gcc/tracer.c

   1 /* The tracer pass for the GNU compiler.
   2    Contributed by Jan Hubicka, SuSE Labs.
   3    Adapted to work on GIMPLE instead of RTL by Robert Kidd, UIUC.
   4    Copyright (C) 2001-2014 Free Software Foundation, Inc.
   5
   6    This file is part of GCC.
   7
   8    GCC is free software; you can redistribute it and/or modify it
   9    under the terms of the GNU General Public License as published by
  10    the Free Software Foundation; either version 3, or (at your option)
  11    any later version.
  12
  13    GCC is distributed in the hope that it will be useful, but WITHOUT
  14    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  15    or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
  16    License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with GCC; see the file COPYING3.  If not see
  20    <http://www.gnu.org/licenses/>.  */
  21
  22 /* This pass performs the tail duplication needed for superblock formation.
  23    For more information see:
  24
  25      Design and Analysis of Profile-Based Optimization in Compaq's
  26      Compilation Tools for Alpha; Journal of Instruction-Level
  27      Parallelism 3 (2000) 1-25
  28
  29    Unlike Compaq's implementation we don't do the loop peeling as most
  30    probably a better job can be done by a special pass and we don't
  31    need to worry too much about the code size implications as the tail
  32    duplicates are crossjumped again if optimizations are not
  33    performed.  */
  34
  35
  36 #include "config.h"
  37 #include "system.h"
  38 #include "coretypes.h"
  39 #include "tm.h"
  40 #include "tree.h"
  41 #include "rtl.h"
  42 #include "hard-reg-set.h"
  43 #include "basic-block.h"
  44 #include "fibheap.h"
  45 #include "flags.h"
  46 #include "params.h"
  47 #include "coverage.h"
  48 #include "tree-pass.h"
  49 #include "tree-ssa-alias.h"
  50 #include "internal-fn.h"
  51 #include "gimple-expr.h"
  52 #include "is-a.h"
  53 #include "gimple.h"
  54 #include "gimple-iterator.h"
  55 #include "tree-cfg.h"
  56 #include "tree-ssa.h"
  57 #include "tree-inline.h"
  58 #include "cfgloop.h"
  59
  60 static int count_insns (basic_block);
  61 static bool ignore_bb_p (const_basic_block);
  62 static bool better_p (const_edge, const_edge);
  63 static edge find_best_successor (basic_block);
  64 static edge find_best_predecessor (basic_block);
  65 static int find_trace (basic_block, basic_block *);
  66
  67 /* Minimal outgoing edge probability considered for superblock formation.  */
  68 static int probability_cutoff;
  69 static int branch_ratio_cutoff;
  70
  71 /* A bit BB->index is set if BB has already been seen, i.e. it is
  72    connected to some trace already.  */
  73 sbitmap bb_seen;
  74
  75 static inline void
  76 mark_bb_seen (basic_block bb)
  77 {
  78   unsigned int size = SBITMAP_SIZE (bb_seen);
  79
  80   if ((unsigned int)bb->index >= size)
  81     bb_seen = sbitmap_resize (bb_seen, size * 2, 0);
  82
  83   bitmap_set_bit (bb_seen, bb->index);
  84 }
  85
  86 static inline bool
  87 bb_seen_p (basic_block bb)
  88 {
  89   return bitmap_bit_p (bb_seen, bb->index);
  90 }
  91
  92 /* Return true if we should ignore the basic block for purposes of tracing.  */
  93 static bool
  94 ignore_bb_p (const_basic_block bb)
  95 {
  96   gimple g;
  97
  98   if (bb->index < NUM_FIXED_BLOCKS)
  99     return true;
 100   if (optimize_bb_for_size_p (bb))
 101     return true;
 102
 103   /* A transaction is a single entry multiple exit region.  It must be
 104      duplicated in its entirety or not at all.  */
 105   g = last_stmt (CONST_CAST_BB (bb));
 106   if (g && gimple_code (g) == GIMPLE_TRANSACTION)
 107     return true;
 108
 109   return false;
