Daily bump.
[official-gcc.git] / boehm-gc / backgraph.c
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1 /*
2 * Copyright (c) 2001 by Hewlett-Packard Company. All rights reserved.
4 * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
5 * OR IMPLIED. ANY USE IS AT YOUR OWN RISK.
7 * Permission is hereby granted to use or copy this program
8 * for any purpose, provided the above notices are retained on all copies.
9 * Permission to modify the code and to distribute modified code is granted,
10 * provided the above notices are retained, and a notice that the code was
11 * modified is included with the above copyright notice.
16 * This implements a full, though not well-tuned, representation of the
17 * backwards points-to graph. This is used to test for non-GC-robust
18 * data structures; the code is not used during normal garbage collection.
20 * One restriction is that we drop all back-edges from nodes with very
21 * high in-degree, and simply add them add them to a list of such
22 * nodes. They are then treated as permanent roots. Id this by itself
23 * doesn't introduce a space leak, then such nodes can't contribute to
24 * a growing space leak.
27 #include "gc.h" /* For configuration information. */
29 #ifdef MAKE_BACK_GRAPH
31 #define MAX_IN 10 /* Maximum in-degree we handle directly */
33 #include "private/dbg_mlc.h"
34 #include <unistd.h>
36 #if !defined(DBG_HDRS_ALL) || (ALIGNMENT != CPP_WORDSZ/8) || !defined(UNIX_LIKE)
37 # error Configuration doesnt support MAKE_BACK_GRAPH
38 #endif
40 /* We store single back pointers directly in the object's oh_bg_ptr field. */
41 /* If there is more than one ptr to an object, we store q | FLAG_MANY, */
42 /* where q is a pointer to a back_edges object. */
43 /* Every once in a while we use a back_edges object even for a single */
44 /* pointer, since we need the other fields in the back_edges structure to */
45 /* be present in some fraction of the objects. Otherwise we get serious */
46 /* performance issues. */
47 #define FLAG_MANY 2
49 typedef struct back_edges_struct {
50 word n_edges; /* Number of edges, including those in continuation */
51 /* structures. */
52 unsigned short flags;
53 # define RETAIN 1 /* Directly points to a reachable object; */
54 /* retain for next GC. */
55 unsigned short height_gc_no;
56 /* If height > 0, then the GC_gc_no value when it */
57 /* was computed. If it was computed this cycle, then */
58 /* it is current. If it was computed during the */
59 /* last cycle, then it represents the old height, */
60 /* which is only saved for live objects referenced by */
61 /* dead ones. This may grow due to refs from newly */
62 /* dead objects. */
63 signed_word height;
64 /* Longest path through unreachable nodes to this node */
65 /* that we found using depth first search. */
67 # define HEIGHT_UNKNOWN ((signed_word)(-2))
68 # define HEIGHT_IN_PROGRESS ((signed_word)(-1))
69 ptr_t edges[MAX_IN];
70 struct back_edges_struct *cont;
71 /* Pointer to continuation structure; we use only the */
72 /* edges field in the continuation. */
73 /* also used as free list link. */
74 } back_edges;
76 /* Allocate a new back edge structure. Should be more sophisticated */
77 /* if this were production code. */
78 #define MAX_BACK_EDGE_STRUCTS 100000
79 static back_edges *back_edge_space = 0;
80 int GC_n_back_edge_structs = 0; /* Serves as pointer to never used */
81 /* back_edges space. */
82 static back_edges *avail_back_edges = 0;
83 /* Pointer to free list of deallocated */
84 /* back_edges structures. */
86 static back_edges * new_back_edges(void)
88 if (0 == back_edge_space) {
89 back_edge_space = (back_edges *)
90 GET_MEM(MAX_BACK_EDGE_STRUCTS*sizeof(back_edges));
92 if (0 != avail_back_edges) {
93 back_edges * result = avail_back_edges;
