1 /* Simple garbage collection for the GNU compiler.
2 Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003
3 Free Software Foundation, Inc.
5 This file is part of GCC.
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)
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.
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
24 #include "coretypes.h"
36 /* Debugging flags. */
38 /* Zap memory before freeing to catch dangling pointers. */
41 /* Collect statistics on how bushy the search tree is. */
44 /* Always verify that the to-be-marked memory is collectable. */
45 #undef GGC_ALWAYS_VERIFY
47 #ifdef ENABLE_GC_CHECKING
49 #define GGC_ALWAYS_VERIFY
52 #ifndef HOST_BITS_PER_PTR
53 #define HOST_BITS_PER_PTR HOST_BITS_PER_LONG
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.
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.
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
71 #define PTR_KEY(p) ((size_t)p << (HOST_BITS_PER_PTR - 8) \
72 | ((size_t)p & 0xff00) << (HOST_BITS_PER_PTR - 24) \
75 /* GC'able memory; a node in a binary search tree. */
79 /* A combination of the standard left/right nodes, indexable by `<'. */
80 struct ggc_mem *sub[2];
82 unsigned int mark : 1;
83 unsigned int context : 7;
84 unsigned int size : 24;
86 /* Make sure the data is reasonably aligned. */
89 #ifdef HAVE_LONG_DOUBLE
99 /* Root of the object tree. */
100 struct ggc_mem *root;
102 /* Data bytes currently allocated. */
105 /* Data objects currently allocated. */
108 /* Data bytes allocated at time of last GC. */
109 size_t allocated_last_gc;
111 /* Current context level. */
115 /* Local function prototypes. */
117 static void tree_insert (struct ggc_mem *);
118 static int tree_lookup (struct ggc_mem *);
119 static void clear_marks (struct ggc_mem *);
120 static void sweep_objs (struct ggc_mem **);
121 static void ggc_pop_context_1 (struct ggc_mem *, int);
123 /* For use from debugger. */
124 extern void debug_ggc_tree (struct ggc_mem *, int);
127 extern void debug_ggc_balance (void);
129 static void tally_leaves (struct ggc_mem *, int, size_t *, size_t *);
131 /* Insert V into the search tree. */
134 tree_insert (struct ggc_mem *v)
136 size_t v_key = PTR_KEY (v);
137 struct ggc_mem *p, **pp;
139 for (pp = &G.root, p = *pp; p ; p = *pp)
141 size_t p_key = PTR_KEY (p);
142 pp = &p->sub[v_key < p_key];
147 /* Return true if V is in the tree. */
150 tree_lookup (struct ggc_mem *v)
152 size_t v_key = PTR_KEY (v);
153 struct ggc_mem *p = G.root;
157 size_t p_key = PTR_KEY (p);
160 p = p->sub[v_key < p_key];
166 /* Alloc SIZE bytes of GC'able memory. If ZERO, clear the memory. */
169 ggc_alloc (size_t size)
173 x = (struct ggc_mem *) xmalloc (offsetof (struct ggc_mem, u) + size);
177 x->context = G.context;
181 memset (&x->u, 0xaf, size);
194 ggc_set_mark (const void *p)
198 x = (struct ggc_mem *) ((const char *)p - offsetof (struct ggc_mem, u));
199 #ifdef GGC_ALWAYS_VERIFY
200 if (! tree_lookup (x))
208 G.allocated += x->size;
214 /* Return 1 if P has been marked, zero otherwise. */
217 ggc_marked_p (const void *p)
221 x = (struct ggc_mem *) ((const char *)p - offsetof (struct ggc_mem, u));
222 #ifdef GGC_ALWAYS_VERIFY
223 if (! tree_lookup (x))
230 /* Return the size of the gc-able object P. */
233 ggc_get_size (const void *p)
236 = (struct ggc_mem *) ((const char *)p - offsetof (struct ggc_mem, u));
240 /* Unmark all objects. */
243 clear_marks (struct ggc_mem *x)
247 clear_marks (x->sub[0]);
249 clear_marks (x->sub[1]);
252 /* Free all objects in the current context that are not marked. */
255 sweep_objs (struct ggc_mem **root)
257 struct ggc_mem *x = *root;
261 sweep_objs (&x->sub[0]);
262 sweep_objs (&x->sub[1]);
264 if (! x->mark && x->context >= G.context)
266 struct ggc_mem *l, *r;
289 } while ((l = *root) != NULL);
294 memset (&x->u, 0xA5, x->size);
301 /* The top level mark-and-sweep routine. */
306 /* Avoid frequent unnecessary work by skipping collection if the
307 total allocations haven't expanded much since the last
309 size_t allocated_last_gc =
310 MAX (G.allocated_last_gc, (size_t)PARAM_VALUE (GGC_MIN_HEAPSIZE) * 1024);
312 size_t min_expand = allocated_last_gc * PARAM_VALUE (GGC_MIN_EXPAND) / 100;
314 if (G.allocated < allocated_last_gc + min_expand)
318 debug_ggc_balance ();
321 timevar_push (TV_GC);
