mono/mini/dominators.c

   1 /*
   2  * dominators.c: Dominator computation on the control flow graph
   3  *
   4  * Author:
   5  *   Dietmar Maurer (dietmar@ximian.com)
   6  *   Paolo Molaro (lupus@ximian.com)
   7  *
   8  * (C) 2003 Ximian, Inc.
   9  * Copyright 2011 Xamarin, Inc (http://www.xamarin.com)
  10  * Licensed under the MIT license. See LICENSE file in the project root for full license information.
  11  */
  12 #include <string.h>
  13 #include <mono/metadata/debug-helpers.h>
  14 #include <mono/metadata/mempool.h>
  15 #include <mono/metadata/mempool-internals.h>
  16
  17 #include "mini.h"
  18
  19 #ifndef DISABLE_JIT
  20
  21 /*
  22  * bb->dfn == 0 means either the bblock is ignored by the dfn calculation, or
  23  * it is the entry bblock.
  24  */
  25 #define HAS_DFN(bb, entry) ((bb)->dfn || ((bb) == entry))
  26
  27 /*
  28  * Compute dominators and immediate dominators using the algorithm in the
  29  * paper "A Simple, Fast Dominance Algorithm" by Keith D. Cooper,
  30  * Timothy J. Harvey, and Ken Kennedy:
  31  * http://citeseer.ist.psu.edu/cooper01simple.html
  32  */
  33 static void
  34 compute_dominators (MonoCompile *cfg)
  35 {
  36         int bindex, i, bitsize;
  37         MonoBasicBlock *entry;
  38         MonoBasicBlock **doms;
  39         gboolean changed;
  40
  41         g_assert (!(cfg->comp_done & MONO_COMP_DOM));
  42
  43         bitsize = mono_bitset_alloc_size (cfg->num_bblocks, 0);
  44
  45         entry = cfg->bblocks [0];
  46
  47         doms = g_new0 (MonoBasicBlock*, cfg->num_bblocks);
  48         doms [entry->dfn] = entry;
  49
  50         if (cfg->verbose_level > 1) {
  51                 for (i = 0; i < cfg->num_bblocks; ++i) {
  52                         int j;
  53                         MonoBasicBlock *bb = cfg->bblocks [i];
  54
  55                         printf ("BB%d IN: ", bb->block_num);
  56                         for (j = 0; j < bb->in_count; ++j)
  57                                 printf ("%d ", bb->in_bb [j]->block_num);
  58                         printf ("\n");
  59                 }
  60         }
  61
  62         changed = TRUE;
  63         while (changed) {
  64                 changed = FALSE;
  65
  66                 for (bindex = 0; bindex < cfg->num_bblocks; ++bindex) {
  67                         MonoBasicBlock *bb = cfg->bblocks [bindex];
  68                         MonoBasicBlock *idom;
  69
  70                         idom = NULL;
  71                         for (i = 0; i < bb->in_count; ++i) {
  72                                 MonoBasicBlock *in_bb = bb->in_bb [i];
  73                                 if ((in_bb != bb) && doms [in_bb->dfn]) {
  74                                         idom = in_bb;
  75                                         break;
  76                                 }
  77                         }
  78                         if (bb != cfg->bblocks [0])
  79                                 g_assert (idom);
  80
  81                         while (i < bb->in_count) {
  82                                 MonoBasicBlock *in_bb = bb->in_bb [i];
  83
  84                                 if (HAS_DFN (in_bb, entry) && doms [in_bb->dfn]) {
  85                                         /* Intersect */
  86                                         MonoBasicBlock *f1 = idom;
  87                                         MonoBasicBlock *f2 = in_bb;
  88
  89                                         while (f1 != f2) {
  90                                                 if (f1->dfn < f2->dfn)
  91                                                         f2 = doms [f2->dfn];
  92                                                 else
  93                                                         f1 = doms [f1->dfn];
  94                                         }
  95
  96                                         idom = f1;