94 avail_back_edges = result -> cont;
95 result -> cont = 0;
96 return result;
98 if (GC_n_back_edge_structs >= MAX_BACK_EDGE_STRUCTS - 1) {
99 ABORT("needed too much space for back edges: adjust "
100 "MAX_BACK_EDGE_STRUCTS");
102 return back_edge_space + (GC_n_back_edge_structs++);
105 /* Deallocate p and its associated continuation structures. */
106 static void deallocate_back_edges(back_edges *p)
108 back_edges *last = p;
110 while (0 != last -> cont) last = last -> cont;
111 last -> cont = avail_back_edges;
112 avail_back_edges = p;
115 /* Table of objects that are currently on the depth-first search */
116 /* stack. Only objects with in-degree one are in this table. */
117 /* Other objects are identified using HEIGHT_IN_PROGRESS. */
118 /* FIXME: This data structure NEEDS IMPROVEMENT. */
119 #define INITIAL_IN_PROGRESS 10000
120 static ptr_t * in_progress_space = 0;
121 static size_t in_progress_size = 0;
122 static size_t n_in_progress = 0;
124 static void push_in_progress(ptr_t p)
126 if (n_in_progress >= in_progress_size)
127 if (in_progress_size == 0) {
128 in_progress_size = INITIAL_IN_PROGRESS;
129 in_progress_space = (ptr_t *)GET_MEM(in_progress_size * sizeof(ptr_t));
130 } else {
131 ptr_t * new_in_progress_space;
132 in_progress_size *= 2;
133 new_in_progress_space = (ptr_t *)
134 GET_MEM(in_progress_size * sizeof(ptr_t));
135 BCOPY(in_progress_space, new_in_progress_space,
136 n_in_progress * sizeof(ptr_t));
137 in_progress_space = new_in_progress_space;
138 /* FIXME: This just drops the old space. */
140 if (in_progress_space == 0)
141 ABORT("MAKE_BACK_GRAPH: Out of in-progress space: "
142 "Huge linear data structure?");
143 in_progress_space[n_in_progress++] = p;
146 static GC_bool is_in_progress(ptr_t p)
148 int i;
149 for (i = 0; i < n_in_progress; ++i) {
150 if (in_progress_space[i] == p) return TRUE;
152 return FALSE;
155 static void pop_in_progress(ptr_t p)
157 --n_in_progress;
158 GC_ASSERT(in_progress_space[n_in_progress] == p);
161 #define GET_OH_BG_PTR(p) \
162 (ptr_t)REVEAL_POINTER(((oh *)(p)) -> oh_bg_ptr)
163 #define SET_OH_BG_PTR(p,q) (((oh *)(p)) -> oh_bg_ptr) = HIDE_POINTER(q)
165 /* Execute s once for each predecessor q of p in the points-to graph. */
166 /* s should be a bracketed statement. We declare q. */
167 #define FOR_EACH_PRED(q, p, s) \
169 ptr_t q = GET_OH_BG_PTR(p); \
170 if (!((word)q & FLAG_MANY)) { \
171 if (q && !((word)q & 1)) s \
172 /* !((word)q & 1) checks for a misnterpreted freelist link */ \
173 } else { \
174 back_edges *orig_be_ = (back_edges *)((word)q & ~FLAG_MANY); \
175 back_edges *be_ = orig_be_; \
176 int total_, local_; \
177 int n_edges_ = be_ -> n_edges; \
178 for (total_ = 0, local_ = 0; total_ < n_edges_; ++local_, ++total_) { \
179 if (local_ == MAX_IN) { \
180 be_ = be_ -> cont; \
181 local_ = 0; \
183 q = be_ -> edges[local_]; s \
188 /* Ensure that p has a back_edges structure associated with it. */
189 static void ensure_struct(ptr_t p)
191 ptr_t old_back_ptr = GET_OH_BG_PTR(p);
193 if (!((word)old_back_ptr & FLAG_MANY)) {
194 back_edges *be = new_back_edges();
195 be -> flags = 0;
196 if (0 == old_back_ptr) {
197 be -> n_edges = 0;
198 } else {
199 be -> n_edges = 1;
200 be -> edges[0] = old_back_ptr;
202 be -> height = HEIGHT_UNKNOWN;
203 be -> height_gc_no = GC_gc_no - 1;
204 GC_ASSERT(be >= back_edge_space);
205 SET_OH_BG_PTR(p, (word)be | FLAG_MANY);
209 /* Add the (forward) edge from p to q to the backward graph. Both p */
210 /* q are pointers to the object base, i.e. pointers to an oh. */
211 static void add_edge(ptr_t p, ptr_t q)
213 ptr_t old_back_ptr = GET_OH_BG_PTR(q);
214 back_edges * be, *be_cont;
215 word i;
216 static unsigned random_number = 13;
217 # define GOT_LUCKY_NUMBER (((++random_number) & 0x7f) == 0)
