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) 2001-2015 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 "hash-set.h"
  41 #include "machmode.h"
  42 #include "vec.h"
  43 #include "double-int.h"
  44 #include "input.h"
  45 #include "alias.h"
  46 #include "symtab.h"
  47 #include "wide-int.h"
  48 #include "inchash.h"
  49 #include "tree.h"
  50 #include "fold-const.h"
  51 #include "rtl.h"
  52 #include "hard-reg-set.h"
  53 #include "profile.h"
  54 #include "predict.h"
  55 #include "input.h"
  56 #include "function.h"
  57 #include "dominance.h"
  58 #include "cfg.h"
  59 #include "cfganal.h"
  60 #include "basic-block.h"
  61 #include "flags.h"
  62 #include "params.h"
  63 #include "coverage.h"
  64 #include "tree-pass.h"
  65 #include "tree-ssa-alias.h"
  66 #include "internal-fn.h"
  67 #include "gimple-expr.h"
  68 #include "is-a.h"
  69 #include "gimple.h"
  70 #include "gimple-iterator.h"
  71 #include "tree-cfg.h"
  72 #include "tree-ssa.h"
  73 #include "tree-inline.h"
  74 #include "cfgloop.h"
  75 #include "fibonacci_heap.h"
  76
  77 static int count_insns (basic_block);
  78 static bool ignore_bb_p (const_basic_block);
  79 static bool better_p (const_edge, const_edge);
  80 static edge find_best_successor (basic_block);
  81 static edge find_best_predecessor (basic_block);
  82 static int find_trace (basic_block, basic_block *);
  83
  84 /* Minimal outgoing edge probability considered for superblock formation.  */
  85 static int probability_cutoff;
  86 static int branch_ratio_cutoff;
  87
  88 /* A bit BB->index is set if BB has already been seen, i.e. it is
  89    connected to some trace already.  */
  90 sbitmap bb_seen;
  91
  92 static inline void
  93 mark_bb_seen (basic_block bb)
  94 {
  95   unsigned int size = SBITMAP_SIZE (bb_seen);
  96
  97   if ((unsigned int)bb->index >= size)
  98     bb_seen = sbitmap_resize (bb_seen, size * 2, 0);
  99
 100   bitmap_set_bit (bb_seen, bb->index);
 101 }
 102
 103 static inline bool
 104 bb_seen_p (basic_block bb)
 105 {
 106   return bitmap_bit_p (bb_seen, bb->index);
 107 }
 108
 109 /* Return true if we should ignore the basic block for purposes of tracing.  */
 110 static bool
 111 ignore_bb_p (const_basic_block bb)
 112 {
 113   gimple g;
 114
 115   if (bb->index < NUM_FIXED_BLOCKS)
 116     return true;
 117   if (optimize_bb_for_size_p (bb))
 118     return true;
 119
 120   /* A transaction is a single entry multiple exit region.  It must be
 121      duplicated in its entirety or not at all.  */
 122   g = last_stmt (CONST_CAST_BB (bb));
 123   if (g && gimple_code (g) == GIMPLE_TRANSACTION)
 124     return true;
 125
 126   return false;
 127 }
 128
 129 /* Return number of instructions in the block.  */
 130
 131 static int
 132 count_insns (basic_block bb)
 133 {
 134   gimple_stmt_iterator gsi;
 135   gimple stmt;
 136   int n = 0;
 137
 138   for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
 139     {
 140       stmt = gsi_stmt (gsi);
 141       n += estimate_num_insns (stmt, &eni_size_weights);
 142     }
 143   return n;
 144 }
 145
 146 /* Return true if E1 is more frequent than E2.  */
 147 static bool
 148 better_p (const_edge e1, const_edge e2)
 149 {
 150   if (e1->count != e2->count)
 151     return e1->count > e2->count;
 152   if (e1->src->frequency * e1->probability !=
 153       e2->src->frequency * e2->probability)
 154     return (e1->src->frequency * e1->probability
 155             > e2->src->frequency * e2->probability);
 156   /* This is needed to avoid changes in the decision after
 157      CFG is modified.  */
 158   if (e1->src != e2->src)
 159     return e1->src->index > e2->src->index;
 160   return e1->dest->index > e2->dest->index;
 161 }
 162
 163 /* Return most frequent successor of basic block BB.  */
 164
 165 static edge
 166 find_best_successor (basic_block bb)
 167 {
 168   edge e;
 169   edge best = NULL;
 170   edge_iterator ei;
 171
 172   FOR_EACH_EDGE (e, ei, bb->succs)
 173     if (!best || better_p (e, best))
 174       best = e;
 175   if (!best || ignore_bb_p (best->dest))
 176     return NULL;
 177   if (best->probability <= probability_cutoff)
 178     return NULL;
 179   return best;
 180 }
 181
 182 /* Return most frequent predecessor of basic block BB.  */
 183
 184 static edge
 185 find_best_predecessor (basic_block bb)
 186 {
 187   edge e;
 188   edge best = NULL;
 189   edge_iterator ei;
 190
 191   FOR_EACH_EDGE (e, ei, bb->preds)
 192     if (!best || better_p (e, best))
 193       best = e;
 194   if (!best || ignore_bb_p (best->src))
 195     return NULL;
 196   if (EDGE_FREQUENCY (best) * REG_BR_PROB_BASE
 197       < bb->frequency * branch_ratio_cutoff)
 198     return NULL;
 199   return best;
 200 }
 201
 202 /* Find the trace using bb and record it in the TRACE array.
