xref: /openbsd-src/gnu/usr.bin/gcc/gcc/ggc-simple.c (revision c87b03e512fc05ed6e0222f6fb0ae86264b1d05b)
1 /* Simple garbage collection for the GNU compiler.
2    Copyright (C) 1998, 1999, 2000, 2001 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 it
7    under the terms of the GNU General Public License as published by
8    the Free Software Foundation; either version 2, or (at your option)
9    any later version.
10 
11    GCC is distributed in the hope that it will be useful, but WITHOUT
12    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
13    or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
14    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 COPYING.  If not, write to the Free
18    Software Foundation, 59 Temple Place - Suite 330, Boston, MA
19    02111-1307, USA.  */
20 
21 #include "config.h"
22 #include "system.h"
23 #include "rtl.h"
24 #include "tree.h"
25 #include "tm_p.h"
26 #include "flags.h"
27 #include "varray.h"
28 #include "ggc.h"
29 #include "timevar.h"
30 #include "params.h"
31 
32 /* Debugging flags.  */
33 
34 /* Zap memory before freeing to catch dangling pointers.  */
35 #undef GGC_POISON
36 
37 /* Collect statistics on how bushy the search tree is.  */
38 #undef GGC_BALANCE
39 
40 /* Always verify that the to-be-marked memory is collectable.  */
41 #undef GGC_ALWAYS_VERIFY
42 
43 #ifdef ENABLE_GC_CHECKING
44 #define GGC_POISON
45 #define GGC_ALWAYS_VERIFY
46 #endif
47 
48 #ifndef HOST_BITS_PER_PTR
49 #define HOST_BITS_PER_PTR  HOST_BITS_PER_LONG
50 #endif
51 
52 /* We'd like a balanced tree, but we don't really want to pay for the
53    cost of keeping the tree balanced.  We'll settle for the next best
54    thing -- nearly balanced.
55 
56    In this context, the most natural key is the node pointer itself,
57    but due to the way memory managers work, we'd be virtually certain
58    to wind up with a completely degenerate straight line.  What's needed
59    is to make something more variable, and yet predictable, be more
60    significant in the comparison.
61 
62    The handiest source of variability is the low bits of the pointer
63    value itself.  Any sort of bit/byte swap would do, but such machine
64    specific operations are not handy, and we don't want to put that much
65    effort into it.  */
66 
67 #define PTR_KEY(p)	((size_t)p << (HOST_BITS_PER_PTR - 8)		    \
68 			 | ((size_t)p & 0xff00) << (HOST_BITS_PER_PTR - 24) \
69 			 | (size_t)p >> 16)
70 
71 /* GC'able memory; a node in a binary search tree.  */
72 
73 struct ggc_mem
74 {
75   /* A combination of the standard left/right nodes, indexable by `<'.  */
76   struct ggc_mem *sub[2];
77 
78   unsigned int mark : 1;
79   unsigned int context : 7;
80   unsigned int size : 24;
81 
82   /* Make sure the data is reasonably aligned.  */
83   union {
84     HOST_WIDEST_INT i;
85 #ifdef HAVE_LONG_DOUBLE
86     long double d;
87 #else
88     double d;
89 #endif
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 PARAMS ((struct ggc_mem *));
114 static int tree_lookup PARAMS ((struct ggc_mem *));
115 static void clear_marks PARAMS ((struct ggc_mem *));
116 static void sweep_objs PARAMS ((struct ggc_mem **));
117 static void ggc_pop_context_1 PARAMS ((struct ggc_mem *, int));
118 
119 /* For use from debugger.  */
120 extern void debug_ggc_tree PARAMS ((struct ggc_mem *, int));
121 
122 #ifdef GGC_BALANCE
123 extern void debug_ggc_balance PARAMS ((void));
124 #endif
125 static void tally_leaves PARAMS ((struct ggc_mem *, int, size_t *, size_t *));
126 
127 /* Insert V into the search tree.  */
128 
129 static inline void
tree_insert(v)130 tree_insert (v)
131      struct ggc_mem *v;
132 {
133   size_t v_key = PTR_KEY (v);
134   struct ggc_mem *p, **pp;
135 
136   for (pp = &G.root, p = *pp; p ; p = *pp)
137     {
138       size_t p_key = PTR_KEY (p);
139       pp = &p->sub[v_key < p_key];
140     }
141   *pp = v;
142 }
143 
144 /* Return true if V is in the tree.  */
145 
146 static inline int
tree_lookup(v)147 tree_lookup (v)
148      struct ggc_mem *v;
149 {
150   size_t v_key = PTR_KEY (v);
151   struct ggc_mem *p = G.root;
152 
153   while (p)
154     {
155       size_t p_key = PTR_KEY (p);