 110 }
 111
 112 /* Return number of instructions in the block.  */
 113
 114 static int
 115 count_insns (basic_block bb)
 116 {
 117   gimple_stmt_iterator gsi;
 118   gimple stmt;
 119   int n = 0;
 120
 121   for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
 122     {
 123       stmt = gsi_stmt (gsi);
 124       n += estimate_num_insns (stmt, &eni_size_weights);
 125     }
 126   return n;
 127 }
 128
 129 /* Return true if E1 is more frequent than E2.  */
 130 static bool
 131 better_p (const_edge e1, const_edge e2)
 132 {
 133   if (e1->count != e2->count)
 134     return e1->count > e2->count;
 135   if (e1->src->frequency * e1->probability !=
 136       e2->src->frequency * e2->probability)
 137     return (e1->src->frequency * e1->probability
 138             > e2->src->frequency * e2->probability);
 139   /* This is needed to avoid changes in the decision after
 140      CFG is modified.  */
 141   if (e1->src != e2->src)
 142     return e1->src->index > e2->src->index;
 143   return e1->dest->index > e2->dest->index;
 144 }
 145
 146 /* Return most frequent successor of basic block BB.  */
 147
 148 static edge
 149 find_best_successor (basic_block bb)
 150 {
 151   edge e;
 152   edge best = NULL;
 153   edge_iterator ei;
 154
 155   FOR_EACH_EDGE (e, ei, bb->succs)
 156     if (!best || better_p (e, best))
 157       best = e;
 158   if (!best || ignore_bb_p (best->dest))
 159     return NULL;
 160   if (best->probability <= probability_cutoff)
 161     return NULL;
 162   return best;
 163 }
 164
 165 /* Return most frequent predecessor of basic block BB.  */
 166
 167 static edge
 168 find_best_predecessor (basic_block bb)
 169 {
 170   edge e;
 171   edge best = NULL;
 172   edge_iterator ei;
 173
 174   FOR_EACH_EDGE (e, ei, bb->preds)
 175     if (!best || better_p (e, best))
 176       best = e;
 177   if (!best || ignore_bb_p (best->src))
 178     return NULL;
 179   if (EDGE_FREQUENCY (best) * REG_BR_PROB_BASE
 180       < bb->frequency * branch_ratio_cutoff)
 181     return NULL;
 182   return best;
 183 }
 184
 185 /* Find the trace using bb and record it in the TRACE array.
 186    Return number of basic blocks recorded.  */
 187
 188 static int
 189 find_trace (basic_block bb, basic_block *trace)
 190 {
 191   int i = 0;
 192   edge e;
 193
 194   if (dump_file)
 195     fprintf (dump_file, "Trace seed %i [%i]", bb->index, bb->frequency);
 196
 197   while ((e = find_best_predecessor (bb)) != NULL)
 198     {
 199       basic_block bb2 = e->src;
 200       if (bb_seen_p (bb2) || (e->flags & (EDGE_DFS_BACK | EDGE_COMPLEX))
 201           || find_best_successor (bb2) != e)
 202         break;
 203       if (dump_file)
 204         fprintf (dump_file, ",%i [%i]", bb->index, bb->frequency);
 205       bb = bb2;
 206     }
 207   if (dump_file)
 208     fprintf (dump_file, " forward %i [%i]", bb->index, bb->frequency);
 209   trace[i++] = bb;
 210
 211   /* Follow the trace in forward direction.  */
 212   while ((e = find_best_successor (bb)) != NULL)
 213     {
 214       bb = e->dest;
 215       if (bb_seen_p (bb) || (e->flags & (EDGE_DFS_BACK | EDGE_COMPLEX))
 216           || find_best_predecessor (bb) != e)
 217         break;
 218       if (dump_file)
 219         fprintf (dump_file, ",%i [%i]", bb->index, bb->frequency);
 220       trace[i++] = bb;
 221     }
 222   if (dump_file)
 223     fprintf (dump_file, "\n");
 224   return i;
 225 }
 226
 227 /* Look for basic blocks in frequency order, construct traces and tail duplicate
 228    if profitable.  */
 229
 230 static bool
 231 tail_duplicate (void)
 232 {
 233   fibnode_t *blocks = XCNEWVEC (fibnode_t, last_basic_block_for_fn (cfun));
 234   basic_block *trace = XNEWVEC (basic_block, n_basic_blocks_for_fn (cfun));