 203    Return number of basic blocks recorded.  */
 204
 205 static int
 206 find_trace (basic_block bb, basic_block *trace)
 207 {
 208   int i = 0;
 209   edge e;
 210
 211   if (dump_file)
 212     fprintf (dump_file, "Trace seed %i [%i]", bb->index, bb->frequency);
 213
 214   while ((e = find_best_predecessor (bb)) != NULL)
 215     {
 216       basic_block bb2 = e->src;
 217       if (bb_seen_p (bb2) || (e->flags & (EDGE_DFS_BACK | EDGE_COMPLEX))
 218           || find_best_successor (bb2) != e)
 219         break;
 220       if (dump_file)
 221         fprintf (dump_file, ",%i [%i]", bb->index, bb->frequency);
 222       bb = bb2;
 223     }
 224   if (dump_file)
 225     fprintf (dump_file, " forward %i [%i]", bb->index, bb->frequency);
 226   trace[i++] = bb;
 227
 228   /* Follow the trace in forward direction.  */
 229   while ((e = find_best_successor (bb)) != NULL)
 230     {
 231       bb = e->dest;
 232       if (bb_seen_p (bb) || (e->flags & (EDGE_DFS_BACK | EDGE_COMPLEX))
 233           || find_best_predecessor (bb) != e)
 234         break;
 235       if (dump_file)
 236         fprintf (dump_file, ",%i [%i]", bb->index, bb->frequency);
 237       trace[i++] = bb;
 238     }
 239   if (dump_file)
 240     fprintf (dump_file, "\n");
 241   return i;
 242 }
 243
 244 /* Look for basic blocks in frequency order, construct traces and tail duplicate
 245    if profitable.  */
 246
 247 static bool
 248 tail_duplicate (void)
 249 {
 250   auto_vec<fibonacci_node<long, basic_block_def>*> blocks;
 251   blocks.safe_grow_cleared (last_basic_block_for_fn (cfun));
 252
 253   basic_block *trace = XNEWVEC (basic_block, n_basic_blocks_for_fn (cfun));
 254   int *counts = XNEWVEC (int, last_basic_block_for_fn (cfun));
 255   int ninsns = 0, nduplicated = 0;
 256   gcov_type weighted_insns = 0, traced_insns = 0;
 257   fibonacci_heap<long, basic_block_def> heap (LONG_MIN);
 258   gcov_type cover_insns;
 259   int max_dup_insns;
 260   basic_block bb;
 261   bool changed = false;
 262
 263   /* Create an oversized sbitmap to reduce the chance that we need to
 264      resize it.  */
 265   bb_seen = sbitmap_alloc (last_basic_block_for_fn (cfun) * 2);
 266   bitmap_clear (bb_seen);
 267   initialize_original_copy_tables ();
 268
 269   if (profile_info && flag_branch_probabilities)
 270     probability_cutoff = PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY_FEEDBACK);
 271   else
 272     probability_cutoff = PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY);
 273   probability_cutoff = REG_BR_PROB_BASE / 100 * probability_cutoff;
 274
 275   branch_ratio_cutoff =
 276     (REG_BR_PROB_BASE / 100 * PARAM_VALUE (TRACER_MIN_BRANCH_RATIO));
 277
 278   FOR_EACH_BB_FN (bb, cfun)
 279     {
 280       int n = count_insns (bb);
 281       if (!ignore_bb_p (bb))
 282         blocks[bb->index] = heap.insert (-bb->frequency, bb);
 283
 284       counts [bb->index] = n;
 285       ninsns += n;
 286       weighted_insns += n * bb->frequency;
 287     }
 288
 289   if (profile_info && flag_branch_probabilities)
 290     cover_insns = PARAM_VALUE (TRACER_DYNAMIC_COVERAGE_FEEDBACK);
 291   else
 292     cover_insns = PARAM_VALUE (TRACER_DYNAMIC_COVERAGE);
 293   cover_insns = (weighted_insns * cover_insns + 50) / 100;
 294   max_dup_insns = (ninsns * PARAM_VALUE (TRACER_MAX_CODE_GROWTH) + 50) / 100;
 295
 296   while (traced_insns < cover_insns && nduplicated < max_dup_insns
 297          && !heap.empty ())
 298     {
 299       basic_block bb = heap.extract_min ();
 300       int n, pos;
 301
 302       if (!bb)
 303         break;
 304
 305       blocks[bb->index] = NULL;
 306
 307       if (ignore_bb_p (bb))
 308         continue;
 309       gcc_assert (!bb_seen_p (bb));
 310
 311       n = find_trace (bb, trace);
 312
 313       bb = trace[0];
 314       traced_insns += bb->frequency * counts [bb->index];
 315       if (blocks[bb->index])
 316         {
 317           heap.delete_node (blocks[bb->index]);
 318           blocks[bb->index] = NULL;
 319         }
 320
 321       for (pos = 1; pos < n; pos++)