218 /* A not very random number we use to occasionally allocate a */
219 /* back_edges structure even for a single backward edge. This */
220 /* prevents us from repeatedly tracing back through very long */
221 /* chains, since we will have some place to store height and */
222 /* in_progress flags along the way. */
224 GC_ASSERT(p == GC_base(p) && q == GC_base(q));
225 if (!GC_HAS_DEBUG_INFO(q) || !GC_HAS_DEBUG_INFO(p)) {
226 /* This is really a misinterpreted free list link, since we saw */
227 /* a pointer to a free list. Dont overwrite it! */
228 return;
230 if (0 == old_back_ptr) {
231 SET_OH_BG_PTR(q, p);
232 if (GOT_LUCKY_NUMBER) ensure_struct(q);
233 return;
235 /* Check whether it was already in the list of predecessors. */
236 FOR_EACH_PRED(pred, q, { if (p == pred) return; });
237 ensure_struct(q);
238 old_back_ptr = GET_OH_BG_PTR(q);
239 be = (back_edges *)((word)old_back_ptr & ~FLAG_MANY);
240 for (i = be -> n_edges, be_cont = be; i > MAX_IN;
241 be_cont = be_cont -> cont, i -= MAX_IN) {}
242 if (i == MAX_IN) {
243 be_cont -> cont = new_back_edges();
244 be_cont = be_cont -> cont;
245 i = 0;
247 be_cont -> edges[i] = p;
248 be -> n_edges++;
249 if (be -> n_edges == 100) {
250 # if 0
251 if (GC_print_stats) {
252 GC_err_printf0("The following object has in-degree >= 100:\n");
253 GC_print_heap_obj(q);
255 # endif
259 typedef void (*per_object_func)(ptr_t p, word n_words, word gc_descr);
261 static void per_object_helper(struct hblk *h, word fn)
263 hdr * hhdr = HDR(h);
264 word sz = hhdr -> hb_sz;
265 word descr = hhdr -> hb_descr;
266 per_object_func f = (per_object_func)fn;
267 int i = 0;
269 do {
270 f((ptr_t)(h -> hb_body + i), sz, descr);
271 i += sz;
272 } while (i + sz <= BYTES_TO_WORDS(HBLKSIZE));
275 void GC_apply_to_each_object(per_object_func f)
277 GC_apply_to_all_blocks(per_object_helper, (word)f);
280 static void reset_back_edge(ptr_t p, word n_words, word gc_descr)
282 /* Skip any free list links, or dropped blocks */
283 if (GC_HAS_DEBUG_INFO(p)) {
284 ptr_t old_back_ptr = GET_OH_BG_PTR(p);
285 if ((word)old_back_ptr & FLAG_MANY) {
286 back_edges *be = (back_edges *)((word)old_back_ptr & ~FLAG_MANY);
287 if (!(be -> flags & RETAIN)) {
288 deallocate_back_edges(be);
289 SET_OH_BG_PTR(p, 0);
290 } else {
291 word *currentp;
293 GC_ASSERT(GC_is_marked(p));
295 /* Back edges may point to objects that will not be retained. */
296 /* Delete them for now, but remember the height. */
297 /* Some will be added back at next GC. */
298 be -> n_edges = 0;
299 if (0 != be -> cont) {
300 deallocate_back_edges(be -> cont);
301 be -> cont = 0;
304 GC_ASSERT(GC_is_marked(p));
306 /* We only retain things for one GC cycle at a time. */
307 be -> flags &= ~RETAIN;
309 } else /* Simple back pointer */ {
310 /* Clear to avoid dangling pointer. */
311 SET_OH_BG_PTR(p, 0);
316 static void add_back_edges(ptr_t p, word n_words, word gc_descr)
318 word *currentp = (word *)(p + sizeof(oh));
320 /* For now, fix up non-length descriptors conservatively. */
321 if((gc_descr & GC_DS_TAGS) != GC_DS_LENGTH) {
322 gc_descr = WORDS_TO_BYTES(n_words);
324 while (currentp < (word *)(p + gc_descr)) {
325 word current = *currentp++;
326 FIXUP_POINTER(current);
327 if (current >= (word)GC_least_plausible_heap_addr &&
328 current <= (word)GC_greatest_plausible_heap_addr) {
329 ptr_t target = GC_base((GC_PTR)current);
330 if (0 != target) {
331 add_edge(p, target);
337 /* Rebuild the representation of the backward reachability graph. */
338 /* Does not examine mark bits. Can be called before GC. */
339 void GC_build_back_graph(void)
341 GC_apply_to_each_object(add_back_edges);
344 /* Return an approximation to the length of the longest simple path */
345 /* through unreachable objects to p. We refer to this as the height */