 235   int *counts = XNEWVEC (int, last_basic_block_for_fn (cfun));
 236   int ninsns = 0, nduplicated = 0;
 237   gcov_type weighted_insns = 0, traced_insns = 0;
 238   fibheap_t heap = fibheap_new ();
 239   gcov_type cover_insns;
 240   int max_dup_insns;
 241   basic_block bb;
 242   bool changed = false;
 243
 244   /* Create an oversized sbitmap to reduce the chance that we need to
 245      resize it.  */
 246   bb_seen = sbitmap_alloc (last_basic_block_for_fn (cfun) * 2);
 247   bitmap_clear (bb_seen);
 248   initialize_original_copy_tables ();
 249
 250   if (profile_info && flag_branch_probabilities)
 251     probability_cutoff = PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY_FEEDBACK);
 252   else
 253     probability_cutoff = PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY);
 254   probability_cutoff = REG_BR_PROB_BASE / 100 * probability_cutoff;
 255
 256   branch_ratio_cutoff =
 257     (REG_BR_PROB_BASE / 100 * PARAM_VALUE (TRACER_MIN_BRANCH_RATIO));
 258
 259   FOR_EACH_BB_FN (bb, cfun)
 260     {
 261       int n = count_insns (bb);
 262       if (!ignore_bb_p (bb))
 263         blocks[bb->index] = fibheap_insert (heap, -bb->frequency,
 264                                             bb);
 265
 266       counts [bb->index] = n;
 267       ninsns += n;
 268       weighted_insns += n * bb->frequency;
 269     }
 270
 271   if (profile_info && flag_branch_probabilities)
 272     cover_insns = PARAM_VALUE (TRACER_DYNAMIC_COVERAGE_FEEDBACK);
 273   else
 274     cover_insns = PARAM_VALUE (TRACER_DYNAMIC_COVERAGE);
 275   cover_insns = (weighted_insns * cover_insns + 50) / 100;
 276   max_dup_insns = (ninsns * PARAM_VALUE (TRACER_MAX_CODE_GROWTH) + 50) / 100;
 277
 278   while (traced_insns < cover_insns && nduplicated < max_dup_insns
 279          && !fibheap_empty (heap))
 280     {
 281       basic_block bb = (basic_block) fibheap_extract_min (heap);
 282       int n, pos;
 283
 284       if (!bb)
 285         break;
 286
 287       blocks[bb->index] = NULL;
 288
 289       if (ignore_bb_p (bb))
 290         continue;
 291       gcc_assert (!bb_seen_p (bb));
 292
 293       n = find_trace (bb, trace);
 294
 295       bb = trace[0];
 296       traced_insns += bb->frequency * counts [bb->index];
 297       if (blocks[bb->index])
 298         {
 299           fibheap_delete_node (heap, blocks[bb->index]);
 300           blocks[bb->index] = NULL;
 301         }
 302
 303       for (pos = 1; pos < n; pos++)
 304         {
 305           basic_block bb2 = trace[pos];
 306
 307           if (blocks[bb2->index])
 308             {
 309               fibheap_delete_node (heap, blocks[bb2->index]);
 310               blocks[bb2->index] = NULL;
 311             }
 312           traced_insns += bb2->frequency * counts [bb2->index];
 313           if (EDGE_COUNT (bb2->preds) > 1
 314               && can_duplicate_block_p (bb2)
 315               /* We have the tendency to duplicate the loop header
 316                  of all do { } while loops.  Do not do that - it is
 317                  not profitable and it might create a loop with multiple
 318                  entries or at least rotate the loop.  */
 319               && (!current_loops
 320                   || bb2->loop_father->header != bb2))
 321             {
 322               edge e;
 323               basic_block copy;
 324
 325               nduplicated += counts [bb2->index];
 326
 327               e = find_edge (bb, bb2);
 328
 329               copy = duplicate_block (bb2, e, bb);
 330               flush_pending_stmts (e);
 331
 332               add_phi_args_after_copy (&copy, 1, NULL);
 333
 334               /* Reconsider the original copy of block we've duplicated.