 322         {
 323           basic_block bb2 = trace[pos];
 324
 325           if (blocks[bb2->index])
 326             {
 327               heap.delete_node (blocks[bb2->index]);
 328               blocks[bb2->index] = NULL;
 329             }
 330           traced_insns += bb2->frequency * counts [bb2->index];
 331           if (EDGE_COUNT (bb2->preds) > 1
 332               && can_duplicate_block_p (bb2)
 333               /* We have the tendency to duplicate the loop header
 334                  of all do { } while loops.  Do not do that - it is
 335                  not profitable and it might create a loop with multiple
 336                  entries or at least rotate the loop.  */
 337               && bb2->loop_father->header != bb2)
 338             {
 339               edge e;
 340               basic_block copy;
 341
 342               nduplicated += counts [bb2->index];
 343
 344               e = find_edge (bb, bb2);
 345
 346               copy = duplicate_block (bb2, e, bb);
 347               flush_pending_stmts (e);
 348
 349               add_phi_args_after_copy (&copy, 1, NULL);
 350
 351               /* Reconsider the original copy of block we've duplicated.
 352                  Removing the most common predecessor may make it to be
 353                  head.  */
 354               blocks[bb2->index] = heap.insert (-bb2->frequency, bb2);
 355
 356               if (dump_file)
 357                 fprintf (dump_file, "Duplicated %i as %i [%i]\n",
 358                          bb2->index, copy->index, copy->frequency);
 359
 360               bb2 = copy;
 361               changed = true;
 362             }
 363           mark_bb_seen (bb2);
 364           bb = bb2;
 365           /* In case the trace became infrequent, stop duplicating.  */
 366           if (ignore_bb_p (bb))
 367             break;
 368         }
 369       if (dump_file)
 370         fprintf (dump_file, " covered now %.1f\n\n",
 371                  traced_insns * 100.0 / weighted_insns);
 372     }
 373   if (dump_file)
 374     fprintf (dump_file, "Duplicated %i insns (%i%%)\n", nduplicated,
 375              nduplicated * 100 / ninsns);
 376
 377   free_original_copy_tables ();
 378   sbitmap_free (bb_seen);
 379   free (trace);
 380   free (counts);
 381
 382   return changed;
 383 }
 384 \f
 385 namespace {
 386
 387 const pass_data pass_data_tracer =
 388 {
 389   GIMPLE_PASS, /* type */
 390   "tracer", /* name */
 391   OPTGROUP_NONE, /* optinfo_flags */
 392   TV_TRACER, /* tv_id */
 393   0, /* properties_required */
 394   0, /* properties_provided */
 395   0, /* properties_destroyed */
 396   0, /* todo_flags_start */
 397   TODO_update_ssa, /* todo_flags_finish */
 398 };
 399
 400 class pass_tracer : public gimple_opt_pass
 401 {
 402 public:
 403   pass_tracer (gcc::context *ctxt)
 404     : gimple_opt_pass (pass_data_tracer, ctxt)
 405   {}
 406
 407   /* opt_pass methods: */
 408   virtual bool gate (function *)
 409     {
 410       return (optimize > 0 && flag_tracer && flag_reorder_blocks);
 411     }
 412
 413   virtual unsigned int execute (function *);
 414
 415 }; // class pass_tracer
 416
 417 unsigned int
 418 pass_tracer::execute (function *fun)
 419 {
 420   bool changed;
 421
 422   if (n_basic_blocks_for_fn (fun) <= NUM_FIXED_BLOCKS + 1)
 423     return 0;
 424
 425   mark_dfs_back_edges ();
 426   if (dump_file)
 427     brief_dump_cfg (dump_file, dump_flags);
 428
 429   /* Trace formation is done on the fly inside tail_duplicate */
 430   changed = tail_duplicate ();
 431   if (changed)
 432     {
 433       free_dominance_info (CDI_DOMINATORS);
 434       /* If we changed the CFG schedule loops for fixup by cleanup_cfg.  */
 435       loops_state_set (LOOPS_NEED_FIXUP);
 436     }
 437
 438   if (dump_file)
 439     brief_dump_cfg (dump_file, dump_flags);
 440
 441   return changed ? TODO_cleanup_cfg : 0;
 442 }
 443 } // anon namespace
 444
 445 gimple_opt_pass *
 446 make_pass_tracer (gcc::context *ctxt)
 447 {
 448   return new pass_tracer (ctxt);
 449 }