156       if (p == v)
157 	return 1;
158       p = p->sub[v_key < p_key];
159     }
160 
161   return 0;
162 }
163 
164 /* Alloc SIZE bytes of GC'able memory.  If ZERO, clear the memory.  */
165 
166 void *
ggc_alloc(size)167 ggc_alloc (size)
168      size_t size;
169 {
170   struct ggc_mem *x;
171 
172   x = (struct ggc_mem *) xmalloc (offsetof (struct ggc_mem, u) + size);
173   x->sub[0] = NULL;
174   x->sub[1] = NULL;
175   x->mark = 0;
176   x->context = G.context;
177   x->size = size;
178 
179 #ifdef GGC_POISON
180   memset (&x->u, 0xaf, size);
181 #endif
182 
183   tree_insert (x);
184   G.allocated += size;
185   G.objects += 1;
186 
187   return &x->u;
188 }
189 
190 /* Mark a node.  */
191 
192 int
ggc_set_mark(p)193 ggc_set_mark (p)
194      const void *p;
195 {
196   struct ggc_mem *x;
197 
198   x = (struct ggc_mem *) ((const char *)p - offsetof (struct ggc_mem, u));
199 #ifdef GGC_ALWAYS_VERIFY
200   if (! tree_lookup (x))
201     abort ();
202 #endif
203 
204   if (x->mark)
205     return 1;
206 
207   x->mark = 1;
208   G.allocated += x->size;
209   G.objects += 1;
210 
211   return 0;
212 }
213 
214 /* Return 1 if P has been marked, zero otherwise.  */
215 
216 int
ggc_marked_p(p)217 ggc_marked_p (p)
218      const void *p;
219 {
220   struct ggc_mem *x;
221 
222   x = (struct ggc_mem *) ((const char *)p - offsetof (struct ggc_mem, u));
223 #ifdef GGC_ALWAYS_VERIFY
224   if (! tree_lookup (x))
225     abort ();
226 #endif
227 
228    return x->mark;
229 }
230 
231 /* Return the size of the gc-able object P.  */
232 
233 size_t
ggc_get_size(p)234 ggc_get_size (p)
235      const void *p;
236 {
237   struct ggc_mem *x
238     = (struct ggc_mem *) ((const char *)p - offsetof (struct ggc_mem, u));
239   return x->size;
240 }
241 
242 /* Unmark all objects.  */
243 
244 static void
clear_marks(x)245 clear_marks (x)
246      struct ggc_mem *x;
247 {
248   x->mark = 0;
249   if (x->sub[0])
250     clear_marks (x->sub[0]);
251   if (x->sub[1])
252     clear_marks (x->sub[1]);
253 }
254 
255 /* Free all objects in the current context that are not marked.  */
256 
257 static void
sweep_objs(root)258 sweep_objs (root)
259      struct ggc_mem **root;
260 {
261   struct ggc_mem *x = *root;
262   if (!x)
263     return;
264 
265   sweep_objs (&x->sub[0]);
266   sweep_objs (&x->sub[1]);
267 
268   if (! x->mark && x->context >= G.context)
269     {
270       struct ggc_mem *l, *r;
271 
272       l = x->sub[0];
273       r = x->sub[1];
274       if (!l)
275 	*root = r;
276       else if (!r)
277 	*root = l;
278       else if (!l->sub[1])
279 	{
280 	  *root = l;
281 	  l->sub[1] = r;
282 	}
283       else if (!r->sub[0])
284 	{
285 	  *root = r;
286 	  r->sub[0] = l;
287 	}
288       else
289 	{
290 	  *root = l;
291 	  do {
292 	    root = &l->sub[1];
293 	  } while ((l = *root) != NULL);
294 	  *root = r;
295 	}
296 
297 #ifdef GGC_POISON
298       memset (&x->u, 0xA5, x->size);
299 #endif
300 
301       free (x);
302     }
303 }
304 
305 /* The top level mark-and-sweep routine.  */
306 
307 void
ggc_collect()308 ggc_collect ()
309 {
310   /* Avoid frequent unnecessary work by skipping collection if the
311      total allocations haven't expanded much since the last
312      collection.  */
313   size_t allocated_last_gc =
314     MAX (G.allocated_last_gc, (size_t)PARAM_VALUE (GGC_MIN_HEAPSIZE) * 1024);
315 
316   size_t min_expand = allocated_last_gc * PARAM_VALUE (GGC_MIN_EXPAND) / 100;
317 
318   if (G.allocated < allocated_last_gc + min_expand)
319     return;
320 
321 #ifdef GGC_BALANCE
322   debug_ggc_balance ();
323 #endif
324 
325   timevar_push (TV_GC);
326   if (!quiet_flag)
327     fprintf (stderr, " {GC %luk -> ", (unsigned long)G.allocated / 1024);
328 
329   G.allocated = 0;
330   G.objects = 0;
331 
332   clear_marks (G.root);
333   ggc_mark_roots ();
334   sweep_objs (&G.root);
335 
336   G.allocated_last_gc = G.allocated;
337 
338   timevar_pop (TV_GC);
339 
340   if (!quiet_flag)
341     fprintf (stderr, "%luk}", (unsigned long) G.allocated / 1024);
342 
343 #ifdef GGC_BALANCE
344   debug_ggc_balance ();
345 #endif
346 }
347 