  97                                 }
  98                                 i ++;
  99                         }
 100
 101                         if (idom != doms [bb->dfn]) {
 102                                 if (bb == cfg->bblocks [0])
 103                                         doms [bb->dfn] = bb;
 104                                 else {
 105                                         doms [bb->dfn] = idom;
 106                                         changed = TRUE;
 107                                 }
 108
 109                                 //printf ("A: bb=%d dfn=%d dom:%d\n", bb->block_num, bb->dfn, doms [bb->dfn]->block_num);
 110                         }
 111                 }
 112         }
 113
 114         /* Compute bb->dominators for each bblock */
 115         for (i = 0; i < cfg->num_bblocks; ++i) {
 116                 MonoBasicBlock *bb = cfg->bblocks [i];
 117                 MonoBasicBlock *cbb;
 118                 MonoBitSet *dominators;
 119                 char *mem;
 120
 121                 mem = (char *)mono_mempool_alloc0 (cfg->mempool, bitsize);
 122
 123                 bb->dominators = dominators = mono_bitset_mem_new (mem, cfg->num_bblocks, 0);
 124                 mem += bitsize;
 125
 126                 mono_bitset_set_fast (dominators, bb->dfn);
 127
 128                 if (bb->dfn) {
 129                         for (cbb = doms [bb->dfn]; cbb->dfn; cbb = doms [cbb->dfn])
 130                                 mono_bitset_set_fast (dominators, cbb->dfn);
 131
 132                         bb->idom = doms [bb->dfn];
 133                         if (bb->idom)
 134                                 bb->idom->dominated = g_slist_prepend_mempool (cfg->mempool, bb->idom->dominated, bb);
 135                 }
 136
 137                 /* The entry bb */
 138                 mono_bitset_set_fast (dominators, 0);
 139         }
 140
 141         g_free (doms);
 142
 143         cfg->comp_done |= MONO_COMP_DOM | MONO_COMP_IDOM;
 144
 145         if (cfg->verbose_level > 1) {
 146                 printf ("DTREE %s %d\n", mono_method_full_name (cfg->method, TRUE),
 147                         cfg->header->num_clauses);
 148                 for (i = 0; i < cfg->num_bblocks; ++i) {
 149                         MonoBasicBlock *bb = cfg->bblocks [i];
 150                         printf ("BB%d(dfn=%d) (IDOM=BB%d): ", bb->block_num, bb->dfn, bb->idom ? bb->idom->block_num : -1);
 151                         mono_blockset_print (cfg, bb->dominators, NULL, -1);
 152                 }
 153         }
 154 }
 155
 156 #if 0
 157
 158 static void
 159 check_dominance_frontier (MonoBasicBlock *x, MonoBasicBlock *t)
 160 {
 161         int i, j;
 162
 163         t->flags |= BB_VISITED;
 164
 165         if (mono_bitset_test_fast (t->dominators, x->dfn)) {
 166                 for (i = 0; i < t->out_count; ++i) {
 167                         if (!(t->flags & BB_VISITED)) {
 168                                 int found = FALSE;
 169                                 check_dominance_frontier (x, t->out_bb [i]);
 170
 171                                 for (j = 0; j < t->out_bb [i]->in_count; j++) {
 172                                         if (t->out_bb [i]->in_bb [j] == t)
 173                                                 found = TRUE;
 174                                 }
 175                                 g_assert (found);
 176                         }
 177                 }
 178         } else {
 179                 if (!mono_bitset_test_fast (x->dfrontier, t->dfn)) {
 180                         printf ("BB%d not in frontier of BB%d\n", t->block_num, x->block_num);
 181                         g_assert_not_reached ();
 182                 }
 183         }
 184 }
 185
 186 #endif
 187
 188 /**
 189  * Compute dominance frontiers using the algorithm from the same paper.