346 /* of p. */
347 static word backwards_height(ptr_t p)
349 word result;
350 ptr_t back_ptr = GET_OH_BG_PTR(p);
351 back_edges *be;
353 if (0 == back_ptr) return 1;
354 if (!((word)back_ptr & FLAG_MANY)) {
355 if (is_in_progress(p)) return 0; /* DFS back edge, i.e. we followed */
356 /* an edge to an object already */
357 /* on our stack: ignore */
358 push_in_progress(p);
359 result = backwards_height(back_ptr)+1;
360 pop_in_progress(p);
361 return result;
363 be = (back_edges *)((word)back_ptr & ~FLAG_MANY);
364 if (be -> height >= 0 && be -> height_gc_no == GC_gc_no)
365 return be -> height;
366 /* Ignore back edges in DFS */
367 if (be -> height == HEIGHT_IN_PROGRESS) return 0;
368 result = (be -> height > 0? be -> height : 1);
369 be -> height = HEIGHT_IN_PROGRESS;
370 FOR_EACH_PRED(q, p, {
371 word this_height;
372 if (GC_is_marked(q) && !(FLAG_MANY & (word)GET_OH_BG_PTR(p))) {
373 if (GC_print_stats)
374 GC_printf2("Found bogus pointer from 0x%lx to 0x%lx\n", q, p);
375 /* Reachable object "points to" unreachable one. */
376 /* Could be caused by our lax treatment of GC descriptors. */
377 this_height = 1;
378 } else {
379 this_height = backwards_height(q);
381 if (this_height >= result) result = this_height + 1;
383 be -> height = result;
384 be -> height_gc_no = GC_gc_no;
385 return result;
388 word GC_max_height;
389 ptr_t GC_deepest_obj;
391 /* Compute the maximum height of every unreachable predecessor p of a */
392 /* reachable object. Arrange to save the heights of all such objects p */
393 /* so that they can be used in calculating the height of objects in the */
394 /* next GC. */
395 /* Set GC_max_height to be the maximum height we encounter, and */
396 /* GC_deepest_obj to be the corresponding object. */
397 static void update_max_height(ptr_t p, word n_words, word gc_descr)
399 if (GC_is_marked(p) && GC_HAS_DEBUG_INFO(p)) {
400 int i;
401 word p_height = 0;
402 ptr_t p_deepest_obj = 0;
403 ptr_t back_ptr;
404 back_edges *be = 0;
406 /* If we remembered a height last time, use it as a minimum. */
407 /* It may have increased due to newly unreachable chains pointing */
408 /* to p, but it can't have decreased. */
409 back_ptr = GET_OH_BG_PTR(p);
410 if (0 != back_ptr && ((word)back_ptr & FLAG_MANY)) {
411 be = (back_edges *)((word)back_ptr & ~FLAG_MANY);
412 if (be -> height != HEIGHT_UNKNOWN) p_height = be -> height;
414 FOR_EACH_PRED(q, p, {
415 if (!GC_is_marked(q) && GC_HAS_DEBUG_INFO(q)) {
416 word q_height;
418 q_height = backwards_height(q);
419 if (q_height > p_height) {
420 p_height = q_height;
421 p_deepest_obj = q;
425 if (p_height > 0) {
426 /* Remember the height for next time. */
427 if (be == 0) {
428 ensure_struct(p);
429 back_ptr = GET_OH_BG_PTR(p);
430 be = (back_edges *)((word)back_ptr & ~FLAG_MANY);
432 be -> flags |= RETAIN;
433 be -> height = p_height;
434 be -> height_gc_no = GC_gc_no;
436 if (p_height > GC_max_height) {
437 GC_max_height = p_height;
438 GC_deepest_obj = p_deepest_obj;
443 word GC_max_max_height = 0;
445 void GC_traverse_back_graph(void)
447 GC_max_height = 0;
448 GC_apply_to_each_object(update_max_height);
451 void GC_print_back_graph_stats(void)
453 GC_printf2("Maximum backwards height of reachable objects at GC %lu is %ld\n",
454 (unsigned long) GC_gc_no, GC_max_height);
455 if (GC_max_height > GC_max_max_height) {
456 GC_max_max_height = GC_max_height;
457 GC_printf0("The following unreachable object is last in a longest chain "
458 "of unreachable objects:\n");
459 GC_print_heap_obj(GC_deepest_obj);
461 if (GC_print_stats) {
462 GC_printf1("Needed max total of %ld back-edge structs\n",
463 GC_n_back_edge_structs);
465 GC_apply_to_each_object(reset_back_edge);
466 GC_deepest_obj = 0;
469 #endif /* MAKE_BACK_GRAPH */