348 /* Called once to initialize the garbage collector.  */
349 
350 void
init_ggc()351 init_ggc ()
352 {
353 }
354 
355 /* Start a new GGC context.  Memory allocated in previous contexts
356    will not be collected while the new context is active.  */
357 
358 void
ggc_push_context()359 ggc_push_context ()
360 {
361   G.context++;
362 
363   /* We only allocated 7 bits in the node for the context.  This
364      should be more than enough.  */
365   if (G.context >= 128)
366     abort ();
367 }
368 
369 /* Finish a GC context.  Any uncollected memory in the new context
370    will be merged with the old context.  */
371 
372 void
ggc_pop_context()373 ggc_pop_context ()
374 {
375   G.context--;
376   if (G.root)
377     ggc_pop_context_1 (G.root, G.context);
378 }
379 
380 static void
ggc_pop_context_1(x,c)381 ggc_pop_context_1 (x, c)
382      struct ggc_mem *x;
383      int c;
384 {
385   if (x->context > c)
386     x->context = c;
387   if (x->sub[0])
388     ggc_pop_context_1 (x->sub[0], c);
389   if (x->sub[1])
390     ggc_pop_context_1 (x->sub[1], c);
391 }
392 
393 /* Dump a tree.  */
394 
395 void
debug_ggc_tree(p,indent)396 debug_ggc_tree (p, indent)
397      struct ggc_mem *p;
398      int indent;
399 {
400   int i;
401 
402   if (!p)
403     {
404       fputs ("(nil)\n", stderr);
405       return;
406     }
407 
408   if (p->sub[0])
409     debug_ggc_tree (p->sub[0], indent + 1);
410 
411   for (i = 0; i < indent; ++i)
412     putc (' ', stderr);
413   fprintf (stderr, "%lx %p\n", (unsigned long)PTR_KEY (p), p);
414 
415   if (p->sub[1])
416     debug_ggc_tree (p->sub[1], indent + 1);
417 }
418 
419 #ifdef GGC_BALANCE
420 /* Collect tree balance metrics  */
421 
422 #include <math.h>
423 
424 void
debug_ggc_balance()425 debug_ggc_balance ()
426 {
427   size_t nleaf, sumdepth;
428 
429   nleaf = sumdepth = 0;
430   tally_leaves (G.root, 0, &nleaf, &sumdepth);
431 
432   fprintf (stderr, " {B %.2f,%.1f,%.1f}",
433 	   /* In a balanced tree, leaf/node should approach 1/2.  */
434 	   (float)nleaf / (float)G.objects,
435 	   /* In a balanced tree, average leaf depth should approach lg(n).  */
436 	   (float)sumdepth / (float)nleaf,
437 	   log ((double) G.objects) / M_LN2);
438 }
439 #endif
440 
441 /* Used by debug_ggc_balance, and also by ggc_print_statistics.  */
442 static void
tally_leaves(x,depth,nleaf,sumdepth)443 tally_leaves (x, depth, nleaf, sumdepth)
444      struct ggc_mem *x;
445      int depth;
446      size_t *nleaf;
447      size_t *sumdepth;
448 {
449   if (! x->sub[0] && !x->sub[1])
450     {
451       *nleaf += 1;
452       *sumdepth += depth;
453     }
454   else
455     {
456       if (x->sub[0])
457 	tally_leaves (x->sub[0], depth + 1, nleaf, sumdepth);
458       if (x->sub[1])
459 	tally_leaves (x->sub[1], depth + 1, nleaf, sumdepth);
460     }
461 }
462 
463 #define SCALE(x) ((unsigned long) ((x) < 1024*10 \
464 		  ? (x) \
465 		  : ((x) < 1024*1024*10 \
466 		     ? (x) / 1024 \
467 		     : (x) / (1024*1024))))
468 #define LABEL(x) ((x) < 1024*10 ? ' ' : ((x) < 1024*1024*10 ? 'k' : 'M'))
469 
470 /* Report on GC memory usage.  */
471 void
ggc_print_statistics()472 ggc_print_statistics ()
473 {
474   struct ggc_statistics stats;
475   size_t nleaf = 0, sumdepth = 0;
476 
477   /* Clear the statistics.  */
478   memset (&stats, 0, sizeof (stats));
479 
480   /* Make sure collection will really occur.  */
481   G.allocated_last_gc = 0;
482 
483   /* Collect and print the statistics common across collectors.  */
484   ggc_print_common_statistics (stderr, &stats);
485 
486   /* Report on tree balancing.  */
487   tally_leaves (G.root, 0, &nleaf, &sumdepth);
488 
489   fprintf (stderr, "\n\
490 Total internal data (bytes)\t%ld%c\n\
491 Number of leaves in tree\t%d\n\
492 Average leaf depth\t\t%.1f\n",
493 	   SCALE(G.objects * offsetof (struct ggc_mem, u)),
494 	   LABEL(G.objects * offsetof (struct ggc_mem, u)),
495 	   nleaf, (double)sumdepth / (double)nleaf);
496 
497   /* Report overall memory usage.  */
498   fprintf (stderr, "\n\
499 Total objects allocated\t\t%d\n\
500 Total memory in GC arena\t%ld%c\n",
501 	   G.objects,
502 	   SCALE(G.allocated), LABEL(G.allocated));
503 }
504