 190  */
 191 static void
 192 compute_dominance_frontier (MonoCompile *cfg)
 193 {
 194         char *mem;
 195         int i, j, bitsize;
 196
 197         g_assert (!(cfg->comp_done & MONO_COMP_DFRONTIER));
 198
 199         for (i = 0; i < cfg->num_bblocks; ++i)
 200                 cfg->bblocks [i]->flags &= ~BB_VISITED;
 201
 202         bitsize = mono_bitset_alloc_size (cfg->num_bblocks, 0);
 203         mem = (char *)mono_mempool_alloc0 (cfg->mempool, bitsize * cfg->num_bblocks);
 204
 205         for (i = 0; i < cfg->num_bblocks; ++i) {
 206                 MonoBasicBlock *bb = cfg->bblocks [i];
 207                 bb->dfrontier = mono_bitset_mem_new (mem, cfg->num_bblocks, 0);
 208                 mem += bitsize;
 209         }
 210
 211         for (i = 0; i < cfg->num_bblocks; ++i) {
 212                 MonoBasicBlock *bb = cfg->bblocks [i];
 213
 214                 if (bb->in_count > 1) {
 215                         for (j = 0; j < bb->in_count; ++j) {
 216                                 MonoBasicBlock *p = bb->in_bb [j];
 217
 218                                 if (p->dfn || (p == cfg->bblocks [0])) {
 219                                         while (p != bb->idom) {
 220                                                 mono_bitset_set_fast (p->dfrontier, bb->dfn);
 221                                                 p = p->idom;
 222                                         }
 223                                 }
 224                         }
 225                 }
 226         }
 227
 228 #if 0
 229         for (i = 0; i < cfg->num_bblocks; ++i) {
 230                 MonoBasicBlock *bb = cfg->bblocks [i];
 231
 232                 printf ("DFRONT %s BB%d: ", mono_method_full_name (cfg->method, TRUE), bb->block_num);
 233                 mono_blockset_print (cfg, bb->dfrontier, NULL, -1);
 234         }
 235 #endif
 236
 237 #if 0
 238         /* this is a check for the dominator frontier */
 239         for (i = 0; i < m->num_bblocks; ++i) {
 240                 MonoBasicBlock *x = m->bblocks [i];
 241
 242                 mono_bitset_foreach_bit ((x->dfrontier), j, (m->num_bblocks)) {
 243                         MonoBasicBlock *w = m->bblocks [j];
 244                         int k;
 245                         /* x must not strictly dominates w */
 246                         if (mono_bitset_test_fast (w->dominators, x->dfn) && w != x)
 247                                 g_assert_not_reached ();
 248
 249                         for (k = 0; k < m->num_bblocks; ++k)
 250                                 m->bblocks [k]->flags &= ~BB_VISITED;
 251
 252                         check_dominance_frontier (x, x);
 253                 }
 254         }
 255 #endif
 256
 257         cfg->comp_done |= MONO_COMP_DFRONTIER;
 258 }
 259
 260 static inline void
 261 df_set (MonoCompile *m, MonoBitSet* dest, MonoBitSet *set)
 262 {
 263         int i;
 264
 265         mono_bitset_foreach_bit (set, i, m->num_bblocks) {
 266                 mono_bitset_union_fast (dest, m->bblocks [i]->dfrontier);
 267         }
 268 }
 269
 270 MonoBitSet*
 271 mono_compile_iterated_dfrontier (MonoCompile *m, MonoBitSet *set)
 272 {
 273         MonoBitSet *result;
 274         int bitsize, count1, count2;
 275
 276         bitsize = mono_bitset_alloc_size (m->num_bblocks, 0);
 277         result = mono_bitset_mem_new (mono_mempool_alloc0 (m->mempool, bitsize), m->num_bblocks, 0);
 278
 279         df_set (m, result, set);
 280         count2 = mono_bitset_count (result);
 281         do {
 282                 count1 = count2;
 283                 df_set (m, result, result);
 284                 count2 = mono_bitset_count (result);
 285         } while (count2 > count1);
 286
 287         return result;
 288 }
 289
 290 void
 291 mono_compile_dominator_info (MonoCompile *cfg, int dom_flags)
 292 {