 335                  Removing the most common predecessor may make it to be
 336                  head.  */
 337               blocks[bb2->index] =
 338                 fibheap_insert (heap, -bb2->frequency, bb2);
 339
 340               if (dump_file)
 341                 fprintf (dump_file, "Duplicated %i as %i [%i]\n",
 342                          bb2->index, copy->index, copy->frequency);
 343
 344               bb2 = copy;
 345               changed = true;
 346             }
 347           mark_bb_seen (bb2);
 348           bb = bb2;
 349           /* In case the trace became infrequent, stop duplicating.  */
 350           if (ignore_bb_p (bb))
 351             break;
 352         }
 353       if (dump_file)
 354         fprintf (dump_file, " covered now %.1f\n\n",
 355                  traced_insns * 100.0 / weighted_insns);
 356     }
 357   if (dump_file)
 358     fprintf (dump_file, "Duplicated %i insns (%i%%)\n", nduplicated,
 359              nduplicated * 100 / ninsns);
 360
 361   free_original_copy_tables ();
 362   sbitmap_free (bb_seen);
 363   free (blocks);
 364   free (trace);
 365   free (counts);
 366   fibheap_delete (heap);
 367
 368   return changed;
 369 }
 370
 371 /* Main entry point to this file.  */
 372
 373 static unsigned int
 374 tracer (void)
 375 {
 376   bool changed;
 377
 378   if (n_basic_blocks_for_fn (cfun) <= NUM_FIXED_BLOCKS + 1)
 379     return 0;
 380
 381   mark_dfs_back_edges ();
 382   if (dump_file)
 383     brief_dump_cfg (dump_file, dump_flags);
 384
 385   /* Trace formation is done on the fly inside tail_duplicate */
 386   changed = tail_duplicate ();
 387   if (changed)
 388     {
 389       free_dominance_info (CDI_DOMINATORS);
 390       /* If we changed the CFG schedule loops for fixup by cleanup_cfg.  */
 391       if (current_loops)
 392         loops_state_set (LOOPS_NEED_FIXUP);
 393     }
 394
 395   if (dump_file)
 396     brief_dump_cfg (dump_file, dump_flags);
 397
 398   return changed ? TODO_cleanup_cfg : 0;
 399 }
 400 \f
 401 static bool
 402 gate_tracer (void)
 403 {
 404   return (optimize > 0 && flag_tracer && flag_reorder_blocks);
 405 }
 406
 407 namespace {
 408
 409 const pass_data pass_data_tracer =
 410 {
 411   GIMPLE_PASS, /* type */
 412   "tracer", /* name */
 413   OPTGROUP_NONE, /* optinfo_flags */
 414   true, /* has_gate */
 415   true, /* has_execute */
 416   TV_TRACER, /* tv_id */
 417   0, /* properties_required */
 418   0, /* properties_provided */
 419   0, /* properties_destroyed */
 420   0, /* todo_flags_start */
 421   ( TODO_update_ssa | TODO_verify_ssa ), /* todo_flags_finish */
 422 };
 423
 424 class pass_tracer : public gimple_opt_pass
 425 {
 426 public:
 427   pass_tracer (gcc::context *ctxt)
 428     : gimple_opt_pass (pass_data_tracer, ctxt)
 429   {}
 430
 431   /* opt_pass methods: */
 432   bool gate () { return gate_tracer (); }
 433   unsigned int execute () { return tracer (); }
 434
 435 }; // class pass_tracer
 436
 437 } // anon namespace
 438
 439 gimple_opt_pass *
 440 make_pass_tracer (gcc::context *ctxt)
 441 {
 442   return new pass_tracer (ctxt);
 443 }