323 fprintf (stderr, " {GC %luk -> ", (unsigned long)G.allocated / 1024);
328 clear_marks (G.root);
330 sweep_objs (&G.root);
332 G.allocated_last_gc = G.allocated;
337 fprintf (stderr, "%luk}", (unsigned long) G.allocated / 1024);
340 debug_ggc_balance ();
344 /* Called once to initialize the garbage collector. */
351 /* Start a new GGC context. Memory allocated in previous contexts
352 will not be collected while the new context is active. */
355 ggc_push_context (void)
359 /* We only allocated 7 bits in the node for the context. This
360 should be more than enough. */
361 if (G.context >= 128)
365 /* Finish a GC context. Any uncollected memory in the new context
366 will be merged with the old context. */
369 ggc_pop_context (void)
373 ggc_pop_context_1 (G.root, G.context);
377 ggc_pop_context_1 (struct ggc_mem *x, int c)
382 ggc_pop_context_1 (x->sub[0], c);
384 ggc_pop_context_1 (x->sub[1], c);
390 debug_ggc_tree (struct ggc_mem *p, int indent)
396 fputs ("(nil)\n", stderr);
401 debug_ggc_tree (p->sub[0], indent + 1);
403 for (i = 0; i < indent; ++i)
405 fprintf (stderr, "%lx %p\n", (unsigned long)PTR_KEY (p), (void *) p);
408 debug_ggc_tree (p->sub[1], indent + 1);
412 /* Collect tree balance metrics */
417 debug_ggc_balance (void)
419 size_t nleaf, sumdepth;
421 nleaf = sumdepth = 0;
422 tally_leaves (G.root, 0, &nleaf, &sumdepth);
424 fprintf (stderr, " {B %.2f,%.1f,%.1f}",
425 /* In a balanced tree, leaf/node should approach 1/2. */
426 (float)nleaf / (float)G.objects,
427 /* In a balanced tree, average leaf depth should approach lg(n). */
428 (float)sumdepth / (float)nleaf,
429 log ((double) G.objects) / M_LN2);
433 /* Used by debug_ggc_balance, and also by ggc_print_statistics. */
435 tally_leaves (struct ggc_mem *x, int depth, size_t *nleaf, size_t *sumdepth)
437 if (! x->sub[0] && !x->sub[1])
445 tally_leaves (x->sub[0], depth + 1, nleaf, sumdepth);
447 tally_leaves (x->sub[1], depth + 1, nleaf, sumdepth);
451 #define SCALE(x) ((unsigned long) ((x) < 1024*10 \
453 : ((x) < 1024*1024*10 \
455 : (x) / (1024*1024))))
456 #define LABEL(x) ((x) < 1024*10 ? ' ' : ((x) < 1024*1024*10 ? 'k' : 'M'))
458 /* Report on GC memory usage. */
460 ggc_print_statistics (void)
462 struct ggc_statistics stats;
463 size_t nleaf = 0, sumdepth = 0;
465 /* Clear the statistics. */
466 memset (&stats, 0, sizeof (stats));
468 /* Make sure collection will really occur. */
469 G.allocated_last_gc = 0;
471 /* Collect and print the statistics common across collectors. */
472 ggc_print_common_statistics (stderr, &stats);
474 /* Report on tree balancing. */
475 tally_leaves (G.root, 0, &nleaf, &sumdepth);
477 fprintf (stderr, "\n\
478 Total internal data (bytes)\t%ld%c\n\
479 Number of leaves in tree\t%lu\n\
480 Average leaf depth\t\t%.1f\n",
481 SCALE(G.objects * offsetof (struct ggc_mem, u)),
482 LABEL(G.objects * offsetof (struct ggc_mem, u)),
483 (unsigned long)nleaf, (double)sumdepth / (double)nleaf);
485 /* Report overall memory usage. */
486 fprintf (stderr, "\n\
487 Total objects allocated\t\t%ld\n\
488 Total memory in GC arena\t%ld%c\n",
489 (unsigned long)G.objects,
490 SCALE(G.allocated), LABEL(G.allocated));
493 struct ggc_pch_data *
496 sorry ("Generating PCH files is not supported when using ggc-simple.c");
497 /* It could be supported, but the code is not yet written. */
502 ggc_pch_count_object (struct ggc_pch_data *d ATTRIBUTE_UNUSED,
503 void *x ATTRIBUTE_UNUSED,
504 size_t size ATTRIBUTE_UNUSED)
509 ggc_pch_total_size (struct ggc_pch_data *d ATTRIBUTE_UNUSED)
515 ggc_pch_this_base (struct ggc_pch_data *d ATTRIBUTE_UNUSED,
516 void *base ATTRIBUTE_UNUSED)
522 ggc_pch_alloc_object (struct ggc_pch_data *d ATTRIBUTE_UNUSED,
523 void *x ATTRIBUTE_UNUSED,
524 size_t size ATTRIBUTE_UNUSED)
530 ggc_pch_prepare_write (struct ggc_pch_data *d ATTRIBUTE_UNUSED,
531 FILE * f ATTRIBUTE_UNUSED)
536 ggc_pch_write_object (struct ggc_pch_data *d ATTRIBUTE_UNUSED,
537 FILE *f ATTRIBUTE_UNUSED, void *x ATTRIBUTE_UNUSED,
538 void *newx ATTRIBUTE_UNUSED,
539 size_t size ATTRIBUTE_UNUSED)
544 ggc_pch_finish (struct ggc_pch_data *d ATTRIBUTE_UNUSED,
545 FILE *f ATTRIBUTE_UNUSED)
550 ggc_pch_read (FILE *f ATTRIBUTE_UNUSED, void *addr ATTRIBUTE_UNUSED)
552 /* This should be impossible, since we won't generate any valid PCH
553 files for this configuration. */