine
  68    specific operations are not handy, and we don't want to put that much
  69    effort into it.  */
  70
  71 #define PTR_KEY(p)      ((size_t)p << (HOST_BITS_PER_PTR - 8)               \
  72                          | ((size_t)p & 0xff00) << (HOST_BITS_PER_PTR - 24) \
  73                          | (size_t)p >> 16)
  74
  75 /* GC'able memory; a node in a binary search tree.  */
  76
  77 struct ggc_mem
  78 {
  79   /* A combination of the standard left/right nodes, indexable by `<'.  */
  80   struct ggc_mem *sub[2];
  81
  82   unsigned int mark : 1;
  83   unsigned int context : 7;
  84   unsigned int size : 24;
  85
  86   /* Make sure the data is reasonably aligned.  */
  87   union {
  88     HOST_WIDEST_INT i;
  89     long double d;
  90   } u;
  91 };
  92
  93 static struct globals
  94 {
  95   /* Root of the object tree.  */
  96   struct ggc_mem *root;
  97
  98   /* Data bytes currently allocated.  */
  99   size_t allocated;
 100
 101   /* Data objects currently allocated.  */
 102   size_t objects;
 103
 104   /* Data bytes allocated at time of last GC.  */
 105   size_t allocated_last_gc;
 106
 107   /* Current context level.  */
 108   int context;
 109 } G;
 110
 111 /* Local function prototypes.  */
 112
 113 static void tree_insert (struct ggc_mem *);
 114 static int tree_lookup (struct ggc_mem *);
 115 static void clear_marks (struct ggc_mem *);
 116 static void sweep_objs (struct ggc_mem **);
 117 static void ggc_pop_context_1 (struct ggc_mem *, int);
 118
 119 /* For use from debugger.  */
 120 extern void debug_ggc_tree (struct ggc_mem *, int);
 121
 122 #ifdef GGC_BALANCE
 123 extern void debug_ggc_balance (void);
 124 #endif
 125 static void tally_leaves (struct ggc_mem *, int, size_t *, size_t *);
 126
 127 /* Insert V into the search tree.  */
 128
 129 static inline void
 130 tree_insert (struct ggc_mem *v)
 131 {
 132   size_t v_key = PTR_KEY (v);
 133   struct ggc_mem *p, **pp;
 134
 135   for (pp = &G.root, p = *pp; p ; p = *pp)
 136     {
 137       size_t p_key = PTR_KEY (p);
 138       pp = &p->sub[v_key < p_key];
 139     }
 140   *pp = v;
 141 }
 142
 143 /* Return true if V is in the tree.  */
 144
 145 static inline int
 146 tree_lookup (struct ggc_mem *v)
 147 {
 148   size_t v_key = PTR_KEY (v);
 149   struct ggc_mem *p = G.root;
 150
 151   while (p)
 152     {
 153       size_t p_key = PTR_KEY (p);
 154       if (p == v)
 155         return 1;
 156       p = p->sub[v_key < p_key];
 157     }
 158
 159   return 0;
 160 }
 161
 162 /* Alloc SIZE bytes of GC'able memory.  If ZERO, clear the memory.  */
 163
 164 void *
 165 ggc_alloc (size_t size)
 166 {
 167   struct ggc_mem *x;
 168
 169   x = (struct ggc_mem *) xmalloc (offsetof (struct ggc_mem, u) + size);
 170   x->sub[0] = NULL;
 171   x->sub[1] = NULL;
 172   x->mark = 0;
 173   x->context = G.context;
 174   x->size = size;
 175
 176 #ifdef GGC_POISON
 177   memset (&x->u, 0xaf, size);
 178 #endif
 179
 180   tree_insert (x);
 181   G.allocated += size;
 182   G.objects += 1;
 183
 184   return &x->u;
 185 }
 186
 187 /* Mark a node.  */
 188
 189 int
 190 ggc_set_mark (const void *p)