 293         if ((dom_flags & MONO_COMP_DOM) && !(cfg->comp_done & MONO_COMP_DOM))
 294                 compute_dominators (cfg);
 295         if ((dom_flags & MONO_COMP_DFRONTIER) && !(cfg->comp_done & MONO_COMP_DFRONTIER))
 296                 compute_dominance_frontier (cfg);
 297 }
 298
 299 /*
 300  * code to detect loops and loop nesting level
 301  */
 302 void
 303 mono_compute_natural_loops (MonoCompile *cfg)
 304 {
 305         int i, j, k;
 306         MonoBitSet *in_loop_blocks;
 307         int *bb_indexes;
 308
 309         g_assert (!(cfg->comp_done & MONO_COMP_LOOPS));
 310
 311         in_loop_blocks = mono_bitset_new (cfg->num_bblocks + 1, 0);
 312         for (i = 0; i < cfg->num_bblocks; ++i) {
 313                 MonoBasicBlock *n = cfg->bblocks [i];
 314
 315                 for (j = 0; j < n->out_count; j++) {
 316                         MonoBasicBlock *h = n->out_bb [j];
 317                         /* check for single block loops */
 318                         if (n == h) {
 319                                 h->loop_blocks = g_list_prepend_mempool (cfg->mempool, h->loop_blocks, h);
 320                                 h->nesting++;
 321                         }
 322                         /* check for back-edge from n to h */
 323                         else if (n != h && mono_bitset_test_fast (n->dominators, h->dfn)) {
 324                                 GSList *todo;
 325
 326                                 /* already in loop_blocks? */
 327                                 if (h->loop_blocks && g_list_find (h->loop_blocks, n)) {
 328                                         continue;
 329                                 }
 330
 331                                 mono_bitset_clear_all (in_loop_blocks);
 332                                 if (h->loop_blocks) {
 333                                         GList *l;
 334
 335                                         for (l = h->loop_blocks; l; l = l->next) {
 336                                                 MonoBasicBlock *b = (MonoBasicBlock *)l->data;
 337                                                 if (b->dfn)
 338                                                         mono_bitset_set_fast (in_loop_blocks, b->dfn);
 339                                         }
 340                                 }
 341                                 todo = g_slist_prepend (NULL, n);
 342
 343                                 while (todo) {
 344                                         MonoBasicBlock *cb = (MonoBasicBlock *)todo->data;
 345                                         todo = g_slist_delete_link (todo, todo);
 346
 347                                         if ((cb->dfn && mono_bitset_test_fast (in_loop_blocks, cb->dfn)) || (!cb->dfn && g_list_find (h->loop_blocks, cb)))
 348                                                 continue;
 349
 350                                         h->loop_blocks = g_list_prepend_mempool (cfg->mempool, h->loop_blocks, cb);
 351                                         cb->nesting++;
 352                                         if (cb->dfn)
 353                                                 mono_bitset_set_fast (in_loop_blocks, cb->dfn);
 354
 355                                         for (k = 0; k < cb->in_count; k++) {
 356                                                 MonoBasicBlock *prev = cb->in_bb [k];
 357                                                 /* add all previous blocks */
 358                                                 if (prev != h && !((prev->dfn && mono_bitset_test_fast (in_loop_blocks, prev->dfn)) || (!prev->dfn && g_list_find (h->loop_blocks, prev)))) {
 359                                                         todo = g_slist_prepend (todo, prev);
 360                                                 }
 361                                         }
 362                                 }