 191 {
 192   struct ggc_mem *x;
 193
 194   x = (struct ggc_mem *) ((const char *)p - offsetof (struct ggc_mem, u));
 195 #ifdef GGC_ALWAYS_VERIFY
 196   if (! tree_lookup (x))
 197     abort ();
 198 #endif
 199
 200   if (x->mark)
 201     return 1;
 202
 203   x->mark = 1;
 204   G.allocated += x->size;
 205   G.objects += 1;
 206
 207   return 0;
 208 }
 209
 210 /* Return 1 if P has been marked, zero otherwise.  */
 211
 212 int
 213 ggc_marked_p (const void *p)
 214 {
 215   struct ggc_mem *x;
 216
 217   x = (struct ggc_mem *) ((const char *)p - offsetof (struct ggc_mem, u));
 218 #ifdef GGC_ALWAYS_VERIFY
 219   if (! tree_lookup (x))
 220     abort ();
 221 #endif
 222
 223    return x->mark;
 224 }
 225
 226 /* Return the size of the gc-able object P.  */
 227
 228 size_t
 229 ggc_get_size (const void *p)
 230 {
 231   struct ggc_mem *x
 232     = (struct ggc_mem *) ((const char *)p - offsetof (struct ggc_mem, u));
 233   return x->size;
 234 }
 235
 236 /* Unmark all objects.  */
 237
 238 static void
 239 clear_marks (struct ggc_mem *x)
 240 {
 241   x->mark = 0;
 242   if (x->sub[0])
 243     clear_marks (x->sub[0]);
 244   if (x->sub[1])
 245     clear_marks (x->sub[1]);
 246 }
 247
 248 /* Free all objects in the current context that are not marked.  */
 249
 250 static void
 251 sweep_objs (struct ggc_mem **root)
 252 {
 253   struct ggc_mem *x = *root;
 254   if (!x)
 255     return;
 256
 257   sweep_objs (&x->sub[0]);
 258   sweep_objs (&x->sub[1]);
 259
 260   if (! x->mark && x->context >= G.context)
 261     {
 262       struct ggc_mem *l, *r;
 263
 264       l = x->sub[0];
 265       r = x->sub[1];
 266       if (!l)
 267         *root = r;
 268       else if (!r)
 269         *root = l;
 270       else if (!l->sub[1])
 271         {
 272           *root = l;
 273           l->sub[1] = r;
 274         }
 275       else if (!r->sub[0])
 276         {
 277           *root = r;
 278           r->sub[0] = l;
 279         }
 280       else
 281         {
 282           *root = l;
 283           do {
 284             root = &l->sub[1];
 285           } while ((l = *root) != NULL);
 286           *root = r;
 287         }
 288
 289 #ifdef GGC_POISON
 290       memset (&x->u, 0xA5, x->size);
 291 #endif
 292
 293       free (x);
 294     }
 295 }
 296
 297 /* The top level mark-and-sweep routine.  */
 298
 299 void
 300 ggc_collect (void)
 301 {
 302   /* Avoid frequent unnecessary work by skipping collection if the
 303      total allocations haven't expanded much since the last
 304      collection.  */
 305   size_t allocated_last_gc =
 306     MAX (G.allocated_last_gc, (size_t)PARAM_VALUE (GGC_MIN_HEAPSIZE) * 1024);
 307
 308   size_t min_expand = allocated_last_gc * PARAM_VALUE (GGC_MIN_EXPAND) / 100;
 309
 310   if (G.allocated < allocated_last_gc + min_expand)
 311     return;
 312
 313 #ifdef GGC_BALANCE
 314   debug_ggc_balance ();
 315 #endif
 316
 317   timevar_push (TV_GC);
 318   if (!quiet_flag)
 319     fprintf (stderr, " {GC %luk -> ", (unsigned long)G.allocated / 1024);
 320
 321   G.allocated = 0;
 322   G.objects = 0;
 323
 324   clear_marks (G.root);
 325   ggc_mark_roots ();
 326   sweep_objs (&G.root);
 327
 328   G.allocated_last_gc = G.allocated;
 329
 330   timevar_pop (TV_GC);
 331
 332   if (!quiet_flag)
 333     fprintf (stderr, "%luk}", (unsigned long) G.allocated / 1024);
 334
 335 #ifdef GGC_BALANCE
 336   debug_ggc_balance ();
 337 #endif
 338 }
 339
 340 /* Called once to initialize the garbage collector.  */
 341
 342 void
 343 init_ggc (void)
 344 {
 345 }
 346
 347 /* Start a new GGC context.  Memory allocated in previous contexts
 348    will not be collected while the new context is active.  */
 349
 350 void
 351 ggc_push_context (void)
 352 {
 353   G.context++;
 354
 355   /* We only allocated 7 bits in the node for the context.  This
 356      should be more than enough.  */
 357   if (G.context >= 128)
 358     abort ();
 359 }
 360
 361 /* Finish a GC context.  Any uncollected memory in the new context
 362    will be merged with the old context.  */
 363
 364 void
 365 ggc_pop_context (void)
 366 {
 367   G.context--;
 368   if (G.root)
 369     ggc_pop_context_1 (G.root, G.context);
 370 }
 371
 372 static void
 373 ggc_pop_context_1 (struct ggc_mem *x, int c)
 374 {
 375   if (x->context > c)
 376     x->context = c;
 377   if (x->sub[0])
 378     ggc_pop_context_1 (x->sub[0], c);
 379   if (x->sub[1])
 380     ggc_pop_context_1 (x->sub[1], c);
 381 }
 382
 383 /* Dump a tree.  */
 384
 385 void
 386 debug_ggc_tree (struct ggc_mem *p, int indent)
 387 {
 388   int i;
 389
 390   if (!p)
 391     {
 392       fputs ("(nil)\n", stderr);
 393       return;
 394     }
 395
 396   if (p->sub[0])
 397     debug_ggc_tree (p->sub[0], indent + 1);
 398
 399   for (i = 0; i < indent; ++i)
 400     putc (' ', stderr);
 401   fprintf (stderr, "%lx %p\n", (unsigned long)PTR_KEY (p), (void *) p);
 402
 403   if (p->sub[1])
 404     debug_ggc_tree (p->sub[1], indent + 1);
 405 }
 406
 407 #ifdef GGC_BALANCE
 408 /* Collect tree balance metrics  */
 409
 410 #include <math.h>
 411
 412 void
 413 debug_ggc_balance (void)
 414 {
 415   size_t nleaf, sumdepth;
 416
 417   nleaf = sumdepth = 0;
 418   tally_leaves (G.root, 0, &nleaf, &sumdepth);
 419
 420   fprintf (stderr, " {B %.2f,%.1f,%.1f}",
 421            /* In a balanced tree, leaf/node should approach 1/2.  */
 422            (float)nleaf / (float)G.objects,
 423            /* In a balanced tree, average leaf depth should approach lg(n).  */
 424            (float)sumdepth / (float)nleaf,
 425            log ((double) G.objects) / M_LN2);
 426 }
 427 #endif
 428
 429 /* Used by debug_ggc_balance, and also by ggc_print_statistics.  */
 430 static void
 431 tally_leaves (struct ggc_mem *x, int depth, size_t *nleaf, size_t *sumdepth)
 432 {
 433   if (! x->sub[0] && !x->sub[1])
 434     {
 435       *nleaf += 1;
 436       *sumdepth += depth;
 437     }
 438   else
 439     {
 440       if (x->sub[0])
 441         tally_leaves (x->sub[0], depth + 1, nleaf, sumdepth);
 442       if (x->sub[1])
 443         tally_leaves (x->sub[1], depth + 1, nleaf, sumdepth);
 444     }
 445 }
 446
 447 #define SCALE(x) ((unsigned long) ((x) < 1024*10 \
 448                   ? (x) \