 363
 364                                 /* add the header if not already there */
 365                                 if (!((h->dfn && mono_bitset_test_fast (in_loop_blocks, h->dfn)) || (!h->dfn && g_list_find (h->loop_blocks, h)))) {
 366                                         h->loop_blocks = g_list_prepend_mempool (cfg->mempool, h->loop_blocks, h);
 367                                         h->nesting++;
 368                                 }
 369                         }
 370                 }
 371         }
 372         mono_bitset_free (in_loop_blocks);
 373
 374         cfg->comp_done |= MONO_COMP_LOOPS;
 375
 376         /* Compute loop_body_start for each loop */
 377         bb_indexes = g_new0 (int, cfg->num_bblocks);
 378         {
 379                 MonoBasicBlock *bb;
 380
 381                 for (i = 0, bb = cfg->bb_entry; bb; i ++, bb = bb->next_bb) {
 382                         if (bb->dfn)
 383                                 bb_indexes [bb->dfn] = i;
 384                 }
 385         }
 386         for (i = 0; i < cfg->num_bblocks; ++i) {
 387                 if (cfg->bblocks [i]->loop_blocks) {
 388                         /* The loop body start is the first bblock in the order they will be emitted */
 389                         MonoBasicBlock *h = cfg->bblocks [i];
 390                         MonoBasicBlock *body_start = h;
 391                         GList *l;
 392
 393                         for (l = h->loop_blocks; l; l = l->next) {
 394                                 MonoBasicBlock *cb = (MonoBasicBlock *)l->data;
 395
 396                                 if (cb->dfn && bb_indexes [cb->dfn] < bb_indexes [body_start->dfn]) {
 397                                         body_start = cb;
 398                                 }
 399                         }
 400
 401                         body_start->loop_body_start = 1;
 402                 }
 403         }
 404         g_free (bb_indexes);
 405
 406         if (cfg->verbose_level > 1) {
 407                 for (i = 0; i < cfg->num_bblocks; ++i) {
 408                         if (cfg->bblocks [i]->loop_blocks) {
 409                                 MonoBasicBlock *h = (MonoBasicBlock *)cfg->bblocks [i]->loop_blocks->data;
 410                                 GList *l;
 411                                 printf ("LOOP START %d\n", h->block_num);
 412                                 for (l = h->loop_blocks; l; l = l->next) {
 413                                         MonoBasicBlock *cb = (MonoBasicBlock *)l->data;
 414                                         printf ("\tBB%d %d %p\n", cb->block_num, cb->nesting, cb->loop_blocks);
 415                                 }
 416                         }
 417                 }
 418         }
 419 }
 420
 421 static void
 422 clear_idominators (MonoCompile *cfg)
 423 {
 424         guint i;
 425
 426         for (i = 0; i < cfg->num_bblocks; ++i) {
 427                 if (cfg->bblocks[i]->dominated) {
 428                         cfg->bblocks[i]->dominated = NULL;
 429                 }
 430         }
 431
 432         cfg->comp_done &= ~MONO_COMP_IDOM;
 433 }
 434
 435 static void
 436 clear_loops (MonoCompile *cfg)
 437 {
 438         guint i;
 439
 440         for (i = 0; i < cfg->num_bblocks; ++i) {
 441                 cfg->bblocks[i]->nesting = 0;
 442                 cfg->bblocks[i]->loop_blocks = NULL;
 443         }
 444
 445         cfg->comp_done &= ~MONO_COMP_LOOPS;
 446 }
 447
 448 void
 449 mono_free_loop_info (MonoCompile *cfg)
 450 {
 451     if (cfg->comp_done & MONO_COMP_IDOM)
 452         clear_idominators (cfg);
 453     if (cfg->comp_done & MONO_COMP_LOOPS)
 454         clear_loops (cfg);
 455 }
 456
 457 #else /* DISABLE_JIT */
 458
 459 void
 460 mono_free_loop_info (MonoCompile *cfg)
 461 {
 462 }
 463
 464 #endif /* DISABLE_JIT */