 449                   : ((x) < 1024*1024*10 \
 450                      ? (x) / 1024 \
 451                      : (x) / (1024*1024))))
 452 #define LABEL(x) ((x) < 1024*10 ? ' ' : ((x) < 1024*1024*10 ? 'k' : 'M'))
 453
 454 /* Report on GC memory usage.  */
 455 void
 456 ggc_print_statistics (void)
 457 {
 458   struct ggc_statistics stats;
 459   size_t nleaf = 0, sumdepth = 0;
 460
 461   /* Clear the statistics.  */
 462   memset (&stats, 0, sizeof (stats));
 463
 464   /* Make sure collection will really occur.  */
 465   G.allocated_last_gc = 0;
 466
 467   /* Collect and print the statistics common across collectors.  */
 468   ggc_print_common_statistics (stderr, &stats);
 469
 470   /* Report on tree balancing.  */
 471   tally_leaves (G.root, 0, &nleaf, &sumdepth);
 472
 473   fprintf (stderr, "\n\
 474 Total internal data (bytes)\t%ld%c\n\
 475 Number of leaves in tree\t%lu\n\
 476 Average leaf depth\t\t%.1f\n",
 477            SCALE(G.objects * offsetof (struct ggc_mem, u)),
 478            LABEL(G.objects * offsetof (struct ggc_mem, u)),
 479            (unsigned long)nleaf, (double)sumdepth / (double)nleaf);
 480
 481   /* Report overall memory usage.  */
 482   fprintf (stderr, "\n\
 483 Total objects allocated\t\t%ld\n\
 484 Total memory in GC arena\t%ld%c\n",
 485            (unsigned long)G.objects,
 486            SCALE(G.allocated), LABEL(G.allocated));
 487 }
 488 \f
 489 struct ggc_pch_data *
 490 init_ggc_pch (void)
 491 {
 492   sorry ("Generating PCH files is not supported when using ggc-simple.c");
 493   /* It could be supported, but the code is not yet written.  */
 494   return NULL;
 495 }
 496
 497 void
 498 ggc_pch_count_object (struct ggc_pch_data *d ATTRIBUTE_UNUSED,
 499                       void *x ATTRIBUTE_UNUSED,
 500                       size_t size ATTRIBUTE_UNUSED)
 501 {
 502 }
 503
 504 size_t
 505 ggc_pch_total_size (struct ggc_pch_data *d ATTRIBUTE_UNUSED)
 506 {
 507   return 0;
 508 }
 509
 510 void
 511 ggc_pch_this_base (struct ggc_pch_data *d ATTRIBUTE_UNUSED,
 512                    void *base ATTRIBUTE_UNUSED)
 513 {
 514 }
 515
 516
 517 char *
 518 ggc_pch_alloc_object (struct ggc_pch_data *d ATTRIBUTE_UNUSED,
 519                       void *x ATTRIBUTE_UNUSED,
 520                       size_t size ATTRIBUTE_UNUSED)
 521 {
 522   return NULL;
 523 }
 524
 525 void
 526 ggc_pch_prepare_write (struct ggc_pch_data *d ATTRIBUTE_UNUSED,
 527                        FILE * f ATTRIBUTE_UNUSED)
 528 {
 529 }
 530
 531 void
 532 ggc_pch_write_object (struct ggc_pch_data *d ATTRIBUTE_UNUSED,
 533                       FILE *f ATTRIBUTE_UNUSED, void *x ATTRIBUTE_UNUSED,
 534                       void *newx ATTRIBUTE_UNUSED,
 535                       size_t size ATTRIBUTE_UNUSED)
 536 {
 537 }
 538
 539 void
 540 ggc_pch_finish (struct ggc_pch_data *d ATTRIBUTE_UNUSED,
 541                 FILE *f ATTRIBUTE_UNUSED)
 542 {
 543 }
 544
 545 void
 546 ggc_pch_read (FILE *f ATTRIBUTE_UNUSED, void *addr ATTRIBUTE_UNUSED)
 547 {
 548   /* This should be impossible, since we won't generate any valid PCH
 549      files for this configuration.  */
 550   abort ();
 551 }